Low-Temperature Solders: Niche No More?


It surprises many people that the foundation metal of almost all solder alloys is tin. Alloy elements such as lead, silver, copper, indium, etc., are extremely important, as they lower the solder melting temperature below tin’s relatively high 232°C and often improve wetting and other process or performance properties.

Figure 1. Bismuth metal. (Source: Indium)

As an example, tin-bismuth near-eutectic solders have a melting range around 140°C with a processing temperature of about 170°C, putting tin-bismuth solders 50°C or so below most common lead-free solders such as SAC 305. A while ago, I posted on tin-bismuth solders, asking if their time had come. This post generated follow-on questions that were answered in a second post.

iNEMI predicts that low-temperature solders, such as these tin-bismuth solders, may become main stream as soon as 2017. In light of this situation, my colleague and friend, Dr. Ning-Cheng Lee, is presenting a workshop on “Properties and Applications of Low Temperature Solders” at SMTAI on Sept. 29, from 8:30-12 noon in room 54.

The course summary is: Since the dawn of the electronic industry, the soldering process has encompassed mainly component manufacturing and printed circuit board assembly, with a hierarchic solder melting range. Components are made using solder alloys with melting temperatures around 300°C, which will not melt in the subsequent PCB assembly process, where the solders typically melt around 200°C. Low-temperature solders, with melting temperatures less than 170°C, are currently used mainly for niche applications. However, the iNEMI roadmap predicts low-temperature soldering to become a mainstream processes by 2017. Low-temperature soldering is greatly desired for assemblies such as heat-sensitive devices, systems with more hierarchic levels, parts with significant differences in their coefficients of thermal expansion, components exhibiting severe thermal warpage, or products with highly miniaturized design. This course will cover several varieties of low-temperature solders with an emphasis on lead-free alloys, their physical, mechanical, and soldering properties, and the applications involved with those alloys.

And the topics covered will be:

· Design of low-temperature solder alloys.

· Indium-bearing solder systems and their properties.

· Bismuth-bearing solder systems and their properties.

· Recent development in bismuth-bearing low-temperature solder alloys.

· Mechanisms of reliability enhancement of new bismuth-bearing solder alloys.

· Applications of low-temperature solders.

Be sure to add this workshop to your list of things to do at SMTAI.


Dr. Ron