Preparation method of copper-clad substrate based on patterned copper foil

Abstract

The invention discloses a preparation method of a copper-clad substrate based on a patterned copper foil. The preparation method comprises the following steps: S1, forming a hollow pattern on a to-be-bonded copper foil; s2, performing selective roughening treatment on the non-bonding surface of the copper foil; s3, forming a micro-convex supporting rib structure on the edge of the hollowed-out pattern on the non-bonding surface of the copper foil; s4, cleaning the to-be-bonded surface of the copper foil and the surface of the ceramic substrate; s5, laminating and assembling the to-be-bonded surface of the copper foil, the ceramic substrate and the bonding material layer to form a laminated structure; s6, sintering and bonding the laminated structure; s7, after the temperature in the furnace is reduced to the room temperature, the sintered copper-clad substrate is taken out; s8, performing edge trimming to remove redundant bonding materials and copper foil corners; and S9, performing ultrasonic cleaning and appearance detection. The method has the advantages that high-precision direct forming of circuit patterns after high-temperature bonding is achieved, a traditional etching process is avoided, and meanwhile the reliability of a bonding interface and the flatness of the whole substrate are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of electronic materials and packaging technology, and in particular to a method for preparing a copper-clad substrate based on patterned copper foil. Background Technology

[0002] Traditional DCB / AMB fabrication processes typically include the following steps: providing a flat copper foil and a ceramic sheet; coating the copper foil onto the surface of the ceramic sheet using solder or eutectic alloy to form a "copper-ceramic-copper" sandwich structure; then, coating the copper foil with photoresist, and through a series of processes such as photolithography, development, etching, and photoresist removal, etching away the unwanted copper layer to finally form the desired circuit pattern.

[0003] However, this traditional process suffers from significant material waste: the etching process requires corroding away large areas of copper outside the circuit pattern, resulting in a substantial waste of precious copper, leading to high costs and environmental problems. Simultaneously, the wet chemical etching stage requires the treatment of etching wastewater, placing significant environmental pressure on the process and creating a lengthy workflow. Side etching can cause deviations between the etched circuit pattern and the mask pattern, making it difficult to fabricate circuits with very fine linewidths / spacings, thus limiting the miniaturization and integration of power modules. Furthermore, residues of etching solution and resist remover may remain, affecting the long-term reliability of the substrate.

[0004] In recent years, some pre-patterned copper foil bonding solutions have emerged, which involve first forming circuit patterns on copper foil through etching or mechanical processing, and then performing bonding. Although this type of solution can avoid etching after bonding, due to the significant difference in the coefficient of thermal expansion (CTE) between the copper foil and the ceramic substrate, the copper foil pattern will undergo uncontrollable thermal expansion and contraction deformation during high-temperature sintering and cooling. This leads to dimensional deviations and positional shifts in the final circuit pattern, and even warping, cracking, or stress concentration at the bonding interface, which seriously affects the accuracy and reliability of the product. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing copper-clad laminate based on patterned copper foil. The method involves performing a differential pre-compensation pattern scaling design on the copper foil pattern and introducing a stress relief structure during the bonding process. This enables high-precision direct forming of the circuit pattern after high-temperature bonding, avoiding traditional etching processes and significantly improving the reliability of the bonding interface and the overall flatness of the substrate.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A method for fabricating a copper-clad laminate based on patterned copper foil, characterized by comprising the following steps: S1. Based on the final required circuit pattern, a cutout pattern is formed on the copper foil to be bonded to complete the patterning process. S2, after patterning, the unbonded surfaces of the copper foil are selectively roughened; S3, then form a micro-convex support rib structure on the edge of the hollowed-out pattern on the non-bonded side of the copper foil; S4, Clean the bonding surface of the patterned copper foil and the surface of the ceramic substrate; S5, the bonding surface of the patterned copper foil, the ceramic substrate and the bonding material layer are stacked and assembled in a preset order to form a stacked structure, and at the same time, the exposed ceramic substrate in the hollow area is filled with graphite paste, a temporary support material that can be decomposed at high temperature. S6, the laminated structure is placed in a tunnel sintering furnace or a vacuum sintering furnace for sintering and bonding; S7. After the furnace temperature drops to room temperature, remove the sintered copper-clad substrate. S8, trim the edges of the copper-clad substrate to remove excess bonding material and copper foil corners; S9. Finally, the copper-clad substrate is ultrasonically cleaned and its appearance is inspected.

[0007] Preferably, in step S1, the final required circuit pattern is scaled to obtain a hollow pattern. The scaling ratio of the dense area of ​​the hollow pattern is 75-95% of the circuit pattern, and the scaling ratio of the sparse area of ​​the hollow pattern is 95-115% of the circuit pattern. The hollow pattern is formed by stamping or laser cutting.

[0008] Preferably, the selective roughening process in step S2 specifically involves: using a picosecond pulsed laser system with a power of 20-50W, a scanning speed of 1500-3000mm / s, and a repetition frequency of 50kHz-200kHz to form a micro-pit array with a depth of 10% of the copper foil thickness on the bonding surface of the copper foil.

[0009] Preferably, the specific method for forming the micro-convex support rib structure in step S3 is as follows: using a picosecond pulsed laser system with a repetition frequency of 500kHz~1MHz, a power of 200~280w, and a scanning speed of 3000~5000mm / s, performing parallel scanning two or more times along the edge of the hollowed-out pattern offset by 10~30μm, so that the copper material at the edge melts but does not completely vaporize, forming molten droplets that accumulate and solidify into convex ribs on the hollowed-out side.

[0010] Preferably, in step S4, cleaning is performed using plasma with a plasma power of 100-200W and a cleaning time of 5-10 minutes.

[0011] Preferably, the bonding material layer in step S5 is selected according to the substrate preparation process, specifically: in the DCB process, the bonding material layer is a copper bonding layer with surface oxidation treatment and an oxide layer weight of 0.15~0.25g / cm²; in the AMB process, the bonding material layer is Ag-Ti-Cu active metal solder foil with a solder thickness of 5~30μm.

[0012] Preferably, in step S5, two patterned copper foils can be stacked simultaneously to form a sandwich-structured double-sided copper-clad laminate.

[0013] Preferably, the sintering and bonding process of the stacked structure in step S6 specifically includes: Preheating and degassing: AMB process: Place the laminated structure in a vacuum sintering furnace, close the furnace door, and evacuate to a vacuum level ≤5×10. -3 Pa; then preheating and degassing treatment is carried out, with the temperature increased to 200~400℃ at a heating rate of 5-8℃ / min, and held for 30~90min; DCB process: The stacked structure is placed in a tunnel sintering furnace, with nitrogen pressure of 0.25-0.3 MPa, oxygen content of <50 ppm, and heating to 900~1000℃ at a heating rate of 10-20℃ / min. Heating and melting: After preheating and degassing, adjust the heating rate to 10~15℃ / min and heat to the melting temperature of the bonding material. For the AMB process, heat to 800~900℃, and for the DCB process, continue heating to 1070~1150℃. Isothermal curing: AMB process: Keep the sintering temperature constant and continue to hold for 60~90 minutes. During this period, the temperature is uniformly controlled through the gas circulation system in the furnace to ensure that the temperature fluctuation in the furnace is ≤±5℃; DCB process: After reaching the melting temperature, hold for 30~45 minutes. Gradient cooling: After isothermal curing, a gradient cooling method is used to cool down. In the first stage, the temperature is reduced to 600-700℃ at a rate of 8-10℃ / min and held for 40-50min. In the second stage, the temperature is reduced to 300-400℃ at a rate of 5-6℃ / min and held for 30-40min. In the third stage, the temperature is reduced to 100-150℃ at a rate of 3-4℃ / min and then allowed to cool naturally to room temperature.

[0014] Preferably, step S8 further includes removing the micro-protruding support rib structure by slight mechanical polishing or chemical flash etching.

[0015] Preferably, in step S9, the ultrasonic cleaning medium is deionized water, the power is 200~300W, and the cleaning time is 15~20min.

[0016] In summary, the present invention has the following beneficial effects: 1. This invention completely solves the problem of pattern deformation caused by high-temperature bonding through regional differential pre-compensation, achieving truly "etch-free" direct molding.

[0017] 2. This invention introduces micro-convex support ribs and temporary support materials to effectively prevent the collapse of fine lines and edges, thereby improving the yield of fine lines.

[0018] 3. This invention employs a multi-stage gradient heating, holding, and cooling sintering process, combined with prior surface pretreatment, to effectively remove impurities and gases from the surfaces of each material layer. This promotes the interfacial reaction between the bonding material and the copper foil and ceramic substrate, forming a stable intermetallic compound bonding layer. Simultaneously, it avoids interfacial stress concentration caused by rapid temperature changes, reduces the probability of defects such as interfacial voids and cracks, and improves the thermal conductivity and insulation performance of the substrate.

[0019] 4. This invention avoids the etching process, reduces environmental pollution, and is applicable to both AMB and DBC processes. It is compatible with various ceramic materials and copper foil thickness combinations, and has broad industrialization prospects. Detailed Implementation

[0020] The specific embodiments of the present invention will be further described below. These embodiments do not constitute a limitation on the present invention.

[0021] A method for fabricating a copper-clad laminate based on patterned copper foil includes the following steps: S1. Based on the final required circuit pattern, a cutout pattern is formed on the copper foil to be bonded to complete the patterning process. The final required circuit pattern is scaled to obtain the cutout pattern. The scaling ratio of the dense area of ​​the cutout pattern is 75~95% of the circuit pattern, and the scaling ratio of the sparse area of ​​the cutout pattern is 95~115% of the circuit pattern. The cutout pattern is formed by stamping or laser cutting.

[0022] S2. After patterning, the non-bonding surface of the copper foil is selectively roughened. Specifically, a picosecond pulsed laser system is used with a power of 20-50W, a scanning speed of 1500-3000mm / s, and a repetition frequency of 50kHz-200kHz to form a micro-pit array with a depth of 10% of the copper foil thickness on the bonding surface of the copper foil.

[0023] S3. Next, a micro-convex support rib structure is formed on the edge of the non-bonded surface of the copper foil cutout pattern. The specific method for forming the micro-convex support rib structure is as follows: a picosecond pulse laser system is used with a repetition frequency of 500kHz~1MHz, a power of 200~280w, and a scanning speed of 3000~5000mm / s. The system performs parallel scanning two or more times along the edge of the cutout pattern offset by 10~30μm, so that the copper material at the edge melts but does not completely vaporize, forming molten droplets that accumulate and solidify on the cutout side to form a convex rib.

[0024] S4. The bonding surface of the patterned copper foil and the surface of the ceramic substrate are cleaned by plasma. The plasma power is 100~200W and the cleaning time is 5~10min.

[0025] S5, the bonding surface of the patterned copper foil, the ceramic substrate, and the bonding material layer are stacked and assembled in a preset order to form a stacked structure. At the same time, the exposed ceramic substrate in the hollow area is filled with graphite paste, a temporary support material that can be decomposed at high temperature. The bonding material layer is selected according to the substrate preparation process. Specifically, in the DCB process, the bonding material layer is a copper bonding layer with an oxidized surface and an oxide layer weight of 0.15~0.25g / cm². In the AMB process, the bonding material layer is Ag-Ti-Cu active metal solder foil with a solder thickness of 5~30μm. Two patterned copper foils can also be stacked at the same time to form a sandwich structure of double-sided copper-clad laminate.

[0026] S6, the laminated structure is placed in a tunnel sintering furnace or a vacuum sintering furnace for sintering and bonding, the specific process being: Preheating and degassing: AMB process: Place the laminated structure in a vacuum sintering furnace, close the furnace door, and evacuate to a vacuum level ≤5×10. -3 Pa; then preheating and degassing treatment is carried out, with the temperature increased to 200~400℃ at a heating rate of 5-8℃ / min and held for 30~90min to remove the moisture, gas and flux volatiles adsorbed on the surface of each layer of material, and to prevent the generation of bubble defects during sintering. DCB process: The stacked structure is placed in a tunnel sintering furnace, with nitrogen pressure of 0.25-0.3 MPa, oxygen content of <50 ppm, and heating to 900~1000℃ at a heating rate of 10-20℃ / min. Heating and melting: After preheating and degassing, adjust the heating rate to 10~15℃ / min and heat to the melting temperature of the bonding material. For the AMB process, heat to 800~900℃, and for the DCB process, continue to heat to 1070~1150℃ to fully melt the bonding material and spread it evenly on the bonding interface. Isothermal curing: AMB process: Keep the sintering temperature constant and continue to hold for 60~90min. During this period, the temperature is uniformly controlled through the gas circulation system in the furnace to ensure that the temperature fluctuation in the furnace is ≤±5℃; DCB process: After reaching the melting temperature, hold for 30~45min to allow the molten bonding material to react with the patterned copper foil and ceramic substrate at the interface to form a stable intermetallic compound bonding layer and improve the bonding strength. Gradient cooling: After isothermal curing, a gradient cooling method is used to cool down. In the first stage, the temperature is reduced to 600-700℃ at a rate of 8-10℃ / min and held for 40-50min. In the second stage, the temperature is reduced to 300-400℃ at a rate of 5-6℃ / min and held for 30-40min. In the third stage, the temperature is reduced to 100-150℃ at a rate of 3-4℃ / min and then allowed to cool naturally to room temperature.

[0027] S7. After the furnace temperature drops to room temperature, remove the sintered copper-clad substrate.

[0028] S8 trims the edges of the copper-clad substrate to remove excess bonding material and copper foil corners. It also removes the micro-protrusion support rib structure through slight mechanical polishing or chemical flash etching. The formation of the micro-protrusion support rib is highly integrated with the hollow pattern processing, which not only improves the bonding yield of fine lines but also maintains the overall process simplicity.

[0029] S9. Finally, the copper-clad substrate is subjected to ultrasonic cleaning, appearance and performance testing. The ultrasonic cleaning medium is deionized water, the power is 200~300W, the cleaning time is 15~20min, the final circuit pattern accuracy error is ≤±0.03mm, the bond shear strength is ≥30MPa, the breakdown voltage is ≥20kV / mm, and the thermal conductivity is ≥180W / (m·K).

[0030] This invention completely solves the problem of pattern deformation caused by high-temperature bonding through regional differential pre-compensation, achieving truly "etch-free" direct molding.

[0031] This invention introduces micro-convex support ribs and temporary support materials to effectively prevent the collapse of fine lines and edges, thereby improving the yield of fine lines.

[0032] This invention employs a multi-stage gradient heating, holding, and cooling sintering process, combined with prior surface pretreatment, to effectively remove impurities and gases from the surfaces of each material layer. This promotes the interfacial reaction between the bonding material and the copper foil and ceramic substrate, forming a stable intermetallic compound bonding layer. Simultaneously, it avoids interfacial stress concentration caused by rapid temperature changes, reduces the probability of defects such as interfacial voids and cracks, and improves the thermal conductivity and insulation performance of the substrate.

[0033] This invention avoids the etching process, reduces environmental pollution, and is applicable to both AMB and DBC processes. It is compatible with various ceramic materials and copper foil thickness combinations, and has broad industrialization prospects.

[0034] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within the scope of its essence and protection. Such modifications or equivalent substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A method for fabricating a copper-clad laminate based on patterned copper foil, characterized in that, Includes the following steps: S1. Based on the final required circuit pattern, a cutout pattern is formed on the copper foil to be bonded to complete the patterning process. S2, after patterning, the unbonded surfaces of the copper foil are selectively roughened; S3, then form a micro-convex support rib structure on the edge of the hollowed-out pattern on the non-bonded side of the copper foil; S4, Clean the bonding surface of the patterned copper foil and the surface of the ceramic substrate; S5, the bonding surface of the patterned copper foil, the ceramic substrate and the bonding material layer are stacked and assembled in a preset order to form a stacked structure, and at the same time, the exposed ceramic substrate in the hollow area is filled with graphite paste, a temporary support material that can be decomposed at high temperature. S6, the laminated structure is placed in a tunnel sintering furnace or a vacuum sintering furnace for sintering and bonding; S7. After the furnace temperature drops to room temperature, remove the sintered copper-clad substrate. S8, trim the edges of the copper-clad substrate to remove excess bonding material and copper foil corners; S9. Finally, the copper-clad substrate is ultrasonically cleaned and its appearance is inspected.

2. The method for preparing a copper-clad laminate based on patterned copper foil according to claim 1, characterized in that: In step S1, the final required circuit pattern is scaled to obtain a hollow pattern. The scaling ratio of the dense area of ​​the hollow pattern is 75-95% of the circuit pattern, and the scaling ratio of the sparse area of ​​the hollow pattern is 95-115% of the circuit pattern. The hollow pattern is formed by stamping or laser cutting.

3. The method for preparing a copper-clad laminate based on patterned copper foil according to claim 1, characterized in that: The selective roughening process in step S2 specifically involves using a picosecond pulsed laser system with a power of 20-50W, a scanning speed of 1500-3000mm / s, and a repetition frequency of 50kHz-200kHz to form a micro-pit array with a depth of 10% of the copper foil thickness on the bonding surface of the copper foil.

4. The method for preparing a copper-clad laminate based on patterned copper foil according to claim 1, characterized in that: The specific method for forming the micro-convex support rib structure in step S3 is as follows: using a picosecond pulsed laser system with a repetition frequency of 500kHz~1MHz, a power of 200~280w, and a scanning speed of 3000~5000mm / s, the system performs parallel scanning two or more times along the edge of the hollowed-out pattern at an offset of 10~30μm, so that the copper material at the edge melts but does not completely vaporize, forming molten droplets that accumulate and solidify into convex ribs on the hollowed-out side.

5. The method for preparing a copper-clad laminate based on patterned copper foil according to claim 1, characterized in that: In step S4, cleaning is performed using plasma with a power of 100-200W and a cleaning time of 5-10 minutes.

6. The method for preparing a copper-clad laminate based on patterned copper foil according to claim 1, characterized in that: In step S5, the bonding material layer is selected according to the substrate preparation process. Specifically, in the DCB process, the bonding material layer is a copper bonding layer with surface oxidation treatment and an oxide layer weight of 0.15~0.25g / cm². In the AMB process, the bonding material layer is Ag-Ti-Cu active metal solder with a solder thickness of 5~30μm.

7. The method for preparing a copper-clad laminate based on patterned copper foil according to claim 1, characterized in that: In step S5, two patterned copper foils can be stacked simultaneously to form a sandwich-structured double-sided copper-clad laminate.

8. The method for preparing a copper-clad laminate based on patterned copper foil according to claim 1, characterized in that: The sintering and bonding process of the multilayer structure in step S6 is specifically as follows: Preheating and degassing: AMB process: Place the laminated structure in a vacuum sintering furnace, close the furnace door, and evacuate to a vacuum level ≤5×10. -3 Pa; then preheating and degassing treatment is carried out, with the temperature increased to 200~400℃ at a heating rate of 5-8℃ / min, and held for 30~90min; DCB process: The stacked structure is placed in a tunnel sintering furnace, with nitrogen pressure of 0.25-0.3 MPa, oxygen content of <50 ppm, and heating to 900~1000℃ at a heating rate of 10-20℃ / min. Heating and melting: After preheating and degassing, adjust the heating rate to 10~15℃ / min and heat to the melting temperature of the bonding material. For the AMB process, heat to 800~900℃, and for the DCB process, continue heating to 1070~1150℃. Isothermal curing: AMB process: Keep the sintering temperature constant and continue to hold for 60~90 minutes. During this period, the temperature is uniformly controlled through the gas circulation system in the furnace to ensure that the temperature fluctuation in the furnace is ≤±5℃; DCB process: After reaching the melting temperature, hold for 30~45 minutes. Gradient cooling: After isothermal curing, a gradient cooling method is used to cool down. In the first stage, the temperature is reduced to 600-700℃ at a rate of 8-10℃ / min and held for 40-50min. In the second stage, the temperature is reduced to 300-400℃ at a rate of 5-6℃ / min and held for 30-40min. In the third stage, the temperature is reduced to 100-150℃ at a rate of 3-4℃ / min and then allowed to cool naturally to room temperature.

9. The method for preparing a copper-clad laminate based on patterned copper foil according to claim 1, characterized in that: Step S8 also includes removing the micro-protruding support rib structure by slight mechanical polishing or chemical flash etching.

10. The method for preparing a copper-clad laminate based on patterned copper foil according to claim 1, characterized in that: In step S9, the ultrasonic cleaning medium is deionized water, the power is 200~300W, and the cleaning time is 15~20min.