The present invention relates to a resin molded semiconductor device, and particularly to improvements in the technology for bonding a wire for connection to a semiconductor pellet to which the wire is to be bonded.
In order for a semiconductor pellet to operate, inputs and outputs of electric signals must be taken out to the external units. For this purpose, aluminum electrodes (pads) on the pellet is connected (wire-bonded) to a lead frame on which the pellet is mounted using a connection wire such as gold wire.
Methods of wire bonding include thermocompression bonding, ultrasonic bonding, and a combination thereof. According to the thermocompression bonding method, in general, a ball (gold ball) on the tip of a connection wire (gold wire), formed by cutting the wire with a hydrogen torch, is attached onto a pad on a pellet with the application of heat and pressure. Specifically, in nailhead bonding the gold ball is held by the capillary and is bonded in a shape like a nailhead. According to the ultrasonic bonding method, the bonding is effected by applying a suitable pressure and ultrasonic vibration.
In such wire bonding methods, the bonding strength of the connection consisting of an alloy layer derived from an aluminum pad and a gold wire, for example, has been supposed to vary in proportion to the thickness of the tall-like portion at the tip of the bonding wire bonded to the pad on the pellet. Accordingly, user's demands have been for thick bonds.
In case of thin bonds, ultrasonic energy acts excessively on the pad and may cause damage. Therefore, thick bonds have generally been employed.
The technology of wire bonding has been described, for example, in Japanese Patent Laid-Open No. 5536/1986.