Smart coating-roadshow-feb-2015-wet-surface-treatment-vitry

Faculté Polytechnique

Electro and electroless plating

Wet surface treatment

[email protected]. Véronique Vitry

Université de Mons

Poss

ible

in li

qu

idp

has

e

Coatings Conversion

Diffusion treatment

Structural modification

Wet surface treatment?

Dr. V. Vitry | UMONS - metallurgie | 12/02/2015

Université de Mons

They represent an important part of the surface treatment industry : 25% of the surface treatment business (paint excluded)

4 main types: - Electroplating

- Electroless plating

- Conversion

- Sol-gel coatings

Liquid phase surface treatment in the industry


Université de Mons

Wet metallic coatings: general principles

Reduction

Concept : oxido-reduction process

Metal deposition

Me1 n++ ne-Me1

External currentsource

ne-

Electroplating

Metal oxidation

Me2Me2n+ + ne-

Displacement

Chemical agent oxidation

Red Ox + ne-

Electroless plating

Origin of the electrons


Université de Mons

Metallic coatings appear during the ‘Ancient History’ by mercury amalgamation

First electrochemical plating processes : pre-Columbian civilizations

Displacement of copper on iron used during the Middle Ages

Historical point of view of wet metalliccoatings


Université de Mons

First electrochemical plating process with external current source: 1805 by Luigi Brugnatelli, friend of Volta who plated gold on silver

Numerous developments during the 19th century:

Silver and gold: Elkington 1836, by displacement

Gold electroplating: 1840 – adhesive and cohesive coating

Nickel : first efficient process : 1843- Bottger(used after that for 70 years)

Electroforming patented in 1837 by Jacobi

Historical point of view of wet metalliccoatings


Université de Mons

Use of external batteries from1839 (Jacobi)

Alloy electroplating since 1842

Electroplating on non-metallic substrates in 1840 (Jacobi) after graphite coating

Electroless nickel deposition in 1844 (Wurtz), but not efficiently

Additives in electroplating baths from 1847, mainly by serendipitous discovery (partial dissolution of molds, fall of various substances in the bath,..…)

Mechanical agitation

Historical point of view of wet metallic coatings


Université de Mons

Large scale use from 1850: street furniture, tableware (Christofle)



Université de Mons

20th century:

‘Watts’ bath in 1916 allows quicker nickel electroplatingmix of nickel sulphate and chloride + boric acid

Development of chromium electroplating in the 20’s

Development of zinc electroplating in the 20’s (increase of automobile production)

Bright nickel is developed in 1934 : watts nickel modified with levelling and shining agents

1950’s : loss of interest of scientific sphere for the technology, deemed ‘mature’

1946: Brenner et Riddell rediscover electroless nickel plating

1949: Schlesinger discovers the borohydride ion

1954: first electroless nickel-boron plating

1978 - 1982: development of high P electroless nickel

1970’s: development of electroplating in the electronic industry



Université de Mons

Principle

The coating is formed on the cathode by the reduction of metallic ions by an external current source.

The metallic ions are generated by the progressive dissolution of the anode.

Amount of deposited metal:

𝑀 =𝜌𝐹 × 𝐼 × 𝑡 × 𝑀𝑀

𝑛 × 𝐹

Electroplating

e-e-

- +

Me2n+

Xn-

Me2

Me2Me1

cathode anode


Université de Mons

How to determine plating conditions?

Low potential

Hull cell with current density gradient

Electroplating


Université de Mons

How to determine plating conditions?

Use of polarisation curves

Electroplating


Good zone

Bad zone (unsufficient coverage)

Dendritic coating

Université de Mons

What do you put in a plating bath?

- Metallic salts Nickel: sulphate and chloride ; sulfamate: Ni (SO3NH2)2

Chrome (VI): Cr2O3

Chrome (III): sulphate or chloride (! Avoid formation of CrVI at the anode)

Gold: cyanide (Au(CN)2); sulphite (Au(SO3)2-3 ), thiosulphate (Au(S2O3)2

-3 )

Copper: sulphate

- Buffers:Boric, sulfuric acids, sodium hydroxide, potassium citrate and nitrate, sodium carbonate, …

- Additives Complexing agents

Brightening agents : heavy metals salts; organic compounds

Electroplating


Université de Mons

Problems due to complex shapes: Throwing power

Current density is influenced by local instabilities (diffusion) and edge effects

This helps!

Pulsed current

Additives

Electroless plating

Electroplating


Université de Mons

Pulsed current:Periodical modification of plating current to

increase coating quality

Effects of pulse plating:

Decrease of thickness variations

Decrease of edge effects

Plating in holes

Better crystallinity

Higher germination (possibility of nanostructured coatings)

Increase of selectivity

Electroplating


Université de Mons

Alloy electroplating

Possible if two metals are reduced simultaneously at a single potential

How to do this?

Similar redox potentials

Electroplating

ic

E(-)

i2

i1

Me1 Me1


Université de Mons



How to do this?

Dissimilar potentials but helpful overpotential

Electroplating


Université de Mons



How to do this?

Modifiying the concentrations (by the use of complexingagents)

Using tensioactive agents to delay the deposition of one metal

Electroplating


Université de Mons

Electroless plating


Concept:

• Deposition by aqueous reduction of the metallic ions by a chemical agent

• No external current source

• Catalytic process

• Suitable for conducting and isolating materials

• OK for hollow parts and blind holes

• Constant thickness

Electroless plating

• External current source

• Non catalytic process

• Suitable only for conducting materials

• Difficult for hollow parts

• Thickness may vary

Electroplating

Université de Mons

Electroless plating


Metal deposition

Me1n++ ne-

Me1

External current

ne-

Oxidation of a metal

Me2Me2n+ + ne-

Oxidation of a chemical reagent

Red Ox + ne-

Global reaction of electroless deposition

Men+ + Red Me + Ox

• Thermodynamics:

Université de Mons

Electroless plating


Kinetics:

catalytic metal

non catalytic

metalAnodic polarisation

Cathodic polarisation

Mixed potential theory

• Deposition occurs at mixed potential

• │Idep│= │Ired│ =│Iox│

Deposition rate

• Influenced by overpotential

Catalytic activity

• Of the substrate (early stages)

• Of the coating (later stages)

Université de Mons

Electroless plating


Bath chemistry

COMPONENTS ROLE

Metallic ions Source of metal to be deposited

Reducing agentSource of electrons + co-deposited metal

Complexing agent

Complexes the metallic ions to

• increase the metallic ions solubility

• increase the stability by avoiding precipitation

BUT decreases the deposition current

StabilizerRegulate deposition speed by blocking a part of the catalytic sites

pH adjuster Regulates pH

Université de Mons

Electroless plating


Metals that can be plated electrolessly

Oth

er

elec

tro

less

allo

ys

Can

be

co-d

epo

site

dw

ith

Co

or

Ni

Can

be

pla

ted

alo

neNi

Co

Cu

Cd

Pb

Sb

Bi

Ag

Au

Pt

Pd

Rh

Ru

Sn

In

P

B

V

Mo

W

Mn

Re

Fe

Zn

Tl

CuNi

CuCo

CuCd

CuAu

PdNiP

PdCoP

PdZnP

AuAg

AuSn

PbSn

AuIn

Université de Mons

Choosing a reducing agent

Redox potential for the reducing agent (including overpotential) < Redox potential for the metal

In the case of nickel:

Electroless plating


Université de Mons

Choosing a complexing agent

Choosing a stabilizer4 classes

S, Se, Te compounds

Oxides : AsO2-, IO3

-, MoO42-

Heavy metal ions: Sn2+; Pb2+; Tl2+,

Oganic acids (maleic, itaconic, ….)

Bath pH is important

Electroless plating

Metal Complexing agents

Ni, Co Acetate, propionate, succinate, hydroxyacetate, aminoacetate,ethylenediamine, malonate, pyrophosphate, malate, citrate, tartrate

Cu Tartrate, acide glycolique, triethyl amine, EDTA, cyanures

Au Cyanure, sulfite, ethanolamine, citrate, chlorure

Ag Cyanure, ammonium

Pd, Pt, Ru Citrate, succinate, acetate, ammonium, ethylenediamine


Université de Mons

Gold electroplating: conductivity and corrosion resistance - electronics

Silver electroplating : high electrical and thermal conductivity – low contact resistance – antibacterial activity

Copper electroplating: high electrical and thermal conductivity – good adhesion

Tin electroplating: corrosion resistance – solderability – non-toxic (food industry)

Chromium electroplating: wear and corrosion resistance - aesthetics

Zinc electroplating: sacrificial protection of steel

Precious metals electroplating: precision mechanics and electronics

Nickel electroplating: high resistance to atmospheric corrosion – magnetic –wear resistance – diffusion barrier – adhesion promoter

Electroless nickel : wear and corrosion resistance – electronics (hard drives)

Various wet metallic coatings and theirproperties

Multipurpose, efficient and relatively cheap


Université de Mons

Electroless nickel


Various electroless nickel grades and their properties

• NH2NH2

Pure Nickel

• NiP with NaH2PO2 : low, mid and high P from 2 to 13 wt.% P

• NiB with NaBH4 or DMAB : can containeither Pb or Tl

Binary alloys

• Ni-P-B

• Ni-X-P or Ni-X-B with X = co-depositedmetal

Ternary alloys

• Co-deposited particles

Composite coatings

• NiB > NiP

Hardness

• NiB > NiP

Wear resistance

• NiB < NiP

Corrosion resistance

Université de Mons

Electroless nickel


Constant thickness

Bright aspect

Columnar growth

Cauliflower-like

surface texture

Smooth coating

Solderability

Properties

Université de Mons

Electroless nickel


Good adhesion

Properties

Low P

Mid P

High P

NiB Tl

NiB-Pb

Université de Mons

Electroless nickel


Hard

Good wear resistance


Hardness, wear and corrosion

resistance improved by heat

treatment

Properties

LowP MidP HighP Ni-B-Tl Ni-B-Pb

TWI As-plated

average 16,29 24,3 19,37 35,59 23,2standard deviation

1,4 1,98 0,02 3,8 1,08

TWIHeat treated

average 10,17 15,525 11,265 19,69 8

standard deviation

0,48 1,515 0,565 3,21 0,29

Université de Mons

Electroless nickel


Hard

Good wear resistance


Hardess, wear and corrosion

resistance improved by heat

treatment

Properties

Université de Mons

Electroless nickel


Applications of electroless nickel

Aeronautics

Automobile

Food industries

Electronics (hard

drives substrates,

printed boards, ..)

Chemical and oil

industries

Polymer injection

Fire arms

Cutting tools

Université de Mons

Wet metallic coatings can solve a lot of technological problems because they are so many of them with very different properties

The bottom line is that Electroplating is a Solution in Search of a Problem. We just need to go out and FIND THE PROBLEMS!

— G. Dan Hutcheon

Closing word


Date post:	16-Jul-2015
Category:	Technology
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