The bonding and packaging of an integrated chip provide connections to the 
outside world. Usually, an IC can be packaged individually or incorporated 
into a hybrid circuit. Packaging the circuit give it some mechanical and 
environmental stability. Additional tests are carried out for chip electrical 
and mechanical behaviors after it is packaged. The two common bonding techniques 
are thermocompression bonding and ultrasonic bonding.The following is a 
discussion of  ball bonds and stitch bonds.

Gold is often used as interconnection material because it is easy to weld to 
silicon by applying enough heat and pressure simultaneously. In order to 
achieve tight contact between the bonding surfaces in thermocompression bonding, 
a very small mechanical scrubbing action is used. Generally, the process takes 
place in a nitrogen environment to prevent oxidation. One of the most often used 
equipment for thermocompression bonding is the nail-head bonder (See Figure 4). 
First, a gold wire with a sphere at its head is fed through the capillary. It 
is then lowered after being aligned with the bonding pad on the die. To form a 
connection, the god sphere is pressed against the die for few seconds to form 
a weld. The temperature during the process is maintained at 
around 300 Celsius. After connection is established on the bonding pad of die, 
the capillary raises the gold to form a lead. Finally a hydrogen torch is used 
to break the wire.



Figure 4: Precedures for making a ball bond.

The alternative to ball-bonds is stitch bonds.  The process is similar (see 
Figure 5), and the bond is made by either by applying heat and pressure or 
ultrasound energy. The wire is fed through the capillary the wedge tool. The 
tail of the wire extends from the hole and is placed parallel to the bonding 
surface. Pressure from the wedge forces the wire onto the bonding pad. The setup 
is similar to the making of a ball bond. In general, the nail-head bonder that 
makes ball bonds has been found to be considerably faster and results in stronger 
bonds.  



Figure 5: Precedures for making a stitch bond.

A few of the common packaging format for IC chips are dual-in-line package (DIP), 
TO-can types, and flat packs. DIPs are most popular among others. They are easy 
to handle and convenient to use in printed circuits. The socket of DIPs can be 
made from ceramic or plastic. Ceramic DIPs have a gold-plated ceramic substrate 
for chip attachment. Either glass or epoxy seals the lid. The TO-can types have 
the die bonded on a gold-plated header. The cap is then attached by resistance 
welding. It is at this stage that the concept of mass production breaks down. Once 
chips are separated into individual pieces, the production cost is very large. 
Therefore, packaging micro-circuits takes up a major fraction of over-all cost 
of manufacture. 

Figure 6: A ball bond made by thermocompression.

Figure 7: A stitch bond made by ultrasound.