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SMT electronics assembly manufacturing forum.


Solder sticking to Stainless Steel Fasteners

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#37110

Solder sticking to Stainless Steel Fasteners | 12 October, 2005

We are currently wave soldering connectors that are held in place by stainless steel screws. About 20% of these screws emerge from the process with varying quantities of solder attached to them. We have just had our solder bath checked and no impurity levels were found to be suspect. I am aware that there are different alloys used to make stainless steel screws and the potential is also high that the screw finish contains impurities that may allow the solder to adhere despite the screw being called stainless. Has anyone else ever come across this type of problem? Do we need to specify a special alloy of stainless fastener in order to alleviate this problem (or is there an alloy more solder resistant than the rest)? We are soldering with OA flux, Eutectic Sn63PB37 with a solder temp of 480F and a dwell of 3 seconds. Any help would be greatly appreciated.

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Slaine

#37240

Solder sticking to Stainless Steel Fasteners | 20 October, 2005

Hi could be relaited to the thermal mass of the screw/bolt. if there is no intermatalic formed and the solder just picks off id say this is likely. the hot wave hits the cold screw and cools the solder enought to leave some behind??

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#37254

Solder sticking to Stainless Steel Fasteners | 20 October, 2005

A highly activated flux will allow intermetallics to form, because the hydrogen halide gas that formes at operating temperature will react with the refractory nickel oxide. Refractory nickel oxide is what makes SS "stainless". This will be worse with lead-free alloys. Solutions are: * Find titanium hardware that is not affected by hydrohalides. * Use a water-soluble temporary mask. * Select a different flux.

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