Joe: I would guess the higher activity level of the OA is causing the screw
heads to pick up the solder. We use an Alpha OA and don't seem to have this
problem on SS hardware. You might want to try a different SS alloy.

As far as masking with things like latex or tape the down side is that you
not only have to apply them you have to take them back off. Tape can also
come off or lift and is hard to conform to 3D surfaces. Latex is hard to
remove from objects like screw heads, it must be picked off.

I don't think nylon will hold up for repeated exposures. You can go exotic
on materials and/or coatings but they will be expensive.

 Since you are using an OA flux I assume you are water washing after
wavesolder. Why not use a water soluble temporary mask. It's cheap and easy
to use. You still need to apply it but there is no manual post removal step,
it comes off in the wash process. We have been using this type of approach
for many years with good success.


Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA


-----Original Message-----
From: Kane, Joseph E [mailto:[log in to unmask]]
Sent: Thursday, January 15, 2004 7:20 AM
To: [log in to unmask]
Subject: [TN] Solder Sticking To SS Screws


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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