Alternates equal to Zinc Chromate finish, for improved electrical conductance

Letter 3617

Alternates equal to Zinc Chromate finish, for improved electrical conductance.

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I am the Mechanical engineering Supervisor for a Telecommunications Company, R & D new product development. Presently we plate our steel units with Zinc Chromate finish and would be interested in alternate plating/coating materials. We are seeing EMI shielding problems with the Zinc Chromate finish, i.e., poor electrical conductance from mating parts. Is there another process that can be used to improve the conductance, optaining optimum corrosion protection, and cost savings?

Alan Wardlow
Petaluma, CA

First of two simultaneous responses--

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Zinc with a clear chromate would have better conductivity than a yellow chromate and would cost the same but have less corrosion resistance.

One of the zinc alloys such as Zn-Ni or Zn-Co will have much better corrosion resistance, should have a tiny bit better better conductivity if you use a thin chromate, will cost more and will not be as cosmetically apealling.

Electroless nickel has superior corrosion resistance and conductivity but costs considerably more.

James Watts
- Navarre, Florida

Secondof two simultaneous responses--

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Hi Alan ,
To be quite frank you are using the cheapest finish for your purposes . It has been shown many times by the motor companies that there is no resistivity to worry about from a Yellow chromate conversion coating over Zinc . The alternatives are all more expensive , they include , Electrolytic Nickel plating at 2 to 3 times the cost of Zinc p[late , and "Eletroless nickel" at 5 times the cost of Electroplated Nickel . If you want more advice I will be in California from 25 October 1999 thru early November and can be contacted at Solin Products in Southern california ( Orange County 714 area code ) and I would be only too pleased to come see you and sort out the problems you have .

best regards

John Tenison - Woods
- Victoria Australia

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Alan, Tin/Zinc plating process offers excellent solderability and I would believe better conductance than zinc/yellow.

Joe Pons
metal finishing shop - Greenville SC

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I believe tin plating is another option. Why is it not mentioned. What are the relative costs and relative merits.

Joe Stoddard
- San Jose, California

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You make a good point, Mr. Stoddard. Tin is a common and good choice for electronics in many cases.

While tin plating is more expensive than zinc plating, it is nearly impossible to quantify the cost difference in the abstract because labor is often the largest part of the cost of plating, and for a small volume of small parts the cost differential could be insignificant whereas for a large volume of large parts the tin could cost double what the zinc costs and maybe more.

Zinc plating offers sacrificial cathodic protection whereas tin does not; this could be important depending on exposure conditions.

Ted Mooney, P.E.
finishing.com
Brick, New Jersey

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