AED703 Printed Circuit Board Design - 1

1
AED703Printed Circuit Board Design - 1

• Instructors
• J. Ebden
• J. Kawenka

2
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

3
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.

4
Growth of the PWB Industry

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

5
In the Beginning

• Engineer
• Concept of Design
• Rough scribble of concept
• Breadboard proofing of concept

6
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

7
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

8
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

9
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

10
Today

• Engineer
• Develop concept and schematic in CAD/CAE tools
• Simulating design replaces hand calculations

11
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

12
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

13
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

14
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

15
Industry standards

• Assembly Level
• IPC-A-610 Acceptability of printed board
  assemblies
• J-STD-001 Requirements for soldered
  electrical and electronic assemblies

16
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 Y14.5 Dimensioning and Tolerancing

17
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

18
Performance Classes for Electronics Products

• Class 1 General
• Some computers and computer peripherals
• Main importance is functionality. Cosmetic
  imperfections not important

19
Performance Classes for Electronics Products

• Class 2 Dedicated Service
• Communications, sophisticated business machines,
  instruments
• Extended life and uninterrupted service desired,
  but not required

20
Performance Classes for Electronics Products

• Class 3 High reliability
• Life support systems, critical weapons systems
• Continued performance or performance on demand is
  required
• Downtime is not acceptable

21
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

22
Type 1 Board
23
Type 2 Board
24
Types of Vias
25
Producibility Levels

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

26
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)

27
Assembly Classes
28
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

29
Types of Components
Passive Components - Basic function of component
does not change when they receive a signal
30
Types of Components
Active Components - Basic function does change
when they receive a signal
31
Package Types
Through-Hole - Components with leads that are
inserted through mounting holes in the
circuit board
32
Package Types
Surface Mount - Components with leads that are
mounted directly onto lands
on the surface of the board
33
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 lt12 mils

34
Passive Components
Tantalum Capacitor
Resistor
35
Passive Components
Ceramic Capacitor
36
Active Components
Small outline transistor (SOT)
37
Through Hole Packages
DIP-24
DIP-14 (7400)
38
Through Hole Packages
PGA
39
Surface Mount Packages
SOIC
SSOIC
40
Surface Mount Packages
PQFP
QFP
41
Surface Mount Packages
2-sided J leaded
4-sided J leaded
42
(No Transcript)
43
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

44
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

45
The Bare Board

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

46
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

47
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
48
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

49
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

50
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

51
Features - continued

• Fixed Component Location
• Connector locations for mating critical component
  locations
• Additional Mechanical Hardware
• Card guides, stiffeners, sockets

52
Features - continued

• 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

53
Documentation - Schematic
Schematic.pdf
54
Documentation - Fabrication Drawing
Fabrication Drawing
55
Documentation - Assembly Drawing
56
Documentation Parts List
57
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

58
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

59
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

60
Assembly

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

61
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

62
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

63
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

64
Assembly - Attachment Methods (continued)

• Hand Solder
• Used for temperature sensitive or odd-form
  components
• Vapour Phase Solder
• Laser Solder
• Bar Solder

65
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

66
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

67
Assembly - Conformal Coating

• Organic coating for environmental protection
• Temperature extremes
• Humidity
• Corrosive atmosphere
• Salt water
• Application methods
• Brush
• Spray
• Dip
• Curtain coat
• Vacuum deposition

68
Assembly - Testing

• Board Level
• Assembly
• Final Assembly

69
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

70
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

71
Assembly - Testing - Assembly Level (continued)

• AOI - (Automatic Optical Inspection)
• Verifies component position and orientation
• AXI - (Automatic X-Ray Inspection)
• Solder joint inspection

72
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

73
Teamwork

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

74
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

75
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

76
Results

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