Soldering Challenges Caused by Warpage of Large Integrated Circuits

Qu (Wisdom) Yanhong and Chris Nash
Indium Corporation
Suzhou, China

Ronald C. Lasky, Ph.D., P.E.
Indium Corporation and Dartmouth College
NH, USA

With the rapid deployment of 5G cellular networks, artificial intelligence, and increased internet traffic, the highly integrated design of server central processing unit (CPU) and graphics processing unit (GPU) chips that support these technologies have posed a series of challenges to the electronic assembly industry. Among them, problems such as the increase in integrated circuit (IC) package size, printed circuit board (PCB) high density interface (HDI) design, and thermal expansion coefficient mismatch between electronic components and PCBs, have become increasingly severe.

These challenges can lead to excessive IC component warpage during the manufacturing process, which can lead to excessive head-in-pillow (HiP) or bridging defects during soldering. This article will explore the challenges posed by warpage of large-size IC packages, typically in the ball grid array (BGA) format, in servers and propose corresponding solutions.

In order to meet the high-performance, high-density integration, and heat dissipation requirements of servers, BGA component size is getting larger and larger. To minimize warping of the BGA and mating receiving PWB, low-temperature tin-bismuth solders have been considered.

In our experiments, however, we found that BGAs exhibit minimum warpage at a reflow temperature of 200-220°C, not the lower temperature of about 180°C that tin-bismuth solders require. Therefore, the best process production window can be obtained by using a solder alloy with a melting point of 200°C and producing it under a peak reflow soldering curve of 220°C. The mixed alloy powder solder paste is such a solder. In addition, the mixed alloy powder solder paste has outstanding drop shock and thermal cycle performance, making it an ideal solder for large BGA components.