Die-shear strength

US 5,204,399 (American) 1991 Thermally conductive thermoplastic polyimide film die attach adhesives and their preparation National Starch and Chemical Investment Holding Corp. R Edelman Adhesive formulations having excellent die shear strength A polyimide-siloxane was prepared from aromatic amines, bis aminophe-noxybutylsiloxane and aromatic dianhydrides... 

Id meet to qualify and assure a reliable part. This assignment, undertaken by NASA MSFC in 1974, led to the first document for the procurement of adhesives to be used in hybrid microcircuits. After further coordination and revisions, this initial document was formally released as a specification in 1978 and revised in 1982 as NASA MSFC-SPEC-592, Specification For The Selection and Use of Organic Adhesives in Hybrid Microcircuits." For the first time, the critical requirements for ionic contaminants, electrical resistivity, die-shear strength, corrosivity, and outgassing were specified. Work on the development and evaluation of adhesives continued into the mid-1980s and, as a result, several commercially available adhesives were qualified." ... 

Lap shear test conditions are not really convenient in electronics involving small dice and two substrates with different thermal expansion coefficients (CTE). The stresses generated during the cure cycle by this CTE mismatch account for possible crack formation and delamination, which in turn may degrade the adhesive strength. The die shear strength method consists in the measurement of the force required to shear the die from the chip carrier. Although any die size can be used, a standard technique is to bond 1.27 X 1.27 mm non-functional silicon dice to silver-plated lead frames. 

For solvated polyimide adhesives the lap shear strength test is not appropriate because the large overlap bond area prevents the full release of the solvent [61]. The authors underline that the die shear strength data are also highly scattered and... 

Figure 46 Variation of the die shear strength of silver-filled epoxy (EP) and polyimide (PI) adhesives as a function of ageing time at 150, 250, and 300°C. (adapted from Ref. [134], Copyright 1977 IEEE.)...

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