Reflow soldering carries a populated board through an oven with heating zones that follow a profile: preheat, a soak to even out temperatures and activate the flux, a peak above the solder's melting point and controlled cooling. For SAC305 lead-free solder the peak is typically about 235 to 250 degrees C, with 45 to 90 seconds above liquidus. Each board's profile is tuned with thermocouples, and a bad one causes tombstoning, voids, cold joints and damaged parts.
Profile the reflow with thermocouples on the big BGA and on the 0402s, the big part lags by 15 degrees.
Also heard as
- reflow soldering
Related terms
Solder paste
Mix of fine solder powder and flux printed onto pads to hold parts in place and form the joints in reflow.
Stencil
Thin laser-cut metal sheet used to print solder paste onto board pads before parts are placed.
Tombstoning
Defect where a small two-terminal chip stands up on one end during reflow, leaving the other end unsoldered.
Voiding
Gas pockets trapped inside solder joints, seen as light spots on X-ray, which weaken them and block heat.