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Die-Breakage and Ultra-low-Looping Mechanisms for Very Thin Overhang Stacked Die
Keywords: Overhang Die, Stacked Die, Wire bonding
3D Stacked die configuration have been a preferred solution for SiP’s (system in package) to increase both system functionality and device performance. And in the realm of mobile devices, the same multiple stacked die has been the memory solution of choice as different memory die can be stacked together while maintaining a similar footprint, thereby significantly improving capacity with the minimum inter-connect length. It is, however, in this scenario that very thin overhang stacked die configuration becomes increasingly necessary and likewise inevitable, which in turn poses a significant challenge in successfully wire bonding an extremely compliant thinner silicon chip. Die-breakage and broken loop are recognized as two of the vital issues that arise in overhang thin die application, and it is within these premises that this article has focused its results. More often than not, for the very thin die overhang devices, the perennial “Die-breakage” becomes immediately apparent even after an extensive parameter characterization with the use of “appropriate” impact and bond force settings, which also undermines the traditional approach in bond quality optimization. Hence, this article presents advanced wire bonding techniques, which are essential to determining dynamic impact limits and force transitions that does not follow the common approach for non-overhang die. It is therefore the aim of this article to address the different mechanisms involved in Die-breakage, and to characterize the maximum allowable die-deflection from a variety of die overhang lengths and die thicknesses. Conversely, this inherent die-deflection for overhang die application, also leads to loop inconsistency and the not uncommon, broken loop at the ball neck for ultra-low loop requirements of multiple stacked die. And as covered in this study, utilizing the developments of the 3100 wire bonder’s built-in process instrumentation and bond head control-switching mode algorithm allow a more responsive reaction to this “wire-payout cancelling effect” from the imminent die rebound, during the start of loop formation.
Jovy Michael G. Sena, Senior Service Engineer
Oerlikon ESEC USA Inc.
Tempe , AZ

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