How voids form
Flux volatiles form bubbles; in conventional reflow soldering, internal pressure prevents the solder from filling them.
industry
IPC-A-610: void rate ≤25% for leaded processes; up to ≤30% for lead-free;
Defense / semiconductor: single void rate ≤1%, overall ≤5% (e.g. IGBT modules).
Failure cases
At 20% void rate, MOSFET thermal resistance rises 6.53% and surface temperature +5.2℃;
At 79% void rate, device thermal resistance jumps 27.18%, risking rupture.
