KR20130054791A - Lead-free solder alloy and method for preparing the same - Google Patents

Abstract

PURPOSE: A lead-free solder alloy and a manufacturing method thereof are provided to improve the mechanical strength and acid resistance of the lead-free solder alloy. CONSTITUTION: A lead-free solder alloy is composed of 1.0-5.0 wt.% of Ag, 10 wt.% of Zn, and the rest of Sn. The ratio of gamma (γ) and epsilon(ε) which is an Ag-Zn alloy phase, is 10-20 vol.% in the alloy. The Ag is 4-5 wt.%. The lead-free solder is applied to manufacture a solder preform.

Description

Lead-free solder alloy and method for preparing the same

The present invention relates to a lead-free solder alloy and a method of manufacturing the same.

Conventional semiconductor packages have used lead frames as mounting means on printed circuit boards. Such a conventional semiconductor package has a structure in which the lead of the lead frame extends to the outside of the package body encapsulating the chip, and is mounted by soldering the lead onto the substrate.

However, the conventional semiconductor package mounted according to the surface mounting technology requires a large mounting area. That is, the conventional semiconductor package requires an additional area equal to the length of the lead of the lead frame extending outward of the package body in addition to the area corresponding to its size, thereby reducing the mounting area by reducing the size of the package. Even if it reduces, there is a limit to the reduction of the mounting area. Thus, one of the major trends of technology development in the semiconductor industry is to reduce the size of semiconductor devices.

In the semiconductor package field, a fine pitch ball grid array (FBGA) package or chip capable of implementing a large number of pins with a small size in accordance with the rapid demand of small computers and portable electronic devices. Semiconductor packages such as a chip scale package (CSP) have been developed. In this case, the semiconductor package is electrically connected between each substrate through the solder ball.

On the other hand, low-melting point (mpn) such as tin-lead solder material, in particular 63% by weight (Sn)-37% by weight of lead (37Pb) to join the substrate and electronic components in the electronic circuit board embedded in the conventional electronic devices 183 ° C.) has been generally used, but in recent years lead-free solder containing lead-free solder material does not contain lead because it is more likely to cause environmental pollution by improper waste disposal. Development of solder materials is actively underway.

One such promising lead-free solder material is Sn-Ag-Cu solder material. Melting point (216 ~ 225 ℃) of standard solder Sn-Ag-Cu alloy is higher than melting point (183 ℃) of conventional Sn-37Pb eutectic alloy and is higher than about 30 ℃ and improves heat resistance of various parts and substrates. Has been asking.

Therefore, a process change is inevitable in order to improve heat resistance of components and substrates that have been conventionally used. In order to solve the problem of the process change, a lot of researches have been conducted to secure high reliability solder material of similar low melting point of the existing Sn-37Pb process alloy.

Among them, the Sn-9Zn eutectic alloy has a melting point (199 ℃) similar to that of the existing Sn-37Pb eutectic alloy, and thus can be applied without changing the manufacturing process. In addition, the Sn-9Zn alloy has high strength, creep characteristics, heat resistance, and is economical. However, its use has been limited because of its excellent reactivity with oxygen and poor wettability with the substrate. At present, the development of atmosphere control (vacuum, gas purging, partial oxygen pressure, etc.) and flux has been proposed as an alternative to inhibit oxidation.

Therefore, in order to improve wettability and interfacial reliability of Sn-9Zn eutectic alloys, research and development through active addition of third elements (Ag, Al, Bi, In, Ga, etc.) are being actively conducted. In particular, much research has been conducted on the addition of Bi to improve the wettability and low melting point. The addition of Bi to the Sn-9Zn eutectic alloy enables low melting point of the alloy, but the oxidation progress has been reported to be accelerated compared to the Sn-9Zn eutectic alloy at the same high temperature and high humidity (85 ° C / 85% RH).

On the other hand, the Sn-Zn-Ag eutectic alloy disclosed in Japanese Patent Application Laid-Open No. 9-94687 and Korean Patent No. 10-690245 disclose a eutectic alloy containing 0.1 to 3.5% by weight and 0.01 to 2% by weight of Ag, respectively. However, it is added to improve the mechanical properties and corrosion resistance, such as the tensile strength of the alloy, still the alloys tend to be less acid resistance.

Therefore, in the present invention, the Zn metal, which is easy to oxidize, may be first alloyed with Ag, and then mixed with Sn, thereby enhancing the acid resistance and ductility of the solder through the addition of an optimal third element and an optimal composition to the existing Sn-Zn alloy. Was completed on this basis.

Accordingly, one aspect of the present invention provides a lead-free solder alloy excellent in acid resistance and ductility.

Another aspect of the present invention is to provide a method for producing a lead-free solder alloy excellent in acid resistance and ductility.

The lead-free solder alloy according to the present invention for achieving the above aspect is an alloy consisting of 1.0 to 5.0% by weight of Ag, 7 to 10% by weight of Zn, and the rest is Sn, in the alloy Ga- (Ag-Zn alloy phase) and γ) and epsilon (ε) phase fractions of 10 to 20% by volume.

In the lead-free solder alloy according to the invention, the content of Ag is characterized in that 4 to 5% by weight.

In the lead-free solder alloy according to the invention, the lead-free solder alloy is characterized in that it is applied to the production of solder preform (preform).

In the lead-free solder alloy according to the present invention, the solder preform is solder paste, solder ball, solder bar, solder wire, solder bump, solder thin plate, solder powder, solder pellet, solder granule, solder ribbon, solder washer ( washer), soldering and solder disks.

In the lead-free solder alloy according to the present invention, the fraction of the gamma (γ) and epsilon (ε) phases of the Ag-Zn alloy phase is characterized in that 16 to 20% by volume.

The method for producing a lead-free solder alloy for achieving another aspect of the present invention comprises the steps of melting 1.0 to 5.0% by weight of Ag and 7 to 10% by weight of Zn to form an alloy ball; Melting the remaining Sn to provide molten Sn; And melting the molten Sn by adding an alloy ball of Ag—Zn to form a solder alloy, wherein the fraction of the gamma (γ) and epsilon (ε) phases of the Ag-Zn alloy phase in the solder alloy is included. It is 10-20 volume%, It is characterized by the above-mentioned.

In the method for producing a lead-free solder alloy according to the invention, the content of Ag is characterized in that 4 to 5% by weight.

In the method of manufacturing a lead-free solder alloy according to the present invention, the lead-free solder alloy is characterized in that it is applied to the production of solder preform (preform).

In the method of manufacturing a lead-free solder alloy according to the present invention, the solder preform is a solder paste, a solder ball, a solder bar, a solder wire, a solder bump, a solder thin plate, a solder powder, a solder pellet, a solder granule, a solder ribbon, It is characterized in that it is selected from the group consisting of a solder washer, soldering and solder disk.

In the method for producing a lead-free solder alloy according to the present invention, the alloy ball has a diameter of 1 to 20 µm.

In the method for producing a lead-free solder alloy according to the present invention, the alloy ball is characterized in that formed by atomizing.

In the method for producing a lead-free solder alloy according to the present invention, the fraction of the Ga-gamma (γ) and epsilon (ε) phases of the Ag-Zn alloy phase in the solder alloy is characterized in that 16 to 20% by volume.

The present invention provides the lead-free lead by forming a fraction of the Ga- gamma (γ) and epsilon (ε) phases of the Ag-Zn alloy phase at 10-20% by volume, while adding Ag to 1-5% by weight of the Sn-Zn-based lead-free solder alloy. There is an effect of greatly improving the acid resistance of the alloy while also improving the mechanical strength of the solder alloy, for example, tensile strength and ductility.

1 is a general Sn-Zn phase diagram according to the composition ratio of Sn and Zn.
FIG. 2 is a scanning electron microscope photograph showing the microstructure of a typical Sn-9Zn solder alloy. FIG.
3 is a scanning electron micrograph showing a change in the microstructure of the alloy after exposure to a conventional solder alloy at 85 ℃ / 85% RH for 1000 hours, (a) is a Sn-9Zn solder alloy, (b ) Is a Sn-8Zn-3Bi solder alloy.
4 is a view schematically showing a concept of oxidation control of Zn according to the addition of Ag to Sn-Zn solder according to an embodiment of the present invention, (a) is a conventional Sn-Zn solder alloy, (b) is According to the present invention, Ag is a Sn-Zn solder alloy.
5 is an X-ray diffraction (XRD) analysis graph of a solder alloy in which an Ag-Zn alloy is formed and then the alloy is mixed with Sn according to an embodiment of the present invention.
6a and 6b are scanning electron micrographs showing the change in the Ga- gamma (γ) and epsilon (ε) phase of the Ag-Zn alloy phase according to the Ag content change in the Sn-Zn-Ag solder alloy according to an embodiment of the present invention 6A, (a) is a Sn-9Zn-1Ag solder alloy, (b) is a Sn-9Zn-2Ag solder alloy, and in FIG. 6B, (c) is a Sn-9Zn-4Ag solder alloy, ( d) is Sn-9Zn-5Ag solder alloy.
7A and 7B are graphs illustrating mechanical properties of a Sn-9Zn-xAg solder alloy, a conventional Sn-9Zn solder alloy, and a Sn-8Zn-3Bi solder alloy according to an embodiment of the present invention.
8A and 8B are scanning electron micrographs of the cross-section of the alloy showing the acid resistance change according to the Ag content change in the Sn-9Zn-xAg solder alloy according to an embodiment of the present invention. Is a Sn-9Zn-1Ag solder alloy, (b) is a Sn-9Zn-2Ag solder alloy, and in FIG. 8B, (c) is a Sn-9Zn-4Ag solder alloy, and (d) is a Sn-9Zn-5Ag solder alloy. Alloy.

Before describing the present invention in detail, the terms or words used in the present specification and claims should not be limited to the ordinary or dictionary meanings, but properly define the concept of terms in order to explain the invention in the best way. Based on the principle that it can be done, it should be understood that it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the constitution of the embodiments described in the present specification is merely a preferred example of the present invention, and does not represent all the technical ideas of the present invention, so that various equivalents and variations And the like.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

As described above, many prior studies have been conducted to improve wettability and interfacial reliability of pads by adding a third element to Sn-Zn eutectic alloys, but there are very few studies for improving acid resistance. To this end, in the present invention, Ag is selected as the third element of the existing Sn-Zn alloy, first alloyed with Zn metal, which is easy to oxidize, and then mixed with Sn to enhance acid resistance of the solder alloy. On the other hand, in the expression method of the term relating to the composition of the alloy used in the present invention, when a representative example is described, 9Zn in the "Sn-9Zn" means 9% by weight of Zn, the remaining component is Sn That is, it means 91% by weight of Sn. Hereinafter, the composition of the alloy will be described in the same manner.

1 is a general Sn-Zn phase diagram according to the composition ratio of Sn and Zn, Figure 2 is a scanning electron micrograph showing the microstructure of a typical Sn-9Zn solder alloy. Referring to FIG. 1, it can be seen that the melting temperature of the Sn—Zn alloy is lowered by adding Zn to Sn. In particular, when Zn is added in the range of about 7 to 10% by weight, it is possible to maintain a melting temperature range of about 199 to 220 ° C which is within the general melting point range (about 206 to 224 ° C) currently used in the industry. Therefore, in the present invention, since the Ag, which is another metal component, raises the melting point, the amount of Zn used is in the range of 7 to 10% by weight.

Meanwhile, referring to FIG. 2, since the Sn-9Zn solder alloy is present in a form in which needle-shaped Zn is independently dispersed in Sn, a base metal, even after the alloy, Zn having high reactivity with oxygen easily reacts with oxygen. It will be less acid resistant. For acid resistance measurements for these conventional solder alloys, the Sn-9Zn solder alloy and Sn-8Zn-3Bi solder alloy were exposed at 85 ° C./85% RH for 1000 hours and the results are shown in FIG. 3. Referring to FIG. 3, it can be seen that a large amount of ZnO is generated in both (a) Sn-9Zn solder alloy and (b) Sn-8Zn-3Bi solder alloy.

According to the present invention, by adding Ag as the third metal element, oxidation resistance was improved through alloying of Zn. In general, the manufacturing method of the solder alloy uses a method of melting and mixing various metal compositions at the same time, but in the present invention, the Ag-Zn alloy is mixed with Sn, which is a base metal. .

When Ag metal is added to SnPb, Sn-3Ag-0.5C, and the like, which are conventional solder alloys, an alloy phase of Sn base metal is formed. However, in the present invention, Zn metal having a high oxidizing power is preferentially melted with Ag in Sn-Zn solder. To alloy the Zn metal. In other words, Zn metals, which are easily oxidized by adding 1-5 wt% Ag metal to Zn in a low-cost Sn-9Zn eutectic alloy, were alloyed first and mixed with Sn to inhibit oxidation.

In the present invention, the amount of Ag used is in the range of 1.0 to 5.0% by weight, but less than 1% by weight has almost no additive effect such as improvement in acid resistance and ductility, and when it exceeds 5.0% by weight, the melting point of the alloy is increased. There is this. In addition, the Ag content is 4 to 5% by weight while satisfying the general melting point range of about 206 to 224 ° C, which is currently used in the industry, to maximize the ductility and acid resistance.

However, in the present invention, Zn and Ag are not simply added to Sn to be melted, but Zn and Ag are alloyed first, and then formed into alloy balls. The diameter of the alloy ball is preferably 1 to 20 μm, and if it is less than 1 μm, the balls tend to agglomerate, and if it exceeds 20 μm, the ductility of the alloy tends to be low. When the Zn-Ag alloy balls thus formed are added to molten Sn and melted together, the fraction of the Ga-gamma (γ) and epsilon (ε) phases of the Ag-Zn alloy phase in the solder alloy is 10-20% by volume, preferably 16 A lead-free solder alloy of ˜20% by volume can be obtained. If the fraction is less than 10% by volume, the improvement of acid resistance of the alloy is lowered. If it exceeds 20% by volume, the acid resistance is improved, but the melting temperature of the alloy tends to increase.

4 is a view schematically showing a concept of oxidation control of Zn according to the addition of Ag to Sn-Zn solder according to an embodiment of the present invention, (a) is a conventional Sn-Zn solder alloy, (b) is According to the present invention, Ag is a Sn-Zn solder alloy. In the case of Fig. 4 (b), Zn in the needle-like structure is combined with Ag and is well dispersed in Sn which is a base metal.

According to the present invention, the alloy ball may be formed by atomizing well known to those skilled in the art. In the atomizing described in the present invention, the molten alloy is contained in a pot, and then the alloy is poured into an area where water or a high-pressure gas mixed with water is sprayed, so that the alloy is the kinetic energy of the water or gas. It is supplied to be divided into a number of fine droplets, and refers to a process of obtaining a solid spherical ball by cooling the divided fine droplets spherical due to the surface energy with water or air.

According to a preferred embodiment of the present invention, in order to form the metal raw material into the alloy ball, first, the raw material is prepared, and then the prepared raw material is melted in a high frequency induction furnace. As is well known, a high frequency induction furnace is also called a high frequency electric furnace, and a device for dissolving a heated object by injecting a heated object into a melting chamber and causing a current to flow in the heated object by induction of a high frequency current flowing through a coil wound around the melting chamber. to be.

Then, the material having passed through the high frequency induction furnace is formed into a powder in a water atomizing device. At this time, the pressure of the water injected from the injector is preferably having a pressure of 100 to 200 MPa, particularly preferably having a pressure of 150 MPa. The material that has passed through the water atomizer is dried in a dryer and the dried material is mesh separated in the separator. The metal powder is thereby classified according to size.

On the other hand, the lead-free solder alloy of the present invention can be applied to the production of solder preform (preform), the solder preform is solder paste, solder ball, solder bar, solder wire, solder bump, solder thin plate, solder powder, solder pellet, solder Such as granules, solder ribbons, solder washers, soldering or solder discs, but are not limited to such.

Thus, in the present invention, it is important to form a fraction of the Ga- gamma and epsilon epsilon phases of the Ag-Zn alloy phase in the Sn-Zn-Ag alloy at 10 to 20% by volume. This cannot be achieved by simply mixing the raw metal, but can be achieved by first forming an Ag-Zn alloy ball and melting it with Sn. The lead-free solder alloy of the present invention thus produced has an effect of greatly improving ductility and acid resistance.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are not intended to limit the scope of the present invention.

Example 1

First, 9Zn-1 to 5Ag solder alloy balls were manufactured. After mixing Zn and Ag in the graphite reactor according to their respective contents, 30 minutes were melted at a temperature of about 700 ° C. while injecting Ar gas. The power and gas pressure conditions of the induction furnace were 9 kW and 500 Torr, respectively. The molten alloy thus obtained was sprayed in an atomizing machine to obtain a metal powder in the form of a ball having a fine diameter, and the sieve was filtered to obtain an alloy ball having a diameter of 1 to 20 μm.

Separately, Sn was placed in a graphite reactor and molten Sn was obtained by melting 30 minutes at a temperature of about 420 ° C while injecting Ar gas. Power and gas pressure conditions of the induction furnace at this time were 9 kW and 500 Torr, respectively. The content of Sn means the remaining amount obtained by subtracting the sum of Ag and Zn contents from 100% by weight.

On the other hand, after putting the Sn and Zn-Ag alloy balls obtained above into a graphite reactor, it melt | dissolved for 30 minutes at the temperature of about 300 degreeC, injecting Ar gas. Power and gas pressure conditions of the induction furnace at this time were 9 kW and 500 Torr, respectively.

XRD analysis was performed to see the alloying change of Zn according to Ag addition in the solder alloy thus obtained, and the results are shown in FIG. 5. As a result, Ag and Zn were first reacted to form an Ag-Zn alloy, which confirmed that about 10% of gamma (γ) and epsilon (ε) phases, which are Ag-Zn alloy phases, were generated.

As described above, the melting point of the alloy gradually increases as the amount of Ag is added, but the melting point range of the alloy according to the present invention, even if Ag is added up to 5% by weight, is a general melting point currently used in the industry. It has a range (206 to 224 ° C). This is shown in Table 1 below.

Solder type Alloy composition Melting point (캜) Leaded solder Sn-37Pb 183
Conventional lead-free solder
Sn-3.5Ag 221 Sn-3.0Ag-0.5Cu 217 Sn-0.7Cu 227 Sn-9Zn 199
Lead-free solder of the present invention
Sn-9Zn-1Ag 206 Sn-9Zn-2Ag 212 Sn-9Zn-4Ag 219 Sn-9Zn-5Ag 224

In addition, in order to examine the histological properties of the alloy of the present invention, the SEM photograph was observed, the results are shown in FIG. Referring to FIG. 6, it was confirmed that the amount of Zn elements reacted with Ag increases as the amount of Ag added to 9Zn increases. On the contrary, the total Zn phases that could inhibit the oxidation resistance showed a tendency to gradually decrease, and almost no Zn phases were observed in the Sn-9Zn-5Ag composition (d) of FIG. 6B. In total, the fraction of the Ag—Zn alloy phase (γ, ε) was found to have 10 to 20% by volume.

7 is a graph showing the mechanical properties of the Sn-9Zn-xAg solder alloy and the conventional Sn-9Zn solder alloy and Sn-8Zn-3Bi solder alloy of the present invention, as can be seen in Figure 7a, the maximum tensile strength is As the Ag content increases, it shows a tendency to increase, and from 4wt%, the maximum tensile strength value equivalent to Sn-9Zn is shown. On the other hand, as can be seen in Figure 7b, in terms of ductility has shown a tendency to increase the ductility with increasing Ag addition.

In addition, in order to examine the acid resistance characteristics of the alloy of Example 1, a high temperature and high humidity test (1000 hours at 85 ℃ / 85% RH) was performed, the overall excellent oxidation resistance compared to Sn-9Zn Indicated. In the case of the Sn-9Zn-2Ag composition of FIG. 8A, some internal oxidation occurred, but internal penetration oxidation did not occur in the remaining alloy composition.

As described above, the lead-free solder alloy according to the present invention has a melting point in a range that can correspond to the reflow profile currently being used as a whole, and exhibits the same or superior strength and ductility characteristics as compared with the Sn-9Zn alloy. Excellent oxidation resistance compared to -9Zn alloy.

Claims (12)

1.0 to 5.0% by weight of Ag, 7 to 10% by weight of Zn, and the remainder is an alloy composed of Sn, the fraction of the Gamma (γ) and epsilon (ε) phase of the Ag-Zn alloy phase in the alloy 10 to 20 parts by volume Lead free solder alloy.
The method according to claim 1,
The lead-free solder alloy, characterized in that the content of Ag is 4 to 5% by weight.
The method according to claim 1,
The lead-free solder alloy is characterized in that it is applied to the manufacture of solder preform (preform).
The method according to claim 3,
The solder preform consists of solder paste, solder balls, solder bars, solder wires, solder bumps, solder laminations, solder powders, solder pellets, solder granules, solder ribbons, solder washers, solder rings and solder discs. A lead-free solder alloy characterized in that it is selected from the group.
The method according to claim 1,
A lead-free solder alloy characterized in that the fraction of the gamma (γ) and epsilon (ε) phases of the Ag-Zn alloy phase is 16-20% by volume.
Melting 1.0 to 5.0% by weight of Ag and 7 to 10% by weight of Zn to form alloy balls;
Melting the remaining Sn to provide molten Sn; And
And melting the molten Sn by adding an alloy ball of Ag—Zn to form a solder alloy.
Here, the method of producing a lead-free solder alloy in which the fraction of the gamma (γ) and epsilon (ε) phase of the Ag-Zn alloy phase in the solder alloy is 5 to 20% by volume.
The method of claim 6,
Method for producing a lead-free solder alloy, characterized in that the content of Ag is 4 to 5% by weight.
The method of claim 6,
The lead-free solder alloy is a method of manufacturing a lead-free solder alloy, characterized in that applied to the production of solder preform (preform).
The method according to claim 8,
The solder preform consists of solder paste, solder balls, solder bars, solder wires, solder bumps, solder sheets, solder powders, solder pellets, solder granules, solder ribbons, solder washers, solder rings and solder discs. A method of producing a lead-free solder alloy, characterized in that it is selected from the group.
The method of claim 6,
A method of producing a lead-free solder alloy, characterized in that the diameter of the alloy ball is 1 to 20 ㎛.
The method of claim 6,
The alloy ball is a lead-free solder alloy manufacturing method characterized in that formed by atomizing.
The method of claim 6,
And a fraction of gamma (γ) and epsilon (ε) phases of the Ag-Zn alloy phase in the solder alloy is 16 to 20% by volume.

Images