Defect of the Month
It’s Reliable, But Didn’t Fill the Hole
Is the board preheat process optimized?
THIS MONTH WE look at incomplete fill of plated through-holes. During any soldering operation a balance of flux and solder/paste chemistry and soldering temperatures creates good and reliable joints. In FIGURE 1 the solder has not filled the hole completely but still exceeds the requirements of IPC-A-610, class 2 of 50%; measured, it may be 75% filled.
Possible reasons for solder not filling the hole in wave or selective soldering is the amount of flux or heat, limiting good penetration and wetting. More likely, however, board preheat is inadequate, causing solder to solidify early.

In the case of manual soldering, the temperature and dwell time of the soldering iron need to be considered. With a good quality circuit board, a joint like this is not very likely to fail.

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Incomplete hole fill close up
Figure 1. Incomplete hole fill.
Bob Willis Caricature
Bob Willis
is a process engineering consultant; His column appears monthly.