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Solder Skips
Unsoldered surface mount joints are referred to solder skips where the termination may not have any solder. It is normally caused by incorrect chip wave height or gassing of the flux on the underside of the board. The fault can be caused, as in this case, by slow wetting of the tin/lead coating. The example shows very thin tin/lead covering the surface of the pad. This will cause poor wetting of the pads and may be a random fault.