SMT/PTH Solder Joint Reliability under Extreme Cold Thermal Cycles

摘要

This paper presents reliability of surface mount technology (SMT) packaging assemblies compared to decades old pin grid array (PGA) assembled with hand soldering that were subjected to extreme cold thermal cycles representative of high-reliability applications for deep-space missions. The advanced SMT packages included commercial-off-the-shelf (COTS) column grid array (CGA), leaded thin small outline (TSOP), leadless quad flat no-lead (QFN), and passive technologies. Tin-lead eutectic solders were used for soldering; they were either in paste form for assembling SMT packages or solid wire for hand soldering plated-through hole (PTH) for PGA ceramic packages. It is a general perception that the PTH technologies are an order of magnitude more robust in thermal cycle reliability than SMTs. However, this may not be true under extreme cold environmental conditions. Design for reliability (DfR) may requires compromising the stand-off height of PGA assembly and the thickness of printed circuit board (PCB) to achieve the desired long-term reliability. This paper presents the key parameters affecting the reliability of SMT package assemblies including TSOP, QFN, CGA, and PGA assemblies as well as associated test results under standard and extreme cold harsh thermal shock/cycle conditions. The standard thermal cycle conditions for high-reliability applications included were in the range of (-55°C to 100°C) and (-55°C to 125°C) whereas extreme cold cycles were harsh (-135°C to 70°C) and (-120°C to 85°C), or milder (-110°C to 20°C). Test results presented include non-destructive optical/SEM and X-ray images and daisy-chain resistances as well as destructive failure analyses performed by X-sectioning. Finally, key findings for various packaging technologies under extreme cold thermal cycles are presented.