Beijing Welder Technology Co.,Ltd

0 preface

Cap-sealing refers to welding the metal cap and metal base together to complete the last packaging proc-ess of metal components. Cap-sealing is an important process in the production of metal components, which quality greatly affects the performance of metal components. Therefore, the precise cap-sealing machineis of great significance for metal packaging field.

1 The working principle of the cap-sealing mechain

The cap-sealing machine adopts resistance welding technology to realize metal packaging. Place the met-al seat and metal cap in the lower electrode, when the upper and lower electrodes are pressed, the capacitor is instantly discharged, and the heat of the discharge melts the welding wires on the contact surface of the metal seat and metal cap to weld them together. Resistance welding operation is simple and easy to realize mechanization and automation. Besides, there is no need to add filler metal solder in the welding process. At the same time, resistance welding operation is a safe, reliable, environmentally friendly welding technology with high productivity and small deformation of the weldment.

Beijing Kexin Mechatronic Research Institute Co., Ltd (Kexin for short), specializing in the research and development of metal packing equipment for more than 30 years, has provided a large number of high-quality and durable precision packing equipments for metal components for the industries of semiconductor, microelectronics, optical communications, sensors and so on. Among them, the capacitor energy storage of FHJ series up to 700J-9000J, capable of welding TO-18, TO-38, TO-46, TO-10 and other TO devices, as well as Box devices, passive crystal devices and so on. The equipment meets the packing requirements of metal components for low oxygen, low water vapor, high environment, high vacuum, etc. The leakage rate is in line with the national military standard, which ensures the dynamic response agility , high stability, high reliability and other requirements of the welding process.

For example, the FHJ-4 cap-sealing machine produced by Kexin is shown in Fig.1. According to the user and market demand, FHJ-4 can be used for the packaging of small-size TO components, which can meet the demand of optical communication industry for welding of electronic components such as TO-18, TO-25, etc.

Fig.1 FHJ-4 cap-sealing machine

The welding head of FHJ-4 cap-sealing machine is shown in Fig.2. When welding, the metal cap and seat are placed in the lower electrode, and the air compression system and nitrogen system are utilized to make the cylinder drive the upper electrode to make up and down movement. When the upper and lower electrodes are pressed, the capacitor is instantaneously discharged. At this time, a complete current circuit is formed between the welding power source, the upper and lower electrodes and the package. At the same time, the heat generated by the discharge melts the weld line on the metal seat to realize the cap-sealing. The TO samples welded by FHJ-4 cap-sealing machine are shown in Fig.3.

Fig.2 The structure of welding head

Fig.3. The TO samples

2 Influence of process parameters on cap-sealing quality

In the welding process with resistance welding technology, the discharge heat formula is as follows.

Q= I²Rt(1)

Where Q is the heat of discharge (unit: J); I is the welding current (unit: A); R is the contact resistance (unit: Ω); t is the discharge time (unit: s).

Therefore, the three important process parameters affecting the quality of cap-sealing are the contact resistance at the welding moment, the discharge time and the welding current.

2.1 Effect of contact resistance on cap-sealing quality

In Equation (1), the contact resistance includes the resistance of the packing itself (metal cap and seat), the contact resistance between metal cap and seat, and the contact resistance between the electrode and the weldment. The shape and size of the packing, the material and shape of the electrode and other factors all affect the resistance of the contact resistance. Among them, the factor that has the greatest influence on the contact resistance is the electrode pressure. Electrode pressure refers to the pressure on the package placed between the upper and lower electrode in the welding process, which means the cylinder drives the upper electrode movement, when the upper and lower electrodes are pressed together, the electrode pressure is generated. Electrode pressure has a significant impact on the contact resistance, when the electrode pressure is too small, the contact resistance increases, the heating speed is too fast, and spatter will be generated; when the electrode pressure is too large, the welding contact area increases, the contact resistance decreases, and the resistance heat generated decreases, which can cause the welding line is not fused, desoldering and other problems. Therefore, the electrode pressure will directly affect the contact resistance, which in turn affects the discharge heat and welding quality.

2.2 Effect of discharge time on cap-sealing quality

In the case of a certain welding current and electrode pressure, the technician can set up a number of different groups of discharge time according to experience to weld a number of packages respectively. Through the microscope to observe the sample after welding, it is easy to find that when the discharge time is too small, the heat generated is too less to melt the wire fully. Lack of heat can result in welding is not sufficient and affect the weldment's airtightness; when the discharge time is too long, the heat generated is so high that the solder melts and overflow seriously. The high heat can even spark spattering and affect the appearance of the product and the application of performance!

2.3 Effect of welding current on cap-asealing quality

Resistance welding is a method of metal packing based on nugget results from package contact surfaces melting with the resistance heat when the welding current passes through the package.

There is a positive correlation between the welding current and the heat of discharge. As the welding current increases, the welding heat increases successively. When the welding current is so large, higher than the upper limit value, that the heat loss is serious, it is easy to produce solder melting overflow, spark spatter or melt through; when the welding current is too small, lower than the lower limit value, the heat generated is not enough, which will lead to welding is insufficient, affecting the weld airtightness. Therefore, in the welding process, welding current is a parameter that must be strictly controlled, and its influence on welding quality is higher than that of contact resistance and discharge time.

In addition, the upper and lower limits of welding current in the cap-sealing process are not set in stone, and the welding current will change with the change of other process parameters. For example, when the electrode pressure increases, the upper and lower limit values of welding current will also increase. At this time, technicians need to adjust the welding parameters. It is worth mentioning that the cap-sealing machine produced by Kexin has a wider adjustment range, which can meet the welding requirements of different materials and sizes of packages.

3 Conclusion

Combined with a large amount of experimental data, as well as process samples, destructive experiments and other methods, it can be concluded that the welding current, discharge time and electrode pressure will have an impact on the heat of discharge of cap-sealing, which in turn affects the quality and performance of the welded product.

In addition, the factors affecting the quality of cap-sealing not only include the above process parameters, but also include the setting of the welding environment, such as nitrogen environment and vacuum environment. Take nitrogen environment as an example, the low oxygen content in nitrogen environment can effectively reduce the production of oxides, improving the wettability and adhesion of the welded joints, and better guarantee the welding quality.