Wire Bonding for advanced microchip packages with gold wire links

Wire Bonding is the most dominant internal interconnection technology in semiconductor packaging. Currently, about 75% to 90% of the world's semiconductor packages utilize this method. In essence, it uses metal wires, thinner than a human hair, to "weld" the chip to the external circuit at the atomic level through energy forms like heat, pressure, and ultrasound, thereby establishing electrical pathways.

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Ball Bonding vs. Wedge Bonding

There are two fundamentally different methods, varying significantly in shape, flexibility, and application:

	Ball Bonding	Wedge Bonding
Core Principle	The wire tip is melted into a ball (Free Air Ball, FAB) by a high-voltage spark, which is then pressed onto the pad.	No ball is formed; the wire is pressed directly onto the pad using pressure and ultrasound.
Bond Shape	First bond is a ball; second bond is a fishtail/crescent shape.	Both bonds are wedge-shaped.
Spatial Freedom	High. The wire feed direction can be freely adjusted after ball formation, suitable for high-density layouts.	Low. The wire must lie in a straight line; flexibility is limited.
Share & Application	Absolutely dominant (>90%). Primarily used for gold/copper wire.	Mainly used for aluminum wire or devices requiring very low loop height.

Material Selection: The Gold, Copper, and Silver

The technology is categorized into three generations based on the energy applied:
◈ Thermocompression Bonding (Earliest): Relies solely on heat (~250-300°C) and pressure. Extremely sensitive to surface cleanliness; largely obsolete.
◈ Ultrasonic Bonding (Mainstream Foundation): Applies ultrasonic vibration at room temperature. Friction generates heat and removes oxides, enabling "cold welding."
◈Thermosonic Bonding (Current Mainstream): A combination of heat (~100-150°C) + ultrasound + pressure. Low temperature and low pressure protect the chip while forming reliable bonds; over 90% of ball bonding uses this method.

Energy Source: Thermocompression, Ultrasonic, and Thermosonic

◈ CAF Resistance: Conductive Anodic Filament (CAF) is a type of internal short circuit caused by humidity. Automotive boards must use special resins to prevent this.
◈ Creepage and Clearance: Especially in Electric Vehicles (EVs), boards must have wide physical gaps between high-voltage (800V) and low-voltage (12V) sections to prevent arcing.
◈ Conformal Coating: Most automotive boards are sprayed with a protective "skin" (silicone or acrylic) to guard against salt, moisture, and fuel vapors.