Source ESB
November 2, 2005
There is concern in the electronics industry that in the rush to produce RoHS-compliant parts, some parts manufacturers are not testing their new components sufficiently. To address this issue, a number of major industry OEMs have joined the iNEMI Hi-Rel Task Force and are urging their suppliers to meet the Tin Whisker Acceptance Test Requirements set out by the International Electronics Manufacturing Initiative (iNEMI). The guidelines are available for free download at the iNEMI site (inemi.org).
OEMs are concerned that the basic tests associated with new product introductions are not in place as component suppliers convert to lead-free parts. “I see component manufacturers focusing on becoming compliant,” says Eric Karofsky, senior analyst at AMR Research Inc. “People are not as concerned about testing because testing is an established part of their procedures.” He notes that it may frustrating to retest products that previous went through testing when they were introduced, but the testing is still getting done. “The difficult part for component manufacturers is how you become compliant,” says Karofsky. “They already know how to test.”
He notes that many suppliers do not normally test to the rigorous standard set out by iNEMI and he expects they will not quickly adopt the iNEMI recommendations. “A lot of companies have testing procedures in place, and they may review them after reading the iNEMI recommendations, but they won’t change their testing to meet iNEMI guidelines,” says Karofsky. “These are manufacturer that will do what their customers mandate; they will meet their own standards and their customers’ standards.”
Many of those customers, however, have signed on to iNEMI’s task force, including some of the biggest consumers of electronic components such as Cisco, Celestica, Delphi, HP, IBM, Intel, Lucent, Solectron and Sun. The big concern addressed in the iNEMI recommendations is tin whiskers, the hair-like growths that can develop on pure tin solders when they’ve been in prolonged high-stress environments. The iNEMI task force guidelines set out time lengths for testing as well as defining failure criteria, the number of parts to be tested and asks for additional bias voltage testing.
The guidelines point out there is no clear understanding what the exact mechanisms are that create tin whiskers, and thus accelerated testing is not sufficient. The time length of testing suggested by the guidelines is a minimum of 4,000 hours in a high-temperature, high-humidity environment. Those making components designed for products with a short lifespan such as cell phones, have balked at extensive testing since they believe their components will be out of service before they can grow whiskers.
The iNEMI guidelines set out some exemptions to the testing. One of the major exemptions is small discrete resistor and capacitor device components with a matte tin over nickel finish. That combination has been accepted as whisker resistant for more than 10 years. Also exempted are various finishes in thicknesses of 80 micro inches or more.
Karofsky notes that the gold standard for testing lead-free components goes to Texas Instruments (TI). “They are one of the best for testing,” says Karofsky. “They’re doing a lot of things right when it comes to testing, from engineering functions to reliability.” He explains that many component manufacturers see testing as a way to make sure their products are reliable. “If components are failing prematurely, companies are going to have branding problems.”
Texas Instruments leads the industry in producing reliable lead-free components in part because the company shifted to lead-free products more than 10 years ago. “We moved a lot of our products to lead-free more than a decade ago,” says Mark Frimann, a TI customer quality engineer who specializes in testing procedures for lead-free products. “We saw some solder gapping advantages to nickel palladium plating.”
He notes that the lead-free products were a hard sell when they were first introduced, since engineers were sold on lead-content solders. When the RoHS directive was passed, TI was already mostly compliant. “This proved to be a good path when RoHS was introduced,” says Frimann. TI has since added gold to its nickel-palladium finish, further reducing any possibility of whiskering.
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