Pressure-assisted tool for sintering nano-silver and sintering method

Abstract

The invention provides a pressure-assisted tool for nano-silver sintering and a sintering method, which are based on a nano-silver sintered film material, adopt a process method of pre-fixing a single chip and synchronously sintering multiple chips, and realize integrated sintering of multiple chips on different assembly surfaces of a high-power module through the integrated pressure-assisted tool. The pressure auxiliary tool is made of a tungsten steel material which is high in structural strength and good in heat conduction performance, the pressure heads with multiple heights are manufactured on the end face, and the heights and the sizes of the pressure heads are used for being matched with the height difference of chip assembling faces and the sizes of chips. Compared with a mode of applying pressure to a single chip and synchronously applying pressure to a plurality of chips on a single assembly surface in the sintering process, the pressure auxiliary tool and the sintering method can greatly improve the sintering assembly efficiency, and can also meet the sintering requirements of the plurality of chips on different assembly surfaces.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor processing, and in particular relates to a pressure-assisted tooling and a sintering method for nano-silver sintering. Background Art

[0002] SiC wide bandgap semiconductor devices are widely used in power modules. Nanosilver sintering is one of the most suitable interface interconnection technologies for high-power devices. Selective sintering in nanosilver sintering uses nanosilver sintering film materials of specific thickness to well control the state of the sintering layer, achieving low-temperature and low-void sintering and high-temperature and high-reliability applications, which can better bring into play the excellent properties of nanosilver materials.

[0003] With the expansion of power module functions and performance optimization, multiple chips need to be sintered on different assembly surfaces of the power module substrate, which introduces new requirements for the nano-silver sintering process. The existing technology usually applies pressure to each chip separately, which can improve the uniformity of sintering pressure and the thickness of the silver sintering layer, but the serial process route greatly reduces the assembly and sintering efficiency of multi-chip modules. How to achieve simultaneous, efficient and reliable sintering of multiple chips on different assembly surfaces is a question worth considering. Summary of the invention

[0004] To this end, the present invention proposes a pressure-assisted tooling and sintering method for nanosilver sintering. Based on nanosilver sintering film materials, a process method of pre-fixing a single chip and sintering multiple chips simultaneously is adopted. The integrated pressure-assisted tooling can realize the integrated sintering of multiple chips on different assembly surfaces of a high-power module. The pressure-assisted tooling of the present invention is made of tungsten steel material with high structural strength and good thermal conductivity. Pressure heads of multiple heights are made on the end face. The height and size of the pressure head are used to match the height difference of the chip assembly surface and the chip size. Compared with the method of applying pressure to a single chip and applying pressure to multiple chips on a single assembly surface simultaneously, the pressure-assisted tooling and sintering method of the present invention can not only greatly improve the sintering assembly efficiency, but also meet the sintering requirements of multiple chips on different assembly surfaces.

[0005] The present invention is based on nano silver sintered film material, adopts a process method of single chip pre-fixation and multi-chip synchronous sintering, and can realize integrated sintering of multiple chips on different assembly surfaces of a high-power module through an integrated pressure-assisted tooling.

[0006] The auxiliary tooling is made of tungsten steel material with high structural strength and good thermal conductivity. Pressure heads of different heights are made on the end face. The height and size of the pressure head are used to match the height difference of the chip assembly surface and the chip size (including chip length, width and thickness). The pressure head size exceeds the corresponding chip size by 0.2mm to 0.3m in all directions, which can ensure that the chip surface is within the pressure coverage range of the pressure head during the chip sintering process.

[0007] The sintering method is implemented as follows:

[0008] Step 1: Prepare an integrated pressure-assisted tooling according to the chip assembly position in the power module.

[0009] Step 2: Use argon and oxygen mixed plasma to clean the surface of the gold-plated substrate to be sintered. The argon and oxygen mixture ratio used for cleaning is 9:1, the cleaning power is set to 200W-300W, and the cleaning time is set to 30s-50s. The substrate uses a high thermal conductivity aluminum nitride high-temperature co-fired ceramic substrate. There are assembly surfaces of different heights on the ceramic substrate according to design requirements.

[0010] Step 3: Under certain pressure and temperature, the nanosilver sintered film is cut with a chip to complete the adhesion of the nanosilver sintered film layer on the back of the chip. The nanosilver sintered film has a thickness of 100 μm to 150 μm, the cutting temperature is set to 120°C to 150°C, the cutting pressure is set to 3Mpa to 5Mpa, and the cutting action time is set to 20 to 40s.

[0011] Step 4: Mount the chip on the aluminum nitride high-temperature co-fired ceramic substrate with high precision, and fix the position under certain pressure and temperature. During fixation, the substrate temperature is set to 100℃~130℃, the suction head temperature is set to 150℃~200℃, the pressure is set to 6~8Mpa, and the action time is 30s~50s.

[0012] Step 5: Repeat steps 4 and 5 to fix multiple chips in the substrate assembly position in sequence.

[0013] Step 6: Cover the upper side of all chips with a layer of high temperature resistant buffer pad to reduce the risk of damage to the chip due to hard contact with the pressure head, and at the same time alleviate the process fluctuation in height during the pressure application process.

[0014] Step seven: Use an integrated pressure-assisted tooling to heat and pressurize multiple chips on the substrate simultaneously, and simultaneously complete high-reliability sintering of multiple chips. During the sintering process, the substrate temperature is set at 200°C to 250°C, and the integrated pressure-assisted tooling sets the chip heating temperature to 250°C to 280°C. The action time is 10min to 15min. After sintering, the nanosilver film layer is about 50% of the pre-sintering layer.

[0015] Furthermore, the thickness of the nanosilver sintered film, the shearing temperature, the shearing pressure and the action time are optimized according to the chip size and the substrate state.

[0016] Furthermore, in step three, for the sintering of the same module, the selected nanosilver sintering film has the same thickness, and the integrated pressure-assisted tooling design can ensure that the thickness of the film layer after sintering is basically the same, which is 40% to 60% of the nanosilver film layer before sintering.

[0017] The beneficial effects of the present invention are

[0018] 1. The present invention adopts the process of single-chip pre-mounting and multi-chip synchronous pressure sintering. By making an integrated pressure-assisted tooling, the synchronous sintering of nanosilver at the bottom of multiple chips on different assembly surfaces of the substrate in the power module is realized, avoiding the serial process of heating and pressurizing each chip in the nanosilver pressure sintering process, and completing the longest high-pressure sintering process at one time, which can greatly improve the chip pressure sintering efficiency.

[0019] 2. The integrated pressure-assisted tooling designed in the present invention adopts tungsten steel material with high structural strength and good thermal conductivity. Multiple pressure heads are made on the end face of the tooling. The pressure heads are highly customized and can realize the synchronous pressing and sintering of assembly surfaces of different heights and chips of different thicknesses. After sintering, high consistency of the thickness of the nano-silver sintering layer can be achieved.

[0020] 3. Each pressure head on the integrated pressure-assisted tooling exceeds the corresponding chip by 0.2mm to 0.3mm in four directions to ensure that the chip surface is within the pressure coverage range of the pressure head during chip sintering.

[0021] 4. The present invention uses a chip to selectively cut the nanosilver sintered film, and optimizes the cutting parameters to achieve a cutting size of the nanosilver sintered film that is close to the chip size, thereby reducing the risk of short circuits and sintering voids during nanosilver sintering, reducing the design spacing requirements between chips on the substrate, and further improving the integration of the module.

[0022] 5. Single chip pre-mounting is based on high-precision assembly equipment to achieve high-precision chip positioning, and assists with a certain pressure and temperature to fix the chip, laying the foundation for direct pressure application on subsequent multiple chips.

[0023] 6. The present invention uses a high temperature resistant buffer pad placed between the integrated pressure-assisted tooling and the chip, which reduces the risk of damage to the chip due to hard contact with the pressure head and is used to alleviate process fluctuations in height during the pressure application process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the pressure-assisted tooling used in the present invention to achieve simultaneous nanosilver sintering of multiple chips on different assembly surfaces.

[0025] Figure 2 Schematic diagram of pressure-assisted tooling.

[0026] Figure 3 Schematic diagram of using chip to cut nanosilver sintered film.

[0027] Figure 4 Schematic diagram of high-precision chip placement and pre-fixation on an aluminum nitride high-temperature co-fired ceramic substrate.

[0028] Figure 5A top view of the assembly positions of multiple chips on a substrate.

[0029] Figure 6 This is a cross-sectional view of the assembly positions of multiple chips on a substrate.

[0030] Figure 7 Schematic diagram of covering a layer of high temperature resistant buffer pad on the chip.

[0031] Figure 8 Cross-sectional view showing the simultaneous nanosilver sintering of multiple chips on different assembly surfaces under pressure-assisted tooling.

[0032] In the figure, 1 is a pressure-assisted tooling; 2 is a pressure head; 3 is a sintering device 1; 4 is a nanosilver sintering layer; 5 is a sintering device 2; 6 is an aluminum nitride high-temperature co-fired ceramic substrate; 7 is a sintering device 3; 8 is a high-temperature resistant buffer pad; 9 is a heatable chip pickup head; 10 is the original attachment carrier of the nanosilver sintering film; 11 is a schematic diagram of substrate heating during the pre-sintering process of the device; 12 is a schematic diagram of suction head heating during the pre-sintering process of the device; 13 is a schematic diagram of suction head pressurization during the pre-sintering process of the device; 14 is a schematic diagram of substrate heating during the sintering process; 15 is a schematic diagram of overall heating of the pressure-assisted tooling during the sintering process; 16 is a schematic diagram of overall pressurization of the pressure-assisted tooling during the sintering process. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] like Figure 2 As shown in the figure, the integrated pressure-assisted tooling is made of tungsten steel material, and multiple pressure heads are made on the end face of the tooling. The height of the pressure head is customized according to the height of the chip assembly surface and the chip thickness, which can realize the synchronous pressing and sintering of chips with different assembly surfaces and different thicknesses. After sintering, the thickness of the nano-silver sintering layer can be highly consistent. The size of the pressure head exceeds the corresponding chip size by 0.2mm to 0.3mm in all directions.

[0035] Argon and oxygen mixed plasma is used to clean the surface of the gold-plated substrate to be sintered. The argon and oxygen mixture ratio used for cleaning is 9:1, the cleaning power is set to 200W-300W, and the cleaning time is set to 30s-50s. The substrate adopts a high thermal conductivity aluminum nitride high-temperature co-fired ceramic substrate. There are assembly surfaces of different heights on the ceramic substrate according to design requirements.

[0036] like Figure 3As shown, under certain pressure and temperature, the chip is used to cut the nanosilver sintered film to complete the adhesion of the nanosilver sintered film layer on the back of the chip. The nanosilver sintered film is selected to have a thickness of 100μm~150μm, the cutting temperature is set to 120℃~150℃, the cutting pressure is set to 3Mpa~5Mpa, and the cutting action time is set to 20~40s. The film thickness, cutting temperature, cutting pressure and action time are optimized according to the chip size and substrate state.

[0037] like Figure 4 As shown, the chip is mounted on an aluminum nitride high-temperature co-fired ceramic substrate with high precision, and the position is fixed under certain pressure and temperature. During the fixation, the substrate temperature is set at 100°C to 130°C, the suction head temperature is set at 150°C to 200°C, the pressure is set at 6 to 8Mpa, and the action time is 30s to 50s.

[0038] repeat Figure 3 and Figure 4 Step 1: fix multiple chips in the substrate assembly position in sequence to achieve Figure 5 and Figure 6 The multi-chip assembly shown;

[0039] like Figure 7 As shown, a layer of high temperature resistant buffer pad is covered on the upper side of all chips to reduce the risk of damage to the chip by hard contact with the pressure head, and at the same time, the process fluctuation in height during the pressure application process can be alleviated;

[0040] like Figure 8 As shown, an integrated pressure-assisted tooling is used to heat and pressurize multiple chips on a substrate simultaneously, and high-reliability sintering of multiple chips is completed simultaneously. During the sintering process, the substrate temperature is set at 200°C to 250°C, and the integrated pressure-assisted tooling sets the chip heating temperature to 250°C to 280°C. The action time is 10min to 15min, and the nanosilver film layer after sintering is 40% to 60% of the layer before sintering.

[0041] The present invention is not limited to the above specific implementations, and the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made to the above implementations based on the technical essence of the present invention shall be included in the protection scope of the present invention.

Claims

1. A pressure-assisted tooling for nano-silver sintering, characterized in that: The auxiliary tooling is made of tungsten steel material, and pressure heads of different heights are made on the end face of the auxiliary tooling. The height and size of the pressure head match the height difference of different chip assembly surfaces and the chip size. The size of the pressure head exceeds the corresponding chip size by 0.2mm to 0.3mm in all directions, ensuring that the chip surface is within the pressure coverage range of the pressure head during the chip sintering process, thereby achieving synchronous crimping and sintering of chips with different assembly surfaces and different thicknesses.

2. A nano-silver sintering method based on the pressure-assisted tooling for nano-silver sintering according to claim 1, characterized in that: The following steps are involved: Step 1: Prepare an integrated pressure-assisted tooling according to the chip assembly position in the power module; Step 2: Use argon and oxygen mixed plasma to clean the surface of the substrate to be sintered. The substrate uses a high-thermal-conductivity aluminum nitride high-temperature co-fired ceramic substrate. The ceramic substrate has assembly surfaces of different heights according to design requirements. Step 3: cutting the nanosilver sintered film with a chip under a certain pressure and temperature to complete the adhesion of the nanosilver sintered film layer on the back of the chip; Step 4: Mount the chip on the substrate and fix its position under certain pressure and temperature; Step 5: Repeat steps 4 and 5 to fix multiple chips in the substrate assembly position in sequence; Step 6: Cover the upper side of all chips with a layer of high temperature resistant buffer pad to reduce the risk of damage to the chip by hard contact with the pressure head, and at the same time alleviate the process fluctuation in height during the pressure application process; Step 7: Use pressure-assisted tooling to heat and pressurize multiple chips on the substrate to simultaneously complete high-reliability sintering of multiple chips.

3. A nano silver sintering method according to claim 2, characterized in that: In the step 2, the mixing ratio of argon and oxygen used for cleaning is 9:1, the cleaning power is set to 200W-300W, and the cleaning time is set to 30s-50s.

4. A nano silver sintering method according to claim 2, characterized in that: In the step three, the thickness of the nanosilver sintered film is selected to be 100 μm to 150 μm, the shearing temperature is set to 120° C. to 150° C., the shearing pressure is set to 3 MPa to 5 MPa, and the shearing action time is set to 20 to 40 seconds.

5. A nano silver sintering method according to claim 2, characterized in that: In the step 4, the temperature of the fixed substrate is set to 100° C. to 130° C., the temperature of the suction head is set to 150° C. to 200° C., the pressure is set to 6 to 8 MPa, and the action time is 30 s to 50 s.

6. A nano silver sintering method according to claim 2, characterized in that: In step seven, the substrate temperature is set at 200°C to 250°C during the sintering process, the integrated pressure-assisted tooling sets the chip heating temperature to 250°C to 280°C, the action time is 10min to 15min, and the nanosilver film layer after sintering is approximately 50% of the pre-sintering layer.

7. A nano silver sintering method according to any one of claims 2 to 6, characterized in that: In step 3, for the sintering of the same power module, the selected nano-silver sintered films have the same thickness, and the thickness of the nano-silver film layer after sintering is 40% to 60% of that before sintering.

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