Lesson 7 Wiring and Cabling Diagrams Electronic Packaging PDF

BACHELOR OF SCIENCE IN COMPUTER ENGINEERING CPE317 – COMPUTER ENGINEERING DRAFTING AND DESIGN LESSON 7 Prepared by: ENGR. SPRINZTSIE MAYE T. GARRUCHA CPE317 Instructor LEARNING OUTCOMES: At the end of this topic, the...

BACHELOR OF SCIENCE IN COMPUTER ENGINEERING CPE317 – COMPUTER ENGINEERING DRAFTING AND DESIGN LESSON 7 Prepared by: ENGR. SPRINZTSIE MAYE T. GARRUCHA CPE317 Instructor LEARNING OUTCOMES: At the end of this topic, the students will be able: 1. To be familiar with the wiring and cabling diagrams used in electronic and electrical drawing. 2. To have knowledge on the electronic packaging including its design, constraints, and materials. 3. To apply design considerations in drawing manually and with the use of appropriate circuit layout simulation tool OUTLINE OF THE TOPIC: 1. Wiring and Cabling Diagrams 2. Electronic Packaging 3. Printed Circuit Assemblies 1 TOPIC 1: WIRING AND CABLING DIAGRAMS The physical relationship is important in an electronic or electrical drawing. This type of drawing is called the wiring diagram and, as its name implies, is a diagram that aids in the assembly or production of the entire electronic package. Wire The correct drawing or representation of wire is critical. There is not just one type of wire used for all assemblies. There are many different sizes, styles, and types of wire and many methods of wiring. Wire is made of material like copper or aluminum that will allow current to flow through it with very little resistance. Since the primary purpose of wire is to connect two points together, it should not alter the overall electrical characteristics or function of the circuit. Connecting wire is generally either a single strand of wire or several strands fixed together as one wire. This wire can be insulated or covered with a material like nylon, enamel, polyester, rubber, or other material that does not conduct electricity very well. The size, or cross-sectional area, of wire can vary. In addition, the size of the insulating material on the wire can vary. The insulating material can be made in many different colors to aid the technician in identifying the wire and its function. All this information must be included on any wiring diagram, since the diagram is often used as the assembly or production drawing. This drawing may be included in a service or instruction manual, and without identification of color and type or size of wire, it would be very difficult for the technician to trace the circuit paths or repair the equipment. Wire Gauge The size of the wire is called the gauge. Wires come in standard sizes identified by whole numbers, which have been set by the American Wire Gauge (AWG) Standards. The smaller the number, the larger the wire is. Figure 1. Different sizes of wires 2 Wire ranges in size from about as fine as a piece of hair to as big around as a small finger, as shown in Figure 1. All different sizes have specific uses, and each size has different electrical characteristics in terms of how much resistance there is in the wire or how much current can safely flow through it. Wire formed from many strands of wire is not gauged in the same manner as solid wire; however, stranded wire does have similar electrical characteristics and limits. The biggest advantage of stranded wire is that it is more flexible than solid wire and should be used where the wire is likely to be moved or when vibrations can occur. The primary disadvantage is that stranded wire with the same overall cross-sectional area as solid wire can only handle about 60% of the current that solid wire can handle. To find the equivalent solid size of stranded wire, multiply the number of strands times the cross- sectional area of each individual strand. The total cross-sectional area corresponds to an AWG equivalent size for the stranded wire on the AWG chart of solid wire. Stranded wire, however, is normally identified by the actual strand, not by the equivalent solid wire. It is identified first by the number of strands and then by the AWG number of the individual strands. The numbers are separated by a slash. For example, 8/34 means a wire made up of 8 strands of #34 wire. Since the cross-sectional area of #34 wire is 39 circular mils, this wire is equivalent to approximately AWG #25 solid wire (8 X 39 = 312 circular mils). Remember that although these strands have approximately the same gauge or physical size as solid wire the maximum amount of current must be derated to about 60%. Insulation Many different types of materials are used to insulate conductors. The insulating material is necessary to provide protection to people and to make certain the wires do not contact other wires or the metal cases. Any time two conductors touch, an electrical connection is made. If a wire is to be used to connect two components, then it may only touch the leads of those two components. It is physically impossible to keep a long loose wire from contacting anything else, so insulation is used to cover the length of the wire. Only the ends are exposed so that they may make contact. Different materials have different insulating properties; therefore, the type of insulation is determined by the particular application. Insulating materials come in a number of different solid colors or in a solid color with one or two stripes of different colors, called tracers. The colors aid in tracing circuit connections of equipment, as well as in fabricating a system. Parts of a Wiring Diagram A wiring diagram has three main labels: the size and type of wire; the size, type, and color of the insulation; and the type of connection to be made. AU connecting wires will end either in bare wire that must be soldered or in terminals, clips, jacks, plugs, or other mechanical means of making connections. All this information must be included on the wiring diagram. The choice between soldering or using some other form of connection is determined by how often the connection might need to be removed, either for repair or for multiple use of the equipment. Equipment with interchangeable sections does not have soldered interconnections. A sliding con tact or quick-disconnect, plug-type assembly is used in stead All wiring diagrams must include at least the components, the connection lines, and the means of connection. The components are frequently represented by a geometric shape showing physical characteristics, as in figure 2, rather than the unique symbols used for electrical characteristics. 3 The connection lines may be represented in a number of different methods. The method of termination is designated by either a pictorial representation of the connector or simply a note identifying the type of terminals. Figure 2. Geometric shapes showing components in wiring diagrams. As with all other diagrams, the wiring diagram starts with a rough sketch. The circuit is divided into smaller sections based on the manner in which it will be assembled. For very simple circuits this may include just one main assembly. The rough sketch establishes the initial space requirements for the final drawing, as shown in Figure 3. All components are represented by their physical characteristics. Even though there is no proper size for these components, guidelines need to be followed. If the wiring diagram will be used in production or assembly, the picture must help locate the actual part. Components are frequently represented larger than life on the sketch. The size of each pictorial representation must show the Figure 3. Rough sketch establishing location of parts and some proportional preliminary space requirements. relationships to adjacent components. 4 For components with multiple leads, any identifying characteristics—such as tabs, slots, and polarity— must be shown on the drawing to ensure proper connections, as in Figure 4. The pictorial representations are usually not pictorials in the sense of showing entire physical characteristics with multiviews or other pictorial methods, but are simply outlines best showing the required mounting space. If all the information cannot be shown in one view, then additional views may be required for final assembly. In many instances a single view of the bottom or actual wiring side of a chassis is sufficient to represent all components and their interconnections, as shown in Figure 5. Figure 4. Component outlines, identifying all tabs, slots, and spacing. Figure 5. Bottom view of chassis indicating all wiring. Unfortunately, like all other electronic or electrical diagrams, there is no easy way to achieve a well-designed, well-balanced, and well-presented wiring diagram. The trial-and-error method must be used to achieve the final drawing. With practice and experience, fewer trials with fewer errors should be possible. 5 TOPIC 2: ELECTRONIC PACKAGING What is electronic packaging ? It is the design and production of enclosures for electronic devices ranging from individual semiconductor devices up to complete systems such as a mainframe computer. Packaging of an electronic system must consider protection from mechanical damage, cooling, radio frequency noise emission and electrostatic discharge. Product safety standards may dictate particular features of a consumer product, for example, external case temperature or grounding of exposed metal parts. Prototypes and industrial equipment made in small quantities may use standardized commercially available enclosures such as card cages or prefabricated boxes. Mass-market consumer devices may have highly specialized packaging to increase consumer appeal. Electronic packaging is a major discipline within the field of engineering. Design Electronic packaging can be organized by levels: Level 0 - "Chip", protecting a bare semiconductor die from contamination and damage. Level 1 - Component, such as semiconductor package design and the packaging of other discrete components. Level 2 - Etched wiring board (printed circuit board). Level 3 - Assembly, one or more wiring boards and associated components. Level 4 - Module, assemblies integrated in an overall enclosure. Level 5 - System, a set of modules combined for some purpose. The same electronic system may be packaged as a portable device or adapted for fixed mounting in an instrument rack or permanent installation. Packaging for aerospace, marine, or military systems imposes different types of design criteria. Electronic packaging relies more on engineering, particularly in mechanical engineering principles such as dynamics, stress analysis, heat transfer and fluid mechanics. High-reliability equipment often must survive drop tests, loose cargo vibration, secured cargo vibration, extreme temperatures, humidity, water immersion or spray, rain, sunlight (UV, IR and visible light), salt spray, explosive shock, and many more. These requirements extend beyond and interact with the electrical design. An electronics assembly consists of component devices, circuit card assemblies (CCAs), connectors, cables and components such as transformers, power supplies, relays, switches, etc. that may not mount on the circuit card. 6 Many electrical products require the manufacturing of high-volume, low-cost parts such as enclosures or covers by techniques such as injection molding, die casting, investment casting, and so on. The design of these products depends on the production method and require careful consideration of dimensions and tolerances and tooling design. Some parts may be manufactured by specialized processes such as plaster- and sand-casting of metal enclosures. In the design of electronic products, electronic packaging engineers perform analyses to estimate such things as maximum temperatures for components, structural resonant frequencies, and dynamic stresses and deflections under worst-case environments. Such knowledge is important to prevent immediate or premature electronic product failures. Design considerations A designer must balance many objectives and practical considerations when selecting packaging methods. 1. Hazards to be protected against: mechanical damage, exposure to weather and dirt, electromagnetic interference, etc. 2. Heat dissipation requirements 3. Tradeoffs between tooling capital cost and per-unit cost 4. Tradeoffs between time to first delivery and production rate 5. Availability and capability of suppliers 6. User interface design and convenience 7. Ease of access to internal parts when required for maintenance 8. Product safety, and compliance with regulatory standards 9. Aesthetics, and other marketing considerations 10. Service life and reliability Packaging Materials Sheet Metal Punched and formed sheet metal is one of the oldest types of electronic packaging. It can be mechanically strong, provides electromagnetic shielding when the product requires that feature, and is easily made for prototypes and small production runs with little custom tooling expense. Cast Metal Gasketed metal castings are sometimes used to package electronic equipment for exceptionally severe environments, such as in heavy industry, aboard ship, or deep under water. Aluminum die castings are more common than iron or steel sand castings. 7 Machined Metal Electronic packages are sometimes made by machining solid blocks of metal, usually aluminum, into complex shapes. They are fairly common in microwave assemblies for aerospace use, where precision transmission lines require complex metal shapes, in combination with hermetically sealed housings. Quantities tend to be small; sometimes only one unit of a custom design is required. Piece part costs are high, but there is little or no cost for custom tooling, and first-piece deliveries can take as little as half a day. The tool of choice is a numerically controlled vertical milling machine, with automatic translation of computer-aided design (CAD) files to toolpath command files. Molded Plastic Molded plastic cases and structural parts can be made by a variety of methods, offering tradeoffs in piece part cost, tooling cost, mechanical and electrical properties, and ease of assembly. Examples are injection molding, transfer molding, vacuum forming, and die cutting. Pl can be post-processed to provide conductive surfaces. Potting Also called "encapsulation", potting consists of immersing the part or assembly in a liquid resin, then curing it. Another method puts the part or assembly in a mold, and potting compound is poured in it, and after curing, the mold is not removed, becoming part of the part or assembly. Potting can be done in a pre-molded potting shell, or directly in a mold. Today it is most widely used to protect semiconductor components from moisture and mechanical damage, and to serve as a mechanical structure holding the lead frame and the chip together. In earlier times it was often used to discourage reverse engineering of proprietary products built as printed circuit modules. It is also commonly used in high voltage products to allow live parts to be placed closer together (eliminating corona discharges due to the potting compound's high dielectric strength), so that the product can be smaller. This also excludes dirt and conductive contaminants (such as impure water) from sensitive areas. Another use is to protect deep-submergence items such as sonar transducers from collapsing under extreme pressure, by filling all voids. Potting can be rigid or soft. When void-free potting is required, it is common practice to place the product in a vacuum chamber while the resin is still liquid, hold a vacuum for several minutes to draw the air out of internal cavities and the resin itself, then release the vacuum. Atmospheric pressure collapses the voids and forces the liquid resin into all internal spaces. Vacuum potting works best with resins that cure by polymerization, rather than solvent evaporation. 8 Porosity Sealing or Impregnation Porosity Sealing or Resin Impregnation is similar to potting, but doesn't use a shell or a mold. Parts are submerged in a polymerizable monomer or solvent-based low viscosity plastic solution. The pressure above the fluid is lowered to a full vacuum. After the vacuum is released, the fluid flows into the part. When the part is withdrawn from the resin bath, it is drained and/or cleaned and then cured. Curing can consist of polymerizing the internal resin or evaporating the solvent, which leaves an insulating dielectric material between different voltage components. Porosity sealing (Resin Impregnation) fills all interior spaces, and may or may not leave a thin coating on the surface, depending on the wash/rinse performance. The main application of vacuum impregnation porosity sealing is in boosting the dielectric strength of transformers, solenoids, lamination stacks or coils, and some high voltage components. It prevents ionization from forming between closely spaced live surfaces and initiating failure. Liquid Filling Liquid filling is sometimes used as an alternative to potting or impregnation. It's usually a dielectric fluid, chosen for chemical compatibility with the other materials present. This method is used mostly in very large electrical equipment such as utility transformers, to increase breakdown voltage. It can also be used to improve heat transfer, especially if allowed to circulate by natural convection or forced convection through a heat exchanger. Liquid filling can be removed for repair much more easily than potting. Conformal coating Conformal coating is a thin insulating coating applied by various methods. It provides mechanical and chemical protection of delicate components. It's widely used on mass-produced items such as axial-lead resistors, and sometimes on printed circuit boards. It can be very economical, but somewhat difficult to achieve consistent process quality. Further information: Conformal coating and Parylene. Glop-top Figure 6. A chip-on-board (COB) covered with dark epoxy 9 Glop-top is a variant of conformal coating used in chip-on-board assembly (COB). It consists of a drop of specially formulated epoxy or resin deposited over a semiconductor chip and its wire bonds, to provide mechanical support and exclude contaminants such as fingerprint residues which could disrupt circuit operation. It is most commonly used in electronic toys and low-end devices. Chip on board Surface-mounted LEDs are frequently sold in chip-on-board (COB) configurations. In these, the individual diodes are mounted in an array that allows the device to produce a greater amount of luminous flux with greater ability to dissipate the resulting heat in an overall smaller package than can be accomplished by mounting LEDs, even surface mount types, individually on a circuit board. Hermetic Metal/Glass Cases Hermetic metal packaging began life in the vacuum tube industry, where a totally leak-proof housing was essential to operation. This industry developed the glass-seal electrical feedthrough, using alloys such as Kovar to match the coefficient of expansion of the sealing glass so as to minimize mechanical stress on the critical metal-glass bond as the tube warmed up. Some later tubes used metal cases and feedthroughs, and only the insulation around the individual feedthroughs used glass. Today, glass-seal packages are used mostly in critical components and assemblies for aerospace use, where leakage must be prevented even under extreme changes in temperature, pressure, and humidity. Hermetic Ceramic Packages Packages consisting of a lead frame embedded in a vitreous paste layer between flat ceramic top and bottom covers are more convenient than metal/glass packages for some products, but give equivalent performance. Examples are integrated circuit chips in ceramic Dual In-line Package form, or complex hybrid assemblies of chip components on a ceramic base plate. This type of packaging can also be divided into two main types: multilayer ceramic packages (like LTCC and HTCC) and pressed ceramic packages. 10 TOPIC 3: PRINTED CIRCUIT ASSEMBLIES Printed Circuit Assemblies Printed circuits are primarily a technology for connecting components together, but they also provide mechanical structure. In some products, such as computer accessory boards, they're all the structure there is. This makes them part of the universe of electronic packaging. Printed Circuit Board Electronic circuits in engineering and industry are normally manufactured by using printed circuit boards (PCBs). These boards are made up of special materials that do not conduct electricity such as fiber and glass. The circuits are designed on the boards with copper tracks instead of wires for the conduction of electricity between the electronic components. The electronic components are fixed in their respective positions by drilling holes on the board, placing the components and then soldering them in appropriate positions so that the copper tracks and components together form a circuit. The printed circuit boards used in all electronic products such as automotive, wireless devices, Robotic applications, etc., offer quick functioning, access, control, monitoring, and precise and exact results when compared to other wiring methods based devices The figure shows how the circuit is arranged on a PCB with the copper layer. Figure 7. 555 Timer Printed Circuit Board 11