Tape automated bonding is a technique used for mounting a die onto a printed circuit board with the use of polymer tape. The die is able to connect to external circuits, if the tape does not already have the circuit attached to it. Through this method of bonding, the bonding sites are connected to the tape conductors so that these circuits are easily accessible. Holes are punched into the tape in order to ease the bumps of the die into their places as well as this direct connection to the circuits, thus permitting an outer lead bond, as opposed to the inner lead bonds which connect the die and tape.
In tape automated bonding, these holes are created through the use of a film. It is moved so that the lead of the tape can be soldered in order to affix appropriately to the die. The remaining chip is then encapsulated in epoxy to allow smoother flow of electricity. The conductor traces of the tape are also cantilevered over the holes so that the bumps of the die and tape meet.
There are two processes by which a tape automated bond can be created. The first, thermosonic bonding, sees that once the bumps of the die are positioned so that the pre-marked tape can fit over them, each bonding site is connected to the lead of the tape point by point. The second type of bond, thermocompression bonding, utilizes a combination of processes at the same time to bond lead and bumps simultaneously. This can also be referred to as gang bonding, in which ultrasonic energy is used. This method is the more commonly used method of bonding.
There are a few different guidelines used in tape automated bonding. Polymer tape is typically 35, 40, or 75 mm in length. It is normally single-sided, although there are two types of metal that can be used. The patterns on the tape are placed there using photolithography. This allows different yet necessary materials to be deposited onto the tape, allowing circuit connections to be made possible.
Tape automated bonding is one of the preferred methods of bonding available to the semiconductor industry. This is for many reasons, including the need for less gold, smaller bonding pads, shorter production time, more uniformity from bond to bond, better electrical connection and more. There are some disadvantages as well to this method, however, due mostly to the time and cost to manufacture each specific bond. Still, in environments where a smaller bond is desired, it bests conventional methods. It can also be most cost-effective when a high production yield is achieved. This can make this form of bonding affordable.