Ceramics Capillary for Copper wire Bonding
Introduction
Wire bonding is to weld the two ends of the lead to the chip pad and the lead frame respectively in a certain environment by means of thermal ultrasonic pressure, so as to realize the connection between the internal circuit and the external circuit of the chip. Up to now, the lead metal materials mainly include gold wire, silver wire, alloy wire, copper wire, etc. the reliability and cost advantages of copper wire are highly concerned by the industry.
For a long time, bond alloy wires have the advantages of high conductivity, corrosion resistance, good toughness and so on, and have been widely used in integrated circuit packaging. However, under the dual pressure of high material prices and falling prices of electronic products, professional institutions and units in the industry continue to seek new low-cost alternative materials. It is found that the electro thermal performance of copper wire is better than that of gold wire. At the same time, because the tensile, shear strength and ductility of copper wire are better than that of gold wire, copper wire with smaller diameter can be used to replace gold wire. The data analysis shows that the shear force of copper wire bonding ball is 15% ~ 25% higher than that of gold wire, and the tensile force is 10% ~ 20% higher than that of gold wire. The impact bending resistance of wire arc is better during plastic packaging. Therefore, the wide application of 一bonding copper wire technology and its promotion to more high-end fields are of great significance.
Copper wire bonding is completely developed on the basis of gold wire bonding. It is improved on the gold wire bonding platform. By adjusting the cleaver process parameters and increasing the process conditions, it is suitable for the production environment of copper wire bonding. After years of hard work, Shangde ceramic cleaver has rich experience in copper wire bonding technology and has been applied to mass production in the industry.
1 Product introduction
Our main business is to manufacture welding wires, chip pick-up tools and customized high-precision tools for the semiconductor, aerospace and medical industries. Provide advanced ceramic cleaver products for bonding aluminum, gold, copper and alloy leads. After years of efforts of the company's R & D team to optimize tools to achieve the highest performance and quality, the company's Cleaver products have hundreds of specifications to meet different needs. We provide perfect customer service and technical support to solve your demanding wire welding requirements. Here are two ceramic cleavers mainly used for copper wire bonding.
Capillary 324：SS-231202-3298-ZH2
Capillary 349：SS-231202-3598-ZH2
Ceramic cleaver vertebral canal 324 and vertebral canal 349 are both suitable for copper wire bonding and have similar size parameters. The difference lies in T-end face diameter, CD inner chamfer diameter and or outer chamfer diameter. Spinal canal 324:T-110um, CD-32um, OR-15um, spinal canal 349:T-120um, CD-35um, OR-20um. Spinal canal 324 has a smaller end face size than 349, so it is more suitable for the bonding scheme with smaller bonding spacing. The corresponding spinal canal 349 has larger t value and CD value, which is suitable for the bonding scheme with larger bonding spacing and can give higher bonding strength. The ideal hot pressing ultrasonic bonding can realize zero tool sliding during wire contact and application of ultrasonic energy. If the sliding of the tool is zero, the ultrasonic energy transmission operates at 100%, which can also reduce the surface wear and improve the service life of the cleaver, which is the value of high-quality cleaver.
2 Improvement of copper wire bonding process
2.1 Prevention of copper wire oxidation
Due to the material characteristics of Cu, it is easy to oxidize in the air for a long time, especially in the high-temperature operation environment of welding. After oxidation, the oxide layer on the surface of copper wire will increase the difficulty of welding and the phenomenon of false welding after welding. Therefore, preventive measures should be taken during the storage and production of copper wires.
In the industry, there are attempts to prevent oxidation by plating a layer of inert metal on the surface of the copper wire. There is a layer of Pa coated copper wire on the market, which can prevent oxidation, and the second welding mechanical property is stronger than that of pure copper. However, the price of Pa plated copper wire is three times higher than that of copper wire, and the mechanical property of the second solder joint is solved, which has little effect on the welding process. Therefore, inert gases are widely used in the industry to prevent oxidation. For copper wire bonding, gas blowing equipment is usually installed on the bonding equipment of gold wire.
2.2 Process parameter control
There are many process parameters that affect the performance of welded joints, including lead, cleaver, base Island, pressure, ultrasonic, temperature and spark discharge. The study of the influence of various process parameters on the properties of welded joints is helpful to improve the welding process.
Suntech capillary copper wire bonding parameter range
3 Solutions to technical difficulties of copper wire bonding
Although copper wire bonding has a series of advantages over gold wire bonding, such as low cost, high conductivity and heat conductivity, and high strength of welding joint, copper wire bonding also has many defects, mainly due to the high hardness of copper wire, which means that greater ultrasonic power and pressure strength are required during bonding, which is easy to cause a series of problems such as substrate fracture, silicon pit and false soldering. The damage and destruction of the chip will bring hidden dangers to the product quality.
3.1 Solutions to friction problems
There is no bonding without friction. In the process of thermal ultrasonic bonding, the friction between the gold wire ball and the substrate contact surface is one of the important conditions to complete the bonding. Through comparison, it is found that with the increase of ultrasonic power, the internal force of the ring becomes smaller until it changes from micro friction to relative sliding. However, copper wire bonding requires high ultrasonic power. For this reason, Shangde ceramic cleaver improves the cleaver powder structure and uses laser ablation to improve the cleaver surface texture, making copper wire bonding more efficient and reliable. At the same time, the conversion efficiency of ultrasonic energy and the service life of the cleaver are improved.
3.2 Solution for aluminum layer extrusion and parameter coupling optimization of pad
Due to the high hardness of the copper wire, the bonding pressure needs to be increased during bonding, which often causes the aluminum layer of the pad to be extruded, and the extruded aluminum is short circuited with the surrounding aluminum strip, making the chip function invalid. Facing the current situation, in order to control the extrusion of aluminum layer, the solution can be to adjust the bonding contact area, bonding pressure, bonding ultrasonic output power and the cleaver with appropriate angle. Increasing the ultrasonic power makes the copper ball easy to soften and deform rapidly, increases the contact area between the copper ball and the pad, and selects a cleaver with a suitable angle, so that the ultrasonic power acts near the center of the copper ball during the bonding process, which can reduce the action time of the ultrasonic power on the pad, thus reducing the risk of the aluminum layer on the pad being extruded.
The final quality of copper wire bonding mainly depends on the heat, pressure, ultrasonic power and the size parameters of the cleaver. The coupling optimization of multiple parameters can effectively improve the bonding quality. It is feasible to explore the coordination of various parameters through experiments to achieve the best effect of the product. However, due to the long test cycle and cost reduction. Shangde ceramics is carrying out the computer simulation experiment of parameter coupling optimization by means of computer numerical simulation, in order to achieve the further effect of parameter optimization.
Numerical simulation of wire bonding
4 Conclusion
Due to the increasingly fierce price competition in the market of semiconductor devices, seeking low-cost materials has become the main way. For the current copper wire material, its low price, good mechanical and electrical conductivity and other advantages have created a great development space, and its application will be more extensive and long-term. The bonding process of copper wire can be controlled and optimized by adjusting appropriate process equipment and process parameters. At present, for integrated circuit packaging, the qualified rate of Shangde ceramic copper wire bonding can reach more than 95%. With further practice and experience, the copper wire process continues to be improved and optimized, which helps the copper wire bonding process to be applied and popularized in multi-level packaging and higher density packaging.
