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24 SMT007 MAGAZINE I MAY 2020 Feature by Pritha Choudhury, Morgana Ribas, Raghu Raj Rangaraju, and Siuli Sarkar MACDERMID ALPHA ELECTRONICS SOLUTIONS Increased digitalization and greater connec- tivity have been driving miniaturization and more complex and integrated designs in elec- tronics. As the real estate on PCBs shrinks, so does the size of packages. However, the drive for finding design solutions for increased per- formance has continued to expand. The solder joint is an essential part of assemblies for elec- tronic devices as it provides electrical, thermal, and mechanical connections. Therefore, sol- dering materials have been evolving to enable such a technological revolution. Restrictions in using lead in soldering mate- rials in the early 2000s have propelled the elec- tronics 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 new soldering materials. Low-temperature sol- ders (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 over- all 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 assem- bly yields, and to lower or eliminate non-wet- ting 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, head- on-pillow, and non-contact opens [1, 3] . Exten- sive 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] . High-reliability, Low-temperature Solder Alloys

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