Page 52


www.us-tech.com


September, 2022


Silver-Free Thick Film Copper Bonds Reliable Metal-Ceramic Substrates


By André Schwöbel, Benjamin Fabian, Daniel Schnee, Miriam Rauer, Anton Miric, and Stefan Gunst, Heraeus Deutschland GmbH & Co. KG


Major applications include motor drives, hybrid/electric vehicles, rail traction, wind turbines, and photovoltaic inverters. The power electronic modules used in these appli- cations must handle high temperatures and harsh conditions, because they operate at high voltage and high current density. One of the key components for highly


H


reliable power electronic modules is a reli- able metal ceramic substrate. To provide reli- able functionality during operation, the sub- strate materials must provide outstanding electrical, thermal, insulation and mechani- cal performance. Addition ally, they must work with commonly used assembly and interconnection technologies like soldering, sintering, and wire bonding.


Silicon Nitride Substrates Due to cost efficiency, Al2O3-based metal


ceramic substrates, i.e. direct copper bonded substrates, are often used for power module manufacturing. However, they cannot fully leverage the potential of wide bandgap semi-


conductors. As a result, silicon nitride Si3N4- based metal ceramic substrates are gaining popularity as materials for power module assembly. silicon nitride shows superior mechanical properties combined with high thermal conductivity. Highly reliable silicon nitride substrates


Peel test sample: the dark color is silicon nitride that has been pulled from the substrate.


Heraeus Electronics, however, has


developed a design-to-cost, highly reliable sil- ver-free thick film copper bonding (TFCB®) technology for joining nitride-based ceramics with copper foils. The paste eliminates the use of an expensive vacuum-based brazing technology.


igh power electronics have become one of the fastest growing market seg- ments in the semiconductor industry.


are typically manufactured with active metal brazing (AMB) technology that uses silver- filled and active metal (i.e. titanium) contain- ing brazing pastes. The precious metal con- tent in the brazing paste and a slow vacuum brazing process are the major price drivers for AMB substrates.


To compare the performance of TFCB to


AMB, various reliability- and application- related tests such as thermal shock, peel strength, high-temperature storage and par- tial discharge tests were conducted.


Phase Formation The phase formation and bonding mech-


anism of TFCB technology on Si3N4 ceramics were characterized by scanning electron


microscopy (SEM). The actual bonding mech- anism is based on the reaction between the


active metal (Titanium) and the Si3N4 ceram- ic, forming a stable TiN layer. Because there is no silver in the TFCB system, typical sil- ver- and copper-rich phases are eliminated, which are known from the standard AMB technology as using high silver-containing brazing filler metal pastes. Nevertheless, the


highest requirements in terms of thermal shock test (TST) performance because of the ceramic’s mechanical robustness. To assess resistance vs. thermomechanical stress of


bonding mechanism towards the Si3N4 ceramic via a TiN reaction layer is similar. Thermal Shock Performance Si3N4-based AMB substrates meet the


TFCB on Si3N4 ceramics, thermal shock tests were performed. The status of the TFCB sub- strates before testing was characterized by scanning acoustic microscopy (SAM). The


integrity of the substrates was reassessed by Continued on page 58


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92