Predrying connectors prior to solder processes

When parts have too much moisture for SMT assembly without blistering, they can be dried prior to the SMT operation.

Drying of both pre-packing and pre-soldering parts is influenced by the relationship between moisture absorption and desorption. The moisture absorption rate is a function of part thickness, time, temperature, and relative humidity. Moisture desorption has the same parameters:
• Thin parts release their moisture faster than thick parts
• Moisture release is faster at higher temperatures
The higher preheat temperatures in typical lead-free solder profiles may provide more safety from blistering for thinner-walled parts than current tin/lead solder profiles, as the higher temperature will give a faster moisture desorption rate.

Moisture desorption tests

Tests on fully moisture saturated bars (moisture content of about 6%) of different thickness and using an IPC/JEDEC J-STD-020B lead-free solder profile of a 250°C peak temperature after drying at 120°C show that:
• parts with a maximum wall thickness of 1mm do not exhibit blistering after 2 hours at 120°C
• parts with a maximum wall thickness of 2mm are dried below blister onset moisture levels after 6 hours at 120°C
• Parts with a maximum wall thickness ≥3mm will take longer than 6 hours to dry sufficiently

Pre-solder drying times