Characterization of the mechanical properties of LTCC ``Green Tape``{trademark} for the MC4352 MET

Abstract

During the qualification of Low Temperature Cofire Ceramic (LTCC) as an enabling WR packaging technology for manufacturing the MC4352 (MET), issues pertaining to the mechanical performance of the DuPont 951 ``Green Tape{trademark}`` tape were investigated. Understanding the fundamental mechanical performance of the DuPont 951 substrate material, including the effect of surface metallization in STS environments, is required to determine MC4352 survivability. Both fast fracture and slow crack growth behavior were characterized for the MET configuration. A minimum stress threshold of 6.5 Kpsi for slow crack growth was established for substrates containing surface conductors, resistors, and resistor glaze. Finite element analysis was used to optimize the MET substrate thickness and to design the supporting structures to limit mechanical loading of the populated substrate below the slow crack growth threshold. Additionally, test coupons that failed during environmental testing are discussed. The root cause of electrical failures was attributed to solder leaching of the thick film metallization. Changes to solder pad configuration were incorporated to reduce the solder-metallization intermetallic from reaching the substrate interface. Finally, four-point bend tests revealed that the YAG laser approach for sizing LTCC substrates induced flaws, which substantially reduced the overall strength of the test samples as compared to samples sized using a diamond saw.