TW202200798A - Alloy wire - Google Patents

Abstract

An alloy wire is provide. The alloy wire includes the first silver element base material. A second element having a surface energy of greater than 1.5J/m2 is added to the silver base material. The center portion of the alloy wire includes slender grains or equi-axial grains and remaining portions of the alloy wire are equl-axial grains. The alloy wire includes annealing twins whose quantity is 20 percent or more of the total quantity of grains of the alloy wire in a cross-sectional view of the alloy wire.

Description

Alloy wire

The present invention relates to an alloy wire, and in particular to an alloy wire used for wire bonding of electronic packages.

Wire bonding is the primary interconnection method for integrated circuit (IC) and light emitting diode (LED) packaging processes. In addition to providing signal and power transmission between the chip and the substrate, the wire bonding wire can also serve as a heat dissipation function. Therefore, the wire bonding wire must have high electrical conductivity, high thermal conductivity, sufficient strength and ductility. Since the encapsulated polymer sealant often contains corrosive chloride ions, and the polymer sealant itself has environmental moisture absorption, the wire must have good oxidation resistance and corrosion resistance.

During the wire bonding process, intermetallic compounds are formed at the bonding interface between the wire and the semiconductor wafer pad. These intermetallic compounds can ensure interfacial bonding, but excessive intermetallic compounds can cause interfacial embrittlement and Kirkendall voids. When using electronic products, the high current density through the wire may also cause electromigration within the wire. It causes a hole at one end of the wire to reduce electrical and thermal conductivity, and even lead to disconnection. In addition, the silver wire may also cause ion migration and cause short circuit when current is passed through the aqueous solution.

In the conventional wire bonding process of metal wires, a heat-affected zone is easily formed near the solder ball joint, and the strength of the solder ball joint is deteriorated due to grain growth. The wire bonding strength is lowered and the product quality is deteriorated.

The present disclosure provides an alloy wire including a silver base material and a first element. The first element has a surface energy greater than 1.5 J/m ² and is added to the silver substrate. The central part of the alloy wire has elongated grains or equiaxed grains, and the rest are equiaxed grains, wherein the alloy wire has twin grains, and in the cross-sectional metallographic diagram of the alloy wire, the number of twin grains It accounts for more than 20% of all grains.

The following provides many different embodiments or examples for implementing different components of embodiments of the invention. Specific examples of components and configurations are described below to simplify embodiments of the invention. Of course, these are only examples, and are not intended to limit the embodiments of the present invention. For example, if the description mentions that the first part is formed on the second part, it may include embodiments in which the first and second parts are in direct contact, and may also include additional parts formed between the first and second parts. , so that the first and second parts are not in direct contact with each other. Additionally, embodiments of the present invention may repeat reference numerals and/or letters in many instances. These repetitions are for the purpose of simplicity and clarity and do not in themselves represent a specific relationship between the various embodiments and/or configurations discussed.

When the terms "about," "approximately," and the like are used herein to describe numbers or ranges of numbers, the term is intended to encompass numerical values that are within a reasonable range including the number described, such as within +/- 10 of the number being described. %, or other numerical values understood by those of ordinary skill in the technical field to which the present invention belongs. For example, the term "about 5 nm" covers a size range from 4.5 nm to 5.5 nm.

According to some embodiments, FIGS. 1A-1C are the round alloy wires 10 of the first form disclosed. FIG. 1A is a partial segment of the alloy wire rod 10 . Fig. 1B is a longitudinal sectional view taken parallel to the longitudinal direction of the alloy wire 10 shown in Fig. 1A. Fig. 1C is a cross-sectional view taken along a direction perpendicular to the length of the alloy wire 10 shown in Fig. 1A.

m至50

m，例如15

m至25

m。Referring to FIG. 1A , the material of the round alloy wire 10 is an alloy wire in which a trace amount, such as 0.001 to 1.0%, of the first element with high surface energy is added to the silver base material. High surface energy first elements include surface energy greater than 1.5 J/m ² , such as Cu, In, Ni, Sb, Sn, Ti, Ru, Ta, other suitable elements, or combinations thereof. The diameter of the round alloy wire 10 is between 10

m to 50

m, e.g. 15

m to 25

m.

Due to the addition of high surface energy elements to the alloy wire, the pollution particles in the external environment are less likely to adhere. Therefore, the surface cleanliness of the wire can be ensured, and the oxidation resistance and corrosion resistance of the wire can be improved.

In addition, when the circular alloy wire is subjected to the Electrical Flame-Off (EFO) step of thermo-compressive wire bonding, the Free Air Ball (FAB) due to surface tension, easier to form spheres. It can avoid eccentric ball or golf ball defects in the wire, and has better packaging workability.

Referring to FIG. 1B , the longitudinal section of the round alloy wire 10 has a face-centered cubic polycrystalline structure having a plurality of crystal grains. Mostly equiaxed grains 12 . The equiaxed grains 12 are bounded by high-angle grain boundaries 14 and have twin grains 16 . In the cross-sectional metallographic diagram of the randomly sampled alloy wire, the number of twin grains 16 accounts for more than 20% of the total number of grains. In some embodiments, in addition to the equiaxed grains 12 , there are also elongated grains 18 in the central portion of the round alloy wire 10 . In some embodiments, the central portions of the round alloy wire 10 are all equiaxed grains 12 , and there are no elongated grains 18 .

m至10

m，如第1D圖所示。在一些實施例中，等軸晶粒12可能出現許多超大晶粒，其粒徑為5

m至10

m，如第1E圖所示。In some embodiments, the size of the equiaxed grains 12 may be very uniform, with an average grain size of 1

m to 10

m, as shown in Figure 1D. In some embodiments, the equiaxed grains 12 may have many oversized grains with a grain size of 5

m to 10

m, as shown in Figure 1E.

In this specification, the "central part of the round alloy wire rod" refers to the part within the range of 30% of the wire rod radius value along the wire rod radius direction from the axis of the wire rod. The central portion of the wire rod has elongated crystal grains 18 and/or equiaxed crystal grains 12 , and the remaining portions are equiaxed crystal grains 12 .

According to some embodiments, FIGS. 2A-2C are the flat ribbon-shaped alloy wire 20 of the second embodiment disclosed. FIG. 2A is a partial segment of the alloy wire 20 . Fig. 2B is a longitudinal cross-sectional view taken parallel to the longitudinal direction of the alloy wire 20 shown in Fig. 2A. Fig. 2C is a cross-sectional view taken along a direction perpendicular to the length of the alloy wire 20 shown in Fig. 2A.

m至200

m，例如100

m至150

m，並且寬度為1000

m至2000

m，例如1500

m至2000

m。Referring to FIG. 2A , the material of the flat ribbon-shaped alloy wire 20 is the same as that of the above-mentioned round alloy wire 10 , and the first element with high surface energy is also added, which will not be repeated here. The thickness of the flat strip-shaped alloy wire 20 is 50

m to 200

m, for example 100

m to 150

m, and the width is 1000

m to 2000

m, for example 1500

m to 2000

m.

Due to the addition of high surface energy elements to the alloy wire, when the flat ribbon-shaped alloy wire is undergoing ultrasonic welding (ultrasonic wedge bonding), it can also show better balling workability.

The driving force for the bonding of the wire and the pad is the total surface energy of the wire and the pad minus the wire/pad interface energy after bonding. The alloy wire of the present disclosure has higher surface energy, and the driving force for bonding the wire to the die pad is also higher, thereby improving the bonding force.

Referring to FIG. 2B , the longitudinal section of the flat ribbon-shaped alloy wire 20 has a face-centered cubic polycrystalline structure having a plurality of crystal grains. Most of them are equiaxed grains 22 . The equiaxed grains 22 are bounded by high-angle grain boundaries 24 and have twin grains 26 . In the cross-sectional metallographic diagram of the randomly sampled alloy wire, the number of twin grains 26 accounts for more than 20% of the total number of grains. In some embodiments, in addition to the equiaxed grains 22 , there are also elongated grains 28 in the central portion of the flat ribbon-shaped alloy wire 20 . In some embodiments, the central portions of the flat ribbon-shaped alloy wire 20 are all equiaxed grains 22 , and there are no elongated grains 28 .

m至10

m，如第2D圖所示。在一些實施例中，等軸晶粒12可能出現許多超大晶粒，其粒徑為5

m至10

m，如第2E圖所示。In some embodiments, the size of the equiaxed grains 12 may be very uniform, with an average grain size of 1

m to 10

m, as shown in Fig. 2D. In some embodiments, the equiaxed grains 12 may have many oversized grains with a grain size of 5

m to 10

m, as shown in Figure 2E.

In this specification, "the center part of the flat strip-shaped alloy wire" refers to the part within the range of 1/3 from the axis of the wire. The central portion of the wire rod has elongated crystal grains 18 and/or equiaxed crystal grains 12 , and the remaining portions are equiaxed crystal grains 12 .

The formation of the annealing twin structure is due to the accumulation of strain energy inside the material due to cold working. During the subsequent annealing heat treatment, these strain energy drives the atoms in some regions to uniformly shear to the unsheared atoms inside the grain to form mirror-symmetrical lattice positions, which are called annealing twins. The mutually symmetrical interfaces are called twin boundaries.

Annealing twinning mainly occurs in face centered cubic (FCC) crystalline materials with the most dense lattice arrangement. In addition to the face-centered cubic crystal structure condition, generally the smaller the stacking fault energy, the more prone to annealing twinning. For example, although aluminum is a face-centered cubic crystal structure material, its lamination energy is about 200 erg/cm ² . Annealing twinning is rare and therefore does not qualify as a material of this disclosure.

In addition, the amount of cold working deformation before annealing heat treatment is also a key condition. The strain energy accumulated by sufficient cold working deformation can provide atomic driving force to generate annealing twins. If the amount of cold working deformation is too large, the nuclei of recrystallized grains (Nuclei of Recrystallized Grains) will be induced in the initial recrystallization (Primary Recrystallization) stage of the annealing heat treatment. Therefore, a large number of fine grains are formed, which reduces the chance of annealing twins, and instead becomes the structure of a generally known metal wire.

The "deformation amount" in this specification refers to the reduction rate of the cross-sectional area of the material due to cold working.

The twin boundary (Twin Boundary) of the twin grains is a tuned (Coherent) crystal structure, which belongs to the low-energy Σ3 special grain boundary, and the crystal orientations are all {111} planes. Compared with the high-angle grain boundary formed by general annealing and recrystallization, the interface of the twin boundary is only 5% of the general high-angle grain boundary (please refer to: George E. Dieter, Mechanical Metallurgy, McGRAW-HILL Book Company, 1976, p.135-141).

Oxidation, sulfidation, and chloride ion corrosion can be avoided due to the lower interfacial energy of twin boundaries. Therefore, it exhibits better oxidation resistance and corrosion resistance. In addition, the symmetric lattice arrangement of such twins is less hindering electron transport. Thus exhibiting better electrical and thermal conductivity. This effect has been demonstrated in copper conductors (see: L.Lu, Y.Shen, X.Chen, L.Qian, and K.Lu, Ultrahigh Strength and High Electrical Conductivity in Copper, Science, vol.304, 2004 , p.422-426).

Due to the lower interfacial energy of the twin boundary, the twin boundary is more stable than the general high-angle grain boundary. Not only is the twin grain boundary itself not easy to move at high temperature, but it also has a locking effect on the high-angle grain boundary around the grain where it is located, so that these high-angle grain boundaries cannot move. Therefore, the overall crystal grains will not have obvious grain growth phenomenon. The original grain size is maintained even when the first contact (solder ball point) is cooled from the molten state to room temperature during wire bonding. That is to say, after the wire bonding of the traditional fine-grained metal wire, the solidification heat of the solder balls accumulates in the wire near the wire, so that the grain grows rapidly to form a heat-affected zone, which reduces the strength of the wire drawing test.

The diffusion rate of atoms across the twin boundaries is low due to the low energy twin boundaries. When using electronic products, it is also difficult to move atoms inside the wire with high-density current. In this way, the electromigration problem of the metal wire is solved. Twin-modified Grain Boundaries in Copper, Science, vol.321, 2008, p.1066-1069.).

Although the crystal grains of the alloy wire of the present disclosure are slightly larger than those of the conventional gold wire, copper wire, aluminum wire and the silver alloy of the Republic of China Invention Patent No. I384082, the twin crystal structure in the alloy wire and the crystal grain in which it is located have the same characteristics. Different crystal orientations (Crystal Orientation). Therefore, the movement of dislocation can be blocked, resulting in a material strengthening effect. This strengthening mechanism is different from the fine-grained metal wire, which relies on high-angle grain boundaries to block the dislocation movement, but it also causes other problems that are not conducive to the quality and reliability of wire bonding.

）與高導熱性，通電流測試亦展現優良的抗電遷移性及抗離子遷移性。The alloy wire of the present disclosure can maintain a tensile strength similar to that of the general fine-grained wire. It can have higher ductility due to the dislocation and the cross slip of atoms through the twin boundary. Although twinning can block dislocation movement, it does not excessively block electron transport. Even though the alloy wire of the present disclosure has high strength, it still maintains its high electrical conductivity (resistivity is lower than 2.5

) and high thermal conductivity, the current test also showed excellent resistance to electromigration and ion migration.

However, the above characteristics will only appear when at least 20% of the grains in the metal wire contain annealing twins. In conventional gold, copper or aluminum wires for wire bonding, there may be occasional twinning structures, but the twinning density is usually below 10% or even completely free of twinning structures.

The components of several embodiments are summarized above so that those with ordinary knowledge in the technical field to which the present invention pertains can more easily understand the viewpoint of the embodiments of the present invention. Those skilled in the art to which the present invention pertains should appreciate that they can, based on the embodiments of the present invention, design or modify other processes and structures to achieve the same objectives and/or advantages of the embodiments described herein. Those with ordinary knowledge in the technical field to which the present invention pertains should also understand that such equivalent processes and structures do not depart from the spirit and scope of the present invention, and they can, without departing from the spirit and scope of the present invention, Make all kinds of changes, substitutions, and substitutions.

10: Round alloy wire 12,22: Equiaxed grains 14,24: High angle grain boundaries 16,26: Twin grains 18,28: elongated grains 20: Flat ribbon-shaped alloy wire

Various aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. It should be noted that, in accordance with standard practice in the industry, the various features are not drawn to scale and are illustrative only. In fact, the dimensions of elements may be arbitrarily enlarged or reduced to clearly represent the features of the present disclosure. FIG. 1A illustrates a portion of a segment of a circular alloy wire, according to some embodiments. FIG. 1B is a longitudinal section view along a direction parallel to the length of the circular alloy wire shown in FIG. 1A , according to some embodiments. FIG. 1C is a cross-sectional view along a direction perpendicular to the length of the circular alloy wire shown in FIG. 1A , according to some embodiments. Figures 1D and 1E illustrate the distribution of equiaxed grains in the round alloy wire shown in Figure 1B, according to some embodiments. FIG. 2A illustrates a portion of a wire segment of a ribbon-shaped alloy wire, according to some embodiments. FIG. 2B is a longitudinal section view along a direction parallel to the length of the ribbon-shaped alloy wire shown in FIG. 2A , according to some embodiments. FIG. 2C is a cross-sectional view along a direction perpendicular to the length of the ribbon-shaped alloy wire shown in FIG. 2A, according to some embodiments. FIGS. 2D and 2E illustrate distributions of equiaxed grains in the ribbon-shaped alloy wire shown in FIG. 2B according to some embodiments.

10: Round alloy wire

12: Equiaxed grains

14: High angle grain boundaries

16: Twin grains

18: Elongated grains

Claims (8)

An alloy wire, comprising: a silver base material; and a first element, the surface energy of which is greater than 1.5J/m ² , added to the silver base material, wherein the central part of the alloy wire has elongated grains or the like Axial grains, other parts are equiaxed grains, wherein the alloy wire has twin grains, and in the cross-sectional metallographic diagram of the alloy wire, the number of twin grains accounts for more than 20% of all grains. The alloy wire as described in claim 1, wherein the first element comprises: Cu, In, Ni, Sb, Sn, Ti, Ru, Ta or a combination thereof. The alloy wire as described in item 1 of the claimed scope, wherein the first element is added in an amount of 0.001 to 1.0% based on the total weight of the alloy wire. The alloy wire rod according to claim 1, wherein the alloy wire rod is a round wire rod. The alloy wire as described in claim 4, wherein the diameter of the round wire is 10

to 50

. The alloy wire as described in claim 1, wherein the alloy wire is a flat strip. The alloy wire as described in claim 6, wherein the thickness of the flat strip is 50

to 200

. The alloy wire as described in claim 6, wherein the width of the flat strip is 1000

to 2000

.

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