Distributed temperature profile in flip chip measured by optical-frequency-domain reflectometry with telecom fiber

The electromigration problem in flip chip becomes one of the focuses of the microelectronic device durability. Temperature is a key parameter for the electromigration life evaluation, due to the occurrence of material structure defect will be accelerated with the rise of temperature. But it is difficult to measure the temperature inside the flip chip packaging structure of large-scale integrated circuits directly with traditional test means. In this paper, a distributed temperature profile test method in interconnect solder joints flip chip has been present, which is measured by the optical-frequency-domain reflectometry (OFDR) with telecom single model fiber. The most distinguishing feature of this method is that the thin flexible optical fiber can directly penetrate into the flip chip from the position of the interconnection solder joint to realize the distributed sensing of the temperature field of the solder joint inside the chip. The modulated linear sweep light directly injected into optical fiber and transmitted forward, and a certain interference pattern formed by back Rayleigh scattering is generated. When the temperature environment of the optical fiber changed, the interference pattern formed by back Rayleigh scattering will change accordingly, which will cause the wavelength shift of the interference pattern, that is similar to the fiber grating effect. Thus, the distributed temperature change can be demodulated from the wavelength shift. The experimental results show that this method can realize the distributed measurement of the internal temperature of flip chip directly, and provides a novel solution for more accurate evaluation of electromigration effect.