Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

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Anti-solder finishing

Carol Zhang

#7582

Anti-solder finishing | 6 February, 2000

I have a board which contains brass spacers. The spacers will pass through the wave during soldering. I found a silicon-rubber cap that can prevent solder climbing up into the spacer. However, the cap influence the wave flow and reduce the solderability of joints that near the cap. Is there any kind of anti-soldering finish that can be provided on the brass spacers, so, it is not necessary to use the cap. Thank you.

Carol

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#7583

Re: Anti-solder finishing | 7 February, 2000

Spacerwoman: Carol is a professional spacer problem fighter (we think). When people have problems with spacers, they call on SPACERWOMAN!!!!! Here she is to save the day � ;-)

Selecting a spacer made of brass is a good choice for many applications, but not for yours, because: � Brass is solderable, as you mentioned, so you get a variable height spacer. Urk!!! � Over time, brass will poison your solder bath, Klein Wassink (ISBN 0-901150-24-X). Doubling your reasons to stay on top of your solder pot analysis, because: - Too much copper causes solder bridging, 4.4.3. - Zinc causes excessive dross in wave solder baths, 4.4.5. � Protecting the brass spacers from solder requires non-value added labor.

Solutions are: � Buying spacers with nickel plating. Nickel oxidizes quickly, making it virtually unsolderable. � Buying spacers with 40um PTFE coating. Same ideal, as they say down South. � Buying spacers made of stainless steel, titanium, or something like that. I�d opt for the SS before the titanium or something like that. Whatever something like that is � ;-) � Buying spacers made of a hi-temperature plastic or fiber. � Adding the brass or other material spacers after wave soldering.

� but how can we attach these spacers to the board??? Call on SPACERWOMAN!!!!!

OK, OK, enough of the Spacerwoman stuff, I'll stop. A temporary fix that may be an improvement over using the rubber boots for Carol is: Covering the spacers with temporary solder stop, either washable or peelable. Neither is a good choice she runs no-clean. � Washable is unwashable, duh!! � Many, peelables are highly ionic and SIR killers and she can�t wash that either. Bummer!!!

My2�

Dave F

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