Analysis of various process parameters that affect the effect of parallel seam welding
Guo Jianbo, Sun Yinhu, Su Xinyue.
Tianshui 749 Electronics***
Abstract:Parallel seam welding is a means of hermetic sealing of integrated circuit tube shells, which is a kind of hermetic sealing with low thermal stress and high reliability. The best effect of parallel seam welding is that the shell reflux area is continuous and void-free, and the shell temperature is not too high. This paper mainly focuses on how to achieve the best effect of parallel seam welding, starting from the working principle of parallel seam welding, analyzes the main process parameters of parallel seam welding, and describes the influence of the change of each parameter on the heat of parallel seam welding and how to cooperate with each other to obtain the best effect of parallel seam welding. Finally, concrete examples are given to illustrate how to set each parameter to get the best results. Therefore, in the process of parallel seam welding, we must pay attention to the selection of seam welding parameters to ensure the best seam welding effect.
1 Introduction. Parallel seam welding is a means of airtight packaging of integrated circuit tube shell, which is a kind of low thermal stress, high reliability of hermetically sealed, in order to obtain high-quality seam welding effect, parallel seam welding between the process parameters of each mutual cooperation is indispensable. Let's start from the parallel seam welding process parameters, and talk about how to get the best effect of parallel seam welding according to the actual operation experience.
2 Description of the best results of parallel seam welding.
Parallel seam welding is done with the help of a parallel seam welding system, through which two conical electrodes are in contact with the cover plate, providing a closed loop for the electric current. When the two electrodes roll along the edge of the metal cover, a series of short high-frequency power pulse signals pass between the two electrodes, which generate extremely high local heat at the contact point between the electrode and the cover, causing the cover to melt and reflux, thus forming a complete and continuous seam weld area. High-quality seam weld results mean that the reflow area is continuous and porosity-free, and the shell temperature is not too high. Therefore, it is very important to achieve this effect by seam-welding the casing with the least amount of total energy input, which melts the metal without overheating the casing. Overheating can cause metal particles to swell, resulting in microcracks or crevices. The metal must melt and reflux in a short time, and this time must be less than the time it takes for heat to be transferred to the shell, so as not to overheat the shell itself.
3 Process parameters that affect the heat of seam welding.
The parallel seam welding process is a process of energy conservation, we set the current to be a series of uniform pulse signals, and there is a stable seam welding speed, then the seam welding heat can be expressed by equation (1):
energy =[**g·power]×t= v 2 rms /r c ×[pw/prt]×t （1）
In Eq. (1), v is the voltage passing through the electrode; r c is the contact resistance between the two electrodes and the cover plate; pw is the pulse width, in ms; PRT is the pulse repetition time, in ms, which refers to the time interval between the rising edges of successive pulses.
There are several parameters that affect the heat of parallel seam welding: seam welding power, pulse width, repetition time, electrode pressure, welding speed, etc. Changing any of these parameters will affect the heat generated during the seam welding process, which is analyzed as follows according to equation (1).
The welding signal of parallel seam welding is a series of pulse trains, each pulse train contains one or more pulses, the pulse width determines the size of each pulse train, and the repetition time determines how often the pulse repeats. Note: For the same shell, once the pulse width and repetition time are set, they are usually left constant, and a small change in the ratio of the two can have a big impact on the actual welding power transferred to the shell. The seam welding power determines the amplitude of the pulse train, and the combination of seam welding power, pulse width and repetition time can accurately control the effective power transmitted to the shell cover. Electrode pressure refers to the pressure of the electrode added to the cover plate during the seam welding process, the electrode pressure directly affects the contact resistance of the electrode to the cover plate, the greater the electrode pressure, the smaller the contact resistance. Seam welding speed refers to the movement speed of the tube shell under the electrode during seam welding, and the seam welding speed also has a certain impact on the seam welding heat, the faster the moving speed, the more heat is required.
Energy = Power Time (2).
When the speed is fast, the time is shorter, so the power has to be increased. However, the energy equation is not completely linear, so the parameters must be coordinated with each other to achieve the best welding results and reduce the temperature of the housing.
4. The best combination of process parameters.
The energy control in the seam welding process can be represented by Fig. 1, Fig. 2, Fig. 3. Fig.1 The seam welding power is determined by a series of 1kHz power signal adjustments. Keeping the effective power low in Figure 2 allows the device to cool down without overheating; The high peak power guarantees good reflow. The correct selection of pulse parameters in Figure 3 allows for a continuous seam weld with very little heat transfer to the device.
Figures 1 and 2 do not indicate the seam weld speed during the welding process, but the speed can be shown by the overlapping reflow regions in Figure 3, each of which represents the heat generated by a series of power bursts. The process parameters that affect the heat of parallel seam welds will vary during energy-conserved seam welding, but the results of the changes need to produce a series of overlapping reflow regions such as those shown in Figure 3 while keeping the shell temperature too high.
As can be seen from Figures 1 and 2, heating is done with the power consumed from the electrode to the cover surface in PW time (Figure 1), and cooling is done in (PRT-PW) time intervals. By using a pulse signal of 1kHz and a programmable duty cycle, the parallel seam welding system allows the metal to flow back quickly without exceeding the heating time constant of the tube shell, thus keeping the integrated circuit cool during the welding process. In a series of "" shaped 1kHz power trains, a pulse of one PW in each PRT cycle provides the weld input power, resulting in the overlapping effect shown in Figure 3.
Therefore, in order to reduce the heat of the tube shell, the pulse must be short during the pulse cycle, but the pulse must also provide enough power to melt the cover, which can only be achieved by carefully selecting the welding parameters. The following two options produce similar welding results, but the most obvious difference is the difference in the effective power transmitted to the tube housing.
Therefore, the selection of optimized pulse parameters can minimize the heat transmitted to the tube shell, and compared with scheme 2, scheme 1 must have a low shell temperature and good seam welding effect in scheme 1.
5 Conclusion. In summary, in order to obtain high-quality seam welding results, the interaction between seam welding parameters is indispensable. In the production process, we must pay attention to the selection of seam welding parameters to ensure the yield of seam welding.