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IPC APEX EXPO Tech Session to Tackle Low-temp Solders
March 19, 2014 |Estimated reading time: 2 minutes
Reliability issues continue to develop rapidly to meet changing customer needs and the rapid technical progress of semiconductors and circuit boards. Shock resistance has become more important as often-dropped portables increase in numbers, and as finer pitches and the evolution of lead-free solder march on, the challenge to improve durability grows.
Indium Corporation will be describing its research into areas that impact reliability and manufacturability at the upcoming IPC APEX EXPO® conference and exhibition in Las Vegas, Nevada, March 23-27. One of the presentations examines the use of low-temperature solders, which are seeing increased use as a way to meet the combined demands of lower costs and higher densities.
A material that's proving to be popular is 57Bi42Sn1Ag, which has a melting temperature of 138 degrees C. A major challenge facing all low-temperature solders is that they're often used in processes that include a number of different solder types. That means that low-temp solders must be able to perform well even when they undergo temperatures greater than 200 degrees C.
Indium's test coupons, which used a range of solder paste, were combined with solder balls that also had a range of materials. These modules then underwent a range of tests, including X-ray inspection.
"All combinations involving bismuth were brittle, caused by the stiffening effect of solder due to the homogenized presence of bismuth in the joint, thus the brittle IMC interface became the weakest link upon shearing," said Ning-Cheng Lee, vice president of technology at Indium. "If BiSnAg is used for BGA assemblies in portable devices, polymeric reinforcement is desired."
The second presentation explains Indium's studies of a low-cost, high reliability package-on-package assembly with a novel epoxy flux on solder paste.
"For BGA or POP with the potential for thermal warpage, solder paste is needed to prevent opens," Lee said. "When reinforcement with epoxy flux is desired, epoxy flux will meet wet solder paste, so a new epoxy flux compatible with solder paste is needed."
Completed modules underwent a number of tests. After the test coupons were examined, the team concluded that when the epoxy and solder paste flux were teamed up to provide the right characteristics, all requirements for testing could be met. Picking a user-friendly epoxy flux system is a critical step, researchers noted.
The first paper is being presented on Tuesday, March 25 as part of the Solder Paste and Epoxy Reliability session (S09) that also includes speakers from Heraeus Materials and Inventec Performance Chemicals. On Wednesday, March 26, Indium's epoxy flux presentation will be teamed with reports from Lockheed Martin Missile & Fire Control, Celestica, AIM and Honeywell Air Transport Systems, in the Solder Mixing/Reliability session S09.