Gold wire bonding is an established process in semiconductor technology for creating electrical connections between the microchip and the connections of the housing (e.g. lead frame or substrate). A fine gold wire is precisely welded onto the contact surfaces (bond pads) using thermal energy, pressure and ultrasound. Due to its excellent conductivity, corrosion resistance and malleability, gold is particularly suitable for reliable and durable connections in power electronics and optoelectronics.
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Bonding with gold wire Process sequence
Gold wire bonding is carried out as a thermosonic process on automated bonding machines. A fine capillary needle guides the gold wire precisely to the first bonding pad. The simultaneous effect of ultrasonic energy, contact pressure and temperature (typically 120-220 °C) breaks down the oxide layer on the metallisation and creates an intermetallic bond between the gold and the pad metallisation. After the first bonding point, the wire is guided into a defined loop and attached to the second pad (e.g. substrate or lead frame). The wire is then torn off using a clamping mechanism, leaving a controlled wire remnant for the next bonding cycle.
Characteristics of gold as a bonding wire
Gold (Au) is used as a bonding wire material due to its specific physical properties. With an electrical conductivity of around 45 × 10⁶ S/m, gold ensures a low ohmic power loss in the connection. Its chemical resistance is crucial for reliability: gold does not form a native oxide layer and is highly resistant to corrosion from environmental influences. The low Vickers hardness (approx. 60-100 HV) and high ductility enable defined deformation of the wire during the bonding process and the realisation of low loop heights without material fatigue.
Influence of surface contamination on gold wire bonding
The quality of the bond connection is largely determined by the condition of the pad surfaces. Organic residues (e.g. from chip production) or oxide layers on the aluminium metallisation reduce the surface energy and hinder intermetallic phase formation. This manifests itself in a lack of adhesion(non-stick on pad / NSOP) or in delamination (lifts) at the interface. To avoid these defects, a plasma process is used before bonding: Ion bombardment (e.g. argon or oxygen plasma) is used to remove contamination and activate the surface, creating reproducible adhesion conditions.
Quality assurance in gold wire bonding
The validation of bonded joints is carried out using destructive mechanical tests in accordance with defined standards (e.g. MIL-STD-883 or DIN EN 62137). In the wire tensile test, the bonded wire is loaded using hooks until the material separates; the measured breaking force must exceed a specific limit value. The ball shear test quantifies the lateral strength of the first bond point by using a shearing tool to press the bond ball parallel to the pad surface. The resulting shear forces provide information about the quality of the intermetallic phase formation and are used for statistical process control (SPC) in series production.
Gold wire bonding FAQ
Gold wire bonding (also known as gold wire bonding) uses wafer-thin gold wires (approx. 15-75 µm thick) to create electrical connections between a microchip and the housing (lead frame) of a printed circuit board. It is the standard procedure for connecting integrated circuits to the outside world.
Gold offers decisive advantages: It is extremely corrosion-resistant (it does not oxidise), can be easily deformed even at very low forces and temperatures and offers excellent electrical conductivity. This makes the connection extremely reliable and durable.
The process is thermosonic. This means that a combination of heat (usually between 150°C and 250°C), ultrasound and pressure is used. The gold wire is passed through a needle (capillary). A ball is melted at the end of the wire using a flame or spark, which is then pressed onto the chip connection (pad). The second connection (to the housing) is then made as a wedge bond.
Yes, common alternatives are copper or aluminium wires. Copper is cheaper and has better electrical conductivity, but is harder and requires more energy for bonding. Aluminium is often used for power applications. Despite its higher price, gold is mainly used where maximum reliability is required or the chip pads are very sensitive, as the bonding process with gold is particularly gentle on the material.
Gold wire bonding is typically used in high-frequency technology, aerospace, medical technology and automotive applications. It is ideal for all assemblies that have to withstand extreme temperature fluctuations or where failure due to corrosion must be avoided at all costs (e.g. in LED modules, sensors or high-performance processors).