Influence of the processing method on the amount and development of voids in miniaturized interconnections

For satisfying the current industrial need of downscaling electronic devices, the die-to-die or die-to-package interconnects need to decrease in size accordingly. In view of that, flip chip bumps, which are currently the smallest interconnect type, have to be further miniaturized. In this study, Cu-Sn-Cu TLP (Transient Liquid Phase) bonded bumps that consist entirely of intermetallics (IMC) are studied. The overall intermetallic properties are not yet well understood. Microstructural inspection of these bumps revealed the presence of voids inside the IMC phase and since the mechanical behavior of the bumps is strongly affected by it, a first study is executed to better understand the cause of voiding. It is shown that the appearance of voids is directly related to processing and especially to the use of cleaning agents. Therefore a study of the three different types of bumps microstructures produced by the use of three types of cleaning agents has been conducted. For understanding the influence of the processing method on the amount and development of voids during ageing, in addition to a study of bumps, Cu-Sn-Cu blanket film sandwich structures have been investigated as well. Addition of an extra layer of Ni into the Cu-Sn-Cu system was performed in order to observe its influence on voiding occurrence.