Environment-friendly solder mask preparation method for ceramic copper-clad plate

Abstract

The invention discloses an environment-friendly solder mask preparation method for a ceramic copper-clad plate, and belongs to the technical field of ceramic copper-clad plate manufacturing. The method comprises the following steps: carrying out pretreatment cleaning on a ceramic copper-clad plate with a surface pattern circuit; accurately positioning the substrate through a visual positioning system and introducing a solder resist pattern; in an oxygen-containing atmosphere, a pulse laser beam is adopted to selectively scan a copper area where a solder mask needs to be formed, a copper oxide solder mask is generated in situ through a laser-induced oxidation reaction, and an unscanned area is kept as an exposed bonding pad; and finally, carrying out post-treatment cleaning and inspection. According to the method, the traditional steps of exposure, development and the like are omitted, digital, convenient, green and environment-friendly fine solder resist pattern manufacturing is achieved, and the method is particularly suitable for solder resist preparation of high-density and fine-pitch ceramic copper-clad plates.

Description

Technical Field

[0001] This invention relates to the field of solder resist preparation technology for ceramic copper-clad laminates, and specifically to an environmentally friendly solder resist preparation method for ceramic copper-clad laminates. Background Technology

[0002] Ceramic-clad copper laminates (DBC, AMB, DPC) are key components of circuit boards, which are fabricated by physically or chemically bonding copper foil to ceramics and then using etching processes. Due to their excellent thermal conductivity and insulation, they are primarily used as heat dissipation and interconnect substrates for power modules (such as IPMs and IGBTs), thermoelectric coolers (TECs), and third-generation semiconductor devices (such as silicon carbide), ultimately finding widespread application in power electronics fields such as new energy vehicles, wind, solar, and energy storage.

[0003] When chips need to be soldered onto the surface of a ceramic copper-clad laminate (CCL), a solder resist layer must be prepared on the surface of the CCL and around the chip soldering area to prevent short circuits caused by disordered solder flow during the soldering process. Currently, the mainstream method for preparing solder resist in the industry is to use liquid photosensitive solder resist ink for printing and patterning. This traditional method typically involves multiple steps, such as... Figure 6 As shown: First, liquid solder resist ink is uniformly coated onto the cleaned copper layer surface of the ceramic copper-clad laminate using screen printing or spraying. Then, the ink is baked at a low temperature to a semi-cured state to facilitate subsequent processing. Next, ultraviolet light is used to irradiate the solder resist ink through a mask (or film) with a predetermined pattern, causing the ink in the irradiated area to undergo a photopolymerization reaction and harden. Then, a chemical developer is used to dissolve and wash away the unexposed ink areas, thereby exposing the solder pads that need to be soldered. Finally, the remaining ink is completely cured at a high temperature to form the final solder resist layer.

[0004] However, this traditional ink-based solder resist method has significant limitations, mainly including: ① Cumbersome process steps: It involves multiple independent steps such as coating, pre-baking, exposure, development, and curing, resulting in a long production process, low efficiency, and long delivery cycle. ② Limited pattern accuracy and alignment capability: Its accuracy is limited by screen tension, the manufacturing precision of the mask itself, and manual or mechanical alignment errors, making it difficult to stably process ultra-fine lines with line width / spacing less than 20μm. Alignment is even more difficult for ceramic substrates that may deform after high-temperature sintering, and the production cost of high-precision masks is also high. ③ Significant environmental pollution problems: The entire process consumes a large amount of solder resist ink, developer, and other chemical reagents, generating volatile organic compound (VOC) emissions and a large amount of chemical waste liquid during production, requiring complex environmental protection facilities, which does not meet the requirements of current green manufacturing and sustainable development. ④ Long-term reliability is questionable: The traditional ink layer and copper layer are mainly bonded by physical-chemical adsorption. Under harsh working environments such as high temperature and humidity, thermal shock, there may be risks of decreased adhesion, delamination, or even cracking, which will affect the service life and reliability of the power module.

[0005] Therefore, it is essential to develop a method for preparing ceramic copper-clad laminates that is convenient, environmentally friendly, highly precise, and has excellent long-term reliability. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides an environmentally friendly method for preparing copper-clad ceramic substrates with solder resist.

[0007] The present invention adopts the following technical solution:

[0008] The first objective is to provide an environmentally friendly solder resist preparation method for ceramic copper-clad laminates, comprising the following steps: S1. Pre-treatment: Clean the ceramic copper-clad board with surface pattern lines to obtain a clean copper surface. S2. Graphic drawing and positioning: Fix the pre-processed ceramic copper-clad board on the laser processing platform, determine the processing benchmark through the vision positioning system, and import the solder resist pattern to be formed into the control system. S3, Laser-induced oxidation imaging: In an oxygen-containing atmosphere, a pulsed laser beam is used to selectively scan the copper area on the ceramic copper-clad laminate that needs to form a solder resist layer, so that the copper in the scanned area reacts with oxygen to generate a copper oxide solder resist layer in situ, while the copper in the unscanned area remains exposed as a solder pad. S4. Post-processing: Cleaning and inspecting the substrate after laser processing.

[0009] Furthermore, in step S1, the cleaning is performed using an alkaline solution and an oxidizing solution for ultrasonic cleaning.

[0010] Furthermore, in step S2, the visual positioning system is a CCD visual alignment system, which can identify alignment marks or circuit patterns on the substrate and perform deformation compensation.

[0011] Furthermore, in step S3, the pulsed laser is an ultraviolet nanosecond laser or a green picosecond laser.

[0012] Furthermore, when using an ultraviolet nanosecond laser, the wavelength is 355nm, the pulse width is 10-30ns, the laser power is 5-15W, the scanning speed is 100-500mm / s, the scanning line spacing is 5-15μm, and the number of scans is 2-10.

[0013] Furthermore, when using a green picosecond laser, the wavelength is 532nm, the pulse width is 1-15ps, the laser power is 3-8W, the scanning speed is 1000-2000mm / s, the scanning line spacing is 3-8μm, and the number of scans is 2-5.

[0014] Furthermore, in step S3, the oxygen-containing atmosphere is pure oxygen or a mixture of nitrogen and oxygen, wherein the volume fraction of oxygen is not less than 20%.

[0015] Furthermore, the thickness of the copper oxide solder resist layer generated in step S3 is 15-25 μm.

[0016] Furthermore, the ceramic copper-clad laminate is one of alumina ceramic direct copper-clad laminate, aluminum nitride active metal brazed ceramic copper-clad laminate, or direct copper-plated ceramic substrate.

[0017] The second objective is to provide a ceramic copper-clad laminate whose surface solder resist layer is prepared by the method described above.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are: 1. Significantly Simplified Process: This invention streamlines the complex steps involved in traditional solder resist processes, such as coating, pre-baking, exposure, development, and curing, into four main steps: "pre-processing—graphic drawing—laser imaging—post-processing." This greatly improves production efficiency and shortens the production cycle and delivery time.

[0019] 2. Achieved high-precision and intelligent alignment: This invention utilizes laser direct writing technology and a CCD-based vision alignment system to achieve ultra-fine solder resist pattern processing with line width / spacing less than 20μm. The vision system can automatically identify and compensate for substrate deformation caused by high-temperature sintering, achieving an alignment accuracy within ±5μm, thus solving the problems of difficult and low-precision alignment in traditional processes.

[0020] 3. Environmentally friendly manufacturing: This invention eliminates the chemicals necessary in traditional processes, such as solder resist ink, developer, and cleaning agents, achieving zero emissions of volatile organic compounds (VOCs) and zero generation of chemical waste liquid, meeting the stringent requirements of green manufacturing and sustainable development.

[0021] 4. Excellent Reliability of the Solder Mask Layer: The solder mask layer formed by this invention is a copper oxide layer grown in situ from a copper substrate through laser-induced oxidation. This solder mask layer has a metallurgical-chemical bond with the copper substrate, resulting in extremely strong adhesion. Its heat resistance, moisture resistance, insulation, and mechanical strength are far superior to traditional physical-chemical bonded ink solder mask layers. It can remain stable under harsh environments such as high temperature and high humidity, and thermal shock, significantly improving the long-term reliability of the final product. Attached Figure Description

[0022] Figure 1 A process flow diagram of an environmentally friendly solder resist preparation method for ceramic copper-clad laminate provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the state of the ceramic copper-clad laminate substrate after pretreatment according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the solder resist pattern area set on the laser software before laser scanning according to an embodiment of the present invention. Figure 4 This is a schematic diagram of a laser beam selectively scanning a solder resist pattern area in an oxygen-containing atmosphere according to an embodiment of the present invention. Figure 5 A schematic diagram of the final structure of the ceramic copper-clad laminate with a copper oxide solder resist layer; Figure 6 This is a flowchart of the traditional liquid ink solder resist process in existing technologies. Detailed Implementation

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0025] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0026] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0027] Example 1: Fabrication of solder resist layer on alumina ceramic DBC substrate using ultraviolet nanosecond laser This embodiment provides a method for preparing solder resist on ceramic copper-clad laminates based on 355nm ultraviolet nanosecond laser-induced oxidation. The overall process flow can be referred to as follows: Figure 1 As shown.

[0028] S1. Pretreatment of Ceramic Copper Clad Laminate: Provide a pre-etched alumina ceramic direct copper-clad (DBC) substrate (0.38mm alumina ceramic core, 0.3mm pure copper substrate on both sides), such as... Figure 2 The illustration shows that the substrate has a clean copper surface. The specific processing steps are as follows: the substrate is placed in a 5%~10% potassium hydroxide solution and a 5%~10% sodium persulfate solution respectively and gently cleaned in an ultrasonic cleaner for 300 seconds to remove organic contaminants and a slight natural oxide layer on the copper surface, thereby obtaining a clean copper surface. After cleaning, it is dried with nitrogen gas.

[0029] S2. Solder mask pattern drawing: The processed copper-clad ceramic board is fixed onto the vacuum adsorption table of the laser processing platform. The platform's CCD vision system identifies two diagonally distributed solid circle markers on the substrate, achieving precise positioning of the processing coordinate system. In computer-aided design (CAD) software, the solder mask pattern to be processed is drawn according to the product's required insulation protection requirements. Figure 3 As shown in the diagram, the bold black lines represent the "solder mask areas" where the solder mask layer needs to be formed, while uncovered areas (such as solder pads) remain open. The graphic file is then imported into the laser processing control system.

[0030] S3. Direct laser scanning imaging: The laser processing cavity was sealed, and oxygen (O2) was introduced into the cavity as the process atmosphere at a flow rate of 10 L / min to maintain a stable oxidation environment. A Marble UV10W-40K ultraviolet nanosecond pulsed laser with a wavelength of 355 nm and a pulse width of 10–30 ns was selected. The laser beam was controlled by a galvanometer scanning system and a dynamic focusing module.

[0031] The laser processing parameters were set as follows: laser power of 10W, scanning speed of 200mm / s, frequency of 60kHz, and hatch spacing of 8μm. A multi-scan strategy was adopted, with 5 scans performed to ensure the uniformity of the oxide layer.

[0032] Based on the solder resist pattern drawn in S2, the control system drives the laser beam to selectively scan the copper areas where a solder resist layer needs to be formed, line by line. The laser focus is precisely concentrated on the copper surface, and the high-energy-density pulses instantly raise the temperature of the copper surface in the scanned area above its oxidation temperature, causing it to react with oxygen in the atmosphere and form a dense, hard, insulating, and continuous blackish-gray copper oxide solder resist layer in situ. Meanwhile, the pad areas, which are not scanned by the laser, retain their original exposed metallic state.

[0033] S4. Post-processing: After laser processing, the oxygen supply is turned off, and the substrate is removed. It is then lightly cleaned for 300 seconds in an ultrasonic cleaner using a 5%–10% potassium hydroxide solution and a 5%–10% sulfuric acid / hydrogen peroxide solution to remove any minor surface dust, followed by drying with nitrogen. Finally, the solder mask pattern is inspected using automated optical inspection (AOI) equipment to ensure it is complete, without any missing spots or overheating, and that the pads are clean and free of oxidation contamination. The solder mask fabrication is then complete. The final product structure can be referenced. Figure 5 The red part in the figure indicates the in-situ generated copper oxide solder resist layer, which precisely covers the design area, and the solder pads are clearly exposed, thus completing the solder resist fabrication.

[0034] Example 2: Fabrication of fine-pitch solder resist layer on aluminum nitride ceramic AMB substrate using green picosecond laser This embodiment describes the preparation of a solder resist layer for fine-pitch chips using a high thermal conductivity aluminum nitride (AlN) active metal brazing (AMB) ceramic copper-clad laminate.

[0035] S1. Preprocessing: We offer aluminum nitride (AMB) substrates with pre-etched ultra-fine lines, a copper thickness of 200 μm, and a minimum line width / spacing of 25 / 25 μm. They are then gently cleaned for 300 seconds in an ultrasonic cleaner using a 5%–10% potassium hydroxide solution and a 5%–10% sodium persulfate solution, effectively removing organic contaminants without damaging the surface.

[0036] S2. Graphic drawing and alignment: A high-resolution CCD vision alignment system (accuracy ±2μm) is used to identify minute etched patterns on the substrate as alignment features. Matching fine solder mask patterns with linewidth / spacing of 20 / 20μm are then drawn in CAD. The software features deformation compensation capabilities to correct for substrate deformation of <0.1% caused by high-temperature sintering.

[0037] S3. Laser scanning imaging: The process atmosphere was synthetic air (N2:O2=4:1) with a flow rate of 15L / min. A green picosecond laser with a wavelength of 532nm and a pulse width of ~10ps was used, resulting in a very small heat-affected zone.

[0038] Processing parameters: average power 5W, scanning speed 1500mm / s, frequency 500kHz, line spacing 5μm, 3 scans. The cold processing characteristics of picosecond lasers make the copper oxidation process more controllable, resulting in a smoother oxide layer surface and better edge steepness.

[0039] S4. Post-processing: Same as in Example 1, perform cleaning and AOI inspection.

[0040] Comparative Example 1: Comparative Example (Traditional Solder Resist Ink Process) like Figure 6 As shown, using the same type of alumina DBC substrate (300μm copper thickness) as raw material, a solder resist layer was prepared using a traditional liquid photoresist ink process. The steps are as follows: S1. Clean the substrate (same as the pretreatment in Example 1).

[0041] S2. Screen printing: Using a 300-mesh screen, liquid solder resist ink is printed onto the substrate surface.

[0042] S3. Pre-drying: Bake in an 80℃ oven for 20 minutes to allow the ink to dry to the touch.

[0043] S4. Exposure: Align a high-precision film with the substrate and expose it under ultraviolet light for 60 seconds.

[0044] S5. Development: Use a 1%~5% sodium carbonate (Na2CO3) solution to spray and develop, remove ink from unexposed areas, expose the pads, and generate chemical waste liquid.

[0045] S6. Curing: Final curing in an oven at 180℃ for 60 minutes.

[0046] S7. Final cleaning and inspection.

[0047] Performance Testing and Comparison A series of standard tests were performed on the samples obtained from the above embodiments and comparative examples. The specific test items, methods, and judgment criteria are as follows: 1. Solder resist thickness: Using a profilometer or laser confocal microscope, randomly select 5 points on the sample surface to measure the solder resist thickness and take the average value.

[0048] 2. Electrical insulation performance test: Under DC1000V conditions, the product is energized between the grooves for 60 seconds. An insulation resistance value >10GΩ is considered valid.

[0049] 3. Solder barrier effect test: The sample was placed in a 310℃ formic acid furnace and tested using Sn. 96.5 Ag3Cu 0.5 Solder paste is applied for 90 seconds. After cooling, the solder is observed under a microscope to see if it overflows the preset solder resist window area.

[0050] 4. Temperature Cycling Test: According to GJB548B-2005, condition C: -55℃ / 150℃, 15 min each at high and low temperatures, transition time <30 s, continuous temperature cycling was performed. After each cycle, an ultrasonic scanning microscope was used to inspect for delamination or cracks between the copper layer, solder mask layer, and ceramic substrate. The number of cycles at which the first failure (delamination) occurred was recorded. If no delamination occurred after ≥45 cycles, the test was considered effective. The data in Table 1 shows the number of cycles at which the first delamination failure occurred.

[0051] 5. Graphic alignment accuracy: The relative positional offset between the theoretical and physical solder resist is measured in a two-dimensional dimension. The smaller the offset, the higher the accuracy.

[0052] The test results are shown in Table 1.

[0053] Table 1

[0054] The above test data demonstrates that the laser-induced oxidation direct solder resist method provided by this invention is comprehensively superior to traditional ink processes in all key performance indicators, including pattern accuracy, insulation, solder resist effect, and environmental reliability. Particularly in terms of pattern accuracy, the embodiments exhibit significant advantages, with offsets far smaller than the comparative examples, solving the high-precision patterning problem in existing technologies. The improved thermal cycling reliability further indicates that the new materials and methods have enhanced stability under extreme conditions. These improvements not only meet the high-performance requirements of modern electronic devices but also provide a solid foundation for future technological upgrades. Overall, the test results fully verify the feasibility and superiority of this invention in practical applications.

[0055] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0056] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0057] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing an environmentally friendly solder resist for ceramic copper-clad laminates, characterized in that, Includes the following steps: S1. Pre-treatment: Clean the ceramic copper-clad board with surface pattern lines to obtain a clean copper surface. S2. Graphic drawing and positioning: Fix the pre-processed ceramic copper-clad board on the laser processing platform, determine the processing benchmark through the vision positioning system, and import the solder resist pattern to be formed into the control system. S3, Laser-induced oxidation imaging: In an oxygen-containing atmosphere, a pulsed laser beam is used to selectively scan the copper area on the ceramic copper-clad laminate that needs to form a solder resist layer, so that the copper in the scanned area reacts with oxygen to generate a copper oxide solder resist layer in situ, while the copper in the unscanned area remains exposed as a solder pad. S4. Post-processing: Cleaning and inspecting the substrate after laser processing.

2. The method for preparing environmentally friendly solder resist for ceramic copper-clad laminates according to claim 1, characterized in that, In step S1, the cleaning is performed using an alkaline solution and an oxidizing solution via ultrasonic cleaning.

3. The method for preparing environmentally friendly solder resist for ceramic copper-clad laminates according to claim 1 or 2, characterized in that, In step S2, the visual positioning system is a CCD visual alignment system, which can identify alignment marks or circuit patterns on the substrate and perform deformation compensation.

4. The method for preparing environmentally friendly solder resist for ceramic copper-clad laminates according to claim 1, characterized in that, In step S3, the pulsed laser is an ultraviolet nanosecond laser or a green picosecond laser.

5. The method for preparing environmentally friendly solder resist for ceramic copper-clad laminates according to claim 4, characterized in that, When using ultraviolet nanosecond lasers, the wavelength is 355nm, the pulse width is 10-30ns, the laser power is 5-15W, the scanning speed is 100-500mm / s, the scanning line spacing is 5-15μm, and the number of scans is 2-10.

6. The method for preparing environmentally friendly solder resist for ceramic copper-clad laminates according to claim 4, characterized in that, When using a green picosecond laser, the wavelength is 532nm, the pulse width is 1-15ps, the laser power is 3-8W, the scanning speed is 1000-2000mm / s, the scanning line spacing is 3-8μm, and the number of scans is 2-5.

7. The method for preparing environmentally friendly solder resist on ceramic copper-clad laminate according to claim 1, characterized in that, In step S3, the oxygen-containing atmosphere is pure oxygen or a mixture of nitrogen and oxygen, wherein the volume fraction of oxygen is not less than 20%.

8. The method for preparing environmentally friendly solder resist on ceramic copper-clad laminate according to claim 1, characterized in that, The thickness of the copper oxide solder resist layer generated in step S3 is 15-25 μm.

9. The method for preparing environmentally friendly solder resist on ceramic copper-clad laminate according to claim 1, characterized in that, The ceramic copper-clad laminate is one of the following: alumina ceramic direct copper-clad laminate, aluminum nitride active metal brazed ceramic copper-clad laminate, or direct copper-plated ceramic substrate.

10. A ceramic copper-clad laminate, characterized in that, The solder resist layer on its surface is prepared by any one of claims 1-9.

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