Direct copper-clad ceramic carrier plate sintering method

Abstract

The technical scheme of the invention provides a direct copper-clad ceramic carrier plate sintering method, which comprises the following steps: a first copper layer sintering step: placing a first copper layer on the upper surface of a ceramic substrate, transferring the ceramic substrate with the first copper layer spread on the upper surface into a sintering furnace, and sintering to form a single-sided copper-clad plate; a second copper layer sintering step: enabling the non-copper-clad surface of the single-sided copper-clad plate to face upwards, spreading a second copper layer on the upper surface of the single-sided copper-clad plate, transferring the single-sided copper-clad plate with the second copper layer spread on the upper surface into a sintering furnace, and sintering to form the copper-clad plate; wherein the first copper layer and the second copper layer have the same thickness, the projections of the geometric centers of the first copper layer and the second copper layer on the surface of the ceramic substrate coincide, and the copper layer area of the first copper layer is 95%-100% of the copper layer area of the second copper layer. Warping control of the sintered double-sided copper-clad plate is realized by controlling the area ratio of the copper layers in the two sintering processes, so that warping of a finished product of the double-sided copper-clad plate meets requirements, heat conduction contact between the double-sided copper-clad plate and a diffusion copper plate is better, and the heat dissipation capability of the double-sided copper-clad plate is improved.

Description

Technical Field

[0001] This application relates to the technical field of sintering processes for ceramic copper-clad laminates, and specifically relates to a sintering method for directly copper-clad ceramic substrates. Background Art

[0002] A directly copper-clad ceramic substrate (DBC) is an electronic basic material made by directly sintering a copper foil on the surface of a ceramic. The double-sided copper-clad laminate has a typical "sandwich" structure, that is, a ceramic chip in the middle, with copper on both the front and back. The DBC material has good thermal conductivity and insulation properties, so it has a very wide range of applications and can be used in electronic device fields such as semiconductor refrigeration chips (TEC), insulated gate bipolar transistor (IGBT) power modules, and solid-state relays. In the IGBT power module, the DBC mainly plays roles such as supporting chip welding and current-carrying. It is often welded to a heat-dissipating copper bottom plate to achieve chip heat transfer. As IGBTs develop towards higher power and higher integration, the IGBT chips have increasingly higher requirements for heat dissipation. How to effectively and quickly dissipate heat is extremely urgent. The heat dissipation transfer path of IGBT power devices from top to bottom is: chip → ceramic copper-clad laminate → substrate → radiator. Finally, the radiator and air transfer heat through convection and radiation, and use active or passive heat dissipation to take away the heat. There is a thermal resistance in the whole conduction process, and the thermal resistance is the main factor affecting the heat dissipation of the IGBT power module. To enhance the heat dissipation effect, under the condition that other conditions remain unchanged, reducing the thermal resistance in the heat transfer process is the main method. The thermal resistance between the DBC and the heat-dissipating copper plate is mainly determined by the welding pores between the two (the thermal conductivity of the pores is much lower than that of the solder paste). The welding pores depend on the warpage matching between the DBC and the heat-dissipating copper plate. Since the heat-dissipating bottom plate generally shows a convex state, the warpage of the DBC must be controlled within a certain range. The warpage of the DBC is mainly formed during the sintering process. Because the DBC sintering process is a two-stage sintering, that is, first sinter a copper sheet, and then sinter another copper sheet. Due to the existence of the ratchet effect and gravity, the warpage formed during the first sintering cannot be offset by the second sintering, and the entire large DBC plate shows a "saddle shape". Therefore, warpage is an inherent property of the DBC. However, in the application of DBC materials, it is necessary to control the warpage degree of the DBC. Excessive warpage will cause the DBC material to be scrapped. Currently, the warpage of the DBC can be controlled through the design of the sintering tooling. During the sintering process, stress is applied using the tooling, that is, during the high-temperature sintering process of the DBC, the warpage of the DBC is adjusted through the action of an externally applied load. This scheme has complex production processes, and the externally loaded tooling will contact the copper surface, causing sintering pollution in a certain range. Another possible problem is that the stress applied during the process may cause residual internal stress in the DBC after sintering and forming, resulting in the failure of the DBC during use. Summary of the Invention

[0003] In view of the fact that the warpage control of DBC sintering is an urgent problem to be solved in applications, however, the current operation process of using tooling to solve sintering warpage still has deficiencies. The present invention provides a method for sintering a direct copper clad ceramic substrate based on copper clad control.

[0004] This application provides a method for sintering a direct copper clad ceramic substrate, comprising the following steps: S1. First copper layer sintering step: Place the first copper layer on the upper surface of the ceramic substrate, transfer the ceramic substrate with the first copper layer spread on the upper surface to a sintering furnace, and sinter to form a single-sided copper clad board; S2. Second copper layer sintering step: Turn the non-copper clad surface of the single-sided copper clad board upwards, spread the second copper layer on the upper surface of the single-sided copper clad board, transfer the single-sided copper clad board with the second copper layer spread on the upper surface to a sintering furnace, and sinter to form a copper clad board; Wherein the first copper layer and the second copper layer have the same thickness and the geometric centers coincide in the projection on the surface of the ceramic substrate, and the copper layer area of the first copper layer is 95%-100% of the copper layer area of the second copper layer.

[0005] Preferably, the first copper layer and the second copper layer have the same width, and the length of the first copper layer is 95%-100% of the length of the second copper layer.

[0006] Preferably, in the first copper layer sintering step, before sintering, remove the oxide layer on the surface of the first copper layer, and then reform an oxide layer on the surface of the first copper layer in an oxidation furnace; And / or, In the second copper layer sintering step, before sintering, remove the oxide layer on the surface of the second copper layer, and then reform an oxide layer on the surface of the second copper layer in an oxidation furnace.

[0007] Preferably, in the first copper layer sintering step, the ceramic substrate is placed on a sintering fixture during sintering, and in the second copper layer sintering step, the ceramic substrate is placed on a sintering fixture during sintering; The sintering fixture is recessed, and the sintering fixture supports the ceramic substrate and the copper clad board only at the four corners.

[0008] Preferably, the length of the second copper layer is 184 mm, and the length of the first copper layer is between 176-184 mm.

[0009] The method for sintering a direct copper clad ceramic substrate of this application realizes the warpage control of the sintered double-sided copper clad board by controlling the area ratio of the copper layers during the two sintering processes, making the finished warpage of the double-sided copper clad board meet the requirements, so as to better conduct heat with the heat dissipation copper plate and improve its heat dissipation capacity. Brief Description of the Drawings

[0010] Figure 1Schematic diagram of the copper clad laminate 1 in the sintering method of the direct copper clad ceramic carrier board of the present application; Figure 2 Flow chart of the sintering method of the direct copper clad ceramic carrier board of the present application; Figure 3 Schematic diagram of the sintering fixture 2 in the sintering method of the direct copper clad ceramic carrier board of the present application; Figure 4 Schematic diagram of the measurement position in the sintering method of the direct copper clad ceramic carrier board of the present application; Figure 5 Relationship curve graph of the length and warpage in the sintering method of the direct copper clad ceramic carrier board of the present application; Figure 6 Placement schematic diagram of the first copper layer 12 and the second copper layer 13 in the sintering method of the direct copper clad ceramic carrier board of the present application; Figure 7 Measured data of the warpage degree of the copper clad laminate 1 in the embodiment of the sintering method of the direct copper clad ceramic carrier board of the present application.

[0011] In the figure: 1: Copper clad laminate; 11: Ceramic substrate; 12: First copper layer; 13: Second copper layer; 19: Single-sided copper clad laminate; 2: Sintering fixture. Detailed implementation manners

[0012] The technical solutions of the present application will be described in detail below in conjunction with the accompanying drawings and specific embodiments. In this specification, the dimensions of the drawings do not represent the actual size ratio. The drawings are only used to reflect the relative positional relationship and connection relationship between components. Components with the same name or the same reference numeral represent similar or identical structures, and are for illustrative purposes only.

[0013] Figure 1 It is a schematic diagram of the structure of the copper clad laminate 1, Figure 2 which is the process and specific steps of the manufacturing steps of the copper clad laminate 1. The operation steps of the technical solution of the present application include: S1. First copper layer sintering step. Place the first copper layer 12 on the upper surface of the ceramic substrate 11, and transfer the ceramic substrate 11 with the first copper layer 12 spread on the upper surface to a sintering furnace for high-temperature sintering to form a single-sided copper clad laminate 19. Here, the upper surface refers to the surface of the ceramic substrate 11 that is upward along the direction of gravity, and the same meaning applies hereinafter.

[0014] S2. Second copper layer sintering step. Place the non-copper-coated surface of the single-sided copper clad laminate 19 upward, spread the second copper layer 13 on the upper surface of the single-sided copper clad laminate 19, and transfer the single-sided copper clad laminate 19 with the second copper layer 13 spread on the upper surface to a sintering furnace for high-temperature sintering to form the copper clad laminate 1.

[0015] The warpage of the copper clad laminate 1 or the single-sided copper clad laminate 19 mainly occurs during the high-temperature sintering process. Generally, during high-temperature sintering, the temperature reaches about 1100 degrees Celsius. At this time, the first copper layer 12 and the second copper layer 13 respectively form oxidation eutectic phases between the surface of the ceramic substrate 11 and the ceramic substrate 11, thus ensuring the bonding between the first copper layer 12, the second copper layer 13 and the ceramic substrate 11.

[0016] The main source of warpage is that the difference in the coefficient of thermal expansion between the copper material and the ceramic substrate causes volume shrinkage differences between the ceramic substrate 11 and the first copper layer 12 and the second copper layer 13 during the heating and sintering process or during the cooling process after sintering. In this case, internal stress is generated, causing the edge after sintering to bend towards the copper layer sintering side, forming a saddle-shaped warpage. Second, the material softens at high temperatures. In order to support the ceramic substrate 11 during warpage and avoid large-area contact with the surface of the ceramic substrate 11, the contact points are set at the edges. Therefore, during sintering, the material may deform under the action of gravity, aggravating the degree of warpage. Practice shows that since the second copper layer 13 and the first copper layer 12 on both sides cannot be formed in a single sintering process, and the secondary sintering process is carried out on the basis of the ceramic substrate 11 on which the first copper layer 12 has been sintered on one side. Therefore, the influence of warpage during the two sintering processes cannot be offset. As a result, the warpage degree of the finally sintered copper clad laminate 1 may still exceed the tolerance.

[0017] In order to better compensate for the warpage degree of the copper clad laminate 1 and limit the warpage degree of the final copper clad laminate 1 within the required range, this solution realizes the control of the warpage degree during the two sintering processes by adjusting different parameters between the first copper layer 12 and the second copper layer 13, thereby realizing refined warpage compensation control.

[0018] Specifically, the adaptation of the warpage degree during the two sintering processes can be realized by controlling the area difference between the first copper layer 12 and the second copper layer 13. Both the first copper layer 12 and the second copper layer 13 are solid non-hollow copper layers. Control the copper layer area of the first copper layer 12 to be 95%-100% of the copper layer area of the second copper layer 13, keep the thicknesses of the two copper layers the same, and ensure that the geometric centers of the two copper layers coincide in the projection on the surface of the ceramic substrate 11. At this time, since the area of the second copper layer 13 is smaller, the warpage amount caused by the internal stress during the sintering process is smaller, which can balance the differences in the warpage amounts during the original two sinterings, thereby reducing the warpage degree of the final product.

[0019] In practical applications, the first copper layer 12 and the second copper layer 13 are usually cut from the same original copper strip, so their thicknesses are the same. At the same time, the problem is that their widths are also the same, both being the width of the copper strip. Therefore, in order to adjust the areas of the first copper layer 12 and the second copper layer 13, it actually evolves into adjusting the length dimensions of the first copper layer 12 and the second copper layer 13. Therefore, it is only necessary to further ensure that the length dimension of the first copper layer 12 is 95%-100% of the length dimension of the second copper layer 13 while ensuring that the thicknesses and widths of the first copper layer 12 and the second copper layer 13 are the same.

[0020] The following are specific embodiments of the present application. Specifically, for the sintering of a conventional DBC "sandwich" structure large board, the selected ceramic chip has a thickness of 0.38 mm, the double-sided copper sheet has a thickness of 0.3 mm, the ceramic chip size is 190*139 mm (standard size), and the copper sheet width dimension is 132 mm (standard size). The width of the copper sheet is a fixed value of the copper sheet manufacturer and cannot be changed, while the length of the copper sheet can be flexibly cut and determined. Therefore, the purpose of the present invention is to control the DBC warpage by using the length difference of the copper sheets on both sides of the ceramic on the basis of the unchanged copper sheet thickness. The present invention defaults that the length of the copper sheet sintered twice is the conventional length, that is, 184 mm, and the length of the copper sheet sintered once is flexibly adjusted according to customer requirements.

[0021] First, place the copper coil on the cutting equipment, use the adjustment side strips on both sides to make the advancing direction of the copper sheet perpendicular to the cutter, set the cutting equipment parameters to 80 times / min, and cut the copper sheet into the first copper layer 12 with a length of 177.5 mm and the second copper layer 13 with a length of 184 mm.

[0022] Use the copper sheet cleaning equipment to remove the surface oil stain and oxide layer of the first copper layer 12 and the second copper layer 13 completely. The cleaning equipment is configured with corresponding degreasing and deoxidizing potions, and the cleaning speed is set to 2 m / min.

[0023] Place the cleaned copper in the oxidation fixture, set the temperature curve of the oxidation furnace, oxidize the copper sheet, and re-form an oxide layer on the surfaces of the first copper layer 12 and the second copper layer 13. The oxidation temperature is set to 200 °C to ensure that the thickness of the oxide layer on the copper sheet surface is uniform.

[0024] Then transfer the first copper layer 12 to the upper surface of the ceramic substrate 11 on the sintering fixture 2, and perform alignment placement by an automated device, place it in the sintering furnace, and set the temperature curve for high-temperature sintering. The oxidized first copper layer 12 is placed at the central position of the ceramic substrate 11 by a manipulator. This operation uses a manipulator to place, and the accuracy of the manipulator parameters is set to ±0.5 mm. The sintering temperature is set to approximately 1100 °C.

[0025] The sintering fixture 2 is as Figure 3As shown. The long and short sides of the fixture are designed to be concave (the schematic diagram shows its arc morphology, not the design dimensions), which is beneficial to the warping and spreading of the DBC large board during sintering. At this time, the ceramic substrate 11 only contacts the sintering fixture 2 at the four corners and is supported by it. The concave setting of the sintering fixture 2 at other positions can avoid the ceramic substrate 11 when the ceramic substrate 11 deforms and warps, and avoid contacting the surface of the ceramic substrate 11, so as to ensure the sintering quality of the copper layer on the surface of the ceramic substrate 11 during the sintering process.

[0026] Place the single-sided copper clad laminate 19 on the sintering fixture 2 with the copper-clad side facing down, transfer the second copper layer 13 to the upper surface of the single-sided copper clad laminate 19 on the sintering fixture 2, place it in a sintering furnace, and set the temperature curve for high-temperature sintering. The sintering temperature is set to about 1100 °C.

[0027] During the two sintering processes, the sintering temperature is the key point to be controlled. If the temperature is heated too fast or cooled too fast, it will cause the ceramic chip to be extremely cold and hot, resulting in the cracking of the ceramic chip. When sintering, the mesh belt speed is set to 100 mm / min. The sintering temperature is 1000 - 1100 °C.

[0028] In order to test the warping degree of the copper clad laminate 1, use a 3D profiler to test the warping of the DBC large board, and use the 9-point method for testing. The measurement positions are as Figure 4 shown. The calculation formula for the warping degree is: Warping = Max(1, 2, 3…9) - Min(1, 2, 3…9). In the above embodiment, the warping amount of the final copper clad laminate 1 can be controlled below 0.82 mm.

[0029] In addition, during the preliminary test process, based on the above sintering process, a comparative experiment was also carried out, and the relationship curve between the copper sheet length X and the warping y under the same ceramic chip thickness and the same sintering fixture was statistically obtained, as Figure 5 shown. Generally, it is required that for a 0.38 mm alumina ceramic chip and a double-sided 0.3 mm copper sheet, the warping of the DBC mother board ≤ 0.8 mm. Therefore, optionally, when the length of the second copper layer 13 is 184 mm, the length range of the first copper layer 12 can be selected between 177.7 mm and 179.4 mm. Preferably, to save the amount of copper sheet used and ensure qualified warping, the copper sheet length is taken as 178 mm.

[0030] In the above process, set the speed of the copper sheet cutting equipment to 80 times / min, and make the copper coil perpendicular to the cutting knife. Perpendicularity is the key control point, as cutting deviation will cause the motherboard to warp. Cut the first piece and measure its size, which is required to be 178 mm. Check whether there is curling at the edge of the copper sheet. Stack the cut copper sheets using a tooling, with 100 sheets in a stack. Transfer them to the copper sheet cleaning equipment. Set the degreasing temperature to 50 ± 2 °C, the pickling temperature to 30 ± 2 °C, and the water washing flow rate to 8 L / min. After cleaning, dry them with hot air at 70 °C. Subsequently, use a surface tension pen to test the surface cleanliness to see if it is clean. Place the cleaned copper sheets into an oxidation fixture, set the speed of the oxidation furnace mesh belt to 100 mm / min, and the oxidation temperature to 200 °C. Place the oxidized copper sheets into an automated equipment, set the manipulator parameters to make its alignment accuracy ±0.5 mm. As Figure 6 shown, grasp and place the copper sheet at the exact center of the ceramic sheet surface. Statistically analyze the warping results (warping ≤ 0.8 mm) of multiple sintered copper clad laminates 1 as Figure 7 shown. It can be seen from the test data that the average warping of the short copper motherboard is about 0.7 mm, while the average warping of the conventional copper motherboard is about 1 mm. The warping of the short copper design meets the customer requirements, with good warping control effect, and can be customized according to requirements. Produce in batches according to this method, and the test results show that this method is effectively applicable to DBC warping control, greatly improving the thermal resistance between DBC and the heat dissipation copper substrate.

[0031] The above content is only a description of the preferred implementation manner of this application, and does not limit the scope of this application. Without departing from the design spirit of this application, various deformations and improvements made by those of ordinary skill in the art to the technical solution of this application should fall within the protection scope determined by the claims of this application.

Claims

1. A method for sintering a direct copper-clad ceramic substrate, characterized in that: The steps include: S1, first copper layer sintering step: placing the first copper layer (12) on the upper surface of the ceramic substrate (11), transferring the ceramic substrate (11) with the first copper layer (12) spread on the upper surface to a sintering furnace, and sintering to form a single-sided copper-clad laminate (19); S2, second copper layer sintering step: placing the non-copper-clad surface of the single-sided copper-clad laminate (19) facing upward, spreading the second copper layer (13) on the upper surface of the single-sided copper-clad laminate (19), transferring the single-sided copper-clad laminate (19) with the second copper layer (13) spread on the upper surface to a sintering furnace, and sintering to form a copper-clad laminate (1); The first copper layer (12) and the second copper layer (13) have the same thickness and their geometric centers overlap when projected on the surface of the ceramic substrate (11), and the copper layer area of ​​the first copper layer (12) is 95%-100% of the copper layer area of ​​the second copper layer (13).

2. The direct copper-clad ceramic substrate sintering method according to claim 1, characterized in that: The first copper layer (12) and the second copper layer (13) have the same width, and the length of the first copper layer (12) is 95%-100% of the length of the second copper layer (13).

3. The direct copper-clad ceramic substrate sintering method according to claim 1, characterized in that: In the first copper layer sintering step, the oxide layer on the surface of the first copper layer (12) is removed before sintering, and then the oxide layer is re-formed on the surface of the first copper layer (12) in an oxidation furnace; and / or, In the second copper layer sintering step, the oxide layer on the surface of the second copper layer (13) is removed before sintering, and then the oxide layer is re-formed on the surface of the second copper layer (13) in an oxidation furnace.

4. The direct copper-clad ceramic substrate sintering method according to claim 1, characterized in that: During the first copper layer sintering step, the ceramic substrate (11) is placed on a sintering fixture (2); during the second copper layer sintering step, the ceramic substrate (11) is placed on a sintering fixture (2); The sintering fixture (2) is arranged in a concave manner, and the sintering fixture (2) supports the ceramic substrate (11) and the copper-clad board (1) only at four corners.

5. The direct copper-clad ceramic substrate sintering method according to claim 2, characterized in that: The length of the second copper layer (12) is 184 mm, and the length of the first copper layer (13) is between 177.7 mm and 179.4 mm.

6. The direct copper-clad ceramic substrate sintering method according to claim 2, characterized in that: The length of the second copper layer (12) is 184 mm, and the length of the first copper layer (13) is 178 mm.

Images