A multi-layer heat dissipation structure welding system and process for integrated circuits

Abstract

The application discloses a multi-layer heat dissipation structure welding system and process for integrated circuits. The system comprises a multi-piece clamp, a brazing device and a laser edge sealing welding device. The multi-piece clamp has a hollow structure and / or a lateral opening structure, and is used for assembling a liquid cooling heat dissipation layer and a packaged vacuum cavity heat uniform layer into a to-be-welded assembly. The brazing device has a forced cooling pressure head, and performs forced cooling close to the upper surface of the packaged vacuum cavity heat uniform layer during welding. The laser edge sealing welding device directly performs edge sealing welding on the heat dissipation structure without disassembling the clamp after brazing is completed. The application also monitors the brazing area temperature and the packaged vacuum cavity heat uniform layer part temperature through a temperature detection unit, and dynamically adjusts the cooling intensity by a cooling control unit. The application can complete laser edge sealing welding without disassembling the clamp, avoids secondary clamping errors, effectively protects the packaged vacuum cavity heat uniform layer, has high welding qualification rate, and is suitable for batch production.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and in particular to a welding system and process for a multilayer heat dissipation structure for integrated circuits. Background Technology

[0002] The most common multilayer heat dissipation structure for integrated circuits is a composite structure of liquid cooling heat dissipation layer and vacuum cavity heat dissipation layer. This structure is formed by brazing the liquid cooling heat dissipation layer and the vacuum cavity heat dissipation layer together. Before brazing, in order to prevent the high temperature of brazing from damaging the vacuum cavity heat dissipation layer, a common practice in the industry is to use the unpackaged vacuum cavity heat dissipation layer. However, if the vacuum cavity heat dissipation layer that needs to be soldered is already packaged, the dielectric in the vacuum cavity heat dissipation layer will be emptied first, and then the dielectric will be refilled and packaged after the soldering is completed, which makes the process complicated.

[0003] Currently, there is no mature welding technology available to reference for safely and firmly welding the vapor chamber heat dissipation layer and the liquid cooling heat dissipation layer of the encapsulated vacuum cavity together, while ensuring the welding qualification rate and production efficiency. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a multi-layer heat dissipation structure welding system and process for integrated circuits, which can safely and firmly weld the packaged vacuum cavity heat dissipation layer and the liquid cooling heat dissipation layer together, and ensure the welding qualification rate and production efficiency.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A multilayer heat dissipation structure welding system for integrated circuits, comprising: A multi-piece fixture assembles multiple sets of liquid-cooled heat dissipation layers and encapsulated vacuum cavity heat dissipation layers to be welded, forming an assembly to be welded. The multi-piece fixture has a hollow structure and / or a side opening structure, leaving gaps for the laser beam to pass through. The brazing equipment has a forced cooling pressure head that is in close contact with the assembly to be welded during welding, and forces cooling on one side of the heat spreader layer of the encapsulated vacuum cavity. Laser edge sealing welding equipment is used to perform laser edge sealing welding on multiple sets of heat dissipation structures that have been brazed and are held in multi-piece fixtures.

[0006] In the welding system described above, the brazing equipment is a vacuum brazing furnace.

[0007] In the welding system described above, the forced cooling pressure head is located on the upper side of the brazing equipment, closely attached to the upper surface of the heat dissipation layer of the encapsulated vacuum cavity, and has a circulating cooling channel inside.

[0008] The welding system described above also includes a temperature detection unit for monitoring the temperature of the brazing area and the temperature of the heat spreader layer in the encapsulated vacuum cavity.

[0009] In the welding system described above, the forced cooling head is connected to an external cooling control unit, which is connected to a cooling medium supply device, and is used to adjust the cooling intensity of the forced cooling head in real time according to the temperature of the brazing area and the temperature of the heat spreader layer in the encapsulated vacuum cavity.

[0010] In the welding system described above, the laser edge sealing welding equipment is a multi-axis laser welding robot that automatically identifies the weld trajectory through a vision positioning system.

[0011] This invention also provides a welding process for a multilayer heat dissipation structure for integrated circuits, employing the welding system described above, comprising: Clamping steps: Assemble and fix the liquid cooling heat dissipation layer and the encapsulated vacuum cavity heat dissipation layer using a multi-piece fixture to form an assembly to be soldered; Brazing steps: The multi-piece fixture holding the assembly to be brazed is placed into the brazing equipment, and the temperature is raised for brazing. At the same time, the vapor chamber layer of the packaged vacuum cavity is cooled by a forced cooling head. Laser edge sealing welding steps: Transfer the multi-piece fixture holding the brazed heat dissipation structure to the laser edge sealing welding station. Without disassembling the multi-piece fixture, start the laser edge sealing welding equipment and perform laser edge sealing welding along the exposed outer peripheral edge of the heat dissipation structure. Unloading steps: After completing the edge sealing welding, remove the clamps and take out the finished product.

[0012] In the welding process described above, during the brazing step, the temperature of the brazing area and the temperature of the heat spreader layer in the encapsulated vacuum cavity are monitored in real time by a temperature detection unit, and the cooling intensity of the forced cooling head is adjusted in real time by a cooling control unit based on the temperature of the brazing area and the temperature of the heat spreader layer in the encapsulated vacuum cavity.

[0013] As described above, the real-time adjustment of the cooling intensity of the forced cooling head in the welding process includes: reducing the cooling intensity when the temperature of the brazing area is lower than the preset target temperature; and increasing the cooling intensity when the temperature of the heat spreader layer in the encapsulated vacuum cavity exceeds the preset tolerance temperature.

[0014] The welding process described above also includes a product inspection step.

[0015] The multilayer heat dissipation structure welding system and process for integrated circuits provided by this invention have the following significant advantages compared with the prior art: The present invention features a forced cooling pressure head located on the upper side, forming a "hot at the bottom and cold at the top" temperature gradient, effectively protecting the heat dissipation layer of the encapsulated vacuum cavity. The cooling intensity is dynamically adjusted by the cooling control unit to ensure the uniformity of brazing quality and safety. The present invention allows for laser edge sealing welding without disassembling the fixture, avoiding positional deviations and efficiency losses caused by secondary clamping. The multi-piece fixture has built-in thermal expansion and contraction compensation to prevent workpiece deformation at high temperatures. Laser edge sealing welding, combined with a vision positioning system, enables high-precision automated welding. Through the collaboration of various devices, the heat dissipation layer of the encapsulated vacuum cavity and the liquid cooling heat dissipation layer, which have not been emptied of the medium (such as water, acetone, or special working fluid), can be safely and firmly welded together, ensuring welding qualification rate and production efficiency, making it suitable for mass production. Attached Figure Description

[0016] Figure 1 This is a process configuration diagram of the multilayer heat dissipation structure welding system for integrated circuits according to the present invention.

[0017] Figure 2 This is a schematic diagram illustrating the brazing working principle of the multilayer heat dissipation structure welding system for integrated circuits according to the present invention.

[0018] Figure 3 for Figure 1 Enlarged view of the contact area between the forced cooling head and the assembly to be welded.

[0019] Figure 4 This is a schematic diagram illustrating the working principle of laser edge sealing welding in the multilayer heat dissipation structure welding system for integrated circuits of the present invention.

[0020] The components represented by the labels in the diagram are: A: Liquid cooling heat dissipation layer, B: Encapsulated vacuum cavity heat dissipation layer, 10: Multi-piece fixture, 20: Brazing equipment, 21: Forced cooling pressure head, 211: Cooling protrusion, 30: Laser edge sealing welding equipment. Detailed Implementation

[0021] Exemplary embodiments of this disclosure will now be described in more detail.

[0022] Example 1, such as Figure 1-4 As shown in the figure, this embodiment of a multi-layer heat dissipation structure welding system for integrated circuits includes at least a multi-piece fixture 10, a brazing device 20, and a laser edge sealing welding device 30, which are described below.

[0023] The multi-piece fixture 10 is an important tooling of the system, used to assemble multiple sets of liquid cooling heat dissipation layers A and encapsulated vacuum cavity heat dissipation layers B to be welded, forming an assembly to be welded. In this embodiment, the liquid cooling heat dissipation layer A is made of oxygen-free copper, and the encapsulated vacuum cavity heat dissipation layer B is an oxygen-free copper shell. The solder is a low-temperature solder (such as Ag20Sn or Ag25Sn) with a melting temperature not exceeding 650°C. It can be in foil or paste form and is pre-placed between the liquid cooling heat dissipation layer A and the encapsulated vacuum cavity heat dissipation layer B according to the corresponding conventional operation.

[0024] In other embodiments, the liquid cooling heat dissipation layer A can also be made of aluminum alloy, and the encapsulated vacuum cavity heat dissipation layer B can also be made of stainless steel or aluminum alloy.

[0025] In this embodiment, the multi-piece fixture 10 is a combination of two upper and lower pressure plates, made of 310S stainless steel. The two pressure plates are designed with a hollow structure and a side opening structure, leaving sufficient gaps for the laser beam to pass through during subsequent laser edge sealing welding. The locking parts of the two pressure plates are provided with thermal expansion and contraction deformation allowance by a pre-tightening spring. During manufacturing, the opening rate of the hollow structure is not less than 60%, and the side opening size ensures that the laser beam can irradiate the edge of the workpiece without obstruction at an incident angle of 15°-45°.

[0026] During the clamping process, the liquid cooling heat dissipation layer A and the encapsulated vacuum cavity heat dissipation layer B are assembled and fixed using the multi-piece fixture 10 to form an assembly to be welded. During clamping, the initial compression of the pre-tension spring provides a clamping pressure of 0.5-1.0 MPa, while allowing the fixture to generate a compensation displacement of 0.2-0.5 mm as the workpiece thermally expands under high temperature.

[0027] The brazing equipment 20 is the main welding equipment of the system. It has a forced cooling head 21 that is in close contact with the assembly to be welded during welding, and forces cooling on one side of the heat spreader layer B of the encapsulated vacuum cavity.

[0028] In this embodiment, the brazing equipment 20 is a vacuum brazing furnace, which can provide 5×10 during the brazing step. -4 Pa-5×10 -3 The vacuum level is Pa. The forced cooling head 21 is located on the upper side of the brazing equipment 20, closely attached to the upper surface of the heat dissipation layer B of the encapsulated vacuum cavity. It has a circulating cooling channel inside, and as shown... Figure 2 As shown, the drive cylinder of the forced cooling head 21 and the cooling medium supply device are both located outside the brazing equipment 20. At the same time, the forced cooling head 21 is connected to an external cooling control unit, which is connected to the cooling medium supply device. The cooling medium is deionized water, and the inlet temperature of the cooling medium is controlled within the range of 15-25℃.

[0029] Because the multi-piece fixture 10 has a hollow skeleton structure, such as Figure 3As shown, the forced cooling punch 21 forms multiple cooling protrusions 211, which can extend downward into the reserved space of the multi-piece fixture 10 and closely adhere to the upper surface of each encapsulated vacuum cavity heat spreader B. Therefore, the number of cooling protrusions 211 is the same as the number of heat dissipation structure sets clamped by the multi-piece fixture 10, such as 6, 12 or 24. The coverage ratio of the surface of the cooling protrusions 211 on the encapsulated vacuum cavity heat spreader B is not less than 70%. The contact pressure is controlled at 0.2 - 0.8 MPa by an external driving cylinder to ensure good heat conduction efficiency. The contact pressure can be centrally controlled through a pressure sensor supporting the driving cylinder. In another embodiment, a pressure sensor can also be separately embedded at the bottom of the independent cooling protrusion 211 to accurately collect the corresponding contact pressure.

[0030] When performing the brazing step, the multi-piece fixture 10 clamping the to-be-welded assembly is placed as a whole into the brazing equipment 20, heated for brazing, and at the same time, the side of the encapsulated vacuum cavity heat spreader B is cooled by the forced cooling punch 21.

[0031] The laser edge-sealing welding equipment 30 is also an important welding equipment of the system, which is used for laser edge-sealing welding of multiple sets of heat dissipation structures that have been brazed and clamped in the multi-piece fixture 10. The laser edge-sealing welding equipment 30 is a multi-axis laser welding robot, which automatically identifies the weld seam trajectory through a vision positioning system. Specifically, in this embodiment, the laser welding robot is a 6-axis articulated robot, the laser is a fiber laser, the output power is adjustable from 100 - 500 W, the shielding gas is argon, and the vision positioning system includes an industrial camera and an image processing module, and generates the weld seam trajectory coordinates by identifying the feature points (such as corner points, edges) of the workpiece edge.

[0032] The laser edge-sealing welding step is closely related to the previous low-temperature brazing process. In the laser edge-sealing welding step, the multi-piece fixture 10 clamping the heat dissipation structure that has been brazed is transferred to the laser edge-sealing welding station. Without disassembling the multi-piece fixture, the laser edge-sealing welding equipment 30 is started, and laser edge-sealing welding is performed along the exposed outer peripheral edge of the heat dissipation structure. The laser power is selected as 150 - 250 W, and the welding speed is 8 - 15 mm / s.

[0033] This embodiment also provides a multi-layer heat dissipation structure welding process for integrated circuits, which includes a clamping step, a brazing step, a laser edge-sealing welding step and a discharging step. When introducing the previous welding system, the detailed operations of the clamping step, the brazing step and the laser edge-sealing welding step have been introduced and will not be repeated. Finally, in the discharging step after the edge-sealing welding is completed, the fixture is disassembled and the finished product is taken out.

[0034] In addition, after the finished product is removed, this embodiment may further include a product inspection step. The product inspection step uses X-ray non-destructive testing equipment to inspect the internal defects of the weld seam of the welded multi-layer heat dissipation structure and reject the unqualified products detected.

[0035] Example 2, based on Example 1, in order to ensure that the heat spreader layer B of the encapsulated vacuum cavity is not damaged by high temperature during the brazing process, this example uses a temperature detection unit to monitor the temperature of the brazing area and the temperature of the heat spreader layer B of the encapsulated vacuum cavity. At the same time, the cooling control unit adjusts the cooling intensity of the forced cooling head 21 in real time according to the temperature of the brazing area and the temperature of the heat spreader layer B of the encapsulated vacuum cavity. The cooling control unit adopts a programmable logic controller (PLC) or an industrial computer, and its output is connected to the frequency converter or proportional regulating valve of the cooling medium supply pump.

[0036] Specifically, in this embodiment, the temperature detection unit includes a first temperature sensor and a second temperature sensor. The first temperature sensor is disposed on the contact surface of the cooling protrusion 211 of the forced cooling head 21 (not shown in the figure). Specifically, a suitable blind hole is opened at the position where all or a selected part of the cooling protrusion 211 contacts the upper surface of the vapor chamber heat spreader B of the encapsulated vacuum cavity. The temperature measuring end of the armored thermocouple is inserted into the blind hole and fixed with high-temperature thermally conductive adhesive. When the cooling protrusion 211 is in close contact with the upper surface of the vapor chamber heat spreader B of the encapsulated vacuum cavity, the first temperature sensor indirectly measures the surface temperature of the vapor chamber heat spreader B of the encapsulated vacuum cavity through the metal thermal conductivity of the cooling protrusion 211. For multiple temperature data, the response principle based on the maximum value is adopted. In addition, considering that there is a cooling medium inside the cooling protrusion 211, the measured temperature is lower than the surface temperature of the vapor chamber heat spreader B of the encapsulated vacuum cavity. This deviation needs to be reserved with a safety margin in the preset tolerance temperature threshold. The wiring of the first temperature sensor is led out along the wiring channel of the forced cooling head 21, transmitted from the inside of the brazing equipment 20 to the outside, and communicates with the cooling control unit. In this embodiment, the second temperature sensor refers to the furnace temperature sensor located inside the brazing equipment 20 near the assembly to be welded. This eliminates the need for the cumbersome design of installing armored thermocouples on the multi-piece fixture 10; the data only needs to be exchanged with the cooling control unit. Thus, the temperature of the brazing area can be indirectly obtained through the furnace temperature sensor located inside the brazing equipment 20 near the assembly to be welded. Actual temperature of the brazing area The conversion relationship is determined through preliminary process calibration (installation of temporary patch thermocouples for temperature measurement) and is corrected in real time according to the current cooling intensity. The correction formula is: ,in: The reference cooling flow rate is the flow rate of the cooling medium used in the calibration experiment. It serves as a reference point and can be a commonly used flow rate value in the process, in L / min; Q is the current cooling medium flow rate, in L / min. And k are calibration constants, where, The reference temperature difference is the temperature difference at the reference cooling flow rate. Under these conditions, furnace temperature Actual temperature of the brazing area The difference between them This is the temperature difference correction factor, which represents the change in temperature difference ΔT when the cooling flow rate changes by 1 L / min, in °C / (L / min).

[0037] The temperature of the brazing area is calculated by using the furnace temperature, eliminating the need to add sensors to the multi-piece fixture 10, simplifying the system structure and improving reliability. During the brazing step, the multi-piece fixture 10 holding the assembly to be brazed is placed into the brazing equipment 20, and the temperature is raised for brazing. At the same time, the forced cooling head 21 cools one side of the heat spreader layer B of the encapsulated vacuum cavity. The temperature detection unit monitors the temperature of the brazing area and the temperature of the heat spreader layer B of the encapsulated vacuum cavity in real time. The cooling control unit adjusts the cooling intensity of the forced cooling head 21 in real time according to the temperature of the brazing area and the temperature of the heat spreader layer B of the encapsulated vacuum cavity. When the temperature of the brazing area is lower than the preset target temperature, the cooling intensity is reduced; when the temperature of the heat spreader layer B of the encapsulated vacuum cavity is close to or exceeds the preset tolerance temperature, the cooling intensity is increased. Specifically, in this embodiment, as a preferred rather than limiting measure, the preset target temperature is 650℃±10℃, and the preset tolerance temperature is 200℃. When the temperature of the brazing area is more than 5℃ lower than the preset target temperature, the cooling intensity (medium flow rate) is reduced by 5-10%. When the temperature of the vapor chamber B in the encapsulated vacuum cavity reaches within 10℃ below the preset tolerance temperature, the cooling intensity (medium flow rate) is increased by 10-15%. When the temperature of the vapor chamber B in the encapsulated vacuum cavity reaches or exceeds the preset tolerance temperature, an alarm is issued and heating is stopped. When the temperature of the brazing area is too low and the temperature of the vapor chamber B in the encapsulated vacuum cavity is close to overheating, the cooling intensity is increased first to protect the vapor chamber B in the encapsulated vacuum cavity, and the heat preservation time is extended to compensate for the insufficient brazing temperature.

[0038] Furthermore, as described in Embodiment 1, as an optional implementation, a pressure sensor may also be embedded at the bottom of the cooling protrusion 211. In this case, the first temperature sensor and the pressure sensor located at the bottom of the same cooling protrusion 211 can provide judgment data on thermal damage to the heat spreader of the encapsulated vacuum cavity. When the temperature change rate collected by the first temperature sensor and the pressure change rate collected by the pressure sensor both exceed a set threshold, a high-temperature cracking warning for the heat spreader of the encapsulated vacuum cavity is issued, triggering a system response. This response may also involve dynamic adjustment of the cooling intensity.

[0039] Other operations are the same as in Example 1 and will not be repeated here.

[0040] It should be noted that, in another alternative implementation, the second temperature sensor can also be a sheathed thermocouple for direct temperature measurement. In this case, a groove can be cut inside the pressure plate of the multi-piece fixture 10, the temperature measuring end of the sheathed thermocouple can be embedded in the groove and fixed with a metal pressure plate, so that the second temperature sensor keeps in contact with the bottom surface of the liquid cooling heat dissipation layer A and monitors the actual temperature of the brazing area without calibration and calculation. Since this solution requires multiple quick-connect connectors to connect the thermocouple to the furnace wall of the brazing equipment 20, it is not the preferred solution and will not be described in detail here.

[0041] The above embodiments are merely preferred implementations of the present invention. For those skilled in the art, any modifications or improvements made without departing from the concept of the present invention should fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A multi-layer heat dissipation structure welding system for integrated circuits, characterized in that, include: The multi-piece fixture (10) assembles multiple sets of liquid cooling heat dissipation layers (A) and encapsulated vacuum cavity heat dissipation layers (B) to be welded, forming a weldable assembly. The multi-piece fixture (10) has a hollow structure and / or a side opening structure, with gaps for the laser beam to pass through. The brazing equipment (20) has a forced cooling head (21) that is in close contact with the assembly to be welded during welding and forces cooling on one side of the heat spreader layer (B) of the encapsulated vacuum cavity. The laser edge sealing welding equipment (30) performs laser edge sealing welding on multiple sets of heat dissipation structures that have been brazed and are held in a multi-piece fixture (10).

2. The welding system according to claim 1, characterized in that, The brazing equipment (20) is a vacuum brazing furnace.

3. The welding system according to claim 1, characterized in that, The forced cooling head (21) is located on the upper side of the brazing equipment (20), closely attached to the upper surface of the heat dissipation layer (B) of the encapsulated vacuum cavity, and has a circulating cooling channel inside.

4. The welding system according to claim 1, characterized in that, It also includes a temperature detection unit for monitoring the temperature of the brazing area and the temperature of the vapor chamber (B) in the packaged state.

5. The welding system according to claim 4, characterized in that, The forced cooling head (21) is connected to an external cooling control unit and a cooling medium supply device. It is used to adjust the cooling intensity of the forced cooling head (21) in real time according to the temperature of the brazing area and the temperature of the heat spreader (B) of the encapsulated vacuum cavity.

6. The welding system according to claim 1, characterized in that, The laser edge sealing welding equipment (30) is a multi-axis laser welding robot that automatically identifies the weld trajectory through a visual positioning system.

7. A welding process for a multilayer heat dissipation structure of integrated circuits, employing the welding system described in any one of claims 1-6, characterized in that, include: Clamping steps: The liquid cooling heat dissipation layer (A) and the encapsulated vacuum cavity heat dissipation layer (B) are assembled and fixed by a multi-piece fixture (10) to form an assembly to be soldered; Brazing steps: The multi-piece fixture (10) holding the assembly to be brazed is placed into the brazing equipment (20) and the temperature is raised for brazing. At the same time, the vapor chamber layer (B) of the packaged vacuum cavity is cooled by the forced cooling head (21). Laser edge sealing welding steps: Transfer the multi-piece fixture (10) holding the brazed heat dissipation structure to the laser edge sealing welding station. Without disassembling the multi-piece fixture, start the laser edge sealing welding equipment (30) and perform laser edge sealing welding along the exposed outer peripheral edge of the heat dissipation structure. Unloading steps: After completing the edge sealing welding, remove the clamps and take out the finished product.

8. The welding process according to claim 7, characterized in that, In the brazing step, the temperature of the brazing area and the temperature of the heat spreader (B) of the encapsulated vacuum cavity are monitored in real time by the temperature detection unit. The cooling intensity of the forced cooling head (21) is adjusted in real time by the cooling control unit according to the temperature of the brazing area and the temperature of the heat spreader (B) of the encapsulated vacuum cavity.

9. The welding process according to claim 8, characterized in that, The cooling intensity of the forced cooling head (21) can be adjusted in real time as follows: when the temperature of the brazing area is lower than the preset target temperature, the cooling intensity is reduced; when the temperature of the heat spreader layer (B) of the encapsulated vacuum cavity exceeds the preset tolerance temperature, the cooling intensity is increased.

10. The welding process according to claim 7, characterized in that, It also includes product testing steps.

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