TW201719686A - Method for fabricating high-conductivity thick aluminum paste - Google Patents

Abstract

A method is provided to fabricate a thick aluminum paste. Distribution of particle size is wide. Solid content is increased. Thus, the problem of multiple pores is solved. A mechanism of alumina surface rupture is used. Sufficient glass powder is coordinated to inhibit exposed liquid of metal aluminum from air oxidation. Furthermore, adjacent exposed liquids of metal aluminum are contacted with each other to form conductive path. Hence, low electrical conductivity of aluminum paste is highly improved. The thick aluminum paste has low cost and high conductivity and can be sintered in air.

Description

Method for manufacturing high conductivity thick film aluminum paste

The invention relates to a method for manufacturing a high-conductivity thick-film aluminum paste, in particular to a problem of improving the low conductivity of a conventional aluminum paste, providing a low-cost, high-conductivity, and thick film conductive which can be sintered in air. Aluminum paste, in particular, refers to an application that can widely replace existing high cost conductive silver pastes with conductive copper pastes that need to be sintered in a reducing atmosphere.

The terminal electrode of the thick film resistor can be divided into three parts, a front end electrode, a side end electrode and a back end electrode, wherein the side end electrode and the back end electrode are only used for the post process electroplating nickel and tin seed layer, and the front side In addition to being used for the post-plating electroplating of nickel and tin seed layers, the terminal electrodes must also be responsible for connecting the path of the resistive layer conduction. Therefore, the conductivity of the front end electrode must be much lower than the resistivity of the resistive layer to form an ohmic contact. . At present, the conductive paste used in the terminal electrode on the market is mainly silver paste, which is also the most mature and widely used thick film conductive paste, which has the advantages of high electrical conductivity and sintering in air, but the cost is too high. Expensive, and as the international silver price continues to rise, the price of silver powder remains high, considering the cost issue, some applications are slowly transferred to low-cost copper as a metal filler, but because copper is easily oxidized, it must be in a reducing atmosphere. Under sintering, the reducing atmosphere sintering furnace is expensive, so the application of copper paste is limited. While aluminum paste has the advantage of low cost and can be sintered in air, the resistivity of commercially available aluminum pastes tends to be high. The main reason for the low electrical conductivity of the traditional aluminum paste is that the metal aluminum naturally forms a thin layer of aluminum oxide on the surface of the air to prevent continuous oxidation inside, and this layer of oxide blocks the contact of the internal metal aluminum and inhibits the aluminum. The shrinkage during the sintering process results in the formation of porous structures such as porous holes and aluminum voids after sintering, resulting in high electrical resistivity, and the microstructure thereof is as shown in Fig. 9. The structure (or defect) of the conventional aluminum paste porous hole and the aluminum empty shell can be clearly seen from the figure. In addition, generally conductive silver paste or copper paste will face a serious problem in filling the holes and metallization lines of the substrate. Generally, the size of the conductive silver paste or copper paste after printing will be caused by the shrinkage of silver paste or copper paste after sintering. The size is reduced. This problem is particularly serious for the hole filling, because the filling hole conductive paste cannot fill the hole and leave a void, which may affect the conductive or thermal conduction behavior, and may even have a gas leakage problem during vacuum packaging. In view of the high cost of silver paste; copper paste, although relatively inexpensive, must be sintered in a reducing atmosphere, limiting the application of copper paste. Metal aluminum has the advantages of high electrical conductivity, low cost, and sintering in air, but it cannot be utilized as an aluminum paste to exhibit its high electrical conductivity. Therefore, the user-like users cannot meet the needs of the user in actual use.

The main object of the present invention is to overcome the above problems encountered in the prior art and to provide a problem of improving the low electrical conductivity caused by defects such as the porous holes of the aluminum paste and the aluminum shell, which can greatly improve the electrical conductivity and achieve a low cost. High-conductivity, thick-film conductive aluminum paste that can be sintered in air, and can widely replace the high-conductivity silver paste with high-conductivity conductive silver paste and conductive copper paste that needs to be sintered in a reducing atmosphere. Manufacturing method. A secondary object of the present invention is to provide a high conductivity thick film aluminum paste which can be applied to a thick film resistor terminal electrode and an LED ceramic substrate metallization process. For the purpose of the above, the present invention is a method for producing a high-conductivity thick-film aluminum paste, which comprises at least the following steps: (A) providing an aluminum powder having different particle diameters, and the size ratio of the aluminum powder is 4±50%: 1±50%; (B) mixing the aluminum powder with a glass powder, wherein the glass powder has a solid content of 7.5 wt%±50%, and the ratio of the aluminum powder to the total solid content of the glass powder 10:1; and (C) the mixture of the aluminum powder and the glass powder is subjected to liquid phase sintering at a sintering temperature of at least 500 ° C. The sintering temperature is such that the aluminum powder in the mixture utilizes a surface alumina cracking mechanism. It is coated with liquid glass powder to cover the cracked surface of all aluminum powder to inhibit the exposure of exposed liquid metal aluminum to the air, and promote the contact of adjacent bare liquid metal aluminum to form a conductive path, which is uniform and non-shrinking. Membrane conductive paste. In the above embodiment of the invention, the thick film conductive paste has a sheet resistance of less than 5 mΩ/sq. In the above embodiment of the invention, the aluminum powder has a large particle size of 4 to 6 μm and a small particle size of 1 to 3 μm.

Please refer to FIG. 1A to FIG. 8 , which are schematic diagrams of the manufacturing process of the present invention, a schematic diagram of the alumina cracking mechanism of the present invention, a schematic diagram of the use of the present invention, and a thermogravimetric weight of the aluminum powder particles of the present invention. The schematic diagram of the surface, the microstructure of the surface of the aluminum powder particles of the present invention, the microstructural diagram of the aluminum powder of different sizes and sizes of the present invention, the thermogravimetric analysis diagram of adding different amounts of glass of the present invention, and the addition of different proportions of glass according to the present invention Microstructure diagram, microstructure diagram of matching and mismatching of aluminum powder and glass powder of the invention, microstructure diagram of novel aluminum paste and traditional aluminum paste of the invention, and thick film resistor end of high conductivity thick film aluminum paste of the invention The schematic diagram of the reliability test results of the electrode and the structure of the invention applied to the hole filling and metallization process of the LED ceramic substrate. As shown in the figure: the present invention is a method for producing a high-conductivity thick-film aluminum paste, which comprises at least the following steps: (A) as shown in FIG. 1A, an aluminum powder 1 having different particle diameters is provided, and the aluminum is provided. The size ratio of powder 1 is 4±50%: 1±50%, wherein the large particle size aluminum powder 1 is controlled at 4-6 μm, and the small particle size aluminum powder 1 is controlled at 1-3 μm; (B) the aluminum powder 1 mixed with a glass frit 2, wherein the glass frit 2 has a solid content of 7.5 wt% ± 50%, and the ratio of the aluminum frit 1 to the glass frit 2 total solid content is 10:1; and (C) the aluminum The mixture of the powder 1 and the glass frit 2 is subjected to liquid phase sintering at a sintering temperature of at least 500 ° C. The sintering temperature is such that the aluminum powder 1 in the mixture is converted from the solid metal aluminum 11 to the liquid metal aluminum 12 by surface oxidation. The aluminum 13 rupture mechanism (as shown in Figure 1B) is coated with liquid glass frit 2 to cover all ruptured surfaces of aluminum powder 1 to inhibit exposure of exposed liquid metal aluminum 12 to air and promote adjacent bare liquid metal aluminum. 12 contact each other to form a conductive path 14 to obtain a uniform density And thick film conductive aluminum paste without shrinkage. If so, a new method of manufacturing a high conductivity thick film aluminum paste is constructed by the above disclosed process. The defect structure of the traditional aluminum paste porous hole and the aluminum empty shell (as shown in Fig. 9), wherein the porous hole can be improved by stacking different particle sizes and increasing the solid content, and the main reason for the aluminum empty shell is that the sintering temperature exceeds The melting point of aluminum (660 ° C) causes the internal metal aluminum to melt and expand. The surface alumina breaks due to the difference in expansion coefficient, and the internal liquid metal aluminum flows out and then oxidizes to form an aluminum shell. In this regard, the present invention makes full use of the above-mentioned innovative technology. When used, as shown in FIG. 1C, a mixture of the aluminum powder 1 and the glass frit 2 is mixed with an adhesive 3 to be printed thereon. After the substrate is sintered, the adhesive 3 is burned off and the glass frit 2 is softened into the liquid glass frit 2, and the surface alumina 13 is broken and the glass powder 2 is used to inhibit the exposure of the exposed liquid metal aluminum 12 to the air. Further, the adjacent bare liquid metal aluminum 12 is brought into contact with each other to form a conductive path. Therefore, the present invention utilizes a thick film conductive aluminum paste which can achieve high conductivity, low cost and can be sintered in air by increasing the solid content. In view of the above-mentioned aluminum powder particle size effect, the present invention firstly uses thermogravimetric analysis to observe the degree of oxidation of large particle size and small particle size aluminum powder and contrasts with Scanning Electron Microscopy (SEM), such as 2A, 2B. As shown in the figure, it can be seen that the large-diameter aluminum powder has a relatively large amount of oxidation at 600-700 ° C and the temperature-holding phase, while the small-diameter aluminum powder does not undergo a large amount of oxidation after oxidation at 500-600 ° C. According to the SEM of FIG. 2B, it can be seen that there is a bulge on the surface of the large-diameter aluminum powder, and the ridge is a phenomenon in which the surface alumina is ruptured after the sintering exceeds the melting point of the aluminum, and the internal liquid metal aluminum flows out and is oxidized, and the small particle diameter is formed. No obvious bumps are produced; this result represents that the aluminum powder with a small particle size of aluminum powder is easily broken. Accordingly, the present invention contemplates that the surface alumina is broken so that the internal metal aluminum is interconnected. Therefore, it is chosen to use large-size aluminum powder as the main material, and small-diameter aluminum powder as the supplement to achieve the purpose of forming the passage and densification. Fig. 3 is a cross-sectional microstructure of the invention for increasing the stacking density of the aluminum film by using the ratio of the size of the aluminum powder of 1:0, 1:1, 4:1, and 0:1, and it is apparent that the small-sized aluminum powder is After the sintering, the surface aluminum oxide layer is not broken, and a conductive path cannot be formed, resulting in high electrical resistivity. However, the large-diameter aluminum powder is ruptured by the oxide layer to cause the adjacent exposed liquid metal aluminum to contact to form a conductive path, thereby obtaining a lower resistivity. Therefore, according to the electrical properties and the degree of compactness of the stack, the optimum ratio of the large particle size to the small particle size aluminum powder is 4:1. After the alumina is broken, it is necessary to have enough liquid glass powder to cover the cracked surface to inhibit its oxidation, and to increase the chance of liquid metal aluminum contact by liquid phase sintering. In this regard, the present invention attempts to add different amounts of glass to 0%, 3%, 7.5%, and 10%, respectively, and uses a thermogravimetric analyzer to observe the relationship between the amount of glass powder added and oxidation as shown in FIG. 4A, and Use the cross-section of Figure 4B to observe the effect of the amount of glass powder added on the microstructure. It can be observed from the thermogravimetric analyzer that the degree of oxidation increases with the addition amount of the glass frit, and there is almost no significant oxidation after the addition to 7.5% of the glass frit. With the cross-section microstructure, it can be found that the addition of glass powder is too small to effectively cover all the aluminum powder and cause the liquid metal aluminum to flow out to produce aluminum shell; adding excessive glass powder will block the contact area of liquid metal aluminum due to resistance and contact. The area is proportional to the high resistivity; thus, it can be seen that the proper addition of the glass powder can not only inhibit oxidation but also increase the chance of contact with the liquid metal aluminum, thereby greatly reducing the resistivity. Therefore, the optimum glass frit addition amount of the present invention is 7.5%, and the ratio of the aluminum powder to the glass frit is 10:1. The present invention utilizes the above results to increase the solids content. Table 1 shows the formulation, electrical properties, and sintering temperature of each aluminum paste. The results are shown in Figure 5. Figure (a) shows that the aluminum powder does not match the proportion of glass powder (25:1). The resistance of the content sheet decreased from 13.59mΩ/sq to 9.51mΩ/sq, which was only about 30% lower; and the resistance of the (a) aluminum powder to the glass powder matched (10:1) increased the solid content sheet resistance from 10.87. The mΩ/sq is greatly reduced to 4.53mΩ/sq, effectively reducing the sheet resistance of about 60%. This result also shows the importance of the ratio of aluminum powder to glass powder, and the cross-section microstructure of Figure 5 can also be seen to match. The ratio of the aluminum powder to the glass powder can effectively increase the conductive path and achieve a dense structure, thereby realizing a high-conductivity, low-cost and thick film conductive aluminum paste which can be sintered in the air. Table I In Fig. 6, (a) is a conventional aluminum paste and (b) is a cross-sectional microstructure of the novel aluminum paste of the present invention, and the difference between the conventional aluminum paste and the novel aluminum paste microstructure of the present invention can be seen that the novel aluminum paste aluminum of the present invention can be seen. Conductive paths are clearly formed between the particles, and the degree of stack compactness is significantly improved. Table 2 compares the characteristics of the novel aluminum paste with various thick film conductors. As can be seen from the comparison results, the present invention can improve the low conductivity of the conventional aluminum paste, provide a low cost, high electrical conductivity, and can be sintered in air. The conductive aluminum paste can widely replace the high-cost conductive silver paste and the conductive copper paste which needs to be sintered under a reducing atmosphere. Table II The invention provides a low-cost, high-conductivity thick-film conductive aluminum paste which can be sintered in air, which can greatly reduce the production cost of producing thick film resistors. When used in a specific embodiment of a thick film resistor terminal electrode, the vulcanization test conditions are: a temperature of 105 ± 2 ° C, a time of 1000 hours, and a saturated sulfur vapor (δR / R < 1%). The 1000-hour reliability vulcanization test shown in Figure 7 shows that the traditional silver-end electrode reacts with sulfur to form silver sulfide, which causes the resistance value to be undetectable or severely drifted after 1000 hours of testing. Conversely, the present invention uses a high conductivity aluminum paste. The application of the thick-film resistor aluminum terminal electrode for 1000 hours vulcanization reliability test results interface is very clean, which means that sulfur and aluminum will not react, so the resistance is very stable after the test. Figure 8 (a) shows the method for filling and metallizing the LED ceramic substrate 5 by using the high-conductivity aluminum paste 4 without shrinking. The result of the figure (b) shows that the conductive aluminum paste 4 of the present invention has printing. The advantages of post-sintering and post-sintering dimensions are completely unchanged. It is apparent that the present invention is particularly helpful for filling or metallized electrodes requiring high precision variations. Therefore, as shown in the above-mentioned sixth to eighth figures, the present invention uses the innovative technology to thoroughly improve the defects such as the porous hole and the aluminum hollow shell, and can greatly improve the electrical conductivity, realize a high electrical conductivity, low cost, and can be sintered in the air. Membrane conductive aluminum paste, and can be applied to thick film resistor terminal electrode, LED ceramic substrate filling and metallization process, internal electrode and terminal electrode of passive component, back conductor paste of solar cell, printed circuit board (PCB) Electrode wafer. Therefore, the present invention has the following technical characteristics and advantages: 1. The object of the present invention is to improve the low conductivity of a conventional aluminum paste, to provide a low-cost, high-conductivity thick-film conductive aluminum paste which can be sintered in air. And can widely replace the existing high-cost conductive silver paste and the application of conductive copper paste to be sintered under a reducing atmosphere. 2. The invention utilizes a wide particle size distribution and a high solid content to solve the problem of the porous hole, and fully utilizes the alumina rupture mechanism to match enough liquid glass powder to promote the internal liquid metal aluminum to contact each other to form a conductive path. Thoroughly improve the low conductivity of aluminum paste. 3. According to the above experiment, it is found that the large-diameter aluminum powder is easy to be broken and forms a conductive path. The small-diameter aluminum powder is not easy to be broken, and it is easy to fill the hole. Therefore, the large particle size is the main method, and the small particle size is supplemented to obtain a stack dense. The electrical size is preferably 4:1. 4. After the alumina is ruptured, the liquid crystal powder must be sufficient to wet all the aluminum powder, thereby inhibiting the exposure of the exposed liquid metal aluminum to the oxidation and increasing the conductivity of the liquid metal aluminum. It is best to suppress the oxidation effect by adding 7.5% glass powder by thermogravimetric analysis, and the ratio of aluminum powder to glass powder is 10:1. 5. After obtaining the optimal size-to-size ratio and the ratio of the best aluminum powder to the glass powder, the solid content is increased in proportion, and the sheet resistance is 4.53 mΩ/sq which is close to the silver paste and the copper paste. In summary, the present invention is a method for manufacturing a high-conductivity thick-film aluminum paste, which can effectively improve various disadvantages of low conductivity of defects such as porous holes and aluminum shells of conventional aluminum paste, and can greatly improve conductivity and realize one. A low-film, high-conductivity, thick-film conductive aluminum paste that can be sintered in air, and can widely replace the existing high-cost conductive silver paste and the conductive copper paste to be sintered under a reducing atmosphere, thereby enabling the present invention The production can be more progressive, more practical, and more in line with the needs of the user. It has indeed met the requirements of the invention patent application, and has filed a patent application according to law. However, the above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto; therefore, the simple equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the invention are modified. All should remain within the scope of the invention patent.

1‧‧‧Aluminum powder 11‧‧‧Solid metal aluminum 12‧‧‧Liquid metal aluminum 13‧‧‧Surface alumina 14‧‧‧Electrical path 2‧‧‧Glass powder 3‧‧‧Adhesive 4‧‧‧Aluminum Paste 5‧‧‧ceramic substrate

Fig. 1A is a schematic view showing the manufacturing process of the present invention. Figure 1B is a schematic view of the alumina rupture mechanism of the present invention. Fig. 1C is a schematic view showing the use of the present invention. Fig. 2A is a schematic diagram showing the thermogravimetric analysis of the sized aluminum powder particles of the present invention. Fig. 2B is a schematic view showing the surface microstructure of the sized aluminum powder particles of the present invention. Fig. 3 is a schematic view showing the microstructure of aluminum powder of different sizes and sizes in the present invention. Figure 4A is a schematic diagram of thermogravimetric analysis of the present invention with different amounts of glass added. Figure 4B is a schematic view showing the microstructure of the present invention in which different proportions of glass are added. Fig. 5 is a schematic view showing the microstructure of the aluminum powder and the glass powder of the present invention. Fig. 6 is a schematic view showing the microstructure of the novel aluminum paste and the conventional aluminum paste of the present invention. Fig. 7 is a schematic view showing the results of reliability vulcanization test of a thick film resistor terminal electrode of a high conductivity thick film aluminum paste of the present invention. Figure 8 is a schematic view showing the structure of the present invention applied to the hole filling and metallization process of the LED ceramic substrate. Figure 9, is a schematic diagram of the microstructure of a conventional thick film aluminum paste after sintering

1‧‧‧Aluminum powder

11‧‧‧Solid metal aluminum

12‧‧‧Liquid metal aluminum

13‧‧‧ surface alumina

14‧‧‧Electrical path

2‧‧‧Glass powder

Claims (3)

The invention relates to a method for manufacturing a high conductivity thick film aluminum paste, which comprises at least the following steps: (A) providing an aluminum powder having different particle diameters, and the size ratio of the aluminum powder is 4±50%: 1±50% (B) mixing the aluminum powder with a glass frit, wherein the glass frit has a solid content of 7.5 wt% ± 50%, and the ratio of the aluminum powder to the glass frit total solid content is 10:1; and (C) The aluminum powder and the glass powder mixture are subjected to liquid phase sintering at a sintering temperature of at least 500 ° C or higher, and the sintering temperature is such that the aluminum powder in the mixture can be covered with the surface alumina cracking mechanism and the liquid glass powder. The ruptured surface of the aluminum powder oxidizes by inhibiting the exposed liquid metal aluminum from contacting the air, and causes adjacent bare liquid metal aluminum to contact each other to form a conductive path, thereby obtaining a dense and non-shrinking thick film conductive aluminum paste. The method for producing a high-conductivity thick-film aluminum paste according to claim 1, wherein the thick-film conductive aluminum paste has a sheet resistance of less than 5 mΩ/sq. The method for producing a high-conductivity thick-film aluminum paste according to the first aspect of the invention, wherein the aluminum powder has a large particle size of 4 to 6 μm and a small particle size of 1 to 3 μm.