High-reliability, Low-temperature Solder Alloys Feature by Pritha Choudhury, Morgana Ribas, Raghu Raj Rangaraju, and Siuli Sarkar MACDERMID ALPHA ELECTRONICS SOLUTIONS
Increased digitalization and greater connectivity have been driving miniaturization and more complex and integrated designs in electronics. As the real estate on PCBs shrinks, so does the size of packages. However, the drive for finding design solutions for increased performance has continued to expand. The solder joint is an essential part of assemblies for electronic devices as it provides electrical, thermal, and mechanical connections. Therefore, soldering materials have been evolving to enable such a technological revolution. Restrictions in using lead in soldering materials in the early 2000s have propelled the electronics industry towards the widespread use of lead-free soldering materials. Since then, the requirement for solder alloys with higher thermal and mechanical reliability is the most important technology driver for designing 24
SMT007 MAGAZINE I MAY 2020
new soldering materials. Low-temperature solders (LTS) are currently being considered for a variety of assembly needs. They have the potential to increase long-term reliability by reducing thermal exposure, to reduce overall materials cost by using low-Tg PCBs and low-temperature compatible components and its carbon footprint. Using low-temperature solders has also been shown to lower energy consumption, to reduce dynamic warpage of BGA packages and PCBs, to increase assembly yields, and to lower or eliminate non-wetting open and head-on-pillow defects [1, 2]. Indeed, dynamic warpage is a serious concern for PoP bottom and PoP memory packages, as they can cause serious soldering defects, such as non-wet opens, solder bridging, headon-pillow, and non-contact opens [1, 3]. Extensive studies have shown that such warpage is highly dependent on the reflow temperature and can be drastically reduced to acceptable levels by keeping the soldering temperature below 200°C [1].
