Wire bonding is the process of attaching thin, fine wires to components using heat and pressure. The wires are typically made of aluminum, copper, silver, or gold.
Wire bonding machines are used to make electrical connections between the components of electronic devices. They are widely used in the aerospace, semiconductor, solar cells, microelectronics, and EV battery industries.
In this article, we’ll go over the types of wire bonders, discuss their limitations, and present how laser welding is used to overcome these challenges in the automotive industry.
What Are the Types of Wire Bonders?
Wire bonding is a versatile technology with multiple types of bonding tools and energy methods. Here are the most important ones.
Ball bonding uses a ball-shaped wire that is welded to the bond pad whereas wedge bonding uses a wedge-shaped wire. Ball bonders present the wire vertically and wedge bonders present it at an angle.
Ultrasonic bonding is a wire bonding process that uses high-frequency mechanical vibrations to create a bond between the wire and the bond pad. Ultrasonic bonding applies this energy with a tool called a sonotrode, which is a specialized horn-shaped tool pressed against the materials to be joined.
Thermocompression bonding refers to processes that use heat and pressure to form a bond between the wire and the bond pad.
Thermosonic bonding refers to processes that combine heat and ultrasonic energy to create a bond between the wire and the bond pad.
Bonding wires can be fine, coated, round or flat. Wires can be made of different materials:
- Copper wires are the most cost-efficient materials and have become the most popular type of wire.
- Gold wires offer chemical stability and an excellent electrical conductivity.
- Silver wires have outstanding electrical and thermal conductivity. With their high reflectivity, they are ideal for optical semiconductor devices.
- Aluminum wires are perfect for devices used in harsh environments, as they have good moisture resistance.
Limitations of Wire Bond Machines
In the automotive industry, wire bonders are used to make interconnections between the cells and busbars of EV battery packs and modules. This process has not only been the cause of important bottlenecks, but shopfloors can also be filled with multiple automatic wire bonders. All of this generates important recurring operative costs and floor space requirements.
Laser Welding Machines: An Alternative to Wire Bonders
Laser welding is increasingly used to replace wire bonding in high-speed, high-volume production lines.
In battery production lines for example, a large quantity of wire bonders is typically needed to keep up with the production pace, as each battery pack and module requires hundreds or even thousands of interconnections. To create more powerful electrical connections, some manufacturers even need to use several thin wires for a single connection, as the size of the wires is limited.
Laser welding machines are much more efficient than wire bonders because they don’t have the same mechanical constraints. A single laser welding machine can replace multiple wire bond machines.
Surface Cleaning Challenges Before Wire Bonding: Plasma Cleaning or Laser Cleaning?
To achieve a good bonding quality and minimize rejects, surfaces must be cleaned before wire bonding (or before laser welding). Contaminants like oxide, grease, and dust must be removed. This is essential to meet the high-quality requirements, for example, of EV batteries.
One of the challenges is the precision of the cleaning process, and manufacturers do not always know whether they should choose plasma cleaning or laser cleaning.
For wire bonding, plasma cleaning is not as precise as laser cleaning. As a result, plasma cleaning treats larger areas than necessary, slowing down the cleaning process for no good reason. It also means that a more powerful exhaust system is needed to handle the dust and fumes, and that its filters need to be changed more often, creating additional maintenance.
Need to Scale Up Production with Laser Welding?
If you think you could benefit from laser welding, contact a laser expert today to discuss your application.