Thermal effects on PCB's with connectors during solder attachment

Abstract

With the increasing complexity of electronic assemblies, a greater number of interconnections between electronic cards are needed. In many cases, longer and higher density connectors are being used to supply this increased number of interconnections. As such the match of the thermal expansion of the printed circuit board (PCB) to that of the connectors is becoming more critical for proper assembly. This paper explores the dimensional changes to the card assemblies as these pin-in-hole (PIH) connectors and other large components are soldered to the card during the wave solder process. The relevant characteristics of both the connectors and the FR4 material are evaluated and the contributions of the significant processing variables are discussed. This includes the dimensional changes to the PCB and the connectors around the glass transition temperature and the melting temperature of the eutectic solder used in the wave solder machine. The distortion due to asymmetrical board lay-up is discussed independently. These effects are then related to the overall flatness of the card assembly after completion of the process. In conclusion there are some recommendations to minimize these effects for specific applications.