Semiconductor Packaging:  Die Attach Process

Die Attach (also known as Die Mount or Die Bond) is the process of attaching the silicon chip to the die pad or die cavity of the support structure (e.g., the leadframe) of the semiconductor package. There are two common die attach processes, i.e., adhesive die attach and eutectic die attach.  Both of these processes use special die attach equipment and die attach tools to mount the die.

Adhesive Die Attach

Adhesive die attach uses adhesives such as polyimide, epoxy and silver-filled glass as die attach material to mount the die on the die pad or cavity. The adhesive is first dispensed in controlled amounts on the die pad or cavity. The die for mounting is then ejected from the wafer by one or more ejector needles.

While being ejected, a pick-and-place tool commonly known as a 'collet' then retrieves the die from the wafer tape and positions it on the adhesive. All of the above steps are done by special die attach equipment or 'die bonders' (see Fig. 1).

      

Fig. 1.  Two examples of die attach machines

The mass of epoxy climbing the edges of the die is known as the die attach fillet.  Excessive die attach fillet may lead to die attach contamination of the die surface.  Too little of it may lead to die lifting or die cracking.

Fig. 2.  Photo shows the D/A adhesive as the grainy

material between the die and the die pad; note the

bond line thickness and the fillet of the adhesive

Another critical aspect of adhesive die attach is the ejection of the die from the wafer tape during the pick-and-place system's retrieval operation. The use of inappropriate or worn-out ejector needle and improper ejection parameter settings can cause die backside tool marks or microcracks that can eventually lead to die cracking.

See also: Die Attach Failures

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