The idea of protecting vias is not new; it began over 20 years ago with the advent of dry-film soldermask (DFSM). In the days of screen-applied thermal soldermasks and through-hole technology, vias were always kept free of soldermask. With the advent of photoimageable DFSM, fabricators discovered, perhaps by accident, that if the film was exposed over the vias, they could be "tented" ― protected from the environment, chemistry, etc. This approach sealed vias without component leads that otherwise often did not fill with solder in assembly. Thus, electrical testing was possible without loss of vacuum or expensive touch-up to fill the empty holes. Also, this benefit came free with the primary soldermasking process.
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