A method for preparing a multi-layer ceramic circuit board

Abstract

The present invention discloses a method for preparing a multi-layer ceramic circuit board, which is formed by stacking and bonding multiple electroplated ceramic substrates (DPC). First, a DPC ceramic substrate with a surface circuit layer and vertical interconnect metal pillars is prepared through a graphic electroplating process; then, a metal solder is prepared on the circuit layer of the DPC ceramic substrate, and multiple DPC ceramic substrates are stacked and aligned and then bonded to achieve mechanical and electrical interconnection between the DPC substrates; finally, a high-temperature resistant insulating glue is filled between the DPC substrates, and after curing, a multi-layer ceramic circuit board is obtained. By utilizing the characteristics of good thermal conductivity / heat resistance, high graphic precision, and vertical interconnection of the DPC ceramic substrate, the present invention realizes mechanical connection and electrical interconnection between the DPC substrates through metal bonding, and prepares a highly reliable and high-precision multi-layer ceramic circuit board, meeting the requirements of miniaturization and integrated packaging of power devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of microelectronic packaging, and more specifically, relates to a method for preparing a multi-layer ceramic circuit board, which effectively improves the integration degree of power devices. Background Art

[0002] With the continuous development of electronic information technology, the application and update of electronic products are also rapidly extending, and their functions are becoming more and more diverse. The third-generation semiconductor materials represented by SiC and GaN have important applications in the fields of automobiles, communications, aerospace, weaponry, etc. due to their large bandgap width, high breakdown voltage, and other characteristics. With the gradual increase in application requirements, chip packaging is gradually developing towards high reliability, high integration density, miniaturization and other performances. However, the packaging of chips on a planar substrate is restricted by the size of the substrate itself. Therefore, it is necessary to stack multiple layers of packaging substrates to improve the overall integration degree of the substrate so as to meet the application requirements.

[0003] Since multi-layer ceramic circuit boards are mostly used to carry electronic components such as semiconductor components and wiring needs to be carried out for these electronic components, it is required that each layer of the multi-layer ceramic circuit board is a ceramic insulating layer and a wiring layer that conforms to the electronic components. The wiring layer includes both a circuit layer on the surface of the substrate that communicates with the electronic components and a pattern layer that bonds the upper and lower substrates, and also includes a via conductor that penetrates the ceramic substrate itself to achieve vertical interconnection. The commonly used multi-layer ceramic circuit board in current microsystem packaging is a low-temperature / high-temperature co-fired ceramic substrate (LTCC / HTCC), which has high integration, can be vertically interconnected, and has high reliability. However, due to the use of screen printing to prepare the substrate wiring layer, the pattern accuracy is reduced (>100 μm), and when multiple layers of ceramic ingredients are stacked and sintered, due to the high temperature (>800 °C), there are problems such as differences in shrinkage ratios, which affect the yield of LTCC / HTCC and increase the cost, seriously hindering its application in electronic devices.

[0004] Therefore, the present invention proposes to use an electroplated ceramic substrate (DPC), in which the planar pattern and the via metal pillars are integrally formed by a pattern electroplating process, without separately preparing the planar pattern and the via filling. Moreover, by utilizing the characteristics that the electroplated pattern is easy to design and prepare, has high pattern accuracy (<50 μm), can be vertically interconnected, and the mature preparation process, it can simply and quickly meet the wiring requirements of the multi-layer ceramic circuit board, realizing high precision and high integration of the substrate; the DPC substrates are stacked and interconnected through a metal solder bonding process (<400 °C) to improve the reliability and yield of the ceramic substrate. Summary of the Invention

[0005] In order to overcome the deficiencies of existing multi-layer ceramic circuit boards in terms of wiring accuracy and yield rate, and to meet the application requirements in the fields of communication, automotive, aerospace, etc., the present invention proposes a manufacturing method for multi-layer ceramic circuit boards, which solves the problems of low wiring accuracy and low yield rate of traditional substrates, can stably withstand 100 - 200 °C for a long time, and realizes the miniaturization and high integration density of multi-layer ceramic substrates.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A multi-layer ceramic circuit board is formed by stacking and bonding multiple electroplated ceramic substrates (DPC). First, a DPC ceramic substrate with a surface circuit layer and vertical interconnect metal columns in the vias is prepared through a graphic electroplating process. Then, a metal solder is prepared on the circuit layer of the DPC ceramic substrate. After stacking and aligning multiple DPC ceramic substrates, they are bonded to achieve mechanical connection and electrical interconnection between the substrates, and a high-temperature resistant insulating glue is filled between the substrates. After curing, a multi-layer ceramic circuit board is obtained.

[0008] In the multi-layer ceramic circuit board of the present invention, the ceramic substrate material is one of alumina, aluminum nitride or silicon nitride, and the thickness is 200 - 1000 μm.

[0009] In the multi-layer ceramic circuit board of the present invention, the surface circuit layer of the DPC ceramic substrate is an electroplated copper layer with a thickness of 100 - 300 μm.

[0010] In the multi-layer ceramic circuit board of the present invention, the metal solder is one of CuSn, AuSn, AgSn, SnAgCu, nano-silver paste, nano-copper paste, and is deposited on the bonding area of the circuit board by screen printing or physical vapor deposition process, with a thickness of 3 - 40 μm. The metal solder bonding process is one of solder bonding, thermocompression bonding or eutectic bonding, the bonding temperature is 200 - 400 °C, the bonding pressure is 0 - 10 MPa, and the bonding time is 15 - 30 minutes.

[0011] In the manufacturing method of the multi-layer ceramic circuit board of the present invention, the manufacturing process of two-layer ceramic circuit boards includes:

[0012] 1) Degreasing, decontaminating and drying the upper and lower DPC ceramic substrates and their circuit layers;

[0013] 2) Preparing the metal solder on the upper surface circuit layer of the lower DPC substrate;

[0014] 3) Aligning the circuit layers of the two DPC ceramic substrates, melting the metal solder through a bonding technique, and after cooling, the two ceramic substrates are bonded together, thereby achieving mechanical connection and electrical interconnection between the two ceramic substrates.

[0015] In the multi-layer ceramic circuit board of the present invention, the high-temperature resistant insulating glue is one of PI polyimide, EPOXY epoxy resin, LCP liquid crystal resin, and Japanese ABF resin, and is filled in the gaps of the DPC ceramic substrate through processes such as vacuum adsorption or pressure injection and cured. The thickness is 200-600 μm, and the curing process temperature is 100-300 °C.

[0016] In the multi-layer ceramic circuit board of the present invention, filling the high-temperature resistant insulating glue between two ceramic substrates includes the following steps:

[0017] 1) Use a syringe to pick up the high-temperature resistant insulating glue and fill it along the outer edge of the gap between the ceramic substrate layers. The syringe filling method is single-sided one-way "I" type or adjacent two-sided one-way "L" type injection;

[0018] 2) Place the substrate flat or tilt it according to the flow direction of the high-temperature resistant insulating glue, and use pressure injection to fill the entire interlayer with the high-temperature resistant insulating glue; alternatively, a vacuum pump can be used to evacuate at the other end, and the high-temperature resistant insulating glue can be filled into the entire interlayer through vacuum adsorption;

[0019] 3) After filling, heat to completely cure the high-temperature resistant insulating glue, thereby forming a stable high-temperature resistant insulating layer between the substrate layers.

[0020] In the multi-layer ceramic circuit board of the present invention, the multi-layer ceramic circuit board is prepared by preparing metal solder on the topmost metal layer, stacking and aligning more DPC substrates for bonding, filling and curing the high-temperature resistant insulating glue between the substrate layers, finally increasing the number of substrate stacking layers and the integration density of the multi-layer ceramic circuit board.

[0021] In summary, compared with the existing manufacturing methods, the present invention mainly has the following advantages:

[0022] 1) The present invention uses DPC substrates as the ceramic circuit boards for each layer, and prepares the surface pattern layer and via metal pillars through the graphic electroplating process, which can not only achieve vertical interconnection, but also has higher electroplating pattern accuracy than the existing manufacturing methods for multi-layer substrates. The DPC substrate manufacturing technology is mature, and the surface pattern layer is easier to process. The wiring design can be carried out according to application requirements, and the yield is higher. Moreover, the surface pattern layer and the metal filling in the through holes of the substrate are integrally prepared by the electroplating process without separate preparation, which not only shortens the process flow but also improves the connection strength between the surface pattern and the via metal.

[0023] 2) The present invention uses the metal solder bonding process to realize the connection between multi-layer ceramic substrates. There are various preparation methods for metal solder. The bonding temperature is 200-400 °C, and the bonding pressure is 0-10 MPa, which is lower than the process temperature of the existing multi-layer ceramic substrate preparation process (>800 °C). It can not only ensure the pattern accuracy of the electroplated metal layer during the bonding process, reduce the shrinkage difference between multi-layer substrates, but also reduce the process conditions, making the preparation of multi-layer substrates simpler and faster.

[0024] 3) The present invention uses a high-temperature resistant insulating glue to fill the gaps between multi-layer ceramic circuit boards. Different from the hot pressing in the existing manufacturing method of multi-layer ceramic substrates, the high-temperature resistant insulating glue will fill the layer gaps by means of pressure injection or vacuum adsorption. It not only adheres to the ceramic substrate to improve the bonding strength between multi-layer substrates, but also seals the welding parts to prevent the solder from flowing back and overflowing to avoid short circuits, thereby improving the reliability of the multi-layer ceramic substrate.

[0025] 4) The metal solder and the high-temperature resistant insulating glue used in the present invention can withstand 100 - 200 °C for a long time, meeting the high-temperature application requirements of multi-layer ceramic circuit boards and being used for power device packaging and integration. Description of the Drawings

[0026] Figure 1 It is a cross-sectional view of a multi-layer ceramic circuit board related to an embodiment of the present invention.

[0027] Figure 2 is Figure 1 The cross-sectional view of the manufacturing process flow of the multi-layer ceramic circuit board shown.

[0028] Figure 3 It is a cross-sectional view of the physical object of a multi-layer ceramic circuit board with the layer gaps filled with PI glue in Example 3.

[0029] Figure 4 It is a cross-sectional view of the physical object of a multi-layer ceramic circuit board with the layer gaps filled with EPOXY glue in Example 4.

[0030] In all the drawings, the same reference numerals are used to represent the same structures, where: 1, 6, 7, 10 are all electroplated copper layers; 2, 8 are all electroplated through-hole copper columns; 3, 9 are all ceramic substrates; 4 is metal solder; 5 is a heat-resistant insulating layer. Detailed Embodiments

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] The following will refer to Figure 2 the process flow of Figure 1 and, in combination with the structure of the multi-layer ceramic circuit board of

[0033] The multi-layer ceramic circuit board of the present invention is stacked by a DPC ceramic substrate 3 and a DPC ceramic substrate 9. The electroplated copper layers 1, 6 and the electroplated through-hole copper columns 2 on the upper substrate surface of the DPC substrate, and the electroplated copper layers 7, 10 and the electroplated through-hole copper columns 8 on the lower substrate surface are all integrally prepared by semiconductor pattern electroplating process, so that 1, 6 and 2 become one body, and 7, 10 and 8 become one body and conduct to form the internal circuit of the substrate. A metal solder 4 is prepared on the metal layer 7 of the lower ceramic substrate 9, and the metal layers 6 and 7 on the substrate surface are stacked, aligned and bonded together to form an interlayer circuit interconnection, and a high-temperature resistant insulating glue is filled in the layer gap to form a heat-resistant insulating layer 5.

[0034] In the invention of this multi-layer ceramic circuit board, the materials of the two DPC ceramic substrates can be alumina, aluminum nitride, silicon nitride, etc. Preferably, the upper and lower substrates are made of aluminum nitride DPC ceramic substrates, and their thermal expansion coefficient is 4.4×10 -6 / ℃, and the thickness of both is 500μm. The metal copper layer and the through-hole metal copper column on the surface of each DPC substrate of the multi-layer ceramic circuit board are integrally prepared by pattern electroplating process. The upper surface of the upper substrate is provided with a circuit layer 1, a chip mounting area for mounting and conducting chips, and a heat dissipation area that does not conduct electricity but is only used to fix the chips and conduct the heat generated by the chips. The lower surface is provided with a pattern layer 6 connected to the lower substrate, the upper surface of the lower substrate is provided with a pattern layer 7 connected to the lower surface of the upper substrate, and the lower surface is provided with a circuit layer 10 connected to the external circuit. The thickness of the electroplated metal copper layer in this embodiment is 120μm.

[0035] In the invention of this multi-layer ceramic circuit board, a metal solder is prepared on the surface pattern layer of the multi-layer ceramic circuit board by screen printing or physical vapor deposition process (PVD) in the bonding area to be bonded of the circuit board; the metal solder is one of CuSn, AuSn, AgSn, SnAgCu, nano-silver paste, nano-copper paste, and the thickness is 3-40μm. The bonding process adopted is one of solder bonding, thermocompression bonding or eutectic bonding, the bonding temperature is 200-400℃, the bonding pressure is 0-10MPa, and the bonding time is 15-30 minutes.

[0036] Refer to Figure 2 the process flow, and in combination with the following several embodiments, further illustrate the method of preparing the metal solder on the pattern layer and the bonding process. Example 1

[0037] In this embodiment, the metal solder is selected as SnAgCu solder paste.

[0038] In this embodiment, the bonding between the DPC ceramic substrate 3 and the DPC ceramic substrate 9 includes the following steps:

[0039] 1) Degrease, decontaminate, and dry the ceramic substrate 3, ceramic substrate 9, and their metal layers;

[0040] 2) Apply SnAgCu solder paste onto the metal layer 7 of the ceramic substrate 9 by screen printing, with a thickness of 40 μm;

[0041] 3) Align the metal layers on the ceramic substrate 3 and ceramic substrate 9, and use the solder bonding process. Under the process conditions of a maximum bonding temperature of 280 °C, a bonding pressure of 2 MPa, and a bonding time of 15 minutes, bond the SnAgCu solder to the substrates together, thereby achieving the mechanical connection and electrical interconnection of the two-layer ceramic substrates. Example 2

[0042] In this example, the metal solder selected is AuSn solder.

[0043] In this example, the bonding between the DPC ceramic substrate 3 and the DPC ceramic substrate 9 includes the following steps:

[0044] 1) Degrease, decontaminate, and dry the ceramic substrate 3, ceramic substrate 9, and their metal layers;

[0045] 2) Deposit AuSn solder onto the metal layer 7 of the ceramic substrate 9 by physical vapor deposition (CVD) process, with a thickness of 3 μm;

[0046] 3) Align the metal layers on the ceramic substrate 3 and ceramic substrate 9, and use the eutectic bonding process. Under the process conditions of a maximum bonding temperature of 320 °C, a bonding pressure of 10 MPa, and a bonding time of 15 minutes, bond the AuSn solder to the substrates together, thereby achieving the mechanical connection and electrical interconnection of the two-layer ceramic substrates.

[0047] In the invention of this multi-layer ceramic circuit board, the high-temperature resistant insulating glue is one of PI polyimide, EPOXY epoxy resin, LCP liquid crystal resin, and Japanese ABF resin. It is filled in the gaps of the DPC ceramic substrates and cured by processes such as vacuum adsorption or pressure injection, with a thickness of 250 - 300 μm, and the curing process temperature is 100 - 300 °C.

[0048] Refer to Figure 2 the process flow, and further illustrate the heat resistance performance and filling process of the high-temperature resistant insulating glue in combination with the following several examples. Example 3

[0049] In this example, the high-temperature resistant insulating glue selected is PI polyimide. The PI glue presents a yellow transparent liquid at room temperature, with a viscosity of 30 - 35 Pa·s and a coefficient of thermal expansion of 3.6×10 -5 / °C.

[0050] In this embodiment, after bonding the ceramic substrate 3 and the ceramic substrate 9 using SnAgCu solder, the process for filling the high-temperature resistant insulating adhesive between the substrates 3 and 9 includes the following steps:

[0051] 1) Pick up the high-temperature resistant insulating adhesive using a syringe and fill it along the edge of the interlayer gap of the ceramic substrate. The filling method of the syringe is one-sided unidirectional "I"-type extrusion;

[0052] 2) Since the PI adhesive has a high viscosity, the substrate is placed flat, and a vacuum pump is used to evacuate air at the other end. The high-temperature resistant insulating adhesive is filled into the entire interlayer through vacuum adsorption;

[0053] 3) Heat up to 80 °C, 120 °C, 150 °C, 200 °C, 220 °C, and 250 °C in sequence according to the processing procedure, and keep heating at each temperature for 20 minutes until the PI adhesive in the heat-resistant layer is completely cured and formed into a stable heat-resistant insulating layer 5.

[0054] Figure 3 is a cross-sectional view of the multi-layer substrate after the PI adhesive is filled and cured. The thickness of the heat-resistant layer 5 filled with the PI adhesive is 265 μm. The PI adhesive turns brownish-brown after curing. The bonding strength tested at room temperature is 22.6 MPa. After heating at 200 °C for 100 hours, the bonding strength is still as high as 18.3 MPa, still maintaining 81% of the initial strength. When using the PI adhesive to fill the heat-resistant layer and performing a hermeticity test after complete curing, no bubbles emerge when immersed in fluorinated oil, and after taking it out after being placed in a nitrogen atmosphere at high pressure (4 standard atmospheres) at room temperature for 2 hours, the nitrogen leakage rate is 1.9×10 -9 Pa·m / s, indicating that the PI adhesive is completely filled and sealed in the substrate. After heating at 200 °C for 100 hours and then performing a hermeticity test, no bubbles still emerge in the fluorinated oil, and after taking it out after being placed in a nitrogen high pressure (4 standard atmospheres) at room temperature for 2 hours, the nitrogen leakage rate is only 3.8×10 -8 Pa·m / s, still maintaining a high hermeticity. At the same time, the PI adhesive filled in the insulating layer does not overflow, indicating that the PI adhesive can withstand a high temperature of 200 °C for a long time as an insulating layer and can maintain a high bonding strength and hermeticity, indicating that the multi-layer ceramic substrate filled with the PI adhesive has high heat resistance and reliable stability. Example 4

[0055] In this embodiment, the high-temperature resistant insulating adhesive is EPOXY epoxy resin. The EPOXY adhesive is a white transparent liquid at room temperature, with a viscosity of 4 - 7 Pa·s and a coefficient of thermal expansion of 3.2×10 -5 / °C.

[0056] In this embodiment, after bonding the ceramic substrate 3 and the ceramic substrate 9 using SnAgCu solder, the process for filling the high-temperature resistant insulating adhesive between the substrates 3 and 9 includes the following steps:

[0057] 1) Use a syringe to pick up the high-temperature resistant insulating glue and fill it along the edge of the gap between the ceramic substrate layers. The filling method of the syringe is one-way "L"-type extrusion on adjacent two sides.

[0058] 2) The EPOXY glue has a small viscosity. Place the substrate obliquely according to the flow direction of the high-temperature resistant insulating glue, and use the pressure injection method to make the high-temperature resistant insulating glue fill the entire interlayer.

[0059] 3) Heat the EPOXY glue to 150 °C in one step and heat it for 1 hour until the EPOXY glue in the heat-resistant layer is completely cured and formed to form a stable heat-resistant insulating layer 5.

[0060] Figure 4 It is a cross-sectional view of the multi-layer substrate after the EPOXY glue is filled and cured. The thickness of the heat-resistant layer 5 filled with the EPOXY glue is 272 μm. The EPOXY glue is still white after curing. The bonding strength tested at room temperature is 19.8 MPa. After heating at 200 °C for 100 hours, the bonding strength is 13.9 MPa, and it can still firmly bond the substrate. When using the EPOXY glue to fill the heat-resistant layer and performing the airtightness test after complete curing, no bubbles emerge when immersed in fluorinated oil, and after being taken out after being placed in a high-pressure nitrogen atmosphere (4 standard atmospheres) at room temperature for 2 hours, the nitrogen leakage rate is 2×10 -8 Pa·m / s, indicating that the EPOXY glue is completely filled and sealed in the substrate. After heating at 200 °C for 100 hours and then performing the airtightness test, no bubbles still emerge in the fluorinated oil, and after being taken out after being placed in a high-pressure nitrogen (4 standard atmospheres) at room temperature for 2 hours, the nitrogen leakage rate is only 5.2×10 -8 Pa·m / s, and it can still maintain a high airtightness. At the same time, the EPOXY glue filled in the insulating layer does not overflow, indicating that the EPOXY glue can withstand a high temperature of 200 °C for a long time as an insulating layer. Although the bonding strength and the degree of maintaining airtightness are weaker than those of the PI glue, the test shows that it can still maintain a high bonding strength and airtightness, meeting the device use requirements, indicating that the multi-layer ceramic substrate prepared by EPOXY filling has high heat resistance and reliable stability.

[0061] In the invention of this multi-layer ceramic circuit board, the multi-layer ceramic circuit board is prepared by preparing a metal solder 4 on the topmost metal layer 1, stacking, aligning and bonding more DPC substrates, then filling and curing a high-temperature resistant insulating glue between the substrate layers, and finally increasing the number of substrate stacking layers and the integration density of the multi-layer ceramic circuit board to produce a multi-layer ceramic circuit board with more layers.

[0062] The above embodiments are only used to illustrate the technical concept and features of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It should not be used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a multi-layer ceramic circuit board, characterized in that, The multi-layer ceramic circuit board is formed by stacking and bonding multiple DPC ceramic substrates. The method first prepares DPC ceramic substrates with surface circuit layers and vertical interconnecting metal columns through a graphic electroplating process, then prepares metal solder on the circuit layers of the DPC ceramic substrates, stacks and aligns multiple DPC ceramic substrates and bonds them to achieve mechanical connection and electrical interconnection between the substrates. Finally, a high-temperature resistant insulating glue is filled between the substrates and cured to obtain a multi-layer ceramic circuit board; the bonding process is one of solder bonding, thermocompression bonding or eutectic bonding, the bonding temperature is 200-400 °C, the bonding pressure is 0-10 MPa, and the bonding time is 15-30 minutes; the high-temperature resistant insulating glue is one of polyimide, epoxy resin, and LCP liquid crystal resin, and is filled and cured in the gaps between DPC ceramic substrates through a vacuum adsorption or pressure injection process, with a thickness of 200-600 μm; Among them, the specific steps for filling the high-temperature resistant insulating glue between two ceramic substrates are as follows: 1) Use a syringe to pick up the high-temperature resistant insulating glue and fill it along the outer edge of the gap between the ceramic substrate layers. The syringe filling method is one-way "I" type injection on one side or one-way "L" type injection on two adjacent sides; 2) Place the substrate flat or tilt it according to the flow direction of the high-temperature resistant insulating glue, and use the pressure injection method to fill the entire interlayer with the high-temperature resistant insulating glue; or use a vacuum pump to evacuate at the other end during filling, and fill the entire interlayer with the high-temperature resistant insulating glue through the vacuum adsorption difference; 3) Cure the high-temperature resistant insulating glue completely by local heating technology for the filled ceramic substrate, thereby forming a stable heat-resistant insulating layer.

2. The method for preparing a multi-layer ceramic circuit board according to claim 1, wherein The material of the DPC ceramic substrate is one of alumina, aluminum nitride or silicon nitride, and the thickness is 100-1000 μm.

3. A method for preparing a multi-layer ceramic circuit board according to claim 1, characterized in that, The surface circuit layer of the DPC ceramic substrate is an electroplated copper layer with a thickness of 100-300 μm.

4. A method for preparing a multi-layer ceramic circuit board according to any one of claims 1-3, characterized in that, The metal solder is one of CuSn, AuSn, AgSn, SnAgCu, nano silver paste, and nano copper paste.

5. According to the method for preparing a multi-layer ceramic circuit board described in claim 4, the metal solder is deposited on the bonding area to be bonded on the circuit layer of the ceramic substrate through a screen printing or physical vapor deposition process, and the thickness is 3-40 μm.

6. A method for preparing a multi-layer ceramic circuit board according to any one of claims 1-3, characterized in that, The curing process temperature is 100-300 °C.

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