Tests die-shear

The push-off shear test or die shear test is normally done by pushing off a bump bonded to the film. The force to shear the bump from the surface is measured with a load cell. This test is commonly used in the microelectronics industry. 

Another shear test was developed and used by Herrmann. Figure 46 is a schematic representation. The apparatus was conceived such that briquettes produced under vacuum in an experimental piston press could be tested within the vacuum chamber, where (1) is the lower (press) piston and (8) is the upper piston. The press die (4) is fitted with a shear slide (9) under a cover plate. To neutralize the radial stresses caused by and depending on compaction pressure, the briquette is first ejected from the die (4) and then refitted with an insertion force of 300 N. Then, the entire shear cell is removed from the press table by... 

There are destructive evaluation techniques that can also be used to find defects. MetaUo-graphic cross sections provide a means to inspect the internal structures of the solder joints, components, and circuit boards, albeit in only a single plane at a time. Mechanical tests (die shear, puU tests, etc.) can also be used to identify defects. However, because these approaches are destructive, and because they require long lead times to obtain results, they are generally inapphcable for real-time process control. They are better suited for process development or failure analysis activities. 

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... 

As stated earlier, adhesion is a major concern in electronic applications involving thin polyimide films either coated on hard substrates or laminated with metal ribbons. In these cases, neither lap-shear nor die-shear techniques allow the determination of the adhesion strength this can be done by using either the 90° peel test or the island blister test whose principles are sketched in Figs 12.26 and 12.27. The 90° peel test provides reliable data for the measurement of practical adhesion, especially useful for comparing the effect of surface treatments on the interfacial adhesion. The standard peel test procedure has been modified to determine the adhesive strength of thin polyimide films coated onto 10-cm silicon wafers. The equipment illustrated in Fig. 12.26 maintains a 90° peel effort during the test conducted at room temperature with a constant rate of crosshead displacement of 2 mm min . ... 

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