EPC’s Phase Eight Reliability Report documents a combined total of over 8 million GaN device-hours with zero failures. The report examines, in detail, the stress tests that EPC devices are subjected to prior to release as qualified products and analyzes the physics of failure.
In this report, product-specific detailed stress test results for over millions of actual device hours are provided. In addition to product qualification stress testing, due diligence is necessary in other areas of reliability such as field experience, failures over device operational lifetime, and board level reliability.
As part of the report, EPC examined all devices returned by its customers, as ‘field failures’; the company says says it has received a total of 127 products returned by customers; of those, it could not find any fault with 37, leaving 90 to be the subject of in-service failure analysis. 75 units were found to have failed due to assembly problems. To achieve very low inductances, EPC uses a chipscale packaging format with solder ball connections; an example failure mode was found to be that poor surface-mount technology had caused problems – for example, incomplete solder flux removal had led to the formation of dendrites (metallic ‘whiskers’) around the solder terminations.
In several other cases – almost all of the remaining failures - EPC’s engineers determined that the circuitry surrounding the GaN device had not been designed with sufficient attention to low inductances to match those of the device packaging. It is well documented that GaN FETs switch extremely fast: in these cases EPC found that the voltage transients, and ringing, generated had exceeded the absolute max values of the FETs.