Beschreibung
Ultrasonic (US) wire bonding is a very complex process during which different
mechanisms occur at different locations of the bonding interface. The change of these
local mechanisms stays unclear. In this study, a 3x4 piezoceramic-based sensor array
was created to in-situ measure the local tangential forces at different locations of the
interface; by analyzing these forces, corresponding mechanisms were derived. The
results showed the largest tangential forces on the two central columns, the smallest
tangential forces on the columns at the four corners, and the largest expansion of the
contact area on the remaining six columns (peripheral columns). In the beginning of
the bonding process, a “1st fast increase – plateau – 2nd fast increase” of tangential
force stage was detected on nearly all columns. In the following process, the tangential
forces on the central columns decreased due to the decrease of the local normal
forces; later, the decrease could be compensated by microweld formation. As the local
normal forces increased, a gradual increase occurred on the peripheral columns. This
increasing stage could also occur on the corner columns while the increase was much
smaller. The specific curves at different moments exhibited complex features
consisting of static and sliding friction, microweld formation and breakage. Compared
to central columns, sliding friction played a more dominating role on peripheral and
corner columns. These findings deepen the understanding of mechanisms occurring at
different locations of the bonding interface and provide potential to enhance the
bonding process via changing the substrate structure.
