Soldering Methods.pdf

Soldering Introduction to Soldering Soldered connections are used in aircraft electrical wiring to form a continuous and permanent metallic connection having a constant electrical value. The importance of establishing and maintaining a high standard of workmanship for soldering op...

Soldering Introduction to Soldering Soldered connections are used in aircraft electrical wiring to form a continuous and permanent metallic connection having a constant electrical value. The importance of establishing and maintaining a high standard of workmanship for soldering operations cannot be overemphasised. Soldering, in simple terms, is a process of joining metal surfaces together with a metal alloy (solder). Solder is designed to melt at a temperature lower than the melting point of the metal it joins. However, most metals exposed to the atmosphere acquire a thin film of tarnish or oxide; the longer the exposure, the thicker the film becomes. This film is present even though it is not visible, and solder alone cannot dissolve it. A soldering flux with a melting point lower than the solder must be used to ‘wet’ the metal and allow the solder to penetrate it and remove the film. The flux melts first, removing the tarnish or metallic oxide, and also preventing further oxide from forming while the metal is being heated to soldering temperature. The solder then melts, floating the lighter flux and the impurities suspended in it to the outer surface and edges of the molten fillet. The solder cools and forms an alloy with the metal. Most of the flux is burned away during the soldering process; any residue is removed by appropriate cleaning methods. The soldering methods used for general aircraft wiring are essentially the same for both production soldering and repair work. For printed circuit assemblies, production methods and repair methods are different. In production, a dip soldering method is used to make several connections at the same time. Soldering repairs, however, are made individually, using techniques similar to those used for soldering general wiring – with special precautions to prevent thermal damage to the heat-sensitive, closely packed circuit elements. Soldering iron 2023-02-06 B-07c Maintenance Practices Page 198 of 255 CASA Part 66 - Training Materials Only  Solder The function of solder is to act as a filler metal while forming a physical and electrical bond. It is an alloy of two or more metals and joins the component parts by the application of heat. Solders can be classified as soft or hard. Soft solder is an alloy consisting of various combinations of tin and lead, with silver and other additives, which melts at temperatures below 370 °C. It may be in bar form to be melted for tinning or in the form of rosin-cored wire for use with a soldering iron. Hard solders, often called brazing alloy, should not be confused with high-temperature soft solders. Hard solder is a silver alloy and is used when greater mechanical strength or exposure to higher temperatures, such as thermocouple connections, is required. Hard solder is not used on printed circuits. Soft solder (left) and hard solder (right) 2023-02-06 B-07c Maintenance Practices Page 199 of 255 CASA Part 66 - Training Materials Only  Soft Solder Different types of solder are used in industry. Solder used for electronics is a metal alloy mainly made of combinations of tin (chemical symbol Sn) and lead (chemical symbol Pb). Other materials may be added for specific purposes, including: silver bismuth antimony copper. Tin-lead solders are also called soft solders. The greater the tin concentration, the greater the solder’s tensile and shear strengths. They have good corrosion resistance and can be used for joining most metals. Soft solder composition When heated, soft solder does not melt instantaneously, but first becomes soft or plastic, then liquid. The solder used to solder wires to electrical connectors, splices and terminal lugs is a combination of 60% tin to 40% lead (60/40 solder). This type is less expensive than 63/37 solder (63% tin to 37% lead) and is suitable for all general uses. 2023-02-06 B-07c Maintenance Practices Page 200 of 255 CASA Part 66 - Training Materials Only  Phase Diagram for Tin-Lead Alloy The behaviour of tin-lead solder is shown by a phase diagram below. This diagram shows that 100% lead melts at 327 °C and 100% tin melts at 232 °C. Solders that contain 19.5% to 97.5% tin remain solid until they exceed 183 °C. The eutectic composition for tin- lead solder is about 63% tin and 37% lead. (Eutectic means the point in an alloy system at which all the parts melt at the same temperature.) The plastic state is the condition in which the alloy is neither a liquid nor a solid. It is caused by solid particles being suspended in the remaining liquid. A 63/37 solder becomes completely liquid at 183 °C. Other compositions do not. Instead, they remain in the pasty stage until the temperature increases to the melting point of the other alloy. For instance, 50/50 solder has a solid temperature of 183 °C and a liquid temperature range of 214 °C. The pasty temperature range is 31 °C – the difference between the solid and the liquid. Solders with lower tin content are less expensive and are primarily used for sheet metal products and other high-volume solder requirements. High-tin solders are used extensively in electrical work. Solders with 60% tin or more are called fine solders and are used in instrument soldering, where temperatures are critical. Aviation Australia Tin-lead alloy phase diagram 2023-02-06 B-07c Maintenance Practices Page 201 of 255 CASA Part 66 - Training Materials Only  Wetting Action Solder forms a metallurgical bond with compatible metals, but it does not do this by fusion, as in welding or brazing. The solder bond is formed by wetting solid metal with liquid solder at the correct temperature. When the hot solder comes into contact with a metal surface, such as copper, a metal solvent action takes place. The hot solder dissolves and penetrates the surface. Wetting action can be described as the free flow and spread of solder to form a uniform, smooth, unbroken and adherent film of solder on a base metal. The wetting action is complete when all of the desired surface area is covered by solder and can be measured by the tangent angle at which the solder meets the surfaces of the metals being soldered. This is called the dihedral angle of wetting, shown in the diagram. Wetting action Dihedral Angle of Wetting Dihedral Angle Degree of Wetting 0° - 20° Excellent 20° - 40° Good 40° - 70° Fair 70° - 90° Marginal 90° - 180° Unacceptable 2023-02-06 B-07c Maintenance Practices Page 202 of 255 CASA Part 66 - Training Materials Only  The completeness of wetting is one of the prime indicators of a solder connection’s quality and reliability. Illustrating this, the illustration shows the difference between dihedral angles of fully wetted, partially wetted and non-wetted solder joints. To assist with inspection of soldered connections, the table shows the relationship between the dihedral angle and the degree of wetting. Lead-Free Solder Although it is one of the most widely used metal elements, lead is known to be toxic to humans because it bio-accumulates in the body. That is, it is retained over time and can have adverse health impacts when a sufficient accumulation has occurred. Once in the body, the lead binds strongly to proteins and inhibits normal synthesis and function. Effects include nervous and reproductive system disorders, delays in neurological and physical development, cognitive and behavioural changes, reduced production of haemoglobin with resulting anaemia, and hypertension. Because lead is very soluble in nature, it can be dangerous for our environment, too. Legislation is being developed worldwide to reduce or remove the lead content in electronic products. This is being taken as an action to reduce environmental impact when such products are discarded. On July 1, 2006, the European Union Waste Electrical and Electronic Equipment Directive (WEEE) and Restriction of Hazardous Substances Directive (RoHS) came into effect, prohibiting the intentional addition of lead to most consumer electronics produced in the EU. The United States and Japan have adopted a RoHS law, and China has a version as well. Nowadays, the transition from tin-lead solder to lead-free solder is rapidly taking on momentum around the world. An example of lead-free solder Lead-free solders in commercial use may contain tin, copper, silver, bismuth, indium, zinc, antimony and traces of other metals. Depending on the specific mix of metals, lead-free solder produces differing liquid, solid and pasty range temperatures. Check with the solder manufacturers for these specifics. 2023-02-06 B-07c Maintenance Practices Page 203 of 255 CASA Part 66 - Training Materials Only  Fluxes As of today, tin-silver-copper (Sn-Ag-Cu) alloy is considered the most acceptable lead-free solder. However, its melting point (~217 °C) is much higher than that of lead-rich solder, which poses new challenges in the soldering process. All metals oxidise to some extent when exposed to the atmosphere. This surface oxidation prevents a good metal-to-metal contact being made and therefore must be removed before solder will adhere to the work piece. Flux is a cleaning agent to remove oxidation during soldering. Heating a metal causes rapid oxidation. Oxidation prevents solder from reacting chemically with a metal. Flux cleans the metal by removing the oxide layer. This operation is shown in the illustration. Flux operation As the iron is moved in the direction shown, the boiling flux floats away the oxide film. The molten solder following the iron then fuses rapidly with the clean surface of the metal. WARNING: Liquid solder flux may generate a flammable vapour. Keep away from open flames and other sources of ignition. Avoid breathing fumes generated by soldering. Eye protection is required. 2023-02-06 B-07c Maintenance Practices Page 204 of 255 CASA Part 66 - Training Materials Only  There are several categories of soldering fluxes: Acid flux (or commonly known fluxes: zinc chloride, hydrochloric, ammoniac) Organic flux Rosin flux. Each flux has its own specific properties and may be used for different soldering technologies. Rosin Flux Rosin flux is usually included in solder wire core. So, when components are soldered with this wire, when heated flux is applied to the joint, the flux flows on the surface and removes oxide. Rosin fluxes may be different types of activity: R – rosin only RMA – rosin mildly activated RA – rosin activated. Surface cleanness determines which activity rosin to use. If the surface is very clean, use R rosin; for less clean surfaces, use RMA or RA rosin flux, but note that they have additional ingredients like organic acids and other acids. This means they leave inert residues after soldering. With soft solder, use only rosin fluxes conforming to Types R (non-activated) or RMA (mildly activated) of ANSI/J-STD-004 (Requirements for Soldering Fluxes). Regardless of the flux used, it is always recommended to clean joints with flux remover in order to avoid corrosion and contamination. Acid Flux Acid flux is most active of the group. It is effective on almost all metals, excluding aluminium and magnesium. But acid (chloride) flux has several significant disadvantages: it is highly corrosive, electrically conductive and difficult to remove from soldered joints. It is used for metal mending and plumbing. You should never use acid flux in electronic device soldering and repair, as it will cause corrosion and even short-circuit a device where gaps between tracks are small. 2023-02-06 B-07c Maintenance Practices Page 205 of 255 CASA Part 66 - Training Materials Only  Organic Flux Organic fluxes have almost the same effect as acid fluxes, but are less corrosive, do not conduct electric current and are easier to remove from soldered joints. But, again, they have corrosive effects if not cleaned well. Organic fluxes are also biodegradable if stored for longer times, making this flux unacceptable for microelectronics. Flux-Core Solder As mentioned earlier, rosin flux is usually included in solder wire core. Flux-cored solder is solder wire with a channel of rosin flux inside. It is the most common form of solder used in electrical/electronics repair and provides a convenient and controlled flux application. Aviation Australia Flux-core solder Due to concerns over atmospheric pollution and hazardous waste disposal, the electronics industry has been gradually shifting from rosin flux to water-soluble (WS) flux, which can be removed with de- ionised water and detergent instead of hydrocarbon solvents. 2023-02-06 B-07c Maintenance Practices Page 206 of 255 CASA Part 66 - Training Materials Only  Solvents Solvents are used as a chemical cleaning agent in the soldering process to: Remove light oils, greases, tarnish and other contaminants from the work piece prior to soldering Remove flux and its residues from the connection on completion of soldering. In the soldering environment, only approved solvents are to be used. The primary solvent now used for soldering is isopropyl alcohol (IPA). IPA is a general purpose solvent for removal of salts, residues (including flux) and other contaminants (such as finger oils) in all electronic equipment. Solvents Cleaning Process Initial cleaning is performed using: Three parts isopropyl alcohol mixed with one part de-ionised/de-mineralised water Water and non-ionic detergent. 2023-02-06 B-07c Maintenance Practices Page 207 of 255 CASA Part 66 - Training Materials Only  Precautions for Solvent Use The use of solvents requires precautions as detailed below: As solvents are flammable, keep them away from excess heat and ignition sources. Solvents remove skin oils; therefore, avoid prolonged skin contact. Avoid breathing fumes and vapours from solvents. Soldering is a safe process if the hazards are recognised and appropriate safety precautions observed. However, if you allow it, the soldering environment can be an extremely dangerous place to work. Complacency or even a momentary lapse in concentration while working in the soldering workshop can result in permanent injury to yourself or others. For this reason, it is important that you fully understand the hazards and work safely. In the event of an accident, you must know the correct first aid techniques and the location of emergency equipment. 2023-02-06 B-07c Maintenance Practices Page 208 of 255 CASA Part 66 - Training Materials Only  Soldering Safety Soldering Safety Hazards Burns High temperatures of soldering equipment and molten solder present a real risk of painful or dangerous burns. Burns may also be caused by chemical substances. To minimise the risk of a burn, observe the following conditions: Do not rest a hot soldering iron on a workbench or chair. Use an appropriate soldering iron holder. Do not flick excess solder from the tip of the soldering iron. Use a clean, dry sponge or cloth to clean hot soldering iron tips. Do not touch joints that have just been soldered. Support large work pieces securely while soldering. 2023-02-06 B-07c Maintenance Practices Page 209 of 255 CASA Part 66 - Training Materials Only  Fluxes and Solvents Many solvents and fluxes generate toxic fumes and vapours, particularly when heated. The effects of poisoning by inhalation or ingestion, either through the skin or mouth, may not be evident immediately. To reduce the possibility of these occurrences, the following should be noted: Wear suitable protective clothing. Use the minimum possible quantity of solvents. Keep solvent containers capped when not in use. Follow the manufacturer’s directions. Provide adequate ventilation. Do not allow degreasing solvents or fluxes to touch or remain on the skin unnecessarily. Wash hands thoroughly before eating or smoking. In addition to the above safety precautions, always ensure you exercise the following common precautions while working in any soldering environment: General Do not smoke, eat, drink or bring food into the work area. Do not work without supervision. Do not participate in horseplay. Keep benches and floors clean and tidy. Before all practical tasks: Ensure all equipment and tools are serviceable prior to use. Remove all jewellery. Roll sleeves down and fasten them. During all practical tasks: Observe applicable safety precautions pertinent to the equipment being used. Wear appropriate Personal Protective Equipment (PPE). After all practical tasks: Disconnect soldering irons from their power source or turn off the power source when they are unattended. 2023-02-06 B-07c Maintenance Practices Page 210 of 255 CASA Part 66 - Training Materials Only  First Aid The two most likely hazards requiring immediate first aid treatment are: Burns Solvent/solder in the eye(s). Burns Most burns from soldering are likely to be minor, and treatment is simple: Immediately cool the affected area under gently running cold water. Keep the burn in the cold water for at least 5 min (15 min is recommended). If ice is readily available, this can be helpful too, but do not delay the initial cooling with cold water. Do not apply any creams or ointments. The burn will heal better without them. A dry dressing, such as a clean handkerchief, may be applied if you wish to protect the area from dirt. Seek medical attention if needed. To reduce the risk of burns: Always return your soldering iron to its stand immediately after use. Allow joints and components a minute or so to cool down before you touch them. Never touch the element or tip of a soldering iron unless you are certain it is cold. Solvent/Solder in the Eye(s) If solvent or solder manages to enter the eyes, the following treatment is to be given: Do not attempt to remove solder. Allow solder to cool and dilute solvent by flushing with copious quantities of water. Place pads on both eyes. Transport patient to medical. 2023-02-06 B-07c Maintenance Practices Page 211 of 255 CASA Part 66 - Training Materials Only  Soldering Tools Heat Application Methods Soldering Iron The most commonly used method of heat application for soldering joints in aircraft electrical wiring is an electrically heated, hand-held soldering iron. In addition to the conventional iron, a pencil iron is frequently used. Pencil irons, except for their smaller size, are identical to conventional irons and are used for precision soldering of small units and miniature assemblies. Resistance Soldering Resistance soldering is frequently used in large-volume production, where the operation is standardised. In this method, a low-voltage transformer is used and the metal to be soldered is heated by the resistance to a flow of electric current. The work is gripped between two electrodes, completing the circuit and heating the metal for soldering. In another application, a carbon pencil is used as one electrode and the metal to be soldered forms the other electrode. When contact is established through the carbon pencil, intense heat is generated at the point of contact. Resistance soldering is well adapted for soldering small parts or for congested assemblies, where it is desired to restrict heat to a small part of the assembly. Torch Soldering Torch soldering is used where high heat is required – as in silver soldering. It uses a flame rather than a soldering iron tip to heat solder. Soldering torches are often powered by butane. This process is also suitable for soft-soldering large work which is not part of an assembly or when the part to be soldered can be removed for soldering. For example, wires may be torch-soldered to large contacts that have been removed from MS connectors. Torch soldering is not suitable for soldering small parts. Dip Soldering Dip soldering is the process of immersing connections in molten solder; one or more connections can be made in a single operation. This process is used on printed circuits, where the conductor pattern is on one side of the board and the components on the opposite side. Joints are mechanically secured and dipped first into liquid flux, then into molten solder. 2023-02-06 B-07c Maintenance Practices Page 212 of 255 CASA Part 66 - Training Materials Only  Soldering Irons The most obvious and useful tool used in soldering operations is the soldering iron. Depending on the type of soldering application, you will find there is a specific iron designed to suit that purpose. The following is a list of the various types commonly used: Instant heat Constant heat Thermostatically controlled Electronically controlled. Instant Heat The instant heat iron, as shown in the illustration, is used for general soldering where high heat is required. Power is controlled by an on/off trigger switch, making the temperature at the tip virtually uncontrollable. Owing to the way instant heat tools operate, they are generally prohibited from use on electronic equipment. Instant heat iron 2023-02-06 B-07c Maintenance Practices Page 213 of 255 CASA Part 66 - Training Materials Only  Constant Heat Illustrated below is the constant heat iron. It is used for general soldering in Automotive/General Service Equipment (GSE) areas where the equipment is not heat sensitive. The tip heats to its idle temperature and, when placed on the connection, drops to its working temperature. Aviation Australia Constant heat iron Thermostatically Controlled The thermostatically controlled iron, as shown below, is also used for general soldering in Automotive/GSE settings and is similar in construction to the constant heat iron. The main difference is a thermostat used to control the tip temperature. To control the tip temperature, the thermostat switches power on and off to the heater element. This action maintains the tip within reasonable temperature limits. Unfortunately, the response time of the thermostat tends to allow a sizeable temperature variation, resulting in the tip temperature ‘hunting’ around a preset level. Aviation Australia Thermostatically controlled iron 2023-02-06 B-07c Maintenance Practices Page 214 of 255 CASA Part 66 - Training Materials Only  Electronically Controlled The diagram below illustrates the most commonly used soldering iron in use today: the electronically controlled soldering iron. Notice in the illustration that the temperature sensor is very close to the tip. This construction provides constant feedback to the control unit, thereby maintaining the tip at a stable working temperature. These irons are also fast heating, have a rapid recovery time and allow a wide range of temperatures to be set. Aviation Australia Electronically controlled iron Soldering Iron Preparation For successful, effective soldering, the soldering iron tip must be tinned to provide a completely metallic surface through which the heat may flow readily from the iron to the metal being soldered. If no tinning is present, the iron oxidises and the heat cannot flow through. Copper has a very high rate of heat conductivity, but copper tips oxidise quickly and must be frequently cleaned and re-tinned. If a tip has become badly burned and pitted as a result of overheating, replace it. 2023-02-06 B-07c Maintenance Practices Page 215 of 255 CASA Part 66 - Training Materials Only  Preparing the Soldering Iron Before using the soldering iron, prepare it as follows: With the iron shut off, file each working surface of the soldering iron tip with a double-cut mill file until it is smooth and a bright copper colour. Remove copper fuzz from dressed edges with a file card. Plug in the iron and apply cored solder just as the bright dressed copper colour is turning to a pigeon-blue, bronze, oxide colour. This allows the flux to ‘wet’ and clean the work area when the solder melts to form an even, bright silver coating on the tip. CAUTION: Do not allow the iron to reach full temperature before starting the tinning operation. Wipe off excess solder with a damp sponge or cloth. Note: Do not file soldering iron tips coated with pure iron. Filing will ruin the protective coating. If the tip is pitted, replace it. Some copper soldering iron tips used in production soldering are coated with pure iron to help prevent oxidation. Follow the manufacturer’s instructions to clean such irons. A clean, damp cloth may be used to wipe the iron. Aviation Australia Preparing the soldering iron 2023-02-06 B-07c Maintenance Practices Page 216 of 255 CASA Part 66 - Training Materials Only  Soldering Iron Maintenance Prior to use, remove the tip from the iron and clean out the black scale from the inside of the iron and from the tip with fine steel wool. When the iron or tip is new, coat the inside of the shank with dry flake graphite or anti-seize material to prevent freezing and to ensure maximum heat transfer. When replacing the tip, make sure it is inserted to the full depth of the casing and seated firmly against the heating element. Caution: Never shake or ‘whip’ an iron to get rid of dross (scum formed on top of molten metal) or excess solder droplets. During use and just before each application, pass the soldering iron tip (with a rotary motion) through the folds of a damp cleaning sponge or wipe on a wiping pad. This will remove the surface dross and excess solder from the working surface. Soldering iron maintenance 2023-02-06 B-07c Maintenance Practices Page 217 of 255 CASA Part 66 - Training Materials Only  Soldering Iron Tips Soldering tips are manufactured from various copper alloys chosen for their high thermal conductivity and excellent heat strength. To extend its useful life, the tip is plated with a combination of iron, nickel and chromium. This is done to protect the bare metals, which oxidise rapidly at soldering temperatures and are easily dissolved by molten solder. To enable a soldering tool tip to readily accept solder, further treatment is applied to the working surfaces of the tip. This process is referred to as tinning. Aviation Australia Various soldering iron tips An iron tip should be tinned (solder applied to the tip after the iron is heated) prior to soldering a component in a circuit. After extended use of an iron, the tip tends to become pitted due to oxidation. Pitting indicates the need for re-tinning. The tip is re-tinned after it has been filed smooth. To maintain the tip in good order, the tip should be kept clean and loaded with excess solder when not in use. 2023-02-06 B-07c Maintenance Practices Page 218 of 255 CASA Part 66 - Training Materials Only  Maintenance of the soldering iron is to be carried out at regular intervals. The minimum requirement of this maintenance is: Remove the tip from the barrel of the soldering iron to prevent seizure of the tip. Use a wire brush to clean the barrel to remove traces of oxidisation. During operation of the iron, ensure that there is always sufficient solder on the tip while in the idle mode. Check the condition of the power leads and have them repaired or replaced as required. Soldering Tip Insertion and Extraction Care must be taken during both the insertion and extraction of the solder tip. Do not rotate or bend the tip, as damage to the temperature sensor may result. Solder tip insertion is to be carried out using the steps illustrated. Removal of the soldering tip and sleeve is performed by grasping the protruding length of sleeve against the tip using tip pliers, and removing by a straight pull. Aviation Australia Solder tip insertion and extraction 2023-02-06 B-07c Maintenance Practices Page 219 of 255 CASA Part 66 - Training Materials Only  Solder Pots The solder pot, as shown in the photo and diagram, is a form of constant heat soldering iron, fitted with a crucible (pot) for molten solder. It is used for pre-tinning components and wires prior to soldering. Solder pots 2023-02-06 B-07c Maintenance Practices Page 220 of 255 CASA Part 66 - Training Materials Only  Resistance Tweezers Resistance tweezers, as shown in the diagram, operate differently to soldering irons. The connection is heated by passing a high current through the terminal. They are commonly used on soldering terminals and plugs, where it is not practical to use a conventional iron. Remember that the current, and consequently the heat, flows between the two points where the probes contact the work. You want to have these points as close to the joint as practical. This avoids overheating the work and un-soldering already finished joints. Remember, no electrical contact, no current flow, no heat. Aviation Australia Resistance tweezers 2023-02-06 B-07c Maintenance Practices Page 221 of 255 CASA Part 66 - Training Materials Only  Heat Sinks The real skill in soldering relates to the speed at which it can be performed. You should be able to solder a typical connection in well under 5 s. Many components are extremely heat sensitive and could be destroyed during the soldering operation by the flow of heat conducted along the lead. Heat sinks are used to absorb this conducted heat. Heat sinks Heat sinks have two basic and essential features: A narrow clamping area which is attached to the component lead A large body area which absorbs and dissipates heat. If no commercial type of heat sink is available and there is a danger of damaging the components to be installed, a heat sink may be improvised from any other tool which has these features. For example: An alligator clip is quick, efficient and easy to handle. Long-nose pliers with smooth jaws may be clamped onto the lead and the jaws held closed by wrapping a rubber band around the handle. 2023-02-06 B-07c Maintenance Practices Page 222 of 255 CASA Part 66 - Training Materials Only  De-Soldering Tools In electronics, de-soldering is the removal of solder and components from a circuit for troubleshooting, for repair purposes and to salvage components. When it is necessary to remove components from a printed circuit assembly, their leads or lugs must first be de-soldered so that they can be readily withdrawn through the board to free the components. There are two ways to remove the solder: With solder wick (also de-soldering wick, copper braid) – the most common method of removing solder from PCBs With a de-soldering pump (solder sucker). In general, you should always first attempt to de-solder a joint using de-soldering wick unless you have significant prior skill using a de-soldering pump. After removing most of the solder from the joint(s), you may be able to remove the wire or component lead straightaway (allow a few seconds for it to cool). If the joint will not come apart easily, apply your soldering iron to melt the remaining traces of solder while simultaneously pulling the joint apart, taking care to avoid burning yourself. 2023-02-06 B-07c Maintenance Practices Page 223 of 255 CASA Part 66 - Training Materials Only  Solder Wick Solder wick is a cheap and very effective way of de-soldering a joint. Take care not to overheat the board. Select a suitable width of braid and press it down onto the cold joint using the hot tip of the iron. Molten solder is drawn up by capillary action into the braid. Once everything has melted and the solder fuses with the braided copper, the wick is lifted along with the solder and is then cut off and disposed of. Do not let the braid solidify on the joint. In the photo, the lower solder wick is soaked with solder (The black spots are impurities). Solder wick 2023-02-06 B-07c Maintenance Practices Page 224 of 255 CASA Part 66 - Training Materials Only  De-Soldering Pump A de-soldering pump may also be used to disconnect a joint. The manual type uses a manually set pump, while de-soldering stations use an integral electric vacuum pump. If using a de-soldering pump, apply the iron first to melt the solder (1–2 s). Ensure the pump is primed and ready to go. Apply the pump to the molten solder and release the spring-loaded plunger. This will draw the solder up into the pump. Repeat if needed. A de-soldering pump 2023-02-06 B-07c Maintenance Practices Page 225 of 255 CASA Part 66 - Training Materials Only  Soldering Process The Soldering Procedure Regardless of the heating method used in the soldering process, a good connection results only if the proper soldering techniques are followed and certain precautions observed. A quality soldered joint can be accomplished only on a mechanical connection of approved geometry, dress and dimensions. The following instructions apply generally to soldering operations. General soldering operation Cleanliness Cleanliness is of the utmost importance in the soldering operation. If possible, soldering should be done in clean, dust-free environment. Areas prone to drafts should be avoided so that the soldering iron will not cool. Parts contaminated with dirt, oil, grime, grease, etc., cannot be successfully soldered. Ensure that the parts are mechanically ‘bright-clean’ before soldering. Clean the parts with a cloth or brush dipped in alcohol or another approved solvent. Badly corroded parts may be cleaned carefully by mechanical means, such as fine abrasive paper or a wire brush. 2023-02-06 B-07c Maintenance Practices Page 226 of 255 CASA Part 66 - Training Materials Only  Pre-tinning Wires to be attached to most electrical connectors must be pre-tinned. Copper wires are usually tinned by dipping into flux and then into a solder bath. In the field, copper wires can be tinned with a soldering iron and rosin core. Tin the conductor for about half its exposed length. This is enough to take advantage of the closed part of a solder cup. Tinning or solder on wire above the cup causes wire to be stiff at the point where flexing takes place. This results in wire breakage. Selection of Flux and Solder The following soft solders may be used on aircraft electrical systems: For general applications at temperatures up to 120 °C, use: Non-activated flux-cored solder, 60% tin, 40% lead, 1.2 mm diameter, qualified to BS441 Non-activated flux-cored solder, 60% tin, 40% lead, 0.7 mm diameter, qualified to BS441. For applications with silver-plated components, use non-activated flux-cored solder, 62% tin, 2% silver remainder lead, 0.9 mm diameter, qualified to Federal Specification QQ-S-571. For high-temperature applications (190 °C) use solid wire solder, 97.5% lead, 1% tin, 1.5% silver, 16 SWG, qualified to SAE AMS 4756. CAUTION: Do not use any corrosive flux in aircraft electrical wiring. Selection of Soldering Iron The sole purpose of the soldering iron is to heat the joint to a temperature high enough to melt the solder. Select a soldering iron with a thermal capacity high enough so that the heat transfer is fast and effective. An iron with excessive heat capacity will burn or melt wire insulation; an iron with too little heat capacity will make a cold joint in which the solder does not alloy with the work. Soldering irons are available in ranges from 20 to 500 W. Irons with ratings of 60, 100 and 200 W are recommended for general use in aircraft electrical wiring. Pencil irons with a rating of 20–60 W are recommended for soldering small parts. The soldering iron recommended for printed circuit soldering is a lightweight 55-W iron with a 315 °C Curies point tip control. This iron has a three-wire cord to eliminate leakage currents that could damage the printed circuits. A soldering iron should also be suited to the production rate. Do not select a small pencil iron where a high steady heat flow is required. 2023-02-06 B-07c Maintenance Practices Page 227 of 255 CASA Part 66 - Training Materials Only  Selection of Soldering Tip The tip transfers heat from the element into the work, and for maximum efficiency, the tip face must suit the joint to be soldered. Generally, the shape of the tip face should provide the best fit into the joint and, consequentially, the best heat flow. The optimum tip face should be between two-thirds and three-quarters of the joint diameter. The illustration provides a rough guide to selecting a suitable soldering tool tip. Choice of soldering tip Screwdriver, chisel and pyramid shapes are recommended. Soldering Iron Tip Before starting the soldering operation, make sure the iron tip is clean, smooth and well tinned. Tinning the tip of the iron helps conduct heat to the components. Securing the Joint Whenever possible, make sure the joint is mechanically secure before soldering. When this is not possible (as with MS connector contacts), make sure it is held rigid during the cooling period. 2023-02-06 B-07c Maintenance Practices Page 228 of 255 CASA Part 66 - Training Materials Only  Application of Heat and Solder Apply flux-core solder at the exact point between the metal and the soldering iron (as shown in the illustration) and hold the iron directly against the assembly. Application of heat and solder Melt the solder on the joint, not the iron. Place the soldering iron firmly against the junction. If heavy ‘rocking’ pressure is necessary, either the iron does not have sufficient heat capacity for the job, it has not been properly prepared or both. Heat Application Time Do not apply heat to the work any longer than the time necessary to melt the solder on all parts of the joint. Amount of Solder Do not use any more solder than necessary. Do not pile up solder around the joint; this is wasteful and results in joints difficult to inspect. Exercise care with silver-coated wire to prevent wicking during solder application. Soldering Iron Holder When the soldering iron is not in active use during operations, keep it in a holder. This protects the operator against burns and the iron against damage. 2023-02-06 B-07c Maintenance Practices Page 229 of 255 CASA Part 66 - Training Materials Only  Protection Against Overheating Do not allow the iron to overheat. Disconnect the iron when it is not in use (between operations), or use a heat-dissipating stand that will keep the iron at a constant temperature. Cooling the Solder Joint When the solder joint has been made, hold the work firmly in place until the joint has set. Disturbing the finished work will result in a mechanically weak joint with high electrical resistance. Allow solder joints to cool naturally. Do not use liquids or air blasts. Post-Solder Cleaning If the correct amount of solder is used and procedure instructions followed carefully, there should be little or no excess flux remaining on the finished joint. If cleaning is required, flux residue should be removed as soon as possible, but no later than 1 hr after soldering. Some fluxes may require more immediate action to facilitate adequate removal. Mechanical means such as agitation, spraying, brushing and other methods of application may be used in conjunction with the cleaning solution. The cleaning solvents, solutions and methods used should not have affected the parts, connections and materials being cleaned. After cleaning, the finished joint should be adequately dried. Clean the oxidation and excess solder from the tip of the soldering iron. Soldering iron station and use of external flux 2023-02-06 B-07c Maintenance Practices Page 230 of 255 CASA Part 66 - Training Materials Only  Soldering Variables Prior to actually soldering, you must evaluate the work piece to be soldered. In order to perform a high-quality solder connection, the following variables must be considered: Soldering temperature Soldering time Soldering tip size and shape Position of the tip Solder gauge Heat bridge. Soldering Temperature It has been found that the most efficient soldering temperature range to form a proper joint is 240– 270 °C. Soldering Time The time it takes to raise the connection to soldering temperature should be no more than 1–2 s. The time the connection is maintained at this temperature is ideally 2–3 s. This tends to keep the soldering time in the region of 3–5 s, well within the safe limits of most components. Soldering Tip Size and Shape Selection of the correct tip relates to the shape and thermal mass of the work piece to be soldered. A small tip thermal mass in relation to a large work piece thermal mass causes the tip temperature to drop radically and the solder joint temperature to rise too slowly. This causes heat dissipation to unwanted areas, which could result in damage or degradation. A large tip thermal mass to a small work piece thermal mass relationship could raise the temperature at such a rapid rate that the reaction time required to complete the soldering process may be beyond the capabilities of the technician to control. This would result in damage or degradation by overheat. Position of the Tip Position the tip so that all parts of the connection will be raised to the selected soldering temperature simultaneously, and in the shortest possible time. 2023-02-06 B-07c Maintenance Practices Page 231 of 255 CASA Part 66 - Training Materials Only  Solder Gauge The gauge of solder must be selected in relation to the size of the work piece. Using large-gauge solder on a small termination will likely cause too much solder to be deposited. Small-gauge solder used on a termination requiring greater amounts is likely to result in overheating due to the excessive time required to feed in the solder. Heat Bridge Even with the correct combination of variables, the thermal link between the tip and the work piece will not be sufficient to raise all the working surfaces of the work piece to soldering temperature within the specified time. The thermal link must be increased by the establishment of a heat bridge. A heat bridge, as shown in the illustration, is a small quantity of solder applied to the junction of the working surfaces and the soldering tip. The solder flows by capillary action and gravity, providing heat transfer paths to all parts of the connection. This technique provides more rapid and even heat transfer/distribution to the working surfaces. Aviation Australia Heat bridge 2023-02-06 B-07c Maintenance Practices Page 232 of 255 CASA Part 66 - Training Materials Only  Tinning Tinning is the process of applying a thin coating of solder to the working surface of a metal. Tinning assists in the transfer of heat from the tip to the work and protects the plating on the tip from corrosion (oxidation) which occurs more rapidly when metals at high temperature are exposed to the air. Tinning also protects the plating on the tip from physical damage when the tip is not in use. All tips must be tinned to work correctly. When properly applied, the tinning should cover the entire working surface of the tip. Aviation Australia Tinning New tips are already tinned by the manufacturer, but prior to using them, it is advisable to check the tinning and tin them again. Excessive tinning causes stiffness which may result in breakage and contamination under insulation. It can be prevented by using anti-wicking tools and tweezers. The solder must completely wet the conductor, penetrate to the inner strands and exhibit 100% coverage. Wire strands must be distinguishable. Wicking of flux or solder must be minimised. When tinning, it is important that the tinning does not extend under the insulation to prevent flux being deposited there (where it cannot be cleaned away). It also provides a length of flexible wire between the tinned portion and the insulation. After tinning, the conductor insulation must not exhibit any damage, such as nicks, cuts or charring. Conductors with damaged insulation cannot be used. 2023-02-06 B-07c Maintenance Practices Page 233 of 255 CASA Part 66 - Training Materials Only  Wire tinning 2023-02-06 B-07c Maintenance Practices Page 234 of 255 CASA Part 66 - Training Materials Only  Inspecting a Finished Solder Joint Acceptable Solder Joint A good soldered joint has a bright silvery appearance, with smooth fillets and feathered non-sharp edges, and its connection is mechanically strong. The entire joint is covered with a smooth, even coat of solder, and the contour of the joint is visible. Unacceptable Solder Joint If the solder balled up on the joint, it was probably not hot enough. A rough, grey-looking joint also indicates improper heating. If the soldering iron tip is not properly tinned, it does not conduct heat adequately to the material being soldered. A solder joint with poor electrical integrity is referred to as ‘cold’. A cold solder joint is not mechanically solid, either. Wiggle the soldered component to verify it is tightly bonded together. Any of the following indicate a poor solder joint and are cause for rejection: Dull grey, chalky or granular appearance – evidence of a cold joint Hair cracks or irregular surface – evidence of a disturbed joint Greyish, wrinkled appearance – evidence of excessive heat Partially exposed joint – evidence of insufficient solder Scorched wire insulation or burned connector inserts Globules, drips or tails of solder. If any of the above conditions are present in a finished solder joint, the joint should be taken apart, parts cleaned and the entire soldering operation repeated using fresh solder and flux. An unacceptable example of a solder joint 2023-02-06 B-07c Maintenance Practices Page 235 of 255 CASA Part 66 - Training Materials Only  Soldering Terminals Many types of terminals are used to connect wires and components in electronic assembly. Each type usually requires modification of the general soldering procedure. Wires must be stripped and pre- tinned before soldering to terminals. There are five common types of terminals: Turret terminal Bifurcated terminal Solder cup terminal Perforated or pierced terminal Hook/pin terminal. Turret Terminal The turret terminal is round. The wire is wrapped around it using long-nose pliers. When soldering, the insulation gap (referenced from the first point of contact of the conductor to the terminal) should be one to two wire diameters, but should not be embedded in the solder joint. The lead outline should be discernible, with a smooth flow of solder on the wire and terminal. The wire contour should be visible at the end of the insulation. Acceptable and unacceptable turret terminal soldering The picture on the right shows a defective turret terminal because the solder fillet is less than 75% of the circumference of the wire and terminal interface. To ensure a proper joint, follow these steps as shown in the illustration: 1. Apply the iron to the point of maximum thermal mass. 2. Create a solder bridge to increase thermal linkage. 3. Apply the solder to the side opposite the iron. 4. Remove the iron tip with a forward wiping motion. 2023-02-06 B-07c Maintenance Practices Page 236 of 255 CASA Part 66 - Training Materials Only  Turret soldering technique Bifurcated Terminal The bifurcated terminal has two upright posts with a slot through the terminal. Soldering a bifurcated terminal The conductors should enter the slot, perpendicular to the posts, and make positive contact with at least one post corner. The lead profile should be discernible, with the wire and terminal interface completely wetted. The solder should be smooth and shiny and fillet the entire wire/lead and terminal interface. When multiple conductors are connected to a terminal, they should be placed in ascending order, with the largest on the bottom, the direction of bend of each additional conductor alternating and the terminations alternating between posts. The end tail should not extend beyond the diameter of the terminal base, except when physical clearance is adequate. End tail overhang may violate minimum electrical clearance. 2023-02-06 B-07c Maintenance Practices Page 237 of 255 CASA Part 66 - Training Materials Only  To solder a bifurcated terminal properly, follow these steps as shown: 1. Apply the iron to the point of maximum thermal mass. 2. Create a solder bridge to increase thermal linkage. 3. Apply the solder to the side opposite the iron. 4. Remove the iron with a wiping motion. Soldering a bifurcate Solder Cup Terminal A solder cup terminal is a hollow, cylindrical terminal designed to accommodate one or more conductors. This style of terminal is principally designed as a precision-machined pin for insertion into connector bodies. Variations include connectors in which the solder cup pin is captive in the connector body (i.e. hermetic connectors), or printed wiring board mounted terminals designed for discrete wire terminations. The wire should be inserted straight into the cup and contact the back wall, extending to the full depth and bottoming in the cup. The assembly should exhibit a proper insulation gap and the cup interior should be pre-tinned. The solder should form a fillet between the conductor and the cup entry slot, following the contour of the cup opening. Solder cup terminal 2023-02-06 B-07c Maintenance Practices Page 238 of 255 CASA Part 66 - Training Materials Only  Soldering a Cup Terminal The procedure for soldering a cup terminal is as follows (see illustration): 1. Trim the pre-tinned wire to the correct length to fit in the cup. 2. Remember to leave one to two diameters of bare wire before the insulation. 3. Twist a small length of solder together so that it has a loop at one end. 4. Place the twisted solder into the cup and cut it to match the length of the cup. 5. Place an iron on the back of the cup. Leave the iron there until the solder begins to melt. Now insert the wire into the cup. Continue to leave the iron on the cup until the flux boils or bubbles (not vaporised) to the surface. Remove the iron, but hold the wire stationary until the solder solidifies. Soldering a cup Acceptable Solder Cup Terminal The solder quantity is the maximum acceptable, but does not spill over (exceed the diameter of the cup) or exhibit a convex profile. 2023-02-06 B-07c Maintenance Practices Page 239 of 255 CASA Part 66 - Training Materials Only  Acceptable solder The solder quantity is sufficient to follow the contour of the cup opening. The termination is fully wetted with complete, slightly concave fillets between the wire and the cup wall. Solder fill is at least 75% around the wire/conductor and terminal interface. Unacceptable Solder Cup Terminal The solder follows the contour of the cup opening, but spills over (exceeds the diameter of the cup) with a convex profile. The solder quantity is insufficient to follow the contour of the cup opening. The termination is fully wetted, but exhibits incomplete fillets along the conductor. The solder surface is not visible in the bottom of the cup. Unacceptable solder 2023-02-06 B-07c Maintenance Practices Page 240 of 255 CASA Part 66 - Training Materials Only  Acceptable Multiple Terminations The maximum number of conductors that can be inserted into the cup is limited to those that can be in contact with the full height of the back wall of the cup. All wires must exhibit proper insulation gaps, but do not need to exhibit equal gaps. It is unacceptable for the number of conductors inserted to exceed the number that can be in contact with the full height of the back wall of the cup. Acceptable Spillage Solder along the outside of the cup (spillage) is acceptable provided the solder deposit approximates tinning and does not interfere with the form, fit or function of the connector. It is unacceptable if the solder deposit interferes with the form, fit or function of the connector. Unacceptable conductors and spillage 2023-02-06 B-07c Maintenance Practices Page 241 of 255 CASA Part 66 - Training Materials Only  Perforated/Pierced Terminal In a perforated terminal, the wire should pass through the eye of the terminal, wrap in contact with both sides of the terminal and not overhang the terminal edge. Insulation clearance should be less than one wire diameter. The lead profile should be discernible, with the wire and terminal interface completely wetted. The solder should be smooth and shiny and fillet the entire wire/lead and terminal interface. It is considered a defect if the solder de-wets from the terminal and the solder contact angle is greater than 90°. Soldering perforated / pierced terminal Hook/Pin Terminal In a hook terminal, the conductor should be wrapped in full contact with the terminal for a minimum of 180º and a maximum of 270º, and should be attached to the hook within the 180º arc. Insulation clearance should be less than one wire diameter, and the wire end should not protrude. The lead profile should be discernible, with the wire and terminal interface completely wetted. The solder should be smooth and shiny and fillet the entire wire/lead and terminal interface. The conductors should be wrapped in full contact for a minimum of 180º. Wraps must alternate direction and not overlap. Terminations should be located more than one wire diameter from the hook end, with the majority located within the 180º arc (hook). Hook / pin terminal 2023-02-06 B-07c Maintenance Practices Page 242 of 255 CASA Part 66 - Training Materials Only  Unacceptable Hook Terminal Soldering Improper wrap location – The termination is not located in the 180º arc of the terminal, with the wrap located less than one wire diameter from the hook end. Soldering defect – The joint does not exhibit a solder fillet joining the wire to the terminal for at least 75% of the wire and terminal contact, or the solder contact angle is greater than 90°. Unacceptable hook terminal soldering 2023-02-06 B-07c Maintenance Practices Page 243 of 255 CASA Part 66 - Training Materials Only  PCB Soldering Soldering on Printed Circuit Boards Printed circuit boards (PCBs) are etched with a pattern of electrically conductive tracks on one or both sides. These tracks provide the connection between individual components whose leads are generally inserted through holes in pads. The boards are laminated and some are made of fibreglass composition, making them strong and resistant to heat, cold, moisture and corrosion. The tracks are bonded to the boards and are made from copper or solder alloy-coated copper. Other metals can also be used, depending on the application. The preparation and precautions prescribed for soldering conventionally wired equipment apply to soldering PCBs. However, due to the delicate nature of the metal foil wiring, pattern-to-pattern bonding and increased heat sensitivity of miniaturised parts, additional cautions are necessary. Soldering on printed circuit boards 2023-02-06 B-07c Maintenance Practices Page 244 of 255 CASA Part 66 - Training Materials Only  PCB Soldering General Precautions Observe the following general precautions when soldering PCB connections: Always handle printed circuit boards by their edges, or with cotton gloves, to avoid contaminating the pads and tracks with oils and grease from your fingers. Oil and grease can prevent the solder from properly wetting the pads and making a good connection. Use solder with a small diameter (1/32 in. maximum) and a low melting temperature to reduce the amount of heat required for soldering. Solder using a temperature-controllable soldering station. Set it to a level which allows a more acceptable solder connection to be made in a maximum of 5 s. Use grounded tip, electrically isolated, ‘spike free’ soldering equipment to prevent damage to solid state devices. Use enough thermal shunts (heat sinks) to sufficiently protect heat-sensitive components. Limit the total time of heat application to the time required to melt solder and provide proper wetting (fusion) of the solder with the terminal pad and component lead. Apply only the minimum heat required to produce satisfactory solder connections. If you experience difficulty in soldering a connection, halt the operation and allow the connection to cool completely before attempting to re-solder. Remove flux and flux residues from solder connections, using solvent within 90 min after the completed connection has cooled, i.e. immediately prior to applying the conformal coating. After cleaning, do not touch the surfaces to be soldered with your bare hands. Store parts to be soldered, when not being processed, to maintain their cleanliness. Do not allow the surfaces to be soldered to contact material other than Teflon, nylon, polyethylene, vinyl or other non-contaminating or non-abrasive material during storage. When coating is being melted, use additional ventilation. 2023-02-06 B-07c Maintenance Practices Page 245 of 255 CASA Part 66 - Training Materials Only  PCB Soldering Techniques The leads of all types of components can be mounted to a PCB in several ways. The straight-through method is the easiest to use. In the clinched method, the lead is bent 90° onto the pad or conductor. This helps stabilise the component during the soldering process. The semi-clinched method has a 45° bend in the lead. A swaged or spaded lead is one that extends beyond the hole and is then flattened so that it is wider than the diameter of the hole. The swaged end helps to hold the component in the proper position during handling and soldering. However, removing this type of lead requires more time and special procedures. Mounting styles on a PCB After the leads of the component are formed, the component is placed into the PCB as shown below. The component is held in place and the leads protruding through the holes are trimmed (cut) to the proper length, depending on the type of termination used. If the termination is the clinched type, the end of the lead is bent over the conductor with a non-metallic tool so as not to scratch the lead. 2023-02-06 B-07c Maintenance Practices Page 246 of 255 CASA Part 66 - Training Materials Only  Mounting a component on a PCB Soldering components onto PCBs requires considerable caution due to the heat sensitivity of both the board and components. The copper foil, which is about 0.0014 to 0.0028 in. thick, is sensitive to heat. A hot soldering iron tip can rapidly deform or lift the board's pads or conductors if too much pressure is applied. Also, if the iron tip is left on one spot for too long, the conductor may lift off the board. The soldering iron should never be pushed down on the pad, but merely rest on it. The illustrations below show the general procedure for soldering leads on a PCB. The solder and iron are placed on the same side of the lead initially to create a solder bridge. The solder is then moved to the opposite side of the lead and allowed to flow for a short time. Soldering technique PCB The solder is removed, and the iron is removed with a wiping action. For a clinched lead, wipe in the direction of the lead, and for a straight-through lead, wipe in an upwards motion. The solder joint is then cleaned with a solvent, such as alcohol, to remove any flux residue. Finally, the solder joint is inspected for acceptable quality. 2023-02-06 B-07c Maintenance Practices Page 247 of 255 CASA Part 66 - Training Materials Only  Solder technique PCB When the solder joint is made, a brown waxy substance is left on the joint. This is a flux residue, and in its original state, it is slightly corrosive. Any flux residue or excess flux must be removed from the joint before soldering can be considered complete. If the flux residue and excess flux are not properly removed, their corrosive nature will gradually destroy the component leads or circuit board tracking material. The flux residue is also tacky and, if not removed, collects dust and debris and often leads to circuit failure over time. Flux residue must be cleaned 2023-02-06 B-07c Maintenance Practices Page 248 of 255 CASA Part 66 - Training Materials Only  Inspecting a PCB Solder In a quality solder connection on a PCB, the solder joint surfaces are smooth, nonporous and undisturbed, with a finish varying from satin to bright. The fillet completely wets all elements of the connection and is concave in shape, feathering out smoothly to the edge of the pad. A good solder connection on PCB Leads terminated straight through the PCB must extend 0.5–2.29 mm beyond the pad surface. Leads may be bent up to 30° from the vertical plane to retain the part during soldering. Inspection of solder connection 2023-02-06 B-07c Maintenance Practices Page 249 of 255 CASA Part 66 - Training Materials Only  Cold Joint A cold joint occurs where the flux has been unable to remove the tarnish from the joint and the viscous solder has displaced flux and bonded directly to the tarnish. At low temperatures, the flux is only partly activated and is therefore less effective at removing tarnish. Indications of a cold joint include: High electrical resistance Intermittent electrical connection Poor wetting of the joint A convex solder fillet A step at the edge of the solder flow. A cold joint Dry Joint or Rosin Bond A rosin bond is formed when the solder is too viscous to push flux away from the component lead and a layer of the flux becomes trapped around the lead. This layer of flux causes a weak bond and a poor electrical connection. Indications of a rosin joint are similar to those for a cold joint but also include an apparent film of flux trapped against the component lead. It is typically caused by dirty or oxidised component leads. 2023-02-06 B-07c Maintenance Practices Page 250 of 255 CASA Part 66 - Training Materials Only  A dry joint 2023-02-06 B-07c Maintenance Practices Page 251 of 255 CASA Part 66 - Training Materials Only  Wire Wrapping Solderless Wire-Wrapping Process The solderless wire-wrapping process is a convenient method used to terminate a wire that does not require soldering to form the connection. Although not commonly used in most aircraft applications, it is still encountered in some equipment types (B747-400). Solderless wire-wrapping is done by helically wrapping a solid uninsulated wire around a specially designed termination post to produce a mechanically and electrically stable connection. Wire wrapping Three major components are used during the solderless wire‑wrapping process: Wrapping wire Wire-wrap post Wire-wrap tool. 2023-02-06 B-07c Maintenance Practices Page 252 of 255 CASA Part 66 - Training Materials Only  Number of Turns in a Wire Wrap The countable turns are those turns of bare wire in intimate contact with the corners of the terminals, starting at the first contact of bare wire with a terminal corner and ending at the last contact of bare wire with a terminal corner. Aviation Australia Number of turns in a wire-wrap Wrapped terminations usually have four to seven turns of bare wire wrapped around the terminal post. The exact number of turns varies depending on the wire gauge used and the terminal size. The two types of wire-wrap classifications are: Class A – Modified Connections Class B – Conventional Connections, prohibited in aircraft. Class A – Modified Connections Class A provides improved vibration characteristics and is the required wrap style for airborne hardware applications. This modified, wire-wrapped joint requires one half to two turns of insulated wire in contact with a minimum of three corners of the wrap post, in addition to the uninsulated wraps. 2023-02-06 B-07c Maintenance Practices Page 253 of 255 CASA Part 66 - Training Materials Only  Class A wire-wrap Class B – Conventional Connections Class A connections are the preferred type and should be used in preference to Class B. Class B connections can only be used in circumstances where wire wraps incorporate: Uninsulated wire Coaxial cable centre conductors Wires having abnormally thick insulation. Class B wire-wrap 2023-02-06 B-07c Maintenance Practices Page 254 of 255 CASA Part 66 - Training Materials Only  As illustrated above, a conventional or Class B wire-wrapped joint consists of a helix of uninsulated continuous solid wire tightly wrapped around a terminal. Notice that the insulation, if present, does not contact the terminal post. Class B connections are only acceptable for use in equipment exposed to little or no vibration. Wire-Wrapping Instructions To strip insulation from wrapping wire: Pull off the cap and remove the wire stripping tool from within the handle. Press the wire to be stripped down into the wire stripper’s slot, approximately 2 cm from the end. Hold the wire stripper with the blade away from you and push the stripper away from you to strip the insulation. To wire wrap: Insert the wire into the tool’s half-moon-shaped hole and out through the groove. Bend the wire over the end of the tool. Align the tool with its round hole over the terminal post and press it down over the post. Hold the wire as you turn the tool clockwise approximately 10 turns to wrap the wire around the post. 2023-02-06 B-07c Maintenance Practices Page 255 of 255 CASA Part 66 - Training Materials Only