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|Effects of Probe Marks on Shear Test of Copper Ball Bonds in Two Pad Aluminum Thicknesses|
|Keywords: wirebond, copper, shear test|
|Motivation for this work is to provide relevant data for a revision of industry standard JEDEC JESD-B116 Wirebond Shear Test Method, and JESD-47 Stress-test-driven Qualification of Integrated Circuits, to add specification limits for copper (Cu) ball bonds. This paper continues the work of reference , evaluating shear test results of Cu ball bonds over a variety of probe marks in two different pad aluminum (Al) thicknesses (0.8µm and 3µm). The shear tool movement direction relative to the bonding hardware ultrasonic generator vibration orientation is one effect on shear force value. The presence of invasive probe marks on thick Al bond pads lowers shear force results, with directionality of the probe scrub mark having an effect as well. Lower values of shear force imply reduced Cu bond reliability. This paper further investigates the physical factors relating to reduced shear force, to explain how the shear test may be employed to best indicate the bond reliability. Scanning electron micrographs (SEM images) and optical microscopic image analysis of Cu bonds, bond contact areas and Al “splash” are studied for correlation with the shear test results. Percent intermetallic coverage of bond contact areas decrease when invasive probe marks are present beneath the bond, which in turn reduces the shear force. Probe mark features are studied as well to discover the characteristics of greatest influence on % IMC coverage and shear test values in each of the pad metal thicknesses.|
|Priscila Brown, Mechanical Engineering Student
Brigham Young University - Idaho