Wire Bonding and Die Attach for PCB Assembly

As electronic components get smaller and more compact, methods like wire bonding and die attach have become essential. These services are increasingly supplanting high-heat methods like soldering in integrated circuit and semiconductor assembly. Below, we’ll look at some of the materials and processes involved in these PCB assembly methods to help you better assess your project’s needs.

Wire Bonding

Wire bonding uses fine diameter wires typically made of soft metals like gold, silver, or aluminum. However, copper has recently become a preferred material in wire bonding for its lower cost and reliability, although copper is a harder metal that requires different controls. All of the different methods of wire bonding use a combination of heat, pressure, and ultrasonic energy to form bonds. Thus the type of metal and type of bond will depend on the specific application.

There are three general methods of wire bonding. One method, thermosonic bonding, uses ultrasonic energy and force to press the wire and material together, then uses heat to bond them. Another method, thermocompression bonding, uses heat and pressure to join the contact surface and the wire. In contrast, ultrasonic bonding, which can be used with any metal, often eliminates the need for heat altogether. Ultrasonic bonding joins the wire to the surface using force and ultrasonic energy alone.

The most popular types of wire bonding combine these various methods. One of the most common bonding types is ball bonding. Ball bonding may use gold, copper wire, or silver. A needle-like device, called a capillary, applies heat to the tip of the wire to form a ball. Next, the ball is pressed against the contact surface and joined with ultrasonic energy.

Wedge bonding applies force and ultrasonic energy and can join higher-diameter wires than ball bonding. The wedge bonding process is often used with aluminum wire, making the process more suitable for semiconductor assembly. Because it requires aligning each wire in a straight line, wedge bonding may be more time-consuming than other earlier methods. However, specialized machines have sped up the process considerably, enabling high-volume production of wedge-bonded components.

Die Attach

Like wire bonding, die-attach eliminates the need for high-heat assembly processes. Instead, silicon chips (dice) are attached to the package, substrate, or another die, using either an adhesive or a eutectic alloy (a combination of metals with the lowest possible melting point). Typically, the eutectic die bond uses alloys of aluminum and silver. Both processes use specialized die-attach tools and equipment. Either process can create voids that affect the quality of the component, making proper testing critical.

Wire bonding and die to attach processes all require expertise, advanced tools and machinery, and testing to ensure the strength and reliability of the bond. NPI Services Inc. specializes in the quickturn assembly of electronic components for any application. We have a proven record in aerospace, defense, space flight, energy, transportation, and medical technologies. No matter how specialized the application or how extreme the environment, NPI’s assembly services can meet your needs. Contact us today to discuss your options for wire bonding and die attach.