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Tin plating thickness for lead frame through-hole soldering

September 12, 2011

I need to solder two leads of a thermistor (tin plated dumet wire) onto two lead frames, the edge of which are molded in the plastic housing but it does have access from both top and bottom for soldering It seems to be a common situation but so far I haven't found any guideline for type and thickness of plating on lead frames online. I could only found info on PCB through hole plating.

The lead frame is made of copper alloy, 0.64 mm thick, about 6.5 x 5.0 mm in size each with the through hole in the middle. I am thinking of use nickel base plating and tin plating on top for soldering. I wonder if someone can give me some advice on what thickness of tin I need to form a good solder joint?

Thanks!

Li Yuan
Mechanical Engineer - Sunnyvale, California

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September 15, 2011

Hi Li Yuan,

I guess your Cu alloy is either C7025 or A194. Both can be directly tin plated for soldering. Process as below:

Mold deflash (electrolytic or chemical deflash to remove mold flash on leads) ---> rinses ---> descaler (remove residue and micro roughen Cu alloy) ---> rinses ---> ~10% MSA predip ---> pure tin plating (MSA base, target ~5-10 microns tin deposit) ---> rinses ---> antitarnish ---> rinses ---> dry

Regards,
David

David Shiu
- Singapore

You are right David I am using C7025. 5-10 micron seems a lot of tin. The process you have is good for hand soldering with wire, correct?

Li Yuan
- Sunnyvale
September 19, 2011