Reliability and Benchmark of 2.5D Non-Molding and Molding Technologies

Non-molding grinding technologies that apply in 2.5-dimensional integrated circuits (2.5D ICs) packaging were investigated. Die chipping failures were found after back-side wafer grinding without molding, if the standard 2.5 IC assembly process flow is followed without any optimization. The finite element analysis (FEA) model used to analyze the stress concentration and summarize as: (1) decreasing the outer grinding force and (2) increasing the die fracture strength to avoid the die chipping. The factors can be divided into three parts: (1) Process, (2) Structure and (3) Material. The optimization of the process are: the grinding recipe, the underfill (UF) fillet height, the UF bleed out distances and the different types of the UFs can be achieved and succeed to build the non-molding 2.5D IC package with back-side wafer grinding without die chipping. This non-molding with back-side wafer grinding test vehicle which we call the 2.5D Plus (2.5D+) is inspected by Scanning Acoustic Tomography (SAT), cross-section and Scanning Electron Microscopy (SEM) observation. There are no delaminations for each interface. There are good qualities of the Controlled Collapse Chip Connection (C4) bumps and micro-bump joints post assembly. The 2.5D+ also shows good reliability performance which passes 1200 thermal cycles test (TCT). The reliability results indicated that the changing of process, structure and material would not induce any side effects to damage the 2.5D+. The comparison between the 2.5D_M and 2.5D+ can be summarized: 3D flow compatible is the advantage for 2.5D_M. The lower cost (10~20%), the shorter cycles time and others application of non-molding packages are the advantages for the 2.5D+.