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AT&S India Private Ltd.

1AT&S PRESENTATION

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WELCOME

TO

Rashmi P.NProject Trainee

PRINTED CIRCUIT BOARDPRINTED CIRCUIT BOARD

MANUFACTURING IN AT&SMANUFACTURING IN AT&S

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Contents

Company overview

Abstract

Introduction

Steps involved in PCB manufacture

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Abstract

A PCB contains a fiber glass epoxy board with thin copperlayers attached to it.

A photographic process is used to etch off the copper where it

is not needed to connect ICs. Prior to etching, all holes are drilled in the PCB and it is

electroplated so that the feed through holes connect to thedifferent copper layers.

Electronic parts are soldered to copper mounting pads left after

etching, and thin copper traces are used to connect the parts.

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Introduction

PCB is the short form for Printed Circuit boards (It is also calledPrinted Wiring Board).

These are basically devices that provide electrical interconnectionsand a surface for mounting electronic components.

A PCB consists of tracks, holes, and pads.

Tracks are basically the wiring paths.

There are different kinds of holes with different diameters on thePCB.

The holes can be plated or non-plated. They might be via holesor component holes.

Pads Depending upon the application different types of padswill be which are designed by customer.

Component legs are inserted through the holes in the PCB& Components are soldered directly to pad areas on thesurface of the board.

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PCBs are classified as:

Single sided boards:

The single sided board (SSB) has circuits on only one side of theboard.

Double sided boards: Double-sided boards have circuits formed on both sides of the

boards. Interconnections between different layers are madethrough PTH (Plating Through Hole).

Multi layer boards: PCB with more than 2 layers are called Multi layer boards. Multi

layer will go upto 24 layer. Interconnections between these layersare achieved through PTH.

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Process Flow

Customer Requirement CAD/CAM Product Engineering

PPC Inspection (stores) Surface Prep Inner Layer Process

DES Post Etch Punch AOI Circubond Multi layering

Pressing X-ray inspection Drilling Deburring PTH &Cu

Plating Outer Layer Process & Photo Printing Solder Mask

Surface Finish Routing Final Inspection & AQL Labeling

& Packaging Shipping

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Customer Requirement

Customer Places a Requisition for production.

Requisition will be in the form of Gerber Data.

Gerber data includes all Product specifications like No.ofLayers, Surface finish, Circuit design, Material.

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CAD/CAM

Creates Production Specifications using Gerber data.

Does IDS( Initial data screening)

Creates all the necessary Programs for:

-Drilling

-Routing & V groove

-AOI

-Photo Printing

-BBT

-FI

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Product Engineering

Quotation-Manual and Complete data package.

Process Feasibility- Checked through MFS.

First article inspection( FAI)

Product Launch Generation ofBOM( Bill of Material)

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PPC

Plans all Production Activities

Prioritizes all orders based on customer requirement.

Check for the availability of materials. MRP( Material Requirement Planning) using BOM

Scheduling and Work centre allotment

Travel Chart generation

Line control-Smooth flow of product in process till dispatch.

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Surface Preparation

Prepares surface for Inner layer processes.

Baking: The Panels are baked after getting them from stores to

Relieve stresses, Get the Mechanical Stability, Take away the

Moisture content. IL Pre-Clean

Blowing & Drying

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Surface Preparation

IL Pre-Clean: Includes the following.

Acid Clean- Sulphuric acid based clean.

Water rinse

Micro Etch- H2O2+ H2SO4used,about 1micron Cu removed.

Water Rinse

Acid Spray-H2SO4 based soln Removes Cu smut and Expose

active surface ofCu.

Blower & Drier- 40 to 70 degres.

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Inner layer Photo Printing

Tacky Cleaning: Takes place @ 42 deg celcius.

Hot Rolling: Panel is Hot rolled between 98-102degrees for

proper bonding and cavity filling.

Lamination: The ploythene cover is removed, then DFPR andMylar will be laminated on both the sides of the panel.

Exposing:. UV light is passed through the photo tool. Negative

photo tool is used, made of Silver Halide. Exposed area will be

polymerized (hardened), unexposed area remains soft. Mylar is

removed before entering into the next process.

**Polythene film b/w DFPR &Photo tool helps to check any abrasion or excess O2

spreading, Panel thickness Max=1.6mm and Min=.15mm, Over Exposure-Shorts

and Under Exposure- random opens in ckt region.

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DES

Develop: Selective removal of Un polymerized DFPR. Sodium

Carbonate is used.

Etching: Unwanted Cu etched off using H2o2+Hcl based

annalyte soln.

Stripping: Polymerized DFPR is stripped using a NaoH

solution.

Water Rinse & Drying.

Post Etch Punch: 4pin Registration done with fiducials as ref.

Its directly responsible for Multilayer in pressing. Accuracy is

very important.

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AOI

AOI Automatic Optical Inspection.

Its a comparison process, using camera and magnifying lens.

Defects are compared with Cam data for validation.

The circuit in the board is checked for Open and Shorts.

Net and Image inspection.

Acceptable re-works are done.

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Circubond

Oxidation process of making the Cu process porous.

Cleaner (Basic clean M Cascade rinse Activator Bond Film

Cascade rinse Drier.

Applying an oxide film onto the surface improves bondingstrength, both mechanically and chemically, prevents

atmospheric oxidation and migration of molecules.

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Lay-up and Pressing

This is a process where multilayer PCBs are made.

Inner cores are attached together with epoxy in the middle

called Layup.

Pressing of Multilayer arrangement is done by applying high

pressure and temperature using Al sheet, Kraft papers and

caul plate.

Pressing in done in two ways:

Hot pressing- 190deg

Cold pressing-50deg(Water cooled)

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Drilling

Flash Trimming- Removal of extra Cu outside the panel. Resin de burring: Surface finish operation. Grinding tool is used.

Removes extra resin that occur over hole during pressing

X-ray inspection: Inspects the fiducials for reference and drill the

stack holes for proper alignment and anti- rotation. Stacking interference: Pins are attached on the panels with base

plate.

Coupon holes: Verification for zero correction and

Concentricity.

Drilling: Done by calling a program from CAM using VCS.

Al plate of 0.2mm thickness is placed on the panels to be drilled

for dissipation of heat and to minimize the burr.

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Deburring

Deburring is to remove the burr and dust from the drilled hole.

The three stages of Deburring are:

Brushing

High Pressure Rinse/Ultrasonic cleaning Drier

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PTH

Creates connectivity between the layers by applying Cu through

the holes.( 3 to5 Microns ofCu is added)

Processes involved in this

P-Desmear

CP-Conductive Polymerization

CU-Copper Plating

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Seleo Cp Process

De Smearing:

Etching: NaPS + H2So4

Triple rinse

Sweller: Resin preparation for easy removal of resin.

Permanganate: The permanganate etch solution removes resin

smear from the inner layers and cleans the hole wall surface

and roughness the epoxy resin surfaces.

Reducer: The glass fibers can be cleaned/etched simultaneously by using anglass etching additive .

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Cp-Conductive Polymerization

Etching:NaPS and H2SO4 used. Roughness the hole wall and panelsurface.

Cleaner: The chemical solution used here ensures proper wetting of thehole wall surface. The temperature of about 70rC is maintained here.

Chemicals used here are cleaner cp, sodium carbonate.

Conditioner: Hole wall gets conditioned making it ready for promoterattack.

Adhesion Promoter: A thin layer of MnO2 is coated on the panel forbetter bonding ofCu. Seleo Cp buffer, additives and NaoH are used.

Poly Conduct: Which is non-conductive in the monomer state, becomesconductive when it is polymerized, this is the basic principle employed in the

Seleo line. The temperature is maintained at 18oC

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Cu Plating.

CGA( centre gap adjustment): Panels are adjusted between 10-12mm to avoid negative effects of current density.

Acid Dip: This avoids the water drag out into the plating stage. The

fingerprints are removed by the action of Sulphuric acid.

Cu Plating: Done using Reverse Pulse plating. Electrolytic process. Around3to5microns in hole, 6to7microns on surface.

Reverse Pulse Plating: Avoids over plating and evolution of O2 leading to air

bubble development.

Rinsed and dried at 50-60 deg.

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Types ofCu Plating

Plate Etch route (also called as Pattern plating route).

Print Etch route (also called as Panel plating route).

Semi panel plate. Tin plating route

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Print Etch Process

w Panel plating route

Cu is plated on the whole panel based on the customer

requirement.( No flash cu plating)

Electro Plating.( SAP and VC

P) Scrubbing for surface preparation.

Photo Printing: Panel is exposed to UV light using Negative

photo film.

Acid Etching: Na2C

o3 etches unexposed DFPR,C

upricC

hlorideremoves unexposed Cu.

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Plate Etch

Pattern plating route( P2, P3)

Photo printing: Panel is exposed to UV light using Positive

photo film.

Electro-less Cu plating( based on Customer Req)

Tin Coating: Stannous sulphate is used.( 1-2 microns) etch

resistant to protect required Cu.

Alkaline Etching: Exposed DFPR is stripped using NaoH, Cu

is stripped using Cupric Ammonium Sulpahte. Tin Stripper: Nitric acid is used.

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Semi panel plating

Pattern plating route( P2, P3)

Scrubbing: Panels are scrubbed.

Cu plating- 10 um cu plated (SAP/VCP)

Pattern Plating- Remaining Cu is plated to fulfill Cust req. Photo printing: Panel is exposed to UV light using Positive photo

film.

Alkaline Etching: Exposed DFPR is stripped using NaoH, Cu is

stripped using Cupric Ammonium Sulpahte. Tin Stripper: Nitric acid is used.

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Criteria for Panel or Pattern plating

Sln

o

Parameter Pattern Plating Panel Plating

1 Board thickness 0.8 to 3.2 mm 0.8 to 1.6mm

2 Aspect ratio 5.33 5.33

3 Base Copper Upto 5 ounce Upto 2ounce

4 Cap on Surface cu

thickness

Not possible Possible

5 PFC holes NO( with zero Neg tol) YES ( with zero Neg tol)

6 Line width/spacing 6/6 mil-isolated tracks

Upto 20 mil PTH

5.5mil restricted by base

cu thickness

7 PTh holes No limit Upto 5mm max

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Solder Mask

Acid Clean- to remove surface contamination, Oxidation

Water wash

Pummice scrubbing: Pummice powder is used for making the

surface rough and better bonding of the ink. Water blast @ high pressure.

Drier: 80 to 90 degrees.

Coating of solder ink on the panel. Includes two processes.

Screen printing & Curtain Coating.

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Solder Mask

Screen Printing:

Resin + Hardener + BC solvent is used(0.7kg+0.35kg+30%)0.7kg+0.35kg+30%)

Screen used is 43T/cm.(Manual Operation)

Ink coated & dried for 40mins.

After drying ink applied on the other side n dried in Oven@

80degrees.

About 30microns of ink coated. (track edge=4um;top=8um)

For greater than 0.35mm dia, Squeezing pressure 20 PSIFor greater than 0.35mm dia, Squeezing pressure 20 PSI

Semi Matt FinishSemi Matt Finish

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Solder Mask

Curtain coating:

Resin+ Hardener+ PM solvent(1.72kg+8.32kg+1.2 liters )

Preheated @ 30deg.

Machine coating based on the wet wt. (Flow rate of ink isadjusted)

Matt finish: Even distribution of ink on the panel surface.

Dried between 90-110deg.

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Solder Mask

Exposing: panel is exposed to UV light using positive film.

Developing: Unexposed solder mask ink is etched using

Na2Co3 soln.

Curing: Tunnel oven-80 to 150deg, tenting jobs not done here.

Box Oven: 80-150 deg, tenting jobs are done here.

UV Bumping: Solder ink hardened by passing through UV light.

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Surface Finish

1.HASL:

Micro etch: mild solder mask scum is removed in this process

Fluxing: It forms a film on copper surface and keep it active even

in a very high temperature. (Improper Fluxing results in solder

shorts and more fluxing leads to Contamination of bath)

Solder leveling: contains molten solder (tin 63% and lead 37%)

Panels dipped and hot air is blown. Care taken for uniform

coating. Hot air is blown @ 389deg using air knives.

Post Cleaning: Hot water spray with Nylon brush- scrubbbed for

removal of excess flux, contaminants like carbon etc..

Dried and inspected. (insufficient drying leads to legend peel off)

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Surface finish

2. ENIG:

Acid cleaner: Deactivates Palladium residue in NPTH where ENiG notrequired.

Micro etch: removes 1.5-2 microns of copper, good adhesion.

Hot sulphuric dip: ensures removal of entrapped micro-etch solutionfrom the partially tented holes

Pre dip: It acidifies surface of the panel to prevent the formation ofpalladium hydroxide.

Activator: it contains palladium ion and dilute sulphuric acid

Electroless nickel: ENiG is deposited, Hypo Phosphite used isresponsible for redn of Ni from ionic to metallic stage.

Immersion gold: in this stage gold deposited on nickel surface bydisplacement reaction.(.06 t 0.12um)

Drying and Rinse.

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Surface Finish

3. Immersion tin:

Cleaner: cleaning the surface, remove oxide layers and dust

Triple rinse: cleans up the chemical residues

Micro etch: Small solder scum is removed.( lesspoor bonding

between Copper and Tin)

Triple rinse: Cleans up the chemical residues.

Stannadip: Tin gets deposited on copper .(0.8to1.4um) by

displacement reaction. Thio-Urea is used to avoid Cu precipitation.

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Surface Finish

Stannatech: 0.8 to 1.4 microns of tin gets coated at this stage,

with a dense satin finish.

Crystallizer: Here temperature is reduced from 700C to 20C.

At this low temperature the Cu thiourea complex turns intocrystalline form, Cu complex is separated from the mixture using

filter,Thiourea is pumped back to stannatec which helps to

achieve required thickness of tin

Constannic: Here Sn4 is converted back into Sn2 and again

pumped back to stannatec module

Thiourea rinse: To avoidCopper precipitation on the PCB.

Water rinse and dryer

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Surface Finish

Legend Printing:

Stencil preparation screen used is 120 T/cm, image exposed

to screen using Uv light, Positive photo film used.

Plugging: Plugging ink mixed and poured on the printing

screen, Screen printed and ink is deposited inside via holes.

Cured for 60 mins at 150C

Legend: Done to identify the locations of the surface mounted

devices which will be later mounted onto the board.

Peelable: Done to mask certain portion of the active region on

the board. Depends upon Customer requirement.

Carbon Printing: A thin layer of Tamura ink is used.

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Routing and V-Groove

Panels are converted into pallets

V-scoring: Only straight line cuts are made,Depth upto o.4 to

0.6 mm is made depending on the thickness of board

Routing: Both straight and contour shapes can be easilyachieved. Router bit tungsten carbide from 0.8 to 2.5mm bits

are available.

4 boards are machined at a time

Beveling: 30 to 40o chamfering is given to connectors

Water wash

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Bare Board Testing

Tests for open and shorts in all circuits:-

For each type of panel a test jig is prepared on bed of nail

system.

Electrical grid in the machine, tests the connectivity in the

circuit.

Acceptable rework of open circuit and short circuit is done and

sent to final inspection.

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Final Inspection and AQL

FINAL INSPECTION- Circuits are optically tested for blocked holes, routingdefects.- For acceptable rework, boards are cured.-All circuits are manually inspected for defects and

compared with the master circuit.

Some of the defects found are : MOP, Alignment shift, routingdefect, shorts, opens.

Then Sent to AQL

3 circuits in a lot are inspected thoroughly for the track width,hole- hole distance, hole track distance, track- trackdistance.

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Labelling, Packing andShipping

Lots passed in the AQL are sent to the packaging section.

Circuits are hot sealed, bar coded and labeled according to

customer specifications.

Then final shipment takes place.

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Thank You

Date post:	09-Apr-2018
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