Pin witness

A general specification requirement is that solder should not so completely surround a pin that it is impossible to see the lead protruding from the solder. This allows the inspector to verify that wetting has actually taken place. The concern is that, if a large amount of solder is applied at low temperature, the pin may be covered by the solder but separated from it by a layer of flux and not properly wetted at all, leading to a joint that is electrically and mechanically suspect. The requirement affects both the soldering conditions and the designed protrusion of the lead.

Bulbous solder fillets with no ‘pin witness’. How do you know whether these pins have been wetted, or are they just covered with solder?

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