JP2023044347A - Low-melting-point solder alloy - Google Patents

Abstract

To provide a solder alloy and a solder joint of high general applicability, wherein the solder alloy is a low-melting-point Sn-Bi solder alloy containing a large amount of Bi, but does not cause a deterioration in the mechanical properties of the solder alloy and the solder joint and can suppress the occurrence of electromigration.SOLUTION: The present invention provides a solder alloy and a solder joint including the solder alloy. The solder alloy has a solder composition comprising Sn of 40 mass%-70 mass% and Bi of 30 mass%-60 mass%, in combination with an element selected from one group or plural groups of the following: a first group being one or more elements selected from the group consisting of Cu, Sb, and Ag; a second group being one or more elements selected from the group consisting of Fe, Co, Ni, Pd, Ru, Rh, Gd, and Pt; and a third group being one or more elements selected from the group consisting of P, Ca, Ti, Mn, As, Cd, In, Te, and Pb, each group having an elemental content of the following: the first group being 0.01 mass%-4 mass%, the second group being 0.005 mass%-0.1 mass%, and the third group being 0.0005 mass%-0.01 mass%. This constitution can suppress the occurrence of electromigration in the solder alloy and the solder joint.SELECTED DRAWING: None

Description

The present invention relates to a Sn—Bi system low melting point solder alloy and a solder joint.

In order to reduce the burden on the global environment, lead-free solder is widely used as a bonding material for electronic parts. and is widely used.
However, these lead-free solder alloys have a higher melting point than conventionally used Sn--Pb eutectic composition solders, and the temperature at the time of soldering is also higher.
Therefore, electronic components and substrates with high heat resistance are required, which is a factor in the increase in product costs. Sn--Bi-based and Sn--In-based solder alloys, which have a low melting point by containing a predetermined amount of In, are used.

By the way, it is known that if a Sn--Bi-based solder alloy contains a large amount of Bi, the solder alloy and solder joints become brittle, and the mechanical properties are degraded.
Therefore, the applicant discloses in Patent Document 1 a technique of forming a highly reliable solder joint by adding predetermined amounts of Sb, Cu, and Ni to an Sn—Bi solder alloy.

On the other hand, in recent years, electronic parts such as CPUs (Central Processing Units) used in electronic devices such as personal computers have been downsized and improved in performance. As a result, an increase in current density occurs.
When the current density increases, it promotes voids and the like caused by electromigration (hereinafter referred to as "EM") in the solder joints that join the terminals and the substrate, resulting in an increase in local resistance values and joints due to hot spots. There is concern about increasing the occurrence of defects due to heat generation of parts.

Therefore, Patent Document 2 discloses a technology for a solder alloy composition that suppresses the generation of EM.

International publication WO2020/209384 Registration No. 6119912

Although it is a low-melting point Sn—Bi solder alloy containing a large amount of Bi, the mechanical properties of the solder alloy and solder joints do not deteriorate, and a versatile solder alloy that has the effect of suppressing the generation of EM and solder joints.

In order to achieve the above object, the present inventors have made intensive studies focusing on Sn--Bi low-melting-point solder alloy compositions. As a first group, one or two or more elements selected from the group consisting of Fe, Co, Ni, Pd, Ru, Rh, Gd, and Pt As the second group, one or two or more elements selected from the group consisting of P, Ca, Ti, Mn, As, Cd, In, Te, and Pb as the third group, and the elements of the first group By containing 0.01% to 4% by mass, 0.005% to 0.1% by mass of elements of the second group, and 0.0005% to 0.01% by mass of elements of the third group , the effect of suppressing the generation of EM was found, and the present invention was completed.

That is, the present invention provides a solder composition containing 40% by mass to 70% by mass of Sn and 30% by mass to 60% by mass of Bi, and one or more selected from the group consisting of Cu, Sb, and Ag. Elements as a first group, one or more elements selected from the group consisting of Fe, Co, Ni, Pd, Ru, Rh, Gd, and Pt as a second group, P, Ca, With one or more elements selected from the group consisting of Ti, Mn, As, Cd, In, Te, and Pb as the third group, the content of the elements in each group is 0.01% to 4% by weight, 0.005% to 0.1% by weight for the elements of the second group, 0.0005% to 0.01% by weight for the elements of the third group, and the single group or By containing elements selected from a plurality of groups, it is possible to suppress EM generated in the solder alloy and solder joints using the solder alloy.

INDUSTRIAL APPLICABILITY The present invention enables solder joints at a low temperature, enables solder joints with high joint reliability, and suppresses the generation of EM, thereby reducing the environmental load and suppressing thermal damage to electronic parts, substrates, and substrates. In addition to making it possible to reduce costs by lowering the heat resistance of electronic components, it also enables high bonding reliability, so it can be widely applied to automobiles and industrial machinery in addition to electronic devices such as personal computers. .

Sn—Bi binary phase diagram.

The present invention will be described in detail below.
The low melting point solder alloy of the present invention has a composition based on 40% to 70% by mass of Sn and 30% to 60% by mass of Bi, and Cu, Sb, Ag, Fe, Co, Ni, Pd, Ru , Rh, Gd, Pt, P, Ca, Ti, Mn, As, Cd, In, Te, and Pb. A solder alloy having excellent properties and an effect of suppressing the generation of EM, a solder joint joined using the solder alloy, and an electronic component using the solder joint.

Recently, a Sn—Bi eutectic composition, which is a low melting point solder alloy, and a composition containing 30% by mass or more of Bi have been tried for soldering, but originally, a solder alloy containing a large amount of Bi was used. It has been pointed out that solder joints are brittle, and the applicant has disclosed in Patent Document 1 that the mechanical properties are improved by adding predetermined amounts of Sb, Cu, and Ni to the Sn—Bi solder alloy. It discloses a technology related to solder alloys and solder joints that are highly reliable.
However, although Patent Document 1 describes the need to deal with the occurrence of EM caused by an increase in current density due to the downsizing and performance enhancement of electronic devices, it does not describe the details or suggestions for dealing with it. not

In addition, Patent Document 2 discloses a solder alloy composition that suppresses the generation of EM with respect to a lead-free solder alloy containing Bi. There is, and the melting point inferred from the disclosed alloy composition is 200 ° C. or higher, which is significantly higher than the solder alloy of the present invention, and as can be seen from the Sn-Bi binary phase diagram shown in FIG. The alloy exhibits a eutectic reaction, and when the Bi content is 30% by mass to 60% by mass, no intermetallic compound is formed, and a specific state is exhibited compared to other alloys. It is difficult to recall or even suggest.

EM is understood to be a phenomenon in which electrons flowing in a metal wiring collide with metal electrons and transport metal atoms, and it is thought that EM generated in solder joints is also accelerated as electricity is supplied.
In the present invention, the effects of the elements contained in the low-melting-point solder alloy based on the Sn—Bi composition are presumed as follows.
(A) Cu, Sb, and Ni are elements that randomize the orientation of Sn crystals and suppress interstitial diffusion, thereby suppressing EM that occurs in solder joints.
(B) Ag, as an element that stops the growth of intermetallic compounds generated at the bonding interface by miniaturizing the intermetallic compounds generated at the solder joint, suppresses sliding dislocations at grain boundaries, and suppresses the generation of EM; Fe, Co, Ni, Ru, Rh, Pt, Ti, Mn, and As.
(C) Pd and In as elements that have good compatibility with Bi in terms of solid solution and formation of intermetallic compounds and suppress the movement of Bi, thereby suppressing the generation of EM.
(D) Cu, Sb, Gd, P, Ca, and Cd are elements that have good compatibility with Sn in solid solution and formation of intermetallic compounds and suppress the movement of Sn, thereby suppressing the generation of EM. , Te, and Pb.
It should be noted that a solder alloy composition that does not contain Cd, Pb, and Te is preferable when considering the reduction of the load on the global environment.

The low melting point solder alloy according to the present invention has, in addition to the Sn—Bi basic composition, Cu, Sb, Ag, Fe, Co, Ni, Pd, Ru, Rh, Gd, Pt, P, Ca, Ti, Mn, One or two or more selected from the group consisting of As, Cd, In, Te, and Pb is contained in a predetermined amount, but other elements are also contained within the range of the effect of the present invention. I don't mind.
Examples thereof include solder alloys such as Ge, Ga, Si, and V, and elements having an antioxidation effect on solder joints.

The low melting point solder alloy according to the present invention can be used in the form of solder paste, solder balls, preforms, wire rods, flux cored solders, and dipping bar solders, and the range having the effect of the present invention , there is no limitation on the form.

The low-melting-point solder alloy according to the present invention and the form of the solder alloy can be produced in each form according to a conventional method.
In addition, joining using the solder alloy according to the present invention can be performed by conventional methods such as flow soldering and reflow soldering.

For example, in the case of solder paste, the Sn--Bi basic composition includes Cu, Sb, Ag, Fe, Co, Ni, Pd, Ru, Rh, Gd, Pt, P, Ca, Ti, Mn, As, Cd, In, A solder alloy containing a predetermined amount of one or more selected from the group consisting of Te and Pb is prepared, processed into powder with an average particle size of 20 to 50 μm by a conventional method, and mixed with flux. can be manufactured by

In addition, this solder paste can be produced by mixing the above-described solder alloy powder and flux, but the flux is not particularly limited in terms of components, properties, etc., as long as the flux has the effect of the present invention. .
For example, the flux can contain rosins, solvents, thixotropic agents, activators, and antioxidants.

The flux composition of the solder paste using the low melting point solder alloy of the present invention will be explained.
[Rosin]
Examples of the rosin include natural rosins such as gum rosin, wood rosin and tall oil rosin, disproportionated rosins, hydrogenated rosins, formylated rosins, fumarated rosins, maleated rosins, and acrylated rosins. modified rosins such as rosins, rosin esters, and the like. These rosins may be used alone or in combination of two or more.
The content of the rosin in the total mass of the flux is preferably 20 to 60% by mass, from the viewpoint of the meltability of the solder paste of the present invention, the effect of the solder ball suppressing force, and the viscosity of the solder paste, and 30% by mass. ~50% by mass is more preferred.

〔solvent〕
Examples of the solvent include alcohols such as octanediol, decanol, and 2-hexyl-1-decanol, butyl carbitol, dibutyl carbitol, hexylene glycol, hexylene diglycol, tripropylene glycol monomethyl ether, and tripropylene glycol. Monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monohexyl ether, diethylene glycol dibutyl ether, diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, triethylene glycol monobutyl ether, methylpropylene triglycol, butylpropylene triglycol, triethylene glycol Glycols such as butyl methyl ether and tetraethylene glycol dimethyl ether, esters such as butyl benzoate and dibutyl maleate, hydrocarbons such as n-hexane and dodecane, terpineol, 1,8-terpine monoacetate, 1,8 - Terpene derivatives such as terpine diacetate and dihydroterpineol. Only one kind of the solvent may be used, or two or more kinds thereof may be used in combination.
The content of the solvent in the total mass of the flux may be determined based on the viscosity and printability of the solder paste, and is preferably 20-50 mass %, for example.

[Thixotropic agent]
The thixotropic agent is not particularly limited as long as it can adjust the viscosity of the solder paste of the present invention to a desired value, but known agents applicable to solder paste or flux can be used. Hydrogenated castor oil, beeswax, carnauba wax, fatty acid amide wax, stearic acid amide, ethylenebisstearic acid amide, ethylenebishydroxystearic acid amide, hexamethylenebishydroxystearic acid amide and the like. The thixotropic agent may be used alone or in combination of two or more.
The content of the thixotropic agent in the total mass of the flux may be determined based on the printability of the solder paste.

[Activator]
Examples of the activator include organic acids such as carboxylic acid, imidazole, and derivatives thereof.
For example, the monocarboxylic acid is not particularly limited, but stearic acid, palmitic acid, oleic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, eicosanoic acid, heneicosanoic acid, docosanoic acid, 2 Monovalent carboxylic acids in which aliphatic hydrocarbons such as decyltetradecanoic acid are substituted with carboxy groups, 12-hydroxydodecanoic acid, 12-hydroxyoctadecanoic acid, 13-hydroxytridecanoic acid, 14-hydroxytetradecanoic acid, 9,16- Hydroxy fatty acids such as dihydroxyoctadecanoic acid, and polyhydroxy fatty acids such as dihydroxyhexadecanoic acid, dihydroxyoctadecanoic acid and dihydroxyeicosanoic acid.
The dicarboxylic acid is not particularly limited, but includes succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid and the like. imidazole, 2-ethyl-4-methylimidazole, 2-butylimidazole, benzimidazole and the like.
The content of the activator in the total mass of the flux may be determined based on the bondability and printability of the solder paste, and is preferably 2 to 20 mass %, for example.

〔Antioxidant〕
Examples of the antioxidant include at least one of phenolic antioxidants and triazole antioxidants, and the phenolic antioxidant includes a methyl group or a t-butyl group at the ortho positions on both sides of the phenolic hydroxyl group. Reshindered phenol antioxidants not substituted with (tertiary butyl groups), partially hindered phenols substituted with methyl groups at only one ortho position and with t-butyl groups at the other ortho position. antioxidants, and fully hindered phenolic antioxidants substituted on both ortho positions with t-butyl groups. Phenolic antioxidants include hindered phenol antioxidants as well as 2,2′-hydroxy-3,3-di(α-cyclohexyl)-5,5′-dimethylphenylmethane.
Examples of the triazole antioxidant include 3-amino-1,2,4-triazole, 3-(N-salicyloyl)amino-1,2,4-triazole, 3-(N-salicyloyl)amino-1 , 2,4-triazole, benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5 -chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 2, 2′-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol], 6-(2-benzotriazolyl)-4-tert-octyl-6′-tert-butyl-4 '-methyl-2,2'-methylenebisphenol, 1,2,3-benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, carboxybenzotriazole, 1-[N,N -bis(2-ethylhexyl)aminomethyl]methylbenzotriazole, 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol, 1-(1',2'-di carboxyethyl)benzotriazole, 1-(2,3-dicarboxypropyl)benzotriazole, 1-[(2-ethylhexylamino)methyl]benzotriazole, 2,6-bis[(1H-benzotriazol-1-yl) methyl]-4-methylphenol, 5-methylbenzotriazole and the like.
Moreover, in the solder paste of the present invention, an antioxidant may be used in combination.

By using the low melting point solder alloy of the present invention for solder joints, EM generated in the solder joints is suppressed, so highly reliable joints are possible, and in addition to electronic devices such as personal computers, in-vehicle and industrial machines, etc. can be expected to be widely applied to

Claims (2)

Bi is 30% by mass to 60% by mass,
As a first group, one or more elements selected from the group consisting of Cu, Sb, and Ag,
As a second group, one or more elements selected from the group consisting of Fe, Co, Ni, Pd, Ru, Rh, Gd, and Pt,
As a third group, one or more elements selected from the group consisting of P, Ca, Ti, Mn, As, Cd, In, Te, and Pb,
The content of the elements in each group is 0.01% to 4% by mass for the elements in the first group, 0.005% to 0.1% by mass for the elements in the second group, and 0 for the elements in the third group. .0005% by mass to 0.01% by mass,
A low-melting-point solder alloy characterized by containing an element selected from a single group or a plurality of groups in the above content, and the balance being Sn and unavoidable impurities. A solder joint formed using the solder alloy according to claim 1 .

Images