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July 1999

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Subject:
From:
Don Vischulis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 27 Jul 1999 17:42:20 -0500
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Poh:

We haven't heard from you in a long time.  Nice to see you back on Technet.

I am not aware of any specification governing solder ball formation or removal.
Material and process qualification is the key in minimizing solder ball formation
during wave soldering.  You may brush the assemblies at your own risk given the
possibility of generating static charges capable of damaging components.  Examine your
isolation requirements to determine the need to remove the solder balls.

In a former life, I worked at an OEM where solder ball formation was a concern.
Initially solder balls, on dry film solder mask, were removed with a bristle brush.  As
we became more educated, it was discovered that the brush could generate static charges
capable of damaging components.

As we worked with the problem, we found that LPI solder masks had fewer solder balls
than dry film masks.  In general matte masks had fewer solder balls than glossy masks.
We discovered that the mask/flux combination was a significant contributor to solder
ball formation.

Our working rules during this time period were that on low voltage circuits solder ball
diameters had to be less than the space between circuits to be acceptable.  The
reasoning was that a solder ball half of the minimum space had little chance of
contributing to a short if it became loose.  Qualification testing of solder masks was
also implemented during this period and only masks with solder ball formation below a
predetermined threshold were approved for use in production.

The answer is longer than the question, but I hope it helps.

Regards,
Don Vischulis
[log in to unmask]

Poh Kong Hui wrote:

> Hi Technetters,
>
> I have a curious question to ask. Is there any specification state the
> amount of solder balls allowed on the bottom side or the side that
> undergo wave-soldering process.
>
> It is rather common to see solder balls formed in-between the leads
> of the connectors, or in-between the leads. However, is there any
> spec. to define the amount of balls allowable on the board.
>
> There are people used to remove the solder balls by brushing away -
> how about the spec ???

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