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At the SMTA International 2019 technical conference, Portland State University and Zymet will present their investigations on enhancing the board level reliability of large WLP’s, for harsh environment applications. WLP’s, which include WLCSP’s and FO-WLP’s, offer a path to lower weight, smaller formfactor, and higher performance.
Figure 1. 12-mm WLCSP’s without adhesive (a), dot-edgebonded with reworkable edgebond adhesive (b), full-edgebonded with reworkable edgebond adhesive (c), and edgefilled with reworkable edgefill adhesive (d).
However, their low coefficient of thermal expansions is not well matched to that of commonly used organic substrates. This mis-match result in early solder joint fatigue and early failures in thermal cycle tests, tests that are more and more difficult to pass as the package gets larger and the conditions become more severe. This limitation constricts the user to using either smaller package sizes or to limiting the use of such packages to less severe environments. The investigation shows that reworkable adhesives can enhance the board level reliability of large WLP’s, even for harsh environment applications.
Thermal cycle testing from -40°C to +125°C was performed on a 12-mm WLCSP that was assembled with SAC solder on a rigid PCB. Non-bonded assemblies (Figure 1a) are compared with those bonded with a reworkable edgebond adhesive, applied in both dot-edgebond and full-edgebond configurations (Figure 1b & 1c), and with a reworkable edgefill adhesive (Figures 1d). The expected poor performance of the non-bonded package is confirmed. All three bonded configurations significantly improved performance, raising characteristic life by 300% to 1000%, depending on the configuration.
The paper, “Multi-axis Loading Effect on Edgebond and Edgefilled WLCSP Thermal Cycling Performance”, will be presented at Session APT4: Wafer Level Packaging, on Wednesday, September 25th, 2019. For more information about reworkable edgebond adhesives and edgefill adhesives, visit Zymet at Booth #941, SMTAi 2019, Rosemont Convention Center, Rosemont, IL, September 22 - 26, 2019. Or, email the company at firstname.lastname@example.org. Zymet is a global supplier of adhesives and encapsulants, focused on the development and manufacture of enabling materials for the electronics industry.