Continued improvements in wire bonding
technology have resulted in new packages with lead counts of up to 304 leads. ASICS and
VLSICS are increasing the lead counts and the density of the new packages. This results in
die pad sizes, lead widths and the center to center spacing (pad pitch) becoming smaller
and smaller. Lead pitches are also being reduced. However, due to the wire approaching the
lead at a very low angle, the lead pitch is typically not considered a critical capillary
Figure 41. This drawing
identifies the primary design constraints.
Today's bonders are equipped with pattern
recognition systems that allow them to bond advanced packages at a rate of up to 9 wires
per second. The capillary must be designed to allow clearance into bonding areas without
damaging the previous bonds or adjacent loops.
Fine pitch (0.006in/152µm or less) ball bonding has become common as applications approach
pad pitch requirements of 0.004in./102µm and below.
algorithms utilize sophisticated bonder head movements that provide looping profiles that
produce the clearance required for fine pitch bonding. This drawing shows how the wire
adjacent to the cone of the capillary is the critical loop height even though the overall
loop height is considerably higher.
Bonding application elements to be
considered in the design of the capillary include:
size and pitch
adjacent to capillary
span or loop length
The metallization material and thickness on both the die and lead, (Is it considered to have
good or poor bondability?)
Is the die
higher or lower with respect to the lead bonds?
Figure 43. This photo shows fine pitch low loop bonds. The pad pitch can be
reduced by forming loops with the wire bending just at or above the ball bond. This region
is commonly referred to as the neck of the ball bond.
(Photo courtesy ASM Corporation)
Figure 44. Many fine pitch
applications incorporate staggered die pads. In the photo above, the row of pads closest
to the pad's edge are low-loop bonds. The row of pads bonded directly behind are higher
loop bonds. On some of the new packages lead bonds are on two tiers, often referred to as
a multilevel package.
(Photo courtesy Kaijo Corporation)
the BASIC CAPILLARY BONDING and DESIGNdocument in