Quali Ty and Reliabili Ty Investi Gation of Pri Nted Circui T Board Micro-vias by X-ray Inspection

A continuous drive to shrink device packages and printed circuit board (PCB) design, so that higher, and better, functionality can be p rovided to the user in an ever smaller footprint, demands the increasing use o f micro -vias onboard. Micro-vi a diam eters o f 200 microns, 100 microns and below are now common. With such small features, the quality of thei r through-hole pl ating during manufacture and the implications of the l ead-free surface mount process and thermal cycling during p roduct li fe can severely affect production quality, yield and field failure rate with resulting costs to reputation and business. The use of high resolution, high magnification x-ray inspection, as part o f product quality control, allows a nondestructive test for investigation of micro-vi a quality and their on-going reliability. This paper will report on the results of x -ray examination o f micro -vias, before and aft er production processing, taken from the last four years o f lead-free assembly experi ence. Examples have been taken following p rocessing by convection reflow, vapour-phase reflow, wave-soldering and rework operations as well as after subjecting cert ain boards to an accelerated thermal cycling regime. Analysis of the defects produced during these procedures will be discuss ed together with suggested guidelines on how to improve inspection quality.