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February 2000

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Fri, 25 Feb 2000 10:37:33 -0800
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Hi Lou,

Solder ball are caused both for PTH and SMT assemblies. Show your boss page 210-214 in
'Failure Modes and Mechanisms in Electronics Packages' (http:// www.wkap.nl). There is a good summary of various factors that affect solder ball formation in Table 6.3  and a list of 6 articles on solder ball formation and studies.

Lou Hart wrote:

> Hi Technetters,
>
> (1)  Solder balls:  I feel a little sheepish to bring up a subject that has been discussed many times before, I'm sure, but let me get an opinion.  Our production manager thinks solder balls on assemblies come from holes in the boards (always FR4) that got wet during cleaning after surface mount reflow and were not dried before wave solder.  He says the vaporizing water blows solder around the board, leading to balls.  Searching through the TechNet archives, I found a posting from Bob Willis in Jan 96 where he says "(solder balls) are always present in some from.  The mask is the key issue, if they can not stick to the mask the problem is solved".  Can I get your comment(s).
>
> (2)  Assembly cleanliness:  How do people assess assembly cleanliness after manufacture?  We use several kinds of flux at different stages of operation here.  Surface mount uses water-based, rework and touchup use organic acid, wave solder uses RMA.  Our cleaner has a formulation supposed to get rid of RMA, but everything goes through it.  What cleanliness measures are or should be used after these cleanings?  I'm most concerned about the final assembly, but am curious about the intermediate stages as well.  The IPC test methods manual has some tests for ionic contamination (Omegameter and Ionograph seems most feasable for production) and some for rosin residue (that seem to require some expensive equipment and take a while).  Questions I'm asking myself are:  Should we be checking both ionic contamination and rosin residue?   And, of course, with what frequency(ies)?
>
> Thanks for any comments.
>
> Lou Hart
> Quality Assurance Manager
> Compunetix
> 412-858-6184
>
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--
____________________________________
Regards,
Pratap Singh

Tel./Fax: 512-255-6820,
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