PCB Design: Preventing Overheating & Component Placement

Printed Circuit Board (PCB)

• Serves as the base for most electronics
• Foundational building blocks of most modern electronic devices
• Commonly made out of fiberglass, composite epoxy, or other composite material

Composition of a PCB

• Consists of silkscreen, soldermask, copper layer (pads/vias, copper tracks/traces), and substrate

Silkscreen

• Used for part numbers, logos, symbols, switch settings, and component reference
• Serves as a legend

Soldermask

• Polymer layer that protects the copper preventing short circuits from environmental contact
• Functions as skin

Copper Layer

• Can be copper foil or a full-on copper coating
• Carries electrical signals to and from PCBs
• Functions as nervous system

Substrate

• Made of fiberglass
• Fiberglass provides core strength, helping the PCB resist breakage
• Functions as a skeleton

Surface-Mount and Through-Hole Technology

• Two methods available for producing electronic circuits.

Surface-Mount Technology (SMT)

• Components are mounted or placed directly onto the surface of the PCB
• Uses surface-mount devices

Through-Hole Technology (THT)

• Components are inserted into drilled holes in the PCB
• Leads are soldered onto the pads or lands on the solder side of the board, usually with a simple soldering iron or wave soldering process
• Is very reliable because there is a stronger connection
• Most manufacturers still use through-hole technology

Surface Mount Technology

• Uses smaller components
• Allows to increase the overall density of the finished electronic product

PCB Manufacturing Information

• PCB design focus should be on the types, kinds, and characteristics of the component and the design factors needed, rather than just the size of the pathways.

PCB Size and Shape

• PCBs must be big enough for the entire component to be mounted on a specific area

Position of the Terminal

• Input, output, and supply voltage should be near the border to facilitate possible troubleshooting or minor repair

High Temperature Dissipation

• Too much heat is one problem with all components; bigger spaces are needed for heat sinks to absorb heat and protect the components

Space for Bolt and Nut

• Placement of good space is needed to facilitate mounting with bolts and nuts to secure the entire board to the chassis

Different Types of Circuit

• Should be grouped according to application to enhance circuit operation and circuit distortion generated by other circuits
• Reasons why the circuit of the power supply is far from the audio circuit

Characteristics of Good PCB Design - 4 C's

Clean

• Should be distinct, enabling easy marking and troubleshooting

Compressed

• Reduces the size for space in the chassis

Creative in Design

• Pattern or image is created

Consistency in Component

• Components should be well-arranged in groups

Characteristics of Properly Designed PCB

• PCB is the lifeline of an electronic device and cannot be erroneous in any manner
• Reliability and dependability are key

High Quality Base Material

• Prevents issues like open circuits and delamination from inflation
• Base material should be tested

Copper Clad Made Tolerant as per International Standard

• Copper cladding meets the IPCA4101 ClassB/L tolerance standards
• Ensures better dielectric layer thickness control.

Hole Wall Thickness

• Hole's wall is clad with copper and is 25 microns thick
• Strengthens resistance to expansion along the z-axis
• Care should be taken to not blow through the hole as it may lead to problems in electrical connectivity arising due to assembling shortcomings

PCB with No Track Cut

• With no line breaks or repairs, the possibility of breaks in circuit flow becomes nil
• Considered highly reliable when free of soldering repair

Impeccably Clean PCB

• High reliability is achieved by being free of dust and solder resistant
• Bad solder points or poor connections will result from uncleared material

Treatments Done on PCB

• Circuit boards undergo stringent quality tests before use
• PCB surface treatments cause shelf life to absorb moisture making soldering difficult

Positional Tolerance on PCB

• PCBs designed with well-defined drill holes, tracks, vias, outline shapes, and mechanical features get high functionality ratings
• The size and tolerances of holes and other features should be well-defined

Thickness of Solder Resist Layer

• Should be tolerant enough to provide great electrical insulation
• Thick solder resist layers reduce peeling risks and improve mechanical impact tolerance
• Copper circuits will be exposed to corrosive agents if the solder resist layer is too thin

Industry Approved Solder Resistant Material

• Poor quality solder resistant ink causes undue hardness and copper board exposure to corrosive substances
• Insulation is improved with best quality solder resist material

Purchase Each Part as per a Pre-Defines Buying Program

• The use of industry approved parts adds to the reliability of printed circuit boards
• Industrial buying should adhere to production plans and quality standards.

Problems Arising from Poorly Designed Printed Circuit Boards

• PCB or printed circuit board is an electronic assembly using copper conductors
• Copper conductors create electrical connections between components
• A thin board connects electronic components to form a circuit
• Commonly used in most modern electronics

Signal Interference

• Signals interference with one another, reducing circuit performance or causing complete failure, if traces are too close together or not shielded properly

Overheating

• Components such as power transistors require proper placement and cooling to prevent overheating, which can cause damage the component to or cause the circuit to fail

Noise

• External or internal noise can degrade performance or cause erroneous readings if the circuit is not properly grounded or shielded

Crosstalk

• Signals can be misinterpreted or lead to data corruption if signals on different traces interfere with each other, known as crosstalk

Manufacturing Defects

• Poorly designed PCBs can cause circuits to fail or function improperly due to manufacturing defects

Summary

• Poorly designed PCBs can lead to performance, reliability, and functionality problems in electronic devices
• It is important to carefully design and test PCB layouts that satisfy the needed requirements specifications and standards

Verification: Identifying Issues in PCB Layouts

• The final step before the start of the manufacturing stage is verification
• CAD tools locate design flaws that can negatively impact the board's functionality or interfere with manufacturing

Connectivity

• Ensuring all parts of a network are connected through a conductive structure

Consistency between Schematic and Layout

• Computer-Aided Design tools have different means of implementing this verification

Design Rule Check (DRC)

• Design rule checks are used to ensure schematic matches all dimensional tolerances and all manufacturing considerations set for a board during the layout stage
• DRCs will check physical parameters

Trace Width and Spacing

• Trace width: Ensures the width of the conductive paths (traces) on the PCB is adequate for the current it must carry
• If the trace is too narrow, it may overheat or not carry enough current that could cause failure
• Trace Spacing: Ensures that the traces are spaced far enough apart to prevent short circuits or electrical interference
• Minimum trace-to-trace distance relies on the manufacturing process and voltage requirements

Via Size and Spacing

• Vias create electrical connections between different PCB layers

Via Size

• Via size (diameter and plating) must be large enough to handle the current and be manufacturable

Via Spacing

• Via spacing ensures adequate spacing to prevent shorts or manufacturing issues during drilling processes

Drill-to-Board Aspect Ratio

• The drill-to-board aspect ratio refers to the relationship between the hole size and the thickness of the PCB
• The ratio ensures the holes are not too large or small for the board's thickness, which could lead to difficulties in drilling, structural weaknesses, or electrical issues

Outline to All Pin Pads

• Checks that PCB outline is far enough away from pin pads
• If the outline is too close to the pads, it could result in mechanical issues during assembly and improper soldering

Silkscreen Clearance

• Ensures graphic and text elements do not overlap with pads, traces, or vias

Pad Sizes

• Verifies pads are correctly sized for the components intended to support

PCB Assembly

• Collect all the components required for assembling the PCB
• Place components in respective positions and check if all the holes, tracks, and pads are as expected
• Start soldering the components on the PCB

PCB Etching Methods

• Involves removal process of unwanted copper (Cu) from the circuit
• Non-circuit copper is removed from the board as per the design of the PCB

PCB Etching Methods include

• Toner Transfer with heat
• Acidic Etching / Alkaline Etching
• Tone transfer without heat

Methods of PCB Etching

• Printing the layout on paper
• Getting board ready for toner transferring
• Transferring the toner from a paper to the PCB
• Etching the copper from the board
• Drilling holes on the PCB
• PCB assembly

PCB Manufacturing Houses vs Making PCB at Home

• Using manufacturing houses is a good idea for developing commercial products
• Making the PCB at home is an alternative solution if the design is simple (usually a single layered board

Acidic Etching

• Used to etch the inner layers in a rigid PCB
• Involves chemical solvents like Ferric chloride, (FECI3) or Cupric Chloride(CUCI2).
• Method is more precise and cheaper but time-consuming, compared to alkaline
• Implemented for the inner layers because the acid doesn't react with the photoresist and doesn't damage the required part

Alkaline Etching Process

• Used to etch the outer layers in a PCB
• Chemicals utilized are chloride copper (CUCI2, 2HO2) + hydrochloride (HCI) + hydrogen peroxide (H2O2) + water (H2O) composition
• It's a fast and bet expensive process
• Whole process implemented in a conveyorized high-pressure spray chamber where the PCB is exposed to a spray of enchant

Cupric Chloride Etching

• Most widely used etchant as it accurately etches off smaller features
• Offers constant rate and continuous regeneration, comparatively at lowers cost
• Etches fine line layers

Ferric Chloride Etching'

• Has limited usage die to the cost of the copper-containing etchant
• An attractive spray etchant due to ease of use, holding capacity for copper, and used in infrequent batch applications
• Can be used with screen ink, photoresists, and gold patterns, but should not be used with tin or tin/lead resists

Steps in PCB Etching

Printing the PCB Layout on a Paper

• Print the layout on paper or magazine
• Take print using laser printer and transfer the toner from the paper to the PCB using heat transfer
• Multiple copies demonstrate that the process can make those boards with a single paper

Getting Board Ready for Toner Transfer

• Cut the piece of paper with layout printed on it with the final size of the board
• Take a copper clad PCB board and mark the size of the board on one corner
• The rectangle size is 4CM x 3CM

Transferring the Toner from Paper to PCB

• Place the board (with paper still wrapped around it) in a bowl of water, while using protection
• Water is to rub the paper off the board, without putting too much pressure
• Remove the paper, you can see a clean transfer of the toner on the copper clad board

Etching the Copper from Board

• Unnecessary copper should be removed the PCB board
• Spoon or two of ferric chloride powder and put it in a thick plastic or steel container
• Drop thee PCB in the container and stir the water for 10 to 15 minutes or until the copper is completely etched

Drilling Holes on the PCB

• Drill holes to mount the components
• Used small hand drill (Motorized drill) to make the holes
• Once the holes, PCB ready for assembly

Getting the Board Ready for Toner Transfer

• Clean the board with deposits of fingerprints so that your copper side rubbing for the board will use a mild emery paper, sand paper or scrub,.
• Clean the copper side with alcohol that also can remove small deposits dirt,.
• Use nail paint remover,.
• Step will eliminate the small deposits that are caused with sand paper
• Use cleaning chemicals with finger prints,.
• Now, surface use for cleaning tools to easily cut fingerprints,..
• Use cleaning tools with paper dirt for fingerprints on the side,.

Transferring the Toner from a Paper to PCB

• Transfer the toner onto a copper side using machines
• Use iron box to cover paper,.
• Damp the paper with a transfer image,.

Explore key design factors in PCB layout to prevent overheating and component failure. Understand the importance of intelligent component placement for signal integrity. Learn about the 4Cs of good PCB design and the function of soldermask layers.