An device case temperature closed-loop control system during burn-in test

Abstract

Burn-in is used to force the failure of marginal devices before using into products. Usually devices are placed in a burn-in oven. The burn-in time mainly depends on the device junction temperature, so the junction temperature control is very important during burn-in test. Usually the oven ambient temperature is closed-loop controlled during burn-in, but the device junction temperature is open-loop, not accurately controlled. Consequently some devices may be at a lower temperature (junction temperature lower than required) and others may be at a higher temperature (junction temperature higher than required) in the same burn-in oven. Latest silicon processing technology results in significant power variations between chips produced even on the same wafer, thus some devices with higher power dissipation will be burned at a hotter temperature, which means a potential for thermal runaway. At the same time, high leakage currents that are rapidly increasing with technology scaling become more crucial during burn-in test with stressed voltage and temperature applied, and excessive leakage may lead to higher junction temperatures, possible thermal runaway. Thermal runaway means temperature increases uncontrollably and can result in damage to the socket. To solve above problems and avoid thermal runaway, each device junction temperature should be stable during burn-in test. Controlling the device junction temperature accurately by each socket is a solution. This paper describes a closed-loop device case temperature control system, which can ensure that the device junction temperature is stable. Each socket becomes a controlled environment during burn-in test for a wide range of influences, for example, process variations and ambient temperatures. Once disturbance occurs, for example, the burn-in oven temperature change, the control system with better dynamic response can get the case temperature quickly back to stable.