Inkjet printing technology for increasing the I/O density of 3D TSV interposers

Behnam Khorramdel,Jessica Liljeholm,Toni Lammi,Gustaf Mårtensson,Matti Mäntysalo,Thorbjörn Ebefors,Mika-Matti Laurila,Frank Niklaus

doi:10.1038/micronano.2017.2

Abstract

Interposers with through-silicon vias (TSVs) play a key role in the three-dimensional integration and packaging of integrated circuits and microelectromechanical systems. In the current practice of fabricating interposers, solder balls are placed next to the vias; however, this approach requires a large foot print for the input/output (I/O) connections. Therefore, in this study, we investigate the possibility of placing the solder balls directly on top of the vias, thereby enabling a smaller pitch between the solder balls and an increased density of the I/O connections. To reach this goal, inkjet printing (that is, piezo and super inkjet) was used to successfully fill and planarize hollow metal TSVs with a dielectric polymer. The under bump metallization (UBM) pads were also successfully printed with inkjet technology on top of the polymer-filled vias, using either Ag or Au inks. The reliability of the TSV interposers was investigated by a temperature cycling stress test (−40 °C to +125 °C). The stress test showed no impact on DC resistance of the TSVs; however, shrinkage and delamination of the polymer was observed, along with some micro-cracks in the UBM pads. For proof of concept, SnAgCu-based solder balls were jetted on the UBM pads.

Highlights

One of the major technology drivers in microelectromechanical systems (MEMS) is to incorporate increasing numbers of functionalities within the same foot print
Inkjet printing and super inkjet (SIJ) technology were demonstrated to be available for use in performing the process of dielectric filling of hollow through-silicon vias (TSVs) with an UV-curable hybrid polymer that has a low Young’s modulus
After baking, SIJ-filled vias suffered from partial detachment of the polymer from the via walls, which could be attributed to weak adhesion

Summary

Introduction

One of the major technology drivers in microelectromechanical systems (MEMS) is to incorporate increasing numbers of functionalities within the same foot print. The interposer provides a possibility to integrate dies that are manufactured with different technologies, such as memory, power, logic, MEMS, and radio frequency (RF)

Methods

Results

Conclusion