What type of via hole plugging is recommended?

FAQ about printed circuit boardsVIA HOLE

The preferred type of plugging for standard product (not including capped via hole) is IPC 4761 type VI filled and covered, with target being complete fill. The image below shows type VI with liquid soldermask coverage.

PCB type VI with liquid soldermask coverage

Single sided plugging is not recommended (including type II tented and covered) due to concerns over entrapment of chemistry or likelihood of solderballs being present with HASL finishes (LF and SnPb).