Ceramic rigid-flex circuit substrate and preparation method thereof

Abstract

The invention provides a ceramic rigid-flex circuit substrate and a preparation method thereof, and the method comprises the specific steps: S1, cleaning a ceramic substrate, and arranging a brazing metal transition layer on the surface of the ceramic substrate; s2, low-melting-point brazing filler metal is sprayed to the surface of the brazing metal transition layer of the ceramic substrate, and a multi-layer flexible circuit board is attached to the surface, sprayed with the low-melting-point brazing filler metal, of the aluminum nitride ceramic substrate to obtain an attached plate; and S3, placing the laminated board in a vacuum or protective atmosphere for welding to obtain the ceramic rigid-flex circuit substrate. The ceramic substrate is adopted, the brazing metal transition layer is introduced to the surface of the ceramic substrate, the welding process of the flexible circuit board and the ceramic substrate is optimized, the problems that heat conduction is difficult, interface thermal resistance is large and uneven or bonding strength is insufficient are effectively solved, and the overall performance and quality of a product are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of surface bonding of metal composite materials, and in particular to a ceramic hard-soft bonding circuit substrate and a preparation method thereof. Background Art

[0002] Ceramic hard-soft circuit substrate is a new type of circuit board that combines the characteristics of hard ceramic substrate and soft circuit board. It has the advantages of high performance, high reliability, space saving and simplified assembly, and has broad application prospects in the fields of automotive electronics, communication equipment and high-end electronic products. With the continuous advancement of technology and the continuous expansion of application fields, the requirements for heat dissipation for high-power packaging are getting higher and higher. Traditional PCB circuit boards can no longer meet the application. Simple ceramic circuit boards are difficult to achieve multi-layer stacking due to process limitations and cannot meet industry applications. Ceramic hard-soft circuit substrates will become one of the important development directions in the field of high-power electronic packaging.

[0003] In addition, there is a large difference in the coefficient of thermal expansion (CTE) between ceramic materials and flexible circuit boards (such as polyimide, etc.). In an environment with high temperature or rapid temperature changes, this thermal stress mismatch may cause stress concentration inside the substrate, and even cause cracks or delamination. And the combination of ceramics and soft materials requires special adhesives or technologies, such as bonding technology. However, these technologies may have problems with heat conduction, large and uneven interface thermal resistance, or insufficient bonding strength, affecting the overall performance and reliability of the substrate. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a ceramic hard-soft combined circuit substrate and a preparation method thereof, which adopts a ceramic substrate, introduces a brazing metal transition layer on the surface of the ceramic substrate, and optimizes the welding process between the flexible circuit board and the ceramic substrate, thereby effectively solving the problems of difficult heat conduction, large and uneven interface thermal resistance or insufficient bonding strength, and improving the overall performance and quality of the product.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a ceramic hard-soft combined circuit substrate, the specific steps are as follows:

[0006] S1: cleaning the ceramic substrate and providing a brazing metal transition layer on the surface of the ceramic substrate;

[0007] S2 sprays a low melting point solder onto the surface of the brazing metal transition layer of the ceramic substrate, and laminates the multi-layer flexible circuit board onto the surface of the aluminum nitride ceramic substrate sprayed with the low melting point solder to obtain a laminated board;

[0008] S3 places the bonded board in a vacuum or protective atmosphere for welding to obtain a ceramic hard-soft combined circuit substrate.

[0009] Furthermore, in S1, the ceramic substrate is an aluminum nitride ceramic substrate with a thickness of 0.3 mm to 1 mm.

[0010] Furthermore, in S1, the cleaning is firstly degreasing with 20g / L to 50g / L acetone degreasing agent and drying; then washing with water at a temperature of 10°C to 70°C for 5min to 20min; and then cleaning with a weak acid salt to decontaminate and activate the surface at a temperature of 10°C to 50°C for 20Sec to 50Sec.

[0011] Furthermore, in S1, a brazing metal transition layer with a thickness of 5 μm to 10 μm is sputtered onto the surface of the cleaned ceramic substrate.

[0012] Furthermore, in S1, the brazing metal transition layer is a CuCrNi alloy.

[0013] Furthermore, in S2, the low melting point solder is AgCuIn24.3Ti.

[0014] Furthermore, in S2, the spraying thickness of the low melting point solder is 10 μm to 50 μm.

[0015] Furthermore, in S2, the multi-layer flexible circuit board adopts a copper substrate, and a 1 μm nickel-gold plating layer is provided on the multi-layer flexible circuit board.

[0016] Furthermore, in S3, the bonding board is heated to 500°C to 650°C in a vacuum or protective atmosphere and kept warm for 15min to 60min for welding, and then cooled to room temperature after welding to obtain a ceramic hard-soft bonding circuit substrate.

[0017] The present invention also provides a ceramic hard-soft combined circuit substrate, which is prepared by the above preparation method.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] The present invention provides a method for preparing a ceramic hard-soft combined circuit substrate. The ceramic substrate is cleaned, which not only improves the cleanliness and activity of the substrate surface, but also helps to reduce the interface thermal resistance and enhance the bonding force of the soldering layer. The uniformity of the substrate surface is also ensured through precise control, which is conducive to the uniform distribution of the subsequent soldering layer and further reduces the thermal resistance. A soldering metal transition layer is arranged on the surface of the ceramic substrate. The soldering metal transition layer serves as a bridge between the ceramic and the flexible circuit board, effectively improving the bonding strength between the two. The presence of the transition layer improves the heat conduction path, reduces the interface thermal resistance, and improves the overall heat conduction efficiency. The flexible circuit board and the ceramic substrate are brazed with low-melting-point solder, which reduces the welding temperature and reduces the damage that high temperature may cause to the ceramic substrate and the flexible circuit board. The welding in a vacuum or protective atmosphere effectively prevents oxidation and contamination during the welding process, improves the welding quality, effectively solves the problems of difficult heat conduction, large and uneven interface thermal resistance or insufficient bonding strength, and improves the overall performance and quality of the product.

[0020] Furthermore, the present invention uses acetone degreasing agent and weak acid salt for cleaning, which effectively removes oil and impurities on the surface of the ceramic substrate, activates the surface, and provides a good bonding interface for subsequent brazing. The temperature and time are precisely controlled during the cleaning process to avoid damage to the substrate caused by excessive treatment or insufficient treatment. Not only does it improve the cleanliness and activity of the substrate surface, it helps to reduce the interface thermal resistance and enhance the bonding force of the brazing layer. It also ensures the uniformity of the substrate surface through precise control, which is conducive to the uniform distribution of the subsequent brazing layer and further reduces the thermal resistance.

[0021] Furthermore, the present invention sputters a brazing metal transition layer on the surface of the ceramic substrate by magnetron sputtering technology, and the thickness is controlled to be 5μm to 10μm. The brazing metal transition layer acts as a bridge between the ceramic and the flexible circuit board, effectively improving the bonding strength between the two; the presence of the transition layer improves the heat conduction path, reduces the interface thermal resistance, and improves the overall heat conduction efficiency.

[0022] Furthermore, the present invention accurately controls the cutting size and drilling accuracy of the copper substrate to ensure the structural stability and accuracy of the multi-layer flexible circuit board; the pulse power copper plating hole filling technology is used to ensure that the holes are filled evenly, thereby improving the electrical conductivity and thermal conductivity of the circuit board. Through the photosensitive film transfer circuit diagram, etching and other processes, the circuit pattern is accurately formed, reducing unnecessary material waste and heat accumulation. Thereby improving the overall performance of the flexible circuit board, including electrical conductivity, thermal conductivity and structural stability; refined process control helps to reduce thermal resistance and improve heat conduction efficiency.

[0023] Furthermore, the present invention selects a low melting point silver-based solder AgCuIn24.3Ti, and performs heating welding in a vacuum furnace or an atmosphere protection furnace. The welding temperature and the holding time are precisely controlled to ensure that the brazing layer is fully melted and forms a good metallurgical bond. The use of low melting point solder reduces the welding temperature and reduces the damage that high temperature may cause to the ceramic substrate and the flexible circuit board. The vacuum or atmosphere protection environment effectively prevents oxidation and contamination during the welding process and improves the welding quality. Accurate control of the welding temperature and the holding time ensures the uniformity and good bonding strength of the brazing layer, and further reduces the interface thermal resistance.

[0024] In summary, the ceramic hard-soft combined circuit substrate of the present invention adopts a ceramic substrate, introduces a brazing metal transition layer on the surface of the ceramic substrate, and optimizes the welding process between the flexible circuit board and the ceramic substrate, which effectively solves the problems of difficult heat conduction, large and uneven interface thermal resistance or insufficient bonding strength, and improves the overall performance and quality of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Multilayer flexible circuit board structure diagram. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] In the present invention, unless otherwise specified, all the embodiments and preferred implementation methods mentioned herein can be combined with each other to form a new technical solution.

[0028] In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0029] In the present invention, unless otherwise specified, percentage (%) or part refers to the weight percentage or weight part relative to the composition.

[0030] In the present invention, unless otherwise specified, the components or preferred components involved can be combined with each other to form a new technical solution.

[0031] In the present invention, unless otherwise specified, the numerical range "a-b" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "6-22" means that all real numbers between "6-22" have been listed in this document, and "6-22" is just an abbreviation of these numerical combinations.

[0032] The “range” disclosed in the present invention is in the form of a lower limit and an upper limit, which can be one or more lower limits, and one or more upper limits, respectively.

[0033] In the present invention, the term "and / or" used herein refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0034] In the present invention, unless otherwise specified, each reaction or operation step can be carried out sequentially or in accordance with the sequence. Preferably, the reaction method herein is carried out sequentially.

[0035] Unless otherwise specified, the professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content may also be applied to the present invention.

[0036] The present invention provides a method for preparing a ceramic hard-soft combined circuit substrate, the specific steps of which are as follows:

[0037] S1. Use 0.3mm-1mm thick aluminum nitride ceramic substrate as the base plate substrate. First, clean the ceramic substrate by degreasing it with 20g / L-50g / L acetone degreasing agent and drying it; then wash it with water at a temperature of 10℃-70℃ for 5min-20min, and clean it with weak acid salt to decontaminate and activate the surface at a temperature of 10℃-50℃ for 20Sec-50Sec;

[0038] S2. Sputter a brazing metal transition layer of 5 μm to 10 μm on the surface of the cleaned substrate by magnetron sputtering, wherein the brazing metal transition layer is a CuCrNi alloy.

[0039] S3, such as Figure 1 As shown, a multi-layer flexible circuit board is prepared:

[0040] S3.1 Split the rolled copper substrate into pieces and cut them into sizes of 150*120*20mm. Use mechanical drilling to drill holes on the surface with a hole diameter of 0.5mm and a tolerance of 0.05mm.

[0041] S3.2. Use pulse power to plate copper holes on the surface, fill and level the holes, and form a uniform metal coating on the hole wall.

[0042] S3.3. Press the photosensitive film onto the plated surface, transfer the circuit pattern onto the photosensitive film, and after development, remove the dry film without the circuit pattern to expose the copper foil outside the circuit pattern.

[0043] S3.4, etch the exposed copper foil; remove the dry film on the surface of the circuit pattern to expose the final circuit pattern, and wash it with 10℃~70℃ clean water for 5 minutes, and then dry it in an oven at 100℃~150℃ for 10 minutes.

[0044] S3.5. Use a 12.5*20 black cover film to cover the required pad position and copper exposure window, and then stick the cover film cover to the etched plate.

[0045] S3.6. Select nickel material and plate a nickel-gold layer on its surface with a thickness of 1 μm as a transition layer to increase the product's resistance to acid and alkali, improve its solderability, and obtain a multi-layer flexible circuit board.

[0046] S4. Spray low melting point solder onto the surface of the brazing metal transition layer of the aluminum nitride ceramic substrate with a spraying thickness of 10μm to 50μm, and bond the multi-layer flexible circuit board onto the surface of the aluminum nitride ceramic substrate sprayed with low melting point solder to obtain a bonded board. Place the bonded board in a vacuum furnace or an atmosphere protection furnace and heat it to 500℃ to 650℃ and keep it warm for 15min to 60min for welding. After brazing, cool it to room temperature to finally obtain a ceramic hard-soft circuit substrate.

[0047] Preferably, the low melting point solder is a silver-based solder AgCuIn24.3Ti.

[0048] The performance of the prepared ceramic hard-soft circuit substrate was tested, and the specific indicators are as follows:

[0049] performance index Solder Wettability ≥98％ Welding porosity ＜1％ Peel strength ≥30N / mm Relative thermal resistance ＜10％ Partial Discharge <10pC@AC8.3Kv / 5s Thermal shock (-55℃~150℃) >300 times Insulation withstand voltage <0.5mA@AC4.0Kv,60s

[0050] Example 1

[0051] The present invention provides a method for preparing a ceramic hard-soft combined circuit substrate, the specific steps of which are as follows:

[0052] S1. Use 0.7mm thick aluminum nitride ceramic substrate as the base plate substrate. First, clean the ceramic substrate, first degrease it with 50g / L acetone degreaser and dry it; then wash it with water at a temperature of 70℃ for 5min, and clean it with weak acid salt to decontaminate and activate the surface at a temperature of 50℃ for 20Sec;

[0053] S2. Sputter a 10 μm brazing metal transition layer on the surface of the cleaned substrate by magnetron sputtering.

[0054] S3, such as Figure 1 As shown, a multi-layer flexible circuit board is prepared:

[0055] S3.1 Split the rolled copper substrate into pieces and cut them into sizes of 150*120*20mm. Use mechanical drilling to drill holes on the surface with a hole diameter of 0.5mm and a tolerance of 0.05mm.

[0056] S3.2. Use pulse power to plate copper holes on the surface, fill and level the holes, and form a uniform metal coating on the hole wall.

[0057] S3.3. Press the photosensitive film onto the plated surface, transfer the circuit pattern onto the photosensitive film, and after development, remove the dry film without the circuit pattern to expose the copper foil outside the circuit pattern.

[0058] S3.4, etch the exposed copper foil; remove the dry film on the surface of the circuit pattern to expose the final circuit pattern, and wash it with 70°C clean water for 5 minutes, and then dry it in an oven at 150°C for 10 minutes.

[0059] S3.5. Use a 12.5*20 black cover film to cover the required pad position and copper exposure window, and then stick the cover film cover to the etched plate.

[0060] S3.6. Select nickel material and plate a nickel-gold layer on its surface with a thickness of 1 μm as a transition layer to increase the product's resistance to acid and alkali, improve its solderability, and obtain a multi-layer flexible circuit board.

[0061] S4. Spray 10 μm thick low-melting point solder AgCuIn24.3Ti on the surface of the brazing metal transition layer of the aluminum nitride ceramic substrate, and bond the multi-layer flexible circuit board to the surface of the aluminum nitride ceramic substrate sprayed with the low-melting point solder to obtain a bonded board. Put the bonded board into a vacuum furnace or an atmosphere protection furnace and heat it to 650°C for 30 minutes for welding. After brazing, cool it to room temperature to finally obtain a ceramic soft-hard combination circuit substrate with a welding wettability of 98.5%, a welding porosity of 0.8%, a peel strength of 35N / mm, a relative thermal resistance of 8.5%, a partial discharge of 8.3pC@AC8.3Kv / 5s, a cold and hot shock of 350 times, and an insulation withstand voltage of 0.42mA@AC4.0Kv, 60s. The performance indicators of the ceramic soft-hard combination circuit substrate in this embodiment meet the performance requirements in the industry.

[0062] Example 2

[0063] The present invention provides a method for preparing a ceramic hard-soft combined circuit substrate, the specific steps of which are as follows:

[0064] S1. Use 0.7mm thick aluminum nitride ceramic substrate as the base plate substrate. First, clean the ceramic substrate, first degrease it with 20g / L acetone degreaser and dry it; then wash it with water at a temperature of 10℃ for 20min, and clean it with weak acid salt to decontaminate and activate the surface at a temperature of 10℃ for 50Sec.

[0065] S2. Sputter a 5 μm brazing metal transition layer on the surface of the cleaned substrate by magnetron sputtering.

[0066] S3, such as Figure 1 As shown, a multi-layer flexible circuit board is prepared:

[0067] S3.1 Split the rolled copper substrate into pieces and cut them into sizes of 150*120*20mm. Use mechanical drilling to drill holes on the surface with a hole diameter of 0.5mm and a tolerance of 0.05mm.

[0068] S3.2. Use pulse power to plate copper holes on the surface, fill and level the holes, and form a uniform metal coating on the hole wall.

[0069] S3.3. Press the photosensitive film onto the plated surface, transfer the circuit pattern onto the photosensitive film, and after development, remove the dry film without the circuit pattern to expose the copper foil outside the circuit pattern.

[0070] S3.4, etch the exposed copper foil; remove the dry film on the surface of the circuit pattern to expose the final circuit pattern, and wash it with 10℃ clean water for 5 minutes, and then dry it in an oven at 100℃ for 10 minutes.

[0071] S3.5. Use a 12.5*20 black cover film to cover the required pad position and copper exposure window, and then stick the cover film cover to the etched plate.

[0072] S3.6. Select nickel material and plate a nickel-gold layer on its surface with a thickness of 1 μm as a transition layer to increase the product's resistance to acid and alkali, improve its solderability, and obtain a multi-layer flexible circuit board.

[0073] S4. Spray 50μm thick low-melting point solder AgCuIn24.3Ti on the surface of the brazing metal transition layer of the aluminum nitride ceramic substrate, and bond the multi-layer flexible circuit board to the surface of the aluminum nitride ceramic substrate sprayed with the low-melting point solder to obtain a bonded board, put the bonded board into a vacuum furnace or an atmosphere protection furnace and heat it to 500℃ for 30min for welding, and cool it to room temperature after brazing to finally obtain a ceramic soft-hard combination circuit substrate with welding wettability of 99%, welding porosity of 0.9%, peel strength of 39N / mm, relative thermal resistance of 8%, local discharge of 8.8pC@AC8.3Kv / 5s, hot and cold shock of 360 times, insulation withstand voltage of 0.4mA@AC4.0Kv, 60s. The performance indicators of the ceramic soft-hard combination circuit substrate in this embodiment meet the performance requirements in the industry.

[0074] Example 3

[0075] The present invention provides a method for preparing a ceramic hard-soft combined circuit substrate, the specific steps of which are as follows:

[0076] S1. Use 0.7mm thick aluminum nitride ceramic substrate as the base plate substrate. First, clean the ceramic substrate, first degrease it with 35g / L acetone degreaser and dry it; then wash it with water at a temperature of 50℃ for 15min, and clean it with weak acid salt to decontaminate and activate the surface at a temperature of 35℃ for 35Sec.

[0077] S2. Sputter a 6 μm brazing metal transition layer on the surface of the cleaned substrate by magnetron sputtering.

[0078] S3, such as Figure 1 As shown, a multi-layer flexible circuit board is prepared:

[0079] S3.1 Split the rolled copper substrate into pieces and cut them into sizes of 150*120*20mm. Use mechanical drilling to drill holes on the surface with a hole diameter of 0.5mm and a tolerance of 0.05mm.

[0080] S3.2. Use pulse power to plate copper holes on the surface, fill and level the holes, and form a uniform metal coating on the hole wall.

[0081] S3.3. Press the photosensitive film onto the plated surface, transfer the circuit pattern onto the photosensitive film, and after development, remove the dry film without the circuit pattern to expose the copper foil outside the circuit pattern.

[0082] S3.4, etch the exposed copper foil; remove the dry film on the surface of the circuit pattern to expose the final circuit pattern, and wash it with 50℃ water for 5 minutes, and then dry it in an oven at 120℃ for 10 minutes.

[0083] S3.5. Use a 12.5*20 black cover film to cover the required pad position and copper exposure window, and then stick the cover film cover to the etched plate.

[0084] S3.6. Select nickel material and plate a nickel-gold layer on its surface with a thickness of 1 μm as a transition layer to increase the product's resistance to acid and alkali, improve its solderability, and obtain a multi-layer flexible circuit board.

[0085] S4. Spray 30μm thick low-melting point solder AgCuIn24.3Ti on the surface of the brazing metal transition layer of the aluminum nitride ceramic substrate, and bond the multi-layer flexible circuit board to the surface of the aluminum nitride ceramic substrate sprayed with the low-melting point solder to obtain a bonded board, put the bonded board into a vacuum furnace or an atmosphere protection furnace and heat it to 600℃ for 30min for welding, and cool it to room temperature after brazing to finally obtain a ceramic soft-hard combination circuit substrate with welding wettability of 98.9%, welding porosity of 0.83%, peel strength of 40N / mm, relative thermal resistance of 8.5%, local discharge of 7.1pC@AC8.3Kv / 5s, hot and cold shock of 365 times, insulation withstand voltage of 0.3mA@AC4.0Kv, 60s. The performance indicators of the ceramic soft-hard combination circuit substrate in this embodiment meet the performance requirements in the industry.

[0086] In summary, the present invention provides a ceramic hard-soft circuit substrate and a preparation method thereof, and the specific steps are as follows: S1 cleaning the ceramic substrate and setting a brazing metal transition layer on the surface of the ceramic substrate; S2 spraying a low-melting-point brazing material on the surface of the brazing metal transition layer of the ceramic substrate, and bonding a multi-layer flexible circuit board to the surface of the aluminum nitride ceramic substrate sprayed with the low-melting-point brazing material to obtain a bonded board; S3 placing the bonded board in a vacuum or protective atmosphere for welding to obtain a ceramic hard-soft circuit substrate. The present invention adopts a ceramic substrate, introduces a brazing metal transition layer on the surface of the ceramic substrate, and optimizes the welding process of the flexible circuit board and the ceramic substrate, which effectively solves the problems of difficult heat conduction, large and uneven interface thermal resistance, or insufficient bonding strength, and improves the overall performance and quality of the product.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a ceramic hard-soft circuit substrate, characterized in that: The specific steps are as follows: S1: cleaning the ceramic substrate and providing a brazing metal transition layer on the surface of the ceramic substrate; S2 sprays a low melting point solder onto the surface of the brazing metal transition layer of the ceramic substrate, and laminates the multi-layer flexible circuit board onto the surface of the aluminum nitride ceramic substrate sprayed with the low melting point solder to obtain a laminated board; S3 places the bonded board in a vacuum or protective atmosphere for welding to obtain a ceramic hard-soft combined circuit substrate.

2. The method for preparing a ceramic hard-soft combined circuit substrate according to claim 1, characterized in that: In S1, the ceramic substrate is an aluminum nitride ceramic substrate.

3. The method for preparing a ceramic hard-soft circuit substrate according to claim 1, characterized in that: In S1, the cleaning is first degreasing with 20g / L to 50g / L acetone degreasing agent and drying; then washing with water at a temperature of 10°C to 70°C for 5min to 20min; and then cleaning with a weak acid salt to decontaminate and activate the surface at a temperature of 10°C to 50°C for 20Sec to 50Sec.

4. The method for preparing a ceramic hard-soft combined circuit substrate according to claim 1, characterized in that: In S1, a brazing metal transition layer with a thickness of 5 μm to 10 μm is sputtered onto the cleaned surface of the ceramic substrate.

5. The method for preparing a ceramic hard-soft combination circuit substrate according to claim 1, characterized in that: In S1, the brazing metal transition layer is CuCrNi alloy.

6. The method for preparing a ceramic hard-soft combination circuit substrate according to claim 1, characterized in that: In S2, the low melting point solder is AgCuIn24.3Ti.

7. The method for preparing a ceramic hard-soft circuit substrate according to claim 1, characterized in that: In S2, the spraying thickness of the low melting point solder is 10 μm to 50 μm.

8. The method for preparing a ceramic rigid-flexible circuit substrate according to claim 1, characterized in that: In S2, the multi-layer flexible circuit board uses a copper substrate, and a 1 μm nickel-gold plating layer is provided on the multi-layer flexible circuit board.

9. The method for preparing a ceramic hard-soft combination circuit substrate according to claim 1, characterized in that: In S3, the bonding board is heated to 500°C to 650°C in a vacuum or protective atmosphere and kept warm for 15min to 60min for welding. After welding, it is cooled to room temperature to obtain a ceramic hard-soft bonding circuit substrate.

10. A ceramic hard-soft circuit substrate, characterized in that: The method is prepared according to any one of claims 1 to 9.

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