– Prevents wire shorts and enables cross bonding.
– Uses existing platforms and lowest-cost packaging infrastructure (wire bonding).
– Is suitable for multi-row, ultra fine pitch and area array wire bonding.
– Is suitable for systems in package, stacked dies and side-by-side chip-to chip bonding.
– Enables flexible routing, simplified substrate and packaging of small dies.
– Enables complex package designs and improves the yield of high-density packaging.
– Allows use of the Z dimension and wasted space created by parallelism of bare wires.
– Enables wire bonding with insulated fine gold or copper wire and low-k pad structures.
– Damaged wire with a hole burned in the insulation layer.
– Non-sticking on lead.
– Low-stitch pull readings.
– Frequent machine stoppages.
– “Kissing effect” after temperature cycling.
– Insulation layer pushed out to one side of the wire during moulding.
c) Solutions and findings
– Provide a ground adjacent to the free end of the insulated wire with a conducting capillary.
– Add a ground at a spool end of the wire at a far side of the insulated wire path from the free end.
– Form a bump on the second wire bond, offset by a distance of about one half of a diameter of the bump.
– Provide a special capillary movement to achieve mechanical abrasion.
– Use a special surface-treated capillary for effective tearing of the insulation layer.
– Choose a proper combination of insulation thickness, melting and coating temperatures, capillary and wire bonding parameters.
– Use shorter EFO gap and lower-EFO current compared to bare wire to achieve optimal FAB quality.
– Provide a coating material that easily cracks only at the stitch bond with available bonding parameters.
– Apply high-initial bonding force with low-ultrasonic energy, apply high-initial impact during touch-down, and provide slight scrub motions to promote coating removal.
– Use a smaller capillary hole, which does not scrape the coating during looping. – Use a smaller capillary outside radius, which maximizes the capillary area contacting the stitch bond.
– Use a matte capillary tip.
– Move the capillary tip with the wire over the stitch bond pad.
– Roughen the outer surface of the capillary tip.