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Silicon contamination in solder joint

blnorman

#24603

Silicon contamination in solder joint | 27 May, 2003

Is anyone aware of any reports, studies, articles on the subject of silicon contamination in SnPb solder joints. We are evaluating repair of conformally coated (silicone) boards. The fear is that we will never totally remove the silicone and once it makes it's way into the solder joint there will be detrimental effects. Our repair folks say the silicone floats to the surface of a repaired joint so it won't be in the joint. Any input?

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#24604

Silicon contamination in solder joint | 27 May, 2003

Hi Bill

You said, "silicon". We assume by your discussion that you ment to say, "silicone".

For background on silicone and soldering, check with Dow Corning [517-496-6000]. They make a OS2 [VOC-free] silicone stripper and should be able to give you background.

It's true that you'll probably never be able to completely remove the silicone, but our concern about silicone is different from the one than the one that you indicate. We believe that silicone affects ability of: * Solder connection to wet. [So, initially we're talking rework and repair activities at your plant.] * Mechanical contacts to make contact.

So, we don't see it as an agent that changes the properties of a properly formed solder connection. We see it as a coating. Your repair folks' "floating" analogy is apt. It's kinda like a coating of oil.

Obviously, "oil" is not a correct analogy from a technical stand-point, but it's not far off-base from a practicle point of view. Your rework troops could get that stuff all over the place, because they'll have the stuff on their hands. Decontamination could be a horror show. You probably need to be careful in recycling packaging materials.

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blnorman

#24615

Silicon contamination in solder joint | 28 May, 2003

Yes we are using "silicones", but to find this contaminant we were looking for "silicon" the element by SEM/EDS.

We use Dow materials and my contact there is checking to see if they have any info.

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#24617

Silicon contamination in solder joint | 28 May, 2003

Wow, you're very correct. I guess we use silicone to calibrate our machine, as follows:

XPS spectral measurements of dimethyl silicone should include O(2s) at 25 eV, Si(2p) at 102 eV, Si(2s) at 153 eV, C(1s) at 285 eV, and O(1s) at 533 eV. The C(1s) sensitivity factor is assigned as 1.00, and the O(2s), Si(2p), Si(2s), and O(1s) sensitivity factors are calculated to give the proper stoichiometry: (C2SiO).

Interesting.

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