Journal of SMT Article
CASE STUDIES IN THE EVALUATION OF MOISTURE SENSITIVITY LEVEL AND RELIABILITY OF DEVICES FOR HIGH-REL APPLICATIONS
Company: Sonoscan, Inc.
Date Published: 10/1/2003 Volume: 16-4
Over the past year we have seen several cases of PCB manufacturers (users) "checking" the MSL of the devices after experiencing unacceptable damage to the devices during their reflow process. Upon laboratory testing, the claimed MSL was not passed per industry standard J-STD-020, which led to some obvious questions. Typically, a discussion between the user and supplier of the device reveals that the supplier has done one of several things. Either their manufacturing process has recently changed, or that the devices are now actually manufactured by a sub-contractor.
Unfortunately, the supplier may not always be aware of any changes the sub-contractor may have done to their device. Some changes may be small in the mind of the sub-contractor, but could strongly affect the MSL of that device. As a few examples, any changes to the molding compound, die attach, or lead frame finish can have a heavy impact on the device's MSL. A generic case study representative of several actual investigations that have gone through this process will be presented here.
High reliability (high-rel) users of devices in the automotive, aerospace, and military industries were able to purchase devices that met their specific environmental needs in the past. Unfortunately the economics have also turned against these industries, forcing them to purchase commercially available devices and screen them for reliability at the operating temperatures and other expected environmental conditions. "Uprating" the devices typically invalidates the warranty from the supplier and places the user in a quandary.
Without any valid reliability data, they cannot guarantee the operation of the device, and they destroy the warranty in the process. High-rel users have also referenced J-STD-020 as a basis for their accept/reject analysis, even though they may be testing the devices under much harsher conditions. A case study showing the typical analysis that a high-rel user has gone through to qualify a device will also be presented.
Key words: MSL, J-STD-020, PEMs, high-rel, uprating.
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