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Developing a New Lead-Free Alloy



Developing a New Lead-Free Alloy
This paper discusses the process for development of a new lead-free alloy for high reliability, high temperature applications.
Materials Tech

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Authored By:


Hector Steen, Ph.D., Brian Toleno, Ph.D.
Henkel Corporation

Transcript


Though the electronics industry is nearing the three year anniversary marking the ban of lead from electronics products, several challenges still remain with existing lead-free materials for certain applications.

The commonly used and accepted tin-silver-copper alloy, also known as SAC alloy, has proven to be a suitable material for the production of many devices, but for those applications that require extremely high reliability, current SAC materials are less than ideal.

In particular, devices that will find end use in automotive, military and aerospace products require a lead-free material that can withstand higher temperature operation life, offer vibration resistance not commonly associated with traditional SAC alloys and deliver high temperature thermal cycling reliability levels beyond those available with current commercialized SAC materials.

This paper discusses development of a new lead free alloy for high reliability, high temperature applications.

Summary


Though the electronics industry is nearing the 3-year anniversary marking the ban of lead from electronics products, several challenges still remain with existing lead-free materials for certain applications. The commonly used and accepted SnAgCu (tin-silver-copper, also known as SAC) alloy has proven to be a suitable material for the production of many devices but, for those applications that require extremely high reliability, current SAC materials are less than ideal.

In particular, devices that will find end use in automotive and military/aerospace products require a lead-free material that can withstand the higher temperatures operation life (e.g. automotive under-the-hood conditions), offer vibration resistance not commonly associated with traditional SAC alloys and deliver high temperature (> 125°C) thermal cycling reliability levels beyond those available with current commercialized SAC materials.

Conclusions


The cooperative efforts of industry and academia have resulted in the successful development of a high operating temperature, lead-free alloy that reflows at the same temperatures as conventional SAC alloys and will enable increased reliability for certain applications, including automotive and defense. Results from testing of the new Innolot alloy show improved reliability in -40°C to +150°C thermal cycling versus that of SAC387. In addition, the new alloy offers comparable vibration resistance to that of SAC387, as proven in vibration testing after 500 thermal cycles, and the drop test performance of Innolot is comparable to that of SAC387.

It should be noted that, because the new alloy contains bismuth, manufacturers employing materials based on this new alloy must ensure that there is no lead on the components or boards. Lead-terminated components or HASL (hot air solder leveled) finished boards used in combination with the Innolot alloy will result in a low melting (98°C) eutectic, which means that joints will fail when exposed to temperatures above about 98°C. There must be no lead in the supply chain when using materials based on this alloy.

This new alloy is a very promising development for the electronics industry, as continued experience with lead-free materials enables improvements and alterations to meet the emerging requirements of various applications. With this new alloy, just as with other alloys, the base alloy is only part of the equation. Only patent holders will have access to the alloy, and optimizing solder paste materials with this alloy for maximum performance will also require flux chemistry expertise and formulation know-how. Partnering with the right supplier - one that can not only deliver a robust material but can also provide in-depth technical support -- will be essential to long-term success

Initially Published in the IPC Proceedings

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