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- November 5, 2022
- PCB knowledge
- (0)
- 05 mins
Wire bonding – introduction and procedure
What is wire bonding
Wire bonding is a method of forming a strong, reliable bond between two parts by using heated metal wire. Wire bonding is very important in the production and use of microelectronic devices. It is a process for connecting two components together electronically by using a conductive wire, typically gold or copper. The equipment used to make these bonds is called a wire bonder.
The machines used for this process are called ultrasonic bonding machines, ultrasonic welders, etc.
The wire bonding has different forms and sizes that make it suitable for many applications. For example, you can use it in automotive industry, aerospace industry , PCB electronics and so on.
Types of wire bonding
There are three main types of wire bonding: Thermo-compression bonding, Thermo-sonic bonding, and Ultrasonic bonding.
Thermo-compression wire bonding
The process of thermo-compression bonding involves creating an electrical connection using two different materials usually metals. The two metals are joined by heat and pressure. Thermo-compression bonding works well for both SMT process and through-hole applications. Gold is ideal for thermo-compression because its low melting point ensures that other components do not get damaged during the process.
Thermo-sonic wire bonding
In thermo-sonic bonding, the wire is heated by passing a current through it and simultaneously pressed against the pad with an ultrasonic vibrator. The heat softens the wire and the ultrasonic vibration moves the metal atoms of both surfaces into intimate contact, creating strong metallurgical bonds between them.
Thermo-sonic bonding is a science that involves balancing heat, pressure, and vibration to make strong connections between electronic devices and components.
Ultrasonic wire bonding
Ultrasonic bonding uses high frequency vibrations to weld metal wires or thermoplastic parts together. It is used in many industries, including aerospace and automotive.
The ultrasonic waves penetrate the material at an angle of about 45° and produce a high-pressure shock wave inside the material which causes it to expand and then contract again when released from pressure through interaction with its surrounding medium (liquid).
What is thermal compression bonding method
Thermal compression bonding is a process that uses heat to create a bond between two pieces of metal.
The bonding tool itself has several parts: the head and stem (the part that you hold), as well as the jaws or clamps that hold it all together. These parts are made from steel or metal alloys depending on what type of thermal compression bonding machine you use; they have various numbers stamped into them indicating their hardness rating or strength level—the higher these numbers are, the better quality material will be used in their construction!
Thermal compression bonding machines are used to bond wires to the pads on a chip. The machines have to be able to handle a wide range of wire sizes, from 0.5mm to 2.0mm in diameter and with diameters ranging from 15 microns up to 3 mm. They also need to be able to handle different types of solders such as rosin-less flux-cored solder or leaded solder, which require different temperatures during bonding.
The forms of wire bonding
Classified by materials
★ Aluminum wire bonding Aluminum wire bonding is used for low-temperature applications and high-speed applications. It can also be used in high-frequency applications.Aluminum wire bonding is very efficient, but it has some limitations: ●It’s not as strong as gold or silver wires. ●It doesn’t work well with flexible materials like carbon fiber composites or PET film because these materials have a lot of internal stress which makes them prone to breaking when pressed together by metal wires against their outer surfaces. ★ Gold wire bonding Gold wire bonding is a popular method of joining wires together. It’s used for the semiconductor industry, as well as in electronics and medical PCBA devices such as pacemakers.
In this type of bonding process, gold wires are placed around each piece of copper wire that you want to join together. Then, an electric current passes through these gold wires as they’re heated up by an arcing process called “fluxing” (which creates heat). The result is that there’s no need for soldering or brazing—just two pieces of metal touching each other!
★ Copper wire bonding
Copper wire bonding is used in microelectronics. It’s a method of using copper wires to join two or more pieces of electronic equipment together. The wires are braided together, then heated until the metal melts and forms a strong bond between them.
Because copper has higher conductivity than other metals, it can carry electricity better than other materials—and this makes it ideal for wiring components together in an electrical circuit.
Classified by shape
The two forms of wire bonding based on shape are loop bonding and ball bonds. ★ Loop bonding, also known as wedge bonding or simply looping is a method of making interconnections between integrated circuit package leads and printed circuit board lands using a ribbon of conductive material. Loop bonding can be used to connect any two points on a printed circuit board (PCB). The technique was first developed by Recticel in the late 1970s and early 1980s to replace point-to-point wiring techniques such as silver plating, which had been used previously with difficulty due to poor mechanical strength and high cost compared with copper foil tape.
★ Ball bonding utilizes the metal-to-metal ball bond technique for wire bonding applications where small diameter spherical balls are employed as connecting linkers between electrical components.
It can be made in normal, reverse and stud bump bonding configurations. All three configurations are employed in automotive electronics to reduce chip size, weight and power consumption.They are recommended since they do not require extra space on the die surface. Ball bonds are used to reduce chip size, weight and power consumption. Procedures for wire bonding
The wire bonding process is a step in the fabrication of integrated circuits. Its procedure involves the following steps:
●The chip is placed on the substrate.
●The chip’s surface is heated so that it becomes molten.
●A wire is then pressed against the molten surface of your device, which causes an electrical connection between them.
How to design wire bonding
The following are some important steps to follow for designing a perfect wire bonding:
●The first step is to select the right type of heat source and apply it on the surface where you want to apply your wires.
●Then, apply pressure on both sides of the work piece with pliers (or vice versa) so that their tips touch each other slightly at their ends. This will ensure that there are no air gaps between them and prevent them from dissolving into each other during soldering operation.
●When this happens, place one side’s tip into its designated spot while pressing down firmly until you hear a snapping sound indicating successful bonding between two surfaces together!
