Bonding is the generic term for processes in semiconductor and assembly technology in which electronic components (e.g. an integrated circuit / IC) are mechanically attached and electrically contacted (see Chip on Board).
The connection is made on a carrier (substrate), such as a printed circuit board or a chip housing, using intermediate means such as solder, adhesive or thermal and pressure processes.
Bonding process
- Wire bonding: Electrical connection of a chip to its connections (pads) via ultra-fine wires (usually gold, aluminium or copper). The wires are connected with pinpoint accuracy using ultrasound, pressure or heat (thermocompression). The standard process for housing wiring.
- Chip bonding (die bonding): Mechanical fixing of the bare semiconductor chip (die) to a carrier (substrate, housing base). Fixation is achieved using adhesives (conductive for contacting, non-conductive for insulation) or solder (e.g. eutectic bonding). Used for mechanical stability and heat dissipation. S. Chip on Board(COB).
- Wafer bonding: Bonding two complete semiconductor discs (wafers) together. Enables complex 3D circuits, MEMS production or the encapsulation of sensors at wafer level (e.g. direct silicon bonding, glass frit bonding).
Wire bonding
Wire bonding can also be used to connect an IC to other electronic components or to connect one printed circuit board (PCB) to another. Wire bonding is generally considered to be the most cost-effective and flexible bonding technology and is used for the assembly of most semiconductor packages. Wire bonding can be used at frequencies above 100 GHz.
Suitable PCB surfaces for gold wire bonding are ENEPIG and electroplated soft gold. Chemical silver, chemical gold (ENIG) and ENEPIG are suitable for bonding with aluminium wire.
Ideally, wire bonding is carried out on clean metal surfaces (bond pads) of the semiconductor component or the carrier material. In practice, however, these surfaces are often contaminated, which can lead to the connection not adhering to the pad (non-stick on pad, NSOP for short) or the bond connections becoming detached (so-called ‘lifts’). Both problems lead to failures, production downtimes and quality losses in production. Targeted plasma treatment in advance can prevent both NSOP and lifts and thus significantly improve quality.
In wire bonding, a distinction is made between ball bonding and wedge bonding.
Ball bonding
In ball bonding, the tip of the wire is melted by an electrical discharge and a ball (free air ball) is formed. The ball is bonded to a semiconductor element or a pad using mechanical force, ultrasonic energy and heat. The connection to an external connection is made by a seam connection.
Wedge bonding process
In the wedge bonding process, no ball is formed, but the connection is made only by mechanical force and ultrasonic energy. It is mainly used for power semiconductors.
