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PLATING ON PLASTICS

Roland P Brassard

Bayer Corporation

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Topics of Discussion

Morphology of ABS and ABS / PC

Preplate Technology

Electroplate Technology

Straight thru vs Bulk processing

Principles of Electrochemistry

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Transmission Electron

Microscopy

Polymer structure of ABS

Polymer structure of ABS /PC

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Scanning Electron Microscopy

Etch Characteristics of ABS

Etch Characteristics of ABS / PC

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Plating Processes

Straight Through

Bulk Process

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Straight Through Process

Rack Plating

Continuous Process from Start to Finish

Minimum of Handling

Less time consuming

Most common method of Plating on Plastics Storage reduced

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Bulk Processing

Labor Intensive

Storage facilities needed

Handling difficulties

Basket preplate

Rack electroplate Accessory solutions

Normally 2 platers

Single type of Application

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Preplate Technology

Cleaners

Pre-etchant

Etchant

Neutralizer

Pre-Activator Activator

Accelerator

Electroless Copper or Nickel

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Preplate Cleaners

Can be Alkaline or Acidic

Used as degreasers to remove smudges,

oils,and fingerprints from the surface

may contain surfactants

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Preplate Pre-Etchants for ABS

Usually Acidic in Nature

Normally a dilute CRO3 / H2SO4 to

initiate surface reactions and break the

surface tension of the Plastic

150-155 F 2 - 4 Minutes

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Pre-Etchants for PC

Can be either acidic or Alkaline

Usually an Organic solvent mixture

Necessary to pre swell the Polycarbonate

to allow better attack of the Chromic /

Sulfuric etchant on the rubber phase andcreate a good pore structure

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Preplate Etchant

Chromic Acid /Sulfuric Acid

150 -160 F

8-10 minutes

55-70 ounces/gallon Chromic Acid

15-17 % by volume Sulfuric Acid

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Preplate Neutralizer

Reduces any residual Hexavalent

Chromium trapped in the pores.

Prepares the surface for Activation

of the Catalyst Hydrochloric (Muriatic) based

Room Temperature to 110 F

2-4 minutes

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Preplate Activation or Catalysis

Seeds the surface pore structure

with a colloidal hydrosol of ionic

Palladium surrounded with a Tin

shell.

Part absorbtion of the catalyst resultsin a color change.

SKIP PLATE can be detected here.

RT to 105F 2-6 minutes

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Preplate Acceleration

Normally an acidic solution or a

Borohydryde which is used to remove

a section of the TIN shell and expose

the PALLADIUM particle to the surface

Desensitizes the racks to prevent Plating

of the vinyl coatings

125 F 1-2 minutes

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Preplate - Electroless Copper

A Chemical Reduction Process

Metallic Salt is reduced to form a

film across the entire application

giving enough electrical conductivity

to allow an electrical current to beapplied for subsequent metallic layering

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Preplate - Electroless Copper

2 HCHO + 4 OH- > 2 HCOO- + 2 H20 +2H-

2 H - + CU ++ > CU + H 2

Copper Chloride,Formaldehyde,SodiumHydroxide, Chelators

100 - 110 F 8-10 minutes

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Preplate -Electroless Nickel

Same principles as Electroless Copper

Alkaline Solution

reducing agent is Sodium Hypophosphite

Room Temperature to 90 F

6-10 minutes

very stable solution

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Electroplate Technology

Copper Strike

Acid Copper

Semi- Bright Nickel

Bright Nickel

Particulate Nickel

Decorative Chromium

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Electroplating Cycle

Interior Finish

Copper strike

Acid Copper

Bright Nickel

Decorative Chrome

Exterior Finish

Copper Strike

Acid Copper

Semi Bright Nickel

Bright Nickel Particulate Nickel

Decorative Chrome

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Copper or Nickel Strike

First Electrolytic Coating

Low Current Amperage

Coating Buildup as lattice work is forming

Copper Sulfate + Sulfuric Acid + Water

with or without Brighteners

80 F 3-5 minutes

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Electroplate -Bright Acid Copper

Thickest Single Coating 0.7-0.8 mils

Very Ductile Coating

Ability to Flex under temperature change

during Thermocycling

Excellent leveling

Copper Sulfate + Sulfuric Acid + Water

Brightener System

80 F 22-45 minutes

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Electroplate-Semi Bright Nickel

Second Thickest Coating 0.5 mils

more ductile than bright nickel

protects the underlying Copper from

oxidation

Nickel Sulfate,Nickel Chloride,Water

Boric Acid,Brightener system

130 F 15-30 minutes

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Electroplate - Bright Nickel

Coating Thickness of 0.3 mils

Gives Bright Mirror Like Finish

Highly Corrosive due to the Brightener

system (highly sulfonated)

Not very ductile

Same components as Semi Bright Nickel

concentrations different as are brighteners

130 F 10-20 minutes

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Electroplate - Particulate Nickel

Required Coating for Automotive and

Plumbing Applications for Corrosion

Protection

Coating Thickness of 0.1 mil

130 F 3-5 minutes

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Electroplate - Decorative Chrome

Final Coating in the Electroplating Process

Thinnest Layer 0.01 mils

Corrosion resistant

Hardness

Not ductile

Hexavalent or Trivalent Chrome

High Currents needed

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Electroplate-Decorative Chrome

Cathodic Reactions

CR2O7= +14 H+ +12 (e) > 2CRo + 7 H2O

Side Reactions

2 H+ 2 (e) > H2

CR2O7= + 14 H ++6(e) > 2CR++++7H20

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Service Requirements

Adhesion of the Metal Plate to Substrate

Appearance / type of finish required

Thermocycle

CASS test

Canadian Standards

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Racking Techniques

Enough contacts located in inconsequential

areas are necessary to distribute the

electrical current evenly

Design of the application will warrant

whether auxillary anodes are necessary

for proper coverage

Factors influencing Plate

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Factors influencing Plate

Distribution

Geometry of Application being Plated

Location of the part in reference to

1.anodes

2.adjacent parts

3.tank walls

4.Plating Solution Characteristics

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Auxilliary Anodes

Used promarily to give a bright

mirror like finish to areas normally

not capable of due to design

Increases plate distribution to these

areas

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Shields

Used to limit the current distribution

at high current areas: primarily edges