JP2013107132A - Lead-free solder alloy and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lead-free solder alloy which is excellent in acid resistance and flexibility, and a method for manufacturing the lead-free solder alloy.SOLUTION: One to five wt.% of Ag is add to an Sn-Zn based lead-free solder alloy and a fraction of a gamma (γ) phase and an epsilon (ε) phase, which are Ag-Zn alloy phases, is formed to be 5-20 vol.%, so that the acid resistance as well as the flexibility of the lead-free solder alloy is greatly improved.

Description

  The present invention relates to a lead-free solder alloy and a manufacturing method thereof.

  Existing semiconductor packages have used lead frames as means for mounting on printed circuit boards. Such an existing semiconductor package has a structure in which the lead of the lead frame extends outside the package body sealing the chip, and is mounted by soldering the lead on the substrate.

  By the way, the existing semiconductor package mounted by surface mounting technology requires a wide mounting area. That is, since the existing semiconductor package requires an additional area as the mounting area of the lead frame extending outside the package body in addition to the area corresponding to the size of the semiconductor package as the mounting area. Even if the mounting area is reduced by the reduction, there is a limit to the reduction of the mounting area. Thus, one of the main trends of technological development in the semiconductor industry is to reduce the size of semiconductor elements.

  Also in the field of semiconductor packages, a fine pitch ball grid array (Fine pitch Ball Grid Array) that can implement a large number of pins while having a small size due to a rapid increase in demand for small computers and portable electronic devices, etc .: Semiconductor packages such as FBGA) packages or chip scale packages (CSP) have been developed. At this time, such a semiconductor package is electrically connected between the substrates via solder balls.

  On the other hand, in an electronic circuit board built in a conventional electronic device, a tin-lead solder material, particularly 63 wt% tin (Sn) -37 wt% lead (37Pb), etc. Materials with a melting point (mp 183 ° C) have been commonly used, but in recent years, the lead contained in tin-lead solder materials can cause environmental pollution due to improper waste disposal Therefore, development of a so-called lead-free solder material that does not contain lead is actively progressing.

  One of the promising lead-free solder materials is Sn-Ag-Cu solder material. The melting point (216-225 ° C.) of the standard solder Sn—Ag—Cu alloy is about 30 ° C. higher than the melting point (183 ° C.) of the existing Sn-37Pb eutectic alloy (183 ° C.). Has been demanding improved heat resistance.

  Therefore, in order to improve the heat resistance of components and substrates that have been used, process change is inevitable. In order to solve the problem of such a process change, many studies have been conducted for securing a high-reliability solder material having a low melting point similar to an existing Sn-37Pb eutectic alloy.

  Among them, the Sn-9Zn eutectic alloy has an advantage that the melting point (199 ° C.) has the same melting point as that of the existing Sn-37Pb eutectic alloy and can be applied without changing the manufacturing process. Further, the Sn-9Zn alloy system is economical because of its high strength, creep characteristics and heat fatigue resistance. However, its use has been limited due to its high reactivity with oxygen and poor wettability with the substrate. Presently, alternatives that can suppress oxidation by developing atmosphere control (vacuum, gas purging, partial oxygen pressure, etc.) and flux are proposed.

  Therefore, in order to improve the wettability and interface reliability of the Sn-9Zn eutectic alloy, research and development by addition of a third element (Ag, Al, Bi, In, Ga, etc.) is actively progressing. In particular, much research has been conducted on the addition of Bi in order to improve wettability and achieve a low melting point. Addition of Bi to Sn-9Zn eutectic alloy can realize a low melting point of the alloy, but oxidation progresses compared to Sn-9Zn eutectic alloy at the same high temperature and high humidity (85 ° C / 85% RH). The rate has been reported to accelerate.

  On the other hand, in the Sn—Zn—Ag eutectic alloy, Patent Documents 1 and 2 disclose eutectic alloys containing 0.1 to 3.5 wt% and 0.01 to 2 wt% of Ag, respectively. This is added to improve mechanical properties such as tensile strength and corrosion resistance of the alloy, and such an alloy still tends to have poor acid resistance.

Japanese Laid-Open Patent Publication No. 9-94687 Korean Registered Patent No. 10-690245 specification

  Therefore, according to the present invention, the addition of the third element optimum for the existing Sn—Zn alloy and the Zn metal that is easily oxidized by the optimum composition are first alloyed with Ag, and then mixed with Sn to thereby prevent the acid resistance of the solder. The present invention has been completed based on this.

Accordingly, an object of the present invention is to provide a lead-free solder alloy having excellent acid resistance and softness.
Another object of the present invention is to provide a method for producing a lead-free solder alloy having excellent acid resistance and softness.

  In order to achieve the above object, a lead-free solder alloy according to the present invention is an alloy composed of 1.0 to 5.0% by weight of Ag, 7 to 10% by weight of Zn, and the remaining Sn, Ag- The fraction of gamma (γ) and epsilon (ε) phases which are Zn alloy phases is 10 to 20% by volume.

  In the lead-free solder alloy according to the present invention, the Ag content may be 4 to 5% by weight.

  In the lead-free solder alloy according to the present invention, the lead-free solder alloy may be applied to manufacture a solder preform.

  In the lead-free solder alloy according to the present invention, the solder preform includes 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 particle (granule), a solder ribbon, and a solder washer. (Washer), solder ring, and solder disk.

  In the lead-free solder alloy according to the present invention, a fraction of gamma (γ) and epsilon (ε) phases, which are the Ag—Zn alloy phases, may be 16 to 20% by volume.

  In order to achieve the above object, a method for producing a lead-free solder alloy according to the present invention comprises the steps of melting 1.0 to 5.0 wt% Ag and 7 to 10 wt% Zn to form an alloy ball; Melting the remaining Sn to provide molten Sn; and adding an Ag—Zn alloy ball to the molten Sn to form a solder alloy, wherein the solder alloy In the present invention, the fraction of the gamma (γ) and epsilon (ε) phases which are Ag—Zn alloy phases is 5 to 20% by volume.

  In the method for producing a lead-free solder alloy according to the present invention, the Ag content may be 4 to 5% by weight.

In the method for producing a lead-free solder alloy according to the present invention, the lead-free solder alloy may be applied to the production of a solder preform.
In the method for producing a lead-free solder alloy according to the present invention, the solder preform is a solder paste, solder ball, solder bar, solder wire, solder bump, solder thin plate, solder powder, solder pellet, solder particle (granule), solder ribbon, It can be selected from the group consisting of solder washers, solder rings and solder disks.

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

  In the method for producing a lead-free solder alloy according to the present invention, the alloy ball may be formed by atomizing.

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

  In the present invention, the Ag-Zn alloy phase gamma (γ) and epsilon (ε) phase fraction is added to 10 to 20 volumes while adding Ag to the Sn—Zn lead-free solder alloy at 1 to 5 wt%. In addition, the mechanical strength of the lead-free solder alloy, such as tensile strength and softness, is improved, and the acid resistance of the alloy is greatly improved.

It is a diagram of the general Sn-Zn phase by the composition ratio of Sn and Zn. 3 is a scanning electron microscope photograph showing the microstructure of a general Sn-9Zn solder alloy. After exposing a conventional solder alloy at 85 ° C./85% RH for 1000 hours, a scanning electron micrograph showing changes in the microstructure of the alloy, (a) is a Sn-9Zn solder alloy, (b ) Is a Sn-8Zn-3Bi solder alloy. 1A and 1B are diagrams schematically illustrating a concept of controlling oxidation of Zn by adding Ag to a Sn—Zn solder according to an embodiment of the present invention, in which FIG. 1A is an ordinary Sn—Zn solder alloy, and FIG. Is a Sn—Zn solder alloy to which is added. 3 is an XRD (X-ray diffusion) analysis graph of a solder alloy obtained by forming an Ag—Zn alloy according to an embodiment of the present invention and then mixing the alloy with Sn. In the Sn-Zn-Ag solder alloy according to an embodiment of the present invention, a scanning electron micrograph showing changes in the gamma (γ) and epsilon (ε) phases, which are Ag-Zn alloy phases, due to a change in Ag content, (A) is a Sn-9Zn-1Ag solder alloy, and (b) is a Sn-9Zn-2Ag solder alloy. In the Sn-Zn-Ag solder alloy according to an embodiment of the present invention, a scanning electron micrograph showing changes in the gamma (γ) and epsilon (ε) phases, which are Ag-Zn alloy phases, due to a change in Ag content, (C) is a Sn-9Zn-4Ag solder alloy, and (d) is a Sn-9Zn-5Ag solder alloy. 3 is a graph showing 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. 3 is a graph showing 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. 1 is a scanning electron micrograph of a cross section of the alloy showing an acid resistance change due to a change in Ag content in a Sn-9Zn-xAg solder alloy according to an embodiment of the present invention, wherein (a) is a Sn-9Zn-1Ag solder alloy. (B) is a Sn-9Zn-2Ag solder alloy. FIG. 2 is a scanning electron micrograph of a cross section of the alloy showing an acid resistance change due to a change in Ag content in a Sn-9Zn-xAg solder alloy according to an embodiment of the present invention, wherein (c) is a Sn-9Zn-4Ag solder alloy. , (D) is a Sn-9Zn-5Ag solder alloy.

  Prior to the detailed description of the invention, the terms and words used in the specification and claims should not be construed in a normal and lexicographic sense, and the inventor will best explain his invention. In order to explain, the terminology must be interpreted into meanings and concepts that meet the technical idea of the present invention in accordance with the principle that the concept of terms can be appropriately defined. Therefore, the configuration of the embodiment described in this specification is merely a preferred example of the present invention and does not represent the entire technical idea of the present invention. Therefore, these may be replaced at the time of the present application. It should be understood that there are various equivalents and variations that can be made.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that a person having ordinary knowledge in the technical field to which the present invention belongs can easily carry out the present invention.

  As described above, a number of previous studies have been conducted to improve the wettability with the pad and the interface reliability by adding a third element to the Sn—Zn eutectic alloy. There is very little research. For this reason, in the present invention, Ag is selected as the third element in the existing Sn—Zn alloy, alloyed with Zn metal that is easily oxidized, and then mixed with Sn to mix the solder alloy. Strengthened acid resistance. On the other hand, in terms of expression of terms relating to the composition of the alloy used in the present invention, a typical example will be described. In “Sn-9Zn”, 9Zn means 9% by weight of Zn, and the rest This component means Sn, that is, 91% by weight of Sn. Hereinafter, the composition of the alloy is described in the same expression system.

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

  On the other hand, referring to FIG. 2, the Sn-9Zn solder alloy is highly reactive with oxygen because the needle-like Zn is dispersed independently of the base metal Sn after the alloy. Zn easily reacts with oxygen to reduce acid resistance. In order to measure the acid resistance of such a conventional solder alloy, the Sn-9Zn solder alloy and the Sn-8Zn-3Bi solder alloy were exposed at 85 ° C./85% RH for 1000 hours, and the results are shown in FIG. It was. Referring to FIG. 3, it can be confirmed that a large amount of ZnO is produced in both (a) the Sn-9Zn solder alloy and (b) the Sn-8Zn-3Bi solder alloy.

  According to the present invention, by adding Ag as the third metal element, it was possible to improve the oxidation resistance by alloying with Zn. Generally, a solder alloy manufacturing method uses a method in which various metal compositions are simultaneously melted and mixed well, but the present invention is characterized in that an Ag-Zn alloy is mixed with Sn which is a base metal. To do.

  If Ag metal is added to SnPb and Sn-3Ag-0.5C, which are conventional solder alloys, an alloy phase of Sn base metal is formed. In the present invention, Zn having high oxidizing power in Sn-Zn solder is used. The metal is preferentially melted with Ag to alloy the Zn metal. That is, in a low-valent Sn-9Zn eutectic alloy, Zn metal which is easy to oxidize is first alloyed and mixed with Sn by adding 1-5 wt% Ag metal to Zn and melting together. Thus, oxidation could be suppressed.

  In the present invention, the amount of Ag used is in the range of 1.0 to 5.0% by weight, but if it is less than 1% by weight, there is almost no additive effect such as improvement in acid resistance and softness. If it exceeds wt%, there is a drawback that the melting point of the alloy rises. At the same time, the content of the Ag is 4 to 5% by weight in order to maximize the softness and acid resistance while satisfying the general range of about 206 to 224 ° C. currently used in the industry.

  However, in the present invention, Zn and Ag are not simply added to Sn and melted, but Zn and Ag are first alloyed and formed into an alloy ball shape. The diameter of the alloy ball is preferably 1 to 20 μm, and if it is less than 1 μm, the ball tends to aggregate, and if it exceeds 20 μm, the softness of the alloy tends to be low. If the Zn—Ag alloy balls formed in this way are added to molten Sn and melted together, in the solder alloy, gamma (γ) and epsilon (ε) phases that are the Ag—Zn alloy phases. A lead-free solder alloy having a fraction of 10 to 20% by volume, preferably 16 to 20% by volume, can be obtained. If the said fraction is less than 10 volume%, the acid-proof improvement of an alloy will fall, and if it exceeds 20 volume%, acid resistance will improve, but there exists a tendency for the melting temperature of an alloy to rise.

  FIG. 4 is a view schematically showing the concept of Zn oxidation control by adding Ag to Sn—Zn solder according to one embodiment of the present invention, (a) is a normal Sn—Zn solder alloy, and (b) is the present invention. Is a Sn—Zn solder alloy to which Ag is added. In the case of FIG. 4B, the needle-shaped structure Zn is bonded to Ag and is well dispersed in the base metal Sn.

  According to the present invention, the alloy balls can be formed by atomizing well known to those skilled in the art. The atomizing described in the present invention means that after pouring a molten alloy into a pot, the alloy is caused to flow in a region where water or a high-pressure gas mixed with water is sprayed, so that the alloy In response to the kinetic energy of the gas, it is divided into a large number of fine droplets, and the divided fine droplets formed into a spherical shape by surface energy are cooled with water or air to obtain a solid-state spherical ball. Say the process.

  According to a preferred embodiment of the present invention, in order to form a metal raw material into an alloy ball, the raw material is first 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, in which an object to be heated is placed in a melting chamber, and an electric current flows through the object to be heated by induction of a high-frequency current flowing in a coil wound around the melting chamber. It is an apparatus that dissolves an object to be heated.

  Thereafter, the material that has passed through the high-frequency induction furnace is formed into powder with a water atomizing device. Under the present circumstances, it is preferable that the pressure of the water injected from an injector has a pressure of 100-200 MPa, and it is preferable to have a pressure of 150 MPa especially. The material that has passed through the water atomizer is dried with a dryer, and the dried material is separated with a mesh-type separator. Thereby, metal powder is classified according to size.

On the other hand, the lead-free solder alloy of the present invention can be applied to the manufacture of a solder preform, and the solder preform is a solder paste, solder ball, solder bar, solder wire, solder bump, solder thin plate, solder powder, solder pellet. , Such as, but not limited to, solder particles, solder ribbons, solder washers, solder rings or solder disks.
Thus, in the present invention, it is important to form the fraction of gamma (γ) and epsilon (ε) phases, which are Ag—Zn alloy phases, in the Sn—Zn—Ag alloy to 10 to 20% by volume. This cannot be obtained by simply mixing the raw metal, but can be obtained by first forming an Ag—Zn alloy ball and melt-mixing it with Sn. The lead-free solder alloy of the present invention thus produced has the effect of greatly improving softness and acid resistance.
EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, the category of this invention is not limited to the following example.

[Example 1]
First, 9Zn-1-5Ag solder alloy balls were manufactured. After mixing Zn and Ag in the graphite reactor in respective contents, they were melted at a temperature of about 700 ° C. for 30 minutes while injecting Ar gas. The induction furnace power and gas pressure conditions were 9 kW and 500 Torr, respectively. The molten alloy thus obtained is sprayed with an atomizing device to obtain a ball metal powder having a fine diameter, and this is sieved with a sieve so that the diameter of the alloy ball is in the range of 1 to 20 μm. An alloy ball was obtained.

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

  On the other hand, the obtained Sn and Zn—Ag alloy balls were put in a graphite reactor, and then melted at a temperature of about 300 ° C. for 30 minutes while injecting Ar gas. The induction furnace power and gas pressure conditions at this time were 9 kW and 500 Torr, respectively.

  The solder alloy thus obtained was subjected to XRD analysis in order to investigate the alloying change of Zn due to the addition of Ag, and the results are shown in FIG. As a result, it was confirmed that approximately 10% of the gamma (γ) and epsilon (ε) phases, which are Ag—Zn alloy phases, were formed by forming Ag—Zn alloy by reacting Ag and Zn first. .

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

  Further, in order to examine the compositional characteristics of the alloy of the present invention, SEM photographs were observed, and the results are shown in FIG. Referring to FIG. 6, it was confirmed that the amount of Zn reacting with Ag increases as the amount of Ag added to 9Zn increases. On the contrary, the total Zn phase that can inhibit the oxidation resistance tended to decrease gradually, and almost no Zn phase was observed in the Sn-9Zn-5Ag composition of FIG. Overall, it was confirmed that the fraction of the Ag—Zn alloy phase (γ, ε) has 10 to 20% by volume.

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

  At the same time, as a result of performing a high temperature and high humidity test (1000 hours at 85 ° C./85% RH) in order to investigate the acid resistance characteristics of the alloy of Example 1, it was generally superior to Sn-9Zn. Shows oxidation resistance. In the case of the Sn-9Zn-2Ag composition of FIG. 8a (a), a little internal oxidation occurred, but no internal permeation oxidation occurred in the remaining alloy composition.

  As described above, the lead-free solder alloy according to the present invention generally has a melting point in a range corresponding to the reflow profile currently used, and is equal to or better than the Sn-9Zn alloy. It exhibits strength and softness properties and superior oxidation resistance properties compared to Sn-9Zn alloys.

  According to the present invention, the addition of the third element optimum to the existing Sn—Zn alloy and the Zn metal that is easily oxidized by the optimum composition are first alloyed with Ag, and then mixed with Sn, whereby the acid resistance of the solder and It can be applied to lead-free solder alloys that reinforce softness and their manufacturing methods.

Claims (12)

  An alloy composed of 1.0 to 5.0% by weight of Ag, 7 to 10% by weight of Zn, and the remaining Sn, and is a component of the gamma (γ) and epsilon (ε) phases that are Ag-Zn alloy phases. Lead-free solder alloy, characterized in that the rate is 10-20% by volume.   The lead-free solder alloy according to claim 1, wherein the Ag content is 4 to 5 wt%.   The lead-free solder alloy according to claim 1, wherein the lead-free solder alloy is applied to manufacture of a solder preform.   The solder preform includes solder paste, solder ball, solder bar, solder wire, solder bump, solder thin plate, solder powder, solder pellet, solder particle (granule), solder ribbon, solder washer, solder ring and solder disk. The lead-free solder alloy according to claim 3, wherein the lead-free solder alloy is selected from the group consisting of:   The lead-free solder alloy according to claim 1, wherein a fraction of gamma (γ) and epsilon (ε) phases, which are the Ag—Zn alloy phases, is 16 to 20% by volume. Melting 1.0 to 5.0 wt% Ag and 7 to 10 wt% Zn to form alloy balls;
Melting the remaining Sn to provide molten Sn; and adding an Ag-Zn alloy ball to the molten Sn to form a solder alloy; and
Here, in the solder alloy, the fraction of gamma (γ) and epsilon (ε) phases which are Ag—Zn alloy phases is 5 to 20% by volume, and the method for producing a lead-free solder alloy.   The method for producing a lead-free solder alloy according to claim 6, wherein the Ag content is 4 to 5% by weight.   The method of manufacturing a lead-free solder alloy according to claim 6, wherein the lead-free solder alloy is applied to manufacture of a solder preform.   The solder preform is composed of solder paste, solder ball, solder bar, solder wire, solder bump, solder thin plate, solder powder, solder pellet, solder particle (granule), solder ribbon, solder washer, solder ring and solder disk. The method for producing a lead-free solder alloy according to claim 8, wherein the lead-free solder alloy is selected from the group consisting of:   The method for producing a lead-free solder alloy according to claim 6, wherein a diameter of the alloy ball is 1 to 20 μm.   The method for producing a lead-free solder alloy according to claim 6, wherein the alloy balls are formed by atomizing.   The lead-free solder alloy according to claim 6, wherein a fraction of gamma (γ) and epsilon (ε) phases as the Ag-Zn alloy phase in the solder alloy is 16 to 20% by volume. Manufacturing method.

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