Greetings All,

I have a PTH TK type resistor component that is formed to fit an SMT 
geometry land pattern. The component is Pb Free component plated using 
Matte Tin over Nickel Flash. Once the component is soldered it exhibits non-
wetting/ poor wetting characteristics thus causing us to rework until we have 
achieved acceptable results. Of course this is not what I would like to see 
occur, but unfortunately at this time it is the process. The installation process 
is as follows:

- Part is formed using a lead forming tool
- Is tinned using 25% RMA for 3 seconds and let to dry (somewhat); then 
soldered (SnPb tin/ lead alloy) for 3-4 seconds in a 600F bath
- It is soldered (SnPb tin/ lead alloy) to the cca using a 6ooF solder iron tip for 
2-3 seconds
- END…

Apparently this has been an issue for years, but just recently was brought up 
to our Engineering department. We tin the component to allow for improved 
wetting characteristics, but this does not provide much improvement. I have 
done some investigation on the internet looking for reports and tests  
performed soldering Matte Tin over Nickel using standard Tin/ Lead alloy, but 
have found very little information regarding this. The component manufacture 
states our process as described to them 'should work without issue, but this is 
not the case.

So my questions are what are the issues related to soldering matte tin over 
nickel flash with tin/ lead alloy? What hand soldering parameters are 
considered optimal/ ideal with a low-mass matte tin plated component 
considering the information provided? Is it possible to get very similar results 
using this combination of metallurgies versus using tin/ lead plating and solder 
materials?

Any help would be appreciated.

Thank You,

Chris

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