Ultrasonic hot pressure welding is a pressure welding method that uses the high-frequency mechanical vibration energy of ultrasonic waves to internally heat and clean the workpiece joints while applying pressure to the workpiece to achieve welding.
Ultrasonic welding is mainly used for wire bonding in the IC chip interconnection process, that is, using gold wires, aluminum wires, and copper wires to achieve electrical connections between chips and lead frames. Because preheating can make the performance of ultrasonic bonded joints better, ultrasonic hot pressure welding is the mainstream of ultrasonic welding.
When the chip is molded, the metal wire arc with a certain length will produce wire swing phenomenon under the impact of the flow of molding material. Since the bonding wire surface currently used usually does not have an insulating layer, the smaller the spacing, the smaller the spacing between adjacent wires. A short circuit between the leads. If the wire swing is severe, it will cause contact between the metal wires, resulting in a short circuit.
In recent years, with the improvement of the integration level of microelectronic devices, the size of microchips has been continuously reduced, chip circuits have become more and more complex, and the diameter of the leads has become smaller and smaller. There are requirements for the control of the wire swing phenomenon. It's getting higher and higher.
The use of enameled wire for wire bonding can effectively solve the above contradictions, and thus X-Wire technology emerged. In 2006, the International Semiconductor Technology Blueprint tasked enameled wire as a potential solution for 25 um wire bonding. In particular, the use of enameled copper wire to replace gold wire has quickly become a hot topic in current research.
Song et al. conducted comparative experiments using gold wires without an insulating film on the surface and gold wires with an insulating film on the surface, and studied their differences in heat-affected zones and the deformability of gold balls.
The enameled wires in wire cutting consumables cannot be connected with traditional linear vibration trajectory ultrasonic equipment.
Tsujino et al. used high-frequency ultrasound with an elliptical sonotrode motion trajectory to study the welding characteristics of insulated copper wires and copper sheets. The outer diameter of the insulated copper wire used is 0.036mm, the thickness of the copper sheet is 0.3mm, and the ultrasonic frequencies are 40, 60, 100 kHz or higher respectively.
The results of the comparative study show that the ultrasonic vibration of the elliptical trajectory can achieve the welding of insulated copper wires, and the high-frequency composite vibration can peel off the insulating material of the solder joint. The strength of the solder joint can basically reach the strength of copper. As the vibration frequency increases, the deformation of the welding part and the fluctuation of the welding strength also decrease. However, the specific material of the insulating layer and the conductive properties of the welded joint are not clearly stated.