A method for preparing a ceramic substrate with high bonding strength

Abstract

The application belongs to the field of brazing, and discloses a preparation method of a ceramic substrate with high bonding strength. The ceramic substrate is prepared through the following steps: surface denitrogenation treatment of silicon nitride ceramic, covering, and hot isostatic pressing sintering. Ag-Cu-Ti solder reacts with the denitrogenated silicon nitride ceramic and copper to form a transition layer, thereby combining the copper and the silicon nitride ceramic. In the preparation method, a small amount of solder is used, and the obtained ceramic substrate has high bonding strength and small volume.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of brazing, and relates to a preparation method of a ceramic substrate with high bonding strength. BACKGROUND

[0002] With the increasing of power density and working temperature of power module devices, the heat dissipation capacity and reliability of the devices to the packaging substrate have higher requirements. The ceramic copper clad substrate not only has the characteristics of good heat dissipation, high insulation, high mechanical strength, and thermal expansion matching with the chip of the ceramic, but also has the characteristics of strong current carrying capacity of oxygen-free copper, good welding and bonding performance, and high thermal conductivity, and is one of the key packaging materials of the power module device.

[0003] At present, the ceramic copper clad substrate is mainly divided into alumina ceramic copper clad substrate, aluminum nitride ceramic copper clad substrate and silicon nitride ceramic copper clad substrate according to different ceramic materials. The reliability of the ceramic copper clad substrate is not only related to the ceramic copper clad process, but more importantly depends on the reliability of the ceramic substrate material. Among them, the silicon nitride ceramic has higher bending strength and fracture toughness compared with alumina ceramic and aluminum nitride ceramic, and is more reliable under high temperature conditions. The ceramic direct copper clad technology widely used in the past is to directly weld ceramic and copper at high temperature, and there is no bonding material between copper and ceramic. In the process of high temperature service, the ceramic will be peeled off due to the thermal stress generated between the ceramic and the copper, so the traditional ceramic direct copper clad substrate is difficult to meet the packaging requirements of the power module device.

[0004] The active metal brazing method is a method for metallizing the surface of ceramic proposed in the last century. It is a method for realizing the joint of ceramic and metal by using the active elements contained in the filler metal to react with the ceramic to form a reaction layer that can be wetted by liquid filler metal. At present, the silicon nitride ceramic active brazing copper clad substrate prepared by the vacuum pressureless brazing method is widely used, the porosity is high, more solder is needed, and the bonding strength between the silicon nitride ceramic and the copper layer is low. And the existing ceramic substrate has a large overall volume and cannot meet the demand of high-precision work. SUMMARY

[0005] To solve the above problems, the present application provides a preparation method of a ceramic substrate with high bonding strength. The silicon nitride ceramic is subjected to surface denitrogenation treatment, and then is prepared by sleeving and hot isostatic pressing sintering. In the preparation method, a small amount of solder is used, and the obtained ceramic substrate has high bonding strength and small volume. The peel strength of the finished silicon nitride ceramic copper clad substrate is 17.709 N / mm.

[0006] The application first carries out laser denitrogenation treatment on the surface of silicon nitride ceramic, selects Ag-Cu-Ti solder, and places the pretreated silicon nitride ceramic, copper and Ag-Cu-Ti solder in a package mold in the order of titanium foil, silicon nitride ceramic, Ag-Cu-Ti solder, copper sheet and titanium foil, carries out vacuum pretreatment, and places the high-vacuum-to-be-welded piece after the pretreatment into a hot isostatic pressing sintering furnace, so that the Ag-Cu-Ti solder reacts with the denitrogenated silicon nitride ceramic and copper to generate a transition layer to combine the copper and the silicon nitride ceramic.

[0007] The above object of the application is achieved by the following technical scheme:

[0008] A high-bond-strength ceramic substrate comprising silicon nitride ceramic, Ag-Cu 27 -Ti 3.3 (a.wt%) solder and copper sheet.

[0009] The preparation method of the above high-bond-strength ceramic substrate comprises the following steps:

[0010] 1) Denitrogenation of ceramic surface: place the cleaned and dried silicon nitride ceramic on a laser workbench, set the laser parameters: laser scanning speed is 90-120 mm / s, scanning power is 70%-90%, line spacing is 0.02-0.05 mm, start laser scanning, and the denitrogenation of the surface of the silicon nitride ceramic is completed when the scanning is completed;

[0011] 2) Package:

[0012] A package is used, and the package material is titanium foil;

[0013] Place the silicon nitride ceramic obtained in step 1) in a package mold in the order of titanium foil, silicon nitride ceramic, Ag-Cu 27 -Ti 3.3 (a.wt%) solder, copper sheet and titanium foil to obtain a packaged sample;

[0014] 3) Vacuumizing:

[0015] Place the packaged sample obtained in step 2) into a spark plasma sintering furnace, reduce the vacuum degree to 10 -3 Pa or below, heat to 400-800 DEG C, when the pressure reaches 6 MPa, maintain for 0.5-1 h, during which the vacuum degree in the furnace cavity is maintained to be not higher than 10 -3 Pa, first reduce the temperature to room temperature at a rate of 5-10 DEG C / min, to obtain a high-vacuum-to-be-welded piece;

[0016] 4) Hot isostatic pressing sintering:

[0017] The high-vacuum-to-be-welded part obtained in step 3) is placed in a hot isostatic pressing furnace, and is kept at a temperature of 700-850 DEG C and a pressure of 100-200 MPa for 0.5-2 h, so as to obtain a ceramic substrate with high bonding strength.

[0018] Further, the cross-sectional area of the titanium foil in step 2) is circular, square or elliptical, and the active metal solder is Ag-Cu-Ti solder (Ag-Cu 27 -Ti 3.3 ).

[0019] Further, the thickness of the copper sheet in step 2) is 0.1-0.2 mm, and the thickness of the active metal solder is 0.03-0.05 mm.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] The preparation method provided by the present application can obtain a ceramic substrate with high bonding strength, and the silicon nitride ceramic substrate prepared by the present application has the characteristics of simple process, low cost and high bonding strength. The present application first performs vacuum packaging and pretreatment on the silicon nitride ceramic substrate, thereby providing a high-vacuum state for subsequent brazing; the uniform pressure and high temperature in the hot isostatic pressing furnace further promote the chemical reaction between the solder and the ceramic and the copper, reduce the cavity rate of the bonding interface, and make the bonding between the silicon nitride ceramic and the copper sheet more compact. The present application improves the bonding capacity of the silicon nitride ceramic and the copper sheet by denitriding the ceramic substrate and brazing in the hot isostatic pressing furnace after packaging, and the interface cavity rate is extremely low.

[0022] Compared with the prior art, the ceramic copper-clad substrate prepared by the present application has the following advantages: (1) small volume and high bonding strength, the overall thickness is less than 1 mm, which is consistent with the development direction of power modules, and with the acceleration of product upgrading, the substrate with small volume and high bonding strength has a wider application space; (2) simple preparation process, less solder required and lower temperature, the prepared silicon nitride ceramic copper-clad substrate has good bonding effect, and after 100 times of thermal cycle test, the silicon nitride ceramic and the copper sheet are still tightly bonded and do not crack. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a cross-sectional view of a finished ceramic substrate.

[0024] Figure 2 It is an SEM image of the cross section of the ceramic substrate.

[0025] Figure 3 It is a line scanning energy spectrum graph (a) of the cross section of the ceramic substrate.

[0026] Figure 4 It is a line scanning energy spectrum graph (b) of the cross section of the ceramic substrate. DETAILED DESCRIPTION

[0027] The application will be described in detail below with specific examples, but the scope of protection of the application is not limited. Unless otherwise specified, the experimental methods used in the application are conventional methods, and the experimental equipment, materials, reagents, etc. can be obtained from commercial channels.

[0028] Example 1

[0029] 1) Denitrogenation of ceramic surface:

[0030] Put the silicon nitride ceramic into anhydrous ethanol and ultrasonically clean for 10 min, then place the dried silicon nitride ceramic on a laser workbench, set the laser parameters of the laser: the laser scanning speed is 100 mm / s, the scanning power is 80%, the line spacing is 0.05 mm, start laser scanning, and complete denitrogenation.

[0031] 2) Cladding:

[0032] Put the silicon nitride ceramic obtained in step 1) into a cladding mold in the order of silicon nitride ceramic, Ag-Cu-Ti solder, copper sheet, and titanium foil, to obtain a cladding sample.

[0033] 3) Vacuumizing:

[0034] Put the cladding sample obtained in step 2) into a spark plasma sintering furnace, reduce the vacuum degree to 10 -3 Pa below, heat to 700℃, when the pressure reaches 6 MPa, maintain for 0.5 h, during which the vacuum degree in the furnace cavity is maintained to be not higher than 10 -3 Pa, after cladding, remove the pressure, first reduce to room temperature at 8℃ / min, to obtain a high-vacuum-to-be-welded piece.

[0035] 4) Hot isostatic pressing:

[0036] Put the high-vacuum-to-be-welded piece obtained in step 3) into the furnace cavity of a hot isostatic pressing furnace, maintain at a temperature of 700℃ and a pressure of 200 MPa for 0.5 h, to obtain a ceramic substrate with high bonding strength.

[0037] The active metal solder Ag-Cu-Ti has a ratio of AgCu 27 Ti 3.3 (a.wt%)

[0038] The active metal solder Ag-Cu-Ti has a thickness of 0.05 mm, and the copper sheet has a thickness of 0.2 mm.

[0039] After peeling test, the peeling strength is 17.709 N / mm.

[0040]

[0041]

[0042]

[0043] The above-described embodiments are merely preferred embodiments of the present application, but are not all the possible embodiments of the present application. Any modification of the above-described embodiments that would occur to one skilled in the art with the benefit of the present disclosure is intended to be included within the scope of the present application as defined in the claims.

Claims

1. A method for preparing a high bonding strength ceramic substrate, characterized in that: First, the surface of the silicon nitride ceramic is laser denitrified. Ag-Cu-Ti solder is selected. The pre-treated silicon nitride ceramic, metallic copper, and Ag-Cu-Ti solder are placed in a sheath mold in the order of titanium foil, silicon nitride ceramic, Ag-Cu-Ti solder, copper sheet, and titanium foil. Vacuum pretreatment is performed. The pre-treated high vacuum weldment is placed in hot isostatic pressing and sintered. The Ag-Cu-Ti solder reacts with the denitrified silicon nitride ceramic and metallic copper to form a transition layer to bond the metallic copper and silicon nitride ceramic. The thickness of the copper sheet is 0.1-0.2mm, and the thickness of the active metal solder is 0.03-0.05mm. The specific steps are as follows: 1) Denitrification of ceramic surface: Place the cleaned and dried silicon nitride ceramic on the laser workbench, set the laser parameters: laser scanning speed of 90-120 mm / s, scanning power of 70%-90%, line spacing of 0.02-0.05 mm, start laser scanning, and denitrification of the silicon nitride ceramic surface is completed when the scanning is completed; 2)Packaging: Using a sheath, wherein the sheath material is titanium foil; The silicon nitride ceramics obtained in step 1) are prepared according to the following methods: titanium foil, silicon nitride ceramics, Ag-Cu 27 -Ti 3.3 ; a.wt%; solder, copper sheet, titanium foil are placed in the encapsulation mold in this order to obtain an encapsulated sample; 3) Vacuuming: The packaged sample obtained in step 2) was placed in a spark plasma sintering furnace and the vacuum degree was reduced to 10 -3 Pa, heat to 700 ° C, when the pressure reaches 6 MPa, maintain it for 0.5 h, during which the vacuum degree in the furnace chamber is maintained at no more than 10 -3 Pa, after the jacketing is completed, the pressure is released and first cooled to room temperature at 8℃ / min to obtain the high vacuum welded parts; 4) Hot isostatic pressing sintering: The high vacuum welded component obtained in step 3) is placed in a hot isostatic pressing furnace and maintained at a temperature of 700° C. and a pressure of 100-200 MPa for 0.5-2 hours to obtain a ceramic substrate with high bonding strength.

2. The method for preparing a high bonding strength ceramic substrate according to claim 1, wherein: The cross-sectional area of ​​the titanium foil wrapped in step 2) is circular, square or elliptical.

3. The method for preparing a high bonding strength ceramic substrate according to claim 2, wherein: The hot isostatic pressing sintering conditions are: temperature 700°C and pressure 200 MPa for 0.5 h.

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