X-ray imaging in pin-in-paste technology

Abstract

Today, pin-in-paste technology is used extensively. With the help of pin-in-paste, through-hole devices can be soldered using a standard surface mount technology (SMT) process and hereby a reduction in wave soldering is possible. This can result in cost savings and a decrease in production cycle time. To ensure successful pin-in-paste soldering the following steps must be taken: solder paste volume calculations for through-hole components; stencil aperture design for the pin-in-paste application; solder paste deposition through stencil printing, application of solder volume increasing techniques after printing; reflow profile optimization; inspections using special methods for each individual process; final tests. The paste is printed into the through-holes. For high quality pin-in-paste solder joints a sufficient volume of paste is a fundamental requirement. Nevertheless, after printing the through-hole-filling is usually unknown. In this paper a new method is described how to accurately determine the volume of solder alloy in solder paste that is present in the through-hole, using X-ray measurements, image processing and calculations. In addition, a method is suggested to determine the measuring characteristics and gray-scale linearity of the X-ray machine.