In the NEDO (New Energy and Industrial Technology Development Organization) project, Osaka University and Denso Co., Ltd. announced that they have discovered a self-healing phenomenon of bonding materials that can be expected to improve the long-term reliability of SiC (silicon carbide) power semiconductors. ..
Power semiconductors are semiconductors used in power converters, etc., and the main cause of failure in their applied products is the peeling of joints. NEDO has been developing a silver sintered material that has better electrical and thermal properties than general solder materials as a bonding material, but the short peeling life was a problem in practical use.
Using a micro-sized and sub-micron size hybrid silver particle paste, a die-attached bonding structure (bonding structure between power semiconductors of different materials and a support substrate) is obtained by a bonding process in the air at a low temperature of 250 ° C for 30 minutes. increase.This silver paste sintering joining method is easier to handle than the conventional joining process, the raw material is much cheaper, the strength is 40MPa or more (higher than solder connection), and the thermal conductivity is 150W / mK or more (5 times more than solder). It has the feature that it can be processed without pressurization or at low pressure of 1MPa or less.
In the experiment, a notch was applied to the test piece of silver sintered material to make a V-shaped groove, and a slight tensile load was applied to introduce a sharp crack at the tip of the notch.This test piece was held at 200 ° C and 300 ° C in the atmosphere, and changes in the tip of the crack and changes in the tensile strength of the test piece were investigated.
Observations with a SEM (scanning electron microscope) confirmed that holding at 200 ° C closed the cracks and started partial joining, and at a temperature of 300 ° C the cracks closed extensively, confirming a clear self-healing phenomenon of the cracks.In addition, when the change in tensile strength of the crack-introduced test piece was examined, it reached the same level as the test piece in which almost no crack was introduced after holding at high temperature for 100 hours.
This phenomenon is that cracks generated in the bonded layer of silver sintered material self-repair under high temperature equipment operating environment, and it is said that the applicability of SiC power semiconductors such as in the automobile field has been greatly enhanced.
