Electronics Assembly Knowledge, Vision & Wisdom
Investigation of Copper Sinter Material for Die Attach
Investigation of Copper Sinter Material for Die Attach
3 different copper powders were tested for their feasibility to use as die attach material for pressure sintering process without prior treatment with reducing agents such as hydrogen or formic acid.
Materials Tech

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Authored By:
Christian Schwarzer, Michael Schnepf, Michael Kaloudis
UAS Aschaffenburg, Aschaffenburg, Germany

Ly May Chew
Heraeus Deutschland GmbH & Co.KG, Hanau, Germany

Thomas Stoll, Jörg Franke
Heraeus Deutschland GmbH & Co.KG, Hanau, Germany

Summary
Die attach on power semiconductor using lead-free technology has attracted considerable interest. Silver sintering has been considered as one of the most promising lead-free die attach solutions over the past years. Pressure silver sintering by far offers superior thermal and electrical conductivity properties which enables power electronics applications to operate at higher temperature. Although silver sintering is a promising technology, the high cost of silver increases the manufacturing cost and consequently impedes the wide adoption of this technology.

Copper is commonly used in the electronics industry mainly due to its unique properties such as good thermal and electrical conductivity. Hence, it is not surprising that recently there are several academic and industrial researches using copper as an alternative die attach material for sintering process. Nevertheless, copper sintering is usually requires an additional reducing process using hazardous gases such as hydrogen and formic acid to prevent copper oxidation as well as to increase the bonding strength.

In this study, we develop a safe-to-use micro-copper sinter paste for pressure sintering under inert atmosphere.

Conclusions
In summary, 3 different copper powders were tested for their feasibility to use as die attach material for pressure sintering process without prior treatment with reducing agents such as hydrogen or formic acid. The results illustrate that spherical-shaped copper powder was not able to create copper joints by pressure sintering process at 573 K with a pressure of 10 MPa for 3 min under N2 atmosphere. In contrast, it was possible to create copper joints by pressure sintering process using flake-shaped copper powders. The shear strength and the failure mode results show that copper flake 2 created stronger copper joint than copper flake 1. This study demonstrate that it is feasible to use copper paste as interconnect material for die attach application by pressure sintering process, even without reducing agents.

Initially Published in the SMTA Proceedings

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