Page 58 - Wire Bonding in Microelectronics

Ultrasonic Bonding Systems and Technologies 37

(A) Thermocompression (Gold) TC Ball Bonding (Rarely Used In 2008)
Advantages Disadvantages
Excellent reliable Au-Au bonds High interface temperature
required (interface 300°C)
Simple 2+ parameter machine setup Very susceptible to contamination
All direction bonding from ball ∗ Large-bonding pads required
Autobonders are faster than wedge Forms plague with Al-chip pads
Negligible cratering compared to US Lower yield than US wedge or TS
and TS
(B) Thermosonic (Gold and Copper Wire) TS Ball Bonding (Dominant
Technology in 2008)
Medium interface temperature Somewhat susceptible to
(~150°C) contamination, >US but <TC
Lower ultrasonic energy (than US Some cratering potential, >TC
wedge)
All direction bonding from ball a 4-Parameter machine setup
Autobonders are fast
Excellent, reliable Au-Au bonds
Lower cratering than US wedge Forms plague with Al-chip pads
(C) Ultrasonic Wedge (Aluminum and Gold Wire) US (~5% Usage in 2008)
Least susceptible to contamination Autowedge bonders slower (<1/2)
than autoball bonders
Al bonds reliably at room temperature X-Y wire-pad orientation required,
(slows bonding processes)
Fine pitch, <50 µm Larger cratering potential, >TC, TS
Excellent, reliable Al-Al bonds Special tools (wedges) needed
for Au-Au, Cu, room temperature
bonding
Highest yield potential, <20 ppm 3-Parameter machine setup
Large-wire Al bonding Al Wire unreliable on Ag
Lowest loops available, <75 µm Au-Wire bonds poorly without heat

a After the ball bond is made, the loop can be formed in any direction; thus this is a non-
directional bonding method which is ideal for fast autobonders.

TABLE 2-1 Comparison of Wire Bonding Technologies