Manufacturing power electronics with silver sintering


ASM SilverSAM: Manufacturing power electronics with silver sintering

Frequently changing loads and high temperatures cause conductive connections in power electronics to age quickly. One solution to this problem involves temperature-resistant materials such as SiC substrates and nano-silver pastes. The high melting point of silver, however, prohibits the use of a melting process to produce the conductive connection, because the electrical components would not survive the high temperatures.

The solution: With silver sintering, nano-silver particles can be shaped to form stable connections without melting. The
ASM SilverSAM (which stands for Silver Sintering Automated Machine) is the automated solution for this process. It can be easily combined with other ASM solutions for paste printing, die-attach and wire bonding. With the efficient ASM SilverSAM, component manufacturers can produce more durable IGBTs with improved electrical and thermal properties.

The process chain

The paste with nano-silver particles is first applied to the DBC (direct-bond copper) or substrate with a DEK printer (Ag paste application). This is followed by the pre-sintering process, which required higher bonding forces as well as bonding heads for temperatures of 100°C (212°F) or more to firmly connect the die to the substrate and keep it from shifting.


Pressure sintering with SilverSAM

The core sintering process uses pressure, heat and time in material-specific combinations to permanently join the silver particles in the paste at temperatures that are far below the silver’s melting point. With the SilverSAM, ASM Back End Systems offers a highly flexible sintering press for the electronics industry. SilverSAM operates with pressures of more than 10 MPa and temperatures between 200°F and 300°C (392°F and 572°F). The sintering surface is 270 mm x 175 mm – enough for two 5x7-inch panels and perfect for carriers with singulated substrates.

The innovative tooling in the SilverSAM can be configured to exert pressure only to the desired surfaces (dies, chips, etc.) and keep cavities or grooves on the substrate untouched. A special film between the die and the tooling protects the components.

The user can combine one to three presses in a single SilverSAM. That way, labs and prototype shops can be equipped with the smallest version, while high-volume factories can use the fully automated SilverSAM version with multiple presses for high throughput and productivity.

After being sintered, the packages are assembled on the base plate via pick-and-place with SMT placement machines. Stable wire connections within the modules can then be created with wedge bonders like the ASM Hercules.