Abstract
In this study, the effect of intermetallic compound (IMC) bridging on the cracking resistance of microbumps with two different under bump metallization (UBM) systems, Cu/solder/Cu and Cu/solder/Ni, under a thermal cycling test (TCT) is investigated. The height of the Sn2.3Ag solders was ~10 µm, which resembles that of the most commonly used microbumps. We adjusted the reflow time to control the IMC bridging level. The samples with different bridging levels were tested under a TCT (−55–125 °C). After 1000 and 2000 TCT cycles (30 min/cycle), the samples were then polished and characterized using a scanning electron microscope (SEM). Before IMC bridging, various cracks in both systems were observed at the IMC/solder interfaces after the 1000-cycle tests. The cracks propagated as cyclic shapes from the sides to the center and became more severe as the thermal cycle was increased. With IMC bridging, we could not observe any further failure in all the samples even when the thermal cycle was up to 2000. We discovered that IMC bridging effectively suppressed crack formation in microbumps under TCTs.
Highlights
We propose a new viewpoint that the microbumps fully transformed into intermetallic compound (IMC) could extend the cracking resistance under thermal cycling
It is obvious that the scallop-type IMC, Cu6 Sn5, quickly formed at (COC) method
The effect of IMC bridging in Cu/solder/Cu and Ni/solder/Cu microbumps on crack formation a thermal cycling test (TCT) was investigated
Summary
In a 3D-IC, multiple thin silicon chips within through-silicon vias (TSVs) are stacked and connected by various microbumps [5,6,7]. Many studies reported that the fast interfacial reaction induces intermetallic compounds (IMCs) in the early stage of bonding. It may quickly consume the entire solder in a short time [8,9,10,11,12,13]. The entire solder may be fully transformed into an IMC joint during the thermal treatment of semiconductor processing. During such fabrication, several reflow processes are required, and IMC formation is inevitable
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