JP2000317682A - Solder powder and manufacture thereof, and solder paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lead free solder powder and a solder paste excellent in practical use, wherein even the solder contains high reactive Zn together with Sn, but the solderability is good and the reaction between the active component and the alloy component in the blux is restrained. SOLUTION: Organic acid salt such as stearic copper etc., is stuck to the surface of the solder powder containing Sn, Zn, further Bi, etc., further, in the flux, nonionic surface active agent is added at 0.5-10 wt.%. The organic acid salt can be produced by blasting solution saturated with the organic acid salt to the solder powder continuously dropped or by dipping the solder powder into his solution. The solubility of the organic acid salt in the saturated solution dipped with the solder powder is gradually lowered by dripping alcohol etc., to form the thin film of the organic acid salt coated on the surface of the soldering powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder powder for use as a solder paste (solder paste) together with a flux, and further relates to a method for producing the solder powder, and a solder paste containing the solder powder and a flux.

[0002]

2. Description of the Related Art In the present specification, a composition composed of, for example, 63% by weight of Sn and the balance of Pb is expressed as 63Sn-Pb according to a common practice among those skilled in the art. Weight percent Bi and the balance Sn
-8Zn-3Bi or the like.

[0003] As a method of soldering electronic parts,
Ironing method, dipping method, reflow soldering method
For example, a reflow method is used for surface mounting of an IC chip or the like, in which a bridge is hardly generated between leads of a surface-mounted component and productivity is excellent. Normally, in the reflow method, a solder paste in which a powder of a solder alloy and a flux are mixed is printed on a predetermined solder portion using a metal mask or a silk screen, and is heated in a reflow furnace to perform soldering.

For soldering by reflow method or the like, Sn
-Pb alloys have been commonly used. The Sn-Pb alloy has a low eutectic composition melting temperature (63 Sn-Pb
The melting temperature is 183 ° C).
It is as low as 230 ° C. Therefore, there is little possibility that the electronic component is thermally damaged. In addition, the Sn-Pb alloy has good solderability. However, since this solder alloy contains Pb, there is a concern that Pb flowing out of the discarded electronic device may adversely affect the human body via groundwater or the like. From such circumstances, Sn-Ag alloy, Sn-Sb
Alloys, Sn-Bi alloys, Sn-Zn alloys and the like have been proposed as lead-free solder alloys.

[0005] In the Sn-Ag alloy, the composition having the lowest melting temperature is the eutectic composition of Sn-3.5Ag, and its melting temperature is 221 ° C. In this case, the soldering temperature is 26
The temperature rises to about 0 to 270 ° C. In Sn—Sb alloy, the composition with the lowest melting temperature is Sn-5Sb,
Regarding the melting temperature of this composition, the solidus temperature is 235 ° C and the liquidus temperature is 240 ° C. In this case, the soldering temperature is
280-300 higher than Sn-3.5Ag alloy
° C. In the Sn-Bi alloy, the eutectic composition Sn-58B
In i, the eutectic temperature is 139 ° C. Although the eutectic temperature is sufficiently low, the Sn-Bi alloy is brittle and hard, and therefore has a problem in mechanical properties such as tensile strength at a soldered portion.

In a Sn—Zn alloy, the eutectic composition Sn-9Z
At n, the eutectic temperature is 199 ° C. This eutectic temperature is equal to the eutectic temperature of 183 of the conventional 63Sn-Pb eutectic solder.
Close to ° C. Moreover, the Sn—Zn alloy has excellent mechanical properties.

However, the Sn-Zn alloy also has a problem in solderability. Therefore, in order to improve the solderability of the Sn—Zn alloy and further improve the mechanical strength, Ag, Cu, Bi, In,
There has been proposed a Sn—Zn-based solder alloy to which Ni, P or the like is appropriately added (for example, Japanese Patent Application Laid-Open No. 9-253882).

[0008] The Sn-Zn based alloy contains Zn in the alloy.
Has a high activity, the solder particles adjacent to each other tend to stick together and tend to increase in viscosity when used as a paste. If the viscosity of the solder paste becomes excessive, it becomes difficult to print the paste on the substrate. Sn-Zn based alloy is Z
Since the surface of n is easily oxidized, the melting point of the alloy tends to increase. Therefore, a method has been proposed in which the viscosity of the paste is reduced by increasing the amount of an activator (for example, amine hydrohalide) in the flux used together with the powder of the Sn-Zn-based solder alloy.

Japanese Patent Application Laid-Open No. 9-327789 proposes an improved flux for suppressing a change in paste viscosity with time. The flux disclosed in the publication contains an organic acid containing a carboxyl group and a hydroxyl group, such as malic acid and tartaric acid. By reacting with Zn, these organic acids suppress the reaction between Zn and other polymers contained in the flux component, and reduce the increase in viscosity in the flux. The flux contains organic compounds such as phthalic acid esters and sorbitan fatty acid esters. These organic compounds are represented by S
By adhering to the surface of the n-Zn-based solder alloy, the reaction of the alloy is suppressed.

[0010] Furthermore, Japanese Patent Application Laid-Open No. 8-215884 attempts to coat the solder alloy powder itself before mixing with a flux. The gazette states that
As a specific method, Bi-43 having a particle size of 10 to 45 μm is used.
A method of immersing a Sn solder alloy powder in an aqueous solution of a corrosion inhibitor such as a benzothiazole derivative, an amine, or thiourea is disclosed.

[0011]

However, as disclosed in Japanese Patent Application Laid-Open No. 9-253882, even a Sn-Zn-based solder alloy in which the characteristics are improved by adding a small amount of a component is not reflowable. , Solderability was not enough. Specifically, there is a problem that the copper foil land portion of the printed circuit board remains as it is without the soldering portion being completely wetted. There is also a problem that the solder paste flows out of the copper foil land between the semiconductor leads and becomes solder balls and adheres to the printed circuit board.

Further, when the amount of the activator in the flux is increased to reduce the viscosity of the solder paste, the activator remaining after soldering is whitened due to aging, and the strength and conductivity are reduced. Occurs.

Further, as described in Japanese Patent Application Laid-Open No. 9-327789, when the particles of the solder alloy are coated with the components in the flux, the contact between the active component also contained in the flux and the solder powder is effectively reduced. Cannot be prevented.

Japanese Patent Application Laid-Open No. Hei 8-215884 specifically describes only a Sn—Bi alloy, which is suitable for preventing a thickening of a solder paste containing a metal having high activity such as Zn. No materials or methods are described.

In the conventional method described in the above publication, the time-dependent change of the Sn—Zn-based solder alloy cannot be sufficiently suppressed. If the thickening cannot be sufficiently suppressed, the so-called pot life is shortened, and when applied to a substrate by screen printing, there is a problem that the solder powder hardly passes through the mesh and causes clogging of a mask or the like.

Accordingly, the present invention provides a solder powder which contains Sn and Zn, has good solderability, and can suppress a reaction between an active component and an alloy component in a flux, and a method for producing the same. The purpose is to provide. Another object of the present invention is to provide a solder paste which contains Sn and Zn, has good solderability, and is suppressed from changing over time.

[0017]

In order to achieve the above object, a solder powder of the present invention is a solder powder constituting a solder paste together with a flux, contains Sn and Zn, and has an organic acid salt adhered to the surface. It is characterized by doing.

According to the solder powder of the present invention, when used together with the flux, the solderability is good and the reaction with the active component in the flux is suppressed.

The first solder paste of the present invention is characterized by containing the above-mentioned solder powder and flux. Further, the second solder paste of the present invention is a solder paste containing a solder powder and a flux,
The solder powder contains Sn and Zn, and the flux contains 0.5 to 10% by weight of a nonionic surfactant.

According to the solder paste of the present invention, the solderability is good and the change with time is suppressed.

Further, in the method for producing a solder powder according to the present invention, the step of preparing a solution saturated with an organic acid salt, and the step of bringing the solder powder containing Sn and Zn into contact with the solution, form a surface of the solder powder. And adhering the organic acid salt to the organic solvent.

Here, the solution saturated with the organic acid salt includes all the solutions in which the organic acid salt is present at the solubility limit (saturated solution) or more (supersaturated solution).

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. A Sn—Zn-based alloy is used as the solder powder, and it is preferable that Bi is added to this alloy. This is because the melting temperature can be reduced to about the melting temperature of the Sn-Pb-based alloy. Sn-Zn-Bi
The composition of the alloy based on Sn:
70 to 95%, Zn: 5 to 30%, and the balance Bi is preferable. Further, a Sn-Zn-Bi-Ag-based alloy containing Ag may be used, and its specific composition is expressed by weight%, Zn: 2 to 10%, Bi: 10 to 30%,
Ag: 0.05 to 2%, with the balance being Sn.

Further, the solder powder is not particularly limited, but preferably has an average particle size of 10 μm to 100 μm.

The organic acid salt is preferably a fatty acid salt, and more preferably a fatty acid salt having 11 or more carbon atoms. As such fatty acid salts, specifically, lauric acid,
Examples include salts of at least one fatty acid selected from myristic acid, palmitic acid and stearates. These fatty acid salts are versatile and safe.

The organic acid salt is preferably a salt of an organic acid contained in the flux in consideration of the reliability of the flux residue in the soldered portion. The organic acid salt may be appropriately selected depending on the flux used in combination, for example,
It is preferably a salt of at least one organic acid selected from phthalic acid, citric acid and stearic acid.

The organic acid salt preferably contains a metal other than an alkali metal as a metal, and more preferably a salt of an organic acid and a base containing a transition metal.

The organic acid salt is preferably an organic acid copper, and specifically, copper phthalate, copper citrate, copper laurate, copper myristate, copper palmitate and copper stearate can be suitably used. Organic acid copper is particularly effective in improving solderability. In order to improve the solderability, it is preferable to attach an organic acid salt such as an organic acid copper to 5% or more of the surface of the solder powder. The reason that the organic acid copper is suitable for improving the solderability is considered to be due to the good affinity between copper and tin.

When it is desired to sufficiently suppress the aging of the solder paste, it is preferable that the organic acid salt is adhered to the surface of the solder powder as a continuous thin film. If the surface of the solder particles is covered with a thin film of an organic acid salt, the reaction between the active component in the flux and the solder alloy is effectively suppressed. The preferred thickness of the thin film is 0.1 μm to 10 μm, particularly 0.1 μm to 5 μm.

The Sn-Zn based alloy solder powder has a problem that the viscosity increases due to the reaction between the active component in the flux and Zn, and the wettability to a copper foil or the like decreases. But,
By coating with an organic acid salt, oxidation of Zn or the like is less likely to occur, and a decrease in solder wettability can be suppressed. Therefore, the amount of the activator added to the flux to secure the wettability can be reduced. Activators such as hydrohalides caused whitening after soldering, but reduced the amount of Sn-Zn-based alloy solder powder and the amount of activator added (for example, 10% by weight of flux). When the flux is used in combination, a favorable result can be obtained from the viewpoint of suppressing the deterioration of the soldered portion. Further, the reduction of the amount of the activator in the flux is preferable from the viewpoint of prolonging the so-called pot life.

When importance is placed on suppressing the aging of the solder paste, organic acid copper is effective, but the organic acid salt preferably contains the same metal as the metal contained in the solder alloy. This is because a strong coating with good affinity is easily obtained. An example of a particularly preferred organic acid salt, stearate, is Sn-Z as a solder alloy.
When an n-Bi alloy is used, the organic acid salt is particularly preferably zinc stearate or bismuth stearate. When a Sn-Zn-Bi-Ag alloy is used, zinc stearate, bismuth stearate, and silver stearate are particularly preferable as the organic acid salt.

As the flux to be used together with the solder powder to which the organic acid salt has been adhered, a conventionally used flux can be used without any particular limitation.
The flux generally contains rosin (base), an activator, a solvent, and the like, and more specifically, a natural rosin, a polymerized rosin, and the like as a base, and an amine hydrohalide such as diethylamine hydrochloride as an activator. And diethylene glycol monobutyl ether and ethylene glycol monophenyl ether as solvents. In addition, a thixotropic agent or the like is appropriately added to the flux.

Preferably, the flux contains a nonionic surfactant. The addition of a nonionic surfactant is effective in improving solderability and suppressing thickening. The amount of the nonionic surfactant added is preferably 0.5 to 10% by weight of the flux.

When a flux to which a nonionic surfactant is added is used, the nonionic surfactant is bonded to the periphery of the solder powder to prevent agglomeration of the solder powders. effective. In addition, the occurrence of solder balls can be suppressed by preventing oxidation in the reflow method.

When used together with the Sn—Zn-based alloy solder powder to which no organic acid salt is attached, the nonionic surfactant is added in a range of 0.5 to 10% by weight of the flux. If the amount is less than 0.5% by weight, the effect of the addition cannot be sufficiently obtained. On the other hand, if the added amount exceeds 10% by weight, the solderability is adversely affected.

The nonionic surfactant is not particularly limited as long as it is nonionic. Polyoxyethylene cetyl ether (for example, "BC-4" manufactured by Nikko Chemicals Co., Ltd.)
0TX "), polyoxyethylene sorbitan monooleate (for example," TO-10M "manufactured by the company) and the like can be used.

Next, a method for producing a solder powder to which an organic acid is attached will be described. The solder powder can be produced by a conventionally used method such as a centrifugal spraying method and a gas spraying method.

A solution saturated with an organic acid salt is prepared with the solder powder. The solvent is appropriately selected depending on the production method to be applied. For example, in a method in which an organic acid salt is attached to the surface of a solder powder by dispersing the solder powder in a solution, a solvent in which the organic acid salt is soluble is preferable. Examples of such a solvent include, when the organic acid salt is a fatty acid salt, an organic solvent such as benzene, toluene, and tetrahydrofuran. Further, a petroleum-based solvent such as kerosene may be used. A saturated solution of an organic acid is, for example, dissolving an organic acid salt in a solvent until it becomes supersaturated,
It can be prepared by filtering this supersaturated solution. Further, it may be used as a supersaturated solution of an organic acid without filtering. Furthermore, a saturated solution of the organic acid salt may be prepared, and the organic acid salt may be deposited on the surface of the solder powder while the solution is brought into a supersaturated state.

On the other hand, in a method in which a solution saturated with an organic acid is sprayed on a solder powder to cause the organic acid salt to adhere to the surface of the solder powder, the solution is not limited to a solvent in which the organic acid salt is soluble, but is slightly soluble or insoluble. May be used. For example, copper stearate, which is a preferred organic acid copper, is hardly soluble in lower alcohols such as methanol, ethanol, and isopropanol. However, lower alcohols are suitable for mass production because they can be easily removed and handled by drying and can be used at low cost. In this method, a supersaturated solution of an organic acid salt is preferably used.

(First Embodiment) Hereinafter, a first embodiment of a method for producing a solder powder will be described. Here, a method of spraying a supersaturated solution of an organic acid salt onto the free-falling solder powder to attach the organic acid salt will be described.

In the present embodiment, as shown in FIG. 1, a supersaturated solution 13 of an organic acid copper is sprayed in a mist form from a spraying device 12 on a solder powder 11 which falls continuously, and the surface of the solder powder 11 is sprayed. The supersaturated solution adheres to. The solder powder 14 to which the solution has adhered further drops from the portion where the supersaturated solution is sprayed from the spraying device 12 and is heated when passing between the hot air dryers 15. By this heating, the solvent evaporates from the surface of the solder powder, and the solder powder 16 to which the organic acid salt is attached is manufactured. This method is excellent in production efficiency, and has an advantage that the amount of the organic acid salt formed on the surface of the solder powder can be easily controlled by adjusting the concentration of the supersaturated solution and the spray amount.

As a surface treatment method for the solder powder, plating and the like can be considered. However, in plating, it is difficult to control a plating solution and to hold a solder powder, resulting in an increase in cost. However, in the above method, the holding of the solder powder is not necessary, and the saturated solution only needs to be sprayed uniformly on the solder powder. As described above, according to the above method, the solder powder to which the organic acid salt is uniformly adhered can be mass-produced at low cost only by controlling the concentration of the saturated solution and the drying temperature.

Further, if the above method is carried out in combination with the classification of the solder powder, the production efficiency is further improved. In this case, the solder powder 11 is supplied from a classifying means such as a sieve 17 that drops the solder powder having a diameter equal to or less than the predetermined diameter while removing the solder powder exceeding a predetermined diameter. As described above, the above method can be performed more efficiently by performing the method continuously with the manufacturing process of the solder powder.

(Second Embodiment) Hereinafter, a second embodiment of a method for producing a solder powder will be described. Here, a method of immersing a solder powder in a supersaturated solution of an organic acid salt and attaching the organic acid salt to the surface of the solder powder will be described.

In this embodiment, the organic acid salt is precipitated on the surface of the solder powder by stirring the supersaturated solution of the organic acid salt in which the solder powder is immersed for a predetermined time. In this case, the amount of the organic acid salt deposited is controlled by the concentration of the supersaturated solution, the amount of the solder powder added, the stirring time, and the like. The solder powder having an organic acid salt adhered to the surface is taken out of the solution and dried to remove the solvent.

As an example, copper stearate is made of Sn—Zn.
A method for attaching the powder to the surface of the base alloy powder will be described.
90 g of the solder powder is added to a supersaturated solution obtained by adding 9 g of copper stearate to 300 ml of ethanol, and the mixture is stirred for 15 minutes at about 800 rpm using a magnetic stirrer.
Thereafter, the supersaturated solution and the solder powder are further separated, and the solder powder is dried in a furnace maintained at 60 ° C. for 30 minutes.
When the surface of the solder powder thus obtained was observed with a scanning electron microscope, copper stearate was deposited on the surface of the solder powder as shown in FIG. Copper stearate covered about 10% of the surface of the solder powder.

As shown in FIG. 2, even if the organic acid salt is only partially adhered to the surface of the solder powder instead of the entire surface, the effect of preventing the oxidation of Zn by the reflow method in the air is effective. is there. That is, when a solder paste prepared by mixing a solder powder and a flux to which an organic acid salt partially adheres is printed on a printed circuit board and heated in a reflow furnace, the temperature of the printed circuit board rises and the melting point of the organic acid salt is increased. When the temperature reaches (for example, the melting point of copper stearate is 120 ° C.), the organic acid salt covers the solder powder to prevent oxidation of Zn by oxygen in the atmosphere. Thus, generation of solder balls in the reflow method is suppressed.

Therefore, although not particularly limited, when the organic acid salt is partially adhered to the surface of the solder particles, the melting point of the organic acid salt is preferably lower than the melting point of the Sn—Zn-based alloy solder particles.

(Third Embodiment) Hereinafter, a third embodiment of a method for producing a solder powder will be described. here,
Soak the solder powder in a saturated solution of organic acid salt, then
A method of performing an operation to lower the solubility of the organic acid salt on the saturated solution will be described.

The operation for reducing the solubility of the organic acid salt is carried out by changing at least one of various conditions which affect the solubility. Such operations include changing the temperature and pressure, adding new solutes and solvents to the saturated solution, and the like. At least one of these operations is applied to the saturated solution while avoiding sudden changes in conditions.

As exemplified above, when an organic solvent is used as a solvent and a fatty acid salt having 11 or more carbon atoms is used as an organic acid salt, a lower alcohol such as methanol, ethanol or isopropanol is added to the saturated solution. Then, the solubility of the organic acid salt can be reduced. In particular, it is preferable that these alcohols are gradually dropped into a saturated solution, since the solubility of the organic acid salt gradually decreases and the organic acid salt can be gradually precipitated.

According to the present embodiment, a thin coating can be formed on the surface of the solder particles by gradually depositing the organic acid salt from the saturated solution of the organic acid salt on the surface of the solder particles. This precipitation process is preferably performed while stirring the solution so that the solder particles remain dispersed in the solution.

In this manner, a coating is applied to cover the individual particles constituting the solder powder. This thin film coating is an organic film with excellent thickness uniformity,
For example, the film thickness is 0.1 to 5 μm, further 0.1 to 2 μm
Even if it is thin, it can be formed as a film covering the entire surface of the solder particles.

As described above, the method described in the present embodiment is suitable for producing a solder powder whose surface is covered with a coating of an organic acid salt.

[0055]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples.

(Embodiment 1) In this embodiment, Sn-8Zn
As described in the second embodiment, a spherical solder powder having a diameter of 20 μm to 40 μm made of a -3Bi alloy is
A solder powder having copper stearate deposited on the surface was prepared by immersing the same in a supersaturated solution of copper stearate dissolved in ethanol. Using the solder powder subjected to the surface treatment in this manner or the solder powder not subjected to the surface treatment, the mixture was mixed with a predetermined flux shown below to prepare a solder paste.

[Sample 1] Flux: 10% by weight Rosin (pine resin) 50% by weight Hardened castor oil (thixotropic agent) 5% by weight Diphenylguanidine HBr (activator) 2% by weight α-Teleneol (solvent) 43% by weight %-Copper stearate treated solder powder: 90% by weight

[Sample 2] Flux: 10% by weight Rosin (pine resin) 48% by weight Hardened castor oil (thixotropic agent) 5% by weight Diphenylguanidine HBr (activator) 2% by weight α-Teleneol (solvent) 40% by weight % Nonionic surfactant (BC-40TX) 5% by weight ・ Untreated solder powder: 90% by weight

[Sample 3] Flux: 10% by weight Rosin (pine resin) 48% by weight Hardened castor oil (thixotropic agent) 5% by weight Diphenylguanidine HBr (activator) 2% by weight α-Teleneol (solvent) 40% by weight % Nonionic surfactant (BC-40TX) 5% by weight-Copper stearate treated solder powder: 90% by weight

[Sample 4] Flux: 10% by weight Rosin (pine resin) 50% by weight Hardened castor oil (thixotropic agent) 5% by weight Diphenylguanidine HBr (activator) 2% by weight α-Telenol (solvent) 43% by weight % ・ Untreated solder powder: 90% by weight

[Sample 5] Flux: 10% by weight Rosin (pine resin) 43% by weight Hardened castor oil (thixotropic agent) 5% by weight Diphenylguanidine HBr (activator) 2% by weight α-Teleneol (solvent) 35% by weight % Nonionic surfactant (BC-40TX) 15% by weight ・ Untreated solder powder: 90% by weight

A reliability test was performed using each of the above solder pastes. As the test board, a printed wiring board whose material was glass epoxy and whose solder land was copper plating was used. This printed wiring board has a thickness of 1
A solder paste was printed using a metal squeegee and a metal mask having a size of 80 μm and having openings formed in a predetermined pattern by etching. As an electronic component for surface mounting, a semiconductor device having 100 pins at a pitch of 0.65 mm and having Pd-plated leads was used. This semiconductor device was mounted on the land where the solder paste was printed, and using an atmospheric hot air reflow furnace,
The solder was melted and joined to the printed wiring board so that the maximum temperature of the soldered portion was 210 ° C.

The degree of oxidation of the solder powder was evaluated by the number of solder balls generated around one semiconductor lead after soldering. The smaller the number of solder balls, the more the oxidation of the solder powder is suppressed. In the evaluation, A, B, C, and D were evaluated in ascending order according to the number of solder balls per semiconductor lead.

The change over time of the solder paste was evaluated by a change in viscosity measured with a Malcolm viscometer after leaving the solder paste contained in a closed container in a thermostat at 25 ° C. As the change in viscosity is small and the standing period until reaching the predetermined viscosity is longer, the change over time of the solder paste is suppressed. The number of days until the viscosity increased by 100 Pa · s from the initial level was measured. Table 1 shows the above results.

(Table 1) ―――――――――――――――――――――――――――― Solder ball generation status Changes over time ――――――――― ――――――――――――――――――― Sample 1 B 7 days Sample 2 C 12 days Sample 3 A 15 days Sample 4 D 3 days Sample 5 D 15 days ―――――― ――――――――――――――――――――――

As shown in Table 1, in Sample 1, the occurrence of solder balls and the change over time of the solder paste were greater in Sample 1 than in Sample 4 using untreated solder powder because copper stearate was adhered to the solder powder. Are both suppressed. Also in Sample 2, the addition of an appropriate amount (5% by weight) of the nonionic surfactant to the flux resulted in a higher number of solder balls and a longer paste time than in Sample 4 to which no nonionic surfactant was added. Changes are both suppressed. Comparing Samples 1 and 2, the effect of the adhesion of copper stearate is great for suppressing the number of solder balls generated, and the effect of the nonionic surfactant is great for suppressing the change over time of the paste. The best result was obtained in Sample 3 using the solder powder to which the organic acid copper was adhered and the flux to which the nonionic surfactant was added.

On the other hand, in Sample 5, to which 15% by weight of the nonionic surfactant was added, the number of generated solder balls was rather increased. This is probably because the nonionic surfactant prevented the molten solder powder from spreading on the copper foil portion.

FIG. 3 shows the state of generation of solder balls.
(Sample 1), FIG. 4 (Sample 2), FIG. 5 (Sample 3) and FIG. 6 (Sample 4). Thus, in both samples, a large difference was observed in the number of solder balls generated around the semiconductor lead.

Embodiment 2 FIG. 7 shows an outline of a solder powder coating process according to this embodiment. Hereinafter, this step will be described.

First, while stirring 1000 ml (780 g) of kerosene with a magnetic stirrer at about 700 rpm, 7.8 g of zinc stearate was added thereto. The amount of zinc stearate charged exceeded the solubility limit of this compound for kerosene, and the solution turned cloudy. This solution was filtered through a filter paper having a mesh diameter of 8 μm to obtain a kerosene saturated solution of zinc stearate.

Next, while stirring this saturated solution with a magnetic stirrer in the same manner as described above, 78 g of Sn-8Z
An n-3Bi alloy solder powder was added. The average particle size of the solder powder was about 30 μm. When this solder powder was observed using a scanning electron microscope, the individual solder particles were substantially spherical.

Further, while continuing to stir the saturated solution in the same manner as above, ethanol was added dropwise little by little. When about 10 ml of ethanol was dropped, the liquid began to become cloudy.
After dropping a predetermined amount of ethanol, the cloudy solution was filtered again, and the residue on the filter paper was dried in an oven at 80 ° C. for 8 hours to obtain a solder powder covered with a thin film. The dropping rate of ethanol was about 2 ml / min, and the total dropping amount of ethanol was 1
Selected from the range of 0 ml to 100 ml.

Using a scanning electron microscope, the solder powder A obtained with the ethanol dripping amount of 100 ml and the solder powder B obtained with the same dripping amount of 10 ml were observed. The results are shown in FIGS. 8 and 9, respectively. It can be seen that the solder powder was coated almost uniformly and the spherical particle shape was maintained. In addition, FE-SEM (Field Emission Sca
The coating thickness of the solder powder A was about 2 μm and the solder powder B was
It was confirmed that the coating thickness of was about 1 μm.

The film thickness of the coating increases as the amount of ethanol dropped increases. It was also confirmed that the film thickness was increased as the stirring time (stirring time after dropping ethanol) was increased and the temperature was lowered. The solder powder shown in FIGS. 8 and 9 was obtained at room temperature (about 25 ° C.).
This was obtained with a stirring time of 10 minutes.

In order to confirm the material of the coating, an FT-IR (Four Four
The absorption spectrum was measured by ier-Transform Infra-Red Spectroscopy (Fourier transform infrared spectroscopy). FIG. 10 shows the spectrum before coating, and FIG. 11 shows the spectrum after coating. As shown in FIG.
In the coated solder powder, the absorption peak due to CH vibration of stearic acid, which is not observed in FIG.
It was observed around 0 cm ^-1 .

On the other hand, in the same manner as above, 78 g of the above solder powder was immersed in a supersaturated solution obtained by adding 7.8 g of zinc stearate to 1000 ml of kerosene. After standing for 0.5 hour, the solution was filtered and the residue was dried to obtain solder powder C. FIG. 12 shows the result of observing the solder powder C using a scanning electron microscope. As shown in FIG. 12, the coating formed on the solder powder C was non-uniform. On the one hand, solder particles with agglomerated precipitates were observed, and on the other hand, there were solder particles that were not completely coated. As described above, it was confirmed that uniform coating could not be obtained simply by immersing the solder powder in the solution.

A solder paste was prepared using the solder powders A to C obtained as described above and the solder powder D without coating. Table 2 shows combinations of the solder powder and the flux. Table 3 shows the composition of the used flux.

(Table 2) ―――――――――――――――――――――――――――――――― Solder powder Flux Solder / Flux Weight ratio ― ――――――――――――――――――――――――――――――― Solder paste A Solder powder A (coating thickness 2μm) Flux A 9: 1 Paste B Solder powder B (coating thickness: 1 μm) Flux A 9: 1 Sorter paste C Solder powder C (incomplete coating) Flux A 9: 1 Salter paste D Solder powder D (no coating) Flux B 9: 1 ――――――――――――――――――――――――――――――

(Table 3) (% by weight) ――――――――――――――――――――――――――――――― Component Flux A Flux B ――――――――――――――――――――――――――――――― Pine resin (polymerized rosin) 55 45 Solvent (ethylene glycol monophenyl ether) 40 35 Activator (diethylamine hydrochloride) 5 20 ―――――――――――――――――――――――――――――――

The content ratios of the activators in the fluxes A and B were determined so that when the solder powder A and the solder powder D were used, the viscosity would be substantially the same as long as screen printing was possible. As shown in Table 2, the amount of activator required was higher in flux B.

The pot lives of the solder pastes A to D were measured. Here, the pot life is a period in which the viscosity of the paste is maintained to such an extent that printing on the substrate is not difficult (about 400 Pa · s or less).
Here, when the pot life is left at room temperature, the viscosity of the solder paste is 200 Pa · s to 400 Pa · s.
Defined as the time required to increase to Table 4 shows the measurement results of the pot life.

(Table 4) ―――――――――――――――――― Sample Pot Life (day) ―――――――――――――――――― Paste A 10 Sorter paste B 5 Sorter paste C 2 Sorter paste D 1 ――――――――――――――――――

As shown in Table 4, the pot life was longer when the coating was uniform and thick. This is because the oxidation of Zn on the surface of the solder particles is suppressed, and the bonding between the particles is suppressed, thereby suppressing the increase in the viscosity of the paste.

Also, screen printing was attempted with a solder paste A to D using a metal mask (perforated stainless steel having a thickness of 150 to 200 μm by laser etching). Other than the solder paste C, there was no problem in passing through the mask.
Although the first printing was possible, the mask was clogged, and it was difficult to print continuously thereafter. This is because the coating was non-uniform, and the oxidation of the solder powder progressed, and the viscosity increased due to the adhesion of the solder particles.

Next, the solder pastes A, B and D were screen-printed on a circuit board, and reflow soldering was performed in the air. For each formed soldering part,
A sulfur dioxide test was performed. Sulfur dioxide test is 40 ℃
The test was performed by visually checking the presence or absence of whitening of the soldered portion after being left in air containing 10 ppm of sulfurous acid gas for 100 hours. As a result, no whitening was observed for the solder pastes A and B, but whitening was observed for the soldered portion with the solder paste D. This is because the solder pastes A and B using the coated solder powder could reduce the amount of the activator compared to the solder paste D.

As described above, by controlling the step of depositing the coating agent from the saturated solution while controlling it, the uniformity of the film thickness to the extent that each particle can maintain the original shape is added to the particles of the solder alloy containing Zn. It was confirmed that an excellent thin film could be coated. This thin-film coating completely covers the surface of the solder particles, but does not hinder the application to screen printing. Also, by using the solder powder having such a thin film coating formed thereon, it is also possible to reduce the amount of the activator in the solder paste, prevent the solder portion from whitening after soldering, improve the pot life, etc. Was realized.

[0087]

As described above, according to the present invention,
It is possible to provide a solder powder which contains Sn and Zn, has good solderability, and can effectively suppress the reaction between the active component and the alloy component in the flux. Also,
It is possible to provide a solder paste that contains Sn and Zn, has good solderability, and is also suppressed from changing over time. This solder paste can be applied to reflow soldering in the atmosphere. INDUSTRIAL APPLICABILITY The present invention is extremely useful in industry as providing lead-free solder powder and solder paste excellent in practicality.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of an apparatus used for manufacturing a solder powder of the present invention.

FIG. 2 is a photograph of an example of the solder powder of the present invention observed with a scanning electron microscope.

FIG. 3 is a photograph showing an example of a state near a semiconductor lead portion mounted using the solder paste of the present invention.

FIG. 4 is a photograph showing an example of a state near a semiconductor lead portion mounted using the solder paste of the present invention.

FIG. 5 is a photograph showing an example of a state near a semiconductor lead portion mounted using the solder paste of the present invention.

FIG. 6 is a diagram showing an example of a state near a semiconductor lead portion mounted using a conventional solder paste.

FIG. 7 is a diagram illustrating an example of steps of a method for producing a solder powder according to the present invention.

FIG. 8 is a photograph of an example of the solder powder of the present invention observed with a scanning electron microscope.

FIG. 9 is a photograph obtained by observing another example of the solder powder of the present invention with a scanning electron microscope.

FIG. 10 is an absorption spectrum obtained by measuring by FT-IR the solder alloy used for preparing the solder powder of the present invention.

FIG. 11 shows a solder powder prepared by coating a thin film on the solder alloy shown in FIG.
It is an absorption spectrum measured by T-IR.

FIG. 12 is a photograph obtained by observing a solder powder prepared in an example for comparison with a scanning electron microscope.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Solder powder 12 Spraying device 13 Supersaturated solution 14 Solder powder with solution 15 Hot air dryer 16 Solder powder with organic acid salt 17 Sieve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 3/34 512 H05K 3/34 512C (72) Inventor Hisahiko Yoshida 1006 Odakadoma, Kadoma, Osaka Matsushita Electric Inside Sangyo Co., Ltd. (72) Inventor Hiroshi Noguchi 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Takao Kusaku 1006 Oji Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Tamotsu Senna 3-45-4 Kamiishihara, Chofu-shi, Tokyo (72) Inventor Tetsuhiko Isobe 2-62-2 Hiyoshihoncho, Kohoku-ku, Yokohama-shi, Kanagawa F-term (reference) 4K018 BA20 BB10 BC29 5E319 BB05

Claims (21)

[Claims] Claims: 1. A solder powder constituting a solder paste together with a flux, comprising: Sn and Zn;
Solder powder characterized in that an organic acid salt is attached to the surface. 2. The solder powder according to claim 1, further comprising Bi. 3. The solder powder according to claim 1, wherein the organic acid salt is a fatty acid salt. 4. The solder powder according to claim 3, wherein the fatty acid salt is a salt of at least one fatty acid selected from lauric acid, myristic acid, palmitic acid and stearic acid. 5. An organic acid salt comprising a transition metal.
The solder powder according to any one of the above. 6. The organic acid salt is an organic acid copper.
The solder powder according to any one of the above. 7. The solder powder according to claim 6, wherein an organic acid copper is attached to 5% or more of the surface. 8. The solder powder according to claim 1, wherein the solder powder is coated with a thin film of an organic acid salt. 9. A thin film of an organic acid salt having a thickness of 0.1 μm to 10 μm
The solder powder according to claim 8, having a thickness of: 10. A solder paste comprising the solder powder according to claim 1 and a flux. 11. The solder paste according to claim 10, wherein the flux contains a nonionic surfactant. 12. The solder paste according to claim 11, wherein the nonionic surfactant is 0.5 to 10% by weight of the flux. 13. A solder paste containing a solder powder and a flux, wherein the solder powder is composed of Sn and Z.
n, wherein the flux comprises 0.5 to 10% by weight of a nonionic surfactant. 14. The solder paste according to claim 13, wherein an organic acid salt is attached to the surface of the solder powder. 15. The flux comprising an activator, wherein the activator is less than 10% by weight of the flux.
15. The solder paste according to any one of items 14 to 14. 16. A step of preparing a solution saturated with an organic acid salt, and a step of attaching the organic acid salt to the surface of the solder powder by contacting the solution with a solder powder containing Sn and Zn. A method for producing a solder powder, comprising: 17. The method according to claim 16, wherein the organic acid salt is attached to the surface of the solder powder by spraying a solution saturated with the organic acid salt onto the solder powder. 18. The method according to claim 17, wherein a solution saturated with an organic acid salt is sprayed on the falling solder powder, and the falling solder powder is heated to remove the solvent in the solution from the surface of the solder powder. The method for producing the solder powder described above. 19. The method according to claim 16, wherein the organic acid salt is attached to the surface of the solder powder by dispersing the solder powder in a solution saturated with the organic acid salt. 20. The method for producing a solder powder according to claim 19, wherein the organic acid salt is precipitated on the surface of the solder powder by reducing the solubility of the organic acid salt in a solution saturated with the organic acid salt. 21. The method according to claim 20, wherein the solubility of the organic acid salt in the solution saturated with the organic acid salt is reduced by dropping an alcohol.