Journal of SMT Article

New Developments In High-Temperature, High-Performance Lead-Free Solder Alloys

Author: Anton-Zoran Miric
Company: W. C. Heraeus GmbH
Date Published: 10/31/2010   Volume: 23-4

Abstract: A new Lead-free electronic solder alloy that addresses the challenges of applications requiring superior lead-free solder joint reliability on both epoxy- and ceramic-based substrates is now available in a variety of forms.

The high reliability & high operating temperature Lead-free alloy known commercially as InnoRel-Innolot is a Tin-Silver-Copper (SAC) metallurgical system with small amounts of Antimony, Bismuth and Nickel added to it. The additional elements harden the alloy and improve its creep strength. Developed by a working group of researchers that include industry suppliers, users and academic partners, this results in significantly improved reliability of solder joints at standard temperatures of 125°C (vs. SAC and SnPb) especially with ceramic chip components. Additionally, this alloy enables operating temperatures of up to 165°C, a substantial improvement over the traditional SAC alloys’ peak operating limits of 125°C.

The alloy represents an excellent solution for circuit assemblies that are located under the hood of automobiles or in other similarly harsh environments, but until recently its application has been limited to Surface Mount Technology only. When applied to ceramic substrates, there is no major benefit in reliability vs. SAC alloy; therefore its usage had been limited to epoxy-based circuit assemblies.

Recent advancements in alloy composition now make it possible to improve its reliability on ceramic substrates that are metalized with thick films or direct bonded copper. Broadening its applications even further, a novel wire drawing process that enables the production of flux-cored wire for manual and automated soldering has been developed and commercialized.

This paper reviews the composition, hardening mechanisms, and performance on the alloy. It then introduces the two innovations that now make it available also for hand soldering and hybrid assembly.

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