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Chapter 5: Printed Wiring Boards. Substrate. The purpose of the substrate for electronic component mounting is: Mechanical support Electrical interconnection Heat conduction. Organic Substrate: Printed Wiring Boards (PWB). Requirements: Electrical properties Mechanical properties - PowerPoint PPT Presentation
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Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 1
Chapter 5: Printed Wiring Boards
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 2
Substrate• The purpose of
the substrate for electronic component mounting is:–Mechanical support
–Electrical interconnection
–Heat conduction
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 3
Organic Substrate: Printed Wiring Boards (PWB)
• Requirements:–Electrical properties–Mechanical properties
–Chemical resistance–Fire resistance–Processability–Adhesion–Low moisture absorption
Fig. 5.1: Woven glass fibre for printed wiring board reinforcement
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 4
Printed Wiring Boards, continued
Table 5.1: Conventional laminates for printed wiring boards. (The designations are according to National Electrical Manufacturers Association, NEMA, USA.)
Reinforcement FlameResin Cotton Woven Mat Glass retard-
Grade Epoxy Polyester Phenolic paper glass glass veil antXXXPC * *FR-2 * * *FR-3 * * *FR-4 * * *FR-5 * * *FR-6 * * *G-10 * *CEM-1 * * * *CEM-2 * * *CEM-3 * * * *CEM-4 * * *CEM-5 * * * *CEM-6 * * *CEM-7 * * * *CEM-8 * * *
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 5
Printed Wiring Boards, continued
Fig. 5.2: Printed wiring board structures with varying complexity: a) Single sided and double sided.b) Double sided through hole plated with bare Cu or Sn/Pb surface.c) Four layer board.d) Six layer board with two Cu/Invar/Cu cores.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 6
Printed Wiring Boards, continued
Fig. 5.3: Photo plotter, schematically.
•Generation of Design Data, Photo- or Laser Plotting
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 7
Single Sided Boards• 1. Drilling / punching of registration holes• 2. Panel cleaning• 3. Printing of etch resist• 4. Etch ing• 5. Stripping• 6. Printing solder resist• 7. Curing of solder resist• 8. Cleaning of solder areas• 9. Deposition of solder coating
• 10. Punching of holes and edge countour (or drilling/milling)
This is a substractive process –Alternative: Additive processes
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 8
Single Sided Boards, continued
Fig. 5.4: Process steps of "print and etch" process for single sided boards
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 9
Double Sided ThroughHole Plated Boards
• 1. Drilling• 2. Cleaning• 3. Activation for chemical plating• 4. Chemical plating• 5. Electrolytic plating• 6. Pattern definition• 7. Tin/lead masking plate• 8. Etching• 9. Fusing• 10. Organic solder resist
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 10
Double Sided ThroughHole Plated Boards, continued
Fig. 5.5:Through hole plated PWB, process steps: a) Panel plating. b) Pattern plating. c) Hot air levelling.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 11
Double Sided Through Hole Plated Boards:Choice of Surface Metallisation and Solder
Resist
Fig. 5.6.a: Selective Sn/Pb surface coverage with hot air levelling. The alternatives, bare Cu or Sn/Pb on all Cu surface, are shown in Figure 5.2 b).
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 12
Choice of Surface Metallisation and Solder Resist, continued
Fig. 5.6.b:"Tenting", i.e. covering of the via holes by dry film solder resist.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 13
Multilayer Printed Wiring Boards
• 1. Drilling• 2. Rinse, Photo process for inner layers• 3. Etch inner layers• 4. Black oxidation for adhesion promotion• 5. Baking• 6. Lamination• 7. Drilling of through holes
Further process as for double layer boards
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 14
Multilayer Printed WiringBoards, continued
Fig. 5.7:Process steps for multilayer printed wiring boards with holes only through the board.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 15
Multilayer PrintedWiring Boards, continued
Fig. 5.8: Types of via holes: a) Through hole. b) Buried hole. c) Blind hole. Figure d) shows a microscope section of a drilled blind via. (Contrave´s "Denstrate" process).
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 16
Fine Line PrintedWiring Boards, additive process
Fig. 5.9 a): The development of minimum line width from 1965 until 1990. The figures in the ovals tell how many conductors can be positioned between the leads of DIP-components with a lead pitch of 0.1" (number of "channels").
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 17
Fine Line PrintedWiring Boards, additive process,
continued• Etch control:
Under etch/etch factor
• Additive process
• Clean-room
• Collimated light.
Fig. 5.9 b): Underetch and etch factor.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 18
Fine Line Printed Wiring Boards: Photolithographic Process
Fig. 5.10.a: Machine for double sided illumination with parallel light, for pattern transfer from photographic film for fine line printed wiring boards.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 19
Fine Line Printed Wiring Boards: Photolithographic Process,
continued
Fig. 5.10.b : Automatic in-line system for lamination of photoresist, illumination and development, in an enclosed clean room atmosphere.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 20
Metal Core Printed Wiring Boards
• Better heat conduction
• TCE matching with ceramic packages
• Most common: Cu/Invar/Cu
Fig. 5.2.d) Six layer board with two Cu/Invar/Cu cores.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 21
Metal Core Boards, continued
Fig. 5.12 a): Cross section of metal core board with one Cu/Invar/Cu core (Texas Instruments).
Fig. 5.12 b):Thermal coefficient of expansion of Cu/Invar/Cu, as function of the composition (Texas Instruments).
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 22
New Materials for PWBs• Higher Tg• Better dimensional stability
• r low, not dependent on T, f, or moisture
• Low losses• Lower TCE • Purpose
– High frequency use– Controlled characteristic impedance– High reliability
• Materials– Cyanate ester– PTFE (Teflon)– Polyimide– and others
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 23
New Materials for PWBs,continued
Fig. 5.13: TCE for FR-4 below and above Tg in a): the x or y
direction, b): the z-direction
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 24
New Materials for PWBs,continued
Table 5.2: Material parameters for polymers for printed wiring boards
Material r
Tan (at 1 MHz)
(T < Tg)
[ppm/ oC]
Tg
[oC]Paper/phenolic 4.7 0.025 95Bisphenol epoxy (FR-4) 4.3 - 5 0.02 33 -60 130Multifunctional epoxy 4.3 -4.5 0.02 140 145 - 180Tetrafunctional epoxy 4.3 -4.6 0.02 55 > 150BT/epoxy 3.5 - 4.2 0.012 100 185 - 225Cyanate ester 2.8 - 3.6 .002 - .005 50 -100 250 -290Polyimide (Pi) 3.0 - 4.6 .002 - .01 35 - 80 230 - 315PTFE (Teflon) 2.1 .001 70 - 120 250 *)*) Melts, no regular glass-transition
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 25
New Materials for PWBs,continued
Fig. 5.14: Frequency dependence of r and tan for FR-4.r :Relative dielectric constant. tan : Loss tangent.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 26
Commercial Products
Table 5.3: Materials parameters for important materials combinations and some commercial products for high performance printed wiring boards.
Material r tan
(at 1 MHz)K
[W/m oC]
(T<Tg)x-y (and z)
[ppm/oC]
Tg
[oC]
FR-4 4.6 .02 0.2 12-16 125(60 )
PTFE/glass 2.35 .001 0.26 24 250(260)
Pi/glass 4.4 -4.8 .01 -.015 0.35 11-14 220 - 270(60)
Pi/quartz 3.4 - 4 .005 0.13 6-8 270(34)
RO2800 2.8 .0014 0.44 16-19 327*)(24)
RO2500#) 2.5 .0025
Fortin/CE 2.8-3.6 .003-.009 0.3 ca. 15 110 - 250(50-350)
Gore 2.4 -2.6 .01 ca. 0.2 12 120 -180(50)
Alumina 10 .0001 30 5-7 -*) Melting point #) Used for flexible boards and high frequency flat cables.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 27
Commercial Products,continued
Fig. 5.15 a): Structure of Rogers material RO2800.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 28
Commercial Products,continued
Fig. 5.15 b): Combination of Gore-Ply and FR-4 gives a simple process, and at the same time low dielectric losses and reduced capacitance to ground.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 29
Commercial Products,continued
Fig. 5.16: Attenuation in (dB) as function of frequency for a one meter long stripline, for the high performance materials Gore, Nelco and polyimide, compared to FR-4.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 30
Commercial Products,continued
Fig. 5.17: Top: Microwire from PCK, with conductors insulated with organic insulation, and a metal foil as ground plane. Bottom: Next generation technology, where each conductor has its own metal shield.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 31
Commercial Products,continued
Fig. 5.18: The equipment head that deposits the conductors on the laminate for Microwire.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 32
Special Boards• Flexible printed wiring boards
–Dynamic or static bending.–Uses: Movable parts and odd shaped, cramped places
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 33
Flexible PrintedWiring Boards, continued
Fig. 5.19: Flexible printed wiring boards: Most of the electronics in Minoltas camera Maxxum 9000 is on two flexible printed circuit boards.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 34
Flexible PrintedWiring Boards, continued
Table 5.4: Properties for materials used for flexible printed wiring boards.
Typical values Unit Glass Epoxy Polyesterbaselaminate
Polyimide base laminate
Solderability °C/s 260/10 230/1 260/10Max. continuousoperating temperature °C 150 110 220Tensile strength kp cm-2 1750 1500 1700
Peel strength to copper kp 4,5 1,8 1,3Moisture absorption % 0,5 0,8 2,5Coefficient of linearexpansion °C-1 1,1 10-5 1,5 10-5 2,0 10-5
Etch shrinkage: Machinedirection/transverse direction
% 0,2 - 0,8 1,0 - 0,55 0,45 - 0,25
Dielectric constant(60 Hz) 3,4 3,25 3,5Dissipation factor(1 kHz) 0,037 0,006 0,003Resistivity ohm cm 1,6 1013 1017 4 1016
Cost ratio(laminate only) 1,4/2 1 2/3Comments Not suitable for
continuous folding use.Max. peel strength tocopper and minimumelongation.
Sensitive to solderheat.Lowest cost.Good physical andelectrical properties
Non-flammable.Outstandingphysical andelectricalproperties.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 35
Flexible PrintedWiring Boards, continued
Fig. 5.20: Cross section of flexible PWB:
Top: Single layer conductor foil.
Bottom: Double layer conductors with through hole plating.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 36
Membrane Switch Panels
• Purpose: Switches and informative instrument fronts.
Fig. 5.21 a): Membrane switch panel, schematically.Top: Structure
Bottom: Cross section of a normal panel and a panel with metal dome.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 37
Membrane Switch Panels,continued
Fig. 5.21 b): Exploded view of simple switch panel
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 38
3 D Moulded Boards
–Combine substrate and chassis, integrated stand-offs, etc.
–Materials: • Polysulphone, polyetherimide, etc.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 39
3 D Moulded Boards, continued
Table 5.5: Materials used for moulded circuit boards, and their properties, compared to epoxy and polyimide
Polymer types Epoxy Polyimide Poly-sulphone
Polyether-sulphone
Polyether-imide
Manufacturer 3M Co. E.I.Dupont UnionCarbide
ICI America G.E.Co
Trade name Scotchcast5133
Pyralin Udel Victrex Ultem
Thermal conductivity(W/m°C)
0,40 0,15 0,22
Glass transitiontemperature [°C]
110-125 260 190 230 215
UL listed temperature[°C]
130 NA 150 180 170
Coeff. of thermal
expansion [10-7/°C]
600 200-400 - - 560
Dielectric const.@1 MHz
6,2 3,50 3,10 3,50 3,15
Dissipation factor@1 MHz
0,02 0,002 0,004 0,006 0,002
Dielectric strength[V/mm]
20000 45000 48000 - 33000
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 40
3 D Moulded Boards, continued
Fig. 5.22.a: 3 dimensional moulded component carrier in a telephone application.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 41
3 D Moulded Boards, continued
Fig. 5.22.b: 3 dimensional moulded component carrier in a power supply application.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 42
3 D Moulded Boards, continued
Fig. 5.23: The process for moulding of a 3-dimensional substrate with Cu conductor patterns deposited on a temporary film.
Electronic Pack….. Chapter 5:
Printed Wiring Boards Slide 43
3 D Moulded Boards, continued
Fig. 5.24: Two steps moulding process for preparation for chemical plating of the conductor pattern on 3-D component substrates. The first moulding is done with a catalytically activated plastic, the second with "passive" plastic, where chemical plating is not sticking. (PCK, USA).