Tracing the cost reduction and efficiency improvement of MLED, Devol's advanced equipment "evolves"

MLED, with its smaller size, tighter arrangement of LED beads, higher pixel density, and advantages such as higher brightness, wide color gamut, high contrast, low power consumption and long lifespan, is regarded as a new product for the upgrade of LED display technology following LED small-pitch display. With the continuous optimization of technology and cost, the display applications of Mini leds are gradually increasing nowadays, and their delicate display effects have gradually been recognized by various industries. Although the number of participating enterprises is increasing day by day and related products are emerging one after another, the MLED display industry is still in its early stage of development. There are still difficulties in each link that need to be overcome urgently, or a better solution is needed in terms of cost. Conversely, as the production of MLED has not yet established a standard process and a fixed system, new technologies and solutions in each process link will offer a new possibility for the future of MLED.

At the 2022 GAogong LED Display Annual Conference, a senior engineer from Devol Advanced Process R&D stated that in the front-end packaging of leds, the connection between the chip and the external circuit is achieved through wire bonding technology, that is, by connecting metal wires to the solder pads. The main materials for wire bonding include copper wires, silver wires, gold wires, and coated target wires, etc. In terms of electrical conductivity, silver wire is definitely better. In terms of reliability, the gold wire is definitely the best. In terms of the strength and hardness of the wire, copper wire is the hardest, while silver wire is the softest. In terms of price, gold wire is definitely the most expensive and copper wire the cheapest. Therefore, different types of wire can be chosen and matched according to the different needs of customers. The lead frame provides circuit connection and the fixing function of the Die. Its main material is copper, and materials such as silver plating and NiPdAu plating are applied on it.

The process parameters and reliable analysis of wire bonding: Under conditions such as soldering, transportation, and use, electronic components usually generate mechanical stress on the solder joints or devices due to vibration, shock, bending deformation, etc., and eventually lead to the failure of the solder joints or devices.

The mechanical failure model of solder joints can be simulated through push-pull force tests to analyze the failure causes of solder joints or devices and evaluate the reliability of materials. The reliable analysis of wire bonding begins with an appearance inspection, including the first solder joint, the second solder joint, and the wire arc.

The differences in the process parameters of wire bonding are generally reflected in the first and second solder joints. Among them, in the welding of one solder joint, especially the copper wire and the plated target wire, A higher ultrasonic energy generally can bring better thrust of the solder ball, but it will also cause more aluminum extrusion, larger ball diameter and P/N connection and other problems at the same time. While a too small ultrasonic energy leads to a weaker bond between the electrode and the solder ball, resulting in ball separation at point A and a decrease in reliability. Similarly, in copper wire welding, achieving an ideal second weld is crucial and challenging due to the high hardness of copper wire, especially the difficulty in controlling the shape of the solder joint in the Y direction.

In the field of LED packaging, the copper wire bonding process has been widely applied. However, due to the inherent properties of copper, copper wires are harder than gold wires and require a higher bonding force to achieve strong bonding performance. If the bonding process parameters are set too high, it will affect the size of the solder balls and easily lead to short circuits in the P/N connection.

This will increase the possibility of pad damage, such as the detachment of point A and the squeezing of electrodes. The damage and destruction to the chip electrodes will bring hidden dangers to product quality. Meanwhile, as packaged products develop towards smaller pitch, chips are also moving towards smaller size, increasing the difficulty of process soldering. Therefore, the coordination of process parameters, the balance of welding force and ultrasonic energy are also crucial. Reducing the bonding force and ultrasonic power by using softer copper wires is beneficial for the welding of small balls. The bonding tool used in thermoultrasonic bonding, also known as a Capillary or split knife, serves as the medium for energy coupling between the ball welding machine and the welding point. Choosing the right split knife is very important for improving the quality of the second joint. The unique roughened surface of the split knife increases the grip between the weld line and the split knife, improving the abnormality of the second joint.

As the market changes, the process parameters of chips will become smaller and smaller, and the process difficulty of the two solder joints will also increase relatively. Dewo Advanced has developed new processes such as multi-stage running-in mode and segmented welding to meet customer requirements. Through the EFO system design, high-speed and high-precision numerical control current is used to dynamically control the current during the ball formation stage, achieving the best heat output for ball formation of gold wires, while shortening the ball formation time and improving the stability of the welded balls. Aiming at the problem of easy fracture of solder joint B, the processes of offset zigzag arc, spatial zigzag arc, M line arc and butterfly line arc are adopted for improvement. To address the issue of the D solder joint being prone to breakage, the standard +D, flat arc +D, and grounded arc processes were adopted for improvement.

Devol Advanced focuses on the application fields of IC and LED packaging, independently developing and innovating, with over 40 core patents. After ten years of accumulation, we have developed a high-precision fully automatic wire bonding machine. It adopts a newly upgraded XY platform and a more stable welding head, providing solutions for special process line arcs. It supports programming for more than ten complex wire bonding programs. Relying on its underlying independent technology, Dewo Advanced focuses on packaging forms, materials, structures, and processes to meet and guarantee the application of the terminal market. By enhancing the domestic configuration, the supply chain becomes more stable and faster, reducing the procurement costs for customers. Moreover, it has a self-built production line with a monthly output of 300 units, enjoying the supply advantages of ensuring quality and quantity as well as rapid delivery.