A multi-layer copper sheet bonding method

Abstract

The application discloses a multilayer copper sheet bonding method, which comprises three procedures of surface treatment impurity removal, copper sheet oxidation and copper sheet sintering. When the copper sheet is oxidized, gradient heating dry oxidation or KOH and K2S2O8 mixed aqueous solution wet oxidation is adopted to perform copper sheet surface oxidation; when sintering, the copper sheet after oxidation is placed between two porous sintering plates, and after being limited by clamping, the sintering condition is adopted to perform temperature rising and temperature dropping under the condition of argon protection, and bonding is completed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of copper sheet bonding, and particularly relates to a multilayer copper sheet bonding method. BACKGROUND

[0002] Copper-copper bonding has superior power handling capability, thermal stability, and more excellent reliability, small resistance and current-carrying capacity compared with traditional solder, and is compatible with the current semiconductor packaging process. Therefore, copper-copper bonding meets the cost and performance requirements at the same time, and is actively pursued by the industry and academia, and is regarded as the next interconnection node of the semiconductor industry.

[0003] At present, the bonding process of copper sheet and copper sheet generally includes brazing, fusion welding, resistance welding, ultrasonic welding and the like. Brazing simultaneously heats copper and filler with a melting point lower than copper, the molten liquid filler is filled in the gap between copper and copper, and after the liquid filler solidifies, the welding is completed; fusion welding heats the contact part of copper and copper to make it reach the molten state, and after the contact part is tightly contacted, the heating is stopped, and after the temperature decreases, the molten contact part will be condensed, that is, the welding is completed; resistance welding realizes the fusion welding between copper sheets by pressing the electrode with a large current, and the current and pressure are key parameters; ultrasonic welding mainly utilizes the fusion between molecular layers formed by mutual friction of the surfaces of two copper sheets.

[0004] However, the thermal conductivity of copper is high, the thermal conductivity coefficient is 401 W / (m·K), the heat transfer is too fast, and the non-welding and non-fusion part is easily formed during welding; the resistance welding and ultrasonic welding have limitations on the size, welding area and thickness of the welded copper sheet, which is not conducive to the popularization and application. SUMMARY

[0005] The present application provides a new multilayer copper sheet bonding method aiming at the defects existing in the existing copper-copper welding process. After the surface of the copper sheet is subjected to impurity cleaning treatment, gradient dry oxidation or wet oxidation is first performed, then the copper sheet is placed between two porous supporting plates, and gradient sintering is performed under the condition of argon protection to complete the bonding.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A, surface treatment

[0008] Select a copper sheet with a surface roughness less than 0.5 μm and a surface flatness less than 5%, immerse the copper sheet in hydrochloric acid with a mass fraction of 10-18% for 3-10 min, then ultrasonically clean in anhydrous ethanol for 3-10 min, finally rinse with pure water and dry to complete the cleaning of the impurities on the surface of the copper sheet.

[0009] B, copper sheet oxidation

[0010] Either dry oxidation or wet oxidation is adopted.

[0011] The dry oxidation step is as follows: the surface-treated copper sheet is heated in gradient under the protection of argon mixed with a certain volume (2% to 10%) of oxygen: heated at a rate of 10 ℃ / min to 500-510 ℃, kept for 4 min; heated at a rate of 5 ℃ / min to 690-700 ℃, kept for 4 min; heated at a rate of 5 ℃ / min to 790-800 ℃, kept for 4 min; heated at a rate of 5 ℃ / min to 800-900 ℃, kept for 20 min; cooled at a rate of 10 ℃ / min to room temperature,

[0012] The wet oxidation step is as follows: the surface-treated copper sheet is placed in a mixed aqueous solution of KOH and K2S2O8, the solution temperature is kept at 40-50 ℃, and the oxidation time is 10-15 min; after the oxidation is completed, the copper sheet is cleaned with pure water, dried in an oven at 180 ℃ for 2 h. The concentration of KOH is 0.55-0.75 mol / L, and the concentration of K2S2O8 is 0.3-0.35 mol / L.

[0013] C. Sintering of the copper sheet

[0014] The oxidized copper sheet is placed flat between two porous support plates, the downward pressure is provided by the weight of the support plates, the copper and oxygen eutectic liquid surfaces are tightly contacted during the sintering process to prevent the generation of voids, and the copper sheet is clamped by using a cylindrical pin with the porous structure of the support plate to prevent dislocation during the sintering process. Under the protection of argon, the sintering conditions are as follows: heated at a rate of 20 ℃ / min to 980-1000 ℃, kept for 15 min; heated at a rate of 5 ℃ / min to 1065-1083 ℃, kept for 40 min; cooled at a rate of 20 ℃ / min to room temperature, and the bonding is completed.

[0015] The thickness of the porous silicon carbide support plate is 8 mm; when clamping, the four edges of the sintered oxidized copper sheet are clamped by using a cylindrical pin with the porous structure of the support plate.

[0016] The present application has the following beneficial effects:

[0017] In view of the characteristics of high thermal conductivity and fast heat transfer of copper, the surface of the copper sheet is oxidized first to form a Cu2O layer with a certain thickness on the surface of the copper, and then the copper sheet is placed flat between two porous support plates and sintered under the protection of argon. The bonding method of the present application avoids the formation of unwelded and unfused parts during welding, and there is no thickness limitation of the copper sheet, which is suitable for the bonding of copper sheets of any thickness, and overcomes the defects that the resistance welding and ultrasonic welding are limited in size, welding area and thickness of the welded copper sheet. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 This is a schematic diagram of the sintering device for the sintering plate.

[0019] Figure 2 A schematic diagram of the structure for the placement of copper sheets inside the firing plate. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the embodiments and accompanying drawings. However, it should be understood that the specific description below is illustrative and not restrictive, and should not be used to limit the scope of protection of the present invention.

[0021] Example 1: Dry oxidation and sintering of copper sheets

[0022] A. Copper sheet cleaning

[0023] Take a copper sheet with a thickness of 0.4 mm, a surface roughness of <0.5 μm, and a surface flatness of <5%, immerse it in 10% hydrochloric acid for 3 min, then ultrasonically clean it in anhydrous ethanol for 3 min, and finally rinse it with pure water and dry it.

[0024] B. Dry oxidation of copper sheet surface

[0025] The copper sheet processed in step A is placed in a tube furnace, argon gas is introduced, and oxygen with a volume ratio of 4% is mixed in. The heating parameters are as follows:

[0026] Heat to 510℃ at a rate of 10℃ / min, and hold for 4 min;

[0027] Heat to 690℃ at a rate of 5℃ / min, and hold for 4 min;

[0028] Heat to 790℃ at a rate of 5℃ / min, and hold for 4 min;

[0029] Heat to 800℃ at a rate of 5℃ / min and hold for 20min;

[0030] Cool to room temperature at a rate of 10℃ / min.

[0031] C. Copper sheet sintering

[0032] like Figure 1 and Figure 2 As shown, the oxidized copper sheet 1 is stacked between two 8mm thick porous silicon carbide sintering plates 2. The weight of the sintering plates 2 provides downward pressure to ensure close contact between the copper oxide eutectic liquid surfaces during sintering, preventing voids from forming. The porous structure of the sintering plates 2 is used to position the copper oxide sheet 1 to be sintered using cylindrical pins 3 to prevent misalignment of the copper sheet 1 during sintering.

[0033] The sintering plate 2 is placed in the furnace under argon protection conditions, and the sintering conditions are as follows:

[0034] 20℃ / min rate heating to 980-1000℃, holding for 15min;

[0035] 5℃ / min rate heating to 1065-1083℃, holding for 40min;

[0036] 20℃ / min rate cooling to room temperature, completing bonding.

[0037] Example 2 Copper sheet wet oxidation and sintering

[0038] A, Copper sheet cleaning

[0039] Take the copper sheet with thickness of 0.4mm, surface roughness <0.5μm, surface flatness <5% and immerse it in 10% hydrochloric acid for 3min, then put it into anhydrous ethanol for ultrasonic cleaning for 3min, finally wash it with pure water and dry.

[0040] B, Copper sheet surface wet oxidation

[0041] Put the surface treated copper sheet into 0.6mol / L KOH and 0.3mol / L K2S2O8 mixed aqueous solution, keep the solution temperature at 50℃, and immerse for 10min; after completing oxidation, wash it with pure water, and put it into 180℃ oven for 2h to complete drying.

[0042] C, Copper sheet sintering

[0043] As shown in Figure 1 and Figure 2 , stack the completed oxidation copper sheet 1 between two 8mm thick porous silicon carbide supporting plates 2, use the weight of the supporting plate 2 to provide downward pressure, ensure that the copper-oxygen eutectic liquid surface is in close contact during sintering process to prevent voids, and use the porous structure of the supporting plate 2 to use a cylindrical pin 3 to clamp the sintered copper sheet 1 to prevent misplacement of the copper sheet 1 during sintering.

[0044] Put the supporting plate 2 into the furnace under argon protection, and the sintering conditions are as follows:

[0045] 20℃ / min rate heating to 980-1000℃, holding for 15min;

[0046] 5℃ / min rate heating to 1065-1083℃, holding for 40min;

[0047] 20℃ / min rate cooling to room temperature, completing bonding.

[0048] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above-mentioned embodiments, and the above-mentioned embodiments and descriptions in the specification are only to illustrate the principles of the present application. Various changes and improvements can be made to the present application without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for bonding multilayer copper sheets, characterized in that, Includes the following steps: A. Surface treatment Select copper sheets with a surface roughness of less than 0.5 μm and a surface flatness of less than 5%, and remove impurities from the surface of the copper sheets by sequentially soaking in hydrochloric acid, ultrasonic cleaning with anhydrous ethanol, rinsing with pure water and drying. B. Copper sheet oxidation Either dry oxidation or wet oxidation can be used. The dry oxidation process is as follows: The surface-treated copper sheet is oxidized under argon protection with a certain volume of oxygen mixed in, using a gradient heating method: heating at a rate of 10℃ / min to 500-510℃, holding for 4 min; heating at a rate of 5℃ / min to 690-700℃, holding for 4 min; heating at a rate of 5℃ / min to 790-800℃, holding for 4 min; heating at a rate of 5℃ / min to 800-900℃, holding for 20 min; and cooling to room temperature at a rate of 10℃ / min. The wet oxidation process is as follows: the surface-treated copper sheet is placed in a mixed aqueous solution of KOH and K2S2O8, the solution temperature is maintained at 40-50℃, and the oxidation time is 10-15 minutes; after oxidation, it is rinsed with pure water and placed in an oven at 180℃ to dry. C. Copper sheet sintering The oxidized copper sheet is placed flat between two porous sintering plates. The weight of the plates provides downward pressure, and the porous structure of the plates is used to hold the copper oxide sheet to be sintered in place with cylindrical pins. Under argon protection, the sintering conditions are as follows: heating at a rate of 20℃ / min to 980-1000℃ and holding for 15 min; heating at a rate of 5℃ / min to 1065-1083℃ and holding for 40 min; cooling at a rate of 20℃ / min to room temperature to complete the bonding.

2. The multilayer copper bonding method according to claim 1, characterized in that: in, In step A, the specific method for removing impurities from the surface of the copper sheet is as follows: Immerse the copper sheet in hydrochloric acid with a mass fraction of 10-18% for 3-10 minutes, then ultrasonically clean it in anhydrous ethanol for 3-10 minutes, and finally rinse it with pure water and dry it to complete the cleaning of impurities on the surface of the copper sheet.

3. The multilayer copper bonding method according to claim 1, characterized in that: in, In step B, during dry oxidation, the volume ratio of oxygen mixed into the argon gas is 2%-10%.

4. The multilayer copper bonding method according to claim 1, characterized in that: in, In step B, during wet oxidation, the concentration of KOH in the mixed aqueous solution of KOH and K2S2O8 is 0.55–0.75 mol / L, and the concentration of K2S2O8 is 0.3–0.35 mol / L. After oxidation, the solution is placed in an oven at 180℃ for 2 hours to complete drying.

5. The multilayer copper bonding method according to claim 1, characterized in that: in, In step C, the thickness of the porous silicon carbide sintering plate is 8mm; during positioning, cylindrical pins are used to position the four sides of the copper oxide sheet to be sintered using the porous structure of the sintering plate.

Images