Many new packages are incorporating pad
pitches of 0.004in./102µm and less. These new fine-pitch designs limit the
accessibility of a capillary to form a ball bond. Without reducing the
capillary tip diameter to below 0.005in.127/µm many applications cannot be
bonded successfully. When the tip diameter is reduced to this size and
smaller, the resulting length of the lead bond becomes shorter. When this
occurs, non-sticks on the lead or poor pull strengths may result.
With wedge bonding, the lead bond is not
degraded as the pitch become narrower. The average small wire wedge has a
foot width (W) of 0.004in./102µm. A "W" dimensions of 0.003in./76µm or
smaller may be called out if necessary. The 0.003in./76µm W allows for
bonding in fine-pitch packages. Wedge bonding is a slower process, but with
the continued miniaturization of packages and die, it offers a viable option
to capillary bonding.
The two wedges above vary in the size of the W dimension. The right wedge has the standard
W=0.004in./102µ, the left wedge has the W=0.003in./76µ. This modification can be
requested by adding "W=003" to the end of the p/n.
These two drawings show the wire profile produced from typical looping parameters used for
wedges. Note that the already bonded wire does not collide with the side of the wedge
because the apex of the loop is behind the wedge. Since the majority of the looping
profiles are at a low angle, the primary fine pitch problem is clearing the adjacent bond.
This drawing shows the primary problem with fine-pitch wedge applications. An option to
provide clearance for the adjacent bonds is to call out a smaller W dimension as shown in
The 45° side chamfer modification may also be
used on fine-pitch wedge applications. The primary benefit of the 45° side
chamfer is the wedge maintains the majority of its mass.
This allows for transferring ultrasonics
more efficiently and the 45° side chamfer can be added to the maxiguide-style
wedge without weakening the guiding slow walls.
This drawing shows a wedge that has the 45° side chamfer. This modification can be
requested by adding "45SC (W=specify)" to the end of the p/n.
the FINE PITCH
WEDGE BONDING Document (in