Bore hole data loggers are required to operate at temperatures around 150◦C and withstand storage at -40◦C with high levels of shock/vibration loading. These conditions place considerable demands on the solder joints of the monitoring/signal processing printed circuit boards (PCBs) within them. Pressure to reduce borehole size and increase logger functionality demands smaller electronic packaging using surface mounted devices (SMDs); these have inherently smaller/weaker solder joints.
Wireline Technologies Ltd was engaged in a new product development programme and was concerned to ensure the highest reliability for the new SMD PCBs. A Product & Process Review followed by a Feasibility Study was undertaken by TWI through the UK government sponsored Joining Forces programme. The company were advised on possible choices for solders and PCB materials/finishes and subsequently set up in-house trials to evaluate various materials, including those recommended by TWI.
Once sufficient testing had been done to identify statistically reliable trends, TWI was asked to analyse samples of failed materials. This analysis was performed using x-ray diffraction and scanning electron microscopy and helped to confirm the nature and cause of the failures, thereby assisting Wireline Technologies to choose the most appropriate materials for their applications.