Preparation method of PI insulating layer and lead sheet for ceramic substrate

Abstract

The invention discloses a preparation method of a PI insulating layer and a lead sheet for a ceramic substrate. The preparation method comprises the following steps: S1, plating a nano metal layer on the surface of the ceramic substrate; s2, coating photoresist, and transferring the pattern of the lead sheet to the ceramic substrate through a photoetching technology; s3, forming a required lead sheet through exposure and development; s4, coating the surface of the lead sheet with diluted PI glue; s5, after the PI glue is coated, carrying out primary baking at 100 DEG C; s6, carrying out second exposure and development, and confirming that the graph is correct; s7, further baking for 5 minutes at the temperature of 100 DEG C, and if the pattern is qualified, continuing curing in the nitrogen environment; and S8, a nitrogen oven is adopted in the PI glue curing process, and curing is conducted according to a specific temperature curve. The bonding performance of the lead wire sheet pattern and the ceramic substrate is greatly improved by organically combining the lead wire sheet pattern with the PI insulating layer and adopting a precisely controlled photoetching process.

Description

Technical Field

[0001] The present invention relates to the field of preparation of a PI insulating layer and a lead sheet, and more particularly to a preparation method of a PI insulating layer and a lead sheet for a ceramic substrate. Background Art

[0002] With the rapid development of electronic technology, especially in the military field, the demand for high-reliability and high-performance electronic devices is increasing, and the selection of electronic packaging materials has become particularly important. Ceramic substrates, as a material with high strength, excellent thermal conductivity and stable electrical properties, are widely used in electronic device packaging under high temperature, high pressure and high frequency conditions. However, ceramic substrates alone cannot provide sufficient insulation, especially under complex environmental conditions, and the reliability of the device may be affected.

[0003] In order to further improve the insulation and protection performance of ceramic substrate packaging, polyimide (PI) material is introduced into the preparation of the insulating layer of the ceramic substrate. In the prior art, the PI insulating layer is mainly prepared by coating or deposition. However, it is technically difficult to achieve high adhesion, uniform coating and precise control of layer thickness on the ceramic substrate. In addition, the preparation of the lead sheet pattern on the ceramic substrate usually relies on photolithography technology, and the function of the lead sheet is realized by forming a metal conductive pattern on the ceramic surface. In order to further improve the packaging reliability, ensure the effective combination of the lead sheet and the PI insulating layer, and ensure the durability of the packaging structure under extreme temperatures and voltages, it is still necessary to provide an optimized preparation method. Summary of the invention

[0004] The present invention aims to provide an improved method for preparing a PI insulating layer and a lead sheet on a ceramic substrate. The method first performs photolithography preparation of the lead sheet on the ceramic substrate, and then coats the PI film on the surface of the lead sheet, thereby forming a packaging structure with good insulation, corrosion resistance and high-voltage breakdown capability. It is particularly suitable for packaging high-reliability electronic devices such as military guided weapons. The specific scheme is as follows:

[0005] A method for preparing a PI insulating layer and a lead sheet for a ceramic substrate, the method comprising the following steps:

[0006] S1: Plating a nano-metal layer on the surface of a ceramic substrate;

[0007] S2: Coating photoresist and transferring the lead sheet pattern to the ceramic substrate by photolithography;

[0008] S3: forming the required lead sheet by exposure and development;

[0009] S4: Apply the diluted PI glue on the surface of the lead sheet;

[0010] S5: Preliminary baking at 100°C after PI glue coating;

[0011] S6: Perform a second exposure and development to confirm that the pattern is correct;

[0012] S7: Further bake at 100°C for 5 minutes. If the pattern is qualified, continue to cure in a nitrogen environment;

[0013] S8: The PI glue curing process uses a nitrogen oven and is cured according to a specific temperature curve.

[0014] Furthermore, the development parameters are as follows: 25% TMAH developer is used for development, the volume of the developer is 50 ml TMAH mixed with 1000 ml water, heated to 55° C., and the development time is 3-5 minutes.

[0015] Furthermore, the specific temperature curve parameters in S8 are:

[0016] During 0-10 min, increase the temperature from 50°C to 150°C; maintain at 150°C to 70 min; during 70-80 min, increase the temperature from 150°C to 220°C; maintain at 220°C to 110 min; during 110-120 min, increase the temperature from 220°C to 300°C; maintain at 300°C to 240 min; during 240-260 min, decrease the temperature from 300°C to 250°C; maintain at 250°C to 290 min.

[0017] Furthermore, the exposure parameter is 60 seconds of photolithography on the soft photolithography board.

[0018] Furthermore, the speed of the glue spreading in S4 is 400r / 30s.

[0019] Furthermore, the initial baking time in S5 is 30 minutes.

[0020] Furthermore, the exposure intensity of the second exposure in S6 is 120 mJ / cm 2 .

[0021] Furthermore, during the curing process of the PI glue in S8, a nitrogen flow rate of 500 ml / min was used, the purity of the nitrogen was 99.99%, and the nitrogen environment was maintained for more than 95% of the total curing time.

[0022] Furthermore, the thickness of the PI glue after curing is controlled between 20 μm and 50 μm.

[0023] Beneficial effects:

[0024] The present invention provides a method for preparing a PI insulating layer and a lead sheet for a ceramic substrate, which specifically includes the following advantages:

[0025] (1) By coating a polyimide insulating layer on a ceramic substrate, the electrical insulation performance of the substrate is significantly improved. PI materials have excellent high voltage resistance, high temperature resistance and chemical stability, ensuring that the prepared insulating layer can effectively prevent electrical breakdown under high voltage environments, making this method particularly suitable for electronic devices with high insulation requirements.

[0026] (2) By organically combining the lead sheet pattern with the PI insulating layer and using a precisely controlled photolithography process, the bonding performance between the lead sheet pattern and the ceramic substrate is greatly improved. Adhesion testing is also performed after development to ensure a strong bond between the lead sheet and the PI layer, thereby improving the overall reliability of the package structure and maintaining long-term stability even in complex working environments.

[0027] (3) The PI insulation layer has undergone high and low temperature impact tests and can undergo repeated temperature change cycles in an environment of -200°C to 300°C without peeling or cracking. Therefore, this preparation method can be applied to demanding application scenarios such as aerospace, military electronic devices, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the temperature curve of PI glue curing.

[0029] Figure 2 It is the photolithography pattern on the surface of the ceramic substrate in the embodiment. DETAILED DESCRIPTION

[0030] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with examples. The examples are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0031] Example:

[0032] A method for preparing PI insulating layer and lead sheet for ceramic substrate

[0033] S1: Plating a nano-metal layer on the surface of a ceramic substrate

[0034] Clean the ceramic substrate to remove dirt and impurities on the surface. Place the cleaned substrate in a vacuum coating machine and place it in a vacuum coating machine until the vacuum reaches 5×10 -6 In an environment of 1.5 Pa, a nano-metal layer (such as gold, chromium, titanium, etc.) with a thickness of 100 nm is plated on the surface of the ceramic substrate by sputtering. The metal layer is used as the conductive layer of the lead sheet.

[0035] S2: Coat photoresist and transfer the lead sheet pattern to the ceramic substrate through photolithography technology. The lead pattern is as follows: Figure 2As shown in the figure, after taking out the substrate, evenly coat it with positive photoresist (such as AZ4620) at room temperature, use a coating machine, set the coating speed to 4000rpm, and last for 30 seconds to ensure that the photoresist is evenly covered on the substrate surface. Put the substrate coated with photoresist into the exposure machine and expose it at 120mJ / cm 2 The exposure intensity was set to 100 and the exposure time was set to 60 seconds.

[0036] S3: Form the required lead sheet through exposure and development

[0037] Immerse the exposed substrate in a developer, which is a 25% TMAH solution, specifically 50 ml TMAH mixed with 1000 ml deionized water. Heat the developer to 55°C and control the development time to 3-5 minutes until the lead sheet pattern appears. After development, rinse the substrate thoroughly with deionized water and blow dry.

[0038] S4: Apply diluted PI glue on the surface of the lead sheet

[0039] On the substrate with the lead sheet pattern, use a glue spreader to apply the diluted PI glue (such as PI-2611). Set the glue spread speed to 400rpm and the duration to 30 seconds to ensure that the PI glue evenly covers the lead sheet surface. The concentration of the diluted PI glue is 10% to 15% to ensure a thinner coating thickness.

[0040] S5: Preliminary baking at 100°C after PI glue coating

[0041] The substrate coated with PI glue was placed on a hot plate and baked at 100°C for 30 minutes. This step is used to remove the solvent in the PI glue and form a preliminarily cured film.

[0042] S6: Perform the second exposure and development to confirm that the pattern is correct

[0043] The preliminarily cured substrate is placed in the exposure machine and the exposure intensity is 120mJ / cm 2 Perform the second exposure for 60 seconds. After exposure, use the same developer and development conditions as S3 to confirm that the pattern is correct. After development, rinse with deionized water again and dry.

[0044] S7: Further bake at 100°C for 5 minutes. If the pattern is qualified, continue to cure in nitrogen environment

[0045] The substrate was placed in an oven and baked for a second time at 100°C for 5 minutes to further remove residual solvent. After confirming that the pattern was correct, the substrate was transferred to a nitrogen oven for final curing.

[0046] S8: The PI glue curing process uses a nitrogen oven and is cured according to a specific temperature curve. The curing temperature curve is shown in the figure below. Figure 1 As shown, the PI glue curing process is carried out in a nitrogen environment, with a nitrogen flow rate of 500ml / min and a nitrogen purity of 99.99%. The curing process is carried out according to the following temperature curve:

[0047] In 0 to 10 minutes, the temperature rises from 50°C to 150°C;

[0048] Maintain the temperature at 150°C for 70 minutes;

[0049] In 70 to 80 minutes, the temperature is raised from 150°C to 220°C;

[0050] Maintain the temperature at 220°C for 110 minutes;

[0051] In 110-120 minutes, the temperature is raised from 220°C to 300°C;

[0052] Maintain the temperature at 300°C for 240 minutes;

[0053] Cool down from 300°C to 250°C within 240-260 minutes;

[0054] The temperature was maintained at 250°C for 290 minutes.

[0055] The temperature curve is designed to ensure the full imidization process of the PI adhesive and prevent the adhesive film from cracking due to rapid heating or cooling.

[0056] S9: The thickness of PI glue after curing is controlled between 20μm and 50μm

[0057] The thickness of the cured PI insulation layer is between 20μm and 50μm, which is measured using a precision thickness gauge to ensure that the insulation and mechanical strength requirements are met.

[0058] S10: Testing

[0059] The prepared ceramic substrate samples were subjected to electrical insulation tests and high and low temperature impact tests. The voltage breakdown test of the PI insulation layer was carried out at a voltage of 1500V, and there was no breakdown of the PI layer. The high and low temperature impact test was carried out in the range of -200℃ to 300℃. After 100 cycles of testing, there was no cracking or peeling of the PI insulation layer.

[0060] As a further improvement, the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a PI insulating layer and a lead sheet for a ceramic substrate, characterized in that: The preparation method comprises the following steps: S1: Plating a nano-metal layer on the surface of a ceramic substrate; S2: Coating photoresist and transferring the lead sheet pattern to the ceramic substrate by photolithography; S3: forming the required lead sheet by exposure and development; S4: Apply the diluted PI glue on the surface of the lead sheet; S5: Preliminary baking at 100°C after PI glue coating; S6: Perform a second exposure and development to confirm that the pattern is correct; S7: Further bake at 100°C for 5 minutes. If the pattern is qualified, continue to cure in a nitrogen environment; S8: The PI glue curing process uses a nitrogen oven and is cured according to a specific temperature curve.

2. The method for preparing a PI insulating layer and a lead sheet for a ceramic substrate according to claim 1, characterized in that: The development parameters are as follows: 25% TMAH developer is used for development, the volume of the developer is 50 ml TMAH mixed with 1000 ml water, heated to 55° C., and the development time is 3-5 minutes.

3. The method for preparing a PI insulating layer and a lead sheet for a ceramic substrate according to claim 1, characterized in that: The specific temperature profile parameters in S8 are: During 0-10 min, increase the temperature from 50°C to 150°C; maintain at 150°C to 70 min; during 70-80 min, increase the temperature from 150°C to 220°C; maintain at 220°C to 110 min; during 110-120 min, increase the temperature from 220°C to 300°C; maintain at 300°C to 240 min; during 240-260 min, decrease the temperature from 300°C to 250°C; maintain at 250°C to 290 min.

4. The method for preparing a PI insulating layer and a lead sheet for a ceramic substrate according to claim 1, characterized in that: The exposure parameters are 60s of photolithography on the soft photolithography board.

5. The method for preparing a PI insulating layer and a lead sheet for a ceramic substrate according to claim 1, characterized in that: The speed of the glue spreading in S4 is 400r / 30s.

6. The method for preparing a PI insulating layer and a lead sheet for a ceramic substrate according to claim 1, characterized in that: The initial baking time in S5 is 30 minutes.

7. The method for preparing a PI insulating layer and a lead sheet for a ceramic substrate according to claim 1, characterized in that: The exposure intensity of the second exposure in S6 is 120mJ / cm 2 .

8. The method for preparing a PI insulating layer and a lead sheet for a ceramic substrate according to claim 1, characterized in that: During the curing process of PI glue in S8, the nitrogen flow rate used was 500 ml / min, the purity of nitrogen was 99.99%, and the maintenance time of the nitrogen environment was more than 95% of the total curing time.

9. The method for preparing a PI insulating layer and a lead sheet for a ceramic substrate according to claim 1, characterized in that: The thickness of the PI glue after curing is controlled between 20μm and 50μm.

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