how_is_a_pcb_made

8/10/2019 How_Is_A_PCB_Made

1/23

How is a PCB Made ?What determines impedance ?

www.polarinstruments.com


2/23

2

M anufactur ing Processes


Manufacturing Processes for a Multi-layer PCB

Section through PCB

Via hole

SMD Pad

The following presentationcovers the main processesduring the production ofa multi-layer PCB.

The diagrams which followrepresent a section througha 6 layer PCB, as indicatedin red.

Tracks under solder mask


3/23

3



Typical Layer Construction - 6 Layer PCB

Layer 1 (Outer)

Layer 6 (Outer)

Layer 2 (Inner)

Layer 3 (Inner)

Layer 4 (Inner)

Layer 5 (Inner)

FOIL

FOIL

PRE-PREG

PRE-PREG

PRE-PREG

INNER LAYER

INNER LAYER

Copper Laminate

Layer build / stackup is one ofthe most important aspects ofcontrolled impedance

Many combinations ofmaterial thickness can beused.

PCB Fabricatorsmanufacturing techniquesvary

Impedance Considerations


4/23

4



Drilling of Bonded Panel

Layer 1

Layer 6

Layer 2

Layer 3

Layer 4

Layer 5

Copper Laminate Drilled Hole

Impedance Considerations Press temperature and

pressure have an effect onthe flatness and henceimpedance. This should bechecked prior to drilling

Drilling itself does not effectimpedance


5/23

5



Electroless Copper ProcessAddition of Copper to all Exposed Surfaces

Layer 1

Layer 6

Layer 2

Layer 3

Layer 4

Layer 5

Copper Drilled Hole

Electroless copper effectscopper thickness on outerlayers (T)

Sometimes other solutionsare used containing carbonetc



6/23

6



Layer 1

Layer 6

Layer 2

Layer 3

Layer 4

Layer 5

Laminating and Imaging of External Layers

UV sensitive film is laminated over top and bottomsurfaces of PCBIt is then exposed and developed, leaving anexposed image of the PCB pattern

Copper

Does not effect impedanceImpedance Considerations


7/23

7



Layer 1

Layer 6

Layer 2

Layer 3

Layer 4

Layer 5

Electro-plating Process 1Additional Copper to all Exposed Surfaces

Laminated Film Plate Additional Copper

Electro-plating increases thecopper thickness on outerlayers (T)

This will always be variationsin the amount of copperadded.

This finished copperthickness should be used instructure calculations



8/23

8



Layer 1

Layer 6

Layer 2

Layer 3

Layer 4

Layer 5

Electro-plating Process 2Add Tin over Exposed Copper Areas

Laminated Film Additional CopperTin Plating

Impedance Considerations Does not effect impedance


9/23

9



Layer 1

Layer 6

Layer 2

Layer 3

Layer 4

Layer 5

Electro-plating Process 3Remove Laminated Film

Laminated Film Removed Tin Plating

Impedance Considerations Does not effect impedance


10/23

10



Etch Process - Remove Exposed Copper

Copper Removed Tin Plating

The etch process producesan etch back or undercut ofthe tracks. This can bespecified by the W / W1parameters

This means that tracks willend up approximately0,025 mm (0.001) thinnerthan the original design.


Layer 1

Layer 6

Layer 2

Layer 3

Layer 4

Layer 5


11/23

11



Layer 1

Layer 6

Layer 2

Layer 3

Layer 4

Layer 5

Tin Strip - Remove Tin Plating

Tin Plating Removed

The Removal of Tin willslightly reduce the copperthickness (T) on the outerlayers



12/23

12



PCB is now complete except forsurface finishes and panel routing

Layer 6

Layer 1

Via Hole SMD PadTracks

Tracks


13/23

13



Solder Mask Application- Curtain Coated Method

Layer 6

Layer 1

Apply Liquid Photo-imageable Resist, then Dry

Some PCB Fabricators choseto check the impedancebefore the solder mask isadded

Structures can be checked inNormal and Coated mode

Thickness of solder maskshould be specified using H1



14/23

14



Solder Mask ApplicationImage, Develop and Cure

Layer 6

Layer 1

UV Image, Develop and Cure


Does not effect impedance


15/23

15



Surface Finish Process

Layer 6

Layer 1

Apply Solder to Exposed Copper Areas

Surface Finish (Tin / Lead /Gold / Silver) is usually onlyadded to pads

If board has no solder maskthe thickness of finish shouldbe added to T.



16/23

16



Component Notation

R34

IC3

SCL2 9624


Does not effect impedance


17/23

17



Routing (includes second stage drilling)


Controlled Impedancecoupons are routed from thepanel

Good controls are necessaryto ensure that coupons canbe matched to manufacturing

panels


18/23

18



Process finished PCB and coupon fortesting



Controls are necessary toensure that coupons can bematched to manufacturing

panels this should beperformed on trial panelsprior to production ramp up.


19/23

19



Why as a designer do you need todiscuss your design with your PCB fabricator?

Impedance ConsiderationsPCB manufacture is a process, it usesmaterials which are not Ideal

FR4 for example is a glass resin mix madeof two substances with differing electricalproperties.

PCB Manufacturers need to make smalladjustments to designs to maximise yields

Glass Er 6 Resin Er 3 (FR4) Resin Er < 3 (High

performance laminates)


20/23

20



Why as a designer do you need todiscuss your design with your PCB fabricator?

Impedance ConsiderationsProcess varies from one fabricator to

another.

Press pressures temperatures may vary

Pre preg and Core may vary from oneSupplier to another.

Supplier variations


21/23

21



Process finished PCB and coupon fortesting



Controls are necessary toensure that coupons can bematched to manufacturing

panels this should beperformed on trial panelsprior to production ramp up.


22/23

Design & test tools for controlled impedance & Signal integrity

PCB Faultfinding systems & software www.polarinstruments.com

2003 Polar Instruments

Your contacts at Polar:

USA: Richard Smith (800) 328 0817

UK / Europe: Neil Chamberlain +44 23 9226 9113Asia / Pacific: Amit Bhardwaj +65 6873 7470
http://www.polarinstruments.com/http://www.polarinstruments.com/


23/23

For more informationplease visit:


2003 Polar Instruments

Your contacts at Polar:

USA: Richard Smith (800) 328 0817

UK / Europe: Neil Chamberlain +44 23 9226 9113Asia / Pacific: Amit Bhardwaj +65 6873 7470
http://www.polarinstruments.com/http://www.polarinstruments.com/

how_is_a_pcb_made

Documents