JPH11347784A - Soldering paste and electronic circuit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure reliability of a connecting part and workability in soldering by not greatly changing a conventional production condition, while avoiding to use a metal of lead etc., adversely affecting an environment. SOLUTION: A soldering paste 10 is constituted so that a solder material is mixed to a flux 3, such solder is constituted so that a first powdery body 1 pulverizing a first alloy (e.g. Sn-Ag group alloy) and a second powdery body 2 pulverizing a second alloy (e.g. Sn-Bi group alloy) having a melting point different from the first alloy are blended.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder paste obtained by mixing a solder material with a flux and an electronic circuit device using the same.

[0002]

2. Description of the Related Art As a bonding material used for connecting electronic parts and the like, there is a material called a solder paste (cream solder). This solder paste is obtained by mixing a powder of molten solder into a flux composed of pine tar, an activator, a thickener, a thixotropic agent, and the like, and adding and kneading the paste to form a paste. .

Conventionally, such solder pastes include Su-Pb
, Su-Pb-Bi and Su-Pb-Ag alloys are used as molten solder. When electronic components are connected with such a solder paste, such an alloy is relatively flexible and absorbs thermal strain generated at the connection parts of the electronic components, so that the reliability of the connection parts can be ensured. it can.

However, as described above, the conventional solder paste contains lead (Pb). If electronic components joined with this lead-containing solder are discarded and exposed to acid rain, the lead contained in the solder may elute and pollute the surrounding environment depending on the conditions. was there.

On the other hand, a so-called lead-free solder using no lead has been developed. As this lead-free solder,
Sn-Ag solder containing tin (Sn) and silver (Ag),
There is Sn-Bi based solder containing tin (Sn) and bismuth (Bi).

FIG. 6 is a binary phase diagram of these solders. FIG. 2A shows the state of the solder in the Sn-Bi solder based on the Bi content and the temperature. In the figure, Sn is in a solid state in a range (A), and is in a semi-molten state in a range (B). In the range (c), both Sn and Bi are in a solid state, and in the range (e), both are in a liquid state.
In (d), Bi is in a semi-molten state.

As shown in FIG. 6A, in the range (a) where the Bi content is very small and Sn is close to 100% by weight, the melting point of the solder is 232.0 ° C., but the Bi content increases. The melting point decreases. On the other hand, when the Bi content is 100
When the weight is close to 27% by weight, the melting point of the solder is 271.4 ° C.
The melting point decreases as the content of i decreases. The temperature E at which the minimum temperatures of the melting points of these two solders coincide is called the eutectic temperature.

At the eutectic point E, when the temperature is raised, the state can be changed from a solid to a liquid without being in a semi-molten state, and the workability is improved. In such Sn-Bi solder, the eutectic point E occurs when the Bi content is around 57% by weight, and the temperature is 138.5 ° C.

FIG. 6B shows a binary state of the Sn-Ag based solder. In the figure, in the range (f), S
n is in a semi-molten state, and both Sn and Ag are solid in the range (h). In the range (g), both Sn and Ag are in a liquid state, and in the range (g), Ag is in a semi-molten state. Also in this figure, a eutectic point E occurs, and at this eutectic point E, the state changes from a solid to a liquid without being in a semi-molten state. In such Sn-Ag solder, the Ag content is 3.5% by weight.
The eutectic point E occurs before and after, and its temperature becomes 221 ° C.

[0010]

However, the above-mentioned Sn-Bi solder has a low melting point of 138.5 ° C., and therefore can be operated at a temperature safe for electronic components. There is a problem of chipping.

On the other hand, in the above-mentioned lead-free solder, Sn-A
As described above, since the melting point of g solder is as high as 221 ° C., the working temperature is 240 to 250 ° C., and there is a risk of heat damage to electronic components. In addition, this Sn-Ag-based solder is
Although the mechanical strength is superior to the n-Pb eutectic solder, there is a problem that the wetting property is inferior to the Sn-Pb eutectic solder.

Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to remove metals such as lead which may adversely affect the environment without greatly changing conventional production conditions. The reliability of the connection,
An object of the present invention is to provide a solder paste capable of securing workability in a soldering operation and an electronic circuit device using the same.

[0013]

According to a first aspect of the present invention, there is provided a solder paste obtained by mixing a solder material with a flux, wherein the solder material comprises a first alloy. And a second powdery material obtained by powdering a second alloy having a melting point different from the melting point of the first alloy. The first alloy contains tin (Sn) and silver (Ag), and the second alloy contains tin (Sn) and bismuth (Bi).

[0014] The invention according to claim 2 of the present application is the solder paste according to claim 1, wherein the amount of silver contained in the first alloy is 0.1 to 5.0% by weight, and The amount of bismuth contained is 42 to 58% by weight, the first powder is 70 to 80% by weight based on the solder material, and the second powder is based on the solder material. 2
0 to 30% by weight.

The invention according to claim 3 of the present application is the solder paste according to claim 2, wherein the first alloy is 0.1%
It contains either -2.0% by weight of copper (Cu) or 1.0-2.0% by weight of indium (In).

According to the solder paste according to the first to third aspects of the present invention, the solder paste is filled between base materials such as electronic parts and heated to melt and harden the solder material. Thereby, the base materials can be joined.

In particular, when the solder material is melted, the alloy of one of the first or second powder materials having a lower melting point is melted first, and the melted alloy starts to be melted later. The melting point of the other powder is lowered by contact with the alloy of the other powder in the semi-molten state. In the solder paste of the present invention, the melting point of the solder material can be adjusted by appropriately mixing powders having different melting points by utilizing such an action.

Further, such an effect can be obtained by blending a Sn-Ag alloy with a Sn-Bi alloy or by further adding Cu or In to these alloys. It is possible to perform highly reliable bonding while improving workability without using metals such as lead which may harm the environment.

At this time, when Cu is added, the creep characteristics of the solder can be improved, while when In is added, the whisker control action can be expected.

Further, according to these solder pastes, the same wetting property and mechanical strength as those of the conventional solder containing lead can be ensured, and the working temperature can be set equal to the conventional solder. There is no need to significantly change production conditions.

According to a fourth aspect of the present invention, an electronic component is connected using the solder paste according to the first to third aspects.

According to the electronic circuit device using the solder paste according to the fourth aspect of the present invention, it is not necessary to use a harmful metal.
There is no fear that the environment will be adversely affected by disposal.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A preferred first embodiment of the present invention will be described in detail below. FIG. 1 shows a solder paste according to the present embodiment.

The solder paste 10 is obtained by mixing a solder material with the flux 3. FIG. 2 shows a state in which the solder paste 10 is printed on a base material 4 such as a substrate by transfer molding or the like. Is shown.

In particular, in the present embodiment, such a solder material comprises a first powder 1 made of a powder of the first alloy and a second alloy 1 having a melting point different from the melting point of the first alloy. Is mixed with the second powder 2 made into a powder.

These first and second powders 1 and 2 are sprayed by, for example, a method in which a molten alloy is sprayed in a powder production apparatus in an inert atmosphere. Can be formed by a method of spraying.

In this embodiment, the first powder 1
Used is an Sn-Ag-based alloy containing tin (Sn) and silver (Ag), and the second powder 2 is an Sn-Bi-based alloy containing tin (Sn) and bismuth (Bi).

The binary state of these alloys is the same as the conventional one (see FIG. 6). That is, in the Sn-Bi alloy, the eutectic point E occurs when the Bi content is around 57% by weight, and its temperature is 138.5 ° C. On the other hand, in the Sn-Ag alloy, the eutectic point E occurs when the Ag content is around 3.5% by weight, and the temperature is 221 ° C.

The flux 3 generally has a function of reacting with an oxide film on the surface of the alloy to activate the oxide film and remove the oxide film. Can be used. Specifically, a paste obtained by adding and kneading pine tar, an activator, a thickener, and a thixotropic agent is used.

Next, the operation of the solder paste 10 will be described. FIG. 2 is an enlarged view of a portion indicated by A in FIG. 1, and FIG. 2A shows a state before the solder paste 10 is heated. In FIG. 1A, an oxide film is formed on the surfaces of the powder 1 and the powder 2.

FIG. 3B shows a state after the solder paste 10 has been heated in a reflow furnace. When the temperature in the reflow furnace rises and reaches 138 ° C,
First, the powdery substance 2 having a low melting point starts to melt and change to a liquid.
On the other hand, in the powder 1, the oxide film on the surface of the powder 2 is activated by the action of the flux and starts to be removed.

At this time, as shown in FIG. 4C, the molten second powder contacts and fuses with the first powder whose surface is activated. As a result, a ternary lead-free alloy in which Bi is added to the Sn-Ag alloy is partially formed, and the liquidus temperature of the first powder drops to 221 ° C., which is the original melting point. The first powder starts to liquefy without waiting.

As described above, by appropriately mixing the powders 1 and 2 having different melting points, the melting point of the solder material can be adjusted, and the workability can be improved by melting the solder material at an appropriate temperature. Can be obtained. The preferred blending amounts of the first and second powders will be described in detail in Examples described later.

Second Embodiment In this embodiment, Sn-Ag is used as the first alloy.
An alloy containing 0.1 to 2.0% by weight of copper (Cu) or 1.0 to 2.0% by weight of indium (In) is used.

According to the solder paste according to the second embodiment, when the second powder is first melted and fused with the second powder by the above-described operation, the Sn-Ag-based B on alloy
An alloy in which Cu or In is further added partially to the alloy to which i is added, whereby the melting point can be more reliably adjusted, and more suitable workability can be obtained.

In particular, when Cu is added, the creep characteristics of the solder can be improved. On the other hand, when In is added, a so-called whisker controlling action that produces needle-like crystals is expected. it can.

Third Embodiment In this embodiment, an electronic circuit device is constructed by connecting electronic components using the solder paste used in the first and second embodiments. FIG. 3 shows the appearance of the electronic circuit device 50a or 50b.

That is, in FIGS. 6A and 6B, a solder paste is applied on a copper pattern for soldering of a printed circuit board 51 or 58 using a screen or the like, and an electronic component 52 to be connected thereon is applied. In a nitrogen atmosphere, for example, 22
By heating and melting at 0 ° C., the joints 53, 55, 57 or 60 of these electronic components are joined on the printed circuit board 51 or 58.

According to the electronic circuit device 50a or 50b using such a solder paste, it is not necessary to use harmful metal such as lead.
There is no fear that the production, use, and disposal of 50b will adversely affect the environment.

[0040]

EXAMPLES Examples of the solder paste according to the present invention will be described below.

<< Test Conditions >> In this example, an Sn-Ag powder alloy was used as the first powder in the present invention, and a Sn-Bi powder alloy was used as the second powder, and a mixture thereof was used. A test was performed on the relationship between the reflow temperature and the solder meltability according to the ratio. FIG. 4 summarizes the results of such a test.

In this test, the Sn-Ag type powder alloy was composed of 96.5% by weight of Sn and 3.5% by weight of Ag, and the Sn-Bi type powdery alloy was composed of 42% by weight of Sn and 58% by weight of Bi. .

In this test, the mixing ratio of these powdered alloys was changed in steps of 20%, and the meltability, ball generation and wettability of the solder at each mixing ratio were examined. 220 ° C, 210
C., 200.degree. C. and 190.degree. C., and the influence of the reflow peak temperature was examined.

The ternary alloy obtained by heating the solder paste according to this embodiment, that is, Sn-Ag-based powder alloy
Regarding the alloy to which i was added, the relationship between the alloy composition after melting and the melting point was examined.
The relationship between the amount of Bi added and the tensile strength and elongation was tested.

<< Test Results >> First, the relationship between the reflow temperature and the melting property of the solder will be described. FIG. 4 shows the relationship between the reflow temperature and the meltability, ball generation and wetting of the solder.

According to the figure, relatively good solder meltability and the like can be obtained in the range indicated by oblique lines in the figure.
In particular, when the reflow peak temperature is in the range of 210 ° C. and 220 ° C., when the Sn-Ag-based powder alloy is 70% to 80%, good results can be obtained in all of the meltability, ball generation, and wetting. it can.

Further, when the Sn-Ag type powder alloy is 70%, even if the reflow peak temperature is 200 ° C., the melting property and
Good results can be obtained in both ball generation and wetting.

It should be noted that the alloy mixture ratio is Sn-Ag based powder alloy 60
%, Some ball generation was observed when the reflow peak temperature was in the range of 200 ° C. to 220 ° C., but good results were obtained with respect to meltability and wettability. Even when the Sn-Ag powder alloy is 90%, the reflow peak temperature is
At 220 ° C., good results can be obtained in all of the meltability, ball generation, and wetting properties.

Next, test results on the alloy composition after melting will be described. Table 1 shows the relationship between the mixing ratio of the Sn-Ag-based powder alloy and the Sn-Bi-based powder alloy, the composition of the alloy after melting, and its melting point.

[0050]

[Table 1] As can be seen from the table, after melting, a ternary alloy containing Sn, Ag, and Bi is generated. In the same table, the mixing ratio of the Sn-Ag alloy is shown in the range of 60 to 80%. In this range, the alloy composition after melting is Bi of 1%.
1.6 to 23.2%. In this range, the solid phase melting point is 138 ° C. and the liquid phase melting point is 200 ° C. to 209 ° C. in any case, so that a good working temperature can be secured.

FIG. 5 shows the relationship between the amount of added Bi and the tensile strength and elongation of the alloy when Bi is added to the Sn—Ag based powder alloy according to the present embodiment.

When the mixture ratio of the Sn—Ag alloy is 70%, the results in Table 1 show that Bi is 1 in the alloy composition after melting.
Although it is 7.4%, referring to FIG. 5A based on this value, the tensile strength when this Bi addition amount is 17.4% is about 110 MPa.
As described above, it can be seen that it is included in the range of good tensile strength. In addition, referring to FIG.
The elongation percentage of the ternary alloy at 17.4% is about 15%, which indicates that appropriate toughness can be obtained.

From the above test results, the most optimal mixing ratio of the Sn-Ag-based powder alloy and the Sn-Bi-based powder alloy is 70-80% for the Sn-Ag-based alloy and 20-30% for the Sn-Bi-based alloy. % Range,
The reflow peak temperature at that time was found to be 200 ° C to 220 ° C.

In the case where the soldering operation is performed at 220 ° C. and there is a temperature variation, care must be taken when mixing the Sn-Ag-based alloy by 90% or more. Also, Sn-B
In a composition in which the i-based alloy is mixed at 40 to 20%, the mixing amount of Bi after melting is 20 to 10%, so attention must be paid to the high-temperature creep characteristics. However, the conventional Sn-Bi It can be said that it is better than -Pb alloy.

[0055]

As described above, according to the solder paste of the present invention and the electronic circuit device using the same, lead or the like which may adversely affect the environment without greatly changing the conventional production conditions. While avoiding the use of metal
The reliability of the connection portion and the workability in the soldering operation can be ensured.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a solder paste according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a range indicated by A in FIG. 1 and schematically shows first and second powder bodies in the present embodiment.

FIG. 3 is a perspective view of an electronic circuit device used in a third embodiment of the present invention.

FIG. 4 is a table showing test results in Examples of the present invention, and shows a relationship between a reflow temperature, a solder melting property, and the like.

FIG. 5 is a graph showing test results in Examples of the present invention, and shows the relationship between the amount of Bi added to a Sn—Ag alloy and tensile strength or elongation.

FIG. 6 is a diagram showing a binary state of a conventional lead-free solder.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st powder (Sn-Ag type powder alloy) 2 2nd powder (Sn-Bi type powder alloy) 3 Flux 10 Solder paste 50a, 50b Electronic circuit device 52, 54, 57, 59 Electronic components

Claims (4)

[Claims] 1. A solder paste obtained by mixing a solder material with a flux, wherein the solder material comprises a first powdery material obtained by powdering a first alloy, and a melting point of the first alloy. And a second powder made of a powder of a second alloy having a melting point different from that of the first alloy, wherein the first alloy is tin (Sn).
And silver (Ag), and the second alloy is tin (Sn).
And a bismuth (Bi). 2. The solder paste according to claim 1, wherein the amount of silver contained in the first alloy is 0.1 to 5.0% by weight.
And the amount of bismuth contained in the second alloy is 42 to
58% by weight, the first powder is 70 to 80% by weight based on the solder material, and the second powder is 20 to 30% by weight based on the solder material. A solder paste, characterized in that: 3. The solder paste according to claim 2, wherein the first alloy comprises 0.1-2.0% by weight of copper (Cu) or 1.0-2.0% by weight of indium (In). Solder paste characterized by containing. 4. An electronic circuit device comprising an electronic component connected by using the solder paste according to claim 1.