Die bonders are made for the purpose of attaching a silicon chip to a die pad of the leadframe of the semiconductor package. They use epoxy dispensing tools to put die attach material like silver-filled epoxy on the die pad. They can be purchased in a standard body style made to fit most die bonders or customized should specific features be required. Die bonders are usually equipped with adaptor heads, so the fast dispensing of tool tips is made easy.
There are two different types of die bonding processes: adhesive die bonding and eutectic die bonding. Adhesive die bonding uses adhesives, as its name would suggest, such as polyimide and epoxy. Die bonders are used to mount the die on the die pad. First the adhesive is dispensed in preset amounts on the die pad and then ejects the die for mounting from the wafer through the use of one or more ejector needles. A tool called a collet then retrieves the die from the wafer tape. It positions it on the adhesive.
The other type of die bonding, eutectic die bonding, is used for hermetic packages. Its name refers to the alloy used to bond the die to the cavity. Eutectic alloys have the lowest melting point of any possible alloy, which makes it the most commonly used die bonding alloy in semiconductor packaging. While the package is being heated, a gold preform is placed on top of the die pad. The die is then mounted over the preform and silicon from the die diffuses into the preform, forming a gold-silicon alloy. More silicon then diffuses into the gold preform, increasing the silicon-to-gold ratio until the eutectic ratio is achieved. The die bonding temperature must be reasonably higher than the melting point of silicon, 363 degrees Celsius, in order to achieve its eutectic melting point.
Die bonders can be used for dispensation or may be deposited on the die pad by stamping with an epoxy stamping tool. These can create various patterns of epoxy on the pad, such as a dot matrix, and all ensure a consistent amount of epoxy is deposited on the die pad each time it is used.