Cleaning Processes For HIC's with Solder Paste

The use of solder paste for hybrid integrated circuit (HIC) assembly is increasing. However the full potential of solder paste has not yet been realized, partly because the fluxing systems may be very different from paste to paste. Therefore choosing the proper cleaning treatment is not trivial. In addition to removing any soldering flux present, the cleaning treatment must also effectively remove any solder spheres formed during reflow. Our work to identify the most effective combinations of cleaning treatments and solder pastes is described. The effects of paste reflow atmosphere on ease of cleaning were investigated. Cleaning techniques were assessed first visually and then by ionic contamination measurements. Those paste/cleaning combinations that seemed most promising were evaluated for accelerated aging performance. It was found that 1) conventional detergent cleaning (with sparging agitation) was more effective for removing solder balls from samples than a solvent degrease or immersion in boiling solvent. 2) The use of ultrasonic agitation resulted in the elimination of isolated solder spheres after reflow. 3) Detergentcleaned samples exhibited slightly lower leakage currents than solventcleaned samples, as well as longer median lives in accelerated aging studies. In addition, specific cleaning techniques were developed for use with the following solder pastes: Alpha 376 RMA, Cermalloy SC3201, DuPont Formon 4684, Fry RMA 96.5/3.5, JMI WA102, JMI SA102, and JMI WC100.