Decapsulation of 3D multi-die stacked package

Abstract

Although a combination of laser, mechanical and chemical techniques can be used to expose a very large and thin die from a multi-die stacked package, package warping and die crack occur in the process of gaining access to each die. The aim of this paper is to investigate the sample preparation technique to access each individual die from a four-die stacked package, while maintaining the structural integrity of each die for further failure analysis.

Sample Preparation for Deprocessing of 3D Multi-Die Stacked Package

“…The mechanical support was necessary to relieve stresses at the package substrate to minimize package warping and prevent die crack. Decapsulation without die crack was achievable and repeatable from Die 4 to Die 1 [9]. The previous results are summarized in Table 1.…”

“…A. Selection of mechanical support for sample preparation for deprocessing of a thin die within the 3D four-die stacked package As deprocessing involves dry etching using reactive ion etching (RIE) to remove the passivation layer, wet chemical etching or polishing to remove the metallization layers and wet or dry etching to remove the oxide/inter-layer dielectric (ILD) layers, other types of mechanical support were investigated apart from the cold mount epoxy used previously [9]. Considerations include coefficient of thermal expansion (CTE) match between the package and mechanical support, chemical resistance to strong acids such as nitric acid, and versatility.…”

“…FOUR-DIE STACKED PACKAGE [9] In PFA, it is a great challenge to precisely isolate a defect or failure found within a 3D package, due to the high density integrated multi-stacked structures, redistribution layers etc. Some form of sample preparation or other fault isolation techniques have to be used in complementary with PFA techniques to improve the resolution or accuracy of isolating failures [6].…”

“…1. Schematic of the cross-section of a four-die stacked package [9] Decapsulation of the four-die stacked package using fuming nitric acid soak to obtain individual intact die usually yielded two dice (while the rest cracked) and the process was not repeatable. Decapsulation of the four-die stacked package itself (whether using laser decapsulation with manual or auto chemical decapsulation) always resulted in die crack.…”

“…A combination of mechanical grinding (Grit 180 (75 µm) SiC grinding paper) to remove the epoxy molding compound (EMC) and each die; and chemical decapsulation techniques (fuming sulphuric acid (20% SO3) mixed to 100% fuming nitric acid (1:1), at 100°C) to remove each die attach layer, was used to decapsulate the four-die stacked package, but package warping occurred when Die 2 was exposed. Thus, a cold mount epoxy mechanical support was used to encapsulate the four-die stacked package prior to decapsulation using the combination of mechanical grinding and chemical decapsulation techniques [9] described above. The mechanical support was necessary to relieve stresses at the package substrate to minimize package warping and prevent die crack.…”