| Abstract: |
Transient liquid phase (TLP) bonding (or solid-liquid interdiffusion bonding) is capable of producing joints with excellent mechanical and thermal properties, and with operation temperatures at or even above the bonding temperature. Due to its comparatively low bonding temperatures (? 300 °C) and the high reliability of the resulting joint, the TLP system Ag-Sn is of particular interest, e.g., for die attach of next-generation SiC-based power-electronics modules. However, reduction of the comparatively long processing times necessary to achieve high-quality joints is highly desirable. In this work, the implementation of an originally furnace-based Ag-Sn TLP bonding process onto a manual flip-chip bonder, equipped for fast heating and application of ultrasound (US), is presented. Employing a rapid heating rate of 20 K/s, a total process time of less than 4 min at 240 °C could be reached, with an average shear strength of (58 ± 22) MPa. The high variance of the shear strength is associated with extended gap formation within the bonding zone, caused by gas entrapment, suppression of Ag3Sn-formation upon rapid heating, and pronounced lateral squeeze out of liquid Sn. Introduction of a weak US pulse, placed immediately after emergence of the liquid phase, lead to enhanced Ag3Sn-formation and efficient removal of entrapped gas, and thus to avoidance of large-scale bond defects. This way, a substantially enhanced shear strength of (104 ± 8) MPa could be achieved.
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