1. Inadequate air flow
a. Low air pressure
b. block or disrupted air knives
c. dwell time (under air pressure)
d. incorrect air setting (on or off too early/late)

2. Orientation of the panel in the HASL process.
3. Temperature of the solder
4. Contaminates in the solder

Of these, cause #1 is the most likely in my experience.

Franklin

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