The ability to perform in situ testing and characterization of both integrated circuits and their interconnecting substrates in complex multi-chip packaging structures is becoming increasingly important as the packages become smaller. An electro-optic probing instrument makes point-to-point electric field measurements internal to microwave circuits instead of limiting the information to that gathered at the input or output ports of a circuit. Although this technique is popular and polyimide is an increasingly popular organic polymer used in advanced packaging applications for high-speed circuits such as multi-chip modules (MCMs), no one has extended the application of electro-optic probing to circuit structures on polyimide and compared the results to more conventional substrates used for electro-optic probing such as GaAs and InP to demonstrate the potential to non-invasively probe circuit structures that are buried in central layers of an MCM.
The present invention, from the Johns Hopkins Applied Physics Lab, improves multi-chip module (MCM) testability by using a new technique to detect on-substrate electric field strength. The invention employs a non-invasive, laser-based instrument to probe the MCM structures fabricated with poled polyimide interlayer dielectrics and thin film metallizations on silicon carriers. Circuit element characteristics of MCMs are probed with laser to detect electric field strength. The electrical, mechanical and optical properties of the electro-optical dielectric layers are determined to investigate the effect of the poling and processing operations on the efficacy of the polyimide as both a dielectric layer and an electro-optic material suitable for laser probing.
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