CN111943708B

CN111943708B - Aluminum nitride ceramic copper-coating method combining screen printing and laser surface cladding

Info

Publication number: CN111943708B
Application number: CN201910409755.XA
Authority: CN
Inventors: 张德库; 熊煜婷; 仇天琳; 代珩; 王克鸿; 周琦; 黄�俊
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2019-05-17
Filing date: 2019-05-17
Publication date: 2022-07-22
Anticipated expiration: 2039-05-17
Also published as: CN111943708A

Abstract

The invention discloses a method for coating copper on aluminum nitride ceramic by combining screen printing and laser surface deposition, which comprises the following steps of preparing slurry prepared by proportioning copper oxide powder and organic ingredients, cleaning an aluminum nitride substrate, oxidizing the surface of the aluminum nitride ceramic, printing the prepared slurry on the aluminum nitride substrate, drying the substrate in a furnace, then paving a copper plate on the copper oxide, performing laser surface melting on the copper plate by utilizing laser surface deposition, and finally performing mechanical processing and polishing on the surface of the obtained material. The contact area of the welding layer is increased through screen printing, and the welding device is used for large-area welding; partial copper is melted by laser through laser surface deposition, and heat is transferred to copper oxide below the copper plate to be melted, so that the copper oxide and aluminum oxide are effectively combined, and the problem that the copper oxide floats upwards due to different densities in the melting process of the copper plate and the copper oxide is solved.

Description

Aluminum nitride ceramic copper-coating method combining screen printing and laser surface cladding

Technical Field

The invention belongs to the field of metal processing, and particularly relates to a method for coating copper on aluminum nitride ceramics by combining screen printing and laser surface deposition.

Background

With the development of electronic technology, the circuit integration level is continuously improved, the circuit is fine and dense, the power consumption in unit area is larger and larger, the heat productivity is increased, and the damage of the device is more easily caused. The ceramic copper-clad plate refers to a special process plate for metallization on the surface of ceramic. The high-performance high-temperature-resistant high-performance high-voltage printed circuit board has become an important electronic packaging material due to the excellent heat conduction characteristic, high insulation property, high current carrying capacity, excellent soldering resistance and high adhesion strength, and can be used for etching various circuit patterns like a PCB (printed circuit board), and is widely applied to the fields of power electronics, high-power modules, aerospace and the like. The current preparation methods are divided into a direct copper-clad method and an active metal welding method.

The direct copper-clad method is the most frequently adopted manufacturing method of the ceramic copper-clad substrate for the high-power module at present, the basic key point is that a layer of Cu [ O ] eutectic liquid phase is formed around metal copper which is coated on the surface of ceramic under the weak oxidation atmosphere, the liquid phase can well wet the surfaces of a Cu foil and a ceramic substrate which are contacted with each other, and interface products such as CuAlO2 are formed, so that the Cu foil and the ceramic substrate are firmly bonded together, but the method is expensive, and the fusion rate and the connection strength are low; the active metal welding is a further development of the direct copper-cladding method, and a reaction layer which can be wetted by liquid brazing filler metal is generated by reacting a small amount of active elements (Ti and Zr) contained in the brazing filler metal with the ceramic, so that the ceramic and the metal are jointed. However, the method has high requirements on process parameters, high cost and low large-area fusion rate, and some active brazing filler metals cannot corrode a copper plate enough and are difficult to be tightly connected.

At present, the ceramic copper clad laminate mainly has two modes (1) of DBC and AMB, and the DBC method is expensive, and a welding layer is easy to fall off and lose efficacy due to the direct massive connection mode, so that large-area connection cannot be carried out. (2) The AMB process has high requirements on process parameters under the condition of ensuring stress and wetting effects, and the influence of difference of thermal expansion coefficients is amplified by overhigh temperature, even loss is caused; the excessive pressure and the excessive time easily cause the solder to flow out seriously to influence the welding rate, and the composition ratio of the active solder and the texture structure of a welding layer also have great influence on the performance of the active solder, so the process difficulty is larger.

Disclosure of Invention

The invention aims to provide a method for coating copper on aluminum nitride ceramics by combining screen printing and laser surface deposition, which has the characteristics of high connection strength and fusion rate, nearly compactness, low cost, simple operation process and short period.

The technical scheme for realizing the purpose of the invention is as follows:

a method for coating copper on aluminum nitride ceramic by combining screen printing and laser surface deposition comprises the following steps:

(1) preparing slurry by proportioning copper oxide powder and organic ingredients;

(2) cleaning an aluminum nitride substrate, and oxidizing the surface of aluminum nitride ceramics;

(3) printing the prepared slurry on an aluminum nitride substrate and putting the substrate into a furnace for drying;

(4) carrying out laser surface melting on the copper plate by utilizing laser surface deposition, and controlling the laser scanning speed to be 60-100mm/min respectively; the method comprises the specific steps of paving copper plates with uniform thickness on the surface of a copper oxide layer, and carrying out layered melting on the copper plates by laser scanning, wherein the copper plates ensure that the thickness of each part is equal so as to enable the melted copper plates to be instantly solidified uniformly; ensuring that the thickness of the copper layer after laser printing is 0.3-0.7 mm;

(5) and (5) performing mechanical processing and polishing on the surface after deposition.

Further, the step (2) specifically comprises: and (3) carrying out ultrasonic cleaning on the aluminum nitride ceramic by using acetone and alcohol, and further oxidizing the surface of the aluminum nitride ceramic, wherein the thickness of aluminum oxide is controlled to be about 1-4 mu m.

Further, when oxidizing the surface of aluminum nitride, the aluminum nitride is placed in a flowing protective atmosphere with an oxygen partial pressure of 0.001 to 0.5atm, wherein the atmosphere is a mixture of oxygen and argon in a ratio of 1: 4, heating to 1100-1500 ℃, and then preserving heat.

Further, the step (3) is specifically: taking the oxidized aluminum nitride ceramic as a printing stock, and printing slurry prepared from copper oxide powder on the surface of the oxidized aluminum nitride ceramic by screen printing under the printing pressure of 50-100N and the thickness of the copper oxide powder of 5-10 mu m; and putting the materials into a vacuum connecting furnace, selecting Ar gas as protective gas, heating the materials at the temperature of 1100-1200 ℃, and simultaneously applying pressure of 5MPa for about 1.5 hours.

Furthermore, the laser surface deposition process parameters are current 350A, pulse 5.5ms, frequency 7Hz and spot size 2.4 mm.

Further, the preparation of the slurry: grinding the copper oxide sealing solder into powder, mixing the powder with organic ingredients to form slurry with proper viscosity, no adhesion and no edge expansion, and smoothly transferring the slurry to an aluminum nitride substrate through meshes, wherein the organic ingredients comprise butanone, PVB and alcohol.

Furthermore, the mesh number for silk-screen printing is 200, the drying temperature is 150-200 ℃, and the drying time is 1-2 hours.

Furthermore, in the copper cladding process, the thickness of the copper plate is measured in real time by a thickness detector, the temperature of a molten pool is measured by a temperature detector, and the output power of the laser is controlled and adjusted.

Compared with the prior art, the invention has the remarkable characteristics that:

1. the invention adopts the mode that the welded welding layers are paved in layers, thereby ensuring the high connection strength, and the invention can carry out large-area connection by using the silk-screen printing, and has high connection strength and low price and cost.

2. The invention adopts a layered covering mode to enable the solder to be almost tightly combined, the thickness of a welding layer is protected by screen printing, the laser is instantly solidified, the solder is not easy to flow out, compared with an AMB process, the process difficulty is greatly reduced, and the preparation period is shortened.

Drawings

FIG. 1 is a schematic view of the assembly of the aluminum nitride ceramic, the ceramic oxide layer, the copper oxide layer and the copper layer alloy according to the present invention.

FIG. 2 is a process flow chart of the aluminum nitride ceramic copper-clad connection method of the present invention.

Fig. 3 is a schematic view of a laser deposited molten copper plate according to the present invention.

FIG. 4 is a schematic view of the alloy assembly of the present invention.

FIG. 5 is a process flow diagram of the present invention.

Fig. 6 is a laser welding diagram of the present invention.

Detailed Description

The present invention will be further described with reference to the following specific embodiments

With reference to fig. 1, 2 and 3, a method for coating copper on aluminum nitride ceramic by combining screen printing and laser surface deposition specifically comprises the following steps:

(1) preparing slurry: preparing slurry from copper oxide powder and organic ingredients, namely mixing the copper oxide powder with the organic ingredients of butanone, PVB and alcohol (the mass ratio of the copper oxide powder to the organic ingredients is 9: 1) by a ball mill, fully grinding and stirring, standing for 15min to discharge air bubbles brought in stirring, and forming the slurry with proper viscosity.

(2) Ultrasonic cleaning of acetone and ethanol is carried out on the aluminum nitride substrate, the workpiece is placed in an ultrasonic cleaning tank, the acetone and the ethanol are used as cleaning liquid, the temperature of the cleaning liquid is controlled to be 40 ℃, and an ultrasonic device is started to generate a high-frequency electric signal higher than 20 kHz. The high frequency oscillating wave oscillates the liquid and produces a large number of small, non-steady-state bubbles and cavities of micron size. The bursting of the bubbles continuously bombards the surface of the workpiece, so that dirt is quickly peeled off, and the cleaning time is controlled to be 1-3 minutes, thereby achieving the effect of cleaning the workpiece. Ensuring the surface to be clean and having no oil stain and impurities.

(3) And oxidizing the aluminum nitride ceramic, wherein when the surface of the aluminum nitride is oxidized, the aluminum nitride ceramic is placed in a flowing protective atmosphere with the oxygen partial pressure of 0.001-0.5 atm, and the atmosphere is formed by mixing oxygen, nitrogen and argon. Then heating to 1100-1500 ℃ and preserving the temperature for a period of time. The thickness of the oxide layer is controlled to be about 1-4 μm.

(4) The paste was printed onto an aluminum nitride substrate using a screen printer. The mesh number for silk-screen printing is 200, the printing pressure is 50-100N, the drying temperature is 150-200 ℃, the drying time is 1-2 hours, the thickness of the printed copper oxide powder is 2-6 mu m, and the printing pressure is 50-100N.

(5) Putting the material obtained by printing into a furnace for drying; selecting the drying temperature of 160 ℃, the heat preservation time of 10min, the heating rate of 3 ℃/min, selecting Ar gas as the protective gas, heating the temperature range of 1100-1200 ℃, simultaneously applying the pressure of 5MPa, and the pressing time of 1.5 h.

(6) And (3) laying a copper plate on the copper oxide by laser deposition for laser melting scanning, and controlling the thickness of the copper powder laid each time to be 30 mu m to ensure that the copper powder is laid uniformly. And (3) carrying out layered melting on the copper powder by laser scanning, wherein the copper powder ensures that the thicknesses of all parts are equal so as to ensure that the melted copper powder is instantly solidified and uniform. The thickness of the copper layer after laser printing is 0.3-0.7 mm.

(7) And (3) carrying out mechanical processing and polishing on the surface of the obtained material, selecting polishing cloth made of different materials to be fixed on a cast iron grinding disc, adding copper chemical polishing solution between the polishing disc and a workpiece to realize copper plate surface polishing under pressure and rotating speed, and uniformly distributing the polishing solution on the polishing cloth in a spraying mode. The polishing pressure is controlled to be (0.5-1) N/cm2, and the rotation speed is controlled to be 1200-1400 (r/min). The surface is bright and smooth, and the etching is convenient.

The finally obtained ceramic copper-clad plate can greatly improve the contact area of a welding layer due to the adoption of screen printing, and is suitable for large-area welding. Meanwhile, laser surface deposition utilizes laser to melt part of copper, and simultaneously transfers heat to copper oxide below the copper plate to melt the copper oxide, so that the copper oxide and aluminum oxide are effectively combined, and the phenomenon that the copper oxide floats upwards due to different densities in the melting process of the copper plate and the copper oxide is solved. The laser printing forming is fast, and the production time can be greatly shortened. The aluminum nitride ceramic copper-clad plate combining the two modes has the advantages of low material cost, high precision, excellent surface quality, short period and improved welding strength and area.

Referring to fig. 1, 2 and 3, the present invention relates to a method for connecting a laser-deposited copper-clad substrate.

As shown in fig. 4 to 6, a copper plate is first laid on a copper oxide by laser welding and then laser melting and scanning are performed. And then the surface of the obtained material is mechanically processed and polished. In laser deposition, part of copper is melted by laser, heat is transferred to copper oxide below a copper plate to be melted, the temperature of a molten pool is detected by a temperature detector in the melting process, and the real-time thickness of the copper plate is detected by a thickness detector. And then feeding back the information to a computer to compare with the molten pool temperature set for the final copper plate thickness and controlling the power of the laser beam in real time so as to control the molten pool temperature. If the temperature of the molten pool is too high, the thickness of the final copper plate can be thinned by continuously maintaining the original laser power. At the moment, timely adjustment of the laser power is important, so that the final copper plate is equal in thickness, copper oxide powder below the copper plate is fully melted, the copper oxide and aluminum oxide are effectively combined, and the phenomenon that the copper oxide floats upwards due to different densities in the melting process of the copper plate and the copper oxide is solved. And (3) carrying out layered melting on the copper plate by laser scanning, wherein the copper plate ensures that the thickness of each part is equal so as to ensure that the melted copper plate is instantly solidified uniformly. The thickness of the copper layer after laser printing is 0.3-0.7 mm. The printed copper layer has high density and excellent mechanical property. And mechanically polishing the printed copper surface to ensure that the surface is bright and smooth and is convenient to etch.

Example 1

And (3) paving a copper plate on the copper oxide by using laser deposition to perform laser melting scanning. The thickness of the copper layer was 0.5 mm. The laser current was 160A, the pulse width was 3.5ms, and the pulse frequency was 25Hz, and the scanning speed of the laser was set at 100 mm/min. And the copper surface is mechanically polished to make the surface bright and flat, so that the etching is convenient. And the manufactured ceramic copper-clad plate is observed by SEM, and the interface bonding strength is close to compactness. The joint was subjected to tensile strength test and had a peel strength of 6.2N/mm.

Example 2

And (3) paving a copper plate on the copper oxide by using laser deposition to perform laser melting scanning. The thickness of the copper layer was 0.5 mm. The laser current is 170A, the pulse width is 3.0ms, the pulse frequency is 25Hz, and the scanning speed of the laser is set to be 60 mm/min. And the copper surface is mechanically polished to make the surface bright and flat, so that the etching is convenient. And the manufactured ceramic copper-clad plate is observed by SEM, and the interface bonding strength is close to compactness. The joint was subjected to tensile strength test and had a peel strength of 6.6N/mm.

Example 3

And (3) paving a copper plate on the copper oxide by using laser deposition to perform laser melting scanning. The thickness of the copper layer was 0.5 mm. The laser current is 170A, the pulse width is 3.5ms, the pulse frequency is 15Hz, and the scanning speed of the laser is set to 80 mm/min. And the copper surface is mechanically polished to make the surface bright and flat, so that the etching is convenient. And the manufactured ceramic copper-clad plate is observed by SEM, and the interface bonding strength is close to compactness. The tensile strength of the joint is tested, and the peel strength is 6.4N/mm

Example 4

And (3) paving a copper plate on the copper oxide by using laser deposition to perform laser melting scanning. The thickness of the copper layer was 0.5 mm. The laser current is 180A, the pulse width is 3.5ms, the pulse frequency is 20Hz, and the scanning speed of the laser is set to be 60 mm/min. And the copper surface is mechanically polished to ensure that the surface is bright and flat, and the etching is convenient. And the interface bonding strength of the prepared ceramic copper-clad plate is close to compactness by SEM observation. The joint was subjected to a tensile strength test and had a peel strength of 6.8N/mm.

Fig. 1, 2, and 3 are SEM observations of the interface of the ceramic copper plate at different laser scanning speeds.

In fig. 1, the upper layer is copper, the lower layer is aluminum nitride ceramic, and the intermediate layer is a bonding layer of copper oxide and aluminum oxide. The thickness of the copper layer was 0.5 mm. The laser current used was 160A, the pulse width was 3.5ms, the pulse frequency was 25Hz, and the scanning speed of the laser was set to 100 mm/min. And the copper surface is mechanically polished to ensure that the surface is bright and flat, and the etching is convenient. The figure is an SEM observation picture of the prepared ceramic copper-clad plate. The joint was subjected to tensile strength test and had a peel strength of 6.2N/mm.

In fig. 2, the upper layer is copper, the lower layer is aluminum nitride ceramic, and the intermediate layer is a bonding layer of copper oxide and aluminum oxide. The thickness of the copper layer was 0.5 mm. The laser current used was 170A, the pulse width was 3.0ms, the pulse frequency was 25Hz, and the scanning speed of the laser was set to 60 mm/min. The figure is an SEM observation picture of the prepared ceramic copper-clad plate. The joint was subjected to tensile strength test and had a peel strength of 6.6N/mm.

In fig. 3, the upper layer is copper, the lower layer is aluminum nitride ceramic, and the intermediate layer is a bonding layer of copper oxide and aluminum oxide. The thickness of the copper layer was 0.5 mm. The laser current used was 180A, the pulse width was 3.5ms, the pulse frequency was 20Hz, and the scanning speed of the laser was set to 60 mm/min. The figure is an SEM observation picture of the prepared ceramic copper-clad plate. The joint was subjected to tensile strength test and had a peel strength of 6.8N/mm.

Claims

1. A method for coating copper on aluminum nitride ceramic by combining screen printing and laser surface deposition is characterized by comprising the following steps:

(1) preparing slurry prepared by proportioning copper oxide powder and organic ingredients;

(3) printing the prepared slurry on an aluminum nitride substrate through screen printing, and putting the substrate into a furnace for drying;

(5) and (5) performing mechanical processing and polishing on the surface after cladding.

2. The method for coating the aluminum nitride ceramic copper by combining screen printing and laser surface deposition according to claim 1, wherein the step (2) is specifically as follows: and (3) carrying out ultrasonic cleaning on the aluminum nitride ceramic by using acetone and alcohol, and further oxidizing the surface of the aluminum nitride ceramic, wherein the thickness of aluminum oxide is controlled to be 1-4 mu m.

3. The method for copper-coating an aluminum nitride ceramic according to claim 2, wherein the aluminum nitride surface is oxidized by subjecting the aluminum nitride surface to a flowing protective atmosphere having an oxygen partial pressure of 0.001 to 0.5atm, wherein the atmosphere is a mixture of 1: 4, heating to 1100-1500 ℃, and then preserving heat.

4. The method for coating copper on aluminum nitride ceramic by combining screen printing and laser surface deposition according to claim 1, wherein the step (3) is specifically: taking the oxidized aluminum nitride ceramic as a printing stock, and printing slurry prepared from copper oxide powder on the surface of the oxidized aluminum nitride ceramic by screen printing under the printing pressure of 50-100N and the thickness of the copper oxide powder of 5-10 mu m; and then placing the materials into a vacuum connecting furnace, selecting Ar gas as protective gas, heating the materials at the temperature of 1100-1200 ℃, and simultaneously applying pressure of 5MPa for 1.5 hours.

5. The method of claim 1, wherein the laser surface deposition process parameters are current 350A, pulse 5.5ms, frequency 7Hz, and spot size 2.4 mm.

6. The method of claim 1, wherein the slurry is provided in the form of a paste: grinding the copper oxide sealing solder into copper oxide powder, then mixing the copper oxide powder with organic ingredients to form slurry with proper viscosity, no adhesion and no edge expansion, wherein the slurry can be smoothly transferred to an aluminum nitride substrate through meshes, and the organic ingredients comprise butanone, PVB and alcohol.

7. The method for copper-cladding aluminum nitride ceramics according to claim 1 or 4, wherein the mesh number for screen printing is 200, the baking temperature is 150 to 200 ℃, and the baking time is 1 to 2 hours.