Through-hole components have been in existence for decades, and the wave soldering process for through-hole components is considered mature. The wave soldering process is subject to more variability than Surface Mount Technology (SMT), and achieving acceptable through-hole-fill on large, thick and thermally challenging PCBs is a process challenge. This challenge is even greater with lead-free manufacturing process.

When changing to a lead-free process, consideration must be given to the characteristics of the lead-free solder alloy, available flux materials, process limits, thermal shock between preheat temperature and solder pot temperature, maximum component temperature limitation, existing equipment, etc. In addition lead-free wave soldering may raise other concerns on Plated Through-Hole (PTH) solder joints quality and reliability, such as voiding, and micro surface cracking. Microfocus X-ray inspection can be performed on the leads of through-hole components for hole-fill and voiding. X-ray images also give a good indication of the amount of cracking in empty PTH barrels.

X-ray images using oblique views as generated by YXLON microfocus systems can confirm the set up and process optimization. Using hole-fill analysis, in-process inspection can confirm the stability of the wave solder pot, the wave solder process and ultimately product quality.