Page 164 - Wire Bonding in Microelectronics

Gold-Aluminum Intermetallic Compounds 141

1µ

FIGURE 5-5 An SEM photograph of an Au wire wedge-bond to Al metallization,
aged at 450°C for 10 min, illustrating the voids, indicated by arrows, which
form around the periphery of the bond. (After Philofsky [5-1, 5-2]; © 1970,
with permission from Elsevier.)

FIGURE 5-6 A closeup of “ultimate” Kirkendall voids around the perimeter.
The gold ball bond was in the center. It dewetted after thermal stress and fell
off. (After Gerling [5-8].)

than either Au or Al; thus, as the compounds form under the bond
(during the first hundred hours or so) the initial resistance increases
by about 8 mΩ [5-15]. This initial resistance increase (< 1000 h) had an
activation energy of 0.4 eV. ∗ Such slight increases are not accompanied

∗ This reported activation energy for initial resistance increase is lower than others
reported in Table 5-12 but this author (GGH) considers the lower value, resulting from
a well-designed experiment to specifically study this increase, to be more accurate.