Toshiki Kurosu

Bonding mechanism between aluminum nitride substrate and Ag-Cu-Ti solder

The bonding mechanism between aluminum nitride (AlN) substrate and silver-copper-titanium solder was studied. The AlN surface was bonded to the solder with the TiN intermediate layer containing free Ti and Al, produced at the interface between the AlN substrate and the solder. There were garnet phases consisting of aluminum oxide and yttrium oxide partially existed on the AlN substrate surface and these were also bonded to the solder. It was observed that the interface between the garnet phases and the intermediate layer had the highest bonding strength of all the regions. The reasons for variations in bonding strength of a copper plate to AlN substrate were also investigated, focusing on the differences in the preparation procedures of the AlN surface. The adhesion strengths of the copper plate were higher for samples using as-fired AlN substrates than those of lapped ones. This was attributed to the existence of a large amount of the garnet phases and no mechanical damage on the as-fired AlN surface, while the lapped AlN surface had a small amount of the garnet phases and was damaged mechanically. >

Packaging technologies of direct-cooled power module

A power module, which includes an insulating plate soldered to a heatsink, is called a direct-cooled power module. There are several packaging technologies to improve a direct-cooled power module in terms of not only reduction of thermal resistance but also elongation of lifetime. Among those approaches, this paper describes optimization of heatsink thickness and prevention of ratchet deformation. The calculation results show that a thicker heatsink is better to avoid liquid leakage although thicker heatsink provides shorter solder-lifetime. A heatsink with Vickers hardness of greater than 60 MPa is expected to prevent ratchet deformation under the condition of thermal cycling between -40oC and 125oC. and hardness is verified as an effective approach to produce reliable direct-cooled power modules.

Advanced direct-water-cool power module having pinfin heatsink with low pressure drop and high heat transfer

In the direct-water-cooled power module, there is a small gap between the heatsink and the channel wall. This gap results in bypass flow that reduces the pressure drop while maintaining high heat transfer. In this paper, we discuss the effect of this gap on both pressure drop and heat transfer over pinfin heatsinks using our semi-analytical model based on mass, momentum, and energy conservation within two control volumes. The first control volume in the model is located within the finned area, and the second one is located in the gap between the tip of the pins and the flow channel. Dimensionless pressure drops could be predicted within an error of 30%, and the predicted Nusselt numbers agreed within an error of 50%.

Effect of Physical Properties of Al–Si Electrode Films on the Deformation Behaviors and the Strength of Thick Al Wire Bonds during Thermal Cycle Test

The deformation behaviors of Al–Si films and the strength change of Al wire bonds on Al–Si films during heating and cooling cycles have been investigated as a function of substrate temperature of the sputtering process; the purpose was to clarify reliability of both Al wire bonds and Al–Si films for use in insulated gate bipolar transistor (IGBT) modules. The extent of deformation in Al–Si films sputtered at 593 K during heating and cooling cycles was the smallest among films sputtered at room temperature (RT), 473 K, and 593 K. The strength of Al wire bonds on Al–Si films sputtered at the three temperatures was the highest for Al–Si films sputtered at 593 K. The reliability of Al wire bonds on Al–Si films formed at 593 K was about two times higher than the bond reliability on Al–Si films formed at RT and 473 K.