A New Method for Non-Destructive Characterization of Through Holes in Printed Circuit Boards

Abstract

Abstract Plated through hole (PTH) quality, including plating roughness, is a critical factor in the manufacture of reliable printed circuit boards (PCBs). Currently, cross-sectioning is most commonly used to assess PTH roughness but sectioning is a destructive process and offers a limited view of the PTH. Therefore, a non-destructive casting method using a silicone elastomer was developed to evaluate PTH roughness. Castings were successfully created from PTHs with aspect ratios as high as 22:1 and the castings accurately replicated the microtopography of the plating. Laser scanning microscopy was used to quantitatively measure the surface roughness of the castings which was shown to correlate to current induced thermal cycling (CITC) coupon cycles to failure, a measurement of PTH reliability. Thus, the casting technique can be used to quickly assess PTH quality and its effect on reliability. In addition to plating roughness, it was demonstrated that the casting technique can be used to evaluate back drill quality, PTH diameter along the length of the barrel, as well as drill and desmear processes by casting non-plated through holes.