Free-air ball formation and deformability with Pd coated Cu wire

Abstract

With 20 µm diameter PCC wire, spherical (well-shaped) free-air balls (FABs) were obtained in both forming gas and N 2 at flow rates between 0.25-0.75 l/min and 0.4-0.5 l/min, respectively. With Cu wire, in comparison, sperical FAB are obtained in forming gas with flow rates between 0.25 and 0.5 l/min while in N 2 gas, FABs are always pointed or golf-clubbed (mis-shaped). Using a shielding gas with Au wire makes the FABs mis-shaped.The FAB deformability is measured as the amount of deformation under a given load. Au had the highest deformability. The FABs made with PCC wire in N 2 had generally the same deformability as Cu FABs in forming gas. The force required to achieve a pre-defined deformed ball height (target) is named "force for target deformation", F TD , and set to half the FAB diameter. Compared to "deformability", the F TD method is more similar to the standard tensile or compression tests that determine yield strength. Deforming a PCC FAB obtained with 0.4 l/min N 2 to the target ball height requires 615 ± 32 mN, a value not significantly different from that for a Cu FAB obtained in 5 l/min forming gas. For comparison, the target deformation requires 394 ± 16 mN for a Au FAB.

Effect of EFO parameters and superimposed ultrasound on work hardening behavior of palladium coated copper wire in thermosonic ball bonding

“…where s = 50.2 mN/lm is the calibration factor [16]. The standard error of the H DEF is also increased with increase of I EFO , similar to the results obtained previously [12].…”

“…The previously reported on-line method is used to evaluate FAB deformability by measuring FAB height (H FAB ) as illustrated in Fig. 1a and b, and deformed FAB height (H DEF ) [11][12][13][14][15][16].…”

“…This result is similar to the results obtained previously [11,12] where deformability of constant diameter Cu FABs increased with the increase of I EFO . In [16], the correlation between force-to-targetdeformation and H DEF is studied. Similarly here, the increase in deformability is expressed by the drop of deformation force require to obtain the same amount of deformation,…”

“…The values of H FAB and H DEF are obtained. In step 2, the correction factor is extracted from the relationship between mean values (without outliers) of deformed ball height versus a range of H FAB and applied to find H DEF (corrected) as described in [16].…”

Simulation of Ultrasonic Stress During Impact Phase in Wire Bonding

“…[1][2][3][4][5][6] One of them is to use ultrasound during impact, i.e. typically a reduced level of ultrasound amplitude during touchdown and initial deformation of the ball.…”