SMT lead-free soldering, pay attention to lead-free. During reflow soldering, the electrolytic capacitor (25V470UF) of the patch bulges;

Two possibilities: 1. The reflux temperature is too high. Generally, the lead-free peak welding temperature is 240 degrees 5 degrees (measured temperature).

The time above 2 17 degrees shall be controlled at 30-90S.

2. There is something wrong with the component. Not conforming to the reflow soldering process.

From these two aspects, I have encountered this phenomenon before, because the board is behind the furnace, which leads to the aluminum electrolysis bulge in the high temperature area.