KR100904196B1 - Soldering material for increasing durability of soldering zone soldering method using the same - Google Patents

Abstract

The present invention is to reduce the thermal diffusion rate during the solidification of the solder by inserting the nanoparticles in the soldering site to slow down the solidification rate, thereby brazing material for strengthening the durability of the soldering site that can minimize the occurrence of thermal deformation, cracks, etc. And it provides a soldering method using the same. The brazing material according to the present invention has a small particle size incorporated into the brazing alloy for scattering phonon as a thermal energy carrier generated at a brazing alloy and a brazing alloy mainly composed of lead and tin. The present invention is intended to include phonon scattering nanoparticles having a viscosity, and when soldering using the same, i) a solid solder material containing phonon scattering nanoparticles is used to the soldering site. And soldering the phonon scattering nanoparticles to the joints through the soldering, and ii) applying the phonon scattering nanoparticles to the soldering site of the soldering target in advance and then applying a general Sn-Pb-based or Soldering for the phonon in the soldering material at the junction by performing soldering using a Sn-Ag-based Pb-free soldering alloy There is a method to contain the particles.

Nanoparticles for soldering, thermal energy carriers (Phonon), scattering, and phonon scattering

Description

Soldering material for increasing durability of soldering zone soldering method using the same}

The present invention relates to a soldering material and a soldering method using the same, and more particularly, a soldering material and a soldering method for strengthening soldering endurance that can suppress deformation and cracking, such as twisting of soldering parts due to residual stress after soldering, to the maximum. It is about.

The durability of various electrical and electronic components is directly related to the durability of the circuit board, that is, the PCB substrate, which implements or mounts a circuit suitable for driving the component, or the PCB substrate. In mounting electronic components and chips on the PCB substrate, it is determined by how well the joints withstand fatigue.

Soldering in which a semiconductor chip, a semiconductor chip package, or an electronic component is mounted on a plastic substrate, a FR4 printed circuit board, a flexible substrate, or the like, without soldering a base metal using a solder material having a relatively low melting point. Is mainly used, and as the brazing material for soldering, a brazing alloy mainly composed of lead and tin is used.

However, in the case of general soldering alloys composed mainly of lead and tin, they have a high thermal diffusion rate in relation to the material properties with low melting point. The phenomenon in which stress remains at the junction part occurs.

Such residual stress causes distortion or crack generation such as torsion in the solder joint where soldering is performed through soldering.In the case where deformation or cracking occurs at the soldered joint, the mechanical strength of the joint decreases eventually. The durability and reliability of the device is inevitably deteriorated.

In addition, when soldering using a soldering alloy such as a lead-free alloy containing tin and silver as a main component, the compound of silver and tin depends on the cooling rate when the soldering alloy solidifies in a molten state. Ag ₃ Sn formed as can be crystallized to the secondary dentite, in the case of the crystallized secondary dentite deteriorates the yield strength throughout the soldering site due to the presence of grain boundaries Cause.

The technical problem to be solved by the present invention is to reduce the thermal diffusion rate of the brazing material in the molten state during soldering to slow the solidification rate, and to suppress the generation of dentite, the soldering material for strengthening the durability of the soldering site and the soldering method using the same To provide.

As a means for solving the above technical problem, the present invention is a soldering alloy containing lead and tin as a main component; And phonon scattering nanoparticles having a small particle size to be incorporated into the brazing alloy to scatter phonons as thermal energy carriers generated at the brazing site. It provides a soldering material for.

Here, it is preferable to apply platinum nanoparticles or silicon nanoparticles having a particle size of 5 nm or less as the phonon scattering nanoparticles, and to be incorporated within 4 to 10 volume% of the total volume of the brazing material.

In addition, the present invention as a means for solving the above technical problem, by using a brazing material containing phonon scattering nanoparticles for scattering phonon as a thermal energy carrier generated in the soldering site for the junction site Provided is a soldering method for performing soldering.

As the nanoparticles for phonon scattering applied to the soldering method, platinum nanoparticles or silicon nanoparticles may be used.

In addition, as another method for solving the above technical problem, after applying the phonon scattering nanoparticles for scattering the phonon as a thermal energy carrier to the joint site in advance and using a soldering alloy containing lead and tin as a main component for the joint site By performing soldering, a soldering method is provided in which the phonon scattering nanoparticles are mixed in a soldering material on the joint portion.

Here, as the phonon scattering nanoparticles applied to the soldering method, platinum nanoparticles or silicon nanoparticles may be used, and when the platinum nanoparticles are mixed as the phonon scattering nanoparticles, the platinum nanoparticles are added to ethanol or isoprophenol solution. Soldering is performed by applying the liquid mixture in which the particles are dissolved to the joint in advance, and when incorporating the silicon nanoparticles as phonon scattering nanoparticles, the liquid mixture in which the silicon nanoparticles are dissolved in the hexane solution is applied to the joint. It is preferable to carry out soldering after applying in advance.

According to the present invention described above, since the scattering of the thermal energy carrier called phonon is induced by the phonon scattering nanoparticles mixed in the junction at the time of solidification of the soldering material, the thermal diffusion rate of the junction is lowered and the solidification rate is increased. It becomes possible to slow down. As the solidification of the brazing material at the junction progresses in this manner, the crystal structure of the brazing material at the junction is very dense and hardly any residual stress occurs, so that deformation or cracking such as torsion after solidification does not occur. As a result, the durability and reliability of the device can be further improved by improving the mechanical strength of the soldered portion.

In the case of the conventional Sn-Ag-based lead-free soldering material, if the cooling rate is too low during solidification, Ag 3 Sn formed as a compound of silver and tin may crystallize out into the dentite, and the dentite formed may have a grain boundary. Accompanied by the problem of lowering the yield strength, but the inclusion of phonon scattering nanoparticles in the present invention by scattering the phonon as a thermal energy carrier, and consequently in the region where the nanoparticles are located It also interferes with the formation of the compound of silver, and therefore also functions to inhibit the production of dentite. This not only slows the solidification rate of the brazing material, but also suppresses the formation of dentite, thereby preventing the reduction of the overall yield strength of the soldering site due to the presence of grain boundaries in the case of Sn-Ag lead-free brazing material. It also has an effect.

Hereinafter, preferred embodiments of the present invention will be described in detail.

The present invention allows the nanoparticles to be included in the soldering portion after the soldering through the soldering method that allows the nanoparticles to be incorporated into the soldering material or soldering portion containing the nanoparticles, thus lowering the thermal diffusion rate and solidifying rate during solidification of the soldering material. By delaying the main point to be able to suppress the occurrence of thermal deformation and cracks of the joint portion through the solder as possible.

In this embodiment, the "soldering material" is at least partially meltable at a relatively low temperature, is a solid metal material at room temperature, and electrically and physically bonded between two electrically conductive members, for example, between electrodes. The materials that can be used in the application are referred to collectively. As an example, it is used as a joining material for electrically and physically joining the external electrode of an electronic component with the wiring etc. which are formed on a circuit board in the process of mounting an electronic component.

According to an embodiment of the present invention, a brazing material having a nano composite structure is provided, including a brazing alloy and nanoparticles having a small particle size incorporated in the brazing alloy. Soldering alloys are Sn-Pb-based soldering alloys mainly composed of tin (Sn) and lead (Pb) or Sn-Ag-based materials containing small amounts of silver (Ag) or other substances mixed with tin (Sn) as a main component. Pb-free solder alloy may be applied, and the nanoparticles may be phonon scattering nanoparticles having an element suitable for scattering thermal energy carriers (Phonon) generated at the junction through soldering.

In the case of Sn-Pb-based general soldering alloy mainly composed of tin and lead, alloys solidified at a cooling rate of 0.1 ° C / sec and alloys solidified at a cooling rate of 1 ° C / sec, as shown in the experimental data of FIG. In comparison, it can be seen that the material properties for the shear of slow cooled alloys (solidified at a cooling rate of 0.1 ° C./sec) are significantly better. In other words, comparing the allowable shear stress at the same shear strain, it can be seen that the allowable shear stress of the slow cooled alloy is larger.

The present invention focuses on the variation of the material properties according to the cooling rate, that is, the solidification rate, and does not use a separate heating furnace for controlling the cooling rate or a chamber for adjusting the cooling rate. By introducing phonon as a thermal energy carrier, phonon scattering nanoparticles with a small particle size are incorporated into the brazing alloy to lower the thermal diffusion rate of the brazing material and slow the solidification rate. It is.

As described above, the improvement of material properties caused by slowing the cooling rate is somewhat different in the case of lead-free Sn-Ag lead-free soldering material, but generally in the case of Sn-Ag-based lead-free soldering material If the cooling rate is too slow, Ag ₃ Sn formed as a compound of silver and tin may crystallize out into the dentite, and the formed dentite has a problem of lowering the yield strength due to accompanying grain boundaries. .

However, the inclusion of phonon scattering nanoparticles in the present invention scatters phonons as thermal energy carriers, which in turn inhibits the formation of tin and silver compounds in the region where the nanoparticles are located, thus producing dentite. In addition, the function of suppressing the pressure of the soldering material is also reduced, thereby not only slowing the solidification rate of the soldering material, but also suppressing the production of dentite, and thus achieving the desired result in the Sn-Ag-based lead-free soldering material.

A phonon scattering nanoparticle having an element suitable for scattering a thermal energy carrier (Phonon) has a substantially high melting point compared to the brazing alloy, and does not dissolve in the melt when the brazing alloy is melted. It is suitable to have a physical property suitable for scattering a thermal energy carrier called 'Phonon' generated at the junction through the resin, but preferably without substantially affecting the properties of the solder alloy. Platinum or silicon nanoparticles that can effectively prevent breakage or cracking of mechanical properties, such as cracks, are suitable.

In the present invention, substantially insoluble in the Sn-Pb-based soldering alloy or the Sn-Ag-based soldering alloy means that the element and the Pb-Sn-based or Sn-Ag-based soldering alloy coexist under high temperature conditions. When the brazing alloy is completely melted and then naturally cooled, the solid in the melt in any form, for example, in the form of an alloy or a compound, at least at the point where the brazing alloy solidifies in the course of decreasing the temperature of the melt. Refers to what can exist as

When platinum is mixed as phonon scattering nanoparticles, the melting of the brazing material through brazing does not mix well with the existing brazing alloy in the corresponding temperature range, thereby suppressing the formation of compounds as much as possible, and thus yielding strength of the soldering site. The degradation can be minimized. This can also be confirmed through the phase diagram shown in FIGS. 2A to 2C.

FIG. 2A shows the phase balance of tin and platinum, FIG. 2B shows the phase balance of silver and platinum, and FIG. 2C shows the phase balance of copper and platinum, respectively. These phase equilibrium can confirm the region where platinum and these brazing materials do not exist as a compound but exist independently when the platinum content is less than 10% in the temperature range during the soldering operation.

Specifically, in the mixture of platinum 10% and tin 90% in Figure 2a, when the temperature is lower than 231 ° C, the melting temperature of the lead-free solder, it can be seen that the mixture does not occur because the state of the mixture is β-tin and platinum. . Similarly, in FIG. 2B, the content of platinum is less than 10% (when the content of silver is 90% or more), and the mixture is silver and platinum. In the case of copper and platinum, they are not shown in the phase equilibrium for the case where the lead-free solder is below the melting temperature (only 300 ° C or more in the drawing), but below that temperature, no alloy of copper and platinum is formed. Although not shown in a separate phase equilibrium, silicon also does not form compounds with these metals in the temperature range during the soldering operation.

On the other hand, the shorter the distance between the nanoparticles compared to the mean path of the phonon (ponon), the more the scattering properties of the phonon by the nanoparticles can be maximized to delay the coagulation rate as much as possible, but excessive coagulation delay This can cause process delays in soldering.

Considering this point, if the nanoparticles exceed 10% by volume of the total brazing material, the distance between the nanoparticles may be too short, which may cause the above problem, so that the soldering site has sufficient time to form a good crystal structure. In order to minimize the delay of the process, the size of the nanoparticles incorporated into the brazing alloy should be incorporated within 10% by volume of the total volume of the brazing material while having a particle size of 5 nm or less based on the diameter. Preferably, more preferably, it is incorporated at 5% by volume of the total volume of the brazing material.

In order to examine the effect of the nanoparticles incorporation amount and its size on the overall thermal conductivity of the brazing material, the thermal conductivity of nanoparticles in the InGaAs alloy, which is a representative alloy in the semiconductor field, was compared. The results are shown in FIG. 3. . That is, FIG. 3 shows the prediction based on the numerical value for the thermal conductivity when the ErAs nanoparticles are added to In _0.53 Ga _0.47 As.

With reference to FIG. 3, it is possible to predict the thermal conductivity when platinum or silicon nanoparticles are put into the lead-free solder material. That is, Figure 3 (a) shows how the nanoparticle content and the average diameter of the particles change the size change of the nanoparticles according to statistical dispersion when 0.3% and 2.4 nm. As shown, it can be seen that the thermal conductivity is reduced by 2 to 3 times with and without the nanoparticles. 3 (b) shows that the thermal conductivity decreases by about 3 times at room temperature when the average diameter and size gradient are fixed at 2.4 nm and 1.5 nm and the content is changed to 0.25-3%.

3 (c) shows the thermal conductivity when the diameter of the nanoparticles is changed after the content and size gradient are fixed at 0.3% and 1.9 nm. As shown in the figure, the thermal conductivity decreases as the nanoparticle diameter decreases. In particular, it can be seen that the thermal conductivity is somewhat reduced only when the size is at least 4.8 nm or less.

In performing soldering so that the phonon scattering nanoparticles are incorporated into a soldering alloy, i) soldering the soldering site by soldering the soldering site using a solid solder material containing the phonon scattering nanoparticles. Method for allowing the phonon scattering nanoparticles to be mixed in the soldering material of the junction portion through, and ii) after applying the phonon scattering nanoparticles to the soldering site of the soldering object in advance, the general Pb-Sn or Sn-Ag-Cu There is a method in which the phonon scattering nanoparticles are included in the soldering material at the joint by performing soldering using an alloy for soldering.

In the case of the method of iii), the soldering is performed on the joint using a solid state soldering material prepared based on a mixture of solid state phonon scattering nanoparticles. It is the same as the soldering method, and in the case of incorporating platinum nanoparticles as phonon scattering nanoparticles in soldering through the same method as in ii), a liquid mixture in which the platinum nanoparticles are dissolved in ethanol or isoprophenol solution is prepared. Soldering is performed by applying to the joints in advance, and when incorporating silicon nanoparticles as phonon scattering nanoparticles, it is preferable to apply the solder mixture beforehand to the joints in a liquid state in which the silicon nanoparticles are dissolved. Do.

The effect expressed by incorporating the phonon scattering nanoparticles into the junction through soldering as described above will be described with reference to the accompanying drawings.

Figure 4 is a schematic diagram showing the thermal phenomenon occurs when the phonon scattering nanoparticles are injected into the solder joint, the temperature difference between any one region (high temperature region) and the other region (low temperature region), as shown At the boundary region, a thermal energy carrier called a phonon (waveform arrow in the figure) is generated, and nanoparticles or alloying atoms are scattered to the phonon as shown in the figure to adjust the thermal conductivity of the soldered portion. Change the thermal diffusivity to slow the solidification rate.

That is, when the phonon scattering nanoparticles having a scattering function for the thermal energy carrier are mixed so as to be properly dispersed in the melt when the brazing alloy is melted, the phonon may be mixed by the phonon scattering nanoparticles that are mixed at the junction when the brazing material solidifies. Scattering of the thermal energy carrier called phonon is induced, which hinders the normal flow of the thermal energy carrier, and thus, the thermal diffusion rate of the junction is lowered, thereby making it possible to slow the solidification rate of the junction through soldering.

When the solidification of the brazing material proceeds gradually as the solidification rate of the joint portion through the solder is hindered by the normal movement of the thermal energy carrier, the crystal structure of the brazing material at the junction portion is very dense and the residual stress is almost Does not occur. As a result, almost no deformation or cracking such as torsion occurs at the joint.

In detail, the thermal diffusivity ( α ) of the solid is α = k / ρC _p. ( k is Thermal conductivity, ρ is density, C _p is specific heat), and thermal deformation and torsion during soldering are caused by the change of solid crystal structure during solidification. In other words, if it is not possible to solidify for a sufficient time, the crystal structure of the solid is changed. As shown in FIG. 5, the temperature T which appears upon solidification in a heat affected zone is an exponential function for time t , where the time constant of the rate of solidification (τ, time constant) ) Is related to the thermal diffusivity α as τ = l ² / α = l ² / ( k / ρC) _p .

In general, the larger the time constant (τ), the slower the solid cools down. In the above equation, the time constant τ increases as the thermal diffusion rate α decreases. Therefore, lowering the thermal diffusion rate α has sufficient time to solidify the melt of the brazing material at the junction, so that the atoms in the solid have enough time to form a good crystal structure. Where l is the approximate length scale of the heat affected zone.

In FIG. 5, τ ₁ indicates that soldering, that is, no nanoparticles are present at the junction, and τ ₂ represents a case where nanoparticles are present at the soldering site. As a function of the temperature and time of FIG. 5, it can be seen that the melt in the presence of nanoparticles due to the decrease in the thermal diffusivity ( α ) causes the melt to cool slowly. If solidification proceeds slowly, since the crystal structure of the brazing material at the junction is very dense and residual stress hardly occurs, deformation or cracking such as twisting or hardening at the junction after hardening hardly occurs.

In general, it is known that quenching can provide high strength when cooling joints through soldering (Ochoa et al., 2003, J. Electrnoic materials, 32 1414). Therefore, when the nanoparticles are added as in the embodiment of the present invention, since the solidification speed for the junction is slowed, there is a concern that the strength of the junction is lowered.

However, in general, the higher the yield strength (yield strength), the lower the fracture strength (fracture strength) due to cracking (see the graph of Figure 6). That is, high strength materials do not easily yield, but tend to break when cracks are present, and low strength materials can easily yield, but fracture resistance due to cracks shows high toughness.

In the case of incorporating nanoparticles as in the embodiment of the present invention, the bonding material, for example, the solder material solidified at the PCB and the bonding portion, in particular, the strength ratio between the solder balls may be reduced. In this case, the stress intensity factor, which is a parameter representing the stress size of the crack tip, may be increased, but the increase is expected to be very small (Lee and Choi, 1988, Engineering Fracture Mechanics, 29). 461).

In other words, the increase in the stress concentration element due to the decrease in the strength ratio due to the incorporation of the nanoparticles is very small, whereas the fracture resistance due to the incorporation of the nanoparticles is increased. It can be seen that the decrease in the strength ratio due to increase rather than decrease the durability of the solder ball, and as a result, the possibility of occurrence of microcracks during solidification is significantly reduced as the solidification rate is slowed down by the nanoparticles. It is clear.

The use of the brazing material provided in the present invention is not limited to the fabrication of electronic circuit boards, but can be used as a bonding material for soldering attachments between various members, and also only physically (or mechanically) between the members. It will be readily apparent to one skilled in the art that it can also be used as a connection material for connection only.

1 is a graph showing the shear strain of the brazing alloy according to the cooling rate difference.

2A, 2B, and 2C are phase diagrams of tin and platinum, silver and platinum, copper and platinum, respectively.

FIG. 3 is a graph showing predictions based on numerical values for thermal conductivity when ErAs nanoparticles are added to In _0.53 Ga _0.47 As. FIG.

Figure 4 is a schematic diagram showing the thermal phenomenon occurring when the phonon scattering nanoparticles are injected into the solder joint.

5 is a view for explaining the relationship between the temperature and time appearing during solidification in the heat affected zone (heat affected zone).

FIG. 6 is a graph showing the relationship between general yield strength and fracture resistance. FIG.

Claims (12)

Soldering alloys including Sn-Pb-based or Pb-free alloys; And Phonon scattering nanoparticles having a small particle size incorporated in the brazing alloy to scatter phonon as a thermal energy carrier generated at a soldering site; Soldering material for strengthening the soldering site durability comprising a. The method of claim 1, The phonon scattering nanoparticles are platinum nanoparticles, brazing material for strengthening the durability of the soldering site, characterized in that. The method of claim 1, The phonon scattering nanoparticles are silicon nanoparticles, brazing material for strengthening the durability of the soldering site, characterized in that. The method according to any one of claims 1 to 3, The phonon nanoparticles for scattering, having a particle size of less than 5nm solder material for strengthening the durability of the soldering site, characterized in that the mixing within 4 ~ 10% by volume of the total volume of the brazing material. Phonon scattering nanoparticles are mixed to scatter thermal energy carriers (Phonon) generated at the soldering site, and soldering is performed using a soldering material including a Sn-Pb-based or Pb-free alloy. Way. The method of claim 5, wherein Said phonon scattering nanoparticles are platinum nanoparticles, The soldering method characterized by the above-mentioned. The method of claim 5, wherein Said phonon scattering nanoparticles are silicon nanoparticles, The soldering method characterized by the above-mentioned. Ponon scattering nanoparticles, which scatter phonons as thermal energy carriers, are pre-coated on the joints, and then soldered to the joints using a soldering alloy containing lead and tin. Soldering method characterized in that the phonon scattering nanoparticles are mixed. The method of claim 8, The nanoparticle for phonon scattering is a platinum nanoparticle, The soldering method characterized by the above-mentioned. The method of claim 9, When the platinum nanoparticles are mixed as phonon scattering nanoparticles, soldering is performed by applying a liquid mixture of platinum nanoparticles dissolved in ethanol or isoprophenol solution in advance to the joint and soldering. The method of claim 8, The nanoparticles for phonon scattering are silicon nanoparticles, The soldering method characterized by the above-mentioned. The method of claim 11, When the silicon nanoparticles are mixed as phonon scattering nanoparticles, the soldering method characterized in that the solder mixture is applied after the liquid mixture in which the silicon nanoparticles are dissolved in a hexane solution is applied in advance to the joint.

Images