A power device laser welding process

Abstract

The application discloses and provides a power device laser welding process with high welding quality and being beneficial to realizing automatic flexible production of a production line. The application uses a laser welding system, and the power device laser welding process comprises the following steps: ①editing a track of a galvanometer control card through a PC industrial computer; ②editing laser energy modulation of a laser control card through the PC industrial computer; ③placing an IGBT module on a jig below a galvanometer module, and making a copper key pin of the IGBT module abut against a copper layer of a copper-clad plate of the IGBT module; ④controlling the galvanometer module to realize swing welding through the galvanometer control card, and synchronously modulating power of a green light continuous laser according to a swing position period, so that the modulated laser is shot on the copper key pin, and the copper key pin is fused on the copper layer of the copper-clad plate. The application is applied to the technical field of the power device laser welding process.

Description

TECHNICAL FIELD

[0001] The present application relates to a laser welding process, in particular to a power device laser welding process. BACKGROUND

[0002] IGBT (Insulated Gate Bipolar Transistor) is an insulated gate bipolar transistor, which is a kind of power device, and has the advantages of high input impedance of MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and low on-voltage of GTR (Giant Transistor). IGBT has the characteristics of large input impedance, small driving power, simple control circuit, small switching loss, high speed and high frequency, and is widely used in aerospace, rail transit, smart grid, new energy, especially new energy vehicle field. Common un-plastic packaged IGBT is shown in FIG. 1. Figure 1

[0003] IGBT packaging involves multiple welding processes, such as the packaging and detection of the gate, collector and emitter three key poles in the post-packaging section-plastic forming-metal packaging process-copper binding packaging process. The power conducting terminal of IGBT module needs to carry hundreds of amperes of large current, and has high requirements on electrical conductivity and thermal conductivity. The IGBT in the automobile also needs to withstand a certain vibration and impact force, and has high requirements on mechanical strength, so the welding technology process of IGBT conducting terminal is very high. The packaging requires that the parameters such as parasitic capacitance and parasitic inductance in the IGBT module are as small as possible to reduce the influence on the circuit performance. High-quality welding points, large welding area of the contact surface between copper band key and ceramic copper-clad plate, and few defects such as welding pores. Therefore, the welding point must be accurate in position and good in quality to ensure that there is no splashing during welding. The temperature at the chip is required when welding the chip close to the welding point, that is, the heat input during welding also needs to be controlled.

[0004] ​Traditional soldering process, although simple process, easy to operate, but there are easy to oxidize, and the welding process release toxic gas, poor environmental performance and other shortcomings. As an alternative ultrasonic welding, due to the power semiconductor welding terminal small, substrate fragile, post-welding substrate mechanical deformation, its incoming material and process requirements more fine. And ultrasonic welding generally requires welding thickness less than 5mm, due to the process changes in the IGBT production process, in the metal packaging process, part of the product thickness greater than 15mm, ultrasonic welding is not the preferred solution of copper key packaging, and ultrasonic welding needs to use a dedicated welding pressure head and base, not conducive to the production line automation flexible production, need to produce corresponding model of the product line. Part of the process flow selection of non-contact laser welding as an alternative, currently trying to use infrared wavelength laser welding copper key. Because of its high requirements for the welding metal surface, oxidation may affect the welding quality, the depth of fusion is unstable, the contact surface fusion area is small, etc., affecting the process of mass production stability and yield. SUMMARY

[0005] The technical problems to be solved by the present application are to overcome the shortcomings of the prior art and to provide a power device laser welding process with high welding quality and conducive to the automation and flexible production of the production line.

[0006] The technical scheme adopted by the present application is: the present application uses a laser welding system, which comprises a green continuous laser, a galvanometer module, a laser control card, a galvanometer control card and a PC industrial computer; the green continuous laser and the laser control card are in serial communication, the galvanometer module and the galvanometer control card are in serial communication, the laser control card and the galvanometer control card are in serial communication, the laser control card and the galvanometer control card are in network communication with the PC industrial computer, the green continuous laser is connected with the galvanometer module through a transmission optical fiber, and the galvanometer module is used to change the direction of the laser beam. The power device laser welding process of the present application comprises the following steps:

[0007] ①editing the trajectory of the galvanometer control card through the PC industrial computer;

[0008] ②editing the laser energy modulation of the laser control card through the PC industrial computer;

[0009] ③placing the IGBT module on the jig below the galvanometer module, and the copper key pin of the IGBT module is attached to the copper layer of the copper-clad plate of the IGBT module;

[0010] ④the galvanometer control card controls the galvanometer module to realize swing welding, and the power of the green continuous laser is modulated synchronously with the swing position, and the modulated laser is applied to the copper key pin to make the copper key pin welded to the copper layer of the copper-clad plate.

[0011] Furthermore, the green continuous laser generates a 515nm wavelength green laser.

[0012] Furthermore, the oscillation mode of the oscillation welding is sinusoidal oscillation.

[0013] Furthermore, when setting the welding oscillation trajectory for the galvanometer module, the oscillation frequency (frequency), initial phase (phase), and control period (dt) of the galvanometer are read. In the welding process, when laser welding a single line, due to heat accumulation, the energy of the weld line is gradually reduced and maintained. The laser power is then modulated as expected = 90% + 10% * sin((2 * PI * frequency * dt) + 0.5 * PI). During oscillation welding, the oscillation period is 2π. The initial phase (phase) is the initial oscillation position of the galvanometer, and PI is a set constant π. The initial phase (phase) and PI are set so that when modulating energy, the modulated power differs from the oscillation position by 1 / 4 of a period. The power is maximized when the velocity component is maximum in the direction of weld line advancement.

[0014] Furthermore, a negative pressure dust extraction device is installed during the welding process to remove the fumes and dust generated during the process.

[0015] Furthermore, the optical continuous laser is a kilowatt-level green laser. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a common unsealed automotive-grade IGBT;

[0017] Figure 2 This is a comparison chart of the absorption rates of metallic copper for green light and infrared light;

[0018] Figure 3 This is a sample image of laser-welded IGBT copper terminals;

[0019] Figure 4 This is a schematic diagram of the components of an IGBT laser welding system;

[0020] Figure 5 This is a schematic diagram of oscillating laser welding;

[0021] Figure 6 This is a schematic diagram of the welding oscillation trajectory set by the galvanometer;

[0022] Figure 7 This corresponds to the energy curves before and after the laser power is modulated by the oscillation of the galvanometer.

[0023] Figure 8 These are cross-sectional comparison images after welding;

[0024] Figure 9 This is a picture showing the actual welding effect of the product. Detailed Implementation

[0025] In this embodiment, the present invention employs a kilowatt-level green laser to perform oscillating welding on the copper bonds of an IGBT module. Laser oscillating welding melts the material using the high energy of the laser beam, while simultaneously utilizing oscillating welding technology to make the laser beam move periodically within the welding area, thereby optimizing the welding process. The present invention also synchronously modulates the laser power with the oscillation position periodically, achieving consistent weld depth in each oscillation cycle. Furthermore, it linearly modulates the laser power in the welding direction, ensuring consistent weld depth from start to finish in a single weld. This results in consistent weld depth at the lap joint, enabling high-quality welding for products sensitive to weld depth and requiring large weld areas.

[0026] The specific system composition and process flow are summarized below:

[0027] 1. Since copper is a highly reflective material, a 515nm wavelength green laser was chosen for welding, compared to infrared lasers (…). Figure 2 The laser is easily absorbed by copper, and its welding stability is not affected by power reduction during power modulation. Furthermore, the high absorption rate of the laser results in a more stable welding process, free from spatter and explosions. Figure 3 As shown.

[0028] 2. The oscillation trajectory and laser energy modulation are edited using an industrial control computer on the galvanometer control card and laser control card. During product processing, the corresponding trajectory and waveform are retrieved via serial communication for welding. (See below.) Figure 4 The diagram shown is a schematic of the overall system.

[0029] 3. In terms of laser process setup, the oscillating welding process is used, such as... Figure 5 As shown, this avoids the problem of thermal stress concentration during welding, thus obtaining a more uniform and stable weld quality and reducing welding defects. The width and length of the welding oscillation are edited via the galvanometer control card according to the size of the copper key pins. The power is set via the laser control card according to the thickness of the copper key pins and the thickness of the copper layer of the copper-clad laminate to meet welding requirements.

[0030] For example, when soldering a common 3mm*2mm copper lead with a thickness of 1mm, the soldering process used is oscillating soldering, with the oscillation pattern being sinusoidal. Figure 6The welding oscillation trajectory is set for the galvanometer. The galvanometer frequency (oscillation frequency), initial phase (phase), and control period (dt) are read. In the welding process, when laser welding a single line, the energy of the weld line is gradually reduced and maintained due to heat accumulation. The laser power is further modulated as expected = 90% + 10% * sin((2 * PI * frequency * dt) + 0.5 * PI). During oscillation welding, the oscillation period is 2π. The initial phase (phase) is the initial oscillation position of the galvanometer, and PI is a set constant π. The initial phase (phase) and PI are set so that when modulating energy, the modulated power differs from the oscillation position by 1 / 4 period, and the power is maximized when the velocity component is maximum in the direction of weld line advancement. Figure 7 The energy curves before and after modulation are shown to correspond to the laser power modulation caused by the galvanometer swing. Figure 8 This is a comparison image of cross-sections after welding.

[0031] The modulation of laser energy relative to the galvanometer's swing position is adjusted based on the width of the copper bonds and heat dissipation requirements of the product, with the amplitude of the power modulation set accordingly. Simultaneously, a negative pressure dust extraction system is used during the welding process to remove fumes and dust, achieving a smooth, burr-free finish.

[0032] Figure 9 shows the welding effect of an actual product. The example product has copper leads of 3mm*2mm with a thickness of 1mm, and a copper layer thickness of 0.35mm on the underlying copper-clad laminate. Using this invention, the welding area can be greater than 85% of the copper bond surface area, and the welding depth is stable without affecting the underlying ceramic layer.

[0033] The beneficial effects of this invention are:

[0034] 1. It adopts a kilowatt-level green laser, and the copper material has a high absorption rate, making the welding process more stable and free of spatter and explosions.

[0035] 2. The use of oscillating welding process increases the fusion area and improves welding stability. By changing the oscillation width, it can adapt to the welding requirements of copper keys of different widths.

[0036] 3. This invention synchronizes the laser power with the oscillation position periodically, solving the product requirement of consistent weld depth when welding products with a thick upper layer and a thin lower layer.

[0037] 4. Using the laser welding process of this invention, automated processing can be easily achieved, greatly improving product production efficiency.

[0038] 5. This invention can process copper bonds with different surface conditions, and has good process compatibility;

[0039] 6. Compared with traditional ultrasonic welding, it improves production efficiency, enhances product quality and yield, and eliminates the need for cumbersome fixture changes during model changeovers, providing strong support for intelligent and flexible production.

[0040] Although the embodiments of the present invention are described with reference to actual solutions, they do not constitute a limitation on the meaning of the present invention. Modifications to the embodiments and combinations with other solutions based on this specification will be obvious to those skilled in the art.

Claims

1. A laser welding process for power devices, using a laser welding system, the laser welding system comprising a green continuous laser, a galvanometer module, a laser control card, a galvanometer control card, and a PC industrial computer; the green continuous laser and the laser control card communicate via serial port; the galvanometer module and the galvanometer control card communicate via serial port; the laser control card and the galvanometer control card communicate via serial port; both the laser control card and the galvanometer control card communicate with the PC industrial computer via network port; the green continuous laser is connected to the galvanometer module via a transmission optical fiber; the galvanometer module is used to change the direction of the laser beam, characterized in that: The laser welding process for power devices includes the following steps: ① The trajectory of the galvanometer control card is edited using the PC industrial control computer; ② The laser energy modulation and editing of the laser control card are performed through the PC industrial control computer; ③ Place the IGBT module on the fixture below the galvanometer module, with the copper bond pins of the IGBT module abutting against the copper layer of the copper-clad laminate of the IGBT module; ④ The galvanometer control card controls the galvanometer module to achieve oscillating welding. The power of the green continuous laser is periodically modulated synchronously with the oscillation position. The modulated laser hits the copper bond pins, so that the copper bond pins are fused to the copper layer of the copper-clad laminate. When setting the welding oscillation trajectory for the galvanometer module, the oscillation frequency, initial phase, and control period dt of the galvanometer are read. In the welding process, when laser welding a line, due to heat accumulation, the energy of the weld line is gradually reduced and maintained, and the laser power is modulated as expected = 90% + 10% * sin((2 * PI * frequency * dt) + 0.5 * PI). In oscillation welding, the oscillation period is 2π, the initial phase is the initial oscillation position of the galvanometer, and PI is the set constant π. The initial phase and PI are set so that when modulating energy, the modulation power and the oscillation position differ by 1 / 4 period. The power is maximized when the velocity component is maximized in the direction of weld line advancement.

2. The laser welding process for power devices according to claim 1, characterized in that: The green continuous laser generates a 515nm wavelength green laser.

3. The laser welding process for power devices according to claim 1, characterized in that: The oscillation mode of the oscillation welding is sinusoidal oscillation.

4. The laser welding process for power devices according to claim 1, characterized in that: Negative pressure dust extraction equipment is installed during the welding process to remove fumes and dust.

5. The laser welding process for power devices according to claim 1, characterized in that: The optical continuous laser is a kilowatt-level green laser.

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