Question 1

What happens if the peak temperature is too high or too low?

Accepted Answer

If peak temperature is too low or time above liquidus (TAL) is too short, incomplete wetting causes cold solder joints, head-in-pillow defects, and opens. If peak temperature is too high, copper dissolution accelerates, flux chars (leaving residues), intermetallic compounds grow excessively, and heat-sensitive components may be damaged.

Question 2

How does a lead-free profile differ from a leaded (SnPb) profile?

Accepted Answer

Lead-free solder (SAC305, liquidus 217°C) requires a peak temperature of 235–250°C, roughly 25–30°C higher than SnPb (liquidus 183°C, peak 210–225°C). Lead-free profiles have tighter process windows and demand better thermal uniformity. Components must be rated to MSL (Moisture Sensitivity Level) for the higher peak temperature per J-STD-020.