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  • Investigation of MOS/DMOS-transistors die Bonding Methods by Applying Au-Si / Ag-Pt Alloys and Nickel-plated and Gold-plated Packages

Student
Title
Supervisor
Faculty
Educational Programme
Final Grade
Year of Graduation
Maxim Ichetovkin
Investigation of MOS/DMOS-transistors die Bonding Methods by Applying Au-Si / Ag-Pt Alloys and Nickel-plated and Gold-plated Packages
D.V. Bykov
Electronic Engineering
(Master’s programme)
8
2018
The purpose of this work was to investigate the die bonding technology of MOS/DMOS transistors with Au-Si / Ag-Pb alloys in nickel-plated and gold-plated packages. Two types of bonding were investigated: Au-Si eutectic, and lead-silver solder PSr-2.5.

To improve the quality of bonding by a eutectic alloy the operation of preliminary purification of the oxide layer from the back surface of the silicon wafer by ion bombardment with argon was applied. In addition, metallization was used: 0.01 μm of titanium and 0.1 μm of gold. Then, cathodic electrodeposition of gold 4-7 μm in thickness was carried out.

It is shown that it is possible to eliminate the formation of voids between the package and the die of the device, and to reduce the thermal resistance (Rt) between them, due to the metallization of the back side of the silicon wafer and the use of preliminary purification of the back side of it. As a result, we obtained an average Rt = 0.48 ° C / W with a die area of 42 mm2. Before soldering with lead-silver solder, a preliminary purification was carried out and further metallization of the back side of the wafer with Ti-Ni coating (0.1 Ti and 0.1 Ni) was made.

It has been revealed that for soldering with PSr-2.5 solder, it is more expedient to use nickel-plated packages, rather than gold-plated packages, since it allows to obtain a smaller Rt. As a result, the average Rt = 0.48 ° C / W for a nickel-plated case was obtained, and 0.66 ° C / W for a gold-plated at a crystal area of 42 mm2.

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