Indium Corporation - Lead-free solder solutions

Since the enactment of the European Union's Restriction of Hazardous Substances (RoHS) law in July of 2006, medical devices have had an exemption because of the lack of long-term reliability data on alternative lead-free solders. With that exemption expiring in July 2014, and the market for hand-held and portable medical devices growing, the medical electronics market is facing an immediate need to find a solution. Dr. Ron Lasky of Indium Corporation talks about the issues involved in finding an alternative lead-free solder alloy.


MDD: What alloys are the best alternatives to lead-containing solders?

Dr. Lasky: Shortly after RoHS was enacted in July 2006, much of the industry settled on 96.5Sn/3.0Ag/0.5Cu (SAC305) as the lead-free alloy of choice. Solder joints manufactured with SAC305 provided excellent reliability in thermal cycle testing; however, as more and more products became mobile, drop shock resistance became a much more important reliability metric for these mobile products. Unfortunately, SAC305 has poor drop shock performance.

Another alternative alloy, SAC105 (98.5Sn/1.0Ag/0.5Cu), provided good drop shock resistance and had the added cost benefit of using less silver, but did not perform as well as SAC305 in thermal cycle testing. So manufacturers compromised by using SAC305 for larger electronic products such as TVs and personal computers, which must perform well in a thermal cycling testing, but switched to SAC105 for mobile devices, such as smartphones.

But what about products that need both superior thermal cycling performance and excellent drop shock results? After years of research, we found that doping low Ag SAC alloys with manganese (which we call SACM) provided just the right solution to this challenge.

What kinds of tests have been done on SACM?

Nearly ten years of lab testing and in-service data show that the SACM alloy achieves high-reliability solder joints. These tests include:

  • JEDEC Drop Test, according to JESD22-B111 - SACM performed equal to, or better than, SnPb and, significantly better than SAC105 and SAC305. This standard test involves dropping a board-level test vehicle in a specified fixture from a defined height.
  • Thermal Cycling Test - samples were subjected to a -40°C to 125°C, 42-minute/cycle that showed that SACM gave better performance than SAC305 and SAC105, as well as SnPb solder.
  • Dynamic Bending Test - a high strain-rate drop test was adopted to measure the failure behavior of second level package reliability for mobile applications. Again, SACM showed better results than SAC305 and SAC105, even after thermal aging (150°C/250 hours).
  • In-Cyclic Bending Test- designed to simulate the potential repeated bending a device might encounter in use. SAC305 did show the best results, but it was closely followed by SACM and SAC105. SAC105, SAC305, and SACM all performed better than SnPb solder in this test.

Full test data is available on our web site at www.indium.com/solder-paste-and-powders/SACM/

Are there other benefits to SACM?

SACM solder paste is specifically designed for the small components and small stencil apertures that are more common in medical electronics manufacturing. It also provides optimal wetting to all common surface finishes.

Gold and gold-containing alloys have historically been used in medical device manufacturing. Are they still being used?

Yes, gold is RoHS-compliant and is an excellent choice as a high-temperature, lead-free, high-reliability solder. Pure gold and gold-containing alloys (usually AuSn) continue to be used in medical device manufacturing. They are available as very fine and standard wire, paste, preforms, and ribbon, depending on the application.

Tell us more about Indium Corporation

Indium Corporation is a global company that still believes in the importance of face-to-face communications. We have manufacturing facilities in the Americas, Europe, and Asia, with regional technical and sales support in areas around the globe where our customers need us. It is important that we maintain close contact with our customers to support their current products, and to help them design their next generation products. With the trend toward manufacturing medical devices in countries or regions where they are actually used, our customers reap enormous benefits from having our technical support engineers within easy traveling distance for face-to-face consultation.

For more information, visit www.indium.com/medical/ or email medical@indium.com.

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