A highly halogen-activated flux will allow intermetallics to form,
because the hydrogen halide gas formes at operating temperature will
react with the refractory nickel oxide, which is why SS is "stainless".
This will be worse with lead-free alloys. The ideal solution would be,
if possible, to find titanium hardware, which is not affected by
hydrohalides. Alternatively, use a water-soluble temporary mask, rather
than a latex one; much less messy and labour intensive!
Brian
Kane, Joseph E wrote:
> Because connector screws get Loctite, we use stainless steel temporary
> hardware on bottom sides of some of our motherboards, and screw heads and
> washers travel through the solder wave. With the switch from RMA to OA
> flux (Alpha 3355-HB), we find that solder now adheres to the hardware.
> Here are some of our options:
>
> 1. Use latex temporary solder mask on hardware. Of course, this will be
> messy and labor-intensive.
>
> 2. Find some 2-56 x 1/2" screws in a material that Sn63 won't stick to.
> Could they make a screw this small in nylon or diallyl pthalate?
>
> 3. Apply some kind of plating or Teflon coat. Of coarse, with buildup on
> the thread, they may not mate anymore.
>
> 4. What about a spray-on coating? Would it be worth trying an anti-seize
> like molybdenum disulfide?
>
> Joe Kane
> BAE SYSTEMS Controls
> Johnson City, NY
>
>
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