introduction to pcb design1 aed703 printed circuit board design - 1 instructors: –j. ebden –j....

Introduction to PCB Design 1

AED703Printed Circuit Board Design - 1

•Instructors:

– J. Ebden

– J. Kawenka


What is a PCB?

• Definition:

Printed Circuit – an electric circuit in which the conducting paths connecting circuit components are affixed to a flat insulating base board*

*Columbia Encyclopedia, 6th ed, 2001


What is a PCB?

• PWB vs PCB

PWB – copper traces and pads create point-to-point connection of components.

PCB – a PWB that contains components that are embedded in the copper.


Growth of the PWB Industry

• In the Beginning• Advances Made• Today• Design Technology Growth


In the Beginning

• Engineer– Concept of Design– Rough “scribble” of concept– Breadboard proofing of concept


In the Beginning

• Designer– Hand draw full schematic– Hand draw layout of component placement

(2X, 4X)– Hand inking of components and board

nomenclature– Drill templates created using dots, donuts,

and symbols


In the Beginning

• Manufacturer– Photo-reduction of taped artwork– Chemical etching of copper laminates– Hand cut silk screens to squeegee on to

board– “Bullseye” drilling of holes– Hand mounting and soldering of

components– Hand probes used to test functionality


Advances Made

• Manufacturing– First to utilize advances in automation and

computers– Digitizing replaces photo-reduction– NC Drill replaced “bullseye” drilling– Photographic imaging to create silk screens– “Pick & Place” machines for component

mounting– Wave soldering machines reduce hand

soldering


Advances Made

• Designing– Hand drawing layouts digitized to create 1X

film artwork– CAD programs developed for board layout– Output of Gerber data to create 1X film

artwork– Output of NC drill tapes


Today

• Engineer

– Develop concept and schematic in CAD/CAE tools

– Simulating design replaces hand calculations


Today

• Designer– CAD tools tie schematic and layout for

“intelligent” designs– Component placement and circuit routing

automated– Data output increased to include: Gerber

data, NC drill data, component placement data, net list data, testing data, etc


Today

• Manufacturer– Use Gerber and NC drill data to fabricate

bare board– Use component placement data to assemble

board– Use net list and testing data to verify final

product


Design Technology Growth

• Smaller product packaging– More functionality per circuit card– Smaller components, surface mount and

micro-technology

• Demand for faster time to market– Panelization for easier handling– Increased automation for faster turn around

• Increased demand for QC


Industry standards

• Board Level

– IPC-4101 Specification for base materials– IPC-L-125 Materials for high speed/high

frequency boards– IPC-2221 Generic standard for printed

board design– IPC-SM-782 Surface mount design and land

pattern– IPC-SM-840 Solder mask standard– IPC-TM-650 Test methods manual


Industry standards

• Assembly Level

– IPC-A-610 Acceptability of printed board assemblies

– J-STD-001 Requirements for soldered electrical and

electronic assemblies


Industry standards

• Documentation

• MIL-STD-100 Engineering Drawing Practices

• ANSI Y14.100 Replaces MIL-STD-100 for non-military

• IPC-D-325 Documentation requirements for printed boards, assemblies, and support drawings

• ASME Y14.5Dimensioning and Tolerancing


Classes and types

• Performance classes– Determined by end use of product

• Board types– Bare board configurations

• Producibility levels– Circuit design complexity

• Assembly classes– Component mounting complexity


Performance Classes for Electronics Products

• Class 1 – General

– Some computers and computer peripherals– Main importance is functionality. Cosmetic

imperfections not important



• Class 2 – Dedicated Service

– Communications, sophisticated business machines, instruments

– Extended life and uninterrupted service desired, but not required



• Class 3 – High reliability

– Life support systems, critical weapons systems

– Continued performance or performance on demand is required

– Downtime is not acceptable


Board Types

• Type 1 - Single sided printed board• Type 2 - Double sided printed board• Type 3 - Multilayer without blind and/or buried

vias• Type 4 - Multilayer with blind and/or buried

vias• Type 5 - Multilayer metal core without blind

and/or buried vias• Type 6 - Multilayer metal core with blind

and/or buried vias


Type 1 Board


Type 2 Board


Types of Vias


Producibility Levels

• Level A - General Design Complexity

(preferred)• Level B - Moderate Design Complexity (Standard)• Level C - High Design Complexity (Reduced Producibilty)


Assembly Classes

• Class A - TH components only• Class B - SMT components only• Class C - Both types (simplistic assembly)• Class X - Both types (complex assembly)

– (TH, SM, fine pitch and BGA)

• Class Y - Both types (complex assembly)– (TH, SM, ultrafine pitch and CSP)

• Class Z - Both types (complex assembly)– (TH, SM, ultrafine pitch, COB, flip-chip and TAB)


Assembly Classes


Components• Types of Components

– Passive vs Active– Symbols and Designations

• Package Types– Through-hole (TH)– Surface Mount (SM)

• Surface Mount Lead Styles• Polarity and Orientation


Types of Components

Passive Components - Basic function of component does not change when they receive a signal

Component Function Symbol Designation

Capacitor Stores anddischargeselectricity

C

Resistor Limits the flow ofelectrical current R

Inductor Creates magneticfield whencurrent flowsthrough

L

+


Types of Components

Active Components - Basic function does change when they receive a signal

C o m p o n e n t F u n c t i o n S y m b o l D e s i g n a t i o n

D io d e O n ly a l l o w s c u r r e n t t ofl o w in o n e d i r e c t i o n .C h a n g e s A C t o D C .V o l t a g e l im i t e r f o r D C( Z e n e r ) . S p e c ia l i t y d io d e s

D o r C R

T r a n s i s t o r L im i t s t h e fl o w o fe le c t r i c a l c u r r e n t Q

I n t e g r a t e dC i r c u i t ( I C )

V a r io u s s i g n a l p r o c e s s in gf u n c t io n s

D e t e r m in e d b yf u n c t io n o fd e v i c e

U

PNPNP N


Package Types

PackageType

Description TypicalComponents

Axial Lead Two leads extending from eachside of the component

Resistors, Capacitors,Diodes, Inductors

Radial Lead Two or more leads extendingfrom side of the component

Capacitors, Diodes,Transistors, Crystals,some ICs

SIP Single Inline PackageA row of leads in a single straightline

Resistor Networks,Capacitor Networks,Diode Arrays

DIP Dual Inline PackageTwo rows of pins in a parallelstraight line

ICs, Sockets, ResistorNetworks, CapacitorNetworks, Diode Arrays

PGA Pin Grid ArrayMultiple pins extending frombottom of component in a gridpattern

ICs, Sockets

Through-Hole - Components with leads that are inserted through mounting holes in the circuit board


Package Types

PackageType

Description TypicalComponents

Chip Usually ceramic bodied package with metaltermination on each end - rectangular

Resistors,Capacitors,Inductors, Diodes

MELF Metal Electrode FaceMetal terminations on each end ofcylindrical body

Resistors, Diodes

LCC Leadless Chip CarrierNo leads, metallization in form ofcastellations for attachment

ICs

SOIC Small Outline Integrated CircuitSimilar to DIP package with leads formedfor surface mounting

ICs

QFP Quad Flat PackLeads extend from four sides of component

ICs

BGA Ball Grid ArraySurface mount version of PGA. Leads aretiny metal balls on bottom of component

ICs

Surface Mount - Components with leads that are mounted directly onto lands on the surface of the

board


Surface Mount Lead Styles

• Gull Wing

• J-Lead

• L-Lead

• Flat Lead

• Ball

• Lead Pitch - Distance from centre of one pin to centre of adjacent pin

– Standard: 20 - 100 mils– Fine: 12 - 20 mils– Ultrafine: <12 mils


Passive Components

Resistor Tantalum Capacitor


Passive Components

Ceramic Capacitor


Active Components

Small outline transistor (SOT)


Through Hole Packages

DIP-24 DIP-14 (7400)


Through Hole Packages

PGA


Surface Mount Packages

SOIC SSOIC



QFP PQFP



2-sided J leaded 4-sided J leaded


Polarity and Orientation

• Polarity - Positive and negative ends of a two pin device

– Positive or anode lead graphical representation

• Capacitor - Identified with a (+) and/or square pad• Diode - Identified flat end of triangle and/or square pad

– Negative or cathode lead graphical representation

• Capacitor - Not defined• Diode - Identified by bar end of diode symbol


Polarity and Orientation

• Orientation - Identification of pin 1 of multi-pin devices

– Dot, notch or number identification on component

– Square pad or silkscreen dot on board surface

– Pin count direction typically counter-clockwise from pin 1


The Bare Board

• Board Styles• Technology / Function• Materials• Features• Documentation• CAD Data• Fabrication


Board Styles

• Rigid– Most common board style– Solid construction, hard mounted into next assembly

• Rigid-Flex– Sectional, multiple rigid boards inter-connected with

flexible circuits

• Flex– Flexible circuits, typically used to replace cabling within

a system

• Hybrid– Very small circuits, generally encapsulated and mounted

onto larger boards


Technology / Function• Analog

– Typical functions are op-amps, voltage converters, power supplies

• Digital– Typical function is signal processing

• RF– Function to produce radio frequencies, usually in the

super high frequency range

• Frequency Ranges:

Low Frequency (LF) = 100 kHz

Medium Frequency (MF) = 300-3000kHz

High Frequency (HF) = 3-30 Mhz

Very High Frequency (VHF) = 30-300 MHz

Ultra High Frequency (UHF) = 300-3000 MHz

Super High Frequency (SHF) = 3-30 GHz


Materials

• FR4– Woven glass reinforcement with epoxy resin binder– FR indicates it meets UL requirements for flame retardance

• PTFE– Polytetrafluoroethylene (Teflon)

• RO4350– Woven glass reinforcement with ceramic filled thermoset

• Polyimide Film– Polyimide resin system without glass reinforcement, used

for flexible film


Features

• Mechanical Outline– Defines overall area for board design

• Clearances– Board edge, mating area at next assembly

• Mounting Holes– Location, size, hardware used (preference =

grid in multiples of 5 mils)

• Tooling Holes – Used throughout fabrication, assembly, and

testing of boards


Features - continued

• Fiducials– Surface features used for optical alignment

of board during assembly

• Keep-out Areas– Areas where no components and/or copper

can be located

• Height Restrictions– Areas where there are potential interference

issues at next assembly



• Fixed Component Location– Connector locations for mating critical

component locations

• Additional Mechanical Hardware– Card guides, stiffeners, sockets



• Design, fabrication, and manufacturing constraints– Board material– Board thickness / Layer stack-up– Via size– Voltages and currents used for circuits– Critical circuit routing requirements– Thermal considerations– Fabrication and assembly methods


Documentation - Schematic

Schematic.pdf


Documentation - Fabrication Drawing

Fabrication Drawing


Documentation - Assembly Drawing


Documentation – Parts List


CAD Data

• Artwork - Format = Gerber– One file for each board layer, solder mask,

silkscreen, and paste mask

• NC Drill - Format = Excellon– Single file supplies X-Y locations for all holes

in the board


CAD Data - continued• Additional files supplied

– IPC-D-350: Printed board description in digital form– Neutral file: Mentor Graphics format, complete

layout data– Geoms file: ASCII description of component

geometries– Nets file: ASCII listing of component pins connect

by net name– Traces file: ASCII listing or each trace on the

board, following each vertex and via


Fabrication

• Determine size of panel• Dry film coating• Expose image and

develop• Etch• Dry film strip• Lamination• X-Ray Inspection• Drill• Copper plating

• Dry film coating• Tin plating/dry film

strip• Etch• Tin strip• Solder mask coating• Expose and develop• Legend - apply and

cure• Tin-Lead plating• Route board outline


Assembly

• Component Mounting• Attachment Methods• Cleaning• Testing• Conformal Coating


Assembly - Component Mounting

• Automatic Insertion - TH components

– Board changes position under insertion head

– Dip Inserter - Tube feeds DIPs into insertion head

– Axial and Radial Inserter - components are sequenced and taped, then fed into lead former, then insertion head


Assembly - Component Mounting (continued)

• Automatic Placement - SM components

– Board remains stationary– Chip Shooter - for mounting chip components– Vacuum Nozzle - selection and placement of larger

components

• Manual Placement

– Unique and odd components formed and mounted by hand


Assembly - Attachment Methods

• Wave Solder - TH assemblies– Fluxing– Preheating– Conveyed over wave of molten solder

• Reflow Solder - SM assemblies– Apply solder paste– Component mounting– Preheating– Solder reflow - Forced convection, Infrared– Cool Down


Assembly - Attachment Methods (continued)

• Hand Solder– Used for temperature sensitive or odd-

form components

• Vapour Phase Solder

• Laser Solder

• Bar Solder


Assembly - Cleaning

• Attachment methods leave behind flux residue that can be conductive or corrosive

• Normal handling through assembly process can leave behind contaminants

• Cleaning method dependent on contamination– Sometimes a simple water solution sufficient– Otherwise a more active cleaning agent required

• “No-Clean” soldering– Uses flux that is non-conductive and non-corrosive– Needs investigation for compatibility with other

materials


Assembly - Testing and Rework

• Initial testing of assembly should be done prior to finalising assembly process. Any rework required per findings in testing is easier to perform

• Possible rework required:– Component replacement– Trace or pad repair– Cuts and jumps


Assembly - Conformal Coating

• Organic coating for environmental protection– Temperature extremes– Humidity– Corrosive atmosphere– Salt water

• Application methods– Brush– Spray– Dip– Curtain coat– Vacuum deposition


Assembly - Testing

• Board Level• Assembly• Final Assembly


Assembly - Testing - Board Level

• Test Coupons (Quality Strip)– Verify fabrication process

• Bare Board Test– Circuit continuity checked at every

termination– Checks for shorts or opens– “Golden Board” test– One or two sided check

• two sided is more expensive• need clam-shell fixture


Assembly - Testing - Assembly Level

• ICT - (In-Circuit Test)– Used to find shorts, opens, wrong parts,

reversed parts, bad devices and other manufacturing defects

• Functional Test– Verifies functionality of entire board or

group of components

• HAST - (Highly Accelerated Stress Test)– Determines reliability of product under

environmental conditions


Assembly - Testing - Assembly Level (continued)

• AOI - (Automatic Optical Inspection)– Verifies component position and orientation

• AXI - (Automatic X-Ray Inspection)– Solder joint inspection


Assembly - Final Assembly

• Functional Test– Verify final assembly performs as specified

(designed)

• Burn- in– Unit turned on and left running for 4-24

hours– Identifies “infant mortality” problems


Teamwork

• Why is teamwork important?• Tools for Interaction• Results


Why is teamwork important?

• Questions for the PCB designer so h/she can produce the best design:– Where is product being used?

• Customer requirements, System engineer

– What is the technology of the design?• Customer requirements, Electrical engineer

– What are the geometric parameters of the board?• Mechanical engineer

– Are there special characteristics to be considered?• Mechanical. Electrical, Manufacturing, Test engineers

– How are the boards fabricated,assembled,tested?• Mechanical. Electrical, Manufacturing, Test engineers


Tools for Interaction

• Concurrent Engineering– Team of multiple functions working together to

develop a single design or product

• Input forms/Checklists– Documented description of need and requirements

• DFM -(Design for Manufacturing)– Communication between designer and

manufacturing

• DFT -(Design for Test)– Communication between designer and test

engineer


Results

• Ease of manufacturing and testing• Early detection of defects• Quicker time to market• Higher product quality• Increased product reliability• Satisfied customer

introduction to pcb design1 aed703 printed circuit board design - 1 instructors: –j. ebden –j....

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