Nebulas Electronics: Advantages and Applications of Wire Bonding Aluminum Wire Ultrasonic Welding Technology

by:CTECHi     2021-08-03

1. What is Wire bonding aluminum wire ultrasonic welding technology?

Aluminum wire ultrasonic welding is actually a wire bonding technology that uses aluminum as the metal wire. Wire bonding is a primary internal interconnection method used to connect to the actual die surface or the first level of internal interconnection of the device logic circuit. This connection method connects the logic signal or the electrical signal of the chip to the outside world. stand up.

Wire bonding has two forms: ball bonding and wedge bonding. Gold wire ball bonding is the most commonly used method. In this process, a molten gold ball is glued to a section of the wire, and it is pressed down as the first solder joint, and then the bent wire is drawn from the first solder joint and renewed. The lunar shape connects the wire (the second wedge-shaped solder joint), and then forms another new ball for the next first ball solder joint. Gold wire ball bonding is classified as a thermoacoustic process, which means that the solder joints are formed under the combined effects of heat (usually 150), ultrasound, pressure, and time. The second pressure welding method is the wedge process. This process mainly uses aluminum wire, but gold wire can also be used, usually at room temperature. Wedge bonding presses down two wedge-shaped solder joints to form a connection. In this process, no ball is formed. The aluminum wire welding process is classified as ultrasonic wire welding, and only parameters such as ultrasonic energy, pressure, and time are used to form a solder joint.

The use of different process types depends on the specific application. For example, gold wire bonding is used in mass production because of the faster process speed. Aluminum wire bonding is used in applications where the package or PCB cannot be heated. In addition, the wedge bonding process has a finer pitch than gold wire bonding. At present, the spacing limit of gold wire pressure welding is 60μm; the use of thin aluminum wire wedge pressure welding can achieve a spacing of less than 60μm.

The metal wire used in this technology, that is, Bonding Wire, is used to achieve electrical connection between the input/output connection point of the circuit in the chip and the internal contact point of the lead frame when the semiconductor device and the integrated circuit are assembled. The inner lead. Bonding Wire, as a connecting inner lead, should have the advantages of high conductivity, strong conductivity, strong bonding force with conductor materials, and stable chemical properties. The diameter of the Bonding Wire is usually between 25 and 75 μm. There are four main materials on the market for bonding wire, namely gold, silver, copper and aluminum.

2. Application of Wire Bonding Technology in the Field of Electric Vehicle Power Batteries

Wire bonding has been widely used in the fields of microelectronics and power electronics since 1970 . At present, Wire bonding technology has a new application field, that is, the growing electric vehicle field, especially in battery connection. In the production process of some electric vehicles, Wire bonding technology is used for the connection between battery packs.

(1) Since Wire bonding was widely used in the field of microelectronics in 1970, some electric vehicle manufacturers began to use Wire bonding for battery connection.

TESLA is a typical representative company using this technology. In 2006, TESLA pioneered the use of wire bonding technology as a technical model for connecting cells into a large battery pack. According to TESLA, the traditional welding process is very time-consuming and prone to failure. At the same time, it is difficult to test whether there is a problem with the connection between the batteries and the conductor.

In addition to simple connection, TESLA also designed a way to use aluminum wire bonding, a fusible connection technology. Aluminum wire welding technology can allow current within the range to pass, but it will fuse when a short circuit generates an overcurrent. TESLA engineers believe that other welding techniques will cause electrical protection problems. Without the protection of a fuse, a single cell may have an internal short-circuit after a fault or damage, causing other cells connected in parallel with it to be unusable.

(2) Advantages:

The traditional brazing and fusion welding technology has been used for many years, and there are some disadvantages. For example, the generation of thermal stress, cleaning problems after welding, lack of flexibility, and difficulty in quality control. Bonding's wire welding and strip welding perform much better than traditional welding in this respect, and each welding point can be well controlled without any adverse effects on the production process.

1. When using aluminum wire welding or aluminum strip welding, it can be carried out at room temperature. No external temperature is required, and the temperature of the welding zone during ultrasonic friction welding will not rise. Other traditional welding methods require heating to melt the metal.

2. Wire bonding is a clean welding technology and does not require any sanitary cleaning after welding. After traditional soldering technology, some flux residues or molten metal explosions need to be removed to avoid reliability problems. For wire bonding, cleaning is only required when there are some contaminants or stubborn oxides on the surface.

3. Wire bonding has good flexibility and strong compatibility, including low gold wire height, multiple pin options, large working range, ribbon or round wire options.

4. The metal wire can have good directional flexibility, and can well control the mismatch between a variety of thermal expansion parameters.

5. Lead connection process, bonding wire can be directly used as a fuse process, no need to use resistance welding to weld nickel sheets, simplifying the production process and reducing equipment investment.

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