Foreword
Thermal grease is currently widely used on the IGBT mounting surface of the heat sink. Its purpose is to fill the gap between the mounting surface of each device and the heat sink to achieve a more uniform and more effective heat dissipation effect and to prevent the device from poor heat dissipation. The temperature is too high and it is damaged. In order to ensure that the thermal grease is evenly distributed on the IGBT, the process of coating is crucial.
Thermal grease coating process
At present, there are mainly two kinds of IGBT thermal grease coating processes, roller printing and screen printing.
1. Roller coating, which is the most widely used coating method currently used.
(1) Clean the mounting surface and radiator of the device with alcohol before installing the IGBT;
(2) Pour the thermal grease into the container and apply thermal grease to the roller brush;
(3) Repeatedly rolling a layer of thermal grease on the IGBT mounting surface, visually measuring whether the grease is applied to the IGBT mounting surface, and finally mounting the IGBT on the heat sink.
2. Screen printing and coating, because it has a certain technical threshold, but the effect is better, mainly used for high-end IGBT coating.
(1) The IGBT coating tooling must be designed first. There are mainly two tooling design methods: according to the coating area of ​​the thermal grease on the mesh area of ​​the screen mesh; the coating thickness, area, and surface area of ​​the thermal grease required by the IGBT. Roughness design;
(2) Invert the IGBT components on the coating tooling;
(3) Close the stencil surface of the tooling and confirm that the IGBT coating die hole coincides with the IGBT radiating surface;
(4) Start the coating operation and scrape the thermal grease from one side of the frame to the other, scraping it back and forth 3-4 times until the thermal grease fills the mesh of the screen.
The principle of automatic coating technology
This technology is based on the screen printing and coating process described above, referring to the manual screen printing and coating operations, and driving the various actuators through the motor to realize the use of mechanical automation for the IGBT coating operation, which avoids the labor intensity of the traditional manual coating. Poor reliability, inefficient operating mode.
Figure 1 Manual screen coating
After the experimental analysis, the effect of screen printing coating was obviously better than that of roller coating. In order to ensure the advanced technology, automatic coating technology was designed and implemented using the principle of screen printing and coating.
Roller coating on the left side of Figure 2 and screen coating on the right
Development of the first prototype of automatic coating equipment
In order to meet the equipment requirements for coating operations, such as intelligent, modular, and stable equipment, automated coating equipment should have at least the following characteristics:
1. Coating module count
2. Adjustable number of draws
3. Thermal grease supply controllable
4. Screen replacement reminder
5. System fault alarm
6. Scan code recording function
7. Manual and electric reset function
Fig. 3 Schematic diagram of various structures of automated coating equipment
Process instructions for automated coating equipment operation
1, the workpiece first scan code records, self-walking to the coating position, and fixed.
2. The screen is pressed down and is ready to be filled with thermal grease. This module is mainly composed of a lifting electric cylinder, a scraper mechanism and a screen adjustment mechanism. The tension on the four sides of the screen can be quickly adjusted. The screen is clamped in the center of the upper and lower fixing plates and can automatically adjust the level of the workpiece.
3. Inject thermal grease. The injection mechanism adopts the piston-type injection principle, the piston is fixed, the stepping motor drives the screw rod to push the material barrel, and the thermal grease is injected into the nozzle from the center of the piston to ensure the injection volume is stable and controllable.
4. The scraper presses and the walking mechanism is coated with thermal grease. The straight line module can achieve a repetitive positioning accuracy of 0.05mm and a stable walking. It can automatically fine-tune the distance (pressure) between the scraper and the screen according to different coating requirements. At the same time, the “blade†of the scraper and the screen parallelism can be adjusted.
5. The blade rises, the screen rises, the workpiece scans and exits, completing an IGBT module coating operation.
The advantages of automated coating equipment
1. The entire actuators of the equipment are all isolated and protected to prevent accidental injury due to accidental contact.
2. Standard design concepts are adopted in the design of non-standard modules. The implementing agencies adopt standard products. Its advantages are compact structure, mature application, reliable performance, and high positioning accuracy (0.05mm) of the linear walking mechanism.
3. The injection head is directly connected with the raw material supply equipment, and the introduction stroke is shortened as much as possible. The injection head adopts standard products and mature technology, which can guarantee the uniformity of the injected raw materials.
4, can quickly realize the screen installation and tension adjustment.
5. It adopts a world-class control system with comprehensive parameter configuration and conforms to the intelligent manufacturing concept.
Figure 4 System Control Interface
Application prospects of automated coating technology and equipment
At present, the coating process in China still remains in the traditional era. When the international high-end equipment was introduced, it failed to digest, absorb, and create well. The imitation related equipment also failed to improve in the market competition, and compared with international brands. Less competitive than competitive. The future development of the automated coating industry should not be limited to the R&D and application of automated coating equipment itself, but also work on relevant raw materials to accelerate the pace of transformation and upgrade to meet the rapidly growing market demand and increasingly diversified Custom requirements. The IGBT thermal grease automation coating equipment developed by North Steel Union opened the era of mechanical automatic production of the coating process. The prototype may be derived from more versions and is expected to be used for power, electronics, rail transit, aerospace, etc. The field has far-reaching implications.
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