Soft-Metal Packaging for Cryogenic-Resistant Power Modules

The Problem

Wire bond printed circuit boards (PCBs) and flex-PCBs need soft encapsulation material to remain flexible for stress relieving. However, there is no soft encapsulation material available for low temperatures, especially for cryogenic temperatures. Currently used materials, like silicone gel and epoxy resin, are ineffective during thermal cycling due to becoming brittle at low temperatures, resulting in increased inductance and parasitic loss. High parasitic loss at cryogenic temperatures means power modules are inefficient and lack durability in thermal cycling.

The Solution

Researchers at the University of Tennessee have proposed a new packaging method for power modules that remains flexible even at cryogenic temperatures. An indium layer of insulating material is directly soldered between the semiconductor die and direct bonded copper layer, resulting in lower loop inductance and better protection against power loss. This packaging method is also more compact than traditional methods. This technology will improve electric component performance and reduce parasitic loss in low temperature applications, such as eVTOL, space, quantum computing, data centers, and other cryogenic applications.

Proposed packaging for a single die (front view):

Semiconductor die is in a sealed area between the support PCB columns. The indium layer provides a thermal interface between the die and the DBC.

Benefits

Benefit
>50% reduction in parasitic loss at cryogenic temperatures
Can withstand mechanical stresses of cryogenic thermal cycling
Compact, lightweight, and easy to manufacture design
Direct solder provides a low inductance connection to the semiconductor die
Encapsulant material properties do not change at cryogenic temperatures

More Information

Gregory Sechrist, JD
Associate Technology Manager, Multi Campus Office
865-974-1882 | gsechris@tennessee.edu

UTRF Reference ID: 24156
Patent Status:

Close up portrait of computer engineer's hand is holding CPU's computer.

Innovators

Dr. Hua "Kevin" Bai

Associate Professor, Min H. Kao Department of Electrical Engineering and Computer Science, UT Knoxville

Dr. Bai received his PhD in Electrical Engineering from Tsinghua University in Beijing, China in 2007. His research interests include EV related battery chargers, motor drive systems, and applications of wide-bandgap devices.

Dr. Fei "Fred" Wang

Professor and Condra Chair of Excellence in Power Electronics, Min H. Kao Department of Electrical Engineering and Computer Science, UT Knoxville

Dr. Wang received his Ph.D. in Electrical Engineering from the University of Southern California in 1990. His research interests include Power Electronics, Power Systems, and Motor Drives.