TW201326435A - Copper-palladium alloy wire formed by solid phase diffusion reaction and the manufacturing method thereof - Google Patents

Abstract

The invention relates to a copper-palladium alloy wire formed by a solid phase diffusion reaction and the manufacturing method thereof. Primarily, the method comprises the following steps: a palladium-containing coating layer is formed on a surface of a core wire made of copper or copper alloy; the core wire is proceeded with vacuum heat treatment so that the palladium-containing coating layer is diffused to a base of the core wire; and a uniform copper-palladium alloy layer is form in the organization of the core wire. Accordingly, comparing to a known bonding wire without proceeding with vacuum heat treatment, it has not only better hardness of the center of the sphere, yield strength of the neck and interface tensile strength but also can pass the stricter high temperature storage test to further improve the reliability of the subsequent burning, molding and wire-processing process for the bonding wire.

Description

Solid phase diffusion reaction copper-palladium alloy wire and manufacturing method thereof

The invention relates to a solid phase diffusion reaction copper-palladium alloy wire and a manufacturing method thereof, in particular to a method for completely diffusing a palladium-containing coating layer onto a core wire base by a vacuum heat treatment process, so as to have better spherical core hardness and neck relief. The strength and the interface joint tensile strength, thereby improving the overall yield and yield, and at the same time, through the more stringent high temperature preservation test, improving the reliability of the subsequent ball forming and wire bonding process of the bonding wire, so that the present invention The bonding wires have good soldering properties and bonding properties.

According to the semiconductor package, the wire used in the wire-bonding (WB) process has always been dominated by gold wires, such as gold wires made of high-purity 4N (purity >99.99 mass%) gold and other trace metal elements. As the bonding line of the packaging process; of course, as the price of gold continues to rise, it has reached a high price of 1,600 US dollars per ounce in recent years, leading to the semiconductor rear-end packaging manufacturers to introduce copper wire process to consider the profit of space; In terms of silver wire, copper wire not only has cost advantages, but also has high conductivity and thermal conductivity, and has excellent reliability at high temperatures; however, the problem of high hardness and easy oxidation of copper wire is still the packaging process. The biggest problem, for example, is that when a copper wire is used, since the difference in thermal expansion coefficient between the resin for sealing and the wire is too large, as the temperature rises after the semiconductor wafer is started, the volume expansion due to heat is generated externally to the copper bonding wire forming the circuit. Stress, especially for semiconductor components exposed to severe thermal cycling conditions, makes it easier to cause interfacial peeling and wire breakage problems in copper bond wires; Needle For the above-mentioned deficiencies, please refer to the "Joint Copper Wire for Packaging and Its Manufacturing Method" disclosed in the Republic of China Invention Patent Publication No. 201207129, which discloses a joint copper for packaging. a wire comprising: silver (Ag), an additive, and copper (Cu); wherein the silver content is 0.1 to 3 wt%; and the additive is at least one selected from the group consisting of nickel (Ni), platinum (Pt), and palladium (Pd). a group consisting of tin (Sn) and gold (Au), and the content of the additive is 0.1 to 3 wt%; further, the volume ratio of the copper to silver eutectic phase is 0.1 to 8% of the total volume, and the bonding The tensile strength of copper wire is above 250MPa, and the conductivity is above 70% IACS; thus, not only the impedance is equivalent to or even lower than the traditional gold wire (>70% IACS), but the conductivity is better, the hardness is moderate and easy. Welding, more spherical welding, can also be used under the harsh conditions of heat cycle.

However, although the above-mentioned bonded copper wire can meet the requirements of cost and soldering, it has the defects of easy oxidation and short life. Therefore, the manufacturer further provides a better lead for the integrated circuit package by a surface coating. Bonding performance; please refer to the "Method for Applying Wire Bonded Palladium Surface Coating and Forming Palladium Surface Coating" as disclosed in the Chinese Patent Publication No. 480292, the surface coating of which is formed on a substrate, including a a palladium layer and one or more material layers; the one or more material layers are sandwiched between the substrate and the palladium layer; and when the hardness of the at least one material is less than 250 (KHN50), the palladium layer has a hardness of less than about 500 (KHN50) Wherein the thickness of the palladium layer is preferably greater than 0.075 microns to prevent oxide formation on the underlying material layer; the substrate material may comprise copper or a copper alloy, and the palladium-plated copper wire is substituted for the gold wire, not only It can save about 70% of the material cost, and the reliability of the palladium-plated copper wire when it is used (such as high temperature resistance and high humidity capacity) can also meet the requirements; in addition, please also refer to Nippon Steel High-tech Materials Co., Ltd. Nippon Steel Micro Metals Co., Ltd. has applied for a series of wirings for semiconductor devices, such as the Republic of China invention patent, the "Wiring for semiconductor devices" disclosed in the announcement No. I342809, and the wiring for semiconductor devices disclosed in the announcement No. I364806. "Secondary bonding wire for semiconductors" disclosed in the announcement No. I364806, the second disclosure The "copper alloy bonding wire for semiconductors" of 01107499, the "copper bonding wire for semiconductors and bonding structure thereof" of the publication No. 201140718, and the "joining structure of a plurality of copper bonding wires" of the Japanese Patent No. 201230903; All of them are provided on a surface of a core material (which may be composed of a metal such as copper, gold or silver), and are provided with a skin layer (which may be composed of palladium, rhodium, iridium, platinum, and silver), so that the above-mentioned bonding wire is actually used. The following defects are often caused: (a) Since the surface of the palladium-plated copper wire (core material) has a palladium layer (skin layer), the hardness is high, and the process current control is not easy, often resulting in uneven thickness of the palladium plating layer, resulting in The overall yield of the packaging process is poor, and the yield is low; (b) When the palladium layer is plated on the copper or copper alloy in the electric frame off (EFO), the palladium layer on the surface makes the ball (free air ball, The ball hardness of FAB) is too hard, resulting in insufficient strength of the neck above the solder ball. After wire bonding (WB), the neck fracture problem often occurs, which leads to the problem of joint interface peeling; (c) copper or copper The surface coating formed on the alloy is at high temperature (16 0 ° C, 24 hours) poor storage test, easy to cause surface foaming, resulting in reduced joint strength, from the point of view of reliability, there are problems; and (d) after the ball, the palladium element is almost the neck The segregation in the area is not conducive to the growth of Intermetallic Compound (IMC).

Nowadays, the inventor is in view of the fact that the palladium-plated copper wire used in the conventional semiconductor package still has many defects in practical implementation, so it is a tireless spirit, and with its rich professional knowledge and many years of practical experience. The invention was assisted and improved, and the present invention was developed based on this.

The main object of the present invention is to provide a method for preparing a solid phase diffusion reaction copper-palladium alloy wire, which mainly comprises the following steps: first, preparing a core wire made of copper or a copper alloy; and then, a palladium-containing coating layer is used. For example, sputtering, evaporation or deposition is formed on the surface of the core wire; finally, the core wire is subjected to vacuum heat treatment to completely diffuse the palladium-containing coating layer onto the matrix of the core wire, and A uniform copper-palladium alloy layer is formed in the structure of the core wire; thereby, the palladium-containing coating layer is completely diffused onto the core wire base by a vacuum heat treatment process, so that the prepared semiconductor package bonding wire not only conforms to the roundness after the ball is formed. Requires, and also has better core hardness and neck relief strength, and produces better interfacial joint tensile strength after the wire bonding process; in addition, the prepared bonding wire can also pass the severe high temperature preservation test. Improve the reliability of the subsequent ball forming and wire bonding process of the bonding wire.

Furthermore, in the above preparation step, the temperature range of the vacuum heat treatment is between 300 ° C and 500 ° C, and the treatment time is between 1 and 3 hours; in addition, the thickness of the palladium-containing coating layer formed on the surface of the core wire is Not more than 120 nm.

Another object of the present invention is to provide a semiconductor package bonding wire obtained by the above preparation method; wherein the solid phase diffusion reaction copper-palladium alloy wire has a spherical core hardness of not more than 50 Hv after the ball is formed, and the neck strength is reduced. The tensile strength of the interface bonding is not less than 7.0 g after the bonding wire is formed by the ball forming and wire bonding; thereby, the semiconductor package bonding wire of the present invention has good soldering and bonding properties. , in line with the market's strong demand for output rate and yield.

(S1)‧‧‧Step one

(S2)‧‧‧Step 2

(S3) ‧ ‧ Step 3

(1)‧‧‧ Bonding wire

(11)‧‧‧ solder balls

(12)‧‧‧ neck

(2) ‧‧‧Part surface

(3) ‧‧‧Fixed devices

(4) ‧‧‧ stretching device

First: Flow chart of the preparation method of the solid phase diffusion reaction copper-palladium alloy wire of the present invention

Second: after the completion of step 2 of the present invention, a photomicrograph of the palladium-containing coating layer formed on the surface of the core wire

The third picture: the micrograph of the palladium-containing coating layer completely diffused to the core base after the completion of the third step of the present invention

Figure 4: Schematic diagram of testing the neck drop strength after the bonding wire of the present invention is formed by burning balls

Fig. 5 is a schematic view showing the tensile strength of the test interface joint after the bonding wire of the present invention is formed by the ball forming and wire bonding

Figure 6: Micrograph of the surface blistering after a 24-hour storage test at 160 ° C for a conventional palladium-free bonding wire without vacuum heat treatment

Figure 7: Micrograph of the palladium bonding wire subjected to vacuum heat treatment of the present invention at 160 ° C for 24 hours storage test

The object of the present invention and its structural and functional advantages will be explained in conjunction with the specific embodiments according to the structure shown in the following drawings, so that the reviewing committee can have a more in-depth and specific understanding of the present invention.

First, the solid phase diffusion reaction copper-palladium alloy wire produced by the manufacturing method of the present invention can be applied, for example, to a terminal or circuit surface of an electronic industrial part such as a printed circuit board circuit, an IC package, an ITO substrate, an IC card, or the like; 1 is a flow chart showing the steps of preparing a solid phase diffusion reaction copper-palladium alloy wire according to the present invention, which comprises the following steps: Step 1: preparing a core wire made of copper or copper alloy; Step 2: The palladium-containing coating layer is formed on the surface of the core wire; wherein the palladium-containing coating layer can be formed on the surface of the core wire by sputtering, vapor deposition or deposition, which is not limited thereto; further, the thickness of the palladium-containing coating layer Preferably, it is not more than 120 nm; and Step 3: vacuum-treating the core wire with the palladium-containing coating layer to completely diffuse the palladium-containing coating layer onto the base of the core wire, and form uniform copper palladium in the metallographic structure of the core wire. The alloy layer, that is, the surface layer of the core wire, has no skin layer as described in the prior art; wherein the temperature range of the vacuum heat treatment may be between 300 ° C and 500 ° C, and the treatment time is between 1 and 3 hours.

Next, in order to enable the reviewing committee to further understand the object, features, and effects achieved by the present invention, some specific practical examples of the solid phase diffusion reaction copper-palladium alloy wire prepared by the present invention are exemplified below, and the present invention is further proved. The manufacturing method can be applied in a practical range, but it is not intended to limit the scope of the invention in any form: first, a copper core wire having a wire diameter (φ) of 20 μm is prepared; and then, a thickness of 30 nm, 70 is respectively plated on the surface of the core wire. For nanometer and 120 nm palladium-coated coating, please refer to the second photo, which is a photomicrograph of the palladium-coated coating on the surface of the core wire; then, the three samples are different at 250 ° C ~ 500 ° C Vacuum heat treatment was carried out for 2 hours at the temperature. The table below shows the results of the thickness of the palladium-containing coating remaining on the surface of the core wire:

It can be seen from the above table that the thicker the palladium-containing coating layer on the surface of the core wire, the higher the heat treatment temperature required for the same heat treatment time, and the palladium-containing coating layer can be completely diffused to the core base; for example, when When the thickness of the palladium coating layer is 70 nm, the palladium-containing coating layer can be completely diffused to the core base at 350 ° C for 2 hours under vacuum heat treatment. Please refer to the third figure for complete diffusion of the palladium-containing coating layer. In addition, when the bonding wire (1) of the present invention is prepared and used in the actual implementation of the wire bonding package, the end portion of the bonding wire (1) is generally formed into a ball by a wire bonding machine. For the solder ball (11), please refer to the fourth and fifth figures, and then solder the ball (11) to the printed circuit board circuit, IC chip, ITO substrate, IC card and other electronic industrial parts by ultrasonic hot pressing. Surface (2), the required wire bonding process can be completed; and the following table shows the solder balls of the above three samples after vacuum heat treatment for 2 hours at different temperatures from 250 ° C to 500 ° C ( 11) The true roundness result can be cleared from the table Chu knows that the copper-palladium alloy wire produced by the preparation method of the invention has the ball-burning property in accordance with the requirement of roundness.

Next, please refer to the fourth figure, which is a schematic diagram of testing the neck drop strength after the ball is formed by the bonding wire of the present invention, and the test method is to fix the neck (12) of the bonding wire (1) as a fixing device. (3) clamping and stretching at the other end of the bonding wire (1) corresponding to the solder ball (11) by a stretching device (4) away from the solder ball (11), thereby testing the bonding wire (1) The strength of the neck (12), the test results of the test samples in seven different heat treatment conditions are as follows: wherein the sample A is coated with a palladium-coated layer of 30 nm thickness on the surface of the core wire, and no vacuum is applied. The heat treatment and the sample B were plated on the surface of the core wire with a palladium-coated layer having a thickness of 30 nm, and subjected to vacuum heat treatment at 300 ° C for 2 hours, and the sample C was plated with a palladium-coated layer having a thickness of 70 nm on the surface of the core wire, and Without vacuum heat treatment, sample D was plated with a palladium-coated layer having a thickness of 70 nm on the surface of the core wire, and subjected to vacuum heat treatment at 350 ° C for 2 hours, and sample E was provided with a palladium-coated layer having a thickness of 120 nm, and Vacuum heat treatment, sample F with a palladium coating of 120 nm thickness, and at 250 ° C Vacuum-heat treatment for 2 hours, sample G with a thickness of 120 nm of palladium-containing coating layer, and vacuum heat treatment at 500 ° C for 2 hours; from the results in the table, it is clear that when the palladium-containing coating layer is completely diffused to the core wire At the base, when a uniform copper-palladium alloy layer is formed in the metallographic structure of the core wire (that is, the samples having a palladium-coated coating layer having a thickness of 0 are B, D, and G), the neck drop strength is significantly greater than that without vacuum heat treatment, and The sample containing the palladium-coated coating layer is not completely diffused to the core base, and as a whole, the joint line (1) obtained by the preparation method of the present invention preferably has a neck drop strength of not less than 140 MPa after the ball is formed. Please refer to the fifth figure again, which is a schematic diagram of the tensile strength of the test interface joint after the bonding wire of the present invention is formed by the ball forming and wire bonding, and the test method is after the bonding wire (1) completes the wire bonding process, The bonding wire (1) corresponds to the other surface of the part (2) and is stretched away from the joint surface by a stretching device (4), thereby measuring Test the bonding strength of the interface bonding wire (1), the test results are as follows: It is clear from the table that the tensile strength of the interface bonding of samples B, D and G is significantly greater than that without vacuum heat treatment, or palladium The sample with the coating layer not completely diffused to the core base has a tensile strength of interfacial bonding of preferably not less than 7.0 g; in addition, the present invention also measures the hardness of the ball (11) of the above seven samples, and the result shows that the sample B , D and G are significantly smaller than the sample which is not subjected to vacuum heat treatment, or the palladium-containing coating layer is not completely diffused to the core base. It is understood that when the palladium-containing coating layer is not diffused or not completely diffused to the core base, the bonding wire (1) After the end of the ball is formed into a solder ball (11), the palladium metal contained in the solder ball (11) is mostly accumulated near the neck portion (12), causing segregation of palladium, causing the neck portion (12) to become a bonding wire ( 1) The relative weakness of the structural strength, and the breakage problem occurs easily here; in contrast, the present invention completely diffuses to the bonding wire (1) of the core base, and the palladium metal is uniformly distributed on the solder ball (11), so the hardness of the spherical core is significantly higher. Small, so that after the line process, you can avoid (12) born neck fracture, leading to peeling of the bonding interface problems, and it is understood, the smaller the hardness of the spherical center of the neck portion described above preferably also on the interface between the bonding tensile strength and yield strength.

Finally, please refer to the following table for the comparison table of the above C and D samples. It is obvious that the sample C without vacuum heat treatment has a palladium-coated layer on the surface of the core wire under the storage condition of 160 ° C for 24 hours. Foaming will occur (as shown in the sixth figure), which will inevitably affect the subsequent ball forming and wire-wrapping process; in contrast, the present invention performs vacuum heat treatment at 350 ° C for 2 hours. D, because the palladium-containing coating layer is completely diffused to the base of the core wire, it can pass the storage test at 160 ° C for 24 hours (as shown in the seventh figure), thereby improving the subsequent process of the bonding wire and the reliability of the implementation.

It can be seen from the above description that the present invention has the following advantages compared with the prior art:

1. The present invention heat-treats a core wire having a palladium-containing coating layer to form a uniform copper-palladium alloy layer in the structure of the core wire. Compared with a conventional bonding wire which is not subjected to vacuum heat treatment, the present invention has a better spherical core. Hardness, neck strength, and interfacial tensile strength can not only avoid the problem that the conventional bonding wire often causes neck fracture during use, resulting in the problem of peeling of the joint interface, and since the palladium-containing coating layer of the present invention completely diffuses to On the core wire base, it is also possible to solve the problem that the thickness of the palladium plating layer is uneven, resulting in poor overall output rate and low yield of the packaging process.

2. The solid phase diffusion reaction copper-palladium alloy wire of the present invention has been completely diffused to the base of the core wire by the palladium-containing coating layer, and can be subjected to a relatively high temperature storage test (160 ° C, 24 hours) to further improve the subsequent burning of the bonding wire. The ball forming and the reliability of the wire bonding process make the bonding wire of the present invention have good soldering properties and bonding properties.

In summary, the solid phase diffusion reaction copper-palladium alloy wire of the present invention and the method for producing the same can indeed achieve the intended use efficiency by the above-disclosed embodiments, and the present invention has not been disclosed before the application. It has fully complied with the requirements and requirements of the Patent Law.爰Issuing an application for a patent for invention in accordance with the law, and asking for a review, and granting a patent, is truly sensible.

The illustrations and descriptions of the present invention are merely preferred embodiments of the present invention, and are not intended to limit the scope of the present invention; those who are familiar with the art, Other equivalent changes or modifications made by the present invention within the scope of the invention are considered to be within the scope of the invention.

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(S2)‧‧‧Step 2

(S3) ‧ ‧ Step 3

Claims (8)

A solid phase diffusion reaction copper-palladium alloy wire manufacturing method comprises the following steps: Step 1: preparing a core wire made of copper or copper alloy; Step 2: forming a palladium-containing coating layer on the surface of the core wire; And step 3: vacuum-treating the core wire with the palladium-containing coating layer to completely diffuse the palladium-containing coating layer onto the base of the core wire, and forming a uniform copper-palladium alloy layer in the structure of the core wire. The method for producing a solid phase diffusion reaction copper-palladium alloy wire according to claim 1, wherein the palladium-containing coating layer is formed on the surface of the core wire by sputtering, vapor deposition or deposition. The method for manufacturing a solid phase diffusion reaction copper-palladium alloy wire according to claim 1, wherein the vacuum heat treatment temperature ranges from 300 ° C to 500 ° C, and the treatment time is between 1 and 3 hours. The method for producing a solid phase diffusion reaction copper-palladium alloy wire according to claim 1, wherein the palladium-containing coating layer has a thickness of not more than 120 nm. A solid phase diffusion reaction copper-palladium alloy wire prepared by the method according to any one of claims 1 to 4. The solid phase diffusion reaction copper-palladium alloy wire according to claim 5, wherein the bonding wire has a spherical core hardness of not more than 50 Hv after the ball molding. The solid phase diffusion reaction copper-palladium alloy wire according to claim 5, wherein the neck line after the fire ball is formed has a neck drop strength of not less than 140 MPa. The solid phase diffusion reaction copper-palladium alloy wire according to claim 5, wherein the bonding wire has a tensile strength of not less than 7.0 g after the ball forming and wire bonding treatment.