A packaging method and system for replacing aluminum paste with copper metal

Abstract

The application provides a packaging method and system for replacing aluminum paste with copper metal, pretreating aluminum powder, removing oxides and impurities on the surface of the aluminum powder; preparing aluminum paste; printing the aluminum paste on a steel plate; observing the size and state of the printed aluminum paste using a microscope; preparing a copper sulfate aqueous solution; printing the aluminum paste on the top of a copper foot support, placing a wafer cut grain on the aluminum paste, and replacing the aluminum paste at a preset replacement temperature for a preset replacement time to obtain the aluminum paste replaced with copper metal. The application can achieve full replacement of the aluminum paste, and adding an interface active agent and hydrochloric acid to the copper sulfate aqueous solution can increase the replacement amount. The use of the additive ETU can also completely replace the aluminum paste under the grain, and the copper sulfate solution also has strong penetration, so that the replacement can react from the left and right gaps. The application can save space, reduce the overall replacement cost, and improve the replacement yield.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of replacing copper metal with aluminum paste, and particularly relates to a packaging method and system for replacing aluminum paste with copper metal. BACKGROUND

[0002] With the progress of the times, packaging technology has also evolved. From the earliest pin insertion socket components, the main forms are: single in-line package (SiP) and dual in-line package (DiP). The disadvantages of these two methods are that the density and frequency are difficult to improve, and it is not easy to meet the needs of high-efficiency automated production.

[0003] Then, lead instead of pin to form surface mount, the main forms include: 1. Small Out-Line Package (SOP); 2. Leadless Chip Carrier (LCC); The advantage is that the lead is thin, short and small in pitch, but it is still insufficient to meet the needs of the development of application-specific integrated circuits (AISC) and microprocessors.

[0004] In the existing scheme, the atomic number of aluminum is 13, the relative density is 2.70 g / cm3, the melting point is about 660.4℃, and the boiling point is about 2519℃. The content of aluminum element in the earth's crust is the first among metals, accounting for 8.3% of the total amount of the earth's crust. Its physical properties: light metal, density is only about one-third of iron, at the same time, aluminum has good electrical conductivity and thermal conductivity (about 59% of copper). Its chemical properties: easy to react with oxygen, exposed to air will generate a dense aluminum oxide Al2O3 (4Al+3O2→2Al2O3, this process is called passivation), effectively preventing further oxidation. Aluminum metal has a wide range of applications because of its excellent electrical conductivity and thermal conductivity and lightness, which can replace copper as a cable material for ultra-high voltage; rich ductility, can be made into aluminum foil and applied to packaging; can be excreted by the human body. Early Canadian researchers found that aluminum was the culprit for Alzheimer's disease, but decades of research have found no evidence that aluminum can cause dementia in the elderly.

[0005] Copper has an atomic number of 29, a relative density of 2.70 g / cm3, a melting point of about 660.4 °C, and a boiling point of about 2519 °C. Its content in the earth's crust is about 0.01%. Its physical properties: not only soft, but also quite good electrical conductivity (59.6 x 106 S / m), thermal conductivity (401 W / (m·K)). Its chemical properties: copper does not react with water, and slowly reacts with oxygen in the air to form a layer of brown copper oxide, copper rust, the same as aluminum oxide, can protect the underlying copper from further corrosion. Copper is most commonly used in the manufacture of electrical wires, although its electrical and thermal conductivity is second only to silver, but much cheaper than silver; copper can also be used to manufacture a variety of alloys, such as brass, which is an alloy of copper and zinc, named for its yellow color, has good mechanical properties and wear resistance, can be used to manufacture precision instruments. Bronze, which is an alloy of copper and tin, is named for its green color, has excellent corrosion resistance, wear resistance and hardness, is commonly used in high-pressure bearings, marine machinery parts resistant to seawater corrosion. Copper ions (copper) are essential elements for both animals and plants, and a lack of copper in the human body can cause anemia.

[0006] The packaging technology and process specifically includes:

[0007] 1. Wafer Sort: The electrical properties of the wafer are measured using a wafer point measurement machine. If any defective dies are detected, ink marks will be placed on the surface of the dies to distinguish between good and bad dies.

[0008] 2. Wafer Saw: The wafer is placed on a metal frame and a blue film is attached to the back of the wafer. This step is to reduce the stress on the wafer during cutting to prevent breakage. Finally, the wafer is placed into a wafer cutting machine for cutting.

[0009] 3. Screen Printing: The copper footrest is placed in the screen printing machine and tin paste is printed on it. The purpose of this step is to connect the die to the copper footrest.

[0010] 4. Die Attach: The cut wafer is placed in the machine, which learns and identifies the ink-marked dies and attaches them to the tin paste.

[0011] 5. Solder Dispensing: A layer of tin paste is applied to the surface of the die and the other side of the copper footrest.

[0012] 6. Clip Mounting: The "L" shaped cover is used to connect the anode side of the die to the other side of the copper footrest.

[0013] 7. Reflow: The semi-finished product from the previous step is placed in a high-temperature oven for reflow. This step is to allow the solder paste to form an interfacial intermetallic compound with the copper pedestal, improving the overall nucleation.

[0014] 8. Cleaning: Ultrasonic cleaning is used to remove flux residue from the soldering agent or possible external contaminants during transportation.

[0015] 9. Molding: The main purpose of molding is to protect the packaged die from harsh external environments, such as damage from external forces, prevent moisture from entering and causing oxidation or corrosion, and effectively dissipate heat from the die.

[0016] 10. Laser Marking: After completing the packaging, the product name and production time are marked on the product using laser technology, allowing for subsequent tracking of product quality.

[0017] 11. Planting: A layer of tin is plated on the copper pedestal using electroplating to optimize electrical properties.

[0018] 12. Trimming: To facilitate mass production, hundreds of components are produced on a single copper pedestal, and then the copper pedestal is separated into individual products through the trimming step.

[0019] 13. Testing: To select products that meet electrical specifications from those that do not.

[0020] 14. Package & Labeling: Intermetallic compounds (IMC) are compounds formed by two or more metal elements in a fixed ratio, which are the result of a chemical reaction and belong to pure substances. Examples include Cu6Sn5, Ni3Sn4, AuSn4, etc. Packaging companies use the formation of an interfacial alloy compound Cu6Sn5 between the solder paste and the copper pedestal surface at high temperatures. Products with surface treatments such as electroplated nickel gold or electroplated nickel gold palladium are often seen on the market, using IMC Ni3Sn4 for secure soldering. The push-pull force testing machine can be used to evaluate whether the soldering is secure, or the high-temperature storage test (HTST) can be used to test the reliability of the solder joints. First, introduce chemical deposition, also known as electroless deposition. Metal gradually deposits on the carrier plate in the plating solution without the need for an external current, which can be considered a redox reaction. The reaction is as follows:

[0021] X n+ +ne - →X.

[0022] However, metal displacement reaction is also classified in electroless plating, the biggest difference is that the selected material is a reducing agent. The principle of displacement reaction is to make the reaction occur by the standard electrode potential of two metals, the metal with more negative oxidation potential replaces the metal with more positive reduction potential in the plating solution and deposits out, such a reaction is called displacement reaction or substitution reaction. Taking copper and aluminum metals as an example, the reaction formula is

[0023]

[0024] Displacement reaction has been widely used, such as depositing silver metal on copper-aluminum alloy through nitric acid aqueous solution, and depositing copper and nickel metal on aluminum substrate from sodium hydroxide solution. The following lists six factors that affect the metal displacement reaction:

[0025] 1. Copper ion concentration: the copper deposition rate increases with the increase of copper ion concentration in the plating solution, when the copper sulfate content is less than 10 g / L, it is basically proportional growth. However, when the copper sulfate content exceeds 12 g / L, the chemical plating copper rate will not increase but will produce a negative reaction, making the displacement reaction unstable.

[0026] 2. Reducing agent concentration: the commonly used reducing agents are formaldehyde and hypophosphite, with the increase of formaldehyde concentration in the plating solution, the reduction potential of formaldehyde also increases. When the concentration of formaldehyde exceeds 8 ml / L, the increase of reduction potential gradually slows down, so the concentration of formaldehyde should be controlled at 9 ml / L.

[0027] 3. Additives: during the displacement reaction, trace amounts of organic substances can be added according to different needs to change the properties of the deposit, such as wetting agent, brightener, etc. However, if the selection of additives is wrong, it will lead to the deterioration of film adhesion and embrittlement.

[0028] 4. pH value: displacement reaction of copper occurs only in a specific pH environment, which can increase the deposition rate and have good deposition uniformity under the appropriate acid-base value. At the same time, pH value also affects the standard electrode potential of metals, resulting in slight differences in displacement reaction results.

[0029] 5. Temperature: temperature can improve the rate of displacement reaction. Each different displacement reaction has a specific temperature limit. When the temperature exceeds the limit, the reaction will be intensified, which will affect the displacement results, so the reaction must be controlled at an appropriate temperature.

[0030] 6. Stirring solution: vigorous stirring during displacement can improve the deposition rate, and electromagnetic vibration or air stirring solution can be selected, which not only stabilizes the solution effect, but also improves the deposition rate. Standard electrode potential is a method for judging the strength of the redox reaction between elements. The standard electrode potential of an element is measured with a standard hydrogen atom as the standard electrode under standard conditions of 1 atm pressure and 25 DEG C, that is, the standard electrode potential value of hydrogen is set to 0. Compared with the standard electrode of hydrogen, the higher the potential is positive, and the lower the potential is negative, indicating that the unit is E°, and the unit is volt (V). Table 1-1 lists the ion reaction formula and standard electrode potential of common metal and non-metal elements.

[0031] Ion reaction formula Standard electrode potential Li + +e - → Li(s) -3.0401 Na + + e - → Na(s) -2.71 Al 3+ +3e - → Al(s) -1.662 Cl2(g) + 2e - → 2Cl - ]]> +1.36 Cu 2+ +2e - →Cu(s)]]> -0.34 Zn 2+ +2e - →Zn(s) -0.7618 Ag + +e - → Ag(s) +0.7996

[0032] When the standard electrode potential measured by the reversible electrode of the measured substance is positive, it indicates that the element is easy to combine with electrons, and the reaction is biased to the reduction reaction, and the larger the positive value is, the stronger the reducing property is; on the contrary, when the standard electrode potential measured by the reversible electrode of the measured substance is negative, it represents that the measured substance is easy to release electrons, and the reaction is biased to the oxidation reaction, and the larger the negative value is, the stronger the oxidation property is. Displacement reaction can be divided into anion displacement reaction and cation displacement reaction according to the ion species of the reaction. Cation displacement reaction refers to that during the reaction, only cations are displaced by cations, which is commonly seen in displacement reactions of metal elements and inorganic salt aqueous solution; anion displacement reaction refers to that during the reaction, only anions are displaced by anions, which is commonly seen in displacement reactions of non-metal elements and inorganic salt aqueous solution.

[0033] The disadvantages of the prior art are:

[0034] Lead heavy metals even if there is only a trace amount of 0.01 micrograms in the body, will damage the function of human organs. It will significantly affect the development of intelligence and bone, cause indigestion and endocrine disorders, and even lead to anemia, hypertension and arrhythmia and other heart diseases, or damage the immune system, and these damaged organs and tissues cannot be restored and will accompany for life. Currently, 90% of blood lead comes from food, and lead in water and food is the main reason for the increase in blood lead content. SUMMARY

[0035] In order to overcome the above-mentioned deficiencies in the prior art, the application provides a packaging method for replacing aluminum paste with copper metal, which can reduce the overall cost of displacement and improve the yield of displacement.

[0036] The packaging method for replacing aluminum paste with copper metal comprises:

[0037] S101, pretreating aluminum powder to remove oxides and impurities on the surface of the aluminum powder;

[0038] S102, preparing aluminum paste;

[0039] S103, printing the aluminum paste using a steel plate printing device;

[0040] S104, observing the size of the printed aluminum paste and the state of the printed aluminum paste using a microscope;

[0041] S105, preparing a copper sulfate aqueous solution;

[0042] S106, printing the aluminum paste on a copper stand, placing a wafer cut grain on the aluminum paste, and performing displacement at a preset displacement temperature for a preset displacement time to obtain a copper metal from the aluminum paste.

[0043] Further, in step S101, a 15% dilute sulfuric acid solution is used to soak the aluminum powder at a temperature of 45-50°C for 5-8 minutes.

[0044] The aluminum powder is then cleaned with deionized water for 10-15 minutes and finally dried in an oven at a temperature of 50-60°C.

[0045] Further, in step S102, the pretreated aluminum powder is mixed with different proportions of resin and organic solvent using a centrifugal mixer.

[0046] The mixture is then mixed and stirred using a three-roll mill.

[0047] Further, in step S103, the prepared aluminum paste is screen printed using a steel plate printing device.

[0048] The screen printing process includes setting screen printing parameters, including squeegee pressure and printing speed.

[0049] The steel plate, squeegee, and copper stand are installed.

[0050] The aluminum paste is spread.

[0051] The aluminum paste printing is performed.

[0052] Further, in step S105, a beaker is filled with deionized water, which is heated to a temperature of 45-50°C using a water bath heating method, and stirred using a magnetic stirrer. Copper sulfate powder is then added and dissolved in the deionized water, and finally sulfuric acid is slowly added to prepare a copper sulfate aqueous solution.

[0053] Further, in S106, the preset displacement temperature is 68-75°C, and the preset displacement time is 60-90 minutes.

[0054] Further need to explain is, in S106, the replacement process doped with 5% copper sulfate powder, add 150ppm to 200ppm surfactant and add 150ppm to 200ppm hydrochloric acid.

[0055] The application also provides a packaging system for replacing aluminum paste with copper metal, which implements the packaging method for replacing aluminum paste with copper metal; the system comprises aluminum powder, resin, sulfuric acid solution, box-type high-temperature furnace, centrifugal mixer, three-roller grinding machine, steel plate printing device, microscope, magnetic stirrer and energy dispersive X-ray spectrometer.

[0056] The aluminum paste is prepared by using aluminum powder and resin; the oxide and impurities on the surface of the aluminum powder are removed by using sulfuric acid solution; and drying is performed in the box-type high-temperature furnace.

[0057] The pretreated aluminum powder, resin and organic solvent are mixed by using the centrifugal mixer; the prepared aluminum paste is mixed and stirred by using the three-roller grinding machine; and the prepared aluminum paste is screen printed by using the steel plate printing device; and the size and state of the printed aluminum paste are observed by using the microscope.

[0058] The copper sulfate aqueous solution is prepared; the aluminum paste is printed on the copper foot support; the crystal grain after wafer cutting is placed on the aluminum paste; the replacement is performed at a preset replacement temperature; and the replacement is performed for a preset replacement time, so that the aluminum paste is replaced with copper metal.

[0059] From the above technical solutions, the application has the following advantages:

[0060] The application can achieve full replacement of the aluminum paste, and the replacement amount is increased by adding the surfactant and hydrochloric acid to the copper sulfate aqueous solution. The use of the additive ETU can also completely replace the aluminum paste under the crystal grain, and the copper sulfate solution has strong penetration, so that the replacement can be performed from the gaps on the left and right sides, thereby improving the replacement efficiency and ensuring the yield of the replacement.

[0061] In the replacement reaction of the aluminum paste, after the aluminum paste is printed on the copper foot support and solidified, the deionized water copper sulfate is used as the solvent for the replacement reaction, and the replacement reaction is performed for 30 minutes, 60 minutes and 90 minutes at different temperatures of 50 DEG C, 60 DEG C and 70 DEG C, respectively, and the microstructure is observed by using the electron microscope, and the material is analyzed by using the energy dispersive X-ray spectrum. The preset temperature replacement can be observed to replace the aluminum paste with copper metal. The crystal grain is placed on the aluminum paste to perform the replacement, the aluminum paste is printed on the copper foot support, and then the crystal grain after wafer cutting is placed on the aluminum paste to perform the replacement, so that the replacement is stable and the yield is high. BRIEF DESCRIPTION OF DRAWINGS

[0062] In order to more clearly illustrate the technical solutions of the present application, the drawings required to be used in the description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0063] Figure 1 Flow chart of the packaging method for replacing aluminum paste with copper metal

[0064] Figure 2 Profile graph of temperature versus replacement result

[0065] Figure 3 Profile graph of time versus replacement result

[0066] Figure 4 Profile graph of doped copper sulfate powder versus replacement result

[0067] Figure 5 Profile graph of interface active agent versus replacement result

[0068] Figure 6 Profile graph of time versus replacement result

[0069] Figure 7 Schematic diagram of full replacement of aluminum paste with copper

[0070] Figure 8 Schematic diagram of replacement result of covering the die

[0071] Figure 9 Replacement result graph of adding ETU to the covering die DETAILED DESCRIPTION

[0072] In the packaging method for replacing aluminum paste with copper metal provided by the present application, lead-containing tin paste is used. The reason for using only lead-containing tin paste is that the packaging process can allow the die to be perfectly combined with the copper stand. The reason is that tin metal and copper metal can form interface alloy intermetallic compounds at 227℃. However, if lead is not contained, the mechanical strength in each alloy is in reverse order, and finally, the process of replacing lead-containing tin paste is required.

[0073] In the present application, aluminum powder is mixed with resin to prepare aluminum paste, and then screen printing equipment is used to print the aluminum paste on the copper stand to observe whether the printing result is the same as that of lead-containing tin paste. Then, a replacement reaction solution is prepared, and the aluminum paste is subjected to replacement reaction at different temperatures and rotation speeds, and the microstructure, composition analysis and electrical property measurement are observed.

[0074] In the present application, the suitable content ratio is found out, so that the aluminum paste does not have a serious phenomenon of opening during printing, and has a better printing result.

[0075] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0076] As shown in the drawings, Figure 1 The packaging method for replacing the substituted aluminum paste with copper metal provided by the present application comprises the following steps:

[0077] S101, pretreating the aluminum powder to remove the oxides and impurities on the surface of the aluminum powder;

[0078] In order to remove the oxides and impurities on the surface of the aluminum powder, the aluminum powder is soaked in a dilute sulfuric acid solution with a weight concentration of 15% at 45-50°C for 5-8 minutes, and the hydrogen ions in the sulfuric acid can reduce the aluminum oxide layer. Then, the aluminum powder is cleaned with deionized water for 10-15 minutes, and finally dried in an oven at 50-60°C.

[0079] S102, preparing the aluminum paste;

[0080] The pretreated aluminum powder is mixed with different proportions of resin and organic solvent through a centrifugal mixer, and then mixed using a three-roller grinding machine. The three-roller grinding machine can effectively uniformly stir the objects with viscosity.

[0081] Specifically, the container filled with materials rotates on its own axis under vacuum while the whole container revolves around a certain radius, resulting in a strong continuous centrifugal force, so that the materials are mixed, stirred and completely defoamed at the same time. The stirring material generates up-and-down convection due to the simultaneous rotation and revolution, and the torque also generates spiral flow. When this movement is carried out under vacuum, the volume of fine bubbles rapidly expands by 760 times, and the bubbles are removed at the interface with the vacuum. The material can be completely defoamed within 2 minutes.

[0082] The three-roller grinding machine uses the friction function generated by the different rotating speeds of the rollers to achieve the effect of grinding and mixing the product raw materials. The rotating speed ratio of the three rollers is 1:3:9 (slow feeding roller: middle roller: fast discharging roller). The three-roller grinding machine passes the sample between the rollers through a fixed rod.

[0083] The three-roller grinding machine includes a slow feeding roller, a center roller and a fast discharging roller. The three adjacent rollers rotate at gradually increasing speeds. The material, usually in a viscous form, is placed between the feeding roller and the center roller. Due to the reduced spacing between the discharging rollers, the material eventually concentrates at the discharging roller. The shear force is very high when the material passes through the feeding roller, mainly due to the different rotating speeds of the two rollers. The material remaining on the center roller moves through the second roller gap between the center roller and the discharging roller.

[0084] S103, printing the aluminum paste using a steel plate printing device;

[0085] Specifically, the prepared aluminum paste is printed using a steel plate printing device; the printing step includes setting printing parameters, including squeegee pressure and printing speed; installing a steel plate, a squeegee, and a copper foot stand; laying the aluminum paste; and performing aluminum paste printing.

[0086] Steel plate printing, also known as pad printing, is a type of intaglio printing. Ink is applied to a steel plate, and a blade is used to remove the ink from the flat surface, leaving only the parts of the pattern where the ink remains. A rubber head is then used to pick up the ink and transfer it to the substrate, allowing printing on various materials such as plastic cases, metals, and high-tech related products. Compared to screen printing, pad printing is more suitable for small areas, fine lines, and uneven surfaces, and the ink thickness is much thinner than that of screen printing.

[0087] S104, observing the size and state of the printed paste using a microscope after printing;

[0088] After printing, the size of the printed paste and whether the paste dries quickly are observed using a microscope, and the aluminum paste formula is adjusted accordingly. The microscope can be an electron microscope that uses a focused electron beam to scan the sample surface point by point to form an image.

[0089] S105, preparing a copper sulfate aqueous solution;

[0090] Fill a beaker with deionized water and heat it to 45-50°C using a water bath heater while stirring with a magnetic stirrer. Then add copper sulfate powder to completely dissolve in the deionized water, and finally slowly add sulfuric acid to prepare the copper sulfate aqueous solution. The displacement conditions can be divided into three main items: temperature, displacement time, and copper sulfate powder concentration. Displacement reactions were performed at 50°C, 60°C, and 70°C, with displacement times of 30 minutes, 60 minutes, and 90 minutes, and copper sulfate powder concentrations of 0%, 5%, and 10%.

[0091] Before placing the crystal grains on the aluminum paste, we first verify whether the displacement solution will affect the electrical properties of the crystal grains. Take 10 crystal grains and place them in the displacement solution under the same displacement conditions. After displacement, rinse with Di-Water and dry. Then analyze the electrical properties using an electrical property tester. Next, perform displacement experiments on covered crystal grains under the same displacement conditions as the previous experiments, measure the electrical properties, and observe whether the aluminum paste below the crystal grains has been displaced.

[0092] S106, print the aluminum paste on the copper foot support, place the wafer cut grain on the aluminum paste, displace at the preset displacement temperature, and after the preset displacement time, obtain the aluminum paste replaced with copper metal.

[0093] The preset displacement temperature is 68-75°C, and the preset displacement time is 60-90 minutes. The displacement process is doped with 5% copper sulfate powder, 150-200 ppm of an interfacial active agent, and 150-200 ppm of hydrochloric acid.

[0094] The substitution of the aluminum paste of the present application is replaced with copper metal packaging method, which is based on chemical displacement reaction as the core, and the aluminum paste is printed on the copper foot support for displacement. By adjusting the resin content, the amount of flux, and other different solid contents, the aluminum paste is fully replaced with copper metal. The displacement is divided into two conditions without placing the grain and with placing the grain. Under different displacement temperatures, displacement times, and copper sulfate powder concentration agents, the differences in the cross-sectional microstructure and electrical properties of each displacement are different. The solid content definition is the mass percentage of the remaining part of the emulsion after drying under specified conditions. Taking the aluminum paste as an example, the formula is as follows:

[0095]

[0096] Observe the printing results of the aluminum paste with different solid contents. First, start with the aluminum paste with a solid content of 40%. It can be observed that the viscosity of the aluminum paste is insufficient, resulting in high fluidity and fast volatility. The printing result has a very serious bleeding phenomenon, with an average bleeding of 1 μm on both sides. It is not suitable for printing.

[0097] Increase the solid content to 50%, and it can be found that the bleeding problem is significantly improved, with an average bleeding of 0.4-0.5 μm on both sides. It has not yet reached the printing standard, which is no obvious bleeding phenomenon. The aluminum paste on the second foot support still has a small amount of bleeding, and the edges of the aluminum paste have a wire drawing phenomenon. Therefore, try to increase the solid content to more than 60%. It can be observed that the bleeding phenomenon has been completely improved. Therefore, it can be known that the increase of the solid content can solve the problem of the fluidity of the paste. In order to meet the needs of subsequent displacement experiments, the solid content is increased to 70%. It can be observed that the printing result of the aluminum paste is also better, and the aluminum paste on the second foot support is more saturated. From the first experiment, it can be found that the solid content can affect the fluidity of the aluminum paste. Increasing the solid content can make the aluminum paste have better printing and reduce the bleeding phenomenon of the aluminum paste.

[0098] The present application first fixes the displacement conditions, and the same concentration of copper sulfate aqueous solution without additives is used for displacement at 50°C, 60°C, and 70°C for 30 minutes. After displacement, the resistance value is measured first, and then the displacement thickness and appearance are observed.

[0099] From Figure 2As can be seen from Table 1, there is almost no displacement at 50°C, so the resistance value is as high as 42.987 mΩ. As the temperature gradually increases to 60°C, there is a slight displacement of aluminum paste into copper metal, but the distribution is scattered, and no dense copper metal is observed. The measured resistance value is 33.292 mΩ. Finally, at 70°C, there is slightly dense copper metal on the surface, and the resistance value is also decreasing to 13.476 mΩ.

[0100] Table 1 Temperature for displacement results

[0101]

[0102] From the previous time, it can be found that there is a better displacement result at 70°C. Therefore, by increasing the displacement time, it is observed whether better displacement can be achieved. Therefore, the displacement temperature is fixed at 70°C, and the displacement time is increased to 60 minutes and 90 minutes. From Figure 3 As can be seen from Table 2, after increasing the displacement time to 60 minutes, the amount of displacement copper increases slightly, and the measured resistance value decreases to 8.492 mΩ. However, when the displacement time is lengthened to 90 minutes, the displacement amount is relatively reduced. It is speculated that it is eroded by the copper sulfate aqueous solution because the displacement time is too long, so the resistance value increases to 24.624 mΩ.

[0103] Table 2 Time for displacement results

[0104]

[0105] After testing the effects of temperature and time on displacement experiments, it is found that displacement cannot achieve full displacement. Therefore, in order to further optimize displacement, this experiment uses doped copper sulfate powder into the aluminum paste. The motivation of this step is that when copper sulfate powder touches copper sulfate aqueous solution, it will dissolve to form a hole, and this hole can increase the contact surface between copper sulfate aqueous solution and aluminum paste, so as to achieve more displacement. This experiment prepared three kinds of aluminum paste with different doping ratios, which are 0%, 5%, and 10%, respectively, at the same displacement temperature of 70°C and displacement time of 60 minutes. From Figure 4 As can be seen from Table 3, when 5% copper sulfate powder is added, a continuous and dense displacement copper metal is formed on the surface of the displacement, but the middle layer and the bottom are not displaced, and the measured resistance value is also reduced to 4.728 mΩ. However, when the aluminum paste with 10% copper sulfate powder is observed, the displacement reaction is reduced. It is speculated that the excessive copper sulfate allows the surface to quickly form copper metal, so that the displacement solution cannot penetrate deeper into the aluminum paste, but instead inhibits the displacement reaction, and the measured resistance value is 14.921 mΩ.

[0106] Table 3 Doped copper sulfate powder for displacement results

[0107]

[0108] From the first three experiments found still not to let the aluminum paste to full replacement, so the next step from the replacement solution of additives to research, a total of 2 kinds of additives will be one to go experiment, respectively, interface active agent, hydrochloric acid. First, the experimental parameters for doping 5% copper sulfate powder of aluminum paste, displacement temperature 70 ℃, displacement time 60 minutes. First interface active agent experiment, respectively, add 50 ppm, 100 ppm, 150 ppm. From Figure 5 With table 4 observation, it can be found that the bottom of the aluminum paste has more displacement copper due to the increase of additives, because the interface active agent can also decompose a little bit of resin, so that the copper sulfate solution has more holes down to the aluminum paste for replacement. Resistance value decreases with the increase of the amount of interface active agent, respectively, 2.874 mΩ, 1.837 mΩ, 1.397 mΩ.

[0109] Table 4 time for displacement results

[0110]

[0111] Then add hydrochloric acid, hydrochloric acid will dilute the chloride ion, chloride ion will adhere to the aluminum powder, so that the aluminum powder and copper ions in the copper sulfate solution produce a bridge, which can increase the amount of aluminum paste replacement. From Figure 6 With table 5 observation, the more the amount of hydrochloric acid, the more displacement copper gradually increases, especially from the bottom of the displacement amount is more obvious, so the resistance value also decreases, respectively, 2.038 mΩ, 1.424 mΩ, 0.988 mΩ.

[0112] Table 5 time for displacement results

[0113]

[0114] From the above data, it is found that when the temperature is insufficient, there is no obvious displacement effect, when the temperature is high to 70 ℃, there is a better displacement result. The displacement time is 60 minutes, which is the most suitable length, if the time is too long, it may be eroded by copper sulfate solution. Doping copper sulfate powder can indeed increase the amount of displacement copper, but adding too much will inhibit the displacement reaction. In order to further let the aluminum paste to full replacement, add interface active agent and hydrochloric acid to copper sulfate solution to promote displacement. And in this verification, displacement temperature 70 ℃, displacement time 60 minutes, doping 5% copper sulfate powder, adding 150 ppm interface active agent, adding 150 ppm hydrochloric acid, the results are as follows Figure 7 It can be found that the thickness of 50 μm of aluminum paste has completed the full displacement of copper metal reaction, and the resistance value is 0.243 mΩ.

[0115] Before applying the grains to the aluminum paste for replacement, we need to verify whether the copper sulfate solution will damage the electrical properties of the grains. Therefore, the grains were first placed directly into a 70°C copper sulfate solution for 60 minutes, then removed, washed with di-water, and dried. The grains were then ground and observed. SEM analysis before and after replacement showed slight erosion of the silver plating on the grain surface, which may be the cause of electrical failure.

[0116] When the die is subjected to a current of IR = 500μA, the minimum breakdown voltage must be greater than 60V; if the current is subjected to a voltage of VR = 60V, and the IR is not greater than 300μA, then the die meets the specifications.

[0117] After verifying that the grains would not be severely damaged by the copper sulfate solution, a grain displacement experiment was conducted on the aluminum paste covering. The grain displacement results at 70°C for 60 minutes were as follows: Figure 8 As shown, it can be observed that the aluminum paste was only slightly displaced at the edges. The central aluminum paste, not in contact with the copper sulfate solution, did not undergo any displacement reaction. However, due to the copper displacement at the edges, the die and copper leads remained connected and conductive, with a measured resistance of 14.684 Ω. Table 6 shows the electrical measurements of the displaced die. It can be found that 8 out of 10 samples failed, therefore it can be inferred that relying solely on copper displacement at the edges is insufficient to achieve a good electrical connection between the die and the copper leads. However, the push-pull force remained at an average value of 907.18 g, similar to that of lead-solder paste.

[0118] Table 6. Measurement of electrochemical properties and push-pull force of grain displacement on the cover.

[0119] Item Name VZ IR Push-pull force Biasl IKA=500uA VCE=60.0V Min Limit 60.00V Max Limit 90.00V 300.0uA Serial# 2 VZCE 3 IR1 F1 F 40.03V F Over 983.31g F2 F 41.02V F Over 692.42g F3 F 41.03V F Over 834.42g P4 67.57V 072.8uA 1042.27g F5 F 40.92V F Over 909.93g P6 66.92V 093.4uA 1124.82g F7 F 39.88V F Over 793.68g F8 F 40.21V F Over 864.23g F9 F 41.22V F Over 919.54g

[0120] Since the aluminum paste only displaces the edges and lacks good electrical properties, we again sought the assistance of an additive: ETU. Figure 9 It can be observed that ETU gives the copper sulfate aqueous solution strong penetrating power, allowing the aluminum paste in the middle to also achieve a displacement effect. However, upon closer observation, it can be found that the aluminum paste after displacement actually has pores, and these pores lead to poor performance of the push-pull force between the back grains and the tripod, with an average push-pull force of 289.93g.

[0121] In the electrical analysis, the measured resistance value was 14.413Ω. The ability to measure the resistance value indicates that aluminum paste replacement of copper allows the die to conduct through the copper leads. As shown in Table 7, only 1 out of 10 samples failed, indicating that the aluminum paste replacement of copper technology at this stage of the process can still maintain the original electrical specifications of the sample.

[0122] Table 7 Results of ETU replacement on top of the crystal grains: electrical measurements and push-pull force.

[0123] Item_Name VZ IR Push-pull force Biasl IKA=500uA VCE=60.0V Min Limit 60.00V Max Limit 90.00V 300.0uA Serial# 2 VZCE 3 IR1 P1 67.27V 237.6uA P2 67.32V 073.2uA 342.67g F3 F 41.03V F Over 228.95g P4 67.57V 072.8uA 404.12g P5 67.21V 081.8uA 298.44g P6 66.92V 093.4uA 199.76g P7 66.06V 093.7uA 273,96g P8 66.97V 073.1uA 273.44g P9 67.22V 084.4uA 268.84g

[0124] Based on the above analysis process, the application uses aluminum paste and chemical displacement reaction to replace aluminum paste with copper metal. This method allows low-cost aluminum paste to exhibit better conductivity of copper metal, and can replace lead-containing tin paste used in packaging. The use of additives ETU can completely replace the aluminum paste under the crystal grains, and the copper sulfate solution also has strong penetration, allowing the displacement reaction to occur from the left and right gaps.

[0125] The application is based on a packaging system that replaces aluminum paste with copper metal. The system includes aluminum powder, resin, sulfuric acid solution, box-type high-temperature furnace, centrifugal mixer, three-roller grinding machine, steel plate printing equipment, microscope, magnetic stirrer, and energy dispersive X-ray spectrometer.

[0126] Aluminum paste is prepared using aluminum powder and resin. The sulfuric acid solution is used to remove the oxides and impurities on the surface of the aluminum powder. Drying is performed in a box-type high-temperature furnace.

[0127] The pretreated aluminum powder is mixed with different proportions of resin and organic solvent using a centrifugal mixer. Then, the three-roller grinding machine is used for mixing and stirring. The prepared aluminum paste is screen printed using the steel plate printing equipment. The size and state of the printed paste are observed using a microscope.

[0128] A copper sulfate aqueous solution is prepared. The aluminum paste is printed on the copper footrest. The crystal grains after wafer cutting are placed on the aluminum paste. The displacement reaction is performed at a preset displacement temperature for a preset displacement time to obtain copper metal from the aluminum paste.

[0129] In the aluminum paste displacement reaction of the application, after the aluminum paste is printed on the copper footrest and solidified, the deionized water copper sulfate is used as the solvent for the displacement reaction. The displacement reaction is performed at three different temperatures of 50°C, 60°C, and 70°C for different times of 30 minutes, 60 minutes, and 90 minutes. The microstructure is observed using an electron microscope, and the material is analyzed using energy dispersive X-ray spectroscopy. The preset temperature can be observed to completely replace the aluminum paste with copper metal. The crystal grains are placed on the aluminum paste for displacement. After the aluminum paste is printed on the copper footrest, the crystal grains after wafer cutting are placed on the aluminum paste for displacement. Because the crystal grains cover the aluminum paste, reducing the contact area between the deionized water copper sulfate and the aluminum paste, the displacement effect is better, and the displacement efficiency is improved.

[0130] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and that the appended claims are intended to cover all such modifications that do not depart from the true spirit and scope of the application. Therefore, the application is not limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A packaging method of replacing a substituted aluminum paste with copper metal, characterized by, The method comprises: S101, pretreating aluminum powder to remove oxides and impurities on the surface of the aluminum powder; S102, preparing aluminum paste; S103, printing the aluminum paste using a steel plate printing device; S104, observing the size and state of the printed aluminum paste using a microscope after printing; S105, preparing a copper sulfate aqueous solution; Fill a beaker with deionized water, heat it to between 45°C and 50°C using a water heating method, and stir it on a magnetic stirrer, then add copper sulfate powder to completely dissolve in the deionized water, and finally slowly add sulfuric acid to prepare the copper sulfate aqueous solution; S106, print the aluminum paste on the copper footrest, place the wafer cuttings on the aluminum paste, displace at a preset displacement temperature, and after a preset displacement time, obtain the aluminum paste replaced with copper metal; The preset displacement temperature is 68°C to 75°C, and the preset displacement time is 60 minutes to 90 minutes; The displacement process is doped with 5% copper sulfate powder, 150ppm to 200ppm surfactant, and 150ppm to 200ppm hydrochloric acid.

2. The packaging method for replacing the substituted aluminum paste with copper metal according to claim 1, wherein In step S101, a dilute sulfuric acid solution with a concentration of 15% by weight is used to soak the aluminum powder at a temperature of 45°C to 50°C for 5 to 8 minutes; Use deionized water to clean for 10 to 15 minutes, and finally put it into an oven to dry at 50°C to 60°C.

3. The packaging method for replacing the substituted aluminum paste with copper metal according to claim 1, wherein In step S102, the pretreated aluminum powder is mixed with different proportions of resin and organic solvent through a centrifugal stirrer; Then use a three-roll mill to mix and stir.

4. The method of claim 1, wherein the copper metal is encapsulated by a copper oxide layer. In step S103, the prepared aluminum paste is screen printed using a steel plate printing device; The screen printing step includes setting screen printing parameters, including squeegee pressure and printing speed; Install the steel plate, squeegee, and copper footrest; Lay the aluminum paste; Perform aluminum paste printing.

5. A packaging system for replacing aluminum paste with copper metal, characterized by, The system is used to implement the packaging method for replacing the substituted aluminum paste with copper metal as claimed in any one of claims 1 to 4; the system comprises: The system implements the packaging method for replacing the substituted aluminum paste with copper metal; the system comprises: aluminum powder, resin, sulfuric acid solution, box-type high-temperature furnace, centrifugal stirrer, three-roll mill, steel plate printing device, microscope, magnetic stirrer, and energy dispersive X-ray spectrometer; The aluminum paste is prepared using aluminum powder and resin; the sulfuric acid solution is used to remove oxides and impurities on the surface of the aluminum powder; and the aluminum paste is dried in the box-type high-temperature furnace; The pretreated aluminum powder is mixed with different proportions of resin and organic solvent through a centrifugal stirrer; then a three-roll mill is used to mix and stir; the prepared aluminum paste is screen printed using a steel plate printing device; and the size and state of the printed aluminum paste are observed using a microscope after printing; The copper sulfate aqueous solution is prepared; the aluminum paste is printed on the copper footrest, the wafer cuttings are placed on the aluminum paste, displacement is performed at a preset displacement temperature, and after a preset displacement time, the aluminum paste is replaced with copper metal.

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