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Wave Soldering Defects - Pad Contamination
The solder joints shown in Figure 1 are
satisfactory, but the solder resist on the pads has resulted in
a reduction in
the solder volume. The resist on the board is directly related
to the poor design rules used on this printed board. The correct
design rules for resist apertures are a 0.002-0.003" annulus
ring around the pads. This clearance is necessary to allow for
misalignment on the board during fabrication. The example in Figure
1 has been designed with resist apertures smaller than the
pad size.
It is worth pointing out that during wave soldering the resist
on the pad may affect the visual appearance of the joints but it
will not cause any problems of reliability. Using a reduced resist
aperture has been used in the past by the author to eliminate solder
shorting. Sometimes it is not always possible to eliminate problems
simply with changes to process parameters. As an alternative, when
all else fails and when the design engineer does not want to change
the design, use a glue dot. Ask your placement engineers to program
in an extra glue dot between the lead which always shorts, this
will be a simple fixit.
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| Figure 1: Here, the
resist apertures are smaller than the pad size. |
Wave Soldering Defects:
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Pad Contamination | | | | |
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