Wirebonding Overview Animation

Summary

The video explains three main wire bonding techniques used in semiconductor packaging: ultrasonic bonding, thermo-compression bonding, and thermosonic bonding. Ultrasonic bonding uses pressure and vibration for cold welding, best for aluminum wire and pad connections. Thermo-compression bonding involves high temperatures and is ideal for gold wires, though it can damage circuits. Thermosonic bonding combines heat, pressure, and vibration, allowing for lower bonding temperatures and is the most common method today. The process creates secure connections between the bond wire and pads, with careful attention to the appearance and integrity of the bonds, especially in thin packages.

Takeaways

• 😀 Ultrasonic bonding combines pressure and vibration to create a cold weld between the bond wire and the bond pad, ideal for bonding aluminum wire to aluminum pads.
• 😀 Thermo-compression bonding uses heat and pressure to form a connection, typically for gold wire, but it requires high temperatures (300-400°C) that can damage integrated circuit materials.
• 😀 Thermosonic bonding uses heat, pressure, and vibration for wire bonding, and it operates at lower temperatures (180-250°C), making it the most common bonding method today.
• 😀 In thermosonic bonding, the wire is first heated to the melting point, creating a ball at the end, and then an ultrasonic tool creates a metallurgical contact with the bond pad.
• 😀 After the first bond is made with the bond pad, the wire is guided to the package lead frame terminal where the second bond is formed using heat, pressure, and ultrasonic energy.
• 😀 The final thermosonic bond produces a ball bond on the bond pad and a stitch or crescent bond on the lead frame.
• 😀 A properly formed thermosonic bond should have a flattened ball-like appearance, centered on the bond pad, with no pinching or necking of the wire.
• 😀 The wire bond should show a small amount of gold-aluminum inter-metallic at the interface between the bond wire and the bond pad metallization.
• 😀 The second bond, made on the package terminal, involves pressing and flattening the gold wire into the package post, creating a stitch bond with inter-metallic at the interface.
• 😀 Thin integrated circuit packages require special bonding techniques to accommodate the wire, and bonding tools can be programmed for sharper bends to ensure a low-profile wire loop.

Q & A

What is ultrasonic bonding?

Ultrasonic bonding is a wire bonding method that uses a combination of pressure and vibration to create a cold weld between the bond wire and the bond pad. It works best when bonding aluminum wire to an aluminum pad.

What are the key differences between ultrasonic bonding and thermo-compression bonding?

Ultrasonic bonding uses pressure and vibration to create a cold weld, while thermo-compression bonding uses a combination of pressure and heat to form a connection. Thermo-compression bonding is more commonly used with gold wires.

What temperature range is typically required for thermo-compression bonding?

Thermo-compression bonding generally requires temperatures between 300 and 400 degrees Celsius, which can sometimes damage integrated circuit materials.

Why is thermo-sonic bonding considered a better option compared to thermo-compression bonding?

Thermo-sonic bonding combines heat, pressure, and vibration, allowing for lower bonding temperatures (between 180 and 250 degrees Celsius). This makes it less likely to damage sensitive materials compared to the high temperatures required for thermo-compression bonding.

What is the most common type of wire bonding used today?

Thermo-sonic bonding is the most common type of wire bonding used today due to its lower bonding temperatures and versatility.

What happens during the thermosonic bonding process?

During thermosonic bonding, the wire is first heated to its melting point, forming a ball at the end. The bonding tool then presses the wire onto the bond pad while applying ultrasonic energy, creating a metallurgical contact. The wire is then spooled out to the package lead frame, where the second bond is formed.

What are the key characteristics of a properly formed thermosonic bond?

A properly formed thermosonic bond should have a flattened, ball-like appearance centered on the bond pad. The wire should not be pinched or necked, and there should be a small amount of gold-aluminum inter-metallic at the interface between the bond wire and the bond pad metallization.

What is a stitch bond, and where is it formed?

A stitch bond is formed at the lead frame terminal of the package. It is created by pressing and heating the wire, which flattens it and forms a stitch-like shape at the connection point.

What role does inter-metallic play in wire bonding?

Inter-metallics, such as gold-aluminum alloys, form at the interface between the bond wire and the bond pad. A small amount of inter-metallic ensures a strong, reliable connection between the two materials.

Why are special bonding techniques needed for thin package designs?

Modern integrated circuit packaging is often thin, requiring special bonding techniques to accommodate the wire in the package. Bonding tools can be programmed to create sharper bends in the wire to ensure a low-profile loop that fits within the confined space.