TW201337009A - Palladium mesh alloy wire without plating thereon and method manufacturing the same - Google Patents

Abstract

The invention relates to a palladium mesh alloy wire without plating thereon and a method manufacturing the same. The manufacturing method comprises the following steps: plating a palladium layer with the thickness of 5-120nm on a surface of a silver baseline, heating it up to 600-800 DEG C and maintaining the temperature for not more than 4 hours so that the palladium on the surface is thermally diffused into the grain boundary grid of the silver baseline to form a grain-boundary band containing palladium. The wire consists of the silver base and grain-boundary band containing palladium. Comparing to the known silver based bonding wire, it has better hardness of the ball, strength of the neck and density of the fusing current. More particularly, it has excellent weather resistance. The invention can be applied to LED manufacturing process directly without using protective gas. Thus it has low impedance and can avoid the application problems of the crooked ball, low strength of the neck and short preservation time caused form the solidification and segregation when the known bonding wires are used.

Description

Uncoated palladium mesh alloy wire and manufacturing method thereof

The invention relates to an uncoated palladium mesh alloy wire and a manufacturing method thereof, in particular to a silver or silver alloy packaged wire without surface plating, which can not only solve the problem that a conventional silver wire must be added with a shielding gas while forming a solder ball. The problem and the reduction of wire metallurgy segregation also have better melting current density and antioxidant effect.

According to the low electrical resistivity, it is a basic requirement for general electronic product packaging wires, and for high-speed operation and high-frequency integrated circuit components (such as high-speed amplifiers, oscillators, power management integrated circuits, and high-speed communication components, etc.) In order to avoid signal delaying and cross talk interference, the resistivity of the wire is more stringent; in addition, to ensure that the product can maintain normal life and function under long-term and severe conditions (weathering Sexuality, reliability considerations are also extremely important; therefore, the packaging industry needs to be able to combine low-impedance and high-reliability wire bonding wires.

At present, common package wires include gold wire, copper wire, silver wire, alloy wire, etc. Taking silver wire as an example, silver is the lowest resistivity element among all materials, and pure silver wire is also generated when wire bonding is performed on the aluminum pad. Brittle intermetallic compound (Ag ₂ Al or Ag ₄ Al); in addition, pure silver wire is prone to ion migration in an aqueous gas encapsulating material, that is, pure silver is hydrolyzed by an electric current in an aqueous gas environment. The silver ions are eluted and reacted with oxygen to become unstable silver oxide (AgO), which deoxidizes to form silver atoms, and grows the leaves of the leaf veins to the positive electrode. Finally, the short circuit of the positive and negative electrodes is caused; therefore, the current pure silver wire does not provide the spheroidality and stability required by the industry; therefore, there are silver-based alloy wires (including elements such as copper, platinum, manganese, chromium, gold, etc.). As a packaged wire, the formed wire still cannot have both low impedance and high reliability.

In addition, in order to solve the problem of oxidation of pure silver bonding wire, some companies have proposed to apply other metal plating on the surface to improve the method of oxidation and corrosion. Please refer to Nippon Steel High-tech Materials Co., Ltd. and Nippon Steel Micro Metals Co., Ltd. Co., Ltd. has applied for a series of wirings for semiconductor devices, the Republic of China invention patent, the "connection wire for semiconductor devices" disclosed in the announcement No. I342809, the "connection wire for semiconductor devices" disclosed in the announcement No. I364806, and the publication No. I364806 The "semiconductor bonding wire" disclosed in Japanese Patent Publication No. 201107499, the "copper bonding wire for semiconductors" of the publication No. 201107418, the "copper bonding wire for semiconductors and the bonding structure thereof", and the bonding of the plurality of copper bonding wires of the publication No. 201230903 The structure of the bonding wire of the above-mentioned prior case is generally formed by a surface layer (which may be composed of palladium, rhodium, ruthenium, platinum, and silver) on a surface of a core material (which may be composed of a metal such as copper, gold or silver). The resulting bonding wire often causes the following defects when actually used: (a) the metal-plated wire has a skin on its surface The layer makes the hardness higher, and the process current control is not easy, which often leads to uneven thickness of the plating layer, resulting in poor overall output rate and low yield in the packaging process; (b) silver or silver alloy plating palladium layer on the ball forming ( When electric frame off (EFO), the palladium layer on the surface makes the core of the free air ball (FAB) hard, resulting in insufficient strength of the neck above the solder ball. After wire bonding (WB), often The problem of neck fracture occurs, which leads to the problem of peeling of the joint interface; and the palladium element also has a segregation problem in the solder ball, and the difference in the structure of the ball portion greatly affects the wire bonding condition.

In addition, generally, the wire bonding wire is melted at the end to form a solder ball, and a gas supply device is continuously supplied with a shielding gas (for example, a mixture of nitrogen, argon or nitrogen-hydrogen) to protect the solder ball, wherein nitrogen and argon are formed. The gas can be coated to protect the solder ball from oxidation, and the hydrogen in the nitrogen-hydrogen mixture can reduce the oxidized portion of the solder ball, which helps to protect the solder ball. Finally, the solder ball is connected to the solder ball. Bonded to the pad of the die or carrier; however, the use of the shielding gas not only increases the manufacturing cost, but also causes improper flow or turbulence when the shielding gas is improperly controlled, which may cause the ball to burn abnormally, so that the wire bonding process is performed. The quality is abnormal, causing problems such as insufficient electrical properties and interface strength; and when the pure silver or silver alloy bonding wire is not spherical in the environment without protective gas, the quality requirement of the process reliability of the LED packaging industry cannot be achieved.

Nowadays, the inventor is in view of the fact that the above-mentioned existing bonding wire for packaging has many defects in practical implementation, so it is a tireless spirit, and with its rich professional knowledge and years of practical experience, Improvements have been made and the present invention has been developed based on this.

The main object of the present invention is to provide an uncoated palladium mesh alloy wire and a manufacturing method thereof, in particular to a silver or silver alloy packaged wire without surface plating, which not only has better ball hardness, neck strength and fusing current density, but also has a better ball hardness, neck strength and fusing current density. It can also solve the problem that the traditional silver wire must be added to the protective gas while forming the solder ball.

In order to achieve the above-mentioned object, the present inventors propose an uncoated palladium mesh alloy wire and a method for fabricating the same, which are produced by plating a palladium layer of 5 nm to 120 nm on a silver substrate surface and heating to a temperature of 600 to 800 ° C. The temperature is continued for less than 4 hours, and the palladium element is completely thermally diffused into the silver base grain boundary grid to form a palladium-containing grain boundary zone; wherein the temperature at which the palladium element is completely thermally diffused is preferably 720 ° C; thereby, Compared with the conventional bonding wire, the present invention not only can maintain low electrical resistance due to the complete solid state diffusion of the palladium particles into the silver-baseline grain boundary grid, but also has a small ball hardness after burning the ball; Avoiding the problem of neck fracture as usual, which leads to the problem of joint interface peeling, and the electrons in the wire can pass through the palladium mesh grain boundary and directly transfer through the silver crystal grain, thus having a lower resistivity. Compared with the non-pure silver wire, it has a large fusing current density; at the same time, the uncoated palladium mesh alloy wire of the invention can avoid the oxidative loss of the conventional bonded silver wire, and the oxidation resistance is also 21 days in an air clean environment. Furthermore, the uncoated palladium mesh alloy wire is in the absence of a protective gas environment, and the experimental results prove that it still has good sphericity, which not only reduces the manufacturing cost of the package, but also does not need to take into account the flow control of the shielding gas, and reduces the process. Factors that affect quality.

In another embodiment of the present invention, the composition of the silver base may comprise 1 to 5 wt.% of a gold element, preferably 3 wt.% of a gold element; thereby, having a better ball hardness and a fusing current density.

The first figure: the microscopic organization diagram of the palladium element completely diffused into the silver basement grain boundary grid after the heat treatment of the uncoated palladium mesh alloy wire of the embodiment 1 of the present invention

Second: Palladium-free alloy line of the second embodiment of the present invention Microscopic organization of the element completely diffused into the silver-baseline grain boundary grid

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 uncoated palladium mesh alloy wire of the present invention is suitable for packaged wires of electronic industrial parts such as IC packages and LED packages; the manufacturing method of the specific embodiment 1 is to apply a palladium layer of 5 nm to 120 nm on a silver base surface. Thereafter, heating to a temperature of 600-800 ° C, continuing the temperature for up to 4 hours, completely diffusing the palladium element into the silver base grain boundary grid, thereby forming a palladium-containing grain boundary band, so that the uncoated palladium of the present invention The mesh alloy wire system is composed of a silver base and a palladium-containing grid grain boundary band. Compared with the conventional silver bond wire, it has better ball hardness, neck strength and fusing current density, and has excellent weather resistance; Referring to the first figure, it is a microscopic organization diagram of the uncoated palladium mesh alloy wire of the first embodiment of the present invention, wherein the palladium element is completely thermally diffused into the silver base grain boundary grid; wherein the preferred heating temperature is 720 ° C; Please refer to the table below, which is plated with a palladium layer with a thickness of 5 nm, 60 nm, 120 nm and 140 nm on the silver baseline (18 μm), and heated to 720 ° C for 30 minutes, 1 hour, 2 hours, 3 hours. And after 4 hours, on the silver baseline surface The experimental data sheet for measuring the residual thickness of the palladium layer; it can be clearly seen that the palladium layer having a thickness of 5 nm to 120 nm, after a temperature of 720 ° C for 30 minutes to 4 hours, the palladium layer on the silver baseline surface will completely diffuse to the silver base crystal. Within the boundary grid, that is, the residue of the surface without palladium.

In addition, the unplated palladium mesh alloy wire of the present invention may have a silver baseline component of 1 to 5 wt. % gold element, preferably contains 3wt. % of the gold element; and in this embodiment 2, a palladium layer having a thickness of 5 nm, 60 nm, 120 nm, and 140 nm is plated on the surface of the silver base, and is heated to 720 ° C for 30 minutes, 1 hour, 2 hours, 3 hours, and After 4 hours, the experimental data table for measuring the thickness of the palladium layer on the silver baseline surface is shown in the following table; it can be clearly seen that the palladium layer having a thickness of 5 nm to 120 nm is contained at a temperature of 720 ° C for 30 minutes to 4 hours. There are 3wt. The palladium layer on the base surface of the silver element of the gold element will also completely diffuse into the silver-baseline grain boundary grid, that is, the residue of the surface without palladium layer. Please refer to the second figure together, which is the second embodiment of the present invention. The plated palladium mesh alloy wire has its palladium element completely thermally diffused into the microstructure of the silver basement grain boundary grid.

Next, the range of practical application of the process of the present invention can be further proved by the following comparative application of the conventional package bonding wire to the specific practical examples 1 and 2, but is not intended to limit the scope of the invention in any form: For the continuous supply of protective gas (such as nitrogen, argon or nitrogen-hydrogen mixture) in the environment, the bonding wire is used to protect the solder ball formed at the end and melt to form a solder ball. The experimental data comparison table; The ball is formed under the environment, and the sphericity of all the samples can be accepted (OK). For the hardness of the ball, the hardness of the ball of the sample ball is measured by a Vicker hardness machine. The solder balls formed in Examples 1 and 2 are significantly smaller in hardness than the non-pure silver wires. It is understood that when the palladium-containing coating layer is not diffused or not completely diffused to the core base, the ends of the bonding wires are formed by burning balls. After soldering the ball, the palladium metal contained in the solder ball mostly accumulates near the neck, causing segregation of palladium, resulting in the neck becoming the strength of the bonding wire structure. The relative weakness is easy to break here; in contrast, the palladium-plated layer of the present invention completely thermally diffuses into the silver-baseline grain boundary grid, so the core hardness is significantly smaller, so that it can be avoided as usual after the wire-laying process In the neck fracture problem, the problem of joint interface peeling occurs; as a result of the experiment, the weld strength of the solder balls formed in the first and second embodiments is significantly larger than that of other bonding wires; The strength of the neck is measured by clamping the neck of the bonding wire with a fixing device (for example, a micro jig), and at the other end of the bonding wire corresponding to the solder ball, with a stretching device facing away from the solder ball. Stretching, thereby testing the strength of the neck of the bonding wire; furthermore, since the palladium particles are completely diffused into the silver-baseline grain boundary grid, electrons in the wire can be transported by the silver crystal grains through the palladium network grain boundaries. It has a lower resistivity and thus has a larger fuse current density than a non-pure silver wire; notably, it contains 3wt. The uncoated palladium mesh alloy wire made of the silver base of the gold element has better ball hardness and fusing current density.

Next, when there is no supply of shielding gas in the environment, the following table shows a comparison table of experimental data for forming the solder balls of the above samples; as can be seen from the table, the supply of shielding gas to the pure silver wire, the Ag+Au+Pd alloy wire, and the palladium plating alloy The sphericity has a significant effect, and the uncoated palladium mesh alloy wire of the present invention still has good sphericity in the absence of a protective gas atmosphere, that is, the present invention can be directly applied to the LED process without requiring a protective gas, not only Considering low impedance and avoiding the application problems of the conventional bonding wire caused by solidification segregation during the use, the neck strength is low, etc. In addition, the present invention also has better oxidation resistance and reaches more than 21 at room temperature. No oxidation in days The effect of solving the problem of short retention time of the conventional bonding wire.

In addition, please refer to the following table to illustrate the sample wiring for the above samples in a protective gas atmosphere, and observe the temperature at 150 ° C, 2000 Hz high temperature storage (HTS) test The intermetallic compound (IMC) condition between the substrate and the substrate; it can be clearly seen that the thickness of the IMC of the first embodiment and the second embodiment is significantly thinner, thereby enhancing the interfacial peel strength and the solder ball joint shear strength, and Good joint reliability.

It can be seen from the above description of the implementation that the present invention is compared with the prior art. Ming has the following advantages:

1. The present invention completely diffuses the palladium layer on the silver baseline surface into the silver baseline grain boundary grid by heat treatment. Compared with the conventional silver bond wire, the present invention has better ball hardness, neck strength and fusing current. The density not only balances the low impedance, but also avoids the problem that the conventional bonding wire often causes the neck to break when it is used, resulting in the problem of peeling of the joint interface.

2. The uncoated palladium mesh alloy wire of the invention still has good spheroidality in the environment without protective gas, which not only reduces the manufacturing cost, but also does not need to take into account the flow control of the shielding gas, and reduces the factors affecting the quality in the process. .

3. The invention can be directly applied to the LED process without protecting gas, and not only the low impedance but also the application problems of the conventional bonding wire caused by solidification segregation during the use, the neck strength is low, and even the storage time is short.

In summary, the uncoated palladium mesh alloy wire of the present invention and the method of manufacturing the same can achieve the intended use efficiency by the above-disclosed embodiments, and the present invention has not been disclosed before the application, and has been completely completed. Meet 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 skilled in the art, which are characterized by the scope of the present invention, Equivalent variations or modifications are considered to be within the scope of the design of the invention.

Claims (5)

The invention discloses a method for manufacturing an uncoated palladium mesh alloy wire by plating a palladium layer of 5 nm to 120 nm on a silver base surface, heating to a temperature of 600 to 800 ° C, and maintaining the temperature for no more than 4 hours, so that the palladium element is completely thermally diffused. The surface of the silver grain boundary grain boundary is formed, thereby forming a palladium-containing grain boundary zone. The method for manufacturing an uncoated palladium mesh alloy wire according to claim 1, wherein the component of the silver base comprises 1 to 5 wt.% of a gold element. The method for producing an uncoated palladium mesh alloy wire according to claim 2, wherein the composition of the silver base line comprises 3 wt.% of a gold element. The method for producing an uncoated palladium mesh alloy wire according to claim 1, wherein the temperature at which the palladium element is completely thermally diffused into the silver base grain boundary grid is 720 °C. An uncoated palladium mesh alloy wire prepared by the method of any one of claims 1 to 4.