Adhesive die attach makes use of adhesives such as epoxy and polyimide to form a bond between a die and a package/substrate/another die.
The properties of an adhesive die bond such as thermal and electrical conductivity are primarily dependent on the adhesive material being used which is selected for the specific application. Adhesive die attach offers the following advantages:
The adhesive is applied by the die bonder to a substrate, package or a die by either dispensing a very small amount of it on the target location or by dipping a fine needle in the adhesive and coating the target location with it. The adhesive is applied very precisely as too much adhesive can cause it to overflow on to the die surface and cause contamination complicating later processes such as wire bonding. Careful control is needed as less than required adhesive will produce to narrow a bond line resulting in a weak bond with poor mechanical strength which may cause die cracking or die lifting.
Epoxy, polyimide and metal filled adhesives are commonly used materials for die attach. A range of adhesives are commercially available which can offer a broad spectrum of different characteristics to suit the specific application of the electronic device.
Epoxies generally have low curing temperatures than polyimides. They generally have poor electrical conductivity and may have low thermal conductivity. Their electrical conductivity is generally improved by adding gold or silver particles to the formulations whereas SiC and BeO particles can be added to an epoxy to improve its thermal conductivity. Polyimides have higher curing temperatures than epoxies and are highly rigid. Some adhesives require metal fillings to improve their thermal and electrical conductivities such as glass which is usually filled with silver particles.
At the Advanced Packaging Facility, a Tresky 3002 FC1-XP semi-automatic die bonder is used for adhesive die bonding. It is equipped with a precise pick and place, an epoxy dispenser and a needle for dip coating. In addition to the precise adhesive application and die placement capability, the packaging facility has a range of curing equipment for adhesives such as ovens, vacuum ovens, drying furnaces and UV belt conveyer. This allows us to use a broad range of adhesives for die bonding to suit the requirements of an application.