An insight into bareboard

1. Printed Circuit Board
Manufacturing
Richard Puthota
Cookson India Ltd
December 2010
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2. Disclaimer
THIS DOCUMENT AND RELATED MATERIALS AND INFORMATION
ARE PROVIDED "AS IS" WITH NO WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY IMPLIED
WARRANTY OF MERCHANTABILITY, FITNESS FOR A
PARTICULAR PURPOSE, NON-INFRINGEMENT OF INTELLECTUAL
PROPERTY RIGHTS, OR ANY WARRANTY OTHERWISE ARISING
OUT OF ANY PROPOSAL, SPECIFICATION, OR SAMPLE.
COOKSON INDIA PVT LTD ASSUMES NO RESPONSIBILITY FOR ANY ERRORS CONTAINED
IN THIS DOCUMENT AND HAS NO LIABILITIES OR OBLIGATIONS FOR ANY DAMAGES
ARISING FROM OR IN CONNECTION WITH THE USE OF THIS DOCUMENT.
COOKSON INDIA PVT LTD MAY MAKE CHANGES TO SPECIFICATIONS,
PRODUCTDESCRIPTIONS, AND PLANS AT ANY TIME, WITHOUT NOTICE.
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3. PCB
A PRINTED CIRCUIT BOARD PROVIDES A MECHANICAL PLATFORM FOR ELECTRONIC COMPONENTS (ACTIVE
SEMICONDUCTORS, RESISTORS, CAPACITORS, CONNECTORS, ETC.)
A PC BOARD PROVIDES 3- DIMENSIONAL ELECTRICAL INTERCONNECT FOR DEVICES INCLUDING SIGNAL, POWER,
AND GROUND CIRCUITS.
A PRINTED CIRCUIT BOARD IS SIMULTANEOUSLY AN ELECTRICAL DEVICE, A MECHANICAL DEVICE, AND A
THERMAL DEVICE.
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4. Capability of a PCB Manufacturer
MEASURING UNITS FOLLOWED IN PCB INDUSTRY
UNITS MICRO INCHES MILS INCHES ANGSTROMS MICRONS MM
MICRO INCH 1 0.001 0.000001 250 0.025 0.000025
MICRON 40 0.04 0.00004 10000 1 0.001
MIL 1000 1 0.001 250000 25 0.025
7
MM 40,000 40 0.04 10 1000 1
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5. PCB Process flow
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6. PCB Process flow ..Confused?
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7. PCB Value flow - simpler way
Sales CAD /CAM Engineering Plotting Inner layer
Processing
Electroless Cu DeSmear Drilling ML Lamination Dev/Etch/Strip
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8. Process flow
Strip / Etch /
Outer-layer Electrolytic Cu Solder mask / LP Hot-Air Leveling
Strip Tin
Processing
Optional
Final Q/C 100% E-Test V - Scoring NC Routing Immersion Gold
Shipping
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9. Why Copper?
Copper is an excellent electrical conductor
Electrical resistivity is approx 1.6 micro ohm cm
An inexpensive metal
Soft and easily workable
Easily processed and patternable by photolithography, using
relatively benign chemicals
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10. Copper Foil
Copper is the dominant metal for interconnection use.
The copper foil is normally specified by weight i.e. one half oz
per square ft (152.5 g/m2), oz per sq ft (305 g/m2).
These correspond to foil thicknesses of 17.5 and 35 microns
respectively.
It is usually produced by electrolytic deposition on a flat
mandril, and is about 99.8% pure and has a tolerance on
thickness of about ± 10%.
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11. Copper Foil
Copper can be easily electrodeposited onto a PCB Laminate –
problems however!
ADHESION!
The adhesion is far superior from bonding copper foil sheets
by the combination of heat, pressure and adhesive.
Common adhesion tests include measurement of Peel
Strength – ‘how easy is it to peel the copper foil off’ and Pull
off Strength – how easy is it to pull up the copper foil from
the substrate
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12. PCB Substrates Reinforcement Materials
Cu FOIL MFG PROCESS PREPREG MFG PROCESS
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13. PCB Substrates Reinforcement Materials
PREPREGS
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14. PCB Substrates ( Laminate) MFG Process Flow
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15. PCB Laminate MFG Process
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16. Tg
The glass transition temperature or Tg of a polymer is the temperature at which a polymer
transitions from a glassy to rubbery state upon heating and reflects the degree of polymer
Chain motion.
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17. PCB Substrates
Typical Dielectric Constants
Material Dielectric Constant
FR4 Fiberglass Epoxy 4.7
Teflon 2.2
Teflon Glass 2.5
Polyimide 3.5
Polyimide Glass 4.2
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18. PCB Substrates
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19. PCB Substrates
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20. PCB Substrates
One important non-electrical characteristic is the maximum
temperature at which boards can be operated. This is also relevant
for the curing of printed epoxies and thick film pastes on the
boards.
Resin Reinforcement Maximum temperature 'C
Phenolic Paper 100
Glass 250
Epoxy Glass 120
Polyester Glass 120
Silicone Glass 250
Teflon Glass 200
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21. Robustness of Boards
The produced laminate boards must be robust enough to withstand
abuse during processing stages and in later life on the finished product.
Abuse can include:
Changes in temperature – sometimes rapid and hot and cold
Flexing – the boards may have to be flexed, particularly during
processing stages.
Resistance to chemicals, e.g. solvents, fluxes, acids etc.
Physical abuse – to a certain extent being dropped!
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22. Single Sided PCB Board Double Sided
PCB Board
Top layer has been patterned in alignment with bottom layer
Holes are drilled through board and then copper is
electrodeposited to interconnect top and bottom layers
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23. Multilayer Boards
On multilayer boards, the individual, copper patterned laminates are stacked on
top and bottom of each other. Insulating layers between the conductors can also
be added.
Often begin with double sided board in middle and work outwards
Laminates then pressed, heated and bonded in a similar process to before.
Holes then drilled in appropriate places for subsequent electrodeposition of
copper to interconnect layers.
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24. FLEXIBLE PCB’s
More and more interest being shown to flexible PCB’s
Applications include flexible interconnections. Advanced
applications include small screens, e.g. mobile phones – and large
‘roll up’ screens
Common substrate choices include polyester, polyimide etc.
Typical problems – flexing substrate can cause metal tracks and
components etc. to ‘peel’ off
Resistance of metal conductors can also be different when
substrate is flexed
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25. FLEXIBLE PCB’s
Flexible circuits can reduce weight of PCB
Flexing can allow easier installation and servicing
Production can be inexpensive
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26. FLEXIBLE DISPLAYS
Flexible Displays can take up less space (rolled up)
– more portable
Active elements can be TFT’s deposited by vapour deposition (amorphous
silicon) – also printed organic materials
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27. Pre Clean
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28. Laminate Photo Resist
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29. Image & Develop
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30. Etch & Strip Photo Resist
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31. Prepare Target & Tooling Holes
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32. AOI
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33. Oxide Coating
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34. Lamination Of a 6 Layer Board
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35. Drill & De-burr
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36. Desmear & Copper Deposition
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37. Coat, Image & Develop Photoresist
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38. Copper & Tin Plate
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39. Strip Photo Resist
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40. Etch & Tin Strip
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41. Solder Mask
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42. Solder Mask
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43. Solder Mask
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44. Solder Mask
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45. Typical Surface Finishing Technologies
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46. Hot Air Leveling
Air knife
off-set
Clamp to
hold PCB
PCB
Solder
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47. Advantage of greater thickness control in Pb Free HAL
Sn/Pb
Stencil
Laminate
Improved gasket sealing
during solder paste
printing on fine features. Lead-
Stencil
Free
Laminate
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48. OSP Organic Solderability Preservative
Manifold
C C
O H
PCB A E
OR T P
C
M
I I
N B S
G T
Coating Chemistry Sump R
Y
Conveyorized Dip
Module
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49. OSP VISUAL INSPECTION CRITERIA
Courtesy : Enthone, Cookson Electronics PRIVILEGED AND CONFIDENTIAL MATERIALS

50. Comparison of PCB Surface Finishes
®
ENTEK HASL FST™ Ni-Au AlphaLevel™
OSP Immersion Sn Immersion Ag
Cost Lowest Medium Medium Highest Low
Fine Pitch Excellent Poor Excellent Good Excellent
Multi Pass Medium Excellent Good Good Good
Wave OK Variable Excellent Good Poor Good
Ease of Mfr Easy Difficult Medium Difficult Easy
Warping Low High Low Low Low
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51. Comparison of PCB Surface Finishes
PROPERTY COMPARISON OF ALTERNATIVE COPPER PROTECTIVE COATINGS
ATTRIBUTES ALTERNATIVE COATINGS
Hot Air Solder Rosin / Resin Benzo - Amidazole/ Immersion Electroless Immersion
PROPERTY OF COPPER COATING
Leveled Coating Triazole Benzimidazole Bismuth Nickel/Gold Silver
Cost Of PCB Fabrication
5 8 10 7 7 1 5
Lowest Cost = 10; Highest = 1
Pin Testability of Bare Board
10 1 3 4 10 10 10
Most Pin Testable = 10; Least = 1
Shelf - Life
9 6 3 6 7 9 9
Longest = 10; Shortest = 1
Ionic Cleanliness
1 5 10 10 10 10 10
Least Contamination =10; Most = 1
CO-PLANARITY(FLATNESS)
1 10 10 10 10 10 10
Flat Pads = 10; Non Planar Pads = 1
Risk of removing Protective Coat
during rework Not easy to 10 2 2 2 10 10 10
remove = 10; Easy to remove = 1
Solderability at Wave Solde ( No
prior Reflow) 10 6 6 6 7 8 9
Highly Solderable = 10; Least = 1
Solderability at Wave Solder (after 2-
3 reflows using no clean flux) 10 1 2 5 7 8 9
Highly Solderable = 10; Least = 1
Wire Bondability
Wire Bondable = 10; 1 1 1 1 1 10 9
Can't wire bond = 1
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52. Tip Plating – Apply Plating Tape
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53. Solder Strip Fingers
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54. Nickel Plate Fingers
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55. Gold Plate Fingers & Strip Tape
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56. Component Mark Printing
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57. Fabrication Rout & Chamfer
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58. Electrical Test (BBT)
Electrical testing checks the boards for
any open or short type defects, before
shipping to the customer.
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59. Key Take Aways
• For a company manufacturing electronic equipment, it is risky to depend on just
one PCB manufacturing source.
• It is important that the PCB manufacturer and the OEM / EMS are thoroughly
knowledgeable about each other’s capabilities and expectations to ensure compatibility and
cooperation.
• There can easily be differences in the perception of quality, or the documentation
package can seem inadequate to the PCB manufacturer, thus requiring additional
communication with subsequent adjustments, and inevitably, this takes time.
• Another important advantage of having a number of regular PCB suppliers is a broader
spectrum of PCB technology at the customer’s disposal.
• This can be very significant in times of great technological changes, especially when
introducing SMT, HDI (High Density Interconnect), or laser drilled boards.
Thus, the conclusion is that any OEM or EMS company should always utilize a number of approved
and regular PCB vendors.
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60. May This Information Improve Your Ability To Weather The Storms
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