Composite solder capable of adapting to different thermal expansion coefficients and rolling process

Abstract

The invention relates to the technical field of semiconductor welding, in particular to a composite welding flux capable of being matched with different thermal expansion coefficients and a rolling technology. According to the composite welding flux, an iron-nickel alloy middle layer is used, and the thermal expansion coefficient of the composite welding flux can be adjusted within the range of 1.4-12 * 10 <-6 > K <-1 > according to the nickel content; the solder can meet the working requirement of a wide bandgap semiconductor material at the high temperature of 200-450 DEG C, and is obviously superior to a traditional tin-based solder and a high-lead solder. Due to the invar effect of the iron-nickel alloy middle layer, the thermal expansion coefficient of the iron-nickel alloy middle layer is highly matched with novel semiconductor materials such as SiC, SiN and GaN, welding joint cracks caused by the difference of the thermal expansion coefficients are effectively avoided, and therefore the problem that due to the fact that the thermal expansion coefficients of existing welding flux are not matched, the welding joint cracks is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor welding, and in particular to a composite solder capable of adapting to different thermal expansion coefficients and a rolling process. Background Art

[0002] As electronic devices, especially power electronic devices, develop towards high power density, miniaturization, high temperature resistance and high reliability, the requirements for supporting power packaging materials, especially connection materials, are getting higher and higher. Taking wide bandgap semiconductor materials (such as silicon carbide SiC and gallium nitride GaN) as an example, these materials have the characteristics of large bandgap width, high breakdown voltage, fast electron drift velocity and high thermal conductivity, which can break through the limitations of switching speed, junction temperature and power density of traditional silicon devices. However, the junction temperature of these new devices can reach 200-450℃ during operation, which puts extremely high requirements on the high temperature resistance of welding materials.

[0003] The service temperature of traditional tin-based solder usually does not exceed 175°C, and the remelting temperature does not exceed 300°C, which is difficult to meet the needs of high-temperature devices. Although high-lead solder (melting point above 300°C) can partially solve this problem, due to the toxicity of lead, it is exempted from the European and American RoHS directives, but its environmental protection issue is still a major challenge.

[0004] In recent years, sintered nano- and micron-silver (Ag) joints have attracted extensive attention due to their excellent electrical and thermal properties. However, sintering silver requires a high-pressure sintering process, which is costly and has the problem of silver electromigration, limiting its large-scale application. Although copper sintering is less expensive, copper is easily oxidized, the quality of the soldered joint is unstable, and higher pressure, temperature, and time are required, which is extremely unfavorable for chip protection.

[0005] In addition, transient liquid phase diffusion welding (TLP), as a new welding method combining diffusion welding and brazing processes, has the characteristics of low-temperature welding and high-temperature service. However, the intermetallic compound (IMC) layer formed by TLP is brittle and is prone to cracks in thermal cycles when the thermal expansion coefficients do not match, affecting the reliability of the welded joint. Summary of the invention

[0006] The purpose of the present invention is to provide a composite solder and a rolling process that can adapt to different thermal expansion coefficients, aiming to solve the problem that cracks occur in the welded joints due to mismatch of thermal expansion coefficients of existing solders.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a composite solder rolling process that can adapt to different thermal expansion coefficients, comprising the following steps:

[0008] preparing an iron-nickel alloy intermediate layer, a plating layer, and Sn and In-based solder layers;

[0009] Clean the surfaces of the iron-nickel alloy and the solder layer;

[0010] Place the solder layer on the surface of the coating and add a soldering flux for rolling to obtain a composite solder foil;

[0011] Anneal the rolled composite solder foil;

[0012] Detect the flatness and thickness uniformity of the surface of the composite solder foil. If it is qualified, proceed to the next step; if not, return to the previous step;

[0013] Stamp the composite solder foil to obtain semi-finished products;

[0014] Test the bonding strength, thermal cycle and coefficient of thermal expansion of the semi-finished products to obtain the finished composite solder.

[0015] Among them, in "Prepare the iron-nickel alloy intermediate layer, the coating layer and the Sn and In-based solder layer", the nickel content of the iron-nickel alloy intermediate layer is 25%-60%, the thickness is 0.1-0.5 mm, the coating layer is Cu, Ni or Ag, the thickness is 1-1000 microns, and the thickness of the Sn and In-based solder layer is 5-50 microns.

[0016] Among them, in "Clean the surfaces of the iron-nickel alloy and the solder layer", the following steps are included:

[0017] Use chemical cleaning agents and mechanical polishing to remove the oxide layer and impurities on the surface of the iron-nickel alloy;

[0018] Use a degreasing agent and ultrasonic cleaning to remove the oil stains on the surface of the solder layer.

[0019] Among them, in "Place the solder layer on the surface of the coating and add a soldering flux for rolling to obtain a composite solder foil", the following steps are included:

[0020] Place the solder layer on the surface of the coating and add a soldering flux to make them fit tightly;

[0021] Set the rolling pressure to 10-50 MPa and the rolling speed to 0.1-1 m / min for initial rolling to reduce the thickness to 80%-90% of the designed thickness;

[0022] Adjust the rolling pressure to 50-100 MPa and keep the rolling speed at 0.1-1 m / min for continuous rolling to reduce the thickness to 60%-70% of the designed thickness.

[0023] Among them, in "Anneal the rolled composite solder foil", the following steps are included:

[0024] Set the working temperature and time of the annealing furnace;

[0025] Place the composite solder foil into an annealing furnace and perform annealing treatment according to the set parameters. After annealing is completed, cool it to room temperature.

[0026] Among them, for "detecting the flatness and thickness uniformity of the surface of the composite solder foil, if qualified, proceed to the next step, if unqualified, return to the previous step", it includes the following steps:

[0027] Use an optical scanner to check and collect the surface flatness and image of the composite solder foil to obtain the collected data;

[0028] Based on the collected data, analyze and judge to obtain a judgment result;

[0029] Based on the judgment result, determine whether to proceed to the next step or return to the previous step for processing.

[0030] In a second aspect, a composite solder that can adapt to different coefficients of thermal expansion, adopting the composite solder rolling process that can adapt to different coefficients of thermal expansion described in the first aspect, includes an intermediate metal layer, two plating layers, and two solder layers;

[0031] The plating layer is Cu, Ni, or Ag. The solder layer includes Sn-based solder and In-based solder. The Sn-based solder includes SnAg, SnCu, SnBi, SnSb, SnZn, SnAu, SnAgCu, SnAgBi, SnAgIn, SnAgSb, SnAgCuBi, SnAgCuIn, SnAgCuSb. The In-based solder includes InAg, InCu, InBi, InSb, InAgCu, InAgBi, InAgSn, InAgSb, InAgCuBi, InAgCuIn, InAgCuSb; the intermediate metal layer is a ferro-nickel alloy.

[0032] A composite solder rolling process that can adapt to different coefficients of thermal expansion according to the present invention includes the following steps: preparing a ferro-nickel alloy intermediate layer, plating layers, and Sn and In-based solder layers; cleaning the surfaces of the ferro-nickel alloy and the solder layers; placing the solder layer on the surface of the plating layer and adding a soldering flux for rolling to obtain a composite solder foil; performing annealing treatment on the rolled composite solder foil; detecting the flatness and thickness uniformity of the surface of the composite solder foil, if qualified, proceed to the next step, if unqualified, return to the previous step; stamping the composite solder foil to obtain a semi-finished product; testing the bonding strength, thermal cycle, and coefficient of thermal expansion of the semi-finished product to obtain a finished composite solder. The composite solder of the present invention uses a ferro-nickel alloy intermediate layer, and its coefficient of thermal expansion can be adjusted according to the nickel content within the range of 1.4 - 12×10 -6 K -1It can be adjusted within a certain range, capable of meeting the working requirements of wide-bandgap semiconductor materials at high temperatures of 200-450°C, and is significantly superior to traditional tin-based solders and high-lead solders. The Invar effect of the iron-nickel alloy intermediate layer makes its coefficient of thermal expansion highly matched with new semiconductor materials such as SiC, SiN, and GaN, effectively avoiding cracks in the welded joints caused by differences in the coefficient of thermal expansion, thus solving the problem of cracks in the welded joints caused by mismatched coefficients of thermal expansion in existing solders. Brief Description of the Drawings

[0033] The present invention can be further illustrated by the non-limiting embodiments given in the drawings.

[0034] Figure 1 It is a flowchart of a composite solder rolling process that can adapt to different coefficients of thermal expansion according to the present invention.

[0035] Figure 2 It is a flowchart for cleaning the surfaces of the iron-nickel alloy and the solder layer.

[0036] Figure 3 It is a flowchart for placing the solder layer on the surface of the plating layer and adding a soldering flux for rolling to obtain a composite solder foil.

[0037] Figure 4 It is a flowchart for annealing the rolled composite solder foil.

[0038] Figure 5 It is a flowchart for detecting the flatness and thickness uniformity of the surface of the composite solder foil. If it is qualified, proceed to the next step; if it is unqualified, return to the previous step. Detailed Description of the Embodiments

[0039] The following details the embodiments of the present invention. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0040] Please refer to Figures 1 to 5 , the present invention provides a composite solder rolling process that can adapt to different coefficients of thermal expansion, including the following steps:

[0041] S1 Prepare an iron-nickel alloy intermediate layer, a plating layer, and a Sn and In-based solder layer;

[0042] The nickel content of the iron-nickel alloy intermediate layer is 25%-60%, the thickness is 0.1-0.5 mm, the plating layer is Cu, Ni, or Ag, the thickness is 1-1000 microns, and the thickness of the Sn and In-based solder layer is 5-50 microns.

[0043] Specifically, an iron-nickel alloy with a nickel content of 25%-60% is selected as the intermediate layer, with a thickness of 0.1-0.5 mm, ensuring a flat surface without obvious defects. A layer of Cu, Ni, or Ag is plated on the iron-nickel alloy surface, with a thickness of 1-1000 microns, ensuring a uniform coating without missing plating. Sn-based or In-based solders are selected, with a thickness of 5-50 microns, ensuring a clean surface without oil stains or oxide layers.

[0044] S2 Clean the surfaces of the iron-nickel alloy and the solder layer;

[0045] S21 Use chemical cleaning agents and mechanical polishing to remove the oxide layer and impurities on the surface of the iron-nickel alloy;

[0046] Specifically, use chemical cleaning agents (alkaline solution or acidic solution) and mechanical polishing (sandpaper polishing) to remove the oxide layer and impurities on the surface of the iron-nickel alloy, ensuring a smooth surface.

[0047] S22 Use degreasing agents and ultrasonic cleaning to remove the oil stains on the surface of the solder layer.

[0048] Specifically, use degreasing agents (acetone or special cleaning agents) and ultrasonic cleaning equipment to remove the oil stains on the surface of the solder layer, ensuring a clean solder surface.

[0049] S3 Place the solder layer on the coating surface and add a soldering flux for rolling to obtain a composite solder foil;

[0050] S31 Place the solder layer on the coating surface and add a soldering flux to make the two fit tightly;

[0051] Specifically, place the solder layer on the coating surface and add a soldering flux (rosin or active soldering flux) to make the two fit tightly.

[0052] S32 Set the rolling pressure to 10-50 MPa and the rolling speed to 0.1-1 m / min for initial rolling, reducing the thickness to 80%-90% of the designed thickness;

[0053] Specifically, set the rolling pressure to 10-50 MPa and the rolling speed to 0.1-1 m / min for initial rolling, reducing the thickness to 80%-90% of the designed thickness.

[0054] S33 Adjust the rolling pressure to 50-100 MPa and keep the rolling speed at 0.1-1 m / min for continuous rolling, reducing the thickness to 60%-70% of the designed thickness.

[0055] Specifically, adjust the rolling pressure to 50-100 MPa and keep the rolling speed at 0.1-1 m / min for continuous rolling, reducing the thickness to 60%-70% of the designed thickness.

[0056] S4 Anneal the rolled composite solder foil;

[0057] S41 Set the working temperature and time of the annealing furnace;

[0058] Specifically, set the working temperature (200 - 400 °C) and time (1 - 3 hours) of the annealing furnace according to the material properties to ensure uniform properties of the solder foil.

[0059] S42 Put the composite solder foil into the annealing furnace and perform annealing treatment according to the set parameters (working temperature (200 - 400 °C) and time (1 - 3 hours)). After annealing is completed, cool it to room temperature.

[0060] Specifically, put the composite solder foil into the annealing furnace and perform annealing treatment according to the set parameters. After annealing is completed, cool it to room temperature.

[0061] S5 Detect the flatness and thickness uniformity of the surface of the composite solder foil. If it is qualified, proceed to the next step; if it is unqualified, return to the previous step;

[0062] S51 Use an optical scanner to check and collect the surface flatness and image of the composite solder foil to obtain the collected data;

[0063] Specifically, use an optical scanner to detect the surface flatness of the composite solder foil, collect image data and analyze surface defects.

[0064] S52 Analyze and judge based on the collected data to obtain the judgment result;

[0065] Specifically, analyze the thickness uniformity of the solder foil based on the collected data to judge whether it meets the design requirements.

[0066] S53 Based on the judgment result, decide whether to proceed to the next step or return to the previous step for processing.

[0067] Specifically, decide whether to proceed to the next step or return to the previous step for adjustment according to the detection result.

[0068] S6 Stamp the composite solder foil to obtain semi-finished products;

[0069] Specifically, select a suitable stamping die and set the stamping pressure and speed. Stamping pressure: 10 - 50 MPa, stamping speed: 0.1 - 1 m / s. Put the composite solder foil into the die and perform stamping to obtain a solder sheet with the required size. Size: 20 × 20 × 0.11 mm.

[0070] S7 Test the bonding strength, thermal cycle and coefficient of thermal expansion of the semi-finished products to obtain the finished composite solder.

[0071] Specifically, the bonding strength of the composite solder foil is detected through tensile tests or shear tests to ensure firm bonding between the solder and the intermediate layer. The solder foil is placed in a thermal cycling device to simulate the actual usage environment and detect its performance stability under multiple temperature changes. A thermomechanical dilatometer is used to measure the thermal expansion coefficient of the solder foil to ensure its match with that of the base material.

[0072] Example 1

[0073] Prepare an iron-nickel alloy intermediate layer with a nickel content of 38% (thickness 0.1 mm), deposit a 25-micron-thick Ni layer on its surface, and select pure Sn foil (thickness 0.05 mm).

[0074] The surface of the iron-nickel alloy is polished and cleaned using NaOH solution and sandpaper, and the surface of the solder layer is cleaned using acetone and ultrasonic waves.

[0075] Place the Sn foil on the Ni coating, add a soldering flux, and perform rolling. The initial pressure is 30 MPa, the speed is 0.5 m / min, and the thickness is reduced to 0.16 mm; the intermediate rolling pressure is 80 MPa, the speed is 0.5 m / min, and the thickness is reduced to 0.105 mm.

[0076] Set the annealing temperature at 150 °C for 20 minutes, and then cool to room temperature after annealing.

[0077] Use an optical scanner to collect surface images, and judge the flatness through CNN analysis. After passing the inspection, proceed to the next step.

[0078] Stamp out solder chips with dimensions of 20×20×0.11 mm.

[0079] The shear strength test result is 12 MPa, there are no cracks after 2000 thermal cycle tests, and the thermal expansion coefficient is 4×10 -6 K -1 , which matches the SiC chip.

[0080] In a second aspect, a composite solder that can adapt to different thermal expansion coefficients is provided. It adopts the composite solder rolling process that can adapt to different thermal expansion coefficients described in the first aspect, and includes an intermediate metal layer, two coating layers, and two solder layers;

[0081] The coating layer is Cu, Ni or Ag. The solder layer includes Sn-based solder and In-based solder. The Sn-based solder includes SnAg, SnCu, SnBi, SnSb, SnZn, SnAu, SnAgCu, SnAgBi, SnAgIn, SnAgSb, SnAgCuBi, SnAgCuIn, SnAgCuSb. The In-based solder includes InAg, InCu, InBi, InSb, InAgCu, InAgBi, InAgSn, InAgSb, InAgCuBi, InAgCuIn, InAgCuSb. The intermediate metal layer is a ferro-nickel alloy.

[0082] Beneficial effects:

[0083] 1. The coefficient of thermal expansion of the ferro-nickel alloy intermediate layer can be adjusted according to the nickel content to meet the working requirements of wide-bandgap semiconductor materials at high temperatures.

[0084] 2. The Invar effect of the ferro-nickel alloy intermediate layer enables its coefficient of thermal expansion to be highly matched with that of the new semiconductor material, effectively avoiding cracks in the welded joints.

[0085] 3. High-lead solders are completely abandoned, and Sn-based or In-based solders are used, meeting environmental protection requirements.

[0086] 4. The rolling process does not require high-pressure sintering, significantly reducing costs and complexity, while improving the stability and reliability of the welded joints.

[0087] 5. The optimized rolling and annealing processes form uniform intermetallic compounds, improving the high-temperature service reliability and thermal fatigue resistance of the welded joints.

[0088] The above-disclosed are only one or more preferred embodiments of the present application, and the scope of rights of the present application cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present application still fall within the scope covered by the present application.

Claims

1. A composite solder rolling process that can adapt to different coefficients of thermal expansion, characterized in that, It includes the following steps: Prepare an iron-nickel alloy intermediate layer, a plating layer, and Sn and In-based solder layers; Clean the surfaces of the iron-nickel alloy and the solder layer; Place the solder layer on the surface of the plating layer and add a soldering flux for rolling to obtain a composite solder foil; Anneal the rolled composite solder foil; Detect the flatness and thickness uniformity of the surface of the composite solder foil. If qualified, proceed to the next step; if unqualified, return to the previous step; Stamp the composite solder foil to obtain a semi-finished product; Test the bonding strength, thermal cycle, and coefficient of thermal expansion of the semi-finished product to obtain a finished composite solder.

2. The composite solder rolling process capable of adapting to different coefficients of thermal expansion according to claim 1, characterized in that, In "Prepare an iron-nickel alloy intermediate layer, a plating layer, and Sn and In-based solder layers", the nickel content of the iron-nickel alloy intermediate layer is 25%-60%, the thickness is 0.1-0.5 mm, the plating layer is Cu, Ni, or Ag, the thickness is 1-1000 microns, and the thickness of the Sn and In-based solder layers is 5-50 microns.

3. The composite solder rolling process capable of adapting to different coefficients of thermal expansion according to claim 2, characterized in that, In "Clean the surfaces of the iron-nickel alloy and the solder layer", it includes the following steps: Use a chemical cleaning agent and mechanical polishing to remove the oxide layer and impurities on the surface of the iron-nickel alloy; Use a degreasing agent and ultrasonic cleaning to remove the oil stain on the surface of the solder layer.

4. The composite solder rolling process capable of adapting to different coefficients of thermal expansion according to claim 3, characterized in that, In "Place the solder layer on the surface of the plating layer and add a soldering flux for rolling to obtain a composite solder foil", it includes the following steps: Place the solder layer on the surface of the plating layer and add a soldering flux to make them closely fit; Set the rolling pressure to 10-50 MPa and the rolling speed to 0.1-1 m / min for initial rolling to reduce the thickness to 80%-90% of the designed thickness; Adjust the rolling pressure to 50-100 MPa and keep the rolling speed at 0.1-1 m / min for continuous rolling to reduce the thickness to 60%-70% of the designed thickness.

5. The composite solder rolling process capable of adapting to different coefficients of thermal expansion according to claim 4, characterized in that, In "Anneal the rolled composite solder foil", it includes the following steps: Set the working temperature and time of the annealing furnace; Put the composite solder foil into the annealing furnace and perform annealing treatment according to the set parameters. After annealing, cool it to room temperature.

6. The composite solder rolling process capable of adapting to different coefficients of thermal expansion according to claim 5, characterized in that, In "Detect the flatness and thickness uniformity of the surface of the composite solder foil. If qualified, proceed to the next step; if unqualified, return to the previous step", it includes the following steps: Use an optical scanner to check and collect the surface flatness and image of the composite solder foil to obtain collected data; Analyze and judge based on the collected data to obtain a judgment result; Based on the judgment result, determine whether to proceed to the next step or return to the previous step for processing.

7. A composite solder that can adapt to different coefficients of thermal expansion, adopting the composite solder rolling process that can adapt to different coefficients of thermal expansion according to any one of claims 1-6, characterized in that, It includes an intermediate metal layer, two plating layers, and two solder layers; The coating layer is Cu, Ni or Ag, the solder layer includes Sn-based solder and In-based solder, the Sn-based solder includes SnAg, SnCu, SnBi, SnSb, SnZn, SnAu, SnAgCu, SnAgBi, SnAgIn, SnAgSb, SnAgCuBi, SnAgCuIn, SnAgCuSb, and the In-based solder includes InAg, InCu, InBi, InSb, InAgCu, InAgBi, InAgSn, InAgSb, InAgCuBi, InAgCuIn, InAgCuSb; the intermediate metal layer is a ferro-nickel alloy.

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