Thermal Compression Bonding with Pre-Applied Underfill for Very Large Die

A study was conducted to determine the feasibility of using a pre-applied underfill (PAUF) and its associated Thermal Compression Bonding (TCB) process for challenging packaging applications such as large die 3D and very large die 2D configurations. Two corresponding test vehicles were employed to evaluate two Non-Conductive Paste (NCP) candidates in a PAUF process with comparison to a Capillary Underfill (CUF) material in a sequential bonding-underfill process. The 3D configuration comprising an 8x10mm die on an interposer-laminate platform demonstrated that appropriate material property selection enabled acceptable Deep Thermal Cycling (DTC) performance of one NCP candidate. It was further established that the PAUF process was essential in order to effectively compensate for the high warpage of this particular platform. In contrast, the 2D configuration comprising a very large (18X18mm) die demonstrated fundamental limitations of current NCP material sets with respect to balancing flow, fillet formation and fatigue protection. Supported by flawless DTC performance, such a large die configuration recommends the use of a CUF material and process.