| Summary: | 碩士 === 國立中正大學 === 機械工程所 === 98 === The purpose of this study was to investigate the influence of the nickel deposited layer on the flex substrate on the bondability and bonding strength of silicon chips flip-bonded onto the flex substrate using thermosonic flip-chip process. Two different flex substrates containing copper electrode were prepared. The first one were electroplated with an additional nickel layer between the copper film and the silver film on the flex substrates. This nickel layer was expected to improve the bondability and bonding strength of silicon chip flip-bonded onto flex substrates. The stacking sequence of the second flex substrate was Ag/Cu/PI. The thickness of the silver layer and the nickel layer were approximately 0.5μm. Thermosonic flip-chip bonding was conducted using an automatic thermosonic flip-chip bonder developed by ITRI. After chips bonded on the flex substrate, a subsequent die-shear test was performed to evaluate the bonding strength in manner with EIA/JEDEC JESD22-B116 standard.
The chip was successfully flip-chip bonded onto flex substrates using thermosonic bonding process. Deposition of a nickel layer on the copper electrodes, 100% bondability of chips bonded on the flex substrates can be obtained and bonding strength exceed the minimum requirements stated in the related specifications. In contrast to a good bonding quality of chips bonded on flex substrates with a nickel layer, inferior bonding strength was found when chips bonded on copper electrodes without nickel layer. The nickel layer was effective to improve the propagation of ultrasonic power to bonding interface between silver bonding layer and gold bumps, bonding strength and bondability thus were enhanced. The adequate bonding parameters of chips thermosonic bonding to flex substrates were:20.66 W in ultrasonic power, 625 gf in bonding force, 0.3 s in bonding time and 200℃ in bonding temperature.
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