Bore hole data loggers are required to operate at temperatures around 150◦C and to 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 (PCB's) within them. Pressure to reduce borehole size and increase logger functionality, demands smaller electronic packaging utilising surface mounted devices (SMD's), these have inherently smaller/weaker solder joints.
Wireline Technologies were engaged in a new product development programme and were concerned to ensure the highest reliability for the new 'SMD' PCB's. They consulted TWI through the Joining Forces* scheme and were advised on possible choices for solders and PCB materials/finishes. Wireline Technologies subsequently set up in-house trials to evaluate various materials, including those recommended by TWI.
Once sufficient testing was done to identify statistically reliable trends, TWI were asked to analyse samples of failed materials. This analysis was performed using XRD and SEM techniques and helped to confirm the nature and cause of the failures, thereby assisting Wireline Technologies choosing the most appropriate materials for their application.
* Joining Forces was a UK government sponsored programme which ran 1994-1999.