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26 SMT Magazine • June 2015 Through-hole technology (THT) is prob- ably the oldest assembly technology in the field of PCB manufacturing. However, even in this modern age of surface-mounted technol- ogy (SMT), it still has its place. Even today, wired components are often assembled using wave soldering—in keeping with the tradition of times past. This has the disadvantage of re- quiring additional manufacturing equipment. It is therefore advisable to use reflow soldering for connectors and other wired components. To this end, through-hole components were devised for automatic assembly and for high thermal loads in the furnace, which led to the birth of the term, through-hole reflow (THR). With this technology, it is now possible to pro- cess components in through-hole technology within the SMT process. But how can these sol- der joints be reliably tested? What technology is needed in order to be able to assess the solder penetration, for example? by Andreas Türk Göpel elecTronic In-line Solder Penetration Testing with 3D X-ray Inspection Acceptance Criteria for THT/THR Solder joints Figure 1 is a schematic representation of a THT solder joint in cross-section. The solder wave flows from the solder source side to the solder target side (component side), due to cap- illary action. In so doing, it wets the connecting surface of the solder side, surrounds the pin and forms a solder meniscus on account of the pro- trusion of the pin on the solder side. Figure 1: Schematic representation of a ThT solder joint in cross-section. ideal soldering with 100% solder penetration. Feature