JPH11245079A - Metal powder for solder paste and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable reflow soldering in the atmosphere and improve paste storage life by coating a surface of solder powder with a coating film which is in a solid condition at a normal temperature and is vanished at solder melting temperature when it is heated by a reflow soldering process. SOLUTION: A globular solder powder 2 constituting a metal powder 1 for the solder paste is composed of a Sn-Zn system material, and its surface is coated with a coating film 3, namely N-methylacetamido CH3 CONHCH3 (the melting point 31 deg.C, the boiling point 206 deg.C) at the thichkness of about 0.1 μm. The solder paste metal powder 1 is mixed with a proper solvent so as to manufacture a solder paste. Ethylene carbonate (CH2 O)2 CO, 2-acetylpyrrole C6 H7 NO, acetamido CH3 OONH2 and the like are used as the coating film 3. Sn-Ag system or Sn-Bi system materials(Sn-9Zn eutectic crystal, Sn-35Ag eutectic crystal, and Sn-58Bi eutectic crystal) can be used as the solder powder 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal powder for a solder paste used for reflow soldering an electronic component to a printed wiring board of an electronic device. In particular, SnP
b Sn is considered to be more reactive than eutectic solder
The present invention relates to a lead-free solder alloy powder such as Zn-based.

[0002]

2. Description of the Related Art A reflow soldering method is one of the methods for automatically soldering electronic components such as semiconductor elements, resistance elements and capacitance elements to a printed circuit board or the like. In this case, usually, Sn-Pb eutectic solder (about 37
A solder alloy having a melting point of 183 ° C., which is called “wt% Pb), is used.

In the reflow soldering, a solder paste is printed on an electrode pad portion such as a printed circuit board by a printing device, and electronic parts to be joined are mounted at predetermined positions by a mounter device.

[0004] The printed circuit board on which the electronic components are mounted is passed through a reflow device and heated according to a predetermined temperature profile to complete the batch soldering. FIG. 9 is a schematic diagram of a reflow soldering process, and FIG. 2 shows an example of a reflow temperature profile.

[0005] That is, as shown in FIG.
A pair of conveyor belts 22a and 22b provided in
The printed circuit board 24 on which the electronic components 23 are mounted is transported in the reflow furnace 20 and heated to perform soldering.

The solder paste used for reflow soldering is a mixture of solder fine powder having a diameter of several tens of μm and flux (rosin, activator, thixotropic agent, solvent, etc.)
Various pastes are used depending on the soldering application.

[0007] In recent years, resoldering pastes have been required to have increasingly higher performance and characteristics due to miniaturization of solder joints due to an increase in mounting density, improvement in soldering quality, environmental protection requirements, and the like. And various issues have arisen.

[0008]

One of those problems is the problem of no cleaning. This is an attempt to eliminate the cleaning step because the use of CFC as a cleaning agent has become impossible due to the so-called CFC regulations. However, there is a concern that no cleaning may affect the reliability of the flux residue.

Therefore, in order to reduce the influence of the flux residue on the reliability, measures such as suppressing the amount of the activator and reducing the amount of halogen that may remain on the substrate after soldering are taken. Has been taken. Also in this case, there is a problem that the solderability is deteriorated, and mounting defects such as unsoldering, solder balls, and poor wetting are likely to occur.

Further, the harmfulness of lead contained in solder alloys has recently been highlighted, and legal regulations on lead have been seriously studied mainly in Europe and the United States. For this reason, research and development of so-called lead-free solders that do not contain lead in the solders have been active.

At present, as a candidate for lead-free solder, Sn
-Ag-based and Sn-Zn-based solders have been mainly studied, but various problems have been pointed out as compared with SnPb eutectic solder.

That is, the Sn-Ag solder is Sn3.
Basically 5Ag eutectic alloy (melting point 221 ° C)
It is a solder to which one or several kinds of additional elements such as i, In, Cu, Sb, etc. are added.
The higher the temperature, the higher the thermal damage to mounted electronic components.

On the other hand, the Sn-Zn based solder has a low melting temperature (about 190 ° C.) and has the merit of realizing a reflow temperature comparable to the current SnPb eutectic solder.
Since a strong oxide film is formed on the surface of Zn, there is a disadvantage that the solderability is significantly deteriorated.

To remedy this drawback, a strong flux is required to remove the oxide film on the solder surface and prevent oxidation, but using such a flux requires a strong cleaning step. There are also problems and problems such as deterioration of paste preservability due to the reaction between strong flux and solder.

[0015]

According to the present invention, there is provided a semiconductor device comprising: a solder powder; and an organic film coated on a surface of the solder powder and vaporized at a temperature lower than a melting temperature of the solder powder. Metal powder for solder paste.

According to the present invention, there is provided the metal powder for solder paste, wherein the organic film is tin fluoride.

According to the present invention, there is provided the metal powder for a solder paste, wherein the organic film is tin bromide.

Further, according to the present invention, the solder powder comprises:
A metal powder for a solder paste, which is a Sn-Zn-based lead-free solder alloy powder.

According to the present invention, the solder powder comprises:
A metal powder for a solder paste, which is a Sn-Ag-based lead-free solder alloy powder. According to the present invention, there is provided a metal powder for a solder paste, wherein the solder powder is a Sn-Bi-based lead-free solder alloy powder.

According to the present invention, there is provided a method of manufacturing a metal powder for a solder paste, wherein the surface of the solder powder is coated with an organic film which is vaporized at a temperature lower than the melting temperature of the solder powder. Is a method for producing a metal powder for a solder paste, which is performed by a plasma apparatus.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view schematically illustrating a metal powder 1 for a solder paste according to an embodiment of the present invention.

That is, the spherical solder powder 2 constituting the solder paste metal powder 1 is made of a Sn—Zn-based material, and the surface thereof is a solid organic film 2 of N-methylacetamide CH ₃ CONHCH ₃ (melting point 31). ° C, boiling point 206
C.) with a thickness of about 0.1 μm.

The solder paste was manufactured by mixing the solder paste metal powder 1 with an appropriate solvent.

In this case, no other additives were added, but if necessary, various rosins, thixotropic materials, activators and the like used in conventional solder paste are added to adjust the paste properties. be able to.

In the soldering operation, the solder paste is printed on electrodes on a printed circuit board by a printing machine, and electronic components to be joined on the printed printed circuit board are mounted by a mounter device. Thereafter, the printed circuit board on which the electronic components are mounted is inserted into the atmospheric reflow device, and heated by a predetermined reflow profile to obtain high-quality bonding.

At this time, a solid organic film 3 of N-methylacetamide covering the surface of the solder powder 2 in a solid state
Since the solder reaches the boiling point (206 ° C.) before reaching the melting temperature, the solder vaporizes and disappears, so that the solder joining is not adversely affected.

That is, in the reflow step, the solid organic film 3 disappears immediately before reaching the solder melting temperature by being heated according to the temperature profile of FIG. It has the effect of exposing the surface. At the melting temperature, the solder powder 2 not covered with the oxide film is melted and completely fused to form a strong solder joint.

Since the solder paste is usually stored in a refrigerator or the like, the surface of the solder powder 2 of the present invention is covered with the solid organic film 3, so that the oxidation reaction on the surface of the metal powder is prevented. There is an effect that good solderability is maintained for a long time without progress.

Similarly, the reaction between the flux agent and the metal powder is suppressed, and the viscosity of the paste is kept constant for a long period of time, so that the paste preservability is improved. This has a remarkable effect in securing the stability of the printing operation.

In the above embodiment, the solid organic film 3
Is coated with N-methylacetamide (melting point: 30 ° C., boiling point: 206 ° C.) to a thickness of about 0.1 μm. As the solid organic film 3, the following substances can be used.

* Ethylene carbonate (CH ₂₀ ) ₂ CO (melting point 36.4 ° C., boiling point 238 ° C.) * 2-acetylpyrrole C ₆ H ₇ NO (melting point 90 ° C., boiling point 220 ° C.) * acetamide CH ₃ OONH ₂ ( Melting point 82 ° C, boiling point 2
21 ° C.) * m-acetotoluid C ₆ H ₄ (CH ₃ ) (NHCOC
H ₃ ) (melting point 66 ° C., boiling point 303 ° C.) * Indane C ₉ H ₁₀ (melting point 51.4 ° C., boiling point 179)
° C.) * N-ethyl--N'- phenylurea _C 2 _H 5 NHC0N
HC ₆ H ₅ (melting point 10 ° C., boiling point 170 ° C.) * Ethyl carbamate H ₂ NCO ₂ C ₂ H ₅ (melting point 48
° C., boiling point 184 ° C.) * 3,5-xylenol _{C 6 H 3 (CH 3)} 2 (0H)
(Melting point 68 ° C., boiling point 219.5 ° C.) * 4-Chlorofucuric anhydride C ₈ H ₃ ClO ₃ (melting point 9
8 ° C., boiling point 295 ° C.) * Phenyl salicylate C ₆ H ₄ (OH) (CO ₂ C ₆ H)
₅ ) (melting point 42 ° C, boiling point 173 ° C) * NN-diphenylformamide HCON (C
₆ H ₅ ) ₂ (melting point 74 ° C., boiling point 191 ° C.) * 0-Nitroaniline C ₆ H ₄ (NO ₂ ) (NH ₂ )
(Melting point 72 ° C., boiling point 16 ° C.) * m-hydroxybenzaldehyde C ₆ H ₄ (OH)
(CHO) (melting point 105 ° C., boiling point 161 ° C.) * Phenyl vinegar vinegar C ₆ H ₅ CH ₂ CO ₂ H (melting point 78 ° C.,
(Boiling point 227 ° C) * Lupinin C10HI ₉ NO (melting point 69 ° C, boiling point 164)
° C) * P-methylaminophenol C ₆ H ₄ (OH) (NH
CH ₃ ) (melting point 87 ° C., boiling point 173 ° C.) In the above-described embodiment, Sn powder is used as the solder powder 2.
-A Zn-based material was used, but a Sn-Ag-based or Sn-Bi-based material was used.
It is also possible to use a solder powder 2 of a system material. Examples of those substances are listed below.

(1) Sn-Zn based solder alloys have the following compositions.

* Sn-9Zn eutectic * Sn-8Zn-3Bi * Sn-8Zn-5In-1Ag * Sn-8Zn-5In-0.1Ag * Sn-9Zn-5In * Sn-5.5Zn-5In-1Bi * Sn-8Zn-2Bi-0.2Cu (2) The Sn-Ag solder alloy has the following composition.

* Sn-35Ag eutectic * Sn-3Ag * Sn-2.7Ag-3Bi * Sn-2.7Ag-5Bi * Sn-2.4Ag-7.5Bi * Sn-2Ag-75Bi-05Cu (alloy H ) * Sn-3.5Ag-0.7Cu * Sn-3.5Ag-1Zn * Sn-3.5Ag-3Bi-3ln * Sn-3.5Ag-0.5Bl-3ln (3) Sn-Bi solder alloy There is a thing of the following composition.

* Sn-58Bi eutectic * Sn-58Bi-1Ag * Sn-58Bi-2Ag * Sn-58Bi-3Ag * Sn-55Bi-2Ag Next, a method for producing solder powder 2 for a solder paste of the present invention will be described. This will be described below.

(Example 1) As a method for forming a tin fluoride film or a tin bromide film on the solder powder 2, various thin film forming methods such as a plasma treatment and an ion implantation method can be applied.

The manufacturing method using the plasma processing apparatus will be described below with reference to FIG.

FIG. 3 is a schematic view of a generally used plasma processing apparatus. The solder powder 2 to be processed is appropriately dispersed and placed on an electrode facing the counter electrode 7 in the plasma processing vessel 5, that is, on the sample stage 7. Thereafter, the inside of the plasma processing container 5 is evacuated, and CF4 gas is introduced. The introduction pressure is from 10 mmHg to 500 mmHg.

A high-frequency voltage is applied to the sample stage 7 by a high-frequency power source 8 connected to the sample stage 7 and CF4 is applied.
Generate gas plasma. By exposing the solder powder 2 to the gas plasma, a tin fluoride film can be formed on the surface of the solder powder 2. At that time, gas pressure,
By changing high-frequency power, processing time, and the like, a tin fluoride film having desired film properties and film thickness can be obtained.

In the above-described processing apparatus, a predetermined tin bromide film can be obtained by changing the introduced gas to a bromide gas.

As tin fluoride, SnF ₂ and SnF ₄ are mainly used.
Are formed on the surface of one or more types of solder powder 2. Both are colorless in the crystalline state, SnF2 has a melting point of 213 ° C,
The boiling point is 850 ° C. SnF ₄ sublimates at 705 ° C.
Also, SnF2 is heated in air, so that Sn0
It becomes F _2.

Therefore, at a reflow temperature of about 200 ° C., a considerably large vapor pressure is exhibited. For example, peak temperature 24
In the reflow profile at O ° C., most of these tin fluoride films are evaporated by heating.

However, as expected from the above characteristics, SnF ₄ tends to vaporize more easily than SnF ₂ . Therefore, it is also possible to control the physical properties of the soot fluoride coating on the solder surface by adjusting the compounding ratio of the two in accordance with the reflow conditions desired to be used.

Tin bromide is mainly composed of SnBr ₂ and SnB.
At least one kind of r ₄ is formed on the surface of the solder powder 2.

SnBr ₂ has a melting point of 215.5 ° C. and a boiling point of 6I.
8 ° C. SnBr ₄ has a melting point of 31 ° C. and a boiling point of 203 ° C. Therefore, it shows a considerably large vapor pressure at a reflow temperature around 200 ° C. For example, SnBF ₄ is 15
Even at 3 ° C., the vapor pressure reaches 200 mmHg.

As an example, in a reflow profile having a peak temperature of 230 ° C., these tin bromide films are mostly vaporized and evaporated by heating. However, as expected from the above characteristics, SnBr ₄ tends to vaporize more easily than SnBr ₂ . It is also possible to control the physical properties of the tin bromide coating on the solder surface by adjusting the mixing ratio of the two in accordance with the reflow conditions desired to be used.

Embodiment 2 FIG. 4 is a schematic view of a high-frequency sputtering apparatus for processing the solder paste powder 1. The processing chamber 10 includes a lower electrode 11 and an upper electrode 12.
Are provided facing each other. The lower electrode 11 is an anode electrode, and the upper electrode 12 has an N-
A target 13 made of methylacetamide is provided, and a high-frequency power source 14 is connected to form a cathode electrode. A dish 15 is formed on the surface of the lower electrode 11, and the solder powder 2 to be processed is appropriately dispersed and placed in the dish 15.

After evacuating the processing container 10, an inert gas such as Ar is introduced from the gas inlet 16 to a predetermined pressure. In this embodiment, the gas pressure is 10 mmTorr.
r. Thereafter, a voltage is applied to the target 13 by the high-frequency power supply 14 to generate plasma, and N-methylacetamide is attached to the solder powder 2 by sputtering of Ar ions. At this time, the vibration device 1 is attached to the lower electrode 11.
7 was connected so that an N-methylacetamide film was uniformly formed on the surface of the solder powder 2. By such a method, an N-methylacetamide film having a thickness of 0.1 μm was uniformly formed on the surface of the solder powder 2.

The Sn—Zn paste has a problem that paste storage stability is short.
This has the effect of improving the paste preservability of the n-Zn based paste.

That is, FIG. 5 shows that the paste using the Sn—Zn-based solder powder 2 of the present invention is stored in a refrigerator,
The results of measuring the viscosity of the solder paste at room temperature for 6 months are shown together with the results of the conventional Sn-Zn solder paste. Note that a spiral viscometer (PCU-2) manufactured by Malcolm Co., Ltd. was used as a measuring device.

As shown in FIG. 5, the viscosity of the conventional Sn-Zn based paste increases within about one month, making printing impossible. On the other hand, the Sn-Zn based solder powder 2 of the present invention is used. The paste used had a substantially constant viscosity even after 6 months, indicating that sufficient printing was possible.

Although the conventional Sn-Ag paste has a problem that solder balls are easily generated, the present invention has an effect of suppressing the generation of solder balls of Sn-Ag paste.

That is, FIG. 6 shows the Sn—Ag of the present invention.
The solder ball generation state of the paste using the solder powder 2 was evaluated based on the degree of cohesion of the solder according to JIS-Z3284.
The results are also shown together with the results of the paste using. The evaluation experiment was performed in the following procedure.

First, a solder paste was printed in a disk shape on an alumina substrate, and a sample subjected to the following heating reflow within one hour after printing was left at room temperature for a predetermined time after printing. An implemented sample was created. The room temperature standing time after printing was 24, 48, 72, and 96 hours.

The heating reflow of the alumina substrate was performed by placing the alumina substrate on a hot plate set at a temperature 50 ° C. higher than the liquidus temperature of the solder alloy for a predetermined time. The alumina substrate removed from the hot plate was observed with a microscope, and the degree of solder aggregation was evaluated according to the criteria shown in FIG.

As shown in FIG. 6, the conventional Sn-Ag
The paste using the system-based solder powder 2 began to deteriorate in the degree of solder cohesion after being left at room temperature for 48 hours, and the cohesion degree became 3 after 72 hours or more.
It can be seen that the paste using Ag-based solder powder 2 has a good cohesion degree of 1 even after being left for 96 hours at room temperature, and generates little solder balls.

In the conventional Sn-Bi-based paste, there is a problem that solder balls are easily generated. However, the present invention has an effect of suppressing the generation of Sn-Bi-based paste solder balls. . FIG. 8 shows the Sn− of the present invention.
The results of the evaluation of the state of generation of solder balls in the paste using the Bi-based solder powder 2 by the same test method as described above are shown together with the results of the conventional Sn-Bi-based solder paste.

As shown in FIG. 8, the paste using the conventional Sn-Bi solder powder 2 starts to deteriorate in the degree of cohesion of the solder after being left at room temperature for 24 hours, and the degree of cohesion becomes 4 after 72 hours. On the other hand, in the paste using the Sn-Bi-based solder powder 2 of the present invention, even after standing at room temperature for 96 hours, the degree of aggregation is as good as 1 and the generation of solder balls is small.

[0060]

As described above, according to the present invention, the surface of the solder powder constituting the metal powder for the solder paste is in a solid state at room temperature, and disappears at the solder melting temperature when heated by the reflow soldering process. S, which was conventionally considered difficult in the air because it was covered with a solid organic film
Reflow soldering in the atmosphere has become possible even with n-Zn-based solder and the like.

Further, since the surface of the solder paste powder does not react with the flux, the paste storability over a long period of time is improved.

In addition, due to the improvement in solderability, the occurrence of joint defects such as solder balls, bridges, and unsoldered, which have often occurred during conventional soldering, has been reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a metal powder 1 for a solder paste according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of a heating temperature profile in a reflow step.

FIG. 3 is a schematic diagram of a plasma processing apparatus.

FIG. 4 is a schematic view of a high-frequency sputtering apparatus for processing solder paste powder 1;

FIG. 5 shows a result of measuring the viscosity of a solder paste at room temperature over a period of 6 months by storing a paste using the Sn—Zn-based solder powder 2 of the present invention in a refrigerator, and comparing the paste with that of the conventional Sn—Zn solder paste. Graph comparing the results.

FIG. 6 shows the solder ball generation status of a paste using the Sn—Ag solder powder 2 of the present invention according to JIS-Z328.
4 is a graph comparing the accumulation evaluated by the degree of agglomeration of the solder according to No. 4 with the result of the paste using the conventional Sn-Ag solder powder 2.

FIG. 7 is a table showing criteria for evaluating the degree of solder aggregation.

FIG. 8 compares the results of evaluation of the state of generation of solder balls in a paste using the Sn—Bi-based solder powder 2 of the present invention with the same test method as above, and the results of a conventional Sn—Bi-based solder paste. Graph.

FIG. 9 is a schematic diagram of a reflow furnace.

[Explanation of symbols]

1: powder for solder paste, 2: solder powder, 3: solid organic film,

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 17, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

Patent application title: Metal powder for solder paste and method for producing the same

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal powder for a solder paste used for reflow soldering an electronic component to a printed wiring board of an electronic device. In particular, SnP
b Sn is considered to be more reactive than eutectic solder
The present invention relates to a lead-free solder alloy powder such as Zn-based.

[0002]

2. Description of the Related Art A reflow soldering method is one of the methods for automatically soldering electronic components such as semiconductor elements, resistance elements and capacitance elements to a printed circuit board or the like. In this case, usually, Sn-Pb eutectic solder (about 37
A solder alloy having a melting point of 183 ° C., which is called “wt% Pb), is used.

In the reflow soldering, a solder paste is printed on an electrode pad portion such as a printed circuit board by a printing device, and electronic parts to be joined are mounted at predetermined positions by a mounter device.

[0004] The printed circuit board on which the electronic components are mounted is passed through a reflow device and heated according to a predetermined temperature profile to complete the batch soldering. FIG. 9 is a schematic diagram of a reflow soldering process, and FIG. 2 shows an example of a reflow temperature profile.

[0005] That is, as shown in FIG.
A pair of conveyor belts 22a and 22b provided in
The printed circuit board 24 on which the electronic components 23 are mounted is transported in the reflow furnace 20 and heated to perform soldering.

The solder paste used for reflow soldering is a mixture of solder fine powder having a diameter of several tens of μm and flux (rosin, activator, thixotropic agent, solvent, etc.)
Various pastes are used depending on the soldering application.

[0007] In recent years, resoldering pastes have been required to have increasingly higher performance and characteristics due to miniaturization of solder joints due to an increase in mounting density, improvement in soldering quality, environmental protection requirements, and the like. And various issues have arisen.

[0008]

One of those problems is the problem of no cleaning. This is an attempt to eliminate the cleaning step because the use of CFC as a cleaning agent has become impossible due to the so-called CFC regulations. However, there is a concern that no cleaning may affect the reliability of the flux residue.

Therefore, in order to reduce the influence of the flux residue on the reliability, measures such as suppressing the amount of the activator and reducing the amount of halogen that may remain on the substrate after soldering are taken. Has been taken. Also in this case, there is a problem that the solderability is deteriorated, and mounting defects such as unsoldering, solder balls, and poor wetting are likely to occur.

Further, the harmfulness of lead contained in solder alloys has recently been highlighted, and legal regulations on lead have been seriously studied mainly in Europe and the United States. For this reason, research and development of so-called lead-free solders that do not contain lead in the solders have been active.

At present, as a candidate for lead-free solder, Sn
-Ag-based and Sn-Zn-based solders have been mainly studied, but various problems have been pointed out as compared with SnPb eutectic solder.

That is, the Sn-Ag solder is Sn3.
Basically 5Ag eutectic alloy (melting point 221 ° C)
It is a solder to which one or several kinds of additional elements such as i, In, Cu, Sb, etc. are added.
The higher the temperature, the higher the thermal damage to mounted electronic components.

On the other hand, the Sn-Zn based solder has a low melting temperature (about 190 ° C.) and has the merit of realizing a reflow temperature comparable to the current SnPb eutectic solder.
Since a strong oxide film is formed on the surface of Zn, there is a disadvantage that the solderability is significantly deteriorated.

To remedy this drawback, a strong flux is required to remove the oxide film on the solder surface and prevent oxidation, but using such a flux requires a strong cleaning step. There are also problems and problems such as deterioration of paste preservability due to the reaction between strong flux and solder.

[0015]

According to the present invention, there are provided a solder powder and a coating film coated on the surface of the solder powder and vaporized at a temperature lower than the melting temperature of the solder powder. Metal powder for solder paste.

According to the present invention, there is provided the metal powder for a solder paste, wherein the coating film is tin fluoride.

Further, according to the present invention, there is provided the metal powder for a solder paste, wherein the coating film is tin bromide.

Further, according to the present invention, the solder powder comprises:
A metal powder for a solder paste, which is a Sn-Zn-based lead-free solder alloy powder.

According to the present invention, the solder powder comprises:
A metal powder for a solder paste, which is a Sn-Ag-based lead-free solder alloy powder. According to the present invention, there is provided a metal powder for a solder paste, wherein the solder powder is a Sn-Bi-based lead-free solder alloy powder.

[0020] According to the present invention, the surface of the solder powder, in the manufacturing method of the solder paste metal powder prepared by coating the coating film to be vaporized at a temperature lower than the melting temperature of the solder powder, the coating film Is a method for producing a metal powder for a solder paste, which is performed by a plasma apparatus.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view schematically illustrating a metal powder 1 for a solder paste according to an embodiment of the present invention.

That is, the spherical solder powder 2 constituting the solder paste metal powder 1 is made of a Sn—Zn-based material, and the surface thereof is coated with N-methylacetamide CH ₃ CNHCH ₃ (melting point: 31 ° C.) , Boiling point 206 ° C)
Are coated with a thickness of about 0.1 μm.

The solder paste was manufactured by mixing the solder paste metal powder 1 with an appropriate solvent.

In this case, no other additives were added, but if necessary, various rosins, thixotropic materials, activators and the like used in conventional solder paste are added to adjust the paste properties. be able to.

In the soldering operation, the solder paste is printed on electrodes on a printed circuit board by a printing machine, and electronic components to be joined on the printed printed circuit board are mounted by a mounter device. Thereafter, the printed circuit board on which the electronic components are mounted is inserted into the atmospheric reflow device, and heated by a predetermined reflow profile to obtain high-quality bonding.

At this time, the coating film 3 of N-methylacetamide, which coats the surface of the solder powder 2 in a solid state, reaches the boiling point (206 ° C.) before the solder reaches the melting temperature, and is thus vaporized and disappears. Therefore, there is no adverse effect on the solder joint.

That is, in the reflow process, the solid coating film 3 disappears immediately before reaching the solder melting temperature by being heated according to the temperature profile of FIG. Has the effect of exposing. At the melting temperature, the solder powder 2 not covered with the oxide film is melted and completely fused to form a strong solder joint.

Since the solder paste is usually stored in a refrigerator or the like, the oxidation reaction on the surface of the metal powder proceeds because the surface of the solder powder 2 of the present invention is covered with the solid coating film 3. The effect is that good solderability is maintained for a long period of time.

Similarly, the reaction between the fluxing agent in the solder paste and the metal powder is suppressed, and the paste has a constant viscosity for a long period of time and has an effect of improving the paste preservability. This has a remarkable effect in securing the stability of the printing operation.

In the above embodiment, the coating film 3 is made of N-methylacetamide (melting point: 30 ° C., boiling point: 20 ° C.).
6 [deg.] C.) with a thickness of about 0.1 [mu] m. As the coating film 3, the following substances can be used.

* Ethylene carbonate (CH ₂₀ ) ₂ CO (melting point 36.4 ° C., boiling point 238 ° C.) * 2-acetylpyrrole C ₆ H ₇ NO (melting point 90 ° C., boiling point 220 ° C.) * acetamide CH ₃ OONH ₂ ( Melting point 82 ° C, boiling point 2
21 ° C.) * m-acetotoluid C ₆ H ₄ (CH ₃ ) (NHCOC
H ₃ ) (melting point 66 ° C., boiling point 303 ° C.) * Indane C ₉ H ₁₀ (melting point 51.4 ° C., boiling point 179)
° C.) * N-ethyl--N'- phenylurea _C 2 _H 5 NHC0N
HC ₆ H ₅ (melting point 10 ° C., boiling point 170 ° C.) * Ethyl carbamate H ₂ NCO ₂ C ₂ H ₅ (melting point 48
° C., boiling point 184 ° C.) * 3,5-xylenol _{C 6 H 3 (CH 3)} 2 (0H)
(Melting point 68 ° C., boiling point 219.5 ° C.) * 4-Chlorofucuric anhydride C ₈ H ₃ ClO ₃ (melting point 9
8 ° C., boiling point 295 ° C.) * Phenyl salicylate C ₆ H ₄ (OH) (CO ₂ C ₆ H)
₅ ) (melting point 42 ° C, boiling point 173 ° C) * NN-diphenylformamide HCON (C
₆ H ₅ ) ₂ (melting point 74 ° C., boiling point 191 ° C.) * 0-Nitroaniline C ₆ H ₄ (NO ₂ ) (NH ₂ )
(Melting point 72 ° C., boiling point 16 ° C.) * m-hydroxybenzaldehyde C ₆ H ₄ (OH)
(CHO) (melting point 105 ° C., boiling point 161 ° C.) * Phenyl vinegar vinegar C ₆ H ₅ CH ₂ CO ₂ H (melting point 78 ° C.,
(Boiling point 227 ° C) * Lupinin C10HI ₉ NO (melting point 69 ° C, boiling point 164)
° C) * P-methylaminophenol C ₆ H ₄ (OH) (NH
CH ₃ ) (melting point 87 ° C., boiling point 173 ° C.) In the above-described embodiment, Sn powder is used as the solder powder 2.
-A Zn-based material was used, but a Sn-Ag-based or Sn-Bi-based material was used.
It is also possible to use a solder powder 2 of a system material. Examples of those substances are listed below.

(1) Sn-Zn based solder alloys have the following compositions.

* Sn-9Zn eutectic * Sn-8Zn-3Bi * Sn-8Zn-5In-1Ag * Sn-8Zn-5In-0.1Ag * Sn-9Zn-5In * Sn-5.5Zn-5In-1Bi * Sn-8Zn-2Bi-0.2Cu (2) The Sn-Ag solder alloy has the following composition.

* Sn-35Ag eutectic * Sn-3Ag * Sn-2.7Ag-3Bi * Sn-2.7Ag-5Bi * Sn-2.4Ag-7.5Bi * Sn-2Ag-75Bi-05Cu (alloy H ) * Sn-3.5Ag-0.7Cu * Sn-3.5Ag-1Zn * Sn-3.5Ag-3Bi-3ln * Sn-3.5Ag-0.5Bl-3ln (3) Sn-Bi solder alloy There is a thing of the following composition.

* Sn-58Bi eutectic * Sn-58Bi-1Ag * Sn-58Bi-2Ag * Sn-58Bi-3Ag * Sn-55Bi-2Ag Next, a method for producing solder powder 2 for a solder paste of the present invention will be described. This will be described below.

[0037]

Embodiment 1 As a method for forming a tin fluoride film or a tin bromide film on the solder powder 2, various thin film forming methods such as a plasma treatment and an ion implantation method can be applied.

The manufacturing method using the plasma processing apparatus will be described below with reference to FIG.

FIG. 3 is a schematic view of a generally used plasma processing apparatus. The solder powder 2 to be processed is appropriately dispersed and placed on an electrode facing the counter electrode 7 in the plasma processing vessel 5, that is, on the sample stage 7. Thereafter, the inside of the plasma processing container 5 is evacuated, and CF4 gas is introduced. The introduction pressure is from 10 mmHg to 500 mmHg.

A high-frequency voltage is applied to the sample stage 7 by a high-frequency power source 8 connected to the sample stage 7 and CF4 is applied.
Generate gas plasma. By exposing the solder powder 2 to the gas plasma, a tin fluoride film can be formed on the surface of the solder powder 2. At that time, gas pressure,
By changing high-frequency power, processing time, and the like, a tin fluoride film having desired film properties and film thickness can be obtained.

In the above-described processing apparatus, a predetermined tin bromide film can be obtained by changing the introduced gas to a bromide gas.

As tin fluoride, SnF ₂ and SnF ₄ are mainly used.
Are formed on the surface of one or more types of solder powder 2. Both are colorless in the crystalline state, SnF2 melting point 213 ° C.,
The boiling point is 850 ° C. SnF ₄ sublimates at 705 ° C.
Also, SnF2 is heated in air, so that Sn0
It becomes F _2.

Therefore, at a reflow temperature of about 200 ° C., a considerably large vapor pressure is exhibited. For example, peak temperature 24
In the reflow profile at O ° C., most of these tin fluoride films are evaporated by heating.

However, as expected from the above characteristics, SnF ₄ tends to vaporize more easily than SnF ₂ . Therefore, it is also possible to control the physical properties of the soot fluoride coating on the solder surface by adjusting the compounding ratio of the two in accordance with the reflow conditions desired to be used.

Tin bromide is mainly composed of SnBr ₂ and SnB.
At least one kind of r ₄ is formed on the surface of the solder powder 2.

SnBr ₂ has a melting point of 215.5 ° C. and a boiling point of 6I.
8 ° C. SnBr ₄ has a melting point of 31 ° C. and a boiling point of 203 ° C. Therefore, it shows a considerably large vapor pressure at a reflow temperature around 200 ° C. For example, SnBF ₄ is 15
Even at 3 ° C., the vapor pressure reaches 200 mmHg.

As an example, in a reflow profile having a peak temperature of 230 ° C., these tin bromide films are mostly vaporized and evaporated by heating. However, as expected from the above characteristics, SnBr ₄ tends to vaporize more easily than SnBr ₂ . It is also possible to control the physical properties of the tin bromide coating on the solder surface by adjusting the mixing ratio of the two in accordance with the reflow conditions desired to be used.

[0048]

Embodiment 2 FIG. 4 is a schematic view of a high-frequency sputtering apparatus for processing a solder paste powder 1. Processing container 1
In 0, a lower electrode 11 and an upper electrode 12 are provided to face each other. The lower electrode 11 is an anode electrode, the upper electrode 12 is provided with a target 13 made of N-methylacetamide on the surface facing the lower electrode 11, and a high frequency power supply 14 is connected to form a cathode electrode. I have. A dish 15 is formed on the surface of the lower electrode 11, and the dish 15
The solder powder 2 to be processed is appropriately dispersed and placed in the inside.

After evacuating the processing container 10, an inert gas such as Ar is introduced from the gas inlet 16 to a predetermined pressure. In this embodiment, the gas pressure is 10 mmTorr.
r. Thereafter, a voltage is applied to the target 13 by the high-frequency power supply 14 to generate plasma, and N-methylacetamide is attached to the solder powder 2 by sputtering of Ar ions. At this time, the vibration device 1 is attached to the lower electrode 11.
7 was connected so that an N-methylacetamide film was uniformly formed on the surface of the solder powder 2. By such a method, an N-methylacetamide film having a thickness of 0.1 μm was uniformly formed on the surface of the solder powder 2.

The Sn—Zn paste has a problem that paste storage stability is short.
This has the effect of improving the paste preservability of the n-Zn based paste.

That is, FIG. 5 shows that the paste using the Sn—Zn-based solder powder 2 of the present invention is stored in a refrigerator,
The results of measuring the viscosity of the solder paste at room temperature for 6 months are shown together with the results of the conventional Sn-Zn solder paste. Note that a spiral viscometer (PCU-2) manufactured by Malcolm Co., Ltd. was used as a measuring device.

As shown in FIG. 5, the viscosity of the conventional Sn-Zn based paste increases within about one month, making printing impossible. On the other hand, the Sn-Zn based solder powder 2 of the present invention is used. The paste used suppresses the reaction between the fluxing agent and the metal powder.
By controlling the viscosity, the viscosity is almost constant even after 6 months, and it can be seen that printing can be sufficiently performed.

Although the conventional Sn-Ag paste has a problem that solder balls are easily generated, the present invention has an effect of suppressing the generation of solder balls of Sn-Ag paste.

That is, FIG. 6 shows the Sn—Ag of the present invention.
The solder ball generation state of the paste using the solder powder 2 was evaluated based on the degree of cohesion of the solder according to JIS-Z3284.
The results are also shown together with the results of the paste using. The evaluation experiment was performed in the following procedure.

First, a solder paste was printed in a disk shape on an alumina substrate, and a sample subjected to the following heating reflow within one hour after printing was left at room temperature for a predetermined time after printing. An implemented sample was created. The room temperature standing time after printing was 24, 48, 72, and 96 hours.

The heating reflow of the alumina substrate was performed by placing the alumina substrate on a hot plate set at a temperature 50 ° C. higher than the liquidus temperature of the solder alloy for a predetermined time. The alumina substrate removed from the hot plate was observed with a microscope, and the degree of solder aggregation was evaluated according to the criteria shown in FIG.

As shown in FIG. 6, the conventional Sn-Ag
The paste using the system-based solder powder 2 began to deteriorate in the degree of solder cohesion after being left at room temperature for 48 hours, and the cohesion degree became 3 after 72 hours or more.
It can be seen that the paste using Ag-based solder powder 2 has a good cohesion degree of 1 even after being left for 96 hours at room temperature, and generates little solder balls.

In the conventional Sn-Bi-based paste, there is a problem that solder balls are easily generated. However, the present invention has an effect of suppressing the generation of Sn-Bi-based paste solder balls. . FIG. 8 shows the Sn− of the present invention.
The results of the evaluation of the state of generation of solder balls in the paste using the Bi-based solder powder 2 by the same test method as described above are shown together with the results of the conventional Sn-Bi-based solder paste.

As shown in FIG. 8, the paste using the conventional Sn-Bi solder powder 2 starts to deteriorate in the degree of cohesion of the solder after being left at room temperature for 24 hours, and the degree of cohesion becomes 4 after 72 hours. On the other hand, in the paste using the Sn-Bi-based solder powder 2 of the present invention, even after standing at room temperature for 96 hours, the degree of aggregation is as good as 1 and the generation of solder balls is small.

[0060]

As described above, according to the present invention, the surface of the solder powder constituting the metal powder for the solder paste is in a solid state at normal temperature and disappears at the solder melting temperature when heated by the reflow soldering process. Having coated with a coating film, in the related art, it has been difficult in the air Sn-
Reflow soldering has become possible in the atmosphere even with Zn-based solder and the like.

Further, since the surface of the solder paste powder does not react with the flux, the paste storability over a long period of time is improved.

In addition, due to the improvement in solderability, the occurrence of joint defects such as solder balls, bridges, and unsoldered, which have often occurred during conventional soldering, has been reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a metal powder 1 for a solder paste according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of a heating temperature profile in a reflow step.

FIG. 3 is a schematic diagram of a plasma processing apparatus.

FIG. 4 is a schematic view of a high-frequency sputtering apparatus for processing solder paste powder 1;

FIG. 5 shows a result of measuring the viscosity of a solder paste at room temperature over a period of 6 months by storing a paste using the Sn—Zn-based solder powder 2 of the present invention in a refrigerator, and comparing the paste with that of the conventional Sn—Zn solder paste. Graph comparing the results.

FIG. 6 shows the solder ball generation status of a paste using the Sn—Ag solder powder 2 of the present invention according to JIS-Z328.
4 is a graph comparing the accumulation evaluated by the degree of agglomeration of the solder according to No. 4 with the result of the paste using the conventional Sn-Ag solder powder 2.

FIG. 7 is a table showing criteria for evaluating the degree of solder aggregation.

FIG. 8 compares the results of evaluation of the state of generation of solder balls in a paste using the Sn—Bi-based solder powder 2 of the present invention with the same test method as above, and the results of a conventional Sn—Bi-based solder paste. Graph.

FIG. 9 is a schematic diagram of a reflow furnace.

[Description of Signs] 1 ... Solder paste powder, 2 ... Solder powder, 3 ... Coating film, ──────────────────────── ─────────────────────────────

[Procedure amendment]

[Submission date] October 15, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H05K 3/34 505 H05K 3/34 505B 512 512C

Claims (7)

[Claims] 1. A metal powder for a solder paste, comprising: a solder powder; and an organic film coated on a surface of the solder powder and vaporized at a temperature lower than a melting temperature of the solder powder. 2. The metal powder for a solder paste according to claim 1, wherein the organic film is tin fluoride. 3. The metal powder for a solder paste according to claim 1, wherein the organic film is tin bromide. 4. The metal powder for a solder paste according to claim 1, wherein the solder powder is a Sn—Zn-based lead-free solder alloy powder. 5. The metal powder for a solder paste according to claim 1, wherein the solder powder is a Sn-Ag-based lead-free solder alloy powder. 6. The metal powder for a solder paste according to claim 1, wherein the solder powder is a Sn-Bi-based lead-free solder alloy powder. 7. A method for producing a metal powder for a solder paste, wherein a surface of the solder powder is coated with an organic film that evaporates at a temperature lower than a melting temperature of the solder powder.
The method for producing a metal powder for a solder paste, wherein the coating of the organic film is performed by a plasma device.