TW201516158A - Tin-silver-copper-bismuth alloy solder ball - Google Patents

Abstract

A composition of tin-silver-copper-bismuth alloy solder ball is disclosed, wherein the content of silver (Ag) is 0.3-4wt%, the content of copper (Cu) is 0.3-1wt%, the content of bismuth (Bi) is 2000 ± 500ppm, in addition to the above disclosures, the remaining content being tin (Sn). As such, the Sn-Ag-Cu alloy added by an appropriate amount of Bi can improve wettability, refine the grains, and increase the mechanical strength of the alloy, so as to improve the thermal cycling test capability for applications in products of high fatigue strength.

Description

Tin-silver-copper-bismuth alloy solder ball

The invention relates to alloy tin balls, in particular to a composition of tin-silver-copper-bismuth alloy tin balls.

In recent years, lead-free alloy solders have been widely developed and put into practical use due to environmental problems and the European Union's Restriction of Hazardous Substances Directive (RoHS). As lead-free solder alloys, there are tins containing tin as a main component. - silver, tin-copper, tin-silver-copper, tin-antimony, tin-antimony, tin-zinc, and other elements based on these, these gold-containing systems will also be Each has its own strengths and weaknesses and is used for different purposes.

Among the above lead-free alloy solders, tin-silver-copper alloy solders are most balanced between wettability and strength. However, silver is contained in tin-silver-copper alloy solder, which is expensive because of the high price of silver. Excessive silver will lead to an increase in cost, which will hinder the popularity of tin-silver-copper alloy solder. If the silver content is reduced in consideration of cost, the fatigue resistance will decrease as its content decreases, and even cause poor connection. The problem.

In order to overcome the above problems, Jincun Yangsi disclosed a low-silver alloy solder in the invention patent No. I383052 of Taiwan, which has a silver content of 0.05 to 2.0 wt%, a copper content of 1.0 wt% or less, a niobium content of 3.0 wt% or less, and a niobium content of 2.0. Below wt%, indium content 4.0 wt% or less, nickel content 0.2 wt% or less, niobium content 0.1 wt% or less, cobalt content 0.5 wt% or less (wherein the aforementioned copper, bismuth, bismuth, The content of indium, nickel, bismuth, and cobalt is not 0), and the remaining part of tin is formed. When the content of bismuth exceeds 2.0% by weight, the alloy solder will become hard and brittle to cause deterioration of the alloy strength. Thereby, an alloy solder having a reduced ductility and strength and a high ductility and strength can be provided.

However, the alloy solder taught by Jin Cunyang Division not only needs to be added A variety of metals can overcome the problems of poor thermal cycle test, fatigue resistance and low strength caused by low silver, and the content of bismuth exceeding 2.0wt% will make the alloy solder hard and brittle, so it needs to be improved. .

The main object of the present invention is to provide a tin-silver-copper-bismuth alloy tin ball which not only refines the crystal grains, but also improves the mechanical strength of the alloy and increases the thermal cycle test capability, and is suitable for products with high fatigue strength.

In order to achieve the above object, a composition of a tin-silver-copper-bismuth alloy solder ball of the present invention comprises silver (Ag), the content of the silver being 0.3 to 4.0 wt%; copper (Cu), The content of copper is 0.3 to 1.0 wt%; bismuth (Bi), the content of the lanthanum is 2000 ± 500 ppm; and tin (Sn), the remaining content disclosed above.

Further, it further contains nickel (Ni), and the content of the nickel is 0.05 to 0.1% by weight.

The present invention further discloses a tin-silver-copper-bismuth alloy solder ball which is formed by the aforementioned composition.

The diameter of the solder ball is 100-890 μm.

Thereby, the tin-silver-copper-nickel alloy solder ball of the present invention and the composition thereof Has the following effects:

1. It has the growth of the thickness of the Inter-Metallic Compound and increases the shear strength, thereby improving the ability of the solder ball to withstand the thermal cycle test.

2. When adding 2000±500ppm of Bi, the wettability of the alloy solder can be effectively improved, and a finer and uniform grain size can be obtained.

The following is a description of the embodiments of the present invention, and the following detailed description of the embodiments of the present invention, The present invention is provided for the purpose of illustrating the technical contents and features of the present invention. Those having ordinary general knowledge in the field of the present invention, after understanding the technical contents and features of the present invention, do not contradict the present invention. In the spirit of the invention, all modifications, substitutions, or limitations of the components are intended to be within the scope of the invention.

1 is a comparison diagram of tin-silver-copper-bismuth alloy solder balls provided by a preferred embodiment of the present invention, mainly showing the effect of adding Bi element on thermal cycle test.

Fig. 2 is a graph showing the tin-silver-copper-bismuth alloy solder balls provided by the preferred embodiment of the present invention, mainly showing the change in wettability of Bi with different contents.

Fig. 3 is a graph showing the tin-silver-copper-bismuth alloy solder balls provided by the preferred embodiment of the present invention, mainly showing the effect of adding different contents of Bi on the interface alloy compound layer.

Figure 4 is similar to Figure 3, mainly showing the tin-silver-copper-bismuth alloy tin of the present invention. The ball undergoes a change in the interface alloy compound layer after repeated reflow.

Figure 5 is a graph showing the tin-silver-copper-bismuth alloy tin ball provided by the preferred embodiment of the present invention, mainly showing the effect of adding different contents of Bi on the shear strength.

Fig. 6 is a view similar to Fig. 5, mainly showing changes in the shear strength of the tin-silver-copper-bismuth alloy solder balls of the present invention after repeated reflow.

Figure 7 is similar to Figure 1, which mainly shows the effect of adding Ni element on the thermal cycle test.

In order to explain in detail the structure, features and effects of the present invention, DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described with reference to the following drawings, wherein: a composition of a tin-silver-copper-bismuth alloy tin ball provided by the preferred embodiment of the present invention, comprising silver (Ag) The content is in the range of 0.3 to 4.0% by weight, the content of copper (Cu) is 0.3 to 1.0% by weight, the content of bismuth (Bi) is 2000 ± 500 ppm, and the content of tin (Sn) is the remaining content disclosed above.

In the part of the thermal cycle test, as shown in Figure 1, in other elements Under the same conditions of the same content, the failure rate of the tin ball with Ag content of 4wt% is obviously better than that of the tin ball with Ag content of 1wt%, but the high content of Ag will make the interface alloy compound layer (IMC) between the low-toughness solder ball and the substrate. It is easy to form a fracture, so that the ball of high silver content has a higher ball drop probability than the low silver content of the tin ball. Therefore, the present invention is an alloy having an Ag content of 1 wt% and an Ag content of 4 wt%, respectively, to overcome the aforementioned drawbacks. A Bi content of 2000 ± 500 ppm was added to the solder balls. It can be seen from Fig. 1 that after the addition of Bi content of 2000±500ppm, the alloy tin ball with Ag content of 1wt% can obviously withstand the thermal cycle test ability. To the alloy tin ball which is close to the Ag content of 4wt%, although the data of the heat cycle test is still slightly lower than the alloy tin ball with the Ag content of 4wt%, the Ag content is 1wt%, and the alloy tin ball with the Bi content of 2000±500ppm is added in cost. It is much lower than the alloy tin ball with an Ag content of 4 wt%.

The invention is the best for verifying that the Bi content is 2000±500ppm. Value, so different content of Bi element was added under the same Sn-1.0wt% Ag-0.5wt% Cu alloy tin ball, and Wetting analysis, microstructure analysis, inhibition of IMC thickness growth analysis and Shear strength analysis.

In the wet part, the wettability of the alloy tin ball refers to a liquid The ability of the metal to spread on a solid surface (ie, the wetting value), for the alloy tin ball, whether it can form a good wettability with the substrate is the key to whether the welding can be completed. As shown in Fig. 2, as the Bi content increases from 0 ppm to 2000 ppm, the wetting value of the alloy tin ball increases from 66.7 to 77.2. When the Bi content exceeds 2000 ppm to 3000 ppm, the wetting value of the alloy tin ball decreases. The trend, as shown by the data, is 77.2 down to 74.1. It can be concluded from the experiment that the addition of 2000 ppm of Bi element under Sn-1.0 wt% Ag-0.5 wt% Cu alloy tin ball can obtain the best wettability.

The aforementioned alloy tin ball is not added with Bi element The Sn grain of Sn-1.0wt%Ag-0.5wt%Cu is mainly cell-like and has a large grain size. When the above-mentioned alloy tin ball is added with 1000 ppm of Bi element, most of the Sn grain is Dendritic distribution, and has a certain directionality, until the aforementioned alloy tin ball is added with 2000 ppm of Bi element, its grain size It becomes finer and evenly distributed; however, when the aforementioned alloy tin ball is added with a Bi element having a content of 3000 ppm, the Sn crystal grains of the structure are instead converted into coarsening. In summary, the addition of an appropriate amount of Bi to the Sn-Ag-Cu alloy tin ball not only makes the grain refinement and homogenization, especially in the addition of 2000 ppm of Bi, which can optimize the alloy strength.

In the part where the thickness of the interface alloy compound (IMC) is suppressed, please Referring to Fig. 3, different amounts of Bi elements are added under the condition of Sn-1.0wt%Ag-0.5wt%Cu alloy tin balls, and the IMC thickness will gradually decrease with the increase of Bi content, such as when the Bi content is 0ppm. The average thickness of the IMC is about 11 μm, and the average value of the IMC thickness is about 7.6 μm when the Bi content is 2000 ppm, which indicates that the addition of the Bi element can effectively suppress the growth of the IMC thickness, but when the Bi content exceeds 2000 ppm. The thickness of the IMC will gradually increase as the Bi content increases. In addition, alloy solder balls are generally used in electronic products and will undergo a multi-pass reflow process, and the present invention considers its importance, so 5 times for Sn-1.0 wt% Ag-0.5 wt% Cu-2000 ppm Bi alloy solder balls. Reflow soldering test, as shown in Fig. 4, Sn-1.0wt%Ag-0.5wt%Cu alloy tin balls without addition of Bi element and Sn-1.0wt% Ag-0.5wt% Cu alloy tin added with 2000ppm Bi The IMC thickness of the ball increases with the number of reflow soldering. It is worth mentioning that the Sn-1.0wt% Ag-0.5wt% Cu-2000ppm Bi alloy solder ball of the present invention is repeatedly reflowed. After that, the rate of increase is much slower than that of the conventional Bi element system, which also shows that the addition of an appropriate Bi element system can effectively suppress the thickness of the IMC. long.

In the part of shear strength, the present invention is based on Nondson Corporation. The multi-function welding strength tester (model Dage series 4000) is used to test the shear strength. Please refer to Figure 5 and Table 1. Sn-1.0wt%Ag-0.5wt%Cu without Bi element The shear strength of the alloy tin ball is 22.46 MPa, which is lower than that of other Sn-1.0 wt% Ag-0.5 wt% Cu alloy tin balls with added Bi element, especially when Sn-1.0 wt% Ag-0.5 wt%. When the content of Bi added to the Cu alloy tin ball is increased, the shear strength is gradually increased. Further, when Bi is added at a content of 1000 ppm to 2000 ppm, the rate of increase of shear strength is slow, and when the content of Bi is more than At 2000 ppm, the shear strength is greatly increased. For example, when the addition of Bi content is 2750 ppm, the shear strength is 44.07 MPa, but according to the value of Table 1 elongation, Sn-1.0 wt% Ag-0.5 wt% Cu. The elongation of the alloy tin ball with the addition of Bi content of 2750ppm decreased to only 0.6%, which means that the addition of too much Bi element will lead to a significant reduction in toughness. In general, the shear strength and elongation data, Sn-1.0wt% Ag- When 0.5wt% Cu alloy tin balls are added with a Bi content of 2000±500ppm, the shear strength is 34.62MPa, 35.31MPa, 42.3M, respectively. Pa, and the elongation are 6.6%, 8.1%, and 6.4%, respectively, especially when the addition of Bi content of 2000 ppm can obtain higher shear strength and good plasticity.

In the part of the Hardness test, the present invention The hardness tester (model FM-100e) produced by FUTURE TECH company is used to test the hardness. The results are shown in Table 2. The Sn-1.0wt%Ag-0.5wt%Cu alloy solder ball without Bi element is added. The hardness is 14.2Hv, which is lower than other Sn-1.0wt% Ag-0.5wt% Cu alloy tin balls with added Bi element, and the test results are similar to those of the aforementioned tensile test, when Sn-1.0wt The more Bi content added to the %Ag-0.5wt%Cu alloy tin ball, the more the hardness increases, which helps to improve the ability of the solder ball to be tested in thermal cycling; however, when Sn-1.0wt% Ag When the Bi content of the 0.5wt% Cu alloy tin ball exceeds 2000ppm, the elongation gradually decreases. As shown in Table 2, the Bi content increases from 2000ppm to 2750ppm, and the elongation decreases from 8.1% to only 0.6%. Looking at the above data of hardness and elongation, Sn-1.0wt%Ag-0.5wt%Cu alloy tin balls can obtain better hardness and elongation when the Bi content is 2000±500ppm, such as hardness of 15.1Hv and 15.4Hv, respectively. 16.3Hv, and the elongation is 6.6%, 8.1%, 6.4%, especially the addition of 2000 ppm of Bi content has the effect of both hardness, thermal cycle test and plasticity.

Please refer to Figure 6, as shown in Figure 6, without the addition of the Bi element. Sn-1.0wt%Ag-0.5wt%Cu alloy tin ball and alloy tin ball with addition content 2000ppm BiSn-1.0wt%Ag-0.5wt%Cu after 5 times of reflow soldering test, the experimental results show that the invention is added The shear strength of the alloy ball of the content of 2000 ppm Bi of Sn-1.0 wt% Ag-0.5 wt% Cu is higher than that of the Sn-1.0 wt% Ag-0.5 wt% Cu alloy tin ball without the addition of Bi element, and the overall test from the test From the aspect of view, the addition of 2000ppm Bi of Sn-1.0wt%Ag-0.5wt%Cu alloy solder ball is better than that of Sn-1.0wt% Ag without Bi addition after several times of reflow soldering. - 0.5 wt% Cu alloy tin ball.

In the preferred embodiment of the present invention, the composition of the alloy tin ball further comprises nickel (Ni), and the content of the nickel is 0.05-0.1 wt%, wherein the Ni element is the fall resistance test of the solder ball. The main component is that Ag ₃ Sn has obvious fibrous and needle-like shape, and the Ag ₃ Sn of the interface alloy compound is coarse and small in shape, and the addition of Ni can refine the structure and appear in the tissue. (Cu _1-x Ni _x ) ₆ Sn ₅ , which has a strengthening effect on the solder ball, but when an excessive amount of Ni is added, excessive (Cu _1-x Ni _x ) ₆ Sn _{5 is formed} , which is in the structure In the present invention, the content of Ni is preferably 0.05 wt%, and the alloy tin ball is added with 0.05 to 0.1 wt% of Ni to form an IMC layer of (CuNi) ₆ Sn ₅ . It can be seen that the addition of an appropriate amount of Ni helps to inhibit the IMC formation of Cu ₃ Sn and prevents the Kirkendall effect from occurring. As the thickness of the aforementioned IMC layer increases with the number of reflow cycles, it has been experimentally found that The thickness of the IMC layer to which Ni is added is not only thicker, but the curvature of the thickness increase is more than 0.05 to 0.1 wt% of the added Ni content, and this is also said. A Sn-1.0wt% Ag-0.5wt% Cu-2000ppm Bi addition amount of Ni-based help suppress the growth of the thickness of the IMC. It is worth mentioning here that, as shown in Fig. 7, when the Sn-1.0wt%Ag-0.5wt%Cu-2000ppm Bi alloy tin ball is added with 0.05wt% Ni, its thermal cycle test ability is compared with that. The aforementioned Sn-1.0 wt% Ag-0.5 wt% Cu-2000 ppm Bi alloy tin ball has an improved effect, and has more recently approached Sn-4.0 wt% Ag-0.5 wt% Cu alloy tin ball.

The present invention utilizes a tin-silver composition composed of the above composition Copper-bismuth alloy solder balls, wherein the alloy tin balls have a diameter of 100 to 890 μm. In the reflow soldering, a Ball Grid Array (BGA), a Chip Scale Package (CSP), and a Flip Chip Package (FCP) are used. The smaller the diameter of the alloy tin ball, the smaller the cross section of the joint of the solder ball will be, so the drop resistance test will also be tested. Therefore, the smaller the diameter of the alloy tin ball, the more the invention can be used. The effect of the drop resistance test, and the solder ball between 100 and 890 μm, can fully exert the drop resistance characteristics of the present invention.

In summary, the tin-silver-copper-bismuth alloy solder ball provided by the present invention The composition not only improves the wettability and refines the grain, but also improves the mechanical strength of the alloy and increases the thermal cycle test capability for use in a wider range of electronic products.

The present invention is not limited to the scope of the present invention, and the alternative or variations of other equivalent elements are also covered by the scope of the patent application.

Claims (4)

A composition of tin-silver-copper-bismuth alloy solder balls, comprising: silver (Ag), the content of the silver is 0.3-4.0 wt%; copper (Cu), the content of copper is 0.3-1.0 Wt%; bismuth (Bi), the content of the lanthanum is 2000 ± 500 ppm; and tin (Sn), the remaining content disclosed above. The composition of the tin-silver-copper-bismuth alloy tin ball described in claim 1, further comprising nickel (Ni), the nickel content being 0.05 to 0.1 wt%. A tin-silver-copper-bismuth alloy solder ball is formed by one of the first to second items of the patent application scope. The tin-silver-copper-bismuth alloy solder ball described in claim 3, wherein the tin ball has a diameter of 100 to 890 μm.