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Morgana Ribas, manager of Alpha's Metals Technology Group in India, presented a paper at the recent SMTA International show in Chicago. She sat down with me to discuss the paper's focus on high thermal reliability, and some of the new high-rel lead-free alloys hitting the market.
Andy Shaughnessy: Morgana, what can you tell us about the paper you presented?
Ribas: The title of the paper is “Development of Lead-free Alloys with Ultra-High Thermal-Mechanical Reliability.” I'm actually introducing Alpha's new ultra-high-reliability alloy called MAXREL Plus. It's an alloy that's especially recommended for demanding applications that require better than SAC305 and SAC405 mechanical and thermal reliability.
Shaughnessy: What are some of the advantages of using this?
Ribas: The advantages are seen especially in market segments such as automotive, LED, and power electronics, which require high thermal reliability. Let me give you a little background on why we came up with this alloy. When we had the advent of lead-free solders, SAC305 and SAC 405, became perhaps the most widely used alloys. They have very high thermal cycling performance, but they were lacking in drop-shock resistance. That's actually how, a few years ago, Alpha came up with the SACX and SACX PLUS family of alloys that have improved drop-shock and thermal fatigue performances.
Shaughnessy: What sort of applications would best be suited for this? Anything with high reliability?
Ribas: Yes, especially applications for harsh environments, particularly automotive if you're looking for under-the-hood applications; that is very much recommended. In addition to that, there is a major application in packaging and many customers in semiconductors have showed strong interest in using MAXREL Plus in their devices. And of course, MAXREL Plus can be used in any other application already using SAC305/405 but delivering an enhanced performance.
Shaughnessy: And it is lead-free?
Ribas: Yes, it is lead-free.
Shaughnessy: What are some of the challenges of using this? Are there any drawbacks to it?
Ribas: It's actually a drop-in replacement for SAC305/405. We are not aware of any disadvantages or drawbacks.
Shaughnessy: Okay. It's a drop-in replacement.
Ribas: It's directly drop-in replacement with improved performance.
Shaughnessy: And you helped develop it?
Ribas: Yes, we have developed it at the Alpha India Research Centre at our lab in Bangalore.
Shaughnessy: Congratulations. What is your background, Morgana?
Ribas: I graduated from the Federal University of Rio Grande do Sul in Brazil with a bachelor's and master's degree in metallurgical engineering, and then left Brazil in 2001 to work as a researcher at Tohoku University in Japan. After that, I moved to the U.S. where I completed my Ph.D. in Material Science at Rice University. Later, I started working for Alpha in Bangalore.
Shaughnessy: Can you give us a summary of the paper that you are presenting this week?
Ribas: Yes. MAXREL Plus has some particular characteristics. So we started by improving the high-temperature properties of this alloy. Its creep strength is about 140% higher than SAC305, and the creep elongation at 150°C is 200% higher than SAC305. So an alloy with improved high-temperature creep properties, results in better thermal fatigue and thermal cycling performance. That's what we saw when we did thermal cycling tests under a quite harsh thermal cycling profile, from -40° to 150°C, with thirty minutes dwell times (hot and cold dwells).
When we did this test we saw that after 2,000 cycles, 100% of the components used in SAC305 had failed, but only 60% of the BGA components we used in MAXREL Plus had failed. We also evaluated the shear strength of chip resistor components after 2,000 thermal cycles. Components using MAXREL Plus have 97% higher shear strength than when using SAC305. And that's mechanical plus thermal reliability performance.
But one of the most interesting data that I think we found is from a vibration test after thermal cycling, which is a test that is very important for the automotive segment. The cross-sections showed that after 1,000 cycles there were very pronounced cracks in the solder joint of the components using SAC305. But there were only very minor cracks when using MAXREL Plus. So these are very important results.
Shaughnessy: That's great—higher reliability and lead free.
Ribas: Yes, and we have done another two studies on BGA packaging and WLCSP. We manufactured the spheres in different sizes and tested these packages. Across the board we saw consistent improvement in thermo-mechanical performance when using MAXREL Plus compared to SAC305 or SAC405 alloys.
Shaughnessy: It sounds like you'll have a ready market for it.
Ribas: Yes, we are very close to launch this alloy as a product. For further inquiries please contact Alpha Global Product Manager for Solder Paste Traian Cucu or Alpha Advanced Materials Global Product Manager for Soldering Products Garian Lim.
Shaughnessy: Thank you for talking to us, Morgana.
Ribas: Thank you very much.