Aluminiumwire bonding is an established contacting process in semiconductor and power electronics in which aluminium wires are used for the electrical connection between chip and housing or printed circuit board.
Process and properties
In contrast to gold wire bonding, the connection in aluminium wire bonding is purely ultrasonic-based (thermally assisted, but usually without additional heat). The wire is welded to the contact pad under pressure and ultrasound - a process known as ultrasonic wedge bonding. Typical wire diameters are between 25 µm and over 500 µm.
Suitable PCB surfaces
Choosing the right PCB surface is crucial for reliable aluminium wire bonding. The following are suitable:
- Immersion Tin - Provides a good bondable, planar surface, but requires careful process control due to limited storage stability.
- Immersion Gold - Also known as ENIG, provides a well controllable bond surface, but the gold layer must be thin enough to ensure a strong bond with the underlying nickel layer.
- ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) - The preferred surface for demanding bonding applications. It combines the advantages of a diffusion-barrier palladium layer with a bondable gold surface and offers maximum reliability, especially for mixed-metal bonding (aluminium on gold).
Areas of application Aluminium wire bonding
Aluminium wire bonding is mainly used where high currents flow or large areas need to be contacted. Typical applications are
- Power semiconductors (IGBTs, MOSFETs, diodes)
- Power modules in electromobility
- High-current applications in industrial and drive technology
- Large chip areas where several bond connections are connected in parallel
Advantages of aluminium wire bonding compared to gold wire bonding
- More cost-effective: aluminium is significantly cheaper than gold
- Higher current carrying capacity: possible due to larger wire cross-sections
- Good electrical conductivity: Aluminium conducts almost as well as gold
- Proven technology: Very robust and reliable process
Aluminium wire bonding: Disadvantages and challenges
Aluminium tends to oxidise on the surface, which can make contacting more difficult. The wire is also more brittle than gold, which can lead to cracks under mechanical stress. Aluminium is rarely used in high-frequency technology due to its lower conductivity compared to gold.
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