Hi Carl -

Your descriptions suggest the following:

Compare your measured profile to the recommended profile from the paste
manufacturer -

Incomplete reflow suggest several possibilities, ie.:
    - too slow a preheat cycle may have expended flux activators prior to
reaching reflow temperature;

    - peak temperature or time at peak temperature insufficient;

The pinholes also suggest several possibilities:

    - organics on the surface of the bare board;

    - flux volatiles not fully expended at time of cool down.

If the problems are localized rather than widespread on the board, it would
suggest that there are some significant variations in thermal mass over this
design, probably as a result of circuit/ground plane density.

Let us know more and we'll try to help narrow the focus on the problem.

Regards - Kelly




-----Original Message-----
From: Carl Barnes <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Monday, October 02, 2000 6:12 PM
Subject: [TN] Soldering Question??


>        Technetters,
>
>Need some help from all the soldering experts out there. We have a group of
>boards that show evidence of poor solder quality throughout the board. To
>the novice eye, it looks like the solder paste did not reflow completely.
>There appears to be small balls of unreflowed solder and small pin holes in
>some of the joints. Most of the quality group thinks that the profile was
>not hot enough. However, when the engineering group came to examine the
>joints, they stated, "Why No, these joints were just the opposite, they
were
>liquidous too long!" Can I get some opinions on this? Any one out there
with
>examples of solder joints that reflect these two scenarios would be
>appreciated. Please send them directly to me. We are having these joints
>cross sectioned, once the pictures come in I will forward to anyone
>interested. Thanks in advance of any help anyone can give.
>
>Carl Barnes
>Production Process Analyst
>
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