CN103985699A - Silver alloy wire - Google Patents

Abstract

A silver alloy wire is composed of silver, palladium and nickel, wherein the content of palladium is 1.8-2.2wt%, the content of nickel is 0.5-2.0wt%, and the balance is silver. By the composition of palladium, nickel and silver and the control of the proportion range of the components, the silver alloy wire has the effects of good performance reliability, routing yield, low resistivity and the like on the premise of reducing the material cost.

Description

Silver alloy wire

technical field

The present invention relates to a silver alloy wire, in particular to a silver alloy wire with silver as the main component, which is specially used for connecting wires in IC (integrated circuit, short for integrated circuit) packaging process.

Background technique

With the advancement of semiconductor technology, the size of components is constantly shrinking, and gradually enters the field of deep sub-micron. When the integration degree of the integrated circuit increases, the surface of the chip cannot provide enough area to make the required interconnection. At this time, it is necessary to use metal connection wires for circuit connection. However, there will be capacitance between the metal connecting wire and the connecting wire, and the metal connecting wire itself will have different resistivity due to different materials. Therefore, the signal will be different due to the different resistivity and capacitance during the transmission process. Produce varying degrees of latency or underclocking. Coupled with the progress of semiconductor manufacturing process, the size of the current metal connecting wires is not only getting smaller and smaller, but also the distance between each other is getting narrower and narrower. Therefore, not only the resistance of the connecting wires is getting larger, but also the capacitance between the connecting wires is also getting smaller Will gradually increase, therefore, the signal transmission speed will be slower and slower. In order to improve the problems of signal transmission delay and frequency reduction, the alloy wires currently used for semiconductor connection will inevitably gradually develop in the direction of low resistivity.

From the perspective of material cost, resistivity, bonding yield, and reliability, etc., the previous metal connecting wires can be roughly divided into gold wires, silver wires, copper wires, and silver alloy wires due to different materials. wait. Among them, gold wire has excellent physical properties such as high stability, soft texture, good ductility, good electrical conductivity, high wire bonding yield, high production efficiency, and fine wire diameter. It is an ideal connecting wire material. However, due to the rising price of gold in recent years, the material cost of using gold wire is not acceptable to customers.

The copper wire includes single crystal copper wire and palladium-coated copper wire. The advantage of using copper wire is that the material cost is low, but one of the disadvantages is that it has high hardness and is easy to break through the aluminum pad. When using it, you need to master more details. , the process is relatively complicated, and it is not easy for manufacturers with general technical capabilities to introduce and use it. The second is that it is easy to oxidize, which requires sealing during storage. At the same time, protective gases such as nitrogen and hydrogen must be used during wiring, which is dangerous when used. In addition, due to the high hardness of copper wire, copper wire and palladium-coated copper wire also have product reliability problems. When used in high-pressure, high-temperature or high-humidity environments, the reliability is not as good as gold wire. Therefore, it cannot be used in High quality product on.

The advantage of using silver wire is that it does not need vacuum packaging during storage, and the hardness of the wire is relatively soft. However, when the silver wire is bonded to the aluminum pad during the wire bonding process, an interim metal compound (IMC for short) will be precipitated at the interface of the molten solder ball. , and in the reliability test environment, the diffusion of silver and aluminum is too fast, which increases the thickness of the intermetallic compound, resulting in solder joint fracture and product failure.

In addition, the Chinese Taiwan TWI373382B1 invention patent provides a composite gold wire, which contains 8-30wt% gold, 66-90wt% silver, and 0.01-6wt% palladium. This kind of composite gold wire is based on the gold component doped with a large amount of silver and palladium that inhibits the growth of boundary metal compounds. The composite silver wire disclosed in the aforementioned invention patent can replace gold wire and copper wire in any packaging form, but the disadvantage is that it still needs to use a relatively high content of gold, so the material cost is still very high. In addition, the composite gold wire The higher the content of palladium and gold, the higher the resistivity, which has an adverse effect on the signal transmission speed.

And Chinese Taiwan No. TW201001652 patent of invention also discloses a kind of alloy wire with silver as the base, adds 0.05-5wt% in this alloy wire and is selected from: platinum (Pt), palladium (Pd), rhodium (Rh), osmium ( Os) and the first additive of the gold (Au) group, and 3ppm-100ppm selected from: beryllium (Be), calcium (Ca), barium (Ba), lanthanum (La), cerium (Ce) and yttrium (Y) The second additive of the group. In addition, US6,723,281B1 also discloses a silver-based substrate, and adds 0.1-3wt% of palladium, and 0.1-3wt% of at least one selected from: aluminum (Al), copper (Cu), chromium (Cr ), titanium (Ti) and cobalt (Co) group elements. The aforementioned invention patents all disclose a silver-based connecting wire, and the composite silver wire is equipped with two kinds of additives selected from different groups. Make the composite silver wire have better physical properties.

However, the higher the palladium content, the higher the resistivity of the composite silver wire. In addition, if the palladium content is low, the composite silver wire is likely to be too thick and form phases with the aluminum pad in a high-temperature, high-pressure or high-humidity environment. Poor boundary metal compounds, so its performance reliability is low. Although the aforementioned patents add elements selected from the second ethnic group, taking copper as an example, due to the problem of easy oxidation of copper, the manufacturing cost in the wire production process and the technical threshold in the wire bonding process are relatively high.

It should be noted that although both the invention patent No. TW201001652 of Taiwan, China and the description of US6,723,281B1 have mentioned that nickel metal can be optionally added to the composite silver wire, the description and examples of the aforementioned patents have never discussed The role played by nickel metal in the composite silver wire has never taught the relationship between the ratio of nickel metal, palladium metal and silver and various physical properties. The present invention mainly improves the silver alloy wire containing palladium, in order to provide a silver alloy wire that can effectively reduce resistivity while maintaining excellent performance reliability and bonding yield under the premise of reducing material cost.

Contents of the invention

The object of the present invention is to provide a silver alloy wire that can achieve a better balance among material cost, resistivity, performance reliability and wire bonding yield.

The silver alloy wire of the present invention is composed of silver, palladium and nickel, wherein the content of palladium is 1.8-2.2wt%, the content of nickel is 0.5-2.0wt%, and the rest is silver.

The silver used in the present invention has a purity of more than 99.99wt%, and the impurities are negligible. And the content of palladium is preferably 1.8-2.2wt%, the best is 2.0wt%. Since the resistivity of palladium is as high as 10.5 μΩ·cm, when the palladium content is higher than 2.2 wt%, the resistivity of the silver alloy wire will gradually increase, which is not conducive to signal transmission. And when the palladium content is lower than 1.8wt%, when the silver alloy wire is used in the bonding of the aluminum pad body, the interface metal compound (IMC) between the silver alloy wire and the aluminum pad body will be generated too quickly, and the The problem of poor performance reliability (Reliability).

The resistivity of the nickel used in the present invention is 6.9μΩ·cm. When the content of nickel is higher, the resistivity of the connecting wire is higher, that is to say, when the content of nickel is higher than 2.0wt%, the resistivity of the connecting wire Will be greater than 3.5μΩ·cm. However, when the nickel content is lower than 0.5 wt%, the performance reliability improvement for the low-resistance silver alloy wire is limited. In the present invention, silver is selected as the substrate, and palladium and nickel are added in a predetermined proportion. The combination of the above composition ratios can form a layer between silver and aluminum pads such as: (Ag-Pd-Ni) ₂ Al, (Ag -Pd-Ni) ₄ Al boundary metal compound, and the formed boundary metal compound has the function of preventing rapid diffusion between silver and aluminum, and inhibiting the growth of boundary metal compound, and achieves better performance reliability. At the same time, by controlling the proportions of nickel and palladium, the resistivity of the silver alloy wire can also be controlled below 3.5 μΩ·cm.

The beneficial effects of the present invention are: by controlling the content of the palladium and adding an appropriate proportion of nickel, the silver alloy wire can achieve low resistivity, excellent performance reliability, and excellent wire bonding yield under the premise of reducing material cost. and so on.

Detailed ways

A preferred embodiment of the silver alloy wire of the present invention is composed of silver, palladium and nickel, wherein the content of palladium is 1.8-2.2wt%, the content of nickel is 0.5-2.0wt%, and the rest is silver with a purity of 99.99wt%. When the content of palladium is lower than 1.8wt%, the performance reliability of the silver alloy wire of the present invention is poor, and if the content of palladium is higher than 2.2wt%, there will be a disadvantage of high resistivity.

The higher the content of nickel added in the present invention, the higher the resistivity of the silver alloy wire. In order to control the resistivity below 3.5μΩ·cm, preferably, the nickel content is not higher than 2.0wt%, but when When the nickel content is less than 0.5wt%, the performance reliability of the silver alloy wire is poor.

When making the silver alloy wire of the present invention, elements such as silver, palladium and nickel are put into a melting furnace in proportion to knead to obtain a molten alloy liquid. Then the alloy liquid is made into rods by continuous casting, and then undergoes press roll, heavy drawing, fine drawing, surface cleaning, drying, and final annealing. ), winding (rewinding) and other processing steps, the silver alloy wire of the present invention can be produced, and the silver alloy wire is specially used in the wire bonding packaging process of semiconductor elements.

The present invention will be further described with reference to the following examples, but it should be understood that the examples shown are for illustrative purposes only and should not be construed as limitations on the practice of the present invention.

Examples of silver alloy wires of the present invention, comparative examples, and descriptions of low-resistance silver alloy wires containing gold, palladium, and silver:

Table 1:

◎: Indicates that the evaluation item is excellent

○: Indicates that the evaluation item is acceptable

△: Indicates that the evaluation item is on the verge of critical

╳: Indicates that the evaluation item is bad

(If the resistivity is greater than 3.5μΩ·cm, it will be judged as bad, if the resistivity is less than 3.5μΩ·cm, it will be judged as good)

PCT: The abbreviation of Press Cooker Test, also known as the pressure cooker test, according to JESD22-A102, the silver alloy wire product is placed in an environment with a temperature of 121°C, a humidity of 100%RH, and a pressure of 29.7psi. Ion beam (Focused Ion Beam, referred to as FIB) to observe the interface metal compound (IMC) between the silver alloy wire and the substrate.

From the experimental results of conventional examples 1-6 in Table 1, it can be seen that when the silver alloy wire contains 1wt% palladium and 1wt% gold, although the wire bonding yield and resistivity of the finished product are good, the performance of the finished product is reliable The accuracy is poor, and when the content of gold or palladium is increased, although the performance reliability can be improved, the resistivity of the silver alloy wire is too high, which is not conducive to the transmission of signals.

As can be seen from the experimental results of Comparative Examples 1-10 in Table 1, if the palladium content of the present invention is lower than 1.8wt%, even if the nickel metal content reaches 0.5wt%, or even as high as 3wt%, its reliability is still unsatisfactory.

When the present invention reduces the usage of nickel metal to 0.1wt% and increases the content of palladium, although it has excellent performance reliability and excellent wire bonding yield, the resistivity of silver alloy wire is slightly higher. In addition, the present invention maintains the content of nickel within the range of 0.5-2.0wt%, but when the amount of palladium is increased to 3wt%, although the physical properties of the silver alloy wire are very good, the performance of the resistivity is relatively low. Difference. If the contents of palladium and nickel are increased to 3wt%, all the physical properties of the silver alloy wire are unsatisfactory.

From the experimental results of Examples 1 and 2 in Table 1, it can be known that the present invention can effectively reduce the material cost by controlling the content of palladium and nickel, and the silver alloy wire obtained also has low resistivity, excellent Performance reliability and excellent wire bonding yield.

Claims (1)

1. A silver alloy wire, which is specially used for IC packaging; it is characterized in that: The silver alloy wire is composed of silver, palladium and nickel, wherein the content of palladium is 1.8-2.2wt%, the content of nickel is 0.5-2.0wt%, and the rest is silver.