Silver-palladium bonding wire and preparation method and application thereof

Abstract

The invention provides a silver-palladium bonding wire and a preparation method and application thereof, and relates to the technical field of bonding wires. Specifically, the method comprises the following steps that raw materials of silver and palladium are subjected to vacuum induction melting, and silver-palladium alloy is obtained; a silver-palladium wire rod with the diameter of 0.1-6 mm is obtained through continuous casting and first drawing; then acid pickling treatment, ultrasonic cleaning and drying treatment are conducted in sequence; performing vacuum heat treatment at a specific temperature to obtain a wire rod covered with a palladium layer on the surface; and finally, carrying out second drawing to obtain the silver-palladium bonding wire with the diameter of 0.02-0.5 mm. According to the method, the pure palladium layer with good binding force can be formed on the surface of the silver-palladium alloy through vacuum heat treatment; and the preparation method of the silver-palladium bonding wire, which is simple in process, high in yield, excellent in quality and green and environment-friendly, is obtained by combining surface treatment with two times of drawing processes, and has an important value for promoting the development of an electronic packaging technology.

Description

Technical Field

[0001] The present invention relates to the technical field of bonding wires, and in particular to a silver-palladium bonding wire and a preparation method and application thereof. Background Art

[0002] With the development of miniaturization and high performance of electronic products, the requirements for chip packaging technology are constantly increasing. Silver-palladium alloy wire is gradually replacing gold wire as the mainstream bonding material due to its good conductivity, oxidation resistance and cost-effectiveness. However, silver-palladium bonding wire faces several key technical challenges in practical applications: insufficient bonding strength, unstable interface bonding, easy cracking or falling off, and long-term reliability, especially in high temperature and high humidity environments, needs to be improved. In addition, the surface state also has a significant impact on the bonding performance of silver-palladium bonding wire, including surface oxidation, roughness and insufficient activity.

[0003] To solve the above problems, the industry currently mainly uses surface modification technology to improve the bonding performance of silver-palladium wire. Existing surface treatment methods, such as electrochemical treatment, chemical treatment and physical treatment, can improve the bonding performance of silver-palladium wire, but they all have problems such as complex processes, environmental pollution and limited effects. These traditional methods require multiple processes, strict parameter control, and it is difficult to ensure product consistency; at the same time, traditional processes use a large number of chemical reagents, generate hazardous waste, and have high processing costs; and the coating bonding strength is not ideal, the durability needs to be improved, and the cost-effectiveness is relatively low.

[0004] In view of this, the present invention is proposed to provide a simple, environmentally friendly and efficient silver-palladium bonding wire surface treatment method, which has important scientific value and engineering significance. Summary of the invention

[0005] The first purpose of the present invention is to provide a method for preparing a silver-palladium bonding wire, which is used to comprehensively solve the following four defects that are widely present in conventional silver-palladium bonding wire surface treatment methods: first, the process flow is complicated, the production line needs to be equipped with a variety of special equipment, and the production cost is high; second, the chemical treatment process uses a large amount of harmful chemical reagents, and the heavy metal waste liquid and waste gas generated seriously pollute the environment; third, the surface treatment process parameter control precision requirements are high, and the product batch consistency is poor; fourth, the coating adhesion and uniformity are not ideal, and the bonding interface stability is poor, which cannot meet the stringent requirements of high-end electronic packaging for bonding wires.

[0006] The second object of the present invention is to provide a silver-palladium bonding wire, comprising a silver-palladium inner core and a high-purity palladium protective layer covering the surface.

[0007] The third object of the present invention is to provide the use of the silver-palladium bonding wire in packaging.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] A method for preparing a silver-palladium bonding wire comprises the following steps:

[0010] (1) subjecting raw materials silver and palladium to vacuum induction melting to obtain a silver-palladium alloy; and obtaining a silver-palladium wire having a diameter of 0.1 mm to 6 mm through continuous casting and first drawing;

[0011] (2) sequentially subjecting the silver-palladium wire to acid washing, ultrasonic cleaning and drying;

[0012] (3) subjecting the wire material treated in step (2) to vacuum heat treatment to obtain a wire material covered with a palladium layer on its surface; wherein the temperature of the vacuum heat treatment is T, and the melting point of the silver-palladium alloy is T m , T m -200<T<T m -30;

[0013] (4) The wire obtained in step (3) is subjected to a second drawing to obtain a silver-palladium bonding wire with a diameter of 0.02 mm to 0.5 mm.

[0014] A silver-palladium bonding wire is prepared according to the preparation method of the silver-palladium bonding wire, and the use of the silver-palladium bonding wire in packaging.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention provides a new process idea for preparing a silver-palladium bonding wire. First, a silver-palladium wire with a relatively large diameter is prepared, and then a multi-stage surface treatment is performed to ensure the surface cleanliness and activity of the wire. A high-purity palladium layer is formed by vacuum heat treatment under specific conditions. Finally, the drawing ratio and speed are precisely controlled to ensure that the surface palladium layer is denser and the bonding force between the silver and palladium layers is improved, thereby obtaining a silver-palladium bonding wire with a palladium protective layer on the surface.

[0017] In the present invention, by designing specific vacuum heat treatment conditions, a palladium layer with good bonding force can be formed on the surface of the silver-palladium alloy; based on this concept and combined with a specific two-drawing process, the present invention obtains a preparation method for a silver-palladium bonding wire with simple process, high yield and excellent quality, which is of great value to promoting the development of electronic packaging technology.

[0018] Compared with similar structure bonding wire products, the preparation process of the present invention has significant advantages and effects over the current electroplating and chemical plating technologies. First, the process flow of the present invention is greatly simplified, which significantly reduces the production complexity and operation difficulty. Except for the consistent alloy smelting and preliminary drawing, the process flow of conventional palladium electroplating includes at least ultrasonic cleaning-electrolytic degreasing-ultrasonic cleaning-pickling-ultrasonic cleaning-electroplating-post-treatment and other steps, while the present invention only requires pickling-ultrasonic cleaning-vacuum heat treatment-drawing to complete. Secondly, the environmental protection performance of the present invention is significantly improved, completely eliminating the generation and treatment problems of heavy metal-containing waste liquid, reducing environmental pollution, and reducing the cost of raw materials and waste treatment. Thirdly, the present invention has advantages in performance such as high bonding degree of palladium layer and high yield rate. These advantages and effects fully demonstrate the technical innovation and industrial application value of the method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 A physical picture of the surface state of Example 1 after surface pretreatment is provided;

[0021] Figure 2 A physical picture of the state after the palladium layer is formed on the surface of Example 1 after vacuum heat treatment is provided;

[0022] Figure 3 Provides a SEM image of the surface palladium layer of Example 1 when it is drawn to a diameter of 2 mm;

[0023] Figure 4 Provides a SEM image of the surface palladium layer of Example 1 when it is drawn to a diameter of 1 mm;

[0024] Figure 5 Provides a SEM image of the surface palladium layer of Example 1 when it is drawn to a diameter of 0.5 mm;

[0025] Figure 6 A SEM image of the surface palladium layer of Example 1 when it was drawn to a diameter of 0.12 mm is provided. DETAILED DESCRIPTION

[0026] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but those skilled in the art will appreciate that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those who do not specify the manufacturer for reagents or instruments used are all conventional products that can be purchased commercially. In addition, the terms "one", "1", "2", etc. are only used for descriptive purposes and cannot be interpreted as indicating or implying relative importance.

[0027] The first aspect of the present invention is to provide a method for preparing a silver-palladium bonding wire, comprising the following steps: (1) subjecting raw materials silver and palladium to vacuum induction melting to obtain a silver-palladium alloy; obtaining a silver-palladium wire with a diameter of 0.1 mm to 6 mm by continuous casting and first drawing; (2) subjecting the silver-palladium wire to acid washing, ultrasonic cleaning and drying in sequence; (3) subjecting the wire treated in step (2) to vacuum heat treatment to obtain a wire covered with a palladium layer on the surface; wherein the temperature of the vacuum heat treatment is T, with the melting point of the silver-palladium alloy as T m , T m -200<T<T m -30; (4) The wire obtained in step (3) is subjected to a second drawing to obtain a silver-palladium bonding wire with a diameter of 0.02 mm to 0.5 mm.

[0028] It is worth noting that in the present invention, the diameter of the silver-palladium wire in step (1) must be greater than the diameter of the silver-palladium bonding wire in step (4), and the second drawing must be carried out. There is no situation where the second drawing is not carried out because the silver-palladium wire is lower than the expected diameter of the silver-palladium bonding wire; for example, when the diameter of the silver-palladium wire takes the lower limit of 0.1 mm, the diameter of the silver-palladium bonding wire is <0.1 mm and ≥0.02 mm.

[0029] In step (1) of the present invention, high-purity silver raw materials and palladium raw materials are first smelted, and the alloy base material is further cast to obtain a wire starting material. By defining the following specific processes and parameters, it is possible to ensure that a wire with a smooth surface and uniform internal structure is obtained in the initial step, providing quality conditions for the subsequent steps.

[0030] As a preferred embodiment, the purity of the raw silver and raw palladium is ≥99.99%; in a more preferred embodiment, the purity of the raw silver and raw palladium is ≥99.999%.

[0031] As a preferred embodiment, in the silver-palladium alloy, the palladium content is ≥0.5wt.%; in a more preferred embodiment, the silver-palladium alloy includes 0.5wt.% to 20wt.% palladium; it can be understood that, excluding the unavoidable trace impurities, the silver-palladium alloy includes 0.5% to % palladium and % to 99.5% silver by mass.

[0032] As a preferred embodiment, the temperature of the vacuum induction melting is 1000°C to 1100°C, the holding time of the vacuum induction melting is 20min to 30min, and the vacuum degree of the vacuum induction melting is greater than 10 -3 Pa; in some optional embodiments, the temperature of the vacuum induction melting includes but is not limited to any one of 1000, 1010, 1020, 1030, 1040, 1050, 1060, 1070, 1080, 1090, 1100 (°C) or a numerical range consisting of any two of them.

[0033] As a preferred embodiment, the continuous casting is carried out under vacuum conditions for reasons of anti-oxidation and prevention of the introduction of impurities. In some more preferred embodiments, the continuous casting adopts a bottom-draw vacuum continuous casting technology, wherein the bottom-draw refers to a process in which the casting is pulled downward in accordance with the gravity of the metal after the molten metal solidifies in the crystallizer. The bottom-draw vacuum continuous casting technology helps to enhance the density and precision of the casting and reduce the generation of internal sand holes, shrinkage holes or cavities, thereby obtaining higher quality casting wire.

[0034] As a preferred embodiment, the continuous casting speed is 10 mm / min to 100 mm / min to ensure that the wire has a uniform and dense organizational structure and to improve the production efficiency of continuous casting under the premise of having good quality.

[0035] As a preferred embodiment, the diameter of the silver-palladium wire after the first drawing includes but is not limited to any one of 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6 (mm) or a numerical range composed of any two of them.

[0036] As a preferred embodiment, the surface reduction rate of the first drawing is controlled at 7% to 30%, and the drawing speed of the first drawing is controlled at 10m / min to 500m / min. The surface reduction rate can be understood as the ratio of the difference in cross-sectional area before and after each drawing to the cross-sectional area before drawing; by controlling the surface reduction rate and the drawing speed, a wire with better mechanical properties such as strength, hardness, and toughness can be obtained, while controlling it to have good surface quality and uniform internal structure, avoiding cracks and oxidation and having good finish.

[0037] In step (2) of the present invention, the surface pretreatment is carried out by pickling and ultrasound, which can not only thoroughly clean the wire after drawing, but also improve the surface activity of the wire, which is helpful for the subsequent heat treatment to form a high-purity surface coating.

[0038] As a preferred embodiment, the acid reagent for the pickling treatment includes an aqueous solution of one or more of hydrochloric acid, sulfuric acid or nitric acid, and the acid concentration is 4wt.% to 10wt.%; in some more preferred embodiments, the acid reagent for the pickling treatment adopts a 5wt.% nitric acid solution.

[0039] As a preferred embodiment, the medium for ultrasonic cleaning includes but is not limited to water, ethanol, acetone, etc.

[0040] As a preferred embodiment, the ultrasonic power of the ultrasonic cleaning is 30W to 100W, preferably 30W to 50W, and the time of the ultrasonic cleaning is 5min to 10min.

[0041] As a preferred embodiment, the drying temperature is 70°C to 90°C.

[0042] In step (3) of the present invention, high temperature and long time vacuum heat treatment is adopted. Since the saturated vapor pressure of silver is much higher than the saturated vapor pressure of palladium at the same temperature, the silver on the surface of the alloy is volatilized and the remaining palladium is attached to the surface through the specific high temperature vacuum environment of this step, thereby obtaining a wire having a high purity palladium layer covered on the surface; at this time, the palladium on the surface is relatively loose, and the subsequent second drawing makes the surface palladium more dense and more closely attached to the substrate.

[0043] As a preferred implementation, after the vacuum heat treatment, the thickness of the pure palladium layer on the surface of the wire is 1 μm to 10 μm.

[0044] As a preferred embodiment, the temperature T of the vacuum heat treatment is based on the melting point of the silver-palladium alloy. m T m -200<T<T m-30; that is, the temperature of the vacuum heat treatment is lower than the melting point of the silver-palladium alloy, and the difference between the two is controlled between 30 and 200; the holding time t (unit: h) of the vacuum heat treatment satisfies: t = a*(T m -T-30)+b, a and b are both empirical parameters set by the present invention, a (unit: h / ℃) = 0.03~0.06, b (unit: h) = 1.5~2.5, and in the more preferred case, b is 2.

[0045] As an optional implementation manner, the temperature of the vacuum heat treatment is 770°C to 1050°C.

[0046] As a preferred embodiment, the vacuum degree of the vacuum heat treatment is greater than 10 -2 Pa, moisture content <1ppm, by ensuring that there is no oxygen and water vapor inside the furnace body of the vacuum heat treatment, oxidation of the wire surface is avoided.

[0047] In the secondary drawing in step (4) of the present invention, the loose surface palladium layer obtained by the previous heat treatment is uniformly and densely loaded on the surface of the silver-palladium substrate while reducing the diameter, making the surface palladium layer denser and increasing the bonding force between the silver and palladium layers.

[0048] As a preferred embodiment, the surface reduction rate of the second drawing is controlled at 10% to 30%, and the drawing speed of the second drawing is controlled at 10m / min to 100m / min. Similarly, in this drawing, it is also necessary to control the surface reduction rate and the drawing speed to obtain a wire with better mechanical properties and surface properties.

[0049] As a preferred embodiment, the diameter of the silver-palladium bonding wire includes but is not limited to any one of 0.02, 0.04, 0.05, 0.06, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 (mm) or a numerical range consisting of any two of them.

[0050] The second aspect of the present invention is to provide a silver-palladium bonding wire product prepared by the preparation method of the silver-palladium bonding wire as described in the first aspect.

[0051] The third aspect of the present invention is to provide the use of the silver-palladium bonding wire product as described in the second aspect in packaging; it can be understood that the use includes but is not limited to other bonding wire products containing the silver-palladium bonding wire, packaging processes based on the silver-palladium bonding wire, electronic products obtained by packaging based on the silver-palladium bonding wire, etc. Any method or product related to packaging when containing the silver-palladium bonding wire belongs to an embodiment of this aspect.

[0052] Example 1

[0053] S1. Alloy wire preparation:

[0054] High purity (>99.99%) silver and palladium raw materials, with a palladium content of 2wt.% and a silver content of 98wt.%, were used for vacuum induction melting. The melting temperature was controlled at 1050°C and the vacuum degree was controlled at 5*10 -4 Pa, the holding time is 25min. The silver-palladium alloy obtained by smelting is subjected to downward vacuum continuous casting technology, and the continuous casting speed is controlled at 20mm / min to form a wire billet with a diameter of 8mm. The obtained wire billet is drawn multiple times, and the surface reduction rate of each pass is controlled at 12%, and the drawing speed is controlled at 25m / min, until a wire with a diameter of 3mm is obtained.

[0055] S2. Surface pretreatment:

[0056] The wire obtained in step S1 was first pickled with a 5wt.% nitric acid solution, and the solution was stirred at a speed of 40r / min, a temperature of 25°C, and a soaking time of 60s. Then, anhydrous ethanol ultrasonic cleaning was performed again, the temperature was controlled at 35°C, the time was controlled at 10min, and the power was controlled at 400W. Then, it was rinsed with deionized water and dried at 80°C for 30min.

[0057] Observe the wire after surface pretreatment obtained in this step. Figure 1 shown.

[0058] S3. Vacuum heat treatment:

[0059] Heat treatment is performed in the wire vacuum heat treatment furnace obtained in step S2, and the vacuum degree is controlled to be higher than 5*10 -4 Pa, the temperature is controlled at 850 ° C, kept at this temperature for 6 hours and cooled with the furnace.

[0060] The wire obtained after vacuum heat treatment in this step is observed, and the actual product is as follows Figure 2 As shown, in Figure 2 It can be seen that a palladium layer is formed on the surface of the wire.

[0061] S4. Drawing process:

[0062] The wire obtained in step S3 is drawn for multiple times, with the surface reduction rate of each pass controlled at 12% and the drawing speed controlled at 50 m / min, until the wire is drawn to 0.120 mm.

[0063] as follows Figure 3 , Figure 4 , Figure 5 , Figure 6The SEM images of the palladium layer on the surface of the wire in this step correspond to the diameters of 2 mm, 1 mm, 0.5 mm, and 0.12 mm, respectively. Figures 3 to 6 The evolution of shows that the surface state of the palladium layer on the wire surface changes with the drawing diameter. It can be seen that the specific drawing process can make the surface palladium layer denser and increase the bonding force between the silver and palladium layers.

[0064] Example 2

[0065] It is basically the same as Example 1, except that the palladium content in S1 is 1 wt.%, and the silver content is 99 wt.%.

[0066] Example 3

[0067] It is basically the same as Example 1, except that the palladium content in S1 is 3wt.%, and the silver content is 97wt.%.

[0068] Example 4

[0069] The process is basically the same as Example 1, except that the temperature in S3 is controlled at 800° C. and kept at this temperature for 8 hours.

[0070] Example 5

[0071] It is basically the same as Example 1, except that in S4, the surface reduction rate of each pass is controlled at 24%, and the drawing speed is controlled at 25 m / min.

[0072] Comparative Example 1

[0073] It is basically the same as Example 1, except that the ultrasonic cleaning in step S2 is eliminated.

[0074] Comparative Example 2

[0075] The process is basically the same as Example 1, except that the temperature in S3 is controlled at 500° C. and kept at this temperature for 8 hours.

[0076] Comparative Example 3

[0077] It is basically the same as Example 1, except that in S4, the surface reduction rate of each pass is controlled at 32%, and the drawing speed is controlled at 10 m / min.

[0078] Comparative Example 4

[0079] It is basically the same as Example 1, except that the palladium content in S1 is 0.1wt.%, and the silver content is 99.9wt.%.

[0080] Test example

[0081] The following performance tests were performed on the bonding wires prepared in the embodiments and comparative examples, and the test results are recorded in Table 1.

[0082] (1) Palladium layer porosity test: The bonding interface between the coating and the substrate is observed by scanning electron microscopy to measure the porosity. Specifically, the scanning electron microscope can provide high-resolution images that can clearly show the coating surface and its pore distribution. Based on the SEM image, the image analysis software is used to calculate the ratio of the area of ​​pores on the coating surface or the bonding interface to the total area to obtain the percentage value of the porosity.

[0083] (2) Yield rate: The above-mentioned embodiments and comparative examples were repeated 100 times, and the number of finished products obtained and the corresponding yield rate were calculated.

[0084] Table 1

[0085] Porosity Yield Example 1 2.5％ 90％ Example 2 3％ 88％ Example 3 1.8％ 92％ Example 4 4.2％ 85％ Example 5 3.8％ 87％ Comparative Example 1 10％ 60％ Comparative Example 2 12.5％ 58％ Comparative Example 3 8％ 50％ Comparative Example 4 18.9％ 45％

[0086] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a silver-palladium bonding wire, characterized in that: The steps include: (1) subjecting raw materials silver and palladium to vacuum induction melting to obtain a silver-palladium alloy; and obtaining a silver-palladium wire having a diameter of 0.1 mm to 6 mm through continuous casting and first drawing; (2) sequentially subjecting the silver-palladium wire to acid washing, ultrasonic cleaning and drying; (3) subjecting the wire material treated in step (2) to vacuum heat treatment to obtain a wire material covered with a palladium layer on its surface; wherein the temperature of the vacuum heat treatment is T, and the melting point of the silver-palladium alloy is T m , T m -200<T<T m -30; (4) The wire obtained in step (3) is subjected to a second drawing to obtain a silver-palladium bonding wire with a diameter of 0.02 mm to 0.5 mm.

2. The method for preparing a silver-palladium bonding wire according to claim 1, characterized in that: In the silver-palladium alloy, the palladium content is ≥ 0.5wt.%; Preferably, the palladium content is 0.5 wt.% to 20 wt.%.

3. The method for preparing the silver-palladium bonding wire according to claim 1, characterized in that: The temperature of the vacuum induction melting is 1000° C. to 1100° C., and the insulation time of the vacuum induction melting is 20 min to 30 min.

4. The method for preparing a silver-palladium bonding wire according to claim 1, characterized in that: The continuous casting speed is 10 mm / min to 100 mm / min.

5. The method for preparing a silver-palladium bonding wire according to claim 1, characterized in that: The surface reduction rate of the first drawing pass is 7% to 30%, and the drawing speed of the first drawing is 10 m / min to 500 m / min.

6. The method for preparing a silver-palladium bonding wire according to claim 1, characterized in that: The ultrasonic power of the ultrasonic cleaning is 30W to 100W, and the time of the ultrasonic cleaning is 5min to 10min.

7. The method for preparing a silver-palladium bonding wire according to claim 1, characterized in that: The holding time of the vacuum heat treatment is t, which satisfies: t = a*(T m -T-30)+b; Wherein, a = 0.03-0.06, b = 1.5-2.5; a is measured in h / °C, b and t are both measured in h; Preferably, the vacuum degree of the vacuum heat treatment is > 10 -2 Pa.

8. The method for preparing a silver-palladium bonding wire according to claim 1, characterized in that: The surface reduction rate of the second drawing pass is 10% to 30%, and the drawing speed of the second drawing is 10 m / min to 100 m / min.

9. The silver-palladium bonding wire prepared by the method for preparing the silver-palladium bonding wire according to any one of claims 1 to 8.

10. Use of the silver-palladium bonding wire as claimed in claim 9 in packaging.

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