TWI795778B - Lead-free solder alloy, solder ball, solder paste, and semiconductor device - Google Patents

Abstract

Provided is a lead-free solder alloy comprising: 2.8% to 3.5% by weight of silver (Ag); 0.7% to 0.9% by weight of copper (Cu); 2% to 4% by weight of bismuth (Bi ); 0.02% to 0.09% by weight of nickel (Ni); 0.003% by weight to 0.01% by weight of germanium (Ge); and the rest of tin (Sn) and unavoidable impurities. Using the solder alloy of the present invention, it is possible to manufacture solder balls, solder pastes, and semiconductor devices that are excellent in thermal cycle reliability, ductility, and drop impact resistance reliability and that can prevent surface oxidation.

Description

Lead-free solder alloy, solder ball, solder paste and semiconductor device

The present invention relates to a lead-free solder alloy, a solder ball, a solder paste, and a semiconductor device, and more specifically relates to a method for incorporating high-priced silver (Ag) with excellent thermal cycle (TC) reliability and drop shock resistance reliability. Lead-free solder alloys, solder balls, solder pastes and semiconductor devices whose content is controlled within an appropriate range.

With the recent development of semiconductor technology, semiconductor products are being used in various fields. In particular, the case of semiconductor products used outdoors for a long time requires high thermal cycling (TC) reliability. In order to improve TC reliability, increasing the content of expensive elements may not only increase the price of the product, but may also lead to a decrease in other physical properties. Therefore, there is a need to develop a composition that can improve TC reliability without sacrificing cost and other physical properties.

The first technical subject to be achieved by the present invention is to provide a lead-free solder alloy which is excellent in TC reliability, ductility and drop shock resistance reliability and which can prevent surface oxidation.

The second technical problem to be achieved by the present invention is to provide a solder ball that is excellent in TC reliability, ductility, and drop shock resistance reliability, and can prevent surface oxidation, and can contain expensive silver (Ag) The content is controlled within an appropriate range.

The third technical subject to be achieved by the present invention is to provide a solder paste that is excellent in TC reliability, ductility, and drop impact resistance reliability, and that can prevent surface oxidation and remove expensive silver (Ag) The content is controlled within an appropriate range.

The fourth technical subject to be achieved by the present invention is to provide a semiconductor device that is excellent in TC reliability, ductility, and drop impact resistance reliability, can prevent surface oxidation, and can reduce the cost of expensive silver (Ag) The content is controlled within an appropriate range.

In order to achieve the first technical task, the present invention provides a lead-free solder alloy comprising: 2.8% by weight (wt%) to 3.5% by weight of silver (Ag); 0.01% by weight to 0.9% by weight of silver (Ag); Copper (Cu); Bismuth (Bi) at 2% to 4% by weight; Nickel (Ni) at 0.02% to 0.09% by weight; Germanium (Ge) at 0.003% to 0.01% by weight; and tin ( Sn) and unavoidable impurities.

In some embodiments, the copper content of the lead-free solder alloy is 0.7 wt % to 0.9 wt % without impairing the wettability of the solder, and can be applied to Cu-OSP pads.

According to another aspect of the present invention, there is provided a lead-free solder alloy, which is characterized by comprising: 2.8% to 3.5% by weight of silver (Ag); 0.01% to 3.5% by weight of silver (Ag); 0.3% by weight of copper (Cu); 2% by weight to 4% by weight of bismuth (Bi); 0.02% by weight to 0.09% by weight of nickel (Ni); and tin (Sn) and unavoidable impurities in the remainder, and Applied to electroplated nickel pads.

According to another aspect of the present invention, there is provided a lead-free solder alloy, characterized in that it comprises: 2.8% to 3.5% by weight of silver (Ag); 0.5% to 0.9% by weight of copper (Cu); 2% by weight to 4% by weight of bismuth (Bi); 0.02% to 0.09% by weight of nickel (Ni); and the rest of tin (Sn) and unavoidable impurities, and applied to the electroless nickel pad.

In some embodiments, the lead-free solder alloy further includes more than one selected from phosphorus (P) and gallium (Ga), and the total content of more than one selected from phosphorus and gallium can be from about 0.0002% by weight to about 0.003% by weight. weight%.

In some embodiments, the lead-free solder alloy may further include about 0.01 wt % to about 0.7 wt % indium (In).

In order to achieve the second technical subject and the third technical subject, the present invention provides a solder ball and a solder paste including the lead-free solder alloy.

In order to achieve the fourth technical subject, the present invention provides a semiconductor device, which includes: a substrate on which a plurality of first terminals are formed; a semiconductor device mounted on the substrate and having a a plurality of second terminals corresponding to one terminal; and solder bumps, respectively connecting the corresponding first terminals and the second terminals. At this time, the solder bump may include the lead-free solder alloy.

When using the solder alloys of the present invention, TC reliability, ductility can be produced Solder balls, solder pastes, and semiconductor devices that are excellent in drop impact resistance and can prevent surface oxidation.

100: Semiconductor device

110: Substrate

112: first terminal

120: Semiconductor device

122: second terminal

130: Conductive connector

FIG. 1 a shows a conceptual diagram of the microstructure in a bonding solder alloy not containing bismuth and a scanning electron microscope (SEM) image after 3000 thermal cycles.

FIG. 1 b shows a conceptual diagram of the fine structure in the solder alloy joined by lead-free solder alloy according to an embodiment of the present invention and a SEM image after 3000 TCs.

Figure 1c is an image showing the cross-section of a solder alloy according to the variation of bismuth content.

2 is an enlarged image showing the results of bonding using the lead-free solder alloys of Examples 1-1 to 1-5.

3 is an enlarged image showing the results of bonding using the lead-free solder alloys of Comparative Example 1-1 to Comparative Example 1-5.

4 is a three-dimensional image and a planar image in a state where only the Ag ₃ Sn intermetallic compound remains by etching to remove other components of the bonding interface of Comparative Example 1-3.

5 is a planar image showing joint interfaces formed using the solder alloys of Comparative Example 1-1, Comparative Example 1-5, Comparative Example 1-6, and Example 1-5.

FIG. 6 is a graph showing the results of evaluating the TC reliability of Example 1-3, Example 1-5, Comparative Example 1-1, and Comparative Example 1-3.

Fig. 7 shows about embodiment 1-1, embodiment 1-3, embodiment 1-5, comparison Graphs of TC reliability test results of Example 1-1, Comparative Example 1-3, and Comparative Example 1-7.

8 is a graph showing the drop impact reliability test results for the solder alloys of Example 1-1, Example 1-3, Example 1-5, Comparative Example 1-1, and Comparative Example 1-3.

FIG. 9 is a microscope image showing a magnified interface of lead-free solder alloys having the compositions of Examples 2-5 to 2-8 bonded to electroless nickel pads.

10 is a graph showing the results of a high-speed shear test performed on lead-free solder alloys having the compositions of Examples 2-5 to 2-8.

Fig. 11a is a cross-sectional image showing the bonding test results of Examples 2-9.

Fig. 11b is a cross-sectional image showing the bonding test results of Example 2-10.

Fig. 11c shows the measurement of the area spread due to the wetting of the solder balls when the solder balls of Examples 2-9 to 2-13 are mounted on Cu pads to which flux is applied and reflowed. the result of.

12 is an image showing a cross section of surface mounting using lead-free solder alloys having the compositions of Example 3-3, Example 3-7, and Example 3-8.

13a is a graph showing changes in oxide formation according to heating times of Example 4-1, Example 4-2, Example 4-4, Example 4-7, and Example 4-8.

FIG. 13b shows the results of measuring the area spread by the solder balls due to wetting when the solder balls of Examples 4-2 to 4-8 were mounted on Cu pads to which flux was applied and reflowed.

13c is a graph showing the drop impact reliability test results of Example 1-1, Example 4-1, and Comparative Example 1-1.

FIG. 14 is a schematic diagram showing a semiconductor device according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the inventive concept will be described in detail with reference to the accompanying drawings. However, the embodiments of the inventive concept can be modified into various forms, and the scope of the inventive concept should not be construed as being limited by the embodiments described in detail below. The embodiments of the inventive concept are preferably interpreted as provided in order to more fully explain the inventive concept to those having ordinary knowledge in the art. The same symbols refer to the same elements throughout. Furthermore, various elements and areas in the drawings are schematically shown. Accordingly, the inventive concepts are not limited by the relative sizes or spacing shown in the drawings.

Terms such as first and second may be used to describe various constituent elements, but the constituent elements are not limited by the terms. The terms are used only for the purpose of distinguishing one constituent element from other constituent elements. For example, a first constituent element may be named as a second constituent element, whereas a second constituent element may be named as the first constituent element, without departing from the scope of rights of the inventive concept.

The terms used in this application are for describing particular embodiments only, and are not intended to limit the inventive concepts. A singular expression includes a plural expression unless the context clearly indicates otherwise. In this application, expressions such as "comprising" or "having" are intended to indicate the presence of features, numbers, steps, actions, constituent elements, components or combinations thereof described in the specification, but it should be understood that the existence or addition of one or more than one other feature or number, action, constituent element, component or the possibility of a combination thereof.

Unless otherwise defined, all terms used herein include technical terms and scientific terms, and have terms that are commonly used in the technical field to which the inventive concept belongs. The same meaning as understood by all persons. In addition, commonly used terms defined in dictionaries should be interpreted as having meanings consistent with terms in the context of related technologies, and it should be understood that unless clearly defined herein, they should not be interpreted as overly formal meanings.

While an embodiment may be achieved differently, a particular process sequence may also be performed differently than illustrated. For example, two processes described consecutively can be performed substantially simultaneously, and can also be performed in the reverse order of the described order.

In the drawings, variations from the shapes shown may be envisioned, for example, depending on manufacturing techniques and/or tolerances. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated in this specification but are to include variations in shapes that result, for example, from manufacturing. All terms "and/or" as used herein include each of the mentioned elements and all combinations of more than one. In addition, the term "substrate" used in this specification may mean the substrate itself or a laminated structure including the substrate and a predetermined layer or film formed on the surface thereof. In addition, in the present specification, "the surface of the substrate" may mean the exposed surface of the substrate itself, or the outer surface of a predetermined layer, film, or the like formed on the substrate.

According to an embodiment of the present invention, a lead-free solder alloy is provided, the lead-free solder alloy mainly contains tin (Sn), including: about 2.8% by weight to about 3.5% by weight of silver (Ag); about 0.01% by weight to Copper (Cu) at about 0.9% by weight; Bismuth (Bi) at about 2% to about 4% by weight; and Nickel (Ni) at about 0.02% to about 0.09% by weight. The lead-free solder alloy may further include other metal elements in a prescribed content, and the rest of the lead-free solder alloy may be composed of tin (Sn) form. However, the lead-free solder alloy may further contain unavoidable impurities.

Here, the "main component" refers to a component exceeding 50 parts by weight with respect to 100 parts by weight of the overall composition of the lead-free solder alloy.

In the lead free solder alloy, "lead-free" means that no lead is intended to be added and that the lead content is zero or an unavoidable impurity level.

Silver (Ag) content

When the content of silver (Ag) in the lead-free solder alloy exceeds about 3.5% by weight, for example, above 3.6% by weight, the size of _Ag3Sn , which is a kind of intermetallic compound, becomes excessive when bonded to the bonding pad. , which may degrade the reliability at the joint interface. Specifically, when the silver content is 3.6% by weight or more, the Ag ₃ Sn intermetallic compound is formed into a plate when bonding to the bonding pad, and the particles of the Ag ₃ Sn intermetallic compound existing in a powder state are reduced. This may result in reduced dispersion strengthening effect, and degrade reliability and bonding characteristics at the bonding interface.

It was confirmed that especially when the silver content was 3.6% by weight or more, the Ag ₃ Sn intermetallic compound grew into a plate shape when bonded to the bonding pad, and the particle percentage of the Ag ₃ Sn intermetallic compound dispersed in the solder was greatly reduced.

In the lead-free solder alloy, if the content of silver (Ag) is less than 2.8% by weight, the size of Cu ₆ Sn ₅ or (Cu,Ni) ₆ Sn ₅ as a kind of intermetallic compound when bonded to the bonding pad Overgrowth may degrade reliability at the bonding interface. Specifically, when the silver content is less than 2.8% by weight, the particle size of Cu ₆ Sn ₅ or (Cu,Ni) ₆ Sn ₅ intermetallic compound at the joint interface is too large under relatively severe melting conditions, so reliable reduced sex.

It was confirmed that intermetallic compounds of Ag ₃ Sn grow more at the joint interface when the solder alloy is subjected to severe conditions such as high temperature continued for a long time or repeated repetitions of high temperature and low temperature, especially when the content of silver is less than 2.8% by weight. Large, greatly reduced percentage of Ag ₃ Sn intermetallic particles dispersed within the solder. It should be understood that when the silver content is less than 2.8% by weight, the pinning effect of the Ag ₃ Sn intermetallic compound particles cannot be properly exerted, but the present invention is not limited by a specific theory.

When considering the phenomena explained above, the content of silver may be from about 2.8% by weight to about 3.5% by weight, from about 2.8% by weight to about 3.1% by weight, from about 3.1% by weight to about 3.3% by weight, or from about 3.3% by weight to about 3.3% by weight. About 3.5% by weight.

Bismuth (Bi) content

When the content of bismuth (Bi) in the lead-free solder alloy is 2% by weight or more, tin sub-grains may be formed in tin (Sn) grains in the solder alloy to be joined. The sub-grains formed within the tin grains improve the strength of the joined solder.

FIG. 1 a shows a conceptual diagram of the microstructure in a bonding solder alloy not containing bismuth and a scanning electron microscope (SEM) image after 3000 TCs. FIG. 1 b shows a conceptual diagram of the fine structure in the solder alloy joined by lead-free solder alloy according to an embodiment of the present invention and a SEM image after 3000 TCs.

Referring to FIG. 1 a , tin grains and Ag ₃ Sn powder and Cu ₆ Sn ₅ powder forming a network distribution between the tin grains were observed. On the other hand, referring to Figure 1b, the network distribution of Ag ₃ Sn powder and Cu ₆ Sn ₅ powder between tin grains is the same as that shown in Figure 1a, but the difference is that the tin grains in Figure 1b include subgrain grain.

The subgrains of the tin grains are formed due to bismuth dissolved in tin, and may be formed due to the distribution of bismuth in a network shape within the tin grains.

Figure 1c is a cross-sectional image showing the structural variation of tin grains according to the bismuth content in the solder alloy. Here, "1 reflow (1 reflow)" means the cross section after one reflow, and "5 reflows (5 reflows)" means the cross section after five reflows. In addition, the portion surrounded by the yellow dotted line in Fig. 1c corresponds to tin grains.

When 1% by weight of bismuth was included, the size of the tin grains was reduced but sub-grains were not yet formed compared to the case where bismuth was not included (“No Bi (No Bi)”). On the other hand, in the solder alloys with a bismuth content of 3% by weight and 4% by weight, it was visually confirmed that a reticular bismuth network was formed in the tin crystal grains, and tin sub-grains were formed.

When the content of bismuth (Bi) in the lead-free solder alloy exceeds 4% by weight, the drop impact reliability of a package manufactured using the solder alloy may be greatly reduced.

Copper (Cu) content

In the lead-free solder alloy, the content of copper (Cu) may be about 0.9% by weight or less. In some embodiments, the copper content of the lead-free solder alloy may be from about 0.01% to about 0.9% by weight. It has been found that, depending on the type of bond pads of the package, interfacial compounds (i.e., intermetallic compounds) at the junction between the bond pads and the lead-free solder alloy may have adverse effects on physical properties such as drop shock reliability. bring big Impact.

In some embodiments, the copper content of the lead-free solder alloy may be from about 0.01% to about 0.3% by weight. At this point, the lead-free solder alloy may be applied to the bond pads with an electroplated nickel layer.

When bonding said lead-free solder alloy having a _copper content of about 0.01 _wt . (Ni,Cu) ₃ Sn ₄ and other intermetallic compounds. When the copper content of the lead-free solder alloy is above about 0.4% by weight, formation such as Cu ₆ Sn ₅ and/or derived therefrom (Cu,Ni) ₆ Sn ₅ and/or (Ni,Cu) ₃ Sn ₄ etc. Two or more intermetallic compounds having different crystal structures are not preferable.

However, when the copper content reaches about 0.7% by weight to about 0.9% by weight, since (Ni,Cu) ₃ Sn ₄ is not formed in the intermetallic compound, and only an intermetallic compound of (Cu,Ni) ₆ Sn ₅ is formed , and thus the characteristics of the interfacial compound may be more stable compared to the case where the copper content forming at least two intermetallic compounds is about 0.4% by weight or more and about 0.6% by weight or less.

In some embodiments, the copper content of the lead-free solder alloy may be from about 0.5% to about 0.9% by weight. At this point, the lead-free solder alloy may be applied to the bond pads with an electroless nickel layer.

The bonding pads with the electroless nickel layer include, for example, electroless nickel-immersion gold (ENIG) and electroless nickel-electroless palladium-immersion gold (ENEPIG) pads. will have about 0.5% by weight to about 0.9% by weight of copper containing When the lead-free solder alloy having a copper content of 0.7% to 0.9% by weight is bonded to bonding pads having such an electroless nickel layer, a bonding interface with good or excellent drop impact reliability can be obtained.

In some embodiments, the copper content of the lead-free solder alloy may be from about 0.7% to about 0.9% by weight. At this point, the lead-free solder alloy may be applied to the bond pads made of copper. The bonding pads may be, for example, organic solderability preservative (OSP) copper pads.

When the lead-free solder alloy having a copper content of about 0.7% by weight to about 0.9% by weight is bonded to a bonding pad made of copper, the consumption of the copper pad is small and the thickness of the intermetallic compound becomes thin, thus improving TC reliability.

Nickel (Ni) content

In the lead-free solder alloy, the content of nickel (Ni) may be about 0.02 wt % to about 0.09 wt %. The TC reliability and drop shock reliability can be improved when the nickel content is within about 0.02 wt. % to about 0.09 wt. %.

Germanium (Ge), phosphorus (P) and gallium (Ga) content

In some embodiments, the lead-free solder alloy may further include one or more selected from germanium (Ge), phosphorus (P) and gallium (Ga) to prevent oxidation. The total content of one or more selected from germanium, phosphorus, and gallium in the lead-free solder alloy may be about 0.0002 wt % to about 0.015 wt %.

In some embodiments, the total content of one or more selected from germanium, phosphorus, and gallium in the lead-free solder alloy can be about 0.0002 wt% to about 0.015 wt%, about 0.0005 wt% to about 0.014 wt%, about 0.001 wt% % to about 0.013 wt. % by weight, about 0.002% by weight to about 0.012% by weight, about 0.003% by weight to about 0.011% by weight, about 0.005% by weight to about 0.010% by weight, or any range between the stated values.

Indium (In) content

In some embodiments, the lead-free solder alloy may further include about 0.01 wt % to about 0.7 wt % indium (In) to prevent oxidation. In some embodiments, the content of indium may be more than about 0.01% by weight and less than about 0.5% by weight. In some embodiments, the content of indium may be more than about 0.01% by weight and less than about 0.1% by weight.

The lead-free solder alloy described above can be provided in the form of solder balls, solder paste, or the like.

The solder paste may include about 3 parts by weight to about 25 parts by weight of flux relative to 100 parts by weight of the lead-free solder alloy. The flux may be, for example, a moderately activated rosin (Rosin Moderately Activated flux, RMA) type paste flux, and may be in a liquid phase at normal temperature. However, the flux is not limited thereto.

The mixture of the solder alloy and the flux can form a paste at normal temperature.

The solder ball may have a diameter of about 50 μm to about 1000 μm, and may be provided by shaping the solder alloy into a spherical shape.

Other said solder alloys may be provided in any state such as cream, bar, wire or the like.

Hereinafter, the constitution and effect of the present invention will be described in more detail by specific examples and comparative examples, but these examples are only used to understand the present invention more clearly, and It is not intended to limit the scope of the invention.

As an example, a lead-free solder alloy having a composition shown in Table 1-1 below was produced, and as a comparative example, a lead-free solder alloy having a composition shown in Table 1-2 below was produced.

2 is an enlarged image showing the results of bonding using the lead-free solder alloys of Examples 1-1 to 1-5. 3 is an enlarged image showing the results of bonding using the lead-free solder alloys of Comparative Example 1-1 to Comparative Example 1-5.

Each of the images of the embodiment and the comparative example in Fig. 2 is from top to Side view section image below, zoomed-in image of solder structure, zoomed-in image of bonding interface.

As shown in FIG. 2 , it can be seen that the lead-free solder alloy of the embodiment does not form a plate-shaped Ag ₃ Sn intermetallic compound at each bonding interface. On the other hand, it was observed that the lead-free solder alloys of Comparative Example 1-2 to Comparative Example 1-5 shown in FIG. 3 formed a plate-like Ag ₃ Sn intermetallic compound having a considerable size at each joint interface.

4 is a three-dimensional image and a planar image in a state where only the Ag ₃ Sn intermetallic compound remains by etching to remove other components of the bonding interface of Comparative Example 1-3.

Referring to FIG. 4 , it was confirmed that a large number of plate-shaped Ag ₃ Sn intermetallic compounds grew to a considerable size.

5 is a planar image showing joint interfaces formed using the solder alloys of Comparative Example 1-1, Comparative Example 1-5, Comparative Example 1-6, and Example 1-5. That is, it is a planar image in a state where only the Ag ₃ Sn intermetallic compound remains after the solder alloy is used to form the joint interface and other components are removed.

Referring to FIG. 5 , after only one reflow was performed for 60 seconds, only slight growth of grains of Cu ₆ Sn ₅ intermetallic compound was observed at the joint interface using the solder alloy of Comparative Example 1-1, and it was observed that when using other solders At the joint interface of the alloy, the crystal grains of the (Cu,Ni) ₆ Sn ₅ intermetallic compound hardly grow and remain in a relatively fine powder form. (Videos tagged "1st reflow")

On the other hand, under severe conditions formed by maintaining a high temperature of 250° C. for 5 minutes using a hot plate and then cooling, there were slight differences at the bonding interface. In the case of Comparative Example 1-6 and Comparative Example 1-1 in which the silver (Ag) content was less than 2.8% by weight or did not contain bismuth, intermetallic compounds of Cu ₆ Sn ₅ and (Cu,Ni) ₆ Sn ₅ were observed. A large number of grains grow. On the other hand, in the case of Examples 1-5 and Comparative Examples 1-5 in which the silver content was 2.8% by weight or more, due to the pinning effect of the Ag ₃ Sn compound powder, the intermetallic of (Cu,Ni) ₆ Sn ₅ The grain growth of the compound is greatly slowed down. (video tagged 'Hot Plate')

The grain size of the Ag ₃ Sn intermetallic compound at the junction interface can adversely affect thermal cycling (TC) reliability.

In order to measure the bonding strength according to the Ag content at the bonding interface, a non-destructive breaking strength test was performed. A plurality of samples in which the solder alloys of Examples 1-3, Examples 1-5, Comparative Example 1-1, Comparative Examples 1-3, and Comparative Examples 1-5 were bonded to copper pads were prepared, and the tip pairs were used to equalize the samples. Force is applied in a lateral direction to measure dislodgement. The fixing strength applied to the shearing tip was set at 1020 gf, the height of the shearing tip was set at 25 μm, and the test speed of the shearing tip was set at 100 μm/sec.

Tables 1-3 show the nondestructive fracture strength test results for each solder alloy tested.

As shown in Tables 1-3, it can be seen that although the silver content of the solder alloys of Examples 1-3 is about 1 wt% lower than that of the solder alloys of Comparative Examples 1-3, they exhibit more excellent strength. In addition, it can be seen that although the silver content of the solder alloys of Examples 1-5 is lower than that of the solder alloys of Comparative Examples 1-5 by about 1% by weight, they also exhibit more excellent strength. The explanation is that since the silver content in the solder alloy is within 3.6% by weight, the Ag ₃ Sn intermetallic compound formed in the plate-like excessive growth at the joint interface is suppressed, thereby exerting the dispersion enhancement effect.

In order to evaluate TC reliability based on the contents of silver and bismuth, many samples in which the solder alloys of Example 1-3, Example 1-5, Comparative Example 1-1, and Comparative Example 1-3 were attached to substrates were prepared. For the samples, cycles were performed between -55°C and +125°C with 30 minutes as a cycle, and the ball shear strength was measured. The shear tip speed was set to 500 μm/sec, the shear tip height was set to 20 μm, and the ball shear strength was measured every 1000 cycles, as shown in FIG. 6 .

Referring to Figure 6, the solder alloy of Comparative Example 1-1 was subjected to 3000 TC cycles after the initial bonding, and the strength decreased by about 25% from 905 gram force (gram force, gf) to 680 gf, and the solder alloy of Comparative Example 1-3 After 3000 TC cycles after the initial engagement, the strength decreased from 1232gf to 1023gf by about 17%.

On the other hand, the solder alloys of Examples 1-3 were subjected to 3000 TC cycles after initial bonding, and the strength decreased by about 10% from 1224gf to 1098gf, and the solder alloys of Examples 1-5 were subjected to 3000 TC cycles after initial bonding , the intensity decreased from 1290gf to 1167gf by only about 9.5%.

Therefore, it was confirmed that the solder alloys of Examples 1-3 and Examples 1-5 having a relatively smaller silver content exhibited better performance than the solder alloys of Comparative Examples 1-3 having a higher silver content. Excellent TC reliability.

In order to study the impact of bismuth content on the reliability of TC, the implementation of Example 1-1, Example 1-3, Example 1-5, Comparative Example 1-1, Comparative Example 1-3 and Comparative Example 1-7 TC reliability test. After making 20 packages for each solder alloy, perform a cycle of -55°C and +125°C in 30 minutes as a cycle and measure the resistance in situ. The data counts the number of defects every 100 cycles, and The result is shown in FIG. 7 .

As shown in FIG. 7 , it can be seen that TC reliability is greatly improved in Cu-OSP pads when bismuth is not included (Comparative Example 1-1) or bismuth is included less than 2% by weight (Comparative Example 1-7). In addition, comparing Example 1-1, Example 1-3, and Example 1-5, it was confirmed that TC reliability was improved as the content of bismuth was increased to 4% by weight. In addition, compared with Example 1-3, it was confirmed that TC reliability decreased in the case of Comparative Example 1-3 in which the silver content was increased to 4% by weight.

In order to study the influence of bismuth content on the drop impact reliability, the drop impact reliability test was performed on Example 1-1, Example 1-3, Example 1-5, Comparative Example 1-1 and Comparative Example 1-3 . In the assembly mechanical shock standard of JESD22-B110A, the drop shock reliability is analyzed using the condition "B" with an acceleration of 1500G and a duration time of 0.5ms. FIG. 8 is a graph showing the results of a drop impact reliability test.

Referring to FIG. 8 , the alloy composition of Example 1-5 having a bismuth content of 4% by weight is close to that of Comparative Example 1-1 containing no bismuth. In addition, the solder alloys of Example 1-1 and Example 1-3 containing about 2% by weight to about 3% by weight of bismuth were more than those containing 4 The solder alloys of Comparative Examples 1-3 with silver in weight % showed more excellent drop impact reliability.

In order to study the impact of the content of nickel on the composition of the intermetallic compound formed at the bonding interface of the Cu-OSP pad, there will be examples 1-2, 1-3, comparative example 1-1 and comparative example Solder alloys of compositions 1-4 were bonded to copper pads, and the formation of bonding interfaces at two points (P1, P2) were analyzed by energy dispersive X-ray spectroscopy (EDS). The compositions of the intermetallic compounds are listed in Tables 1-4.

As shown in Tables 1-4, in the case of the solder alloy of Comparative Example 1-1 not containing nickel, an intermetallic compound of Cu ₆ Sn ₅ was formed. On the other hand, in the case of the solder alloys of Examples 1-2, 1-3, and 1-4 containing nickel, an intermetallic compound of (Cu,Ni) ₆ Sn ₅ was formed.

Compared with Cu ₆ Sn ₅ , it is known that (Cu,Ni) ₆ Sn ₅ is superior in properties such as strength, thermal expansion coefficient, and deformation stress, and is also superior in TC reliability and drop impact reliability. Therefore, the content of nickel is preferably more than 0.02 wt%, so as to form an intermetallic compound of (Cu,Ni) ₆ Sn ₅ at the joint interface.

As an additional example, a lead-free solder alloy having a composition as shown in Table 2-1 below was manufactured, and a bonding test to a metal pad was performed.

In Table 2-1, electroplating nickel refers to forming an electroplating nickel layer on a copper pad by electroplating, and forming a gold layer thereon. In addition, in Table 2-1, electroless nickel plating (ENEPIG) refers to sequentially forming an electroless nickel plating layer and an electroless palladium plating layer on copper pads by electroless plating, and forming a gold layer thereon. Here, ENEPIG means electroless nickel-electroless palladium-immersion gold (electroless nickel-electroless palladium-immersion gold), ENIG Indicates electroless nickel-immersion gold (electroless nickel-immersion gold). Copper pads are bonding pads with a pure copper surface.

Electroplated Nickel Pads

In the bonding tests of Example 2-1 to Example 2-4, reflow was performed once and 10 times for each of the others, and then the reflow formed at the bonding interface was performed at two points (P1, P2), respectively. The types and compositions of intermetallic compounds were analyzed, and the results are summarized in Table 2-2 below.

In the case of Example 2-1 in which the Cu content was 0.001% by weight, an intermetallic compound of Ni ₃ Sn ₄ was formed even if reflow was repeated, and there was no large compositional change. Since an intermetallic compound is formed, the reliability of the bonding interface is high.

In the case of Example 2-2 in which the Cu content was 0.2% by weight, even if the reflow was repeated, the composition slightly changed, but an intermetallic compound of Ni ₃ Sn ₄ and (Ni,Cu) ₃ Sn ₄ was roughly formed. Since (Ni,Cu) ₃ Sn ₄ is a part of Ni ₃ Sn ₄ replaced by Cu, and the crystal structure is the same as each other, the stress in the joint interface is not large, so the reliability of the joint interface is high.

In the cases of Example 2-3 and Example 2-4 in which the Cu contents were 0.5% by weight and 0.8% by weight, respectively, it can be seen that (Cu,Ni) ₆ Sn ₅ in which a part of Cu of Cu ₆ Sn ₅ is replaced by Ni is produced, Then reflux is repeated to generate (Ni,Cu) ₃ Sn ₄ . This is because the basic crystal structure changes from Cu ₆ Sn ₅ to Ni ₃ Sn ₄ structure, and a large stress will be generated in the interface compound layer, thereby greatly reducing TC reliability and impact resistance reliability.

In addition, comparing Example 2-3 with Example 2-4, it can be confirmed that the higher the Cu content, the higher the Cu content at the interface compound in the product after 10 reflows. Therefore, in Example 2-3 having a Cu content of 0.5% by weight, two interfacial compounds ((Ni,Cu) ₃ Sn ₄ , (Cu,Ni) ₆ Sn ₅ ) with a large difference in crystal structure were simultaneously formed, and vice versa , in Examples 2-4 having a Cu content of 0.8% by weight, an interfacial compound ((Cu,Ni) ₆ Sn ₅ ) was formed to have more stable physical properties.

Therefore, it can be seen that in the electroplated nickel contact pad, the Cu content is 0.001 wt % to 0.3 wt % in Example 2-1 and Example 2-2 and the Cu content is 0.7 wt % to 0.9 wt % in Example 2-4 Compared with Example 2-3, which has a Cu content of 0.5% by weight, it has a more favorable effect. However, Example 2-2 having a Cu content of 0.001 wt % to 0.3 wt % is more preferable than Example 2-4 having a Cu content of 0.7 wt % to 0.9 wt %.

Electroless Nickel Plated Pads

In the joining test of embodiment 2-5 to embodiment 2-8, will have its etc. Solder alloys of each composition were bonded to electroless nickel (ENEPIG and ENIG) pads, and their cross-sections were observed. FIG. 9 is an enlarged SEM image of the bonding interface of each section.

Referring to FIG. 9, a phosphorus-rich (P) (phosphorus(P)-rich) nickel layer is formed at the bonding interface between the solder alloy and the electroless nickel-plated pad, and this phosphorus-rich nickel layer makes the drop impact reliable. sex decline. However, it has been confirmed that the higher the copper content of the solder alloy layer, the thinner the thickness of the phosphorus-rich nickel layer, and therefore, the drop impact reliability is improved.

In order to confirm the drop impact reliability, 100 samples each of the solder alloys of the Examples bonded to the electroless nickel-plated pads were prepared, and a high speed shear test (HSST) was performed on the same. The tip speed was 500 mm/sec and the tip height from the bonding surface was 20 micrometers (μm).

If the area of solder remaining on the surface removed by the tip hitting the solder part exceeds 75%, it is judged to be ductile (ductile); if it exceeds 50% but less than 75%, it is judged to be quasi-ductile (quasi) -ductile); if it exceeds 25% and is less than 50%, it is judged as semi-brittle (quasi-brittle); if it is less than 25%, it is judged as brittle (brittle).

Then, the ratio of each property was calculated for the samples of each Example, and a bar graph as shown in FIG. 10 was drawn. Referring to FIG. 10 , it can be seen that the higher the copper content, the higher the ratio of samples judged to be ductile, and the lower the copper content, the higher the ratio of samples judged to be brittle. As a result of HSST, it can be seen that the closer to brittleness, the lower the drop impact reliability, and the closer to ductility, the better the drop impact reliability. Therefore, for electroless nickel plated pads such as ENEPIG, the drop impact is reliable with increasing copper content The better the sex.

copper pad

In the bonding tests of Examples 2-9 and Examples 2-10, a solder alloy having a composition of each of them was bonded to a copper pad by one reflow, and the cross section thereof was observed. In addition, after reflowing once, it was kept under severe conditions, that is, a high temperature of 250° C. for 5 minutes, and the cross section was observed.

Fig. 11a is a cross-sectional image showing the bonding test results of Example 2-9, and Fig. 11b is a cross-sectional image showing the bonding test results of Example 2-10.

In the solder alloys of Examples 2-9, the thickness of the copper pad was about 44.9 microns (μm) after one reflow, and about 37.6 μm after being placed under harsh conditions for 5 minutes. Consequently, the thickness of the copper pad is reduced by about 7.3 μm, which corresponds to about 16.3% when compared to the thickness after one reflow.

In the solder alloys of Examples 2-10, the thickness of the copper pad is about 45.9 μm after one reflow, and the thickness of the copper pad is about 42.6 μm after being placed under severe conditions for 5 minutes. Consequently, the thickness of the copper pad is reduced by about 3.3 μm, which corresponds to about 7.2% when compared to the thickness after one reflow.

The thicker the intermetallic compound at the bonding interface, the lower the thermal cycle (TC) reliability and impact resistance reliability. As shown in FIG. 11a and FIG. 11b , when the copper content is relatively higher, the consumption of copper pads is reduced, thus obtaining thinner intermetallic compounds, and improving TC reliability and shock resistance reliability.

However, as shown in Example 2-11 to Example 2-13, it was observed that the melting point of the alloy became higher when the Cu content was increased above 1.0 wt%, and Fig. 11c The wetting properties of the solder balls shown are reduced. 11c shows the results of measuring the area spread by solder balls being wetted when the solder balls of Examples 2-9 to 2-13 are reflowed on Cu pads to which flux is applied.

To sum up, in the case of electroplated nickel pads, it is advantageous in terms of reliability that the copper content is about 0.3% by weight or less. In addition, in the case of electroless nickel plated pads, a copper content of about 0.5% by weight to about 0.9% by weight is advantageous in terms of drop impact reliability. In addition, in the case of copper pads, the copper content may be about 0.7 wt% to about 0.9 wt% to ensure TC reliability, impact resistance reliability, and stable wetting characteristics, thus being advantageous in terms of bonding quality.

In order to prevent the oxidation of the solder alloy and to study the influence of germanium (Ge) and indium (In) that can be added to the solder alloy according to some embodiments of the present invention, a solder alloy having the composition shown in Table 3-1 below was prepared. solder balls.

In the case of Example 3-5 and Example 3-6 not containing indium, it was confirmed that Brightness was good after manufacture, but became discolored and decreased in brightness after rubbing was applied.

Furthermore, as shown in FIG. 12 , in the case of Examples 3-7 and 3-8 containing 0.5% by weight or more of indium, it was found that voids were captured in the bumps during surface mounting.

In order to prevent the surface of the lead-free solder alloy from being thermally oxidized, and in order to study the influence of germanium (Ge) and phosphorus (P) that can be added to the lead-free solder alloy according to some embodiments of the present invention, preparations have the following table 4-1. Solder balls were prepared from solder alloys of the indicated composition.

13a is a graph showing changes in oxide formation according to heating times of Example 4-1, Example 4-2, Example 4-4, Example 4-7, and Example 4-8. Referring to Figure 13a, it is observed that in the case of Example 4-1 that does not contain Ge and P, Dross of metal oxides is formed at a relatively rapid rate. As a comparison, it was observed that in the case of Example 4-2 and Example 4-4 containing Ge, the dross of the metal oxide was formed at a slower rate. In other words, it was confirmed that Ge can retard the rate at which the surface of the lead-free solder alloy is thermally oxidized. On the other hand, it was confirmed that in the case of Examples 4-7 and 4-8 containing P, the rate of formation of metal oxide scum was further delayed.

FIG. 13b shows the results of measuring the area spread by the solder balls due to wetting when the solder balls of Examples 4-2 to 4-8 were mounted on Cu pads to which flux was applied and reflowed.

Referring to FIG. 13 b , it was observed that the solder balls of Examples 4-2 to 4-4 having a Ge content of 0.003 wt % to 0.01 wt % stably maintained ductility.

In addition, it can be observed that when the P content is 0.003% by weight, the ductility is relatively good, but when the P content is 0.005% by weight, the ductility rapidly deteriorates. In this aspect, it can be seen that the P content is preferably about 0.003% by weight or less, such as about 0.0002% by weight to about 0.003% by weight.

In order to study the influence of the contents of germanium and phosphorus on the drop impact reliability, a drop impact reliability test was performed on Example 1-1, Example 4-1, and Comparative Example 1-1. In the assembly mechanical shock standard of JESD22-B110A, the drop shock reliability is analyzed using the condition "B" using an acceleration of 1500G and a duration time of 0.5ms. 13c is a graph showing the drop impact reliability test results of Example 1-1, Example 4-1, and Comparative Example 1-1.

Referring to Figure 13c, it was confirmed that compared with the solder ball of Comparative Example 1-1, the embodiment The solder balls of 1-1 and Example 4-1 had significantly excellent drop impact reliability. Therefore, it can be seen that in order to ensure excellent drop impact reliability, it is necessary to add Ge or P. Specifically, the content of Ge is preferably the content of Example 4-2 to Example 4-4, that is, about 0.003 wt % to 0.01 wt %, and the content of P is preferably about 0.0002 wt % to about 0.003 wt %.

<Manufacturing of Solder Paste>

Use vacuum gas atomizer (atomizer) to manufacture respectively have the composition of embodiment 1-1 to embodiment 1-5, embodiment 2-1 to embodiment 2-10 and embodiment 3-1 to embodiment 3-8 powder, followed by a sieve to obtain a type 4 powder having a diameter of approximately 20 μm to 38 μm. At this time, the melting temperature was 550° C., and argon (Ar) was used as the gas.

Then, 12 parts by weight of a flux for RMA type paste was added with respect to 100 parts by weight of the powder, and then mixed using a paste mixer at a speed of 1000 rpm for 3 minutes and 30 seconds to manufacture a solder paste.

<Manufacturing of welding rods and solder balls>

Alloy electrodes with the composition of Example 1-1 to Example 1-5, Example 2-1 to Example 2-10 and Example 3-1 to Example 3-8 were prepared using a vacuum degassed alloy device , and the process temperature at this time is 500°C. In addition, in order to manufacture the alloy electrode, a bubbling process and a vacuum degassing process are performed, followed by tapping.

In addition, a solder ball having a diameter of 0.3 mm was produced using the produced alloy electrode.

Another aspect of the present invention provides a semiconductor device. Fig. 14 shows a semiconductor device (100) according to an embodiment of the present invention.

Referring to FIG. 14, a substrate (110) formed with a plurality of first terminals (112) is provided. The substrate (110) can be, for example, a printed circuit board (printed circuit board, PCB) or a flexible printed circuit board (flexible printed circuit board, FPCB).

The plurality of first terminals (112) can be pads on which conductive connectors can be combined, and can have a structure in which a single metal layer or multiple metals are laminated. In addition, the first terminal (112) may be made of two or more alloys of copper (Cu), aluminum (Al), nickel (Ni) or the like, but is not limited thereto.

A semiconductor device (120) having a plurality of second terminals (122) corresponding to the plurality of first terminals (112) may be mounted on the substrate (110). The second terminal (122) can be, for example, flash memory, phase-change RAM (phase-change RAM, PRAM), resistive RAM (resistive RAM, RRAM), ferroelectric RAM (ferroelectric RAM, FeRAM), Solid-state magnetic memory (magnetic RAM, MRAM), etc., but not limited thereto. The flash memory may be, for example, NAND flash memory. The semiconductor device (120) can be formed by one semiconductor wafer, and can also be formed by stacking multiple semiconductor wafers. In addition, the semiconductor device (120) itself may be a semiconductor chip, and may also be a semiconductor package in which a semiconductor chip is mounted on a package substrate and the semiconductor chip is sealed with a sealing material.

The plurality of first terminals (112) and the corresponding plurality of second terminals (122) can be connected by conductive connectors (130). At this point, the The conductive connector (130) may have the same composition as the lead-free solder alloy having the composition described above.

When the substrate (110) and the semiconductor device (120) are connected by the above-mentioned conductive connector (130), since the impact resistance and thermal shock characteristics are excellent, a highly reliable solder joint can be obtained.

Although the embodiments of the present invention as described above are described in detail, those skilled in the art can implement the present invention without departing from the spirit and scope of the present invention limited by the appended patent scope. Various deformations. Therefore, variations of the foregoing embodiments of the present invention do not depart from the teachings of the present invention.

Claims (8)

A lead-free solder alloy comprising Sn-Bi subgrains formed by a bismuth network within tin grains, comprising: 2.8% to 3.5% by weight of silver (Ag); 0.7 to 0.9% by weight of copper (Cu ); 2% to 4% by weight of bismuth (Bi); 0.02% to 0.09% by weight of nickel (Ni); 0.01% to 0.1% by weight of indium (In); 0.003% to 0.01% by weight of germanium (Ge); and the rest of tin (Sn) and unavoidable impurities. The lead-free solder alloy as claimed in claim 1, wherein the content of copper is 0.8wt% to 0.9wt%, does not impair the wettability of solder, and is applied to Cu-OSP pads. A lead-free solder alloy comprising Sn-Bi sub-grains formed by a bismuth network in tin grains, characterized in that it comprises: 2.8% by weight to 3.5% by weight of silver (Ag); 0.01% by weight to 0.3% by weight of Copper (Cu); Bismuth (Bi) at 2% to 4% by weight; Indium (In) at 0.01% to 0.1% by weight; Nickel (Ni) at 0.02% to 0.09% by weight; and tin ( Sn) and unavoidable impurities, and applied to electroplated nickel pads. A lead-free solder alloy comprising a Sn-Bi sub-grain formed by a bismuth network in a tin grain, characterized in that it comprises: 2.8% to 3.5% by weight of silver (Ag); 0.5% to 0.9% by weight of Copper (Cu); Bismuth (Bi) at 2% to 4% by weight; Indium (In) at 0.01% to 0.1% by weight; Nickel (Ni) at 0.02% to 0.09% by weight; and tin ( Sn) and unavoidable impurities, and applied to electroless nickel plated pads. The lead-free solder alloy as described in any one of claim 1 to claim 4, further comprising: more than one selected from phosphorus (P) and gallium (Ga), a total of more than one selected from phosphorus and gallium The content is about 0.0002% by weight to about 0.003% by weight. A solder ball, comprising the lead-free solder alloy described in any one of claim 1 to claim 4. A solder paste comprising the lead-free solder alloy described in any one of claim 1 to claim 4. A semiconductor device, characterized by comprising: a substrate formed with a plurality of first terminals; a semiconductor device mounted on the substrate and having a plurality of second terminals corresponding to the plurality of first terminals; and A conductive connector for connecting the corresponding first terminal and the second terminal respectively, the composition of the conductive connector is the same as that of the lead-free solder alloy described in any one of claim 1 to claim 4 same.

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