Thermo-mechanical reliability of a lead-free radio frequency power amplifier with GaN/SiC power transistors

Purpose and goal

The project has developed knowledge of risks and opportunities with GaN/SiC transistors in combination with lead-free solders for RF applications. This is an important aspect of Saab EDS to formulate design criteria of products that rely on semiconductor technology of SiC and GaN. Among other things, we have seen an uneven temperature distribution which affects both the chip and solder and position on a future PCB. SP and Acreo together have increased knowledge about the testing of RF transistors and electrical and material characterization of semiconductor components of SiC and GaN.

Results and expected effects

Power cycling equivalent to 20 years of use, resulting in nine defaulting transistors out of 21. The RF characteristics of these demonstrators show a vague deterioration. It is clearly seen how the ability to lead DC current has deteriorated gradually. The thermo-mechanical effects from temperature variations of 100 deg. and 2300 cycles do not affect the lead-free solders significantly. In comparison no difference is seen for lead solder. IR measurements in combination with modeling shows an uneven temp. distribution across the transistor which influences the various solders.

Approach and implementation

This was an ambitious project that included the design and production of demonstrators made up of RF PCBs designed with commercial RF transistor, two kinds of lead material and two kinds of thermally conductive material. Two long-term tests and several characterization methods have been performed. The project has been delayed due to delivery problems of components. Despite this, the project has been completed according to the original experimental plan thanks to an extension of the project period and the financial contribution from all project partners