Are you vacuuming the right way?

This month we see a solder paste print deposit with what appears to be migration of paste particles away from the main pad. If this is just a one-off, a careful wipe with acotton bud would avoid an unnecessary wash-off and reprint. Ensure the PCB surface finish can withstand a wash-off process; some surface finishes don’t like it. Wash-off can affect wetting and final solderability.

A few reasons for this defect, each of which could be the root cause:

• Double printing or excess squeegee pressure
• Solder paste contamination on the bottom of the stencil from a previous print
• Misplaced or missing component
• Vacuum hold-down of PCBs during printing with exposed vias under BGAs.

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