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

Predrying connectors prior to solder processes

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