Unwanted microwave oscillator frequency shifts induced by bipolar junction transistor die attach

Two space qualified frequency synthesizers were found to exhibit noise bursting during testing, following X-ray examination, in July 1994. An inter-company, cross-functional investigation team was formed to determine root cause because of the potential impact on flight hardware. The source of the problem was isolated to poor bonding of a bipolar junction transistor (BJT). The root cause of the noise bursting phenomena was not positively identified, but there is strong correlation to the die attachment process of the BJT in the oscillator of the VCO and a soft correlation with the BJT environment.