KR100438409B1 - Composite solders and process method of composite solders - Google Patents

Abstract

The present invention relates to a composite solder for improving creep strength and reliability in solder and solder ball materials and a method of manufacturing the same.

The composite solder production method of the present invention is economical and effective to disperse the intermetallic compound reinforcement in the form of particles in the solder base without the use of a solid powder.

In the manufacturing method of the composite solder of the present invention, the intermetallic compound to be a reinforcing material during the solidification process is melted by heating and dissolving a solder alloy having a composition formed in the solder base at a liquid line or higher, and solidifying the intermetallic compound in the solder base. Steps,

And a plastic working step of crushing the intermetallic compound in the solder alloy into fine particles by plastic working such as rolling or drawing.

Since the intermetallic compound uniformly crushed in the solder alloy according to the present invention has a higher melting point than the solder base, the intermetallic compound can remain in the particulate state in the matrix because the solid state can be maintained without melting in the solder process or the reflow process. Therefore, the strength of the joint can be improved.

Description

Composite solders and process method of composite solders

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite solder for increasing creep strength and reliability in solder and solder ball materials, and to a method of manufacturing the same.

With the development of the multimedia and telecommunications industry, computers, notebooks, mobile phones, and other electronic components are becoming smaller and lighter. Accordingly, with the miniaturization of electronic packages and the development of surface mount technologies, the reliability of solders for electrical and mechanical connection in packages is becoming important. Chips and substrates, and the solder that connects the chip and the chip, the substrate and the substrate is broken by fatigue and creep because the chip operates at a high temperature of more than 100 ℃.

In order to increase resistance to such breakdown, studies have been conducted on composite solders reinforced by adding fine dispersed phases to solders. The disperse phase acting as a reinforcement enhances the reliability of the solder by suppressing the occurrence of cracks, preventing grain boundary sliding, and increasing fatigue strength by inhibiting the growth of the interfacial reaction layer between the solder and the substrate.

The simplest method of manufacturing a conventional composite solder is a method of mixing solid powders such as Cu ₆ Sn ₅ and Ni ₃ Sn ₄ with molten tin-silver (Sn-Ag) solder and then solidifying them. In this case, the powder is uniformly distributed in the molten solder by mechanically mixing the molten solder and the powder. There is also an in-situ method in which molten tin-silver solder and copper (Cu) powder are mixed to react the copper powder with tin (Sn) in the molten metal to obtain Cu ₆ Sn ₅ particles in the solder base. These methods mix the powder and flux together with the molten solder to remove the oxide film of the powder to improve wettability.

Another method is to mix solder powder and reinforcement powder into a paste.

However, when the powder is used, the manufacturing cost of the powder is high and the solvent for improving wettability is a cause of environmental pollution. In addition, when the powder is fine, the solder melted by the oxide film and wettability deteriorate, making it difficult to mix. In addition, when mechanically mixing the molten solder in order to distribute the powder uniformly in the matrix there is a problem that the oxidation of the molten surface is further accelerated.

As a method for uniformly dispersing the particle reinforcing material in the solder base, magnetic powders such as iron may be more uniformly distributed in the substrate by applying a magnetic field. However, because this method requires the application of magnetic fields, this technique can be applied only to particles that are complicated and magnetic.

The present invention is an economical and effective method for producing a composite solder which disperses an intermetallic compound reinforcement in the form of particles in a solder base without using a solid powder. First, the alloy composition is controlled so that the intermetallic compound, which will be a reinforcing material in the solidification process, is formed in the solder base in the form of primary resin, cell, plate, or particles. The alloy thus cast can be crushed into fine particles by plastic processing such as rolling or drawing, and uniformly redistributed to the substrate by plastic deformation.

The intermetallic compound thus formed has a higher melting point than the solder base, so that the solid state can be maintained without melting in the soldering process or the reflow process, so that the intermetallic compound can be present in the granular state in the matrix, thereby improving the strength of the joint. .

1 is a tin-copper (Sn-Cu) state diagram.

2 is an exemplary diagram in which the Cu ₆ Sn ₅ intermetallic compound having a dendritic form is redistributed while being crushed by rolling.

Figure 3 is a photograph showing the solidification structure of the alloy having a 90.2Sn-6.9Cu-2.9Ag composition

4 is a structure photograph of a thin plate rolled alloy of FIG.

5 is a photograph showing the microstructure of a solder ball sphericalized by cutting the rolled thin plate of FIG. 4 into a disk shape and then remelting it;

6 is a photograph of the structure immediately after reflow soldering of the solder ball of Sn-3.5Ag composition and the composite solder ball of FIG.

Figure 7 is a tissue photograph of the annealing the solder ball of Figure 6

8 is a chart showing the shear strength by the ball shear test (ball shear test) of the solder ball of Figures 6 and 7

In the manufacturing method of the composite solder of the present invention, the intermetallic compound to be a reinforcing material during the solidification process is melted by heating and dissolving the solder alloy of the composition formed in the solder base at a liquid line or higher to form a metal compound in the solder base. Steps,

And crushing the intermetallic compound in the solder alloy into fine particles by plastic working such as rolling or drawing.

The intermetallic compound is Cu ₆ Sn ₅ , Ni ₃ Sn ₄ , FeSn ₂ , Cu ₃ Sn, AgIn ₂ , AuSn ₄ , AuSn, InSn ₄ , PdSn ₄ , PdSn ₃ , Sb ₂ Sn ₃ , SbSn, Sn ₄ Sr Ti ₆ Sn ₅ is selected from among these intermetallic compounds in the form of dendritic, cellular, plate or particle in the solder base in the casting step, and may be broken into fine particles in the plastic working step.

In the present invention, the known composition of the solder alloy is composed of tin (Sn) as the main component and selected from lead (Pb), silver (Ag), bismuth (Bi), indium (In), and copper (Cu). One or two or more alloys, an alloy containing gold (Ag) or indium (In) as a main component, and any one or two or more selected from silver (Ag), bismuth (Bi) and copper (Cu) Alloys can be used and these bases form one of the above intermetallic compounds as primary.

When solder alloy is cast, the melting temperature of the alloy should be heated to a temperature above the liquidus line in the state of solder alloy to dissolve the solder alloy, and when casting the solder alloy, the cooling rate of the molten metal is increased so that dendritic, plate, cell and particle After finely obtaining the intermetallic compound in the form can be broken into finer particles in the firing process of the rolling process or drawing process. Large cooling rates can be achieved by casting into molds, continuous casting, strip casting, melt spinning, or by quenching liquids such as water and oil.

As described above, the intermetallic compound in the dendritic, cellular, plate, and particle form has a superlattice structure, and thus has brittleness, so that it can be easily broken into particles in plastic processing such as rolling and drawing processing.

The core of the present invention is to redistribute by controlling the alloy composition to solidify the intermetallic compound in the solder base in the first base, and then crushed by plastic working. At this time, since the melting point of the formed intermetallic compound is higher than the melting point of the solder base, it does not chemically react with the solder in the soldering process, remelting spheroidization, reflow process, etc., and thus remains solid without melting.

The present invention relates to Cu ₆ Sn ₅ , Ni ₃ Sn ₄ , FeSn ₂ , Cu ₃ Sn, AgIn ₂ , AuSn ₄ , AuSn, InSn ₄ , PdSn ₄ , PdSn ₃ , Sb ₂ Sn ₃ , SbSn, Sn ₄ Sr or Ti ₆ brittle, such as Sn ₅ can be applied to a strong intermetallic compound.

Hereinafter, the present invention will be described by the following examples. However, these do not limit the rights of the present invention.

<Example 1>

A method for producing a composite solder in which Cu ₆ Sn ₅ particle reinforcing material is dispersed in a tin (Sn) matrix is described. 1 is a tin-copper (Sn-Cu) state diagram. The process temperature of Sn and eta (η) phase is 227 ° C, and the process composition is 99.3Sn-0.7Cu. When the alloy is made with a Cu composition of 0.7 wt% or more, an eta (η) phase Cu ₆ Sn ₅ intermetallic compound appears as a primary crystal in a dendritic form, and the matrix is solidified in a Sn-Cu process structure.

If Cu is more than 7.6 wt%, the epsilon (ε) phase also appears at 415 ° C or higher, but changes to eta (η) phase at a deviation of 415 ° C or lower. The volume fraction of the eta (η) phase is controlled by the Cu content, for example a 10 vol% eta (η) phase is obtained at 5.2 wt% Cu.

In the melting method of the alloy, when the Sn ingot and Cu ingot are mixed and heated to a temperature above the liquidus, the Sn ingot having a low melting point is melted first, and then the Cu ingot is dissolved into the Sn molten metal. At this time, in order to suppress oxidation of the molten metal, an inert gas atmosphere such as nitrogen (N ₂ ) or argon (Ar) is made.

When the cast ingot is plastically processed by rolling or drawing process, the hard and brittle Cu ₆ Sn ₅ intermetallic compound is broken into particles on the resin, which is redistributed uniformly in the solder base, increasing the number of rolling and casting the ingot By rolling in several directions, finer particles can be obtained and the distribution of particles becomes more even.

2 shows an exemplary diagram in which the Cu ₆ Sn ₅ intermetallic compound having a dendritic form is redistributed while being crushed by rolling.

<Example 2>

Ingots of tin (Sn), silver (Ag), and copper (Cu) were used as a raw material to prepare solder alloys having a composition of 90.2Sn-6.9Cu-2.9Ag.

3 is a photograph showing a solidification structure of an alloy having a composition of 90.2Sn-6.9Cu-2.9Ag. In this alloy, a dendritic Cu ₆ Sn ₅ intermetallic compound appears as a primary and a ternary process structure (L → βSn + Cu ₆ Sn ₅ + Ag ₃ Sn).

4 is a texture photograph of a thin plate rolled alloy having a composition of 90.2Sn-6.9Cu-2.9Ag of FIG. 3, showing that the Cu ₆ Sn ₅ intermetallic compound shown in FIG. 3 is crushed. 5 is a microstructure of a solder ball (16vol% Cu ₆ Sn ₅ particles of the disc-forming method) by cutting the rolled thin plate of FIG. 4 into a disc shape using a punch and then remelted by putting it in hot oil. ).

6 shows the reflow soldering of the solder balls of FIG. 5 and the left balls of the Sn-3.5Ag composition. At this time, the two solder balls are equally soldered by flowing in a reflow furnace at the same time. In the right figure of FIG. 6, Cu ₆ Sn ₅ particles have a higher density than solder bases, and thus settling occurs. Therefore, the upper part of the solder ball can be seen that the Cu ₆ Sn ₅ particles do not exist.

The left solder ball of FIG. 7 is the left solder ball of FIG. 6, and the right solder ball of the right solder ball of FIG. 6 is annealed at 150 ° C. for 10 days. As a result, coarsening of Cu ₆ Sn ₅ particles as well as the reinforcing material is performed. In order to test the reliability of the solder over time, it was annealed at 150 ° C for 10 days above the actual operating temperature of the chip.

FIG. 8 is a ball shear test of the solder ball of FIG. 6 and the solder ball of FIG. 7. The shear strength immediately after the reflow solder is similar to that of the solder ball of the Sn-3.5Ag composition, but the composite solder ball is annealed. It is larger than the solder ball of Sn-3.5Ag composition.

The composite sulfer produced by the present invention has the following effects.

First, a low cost / high reliability particle composite solder can be made because the particle composite solder is made in-situ using ingot metal without using powder.

Second, the present invention can be applied to the lead-free solder and is environmentally friendly because no powder is used.

Third, since the present invention is rolled or drawn, it is possible to produce a product using a preform solder, a wire solder, and a solder ball.

Fourth, a very fine and uniformly distributed particle composite solder can be obtained by crushing / redistributing the intermetallic compound into particles by plastic working such as rolling or drawing.

Fifth, the base has the same melting point as the composition of commercially available solder, and the finely dispersed particle reinforcement in the base prevents grain boundary slipping, and becomes a nucleation site, making grains finer, thereby suppressing the formation and propagation of cracks. By doing so, the reliability of the solder can be improved.

Claims (7)

In the manufacturing method of a composite solder reinforced with an intermetallic compound, (a) mixing a metal element constituting an intermetallic compound having a higher melting point than the solder base to a solder base of a process composition, and heating and dissolving it above a liquidus line; (b) solidifying the melt obtained in step a to form an intermetallic compound in the solder base; And (c) a method of manufacturing a composite solder, comprising the step of plastic working the intermetallic compound in the solder base. The method of claim 1, wherein the intermetallic compound is Cu ₆ Sn ₅ , Ni ₃ Sn ₄ , FeSn ₂ , Cu ₃ Sn, AgIn ₂ , AuSn ₄ , AuSn, InSn ₄ , PdSn ₄ , PdSn ₃ , Sb ₂ Sn ₃ , SbSn , Sn ₄ Sr, Ti ₆ Sn _{5 A} method for manufacturing a composite solder, characterized in that one selected from The method of manufacturing a composite solder according to claim 1, wherein the plastic working is drawing or rolling. The composition of claim 1, wherein the solder base is composed of tin (Sn) as a main component, and at least one selected from lead (Pb), silver (Ag), bismuth (Bi), indium (In), and copper (Cu). Method for producing a composite solder characterized in that the alloy containing The method of manufacturing a composite solder according to claim 1, wherein the composition of the solder base is an alloy composed mainly of gold (Ag). The composite solder according to claim 1, wherein the composition of the solder base is an alloy containing indium (In) as a main component and one or two or more selected from silver (Ag), bismuth (Bi), and copper (Cu). Manufacturing Method delete