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Part 12: Lead-free Reliability - Enticing and Intriguing Status
December 31, 1969 |Estimated reading time: 4 minutes
It is correct that there is not an element on earth that can single-handedly replace lead. But an alloy system can and should. SAC is lead-free, but lead-free is not necessarily SAC. In the lead-free world, solder systems beyond SAC will deliver the desired properties for high-performance electronics.
It has passed the ten-year mark since the first lead-free electronic gadget was introduced to the marketplace. What is the track record of lead-free electronic products? The answer, surely, will not be uniform. It varies with each industry sector. It also depends on the specific OEM or producer when the design and manufacturing process are put into the equation.
However, as we combine historical hindsight by examining the results with some foresight comments that were published before the industry launched the selected system, an enticingly intriguing picture is revealed.
Beyond the lead-free world, from dazzling hardware handsets to ever-advancing software that works within the hardcover, new products continue flooding into the market. Their escalating functionality is mind-boggling. What has fast-tracked these new products? A short answer is innovation. Although the word "innovation" is becoming a cliché, it denotes the true meaning to all industries in their top and bottom line of business regardless of product categories.
For last ten years, when we talked and wrote about lead-free, we referred to SnAgCu (SAC) systems. Today, when we think about lead-free, it is extemporaneously meant SAC. Fortunately and unfortunately, SAC is lead-free, but lead-free is not necessarily SAC, which bears a humongous gap in concept, practice, and results. SAC was selected as a lead-free alloy for several reasons. Nonetheless, SAC is not and should not be the lead-free world.
In my last two columns, I covered the merits of ternary SnAgCu and binary SnCu, as well as the issues that were both anticipated and observed. I have also touched on the power of metallurgy, which controls the correlation between solder metallurgy and solder joint performance. Among a wide array of global production results and the product field performance that have been generated during the last decade, some are deemed positive and some remain to be resolved. It is indicative that not all test results appear to be in congruence, yet all product performance and test results manifest the criticality of sound scientific and engineering practices. Solder metallurgy and its ability to anticipate the relative performance are rewardingly powerful.
Solder joint reliability does not speak for system reliability. Indeed, system reliability hinges on the integrated knowledge and execution in all aspects of the PCB assembly, comprising materials, components, PCB, process, testing, and manufacturing know-how.
Regardless, what is universally true is that the product reliability cannot outperform the intrinsic properties that a solder joint alloy can deliver. And the fact is that when one solder joint fails, the system fails.
It is correct that there is not an element on earth that can single-handedly replace lead (Pb). But an alloy system can and should. With the last ten years' efforts essentially being focused only on SAC systems, conspicuously commodious room exists for new solder alloys either from new material developments or from a broad-based evaluation of existing alloys that were already disclosed by companies and researchers. From the perspective of metallurgical science and engineering, the SAC performance demonstrated on the production floor, in the testing laboratories, and in the field has come as no surprise. I have mentioned a couple of key points in this regard in an interview conducted by Dr. Andy Mackie of Indium Corporation in August 2009 (View the interview at http://tiny.cc/indium).
Within the SAC system, decreasing Ag content has recently drawn attention and been put in applications. A lower Ag dosage in a SAC system does bring advantages in specific properties if/when meeting that specific criterion is the priority. Keep in mind, however, that a lower Ag dosage expends some other positive properties. It should be noted that this approach does not change the overall characteristic behavior of SAC ternary system.
The true improvements will have to go outside the SAC ternary system. The core values explained in my last column come into play. The success of lead-free reliability is incumbent upon the supply side of solder materials. OEMs play an important role in propelling design-for-performance. Additionally, EMS operations can take up the initiative by selecting the right material for the targeted reliability through engineering ingenuity. Now, we have to resort to that old cliché – innovate and work out of the existing box for better performance. SMT
APPEARANCES
Dr. Hwang delivers a comprehensive 12-part webinar series on Lead-free Reliability. She will present lectures at SMT Hybrid & Packaging, Nuremberg, on June 8, 2010.
Jennie S. Hwang, Ph.D., an SMT Advisory Board member, is inducted to the WIT International Hall of Fame, elected to the National Academy of Engineering, and named an R&D-Stars-to-Watch. Since the inception of SMT manufacturing, she has helped improve SMT yield and solved reliability issues. Having held executive positions with Lockheed Martin Corp., Sherwin Williams Co., SCM Corp, IEM Corp., she is a principal of H-Technologies Group providing business and manufacturing solutions. She is a member of the U.S. Commerce Department's Export Council, and serves on the board of Fortune 500 NYSE companies and civic and university boards. She is an international speaker and author on trade, business, education, and more. Contact her at (216) 577-3284; JennieHwang@aol.com.
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