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Trouble in Your Tank: PTH Voids: Getting to the Root Cause, Part 2

Introduction

While there are many causes for PTH voids, one should also consider poor drilling practices, multilayer lamination issues and the fact that higher performance resin materials are more difficult to desmear, all of which can lead to voids.

In Part 1 of this series, I approached the subject of PTH voids at the root cause as attributable to the difficulty of desmearing the more chemically resistant, high-performance laminate materials. In addition to the greater chemical resistance, these materials also present challenges with respect to drill debris that can lodge in the hole wall, and multilayer lamination challenges.

Debris

Debris remaining in the hole may become loosened later in the fabrication process, leading to a void within the via. Debris is typically caused by poor evacuation of drill chip particles. The vacuum on the drill machine is designed to remove debris from the through holes. Obviously, if the vacuum is insufficient, it is not uncommon for debris to remain. Proper selection of drilling feeds and speeds, drill retraction rates and sufficient vacuum will ensure reasonably clean vias.

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Editor's Note: This article originally appeared in the July 2013 issue of The PCB Magazine.