KR20210086520A - Low radiation solder ball and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a low-radiation solder ball and a manufacturing method thereof. The solder ball of one aspect of the present invention comprises: a core including a first metal; a diffusion layer including a second metal different from the first metal and provided on the core; and a solder layer provided on the diffusion layer and having an alloy component constituting a solder alloy and impurities contained in the solder alloy. The solder ball of the present invention includes 99.9 to 99.9989 wt% of a main component comprising the first metal, the second metal, and the alloy component. An alpha ray emission is equal to or less than 0.002cph/cm². An object of the present invention is to reduce occurrence of soft errors in semiconductor chips by reducing alpha particles emitted from the solder ball.

Description

Low radiation solder ball and manufacturing method thereof

One aspect of the present invention relates to a solder ball that can be used for soldering bonding of components in electronic component packaging and a method for manufacturing the same, and more particularly, to a low-radiation solder ball having a low radiation emission amount and a method for manufacturing the same.

Background to the present disclosure is provided herein, which does not necessarily imply known art.

In general, a semiconductor package is manufactured by vertically and horizontally adjacently arranged while stacking semiconductor chips vertically on a wafer. In this case, the semiconductor chip has bumps formed on its edges to electrically connect the semiconductor chips stacked up and down, thereby manufacturing a semiconductor package having a high degree of integration.

As the degree of integration of the semiconductor device increases, the size of the bump becomes smaller. As a way to keep the size of the bump small and keep the size constant, a method of forming the bump using a solder ball is widely applied.

Solder balls can be broadly classified into metal solder balls and plastic core solder balls. A metal solder ball consists of a single solder in a spherical shape, and a plastic core solder ball forms a metal layer on the surface of a spherical plastic core and includes a solder layer at the outermost part. Since the plastic core solder ball has a plastic core, it has the ability to resist impact. However, since the metal solder ball is entirely made of metal, it lacks the ability to absorb shock. Instead, it has superior electrical and thermal conductivity compared to the plastic core solder ball. There is this.

In general, a metal solder ball is manufactured by forming a barrier layer for suppressing overgrowth of an intermetallic compound on metal particles serving as a spacer and plating the solder to enable soldering. In order to manufacture a copper core solder ball using copper as the metal particle core of a metal solder ball, a technique for manufacturing copper particles of uniform size and a technique for plating so that defects such as voids, aggregation, and thickness deviation do not occur when forming a plating layer need.

In recent years, since semiconductor devices using tin as a raw material in the solder have increased in density and high capacity, a lot of alpha radiation is emitted from tin disposed in the vicinity of the semiconductor chip, resulting in a soft error in which information of the memory cell is lost. The risk of becoming

The soft error occurs because high-energy alpha particles are emitted from radioactive isotopes such as lead and bismuth present in tin or solder. In general industrial tin, impurity elements that can emit alpha particles, a type of radiation, are present. ( ²¹⁰ Pb, ²¹⁰ Bi, ²¹⁰ Po, etc.).

In order to manufacture Ultra Low Alpha grade tin with an alpha ray emission of 0.002 cph/cm ² or less, it is generally refined to have a purity of 99.999% or more. In this case, tin is generally refined by electrolytic refining, and the higher the purity, the higher the refining cost. In particular, expensive high-purity reagents and ion exchange membranes are consumed to manufacture tin of high purity of 99.999% or more, which increases the manufacturing cost. Therefore, there is a demand for technology development for the use of solder balls with ultra-low alpha characteristics and securing production economy. is increasing

Korean Patent Registration No. 10-1141762

A solder ball, which is an aspect of the present invention, is intended to solve the above problems, and to reduce the occurrence of soft errors in semiconductor chips by reducing alpha particles emitted from the solder balls.

In addition, it is an object of the present invention to provide a method of manufacturing a solder ball having ultra-low alpha (ULA) characteristics without performing refining at a high purity of 5N and a material having an ultra-high purity of 5N (99.999% or more) level. have.

One aspect of the present invention is

a core comprising a first metal;

a diffusion layer comprising a second metal different from the first metal and provided on the core; and

a solder layer provided on the diffusion layer, the alloy component constituting the solder alloy, and an impurity included in the solder alloy;

It is a solder ball containing 99.9 wt% to 99.9989 wt% of the main component consisting of the first metal, the second metal and the alloy component, and the alpha-ray emission amount is 0.002 cph/cm ^{2 or less.}

Here, it is preferable that the content of the impurities is 11 ppm to 1000 ppm,

The impurities include radioactive isotopes emitting the alpha rays,

The solder alloy may include an alloy of Sn and at least one metal selected from the group consisting of Au, Ag, Cu, Ni, Bi, Zn, Pd, In, Pb and Po.

In addition, the second metal preferably contains nickel,

It is preferable that the ratio (w2/w1) of the sum of the weights of the first metal and the second metal (w1) and the weight of the solder layer (w2) is 0.05 to 0.95,

The diffusion layer may include an alloy of the first metal and the second metal formed by diffusing the first metal and the second metal at an interface between the core and the diffusion layer.

In addition, it is preferable that the ratio of the second metal continuously increases from the bottom to the top of the diffusion layer, and the thickness of the solder layer is preferably 2 μm to 2,000 μm.

Another aspect of the present invention is

a second metal plating step of forming a diffusion layer including a second metal different from the first metal on the surface of the core including the first metal; and

A solder layer forming step of plating a solder layer having an alloy component constituting a solder alloy on the diffusion layer and an impurity included in the solder alloy,

The solder layer forming step is a solder ball manufacturing method that is a step of plating the solder layer using an anode having a purity of 99.9 wt% to 99.9989 wt% of tin and a plating solution having a purity of a metal salt of 99.9 wt% to 99.9989 wt%.

At this time, it is preferable to include the step of removing the radioactive isotope contained as an impurity in the anode or the metal salt.

Another aspect of the connection structure includes the above-described solder ball, and the solder ball is provided between an electrode included in a substrate and a connection terminal connected to the electrode, and is reflowed to electrically connect the electrode and the connection terminal. A connection structure is good.

In the solder ball, which is an aspect of the present invention, by forming a solder layer using a solder alloy from which impurities emitting alpha ray are removed to suppress emission of alpha ray from the solder layer of the solder ball, it is possible to prevent the occurrence of soft errors in electronic products, and also Since there is no problem with the disposal of waste, it has the advantage of not causing environmental pollution.

In addition, it is possible to increase the package density by replacing the spacer, and there is an effect of obtaining a junction and a connection structure having superior shear strength, thermal shock, drop, heat and electrical conductivity compared to a junction using a conventional solder ball.

1 is a schematic diagram showing the structure of a solder ball according to an embodiment of the present invention.
2 is a photograph of the manufactured solder ball.
3 is a photograph of a cross-section of the manufactured solder ball.
4 shows a phase diagram of NI and Bi.
5 is a diagram schematically illustrating a process in which alpha particle emission impurities and the metal in the diffusion layer are diffused while forming an intermetallic compound in the solder layer and diffusion layer of the solder ball.
6 is a photograph of a cross-sectional connection structure of a package using a solder ball.

Prior to describing the present invention in detail below, it is to be understood that the terminology used herein is for the purpose of describing specific embodiments and is not intended to limit the scope of the present invention, which is limited only by the appended claims. shall. All technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art, unless otherwise stated.

Throughout this specification and claims, unless stated otherwise, the term comprise, comprises, comprising is meant to include the stated object, step or group of objects, and steps, and any other object. It is not used in the sense of excluding steps or groups of objects or groups of steps.

On the other hand, various embodiments of the present invention may be combined with any other embodiments unless clearly indicated to the contrary. Any feature indicated as particularly preferred or advantageous may be combined with any other feature and features indicated as preferred or advantageous. Hereinafter, embodiments of the present invention and effects thereof will be described with reference to the accompanying drawings.

A solder ball according to an embodiment of the present invention includes a core 1 , a diffusion layer 10 , and a solder layer 20 . 1 schematically shows the structure of a solder ball according to an embodiment of the present invention.

The core 1 is a spherical material located inside the solder ball, and a metal core including the first metal may be used.

The core 1 may be made of a single first metal or an alloy including the first metal, and the first metal may be copper, gold, silver, tin, bismuth, or zinc. The core 1 may be an alloy of at least any one or more metals selected from the group consisting of copper, gold, silver, tin, bismuth, and zinc, and may be an alloy having a lower melting point than copper. For example, the core 1 may be composed of a single metal using copper (Cu) as a first metal, and an alloy of at least any one of Au, Ag, Sn, Bi, and Zn and copper as the first metal. In this case, it is preferable that the ratio of copper as the first metal in the composition of the core 1 is 99.999 wt% to 85 wt%.

If the composition ratio of copper in the core 1 is lower than the corresponding range, there is a problem in that the electrical conductivity and thermal conductivity are lowered after soldering, and the sphericity is decreased due to the solidification and shrinkage of the alloy, or curvatures or dimples are formed on the surface. There is a problem in that the plating is formed non-uniformly, and the solder ball cannot form a uniform connection part.

When the composition ratio of copper in the core 1 is higher than the corresponding range, an excessive increase in cost in the refining process may be a problem.

The diameter of the core 1 may vary depending on the thickness of the diffusion layer 10 to be described later, and the diameter of the core 1 may be 5 μm to 10,000 μm, and preferably, the diameter of the core 1 is 20 μm to 20 μm. It may be 1,000 μm.

The core 1 may consist of 5 to 95 wt% of the total solder balls, preferably 10 to 80 wt%. If the proportion of the core 1 in the total solder balls is out of the range, there is a problem that the area occupied by the joint thickness is small at 5 wt% or less, so that it cannot serve as a spacer. At 95 wt% or more, there is a risk of non-bonding due to the small amount of liquid. have.

The core 1 has a melting point of 500 degrees or more and has a melting point higher than that of the solder layer 20, and may preferably have a melting point of 500° C. to 1080° C.

The diffusion layer 10 is a layer positioned between the core 1 and the solder layer 20, and the first metal atoms included in the core 1 and tin or other metal atoms of the solder layer 20 are diffused to form a metal. The plating layer of the second metal introduced to prevent the formation of the inter-compound includes a region where the first metal atom included in the core 1 is diffused at a high temperature to form a solid solution.

That is, the diffusion layer 10 is a layer made of a solid solution containing the first metal and the second metal due to diffusion between metal atoms at the interface of the coating layer including the second metal formed on the surface of the core 1 by heat treatment.

The diffusion layer 10 includes a first metal included in the core 1 and a second metal having magnetism.

The second metal is not limited as long as it is a metal having magnetism, but it is better to select an appropriate metal according to the first metal. As a preferred example, when copper is used as the first metal, the crystal structure is the same or similar, and the size of the atoms is different. It is preferable that nickel with a small valence is the second metal.

The diffusion layer 10 has a lower portion close to the core 1 and an upper portion close to the solder layer 20 . In the lower part of the diffusion layer 10 close to the core 1, the relative ratio of the second metal is low, and in the upper part of the diffusion layer 10 far from the core 1, the relative ratio of the second metal is high, and the second metal is higher from the bottom to the top. It can be configured to continuously increase the proportion of metal.

In a preferred example, when the core 1 includes copper as the first metal, the diffusion layer 10 includes copper and nickel as the first and second metals, and copper-nickel in the lower portion of the diffusion layer 10 . The alloy has a high proportion of copper, but the proportion of nickel in the copper-nickel alloy increases toward the upper part of the diffusion layer 10, and the proportion of nickel in the upper part of the diffusion layer 10 may be 50% or more or 99.9% or more. .

In addition, the ratio of the second metal in the lower part of the diffusion layer 10 is more than 0 wt%, and the ratio of the second metal gradually increases from the lower part to the upper part of the diffusion layer 10 to be 50 wt% or more or the second metal in the upper part The ratio of may be made of 99.9wt% or more.

The diffusion layer 10 may be formed to a thickness of 0.1 μm to 100 μm, preferably 0.5 μm to 80 μm, and more preferably 1 μm to 50 μm. The ratio d1/D of the diameter D of the core 1 and the thickness d1 of the diffusion layer 10 may be in the range of 0.00001 to 20, preferably in the range of 0.0005 to 0.5. If the thickness of the diffusion layer 10 or the ratio with the diameter of the core 1 is smaller than the corresponding range, diffusion of the solder and the first metal layer metal in the solder layer 20 and the generation of intermetallic compounds cannot be prevented, and the corresponding range If larger, there may be problems in that the cost of forming the second metal layer is increased, and the effect of reducing the magnetism through heat treatment is lowered.

The core 1 may contain impurities such as tin, but it is preferable not to include impurities emitting alpha rays, and the core 1 is provided inside the core solder ball. As a result, the emission of alpha rays may not be observed.

When the mass (M ₁₎ of the first metal and the mass (M ₂ ) of the second metal in the total solder ball and the mass (S) of the solder layer 20 were analyzed, the content of the second metal, that is, M ₂ /(M) _{The value of 1} +M ₂ +S)*100(%) may be 1 to 75 wt%, preferably 2 to 50 wt%.

If the ratio of the second metal is larger than the corresponding range, the content of the core 1 compared to the solder layer 20 is too high, so that the bonding function as a solder ball may be deteriorated and the usability may be deteriorated.

Since the diffusion layer 10 is formed including the second metal, the ratio of the diffusion layer 10 in the total solder ball may be equal to or greater than the ratio of the second metal, and may preferably be in the range of 2 to 75 wt%.

When the ratio of the diffusion layer 10 is larger than the corresponding range, the content of the core 1 is also too high, so that the bonding function as a solder ball may be deteriorated, and the usability may be deteriorated.

The solder layer 20 is a metal layer formed on the diffusion layer 10. It is melted during soldering and can provide a joint, so it can be expressed as the solder layer 20, and has a lower melting point than the core 1 and the first metal layer. have

The solder layer 20 is preferably made of lead-free solder containing Sn and not including lead (Pb) as a main component. The solder layer 20 is preferably made of a solder alloy having a melting point below the melting point of the first and second metals.

The composition of the solder alloy constituting the solder layer 20 is not particularly limited, and may be a binary alloy or a ternary or higher alloy.

The binary alloy is an alloy of two metals selected from the group consisting of Ag, Cu, Bi, Ni, Pd, Au, Ge, In and Sn, and the ternary alloy is Sn, Ag, Cu, Bi, In, Ni , Pd, Pb, Po, Au, and three alloys selected from the group consisting of Ge, or two metals selected from the group consisting of Ag, Cu, Bi, In, Ni, Pd, Pb, Po, Au and Ge An alloy consisting of Sn and Sn may be used, and it is preferable to use a solder alloy having a composition that does not contain an element emitting alpha rays as a main component.

An embodiment of the present invention uses a SAC-based solder alloy including Sn, Ag, and Cu as the solder alloy, and most known solder alloys used in the art and commonly used may be used.

For an example of a specific composition, the metal included in the solder layer 20 to form an alloy with Sn may be included in an amount of 0.1 wt% to 95 wt%.

In the case of the SnAgCu alloy, Cu may be included in an amount of 0.1 wt% to 3.0 wt%, and Ag may be included in an amount of 0.1 wt% to 8.0 wt%. As another example, in the case of a SnBi alloy, Bi may be included in an amount of 0.1 to 95 wt%.

The solder layer 20 may have a thickness of 2 μm to 2,000 μm, preferably 5 μm to 1,000 μm, and the weight sum w1 of the first and second metals of the core 1 and the diffusion layer 10 . The ratio (w2/w1) of the weight (w2) of the solder layer 20 may be in the range of 0.05 to 0.95, preferably 0.1 to 0.8.

When the weight ratio of the solder layer 20 is lower than the corresponding range, there is a risk of non-bonding due to a small amount of liquid phase, and the core 1 serves as a spacer by occupying all of the area occupying the joint thickness at a ratio greater than the corresponding range. There is a problem that cannot be done.

The solder layer 20 has a melting point of 80° C. to 450° C., and has a melting point lower than that of the core 1 and the diffusion layer 10, so that soldering of the solder ball is possible. For example, when the solder layer 20 having a composition of 34Sn-46Bi-20In is used, a melting point of about 85° C. is obtained.

The solder ball of the present invention is characterized in that the amount of radiation such as alpha rays is small. When the solder alloy is manufactured, radioactive isotopes emitting radiation such as alpha rays are included as impurities other than the main components of the solder alloy, so that alpha rays are emitted. .

The solder alloy is composed of an alloy component that is essentially included as a composition of the alloy to be formed, and a trace amount of an impurity that is unintentionally included and is not an essential component. Solder balls may emit alpha rays or alpha particles due to radioactive isotopes among impurities contained in the solder alloy. The emitted alpha rays are generated by radioactive decay of impurity elements included in the solder layer 20, for example, ²¹⁰ Pb, ²¹⁰ Bi, ²¹⁰ Po, etc., and the alpha particles emitted from the electronic device may cause a soft error. do.

²¹⁰ Pb is a radioactive element with a half-life of 22.3 years, and it is converted to ^{210 Bi through beta decay that emits beta rays or the process of emitting beta and gamma rays. When 210} Bi emits beta rays, neutrons are converted to protons to become ²¹⁰ Po. After that, ^{210 Po is changed to 206} Pb by alpha decay that emits alpha rays, and in this process, about 5.6 MeV of alpha rays are emitted.

A solder ball having a reduced alpha ray emission amount can be manufactured by removing the alpha ray emitting element during the formation of the solder ball, and the manufactured solder ball has a ^{characteristic of 0 to 0.002 cph/cm 2} , so the probability of causing a soft error in an electronic device This is very low.

In order to have ultra-low alpha (ULA) characteristics that satisfy 0 to 0.002cph/cm ² in the amount of alpha particles generated, the content of impurity atoms that generate alpha particles is small and the sum of the main components is 99.9% (3N) when manufacturing the solder ball. It is necessary that a high-purity material that is higher than that is used is used.

In the present specification, the main component refers to a component that can be expressed as constituting the composition during the manufacture of the alloy or must be understood to be essentially included in a certain amount or more in order to implement the characteristics of the composition in general, for example, the core (1) The first metal included in the second metal coated on the surface of the core 1 and included in the diffusion layer 10, Sn, Cu or Ag included in the tin alloy forming the solder layer 20 are main components. It may be defined and specifically refers to an element intentionally included excluding unintended impurities.

The low-radiation solder ball according to an embodiment of the present invention removes the alpha-ray emitting element even when the sum of the main components of the total solder ball is 99.9% (3N) to 99.998% (4N), so that the alpha-ray emission amount is reduced, so that the alpha particle is 0 to 0.002cph/cm ^{It shows} the ULA characteristics generated by 2

^{This is because 210} Pb, ²¹⁰ Bi, and ²¹⁰ Po, which emit alpha rays in the solder ball of the present invention, are selectively removed, so lower alpha ray emission is possible compared to alloys in which the sum of the main components is generally 99.9% (3N) to 99.998% (4N) because it does

The concentration range of impurities contained in tin is shown in Table 1 below using the OES analysis results of raw tin.

Tin Raw Material OES Analysis 2N tin After 2N tin purification 3N Tin After 3N tin purification 4N tin After purification of 4N tin Sn 99.024 99.1108 99.9551 99.983 99.9932 99.995 Ag 0.0635 0.0662 0.0092 0.0082 0.0001 0.0001 Cu 0.6064 0.7105 0.0024 0.0036 0.0006 0.0009 Ni 0.0096 0.0102 0.0022 0.0026 0.0022 0.0022 Pb 0.1737 0.0131 0.0074 0 0.0017 0 Sb 0.0654 0.0622 0.0048 0.0011 0.0005 0.0003 Al 0.0003 0.0003 0.0002 0.0002 0.0002 0.0003 CD 0.0001 0.0001 0 0 0 0 Fe 0.0164 0.0172 0 0 0 0 Bi 0.0331 0.0071 0.0157 0.0002 0.0004 0.0001 In 0.0029 0.0001 0.002 0.0001 0.0001 0.0001 Au 0.0003 0.0003 0 0 0 0.0003 Co 0.0004 0.0004 0 0 0 0 S 0.0015 0.0008 0.0008 0.0008 0.0008 0.0007 Pd 0.0003 0.0002 0.0002 0.0002 0.0002 0 Alpha particle emission
(cph/cm ² ) 2 0.242 0.4 0.0016 0.002 0.0011

In order to have ultra-low alpha characteristics, it seems possible to use 4N tin with an alpha particle emission of 0.002 or less, but even in the case of 3N tin, the alpha particle emission after purification is measured to be 0.002 or less, indicating that it can be used to obtain ultra-low alpha characteristics. have.

Here, the main component of the entire solder ball means including all the main components of the core 1, the main components of the diffusion layer 10 or the coating layer, and the main components of the solder alloy included in the solder layer 20, and each of the solder balls It refers to all components excluding impurities in the composition, and it is possible that the main components of the core 1 and the diffusion layer 10 include the same elements as the main components of the solder alloy.

In the solder ball according to an aspect of the present invention, it is important that the purity of the solder alloy used for the solder layer 20 and the tin for manufacturing the solder alloy is high, so that the content of the main component is high.

Specifically, the tin used during plating for forming the solder layer 20 is preferably refined tin having high purity by removing impurities, and at this time, the content of the main element is 99.9wt% or more, preferably 99.9~ 99.99 wt% of tin may be used so that the high-purity solder layer 20 can be plated.

When the purity of the solder alloy and the tin is lower than the corresponding range, the content of impurities emitting alpha rays is increased, so there is a problem in that the low radiation of the solder ball, particularly the ultra-low alpha (ULA) effect, is not obtained.

The solder ball according to an embodiment of the present invention includes an intermetallic compound in which the alpha particle emission impurities included in the solder layer 20 are formed together with a metal such as a second component present in the diffusion layer 10 .

4 is a diagram showing the phase equilibrium diagram of nickel, which is a kind of impurity emitting alpha particles, and nickel, which is preferable as a second metal. In the phase equilibrium diagram, an intermetallic compound (IMC) formed by combining nickel and bismuth. can be formed.

5 is a diagram illustrating a process in which impurities contained in the solder layer 20 form an intermetallic compound with the metal of the diffusion layer 10 and diffuse into the diffusion layer 10 or the core 1 .

When impurities emitting alpha particles form an intermetallic compound with metal atoms included in the diffusion layer 10 and are diffused therein, the content of impurities included in the solder layer 20 is lowered and diffuses into the inside. Since the alpha particle is not emitted from the alpha particle emission impurities to the outside of the solder ball, the alpha ray emission amount of the entire solder ball is greatly reduced.

In addition, due to this effect, even without going through high-concentration material or high-purity smelting, impurities emitting alpha particles can be selectively reduced in the solder layer 20, so when using a material having a purity level of 3N or 4N Ultra-low alpha level effects can be obtained.

Another aspect of the present invention is a method for manufacturing a low-radiation solder ball.

A method of manufacturing a low-radiation solder ball includes a core preparation step of preparing a core 1 containing a first metal, a second metal coating step of forming a coating layer containing a second metal on the surface of the core 1, a coated core It is preferable to include a diffusion layer forming step of heat-treating (1) to form a diffusion layer 10, a solder layer forming step of manufacturing a solder ball by plating a solder alloy on the diffusion layer 10, and in the solder layer forming step, the It is preferable to include an impurity removal step of removing impurities in the solder alloy used during plating to prepare a solder alloy having low radiation characteristics.

That is, the solder layer forming step may further include an impurity removal step of removing radioactive isotopes of a raw material used in forming the solder layer 20 .

The core preparation step may be a step in which the manufactured core 1 is prepared, and may be a step in which the metal core 1 is manufactured in a predetermined size through an orifice in a molten metal including the first metal.

As the first metal, which is the material of the core 1, for example, copper (Cu) or an alloy containing copper (Cu) may be used, which is then melted by induction heating through a high-frequency induction furnace and then fixed using a vibrator. It can be manufactured to a desired diameter through an orifice hole. At this time, the desired diameter of the core 1 may be adjusted by frequency and pressure.

When manufacturing the core 1, it is possible to intentionally include a metal component other than copper in pure copper, and when the core 1 is made into a spherical shape by adding some metal component, cracking of the core 1 due to condensation occurs However, dimple formation can be prevented and a core with high sphericity can be manufactured.

After the core preparation step, the step of washing and selecting the core 1 may be further included. The prepared core (1) is washed by immersion or stirring by an alcoholic solution, a basic solution, or an acidic solution (equipment or reagent), ultrasonic stirring, etc. have.

The second metal coating step is a step of forming a second metal coating layer on the surface of the prepared core 1 . When the solder layer 20 is formed directly on the surface of the core 1, the second metal coating layer is used to prevent the metal atoms of the core 1 from diffusing into the solder layer 20 to form an intermetallic compound or to form a void. is introduced Methods such as electrolytic plating, electroless plating, physical vapor deposition, and chemical vapor deposition may be used for plating the second metal, and electrolytic plating or electroless plating is preferably used.

The second metal layer may be formed in a range of 0.5 to 50 μm regardless of the size of the core 1, preferably in a range of 0.5 to 10 μm, and more preferably in a range of 1 to 10 μm.

When the electroless plating method is used as an example of the plating step, the material of the second metal plating solution in a bath is charged into the electroless plating solution and stirred to proceed. The electroless plating is continuously stirred until the reaction is complete. After the reaction is started, the reaction may be performed for about 1 to 2 hours, and the reaction time may vary by appropriately adjusting depending on the charging amount of the core 1 and the metal ion concentration and amount of the electroless plating solution.

As another example of the second metal coating step, a barrel plating method may be used, and the plating coating proceeds as the cathode rotates to reduce the aggregation between core ball particles due to plating and increase the sphericity to form the second metal coating layer. .

A step of washing and sorting the semi-finished product manufactured after the second metal coating step may be additionally included. The core plated with the second metal is washed by immersion or stirring, ultrasonic stirring, etc. by alcohol-based solution, basic solution, or acidic solution (equipment or reagent), size selection using mesh, and sphericity selection using a spherical separator can do.

In addition, a diffusion layer 10 in which the first metal and the second metal are thermally diffused and alloyed by heat treatment of the semi-finished product of the core 1 having the coating layer formed thereon may be provided, and the surface of the core 1 provided with the diffusion layer 10 will be described later. It is preferable to manufacture a solder ball by plating the solder layer 20 .

The solder layer forming step is a step of forming a solder layer 20 including Sn or an alloy of Sn on the surface of the core 1 on which the diffusion layer 10 is formed, and an electrolytic plating method may be mainly used.

The core (1) on which the diffusion layer (10) is formed is placed in a barrel, and the metal or alloy to be plated is hung on the anode, and the cathode is hung on the metal core (1), which is the object to be plated, to perform electrolytic plating. During plating, the temperature is maintained at 10 to 70° C., and the current density is preferably 0.2 to 50 ASD for 5 minutes to 200 hours. At this time, the plating may be performed by removing ^{impurities (210} Pb, ²¹⁰ Bi, ²¹⁰ Po, etc.) emitting alpha rays to the solder layer plating solution and the anode.

It is preferable that an impurity removal step for removing impurities contained in the solder alloy and material used when the solder layer 20 is formed is included before the solder layer forming step. The step of removing impurities may be a step of refining tin, a raw material, to prepare a tin electrode for plating the solder layer 20 or an organic acid tin solution in which tin is oxidized.

A raw material tin may be used as a material used for refining, and 99% to 99.99% of tin is preferably used for an efficient process, and more preferably, 99.9 to 99.99 wt% of tin is used.

If the purity of tin used as a raw material is too low, impurities may not be sufficiently removed during the refining process, so low-radiation characteristics may not be obtained or the refining efficiency may be lowered. If the purity of tin is too high, the price of the raw material may increase. There is a problem that the economical efficiency is lowered because the

In the step of removing impurities, tin prepared before purification is washed by immersing it in a washing tank containing 7 to 12% diluted hydrochloric acid solution for about 5 to 10 minutes. The washed tin is further washed with a solvent such as distilled water, acetone or alcohol in a washing tank and then dried using nitrogen gas or the like.

As impurities are removed through refining treatment of tin, and the purity increases, the number of alpha particles emitted from the solder layer 20 decreases, thereby reducing radiation emission. In particular, 99.9% (3N) to 99.99% (4N) material is purified Radioactive isotopes emitting alpha particles such as lead, bismuth, and antimony from one material are greatly reduced, so that alpha particles emitted from the solder alloy and the solder layer 20 are reduced, so that ultra-low alpha (ULA) characteristics can be obtained.

In particular, according to an embodiment of the present invention, when the solder layer 20 is formed on the surface of the core 1 on which the diffusion layer 10 is formed, it is included in the solder alloy of the solder layer 20 to emit alpha particles. The radioactive elements may form an intermetallic compound (IMC) together with the second metal contained in the diffusion layer 10, and the intermetallic compound containing the radioactive element by intermetallic diffusion is formed in the diffusion layer 10 or the core 1 is diffused to the inside of the , and, thereby, the radioactive element is present in a lower concentration in the solder layer 20, thereby having an advantageous effect that ultra-low alpha characteristics can be obtained.

The reaction temperature, current density, and time of the solder layer forming step may vary depending on the size of the core, the thickness of the diffusion layer 10 and the target thickness of the solder layer 20 .

A step of washing and sorting the solder ball product manufactured after the step of forming the solder layer may be further included. Solder balls are washed by immersion, stirring, ultrasonic stirring, etc. by alcohol-based solution, basic solution, or acidic solution (equipment or reagent).

The core solder ball manufactured through the present invention is characterized in that the alpha ray emission amount is 0.002 cph/cm ^{2 or less by removing impurity elements (210} Pb, ²¹⁰ Bi, ^{210 Po, etc.) that can emit alpha particles.}

The present invention discloses a low-alpha or ultra-low-alpha solder ball capable of maximally suppressing the occurrence of soft errors caused by alpha radiation in a semiconductor device and a method for manufacturing the same, in accordance with the Restriction of Hazardous Substances Directive (WEEE) or RoHS ) can allow low-alpha or ultra-low-alpha solder balls to be utilized in the electronics industry.

In addition, when selective purification of radioactive isotopes emitting alpha particles, such as lead, bismuth, and antimony, is performed to make ultra-low alpha tin with an alpha ray emission amount of 0.002 cph/cm ^{2 or less, expensive reagents and ion exchange membranes are not consumed.} This has the advantage of reducing costs.

In another aspect of the present invention, there is a connection structure of a package formed using a solder ball.

The connection structure of an electronic component or semiconductor device includes a solder ball provided between a connection terminal of the electronic component or semiconductor device and an electrode of a substrate facing the connection terminal of the semiconductor device to thermally and electrically connect the connection terminal and the pad. Hereinafter, the same content as described above with respect to the above-described solder ball will be omitted and described.

6 is a photograph taken with an electron microscope of a cross section of a package formed using a solder ball according to an embodiment of the present invention.

The connection structure may be obtained by soldering a conductive paste including a solder ball as a means for electrically connecting the substrate electrode and the connection terminal to the electrode included in the substrate.

As shown in FIG. 9 , a solder ball may be positioned between the substrate electrode and the connection terminal provided on the upper and lower sides, and the solder alloy of the solder layer after reflow is performed between the electrode and the connection terminal while the core serves as a spacer inside. By electrically connecting them, a stable package connection structure can be obtained.

The connection structure of this aspect is not limited to the structure of the drawing, and in general, a person skilled in the art can form using a solder ball, including various connection structures that can be used when bonding and connecting packages using solder balls. It can be applied to all connection structures of packages.

Since the formed connection structure has an ultra-low alpha characteristic due to a very low content of alpha ray emitting material included in the solder layer and high purity of main components, it is possible to effectively prevent problems such as various soft errors that may occur in the package due to alpha ray emission. can

Example

Example 1

After melting copper (Cu) 5 kg and impurity metal 5 g through a high-temperature high-frequency induction furnace to prepare a molten metal having a copper ratio of 99.9%, a core having a diameter of 180 μm was manufactured.

After the manufactured core was washed using an ultrasonic stirring method, size selection was performed using a mesh.

To form a coating layer, a core to be plated was placed in a barrel, and then a cathode was hung to carry out nickel electroplating. During plating, the temperature was maintained at 10 to 50° C., and the current density was 0.2 to 50 ASD for 5 minutes to 200 hours to form a second metal layer with a thickness of 2 to 3 μm on the surface of the core.

After the prepared core is immersed in an acidic solution, washing is performed.

For plating the solder layer, tin was purified to remove elements emitting alpha rays, solidified, and then ionized with organic acid ions to prepare a metal salt and added to the plating solution. 99.998% (4N) purity of tin to be plated, from which impurities of alpha ray emitting elements have been removed, is hung on the anode, and the cathode is hung on the metal core to be plated, 99.998% (4N) pure tin from which impurities of alpha ray emitting elements are removed It was immersed in a plating solution containing salt, copper salt, and silver salt, and electroplating was performed with Sn96.5wt%, Ag3.0wt%, and Cu 0.5wt% targets. During plating, the temperature was maintained at 10 to 50° C., and the current density was maintained at 0.2 to 50 ASD for 5 minutes to 200 hours to form a solder layer with a thickness of 17 to 18 μm, and a solder ball having a diameter of 220 μm was obtained.

Example 2

The anode used for plating the solder layer in Example 1 was made of 99.9% (3N) tin to be plated with alpha-ray-emitting element impurities removed, and a metal salt of 99.9% (3N) purity from which alpha-ray-emitting element impurities were removed was used. A solder ball was manufactured by performing an experiment in the same manner except that it was immersed in the included plating solution.

comparative example

Comparative Example 1

A solder ball was manufactured in the same manner as in Example 1, except that the anode used for plating the solder layer was changed to 99% (2N) tin.

Comparative Example 2

A solder ball was manufactured in the same manner as in Example 1, except that the metal salt used for plating the solder layer was prepared using 99% (2N) tin.

Experimental example

Experimental Example 1

The alpha ray emission amount of the solder balls of Examples and Comparative Examples was measured with an alpha ray measuring device, and the content of each component was measured by performing ICP analysis, which is summarized in Table 2 below.

ICP analysis value Example 1 Example 2 Comparative Example 1 Comparative Example 2 Main metal content (wt%) 99.9979 99.9755 99.9115 99.8318 Sn 36.8955 36.6927 36.8847 36.6493 Ag 1.2694 1.2731 1.2962 1.2812 Cu 58.0348 58.2092 57.9588 58.0911 Ni 3.7982 3.8005 3.7718 3.8102 Pb 0 0 0.0289 0.0511 Sb 0.0002 0.0066 0.0262 0.0833 Al 0.0003 0.0003 0.0002 0.0001 CD 0 0 0.0001 0.0001 Fe 0 0.0115 0.0163 0.0122 Bi 0.0001 0.0002 0.0093 0.0147 In 0.0001 0.0001 0.0001 0.0001 Au 0.0003 0 0.0002 0.0002 S 0.0011 0.0058 0.0072 0.0064 Alpha particle emission
(cph/cm ² ) 0.0013 0.0018 0.23 0.36

The sum of the contents of tin, silver, copper, and nickel, which are the main metals of the solder ball of Example 1, was 99.9979% (4N), and the alpha radiation emission amount was ^{measured to be 0.0013 cph/cm 2} , indicating ultra-low alpha characteristics.

The sum of the contents of tin, silver, copper, and nickel, which are the main metals of the solder ball of Example 2, is 99.9755% (3N), and the alpha radiation emission amount is ^{measured to be 0.0018 cph/cm 2} , indicating ultra-low alpha characteristics.

The sum of the contents of tin, silver, copper, and nickel, which are the main metals of the solder ball of Comparative Example 1, is 99.9115% (3N), and the alpha radiation emission amount is ^{measured as 0.23 cph/cm 2} , which is out of the ultra-low alpha range.

The sum of the contents of tin, silver, copper, and nickel, which are the main metals of the solder ball of Comparative Example 2, was 99.8318% (2N), and the alpha radiation emission was ^{measured as 0.36 cph/cm 2} , which was outside the ultra-low alpha range.

The solder ball manufactured as a result of this example uses a positive electrode and a metal salt with a purity of 99.9% (3N) to 99.99% (4N) of the main components, and a solder ball having an ultra-low alpha characteristic of ^{0.002 cph/cm 2 or less.} showed that it could

1: core 10: diffusion layer
20: solder layer

Claims (12)

a core comprising a first metal;
a diffusion layer comprising a second metal different from the first metal and provided on the core; and
a solder layer provided on the diffusion layer, the alloy component constituting the solder alloy, and an impurity included in the solder alloy;
A solder ball containing 99.9 wt% to 99.9989 wt% of a main component consisting of the first metal, the second metal, and the alloy component, and an alpha-ray emission amount of 0.002 cph/cm ² or less. According to claim 1,
A solder ball having an impurity content of 11 ppm to 1000 ppm. According to claim 1,
The impurity is a solder ball containing a radioactive isotope emitting the alpha rays. 4. The method of claim 3,
The solder alloy is a solder ball comprising an alloy of Sn and at least one metal selected from the group consisting of Au, Ag, Cu, Ni, Bi, Zn, Pd, In, Pb and Po. 4. The method of claim 3,
The second metal is a solder ball containing nickel. 4. The method of claim 3,
A ratio (w2/w1) of the sum of the weights of the first metal and the second metal (w1) and the weight of the solder layer (w2) is 0.05 to 0.95. 4. The method of claim 3,
The diffusion layer is a solder ball including an alloy of the first metal and the second metal formed by diffusion of the first metal and the second metal at an interface between the core and the diffusion layer. 8. The method of claim 7,
The diffusion layer is a solder ball in which the ratio of the second metal continuously increases from the bottom to the top. 4. The method of claim 3,
The solder layer has a thickness of 2 μm to 2,000 μm. a second metal plating step of forming a diffusion layer including a second metal different from the first metal on the surface of the core including the first metal; and
A solder layer forming step of plating a solder layer having an alloy component constituting a solder alloy on the diffusion layer and an impurity included in the solder alloy,
The solder layer forming step is a step of plating the solder layer using an anode having a purity of 99.9 wt% to 99.9989 wt% of tin, and a plating solution having a purity of 99.9 wt% to 99.9989 wt% of a metal salt. 11. The method of claim 10,
Solder ball manufacturing method comprising the step of removing the radioactive isotope contained as an impurity in the anode or the metal salt. It comprises the solder ball of any one of claims 1 to 9,
The solder ball is provided between an electrode included in the substrate and a connection terminal connected to the electrode, and is reflowed to electrically connect the electrode and the connection terminal.

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