We are starting "LINK-US Lab" to share LINK-US's vision for the future of bonding and related technologies. LINK-US, which proposes innovative technology in the ultrasonic bonding field, covers all fields in which ultrasonic waves are applied, and LINK-US technical staff will provide detailed explanations.

On the LINK-US Lab～Part1, we will explain the bonding technology by profession. How process do you image from the word “bonding”?

The point is to attach something in short, but if we define it in more engineering terms, "bonding" is a technique or method for integrating two or more materials or parts. The point is to attach something in short, but if we define it in more engineering terms, "bonding" is a technique or method for integrating two or more materials or parts. There are many ways to integrate two or more objects.

This time, we will categorize and explain in detail these types of "bonding." Our company name, LINK-US, also expresses our hope that we can link people together and create new connections.

1. Meaning of “bonding”

The engineered meaning of “bonding” would be defined as a technology that “transforms individual parts into parts of a whole.” In other words, “bonding” is an important process that adds function by uniting component A with component B. Since bonding is a technique to add a desired function by integrating, there are several different methods depending on the requirements of the desired function.

In addition, today, the durability, beautiful appearance, and environmental impact of bonding are being considered in addition to simply holding components. Therefore, bonding technologies are constantly evolving and diversifying. Now let's look at several different bonding methods.

2. Type of bonding technologies

There are various methods of classifying joints, depending on the bonding phenomenon, construction method, and other cut-off points.
Let us classify them based on the joining phenomenon (principle), here.

Type of bonding in manufacturing site

In this part, we will focus on the bonding phenomenon and explain them divided into four parts. In reality, the bonding is a combination of multiple phenomena, so please consider this as one way of looking at it.

• Mechanical bonding
• Chemical bonding
• Physical bonding
• Metallurgical bonding

Let's take a closer look at each of these.

1. Mechanical bonding

a. Screw bonding

Screw bonding is a method of fastening parts using screws, bolts, and nuts. Fastening force is generated by the frictional force of the screw threads, firmly fixing the parts together. This method allows for repeated disassembly and reassembly and facilitates repair and replacement. However, they may loosen due to vibration or impact and may need to be reinforced with lock washers or adhesives.

b. Rivet bonding

Rivet bonding is a method of fixing materials by crimping them together using a component called a rivet. The rivet tips are crushed with a tool, and it crimps the materials together. Although strong, once joined, they are difficult to disassemble, and rivets must be removed for repair.

c. Caulking press

Caulking press is a method of fixing a part by plastic deformation of a part using a caulking tool. For example, bonding is performed by spreading the edges of parts. It is capable of stable bonding at high speeds and is suited for mass production. However, parts are deformed, and once bonded, it is difficult to undo.

d. Snap fit

This is a method of bonding parts by mating them with each other. Often used for plastic products and appliance covers. It can be easily bonding and disassembled without the use of tools. However, parts may be deformed and repeated use may cause wear and tear on parts.

e. Clinching

This is a method of bonding metal sheets by pressing them together and causing plastic deformation, without using welding or adhesives. The tool applies localized pressure to form a bonding point. It is possible to bond different materials and does not cause heat distortion. However, it requires high processing precision and specialized equipment.

■Specific Applications and Selection Criteria

・“Screw bonding” or “Snap fit” is suitable when the frequency of disassembly is high.

・Rivet bonding” or “Clinching” is preferred when the high strength is required.

・“Caulking press” or “Snap fit” is advantageous when the production cost is to be reduced.

Mechanical bonding can achieve efficient and reliable product design by selecting the best method for the application and conditions.

2. Chemical bonding

Bonding using chemical properties

This method uses the chemical properties of substances to bond parts together. Because it utilizes chemical reactions and intermolecular forces, the bonding is highly integrated and used especially when high airtightness and durability are required. 
The following is a description of typical types of chemical bonding and their characteristics.

a. Adhesive bonding

This method uses an adhesive to bond the surfaces to each other. As the adhesive cures, it forms a strong bond between the parts. Different materials (e.g., metal and plastic) can be bonded together, no major processing of the part is required, and the bonding area is lightweight and smooth in appearance. However, they can take a long time to cure, and some adhesives are sensitive to temperature and humidity.

■Main types

Epoxy resin adhesives: High heat resistance and adhesive strength. Used for bonding metals and ceramics.

Acrylic adhesive: Cures in a short time and is suitable for bonding plastics and metals.

b. Brazing

(Blazing/Soldering) 

This is a method of bonding by pouring molten metal (brazing) into the joint. The base material itself is not melted but is bonded by the chemical bonding of the brazing material. It is possible to bond dissimilar metals, and since the base material is not melted, there is little thermal effect. It is also strong and airtight. However, it requires specialized equipment and skilled techniques, and often requires work in high-temperature environments.

■Main types

Soft soldering: low-temperature brazing used for electronic substrates and wiring.

Hard brazing: High temperature brazing used for joining piping and mechanical components.

c. Welding

This method involves partially melting the joint between parts and forming a chemical bond as the material cools and solidifies. This method provides high strength and airtightness and allows for a permanent bond. In addition, the parts are integrated after bonding, improving rigidity. However, disassembly and repair are difficult, and there is a risk of distortion and material deterioration due to heat effects.

■Main types

Arc welding: Common for bonding metallic materials.

Laser welding: High-precision and high-speed bonding.

Spot welding: Suitable for bonding sheet metal.

d. Use of adhesive film or tape

This method uses adhesives processed into film or tape form and is particularly suitable for applications requiring simplicity and precision. Uniform bonding is possible, no curing time is required, and the product can be used immediately. However, heat resistance and chemical resistance may be limited, and strength may be limited.

■Usage scenarios and selection criteria

“Brazing” and “Welding” are suitable when high strength and durability are required.

“Adhesive bonding” and “Adhesive tape" are effective when weight reduction and bonding of different materials are required.

“Soft soldering" is often used for electronic components that require precision.

Chemical bonding can achieve high performance and reliability by understanding its characteristics and selecting the appropriate method according to the material and application.

3. Physical bonding

When bonding materials together, this method does not use chemical reactions or metallurgical bonding to join materials together, but rather utilizes physical forces and surface properties. This method utilizes pressure, friction, suction, or form mating between parts. The following is a description of typical physical joining methods and their characteristics.

a.Mating

(Interference fit / Press fit)

Mating is a method of bonding parts by fitting them together using their dimensional accuracy. The joint is secured by a slight dimensional difference and a press fit. It exhibits high strength and rigidity and can be disassembled and reassembled after bonding. However, high-precision machining is required, and special tools may be needed for disassembly.

・Features

Principle: Utilizes the frictional force of the bonding surface and elastic deformation of the material.

Applications: Mounting bearings, bonding shafts and wheels.

Friction welding is a method of bonding parts by generating frictional heat by moving them relative to each other while they are strongly pressed against each other.

・Features

Principle: To make the joints adhere to each other using frictional force.

Applications: Shaft joints and flange joints of rotating part

Vacuum adsorption is a bonding method that uses air pressure differences to secure parts. By creating a vacuum, a suction force is generated on the bonding surface.

・Features

Principle: Utilizes the pressure difference between atmospheric pressure and vacuum.

Applications: Holding hand parts of robot arms and glass plates.

This is a method of bonding using the magnetic force of a magnet. The use of magnets strongly adsorbs the joint

・Features

Principle: Utilizes the magnetic force between magnets or between magnets and metal parts.

Applications: Tool holding, fixing of electronic devices, joining of covers for home appliances.

This is a method of bonding parts by providing hooks or claw shapes on the parts and hooking them together. This method is mainly used for plastic parts.

・Features

Principle: Fitting together using the shape of the parts.

Applications: Fixing of home appliances and automotive parts.

Electrostatic bonding is a method of joining parts using electrostatic force. It is particularly suitable for joining lightweight parts and thin films.

・Features

Principle: Utilizes electrostatic attraction between charged materials.

Applications: Temporary fixing of electronic devices and micro components.

■Advantages and challenges of Physical bonding

Advantages

・Relatively easy to disassemble and reassemble.

・Does not damage joints by taking advantage of the characteristics of the materials.

・Environmentally friendly without using chemicals or heat.

Challenges

・Bonding strength may be lower than chemical or metallurgical joints.

・Wear and loosening may occur due to repeated use.

・Performance may deteriorate under certain conditions (vibration and temperature changes).

・"Snap bonding“ or ”Vacuum adsorption" is used when handiness and frequency of disassembly are important.

・Mating” is used when high strength is required.

・"Electrostatic bonding“ and ”Magnetic bonding" are used for precision parts and electronic devices.

Physical joining is often easy to perform without the need for tools or special equipment and contributes to more efficient product design and assembly processes. By selecting the appropriate method, it is possible to achieve a balance between cost and performance.

4. Metallurgical bonding

This is one of the bonding methods for metallic materials and refers to a technique in which metals are bonded to each other at the atomic level in the joining area. This bonding method utilizes the physical and chemical properties of metals, the basis of metallurgy, and is widely used when high strength and durability are required. The following is a description of typical metallurgical joining methods.

Welding is the most typical method of metallurgical bonding. The metal atoms form covalent bonds as the joint is melted and cooled.

■ Characteristics

Principle: Localized melting of metal, sometimes adding welding rod or welding wire。

Applications: Structures (bridges, buildings), automobiles, aircraft, etc.

■Main types

・Arc welding: Melts metal with electrical energy. High usage rate　and low-cost.

・Laser welding: Melts metal with a high-energy laser. Suitable for bonding thin materials with high precision.

・Friction stir welding (FSW): Bond metals in a solid state using the frictional heat of the tool. Used in the aerospace and railroad industries.

Brazing is a method of bonding without melting the base material. The molten brazing material (metal alloy) covers the joint and cools to form a metallurgical bond.

■Characteristics

Temperature: Processed at a temperature lower than the melting point of the base material.

Applications: Piping, heat exchangers, electronic components, etc.

Advantages: Retains the shape and characteristics of the base material and can be used to bond dissimilar metals.

In diffusion bonding, metal surfaces are brought into close contact with each other in a high-temperature, high-pressure environment, and bonds are formed using atomic diffusion.

■Characteristics

Conditions: The bonding surfaces must be very smooth.

Applications: High performance components in the aerospace and nuclear industries.

Advantages: No melting, low thermal effects, high precision.

Sintering is a method of integrating metal powders by baking them at high temperatures and is part of powder metallurgy technology.

■Characteristics

Conditions: Diffusion and grain recombination between powder particles.

Applications: Tool parts, gears, automotive engine parts, etc.

Advantages: Can fabricate parts with complex geometries and high hardness materials.

Ultrasonic bonding is a method of applying high-frequency vibration to break oxide films on metal surfaces and form atomic bonds.

■Characteristics

Conditions: Vibration and pressure are applied simultaneously.

Application: Bonding of electronic devices and small parts.

Advantages: Low thermal effects, joining of dissimilar materials possible.

Advantages

・High bonding strength and durability.

・Airtightness and electrical conductivity can be ensured.

・Many technologies that can bond dissimilar metals.

Challenges

・Often requires work in high-temperature environments.

・Often requires work in high-temperature environments.

・Once bonded, it may be difficult to disassemble or modify.

・Type of materials to be bonded: homogeneous or dissimilar metals.

・Operating environment: Need to withstand high temperatures, high pressure, corrosion, etc.?

・Cost and efficiency: Mass production or single piece production?

・Accuracy requirements ：”Diffusion bonding” and “Ultrasonic bonding” are suitable when precise bonding is required.

Metallurgical bonding is a technique that takes full advantage of the properties of metallic materials and is essential for products that require strength and performance.

Although not mentioned now, there are also technologies for 3D modeling using metal powders and lasers.

It is important to select the appropriate method depending on the application and conditions, but it must be difficult to distinguish between such a wide variety of joining technologies.

If you have any questions or concerns, please feel free to contact us at any time.

In this part, we took a broad look at the different types of bonding. In the next part, we will take a deeper look at ultrasonic bonding, focusing on the differences from other types of bonding.

In this part, we took a broad look at the different types of bonding. In the next part, we will take a deeper look at ultrasonic bonding, focusing on the differences from other types of bonding.