JPH09206983A - Soldering material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soldering material without a fear of environmental pollution, having sufficient mechanical strength, and approximately showing the same melting temp. property as a conventional tin-lead soldering material. SOLUTION: This soldering material is composed of, by wt., 0.5-10% zinc, 0.5-8% bismuth and substantially the balance tin (however, the chemical composition consisting of, by wt., >5% to <10% zinc, >3% to <8% bismuth and substantially the balance tin is excluded). Namely, the soldering material is specified to be the chemical composition within the area enclosed with line segments AB, BC, CD, DE, EF and FA.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solder material.

[0002]

2. Description of the Related Art The industry is highly developed, and the electronic circuit industry is also advancing the sophistication of the mounting technology for electronic circuit elements. Solders composed of tin and lead, which have been evaluated for their properties, are still widely used.

When lead accumulates in the human body, extensor paralysis of the arms and arms, colic (pain-like pain in the abdomen), lead green (a dark green to blue line formed in the part of the gums that contacts bacteria), Lead poisoning symptoms such as anemia appear, and it is a harmful substance to the human body.

In recent years, the problem of environmental pollution has been pointed out mainly in the United States and Europe, and legislation on regulation for environmental pollution has been actively discussed. Furthermore, as a practical problem, industrial wastes and electrical product wastes (solder containing a large amount of lead is used) that are generated in large quantities have been pointed out as causes of environmental pollution.

Therefore, it is desired to use a lead solder substitute material having the characteristics of a lead-zinc alloy solder (hereinafter, referred to as lead solder). Tends to be high. This tendency leads to a problem of causing thermal damage to electronic components to be joined (soldered). Further, if an attempt is made to develop an electronic component that can withstand soldering at high temperature, such an electronic component will increase in cost, and the manufacturing cost of electronic equipment will increase.

The current solder is a tin-lead alloy having a eutectic composition, which has a composition of 63% by weight tin and 37% by weight lead, and the eutectic temperature is about 183 ° C. Therefore, in mounting electronic circuit elements, there is a demand for a solder material that can be used in the joining temperature region using lead solder as much as possible. However, the present situation is that a satisfactory solder material has not yet been developed. There are various lead-free solder materials. Among them, tin-silver alloy solder, for example, has a high eutectic temperature of 221 ° C, which increases the cost due to the inclusion of expensive silver. .

[0007]

In view of the above circumstances, an object of the present invention is to be harmless to living organisms and not to cause environmental pollution.
Moreover, it is to provide a solder material that can be bonded at a temperature substantially equal to that of the current lead solder.

[0008]

That is, according to the present invention, zinc is
0.5 to 10% by weight, bismuth 0.5 to 8% by weight, the balance substantially consisting of tin (provided that zinc exceeds 5% by weight, less than 10% by weight, bismuth exceeds 3% by weight,
The chemical composition is less than 8% by weight and the balance is substantially tin. ) Is included in the solder material.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Of the above chemical compositions, zinc is 5
To 10% by weight, bismuth 0.5 to 3% by weight, and the balance being substantially tin, the solder material shows a substantially single absorption peak temperature in the differential scanning calorimetry described below, It is particularly suitable for use in mounting a wiring board.

Among the above chemical compositions, a solder material having a chemical composition of 0.5 to 5% by weight of zinc, 0.5 to 8% by weight of bismuth, and the balance of substantially tin is used in the above-mentioned differential scanning calorimetry. Since it exhibits a plurality of absorption peak temperatures and has a wide melting temperature range, the joining work is easy and suitable for joining other than mounting of a printed wiring board (for example, soldering using a soldering iron (iron)).

The "solder material" is a concept that includes not only the alloy having the above composition but also the simple substance or a mixture of these simple substances before alloying which constitutes this alloy.

In addition, the above "the balance consists essentially of tin"
The term does not exclude that the balance consists of tin and unavoidable impurities, and positively contains a small amount of a third element other than tin, zinc and bismuth.

[0013]

Embodiments of the present invention will be described below.

The characteristics required for solder include various characteristics such as melting temperature characteristics, mechanical strength, solderability (wettability with respect to materials to be joined) and the like. Below, the results of mainly examining the mechanical strength and melting temperature characteristics of the lead-free tin-zinc-bismuth ternary alloy will be described. In this example, the mechanical strength was examined using brittleness as a characteristic value. Regarding the melting temperature characteristics, since the eutectic temperature of lead solder is 183 ℃, we examined that the melting point should have a melting point of about 200 ± 20 ℃.

<Preparation of solder sample> Purity 99.999% by weight
Granular tin (hereinafter,% by weight is simply expressed as%), purity 99.99
Using a 99% granular zinc and 99.9999% pure bismuth ingot, the ingots were weighed so as to have the composition shown in Table 1 below and the total amount was 33 g, and these were filled in a crucible having a capacity of 5 cc.

[0016]

Next, the above raw materials in the magnetic crucible were melted in the atmosphere while blowing nitrogen gas from the nozzle at a flow rate of 3 liters / minute, so that the molten metal had a uniform composition at 400 ° C.
After holding for 2 to 3 hours, a rod-shaped solder sample was prepared by casting.

The solder sample has a diameter of 4 to 6 mm and a length of 100.
It was manufactured by pouring the molten metal into a metal mold manufactured to have a size of about mm. With this pouring, the wettability and spreadability of the solder to the metal can be evaluated qualitatively. Therefore, the mold should be 55 ± 5 when pouring.
The temperature was kept at ° C. After this pouring, the remaining molten solder was poured into a ceramic tube and the solidified state was observed.

4A and 4B show a mold used for preparing a solder sample. FIG. 4A is a sectional view (a sectional view taken along line aa in FIG. 4B) and FIG. 4B is a plan view. .

The mold 30 is made of metal (made of pure iron in this example), is composed of a pair of molds 31 and 32, and has a conical shape on a vertically installed cavity 34 having an inner diameter of 4 to 6 mm and a length of 100 mm. The receiving port 33 is provided and configured. At the lower end of the cavity 34, a small-diameter gas vent hole 35 that opens to the upper surface of the mold is provided. That is, the solder sample is made by a drop casting scheme.

Although a solder sample having a length of 100 mm is usually obtained by pouring into the mold, the flowability may be poor and the length may not reach 100 mm depending on the composition of the molten metal. When the contents of zinc and bismuth increase, the fluidity of the molten metal tends to deteriorate. To give a few examples, the solder samples of Sample No. 16 (93.0% Sn, 2.0% Zn, 5.0% Bi) and Sample No. 17 (95.0% Sn, 2.0% Zn, 3.0% Bi) have different lengths. 70 mm, sample No. 9 (82.0% Sn, 8.0
% Zn, 10.0% Bi) solder sample had a length of 60 mm.

<Mechanical Strength> From the results of the examination of melting temperature characteristics described later, it was found that the addition of bismuth can lower the melting temperature, but on the other hand, there is a concern that the soft solder will become brittle when it contains bismuth. . Therefore, in order to investigate the degree of brittleness, the solder sample is cut with a chisel,
A test for observing the fracture surface was conducted.

That is, as shown in FIG. 5, the solder sample 20 placed on the anvil 24 is cut by a flat chisel 23. At this time, the impact load by a hammer (not shown) is set to be substantially constant.

Then, as shown in FIG. 6, by observing the fracture surface of the cut solder sample, the width of the fracture surface (brittle fracture surface) portion 22 presenting a fine uneven surface under the ductile fracture fracture surface 21. The ratio L '/ L between L'and the diameter L of the solder sample was determined. The results are shown in Table 2 below.

[0025]

The smaller the value of L '/ L, the smaller the brittleness and the better the mechanical strength. In Table 2, L '
If / L is 0, the symbol is ◯,> 0 to 0.2 is the symbol □, and 0.2 to 0.
The symbol ◇ for 3, the symbol △ for 0.3 to 0.4, and the symbol ▽ for> 0.4
Are attached respectively.

FIG. 1 is a graph showing the results shown in Table 2 in relation to the chemical composition of the solder sample. Table 2 in FIG.
The numbers attached to the symbols shown in indicate the sample numbers.

From FIG. 1, the chemical compositions with slight brittleness and good mechanical strength are shown by line segment AB, line segment BC, line segment CD, and line segment D.
It can be understood that it exists in a region surrounded by E, line segment EF, and line segment FA. However, point A is 99.0% Sn, 0.5% Z
n, 0.5% Bi, point B is 89.5% Sn, 10.0% Zn,
0.5% Bi, point C 87.0% Sn, 10.0% Zn, 3.0%
Bi, point D is 92.0% Sn, 5.0% Zn, 3.0% Bi
Point E shows 87.0% Sn, 5.0% Zn, 8.0% Bi, and point F shows 91.5% Sn, 0.5% Zn, 8.0% Bi, respectively.
In addition, the lower limit of the overall good content including the melting temperature characteristics of zinc and bismuth will be described later with reference to FIGS.
This is made clear by FIGS. 10 and 11.

From the chemical composition of Table 1 and the results of Table 2, the change of L '/ L with the zinc content with the bismuth content kept constant and the L' / L with the bismuth content with the zinc content kept constant. 2 and FIG. 3 are obtained by obtaining the change of

From FIG. 2, it can be seen that when the bismuth content is 3.0% or less, when the zinc content exceeds 10.0%, L '/ L sharply increases and becomes brittle. Also, in the composition where bismuth exceeds 3.0%, it is found that when zinc exceeds 3.0%, L '/ L sharply increases and becomes brittle. From FIG. 3, it can be seen that when the content of zinc is 5.0% or less, the content of bismuth exceeds 8.0%, L '/ L rapidly increases and becomes brittle. Further, in the composition in which zinc exceeds 5.0%, it is found that when bismuth exceeds 3.0%, L '/ L sharply increases and becomes brittle.

From the above results, the preferable upper limit of the zinc content is 10.0% when the bismuth is 3.0% or less, and the bismuth content is 3.0%.
When it exceeds%, it is 5.0%. Further, the preferable upper limit of the bismuth content is 8.0% when the zinc content is 5.0% or less, and the zinc content is 5.0%.
When it exceeds%, it is 3.0%.

<Melting Temperature Characteristic> Differential scanning calorimeter (DS
C: Differential Scanning Calorimeter) was used to examine the melting temperature characteristics of each solder sample. The test conditions are as follows. 4 to 5 mg of each solder sample was sampled, sealed in an aluminum container, heated to 250 ° C. at a rate of 5 ° C./minute, held at this temperature for several minutes, and then cooled at the same rate.

FIGS. 7 and 8 show sample N of each solder sample.
o.5 (87.0% Sn, 10.0% Zn, 3.0% Bi), sample No.
15 (92.0% Sn, 3.0% Zn, 5.0% Bi)
It is a chart figure obtained by the above-mentioned test.

In Sample No. 5, one absorption peak at the time of temperature rise was observed, but in Sample No. 15, two absorption peaks were observed. The temperature of the absorption peak is T _P, and the temperature corresponding to the solid phase temperature at the point of extrapolation from the peak temperature to the baseline (not shown in the figure) is T _S, and the liquidus temperature on the opposite side is The corresponding temperature was designated as T _L.

Table 3 below summarizes the DSC test results of each solder sample. In Table 3, the symbol ◯ has an absorption peak of 1
Symbol ⊚ indicates that two absorption peaks were observed.

[0036]

[0037]

FIG. 9 is a graph showing the test results shown in Table 3 in relation to the chemical composition of the solder sample. In FIG.
The numbers attached to the symbols shown in Table 3 indicate the sample numbers.

Solder exhibiting a single absorption peak in DSC has a narrow melting temperature range and can relatively lower the heating temperature at the time of joining, and is therefore suitable for mounting on a printed wiring board. On the other hand, the solder exhibiting two absorption peaks by DSC has a wide melting temperature range, and therefore the work is easy for joining other than mounting the printed wiring board, for example, using a soldering iron (iron). It is advantageous.

Therefore, the solder having the chemical composition in the region surrounded by the line segment GB, the line segment BC, the line segment CD, and the line segment DG in FIG. 9 is particularly suitable for mounting on a printed wiring board. The chemical compositions indicated by points A, B, C, D, E, and F in FIG. 9 are as described above. Point G in FIG. 9 is 94.5% Sn, 5.0%
The chemical composition of Zn and 0.5% Bi is shown. Sample No. 4,
Although 12, 13, and 28 have two absorption peaks, any of them has a small difference in absorption peak temperature and is regarded as a composition showing a single peak. The difference in absorption peak temperature is 6 ℃ for sample No.4, sample No.12 and sample No.28, sample No.13
At 5 ° C.

Further, line segment AG, line segment GE, and line segment E of FIG.
The solder having the chemical composition in the region surrounded by F and the line segment FA is suitable for use in various joints other than mounting of the printed wiring board.

From the chemical composition of Table 1 and the results of Table 3, the change of the absorption peak temperature T _{P1 with} the zinc content with the bismuth content kept constant and the absorption peak temperature with the bismuth content with the zinc content kept constant When the change of T _P1 is calculated,
10 and 11 are obtained.

From FIGS. 10 and 11, it can be understood that both zinc and bismuth have the action of lowering the absorption peak temperature, and facilitate the joining by soldering. The above-mentioned effects are remarkable when both zinc and bismuth are 0.5% or less. Therefore, it is advantageous to contain both zinc and bismuth by 0.5% or more.

Next, an example using the solder according to the present invention will be described.

FIG. 12 shows a mounting process of the printed wiring board. First, as shown in FIG. 12 (A), through holes 4 are formed in an insulating substrate 2 of a printed wiring board, and then conductive layers (for example, copper patterns) 5 are formed on the front and back of the substrate 2 through the through holes 4 by through hole plating. To form.

Next, as shown in FIG. 12B, a solder resist 6 is applied by printing around the copper pattern 5, and a pre-flux 7 is applied to prevent the copper pattern 5 from being oxidized.

Next, as shown in FIG. 12C, the liquid flux 8 is applied onto the preflux 7 on the back surface of the substrate 2. Among the fluxes previously proposed by the applicant as Japanese Patent Application No. 7-174121, hydrogenated rosin ethylamine salt 1 as a flux agent is used as the liquid flux.
0.0%, ethylamine hydrochloride 0.2%, water as solvent 69.
A mixture of 8% and isopropyl alcohol 20.0% was used. This liquid flux has good drying properties and wettability, and is less affected by volatile organic compounds on the environment.

Next, as shown in FIG. 12D, cream solder (solder paste) 13 is provided on the front side surface around the through hole 4 by adhesion or screen printing.

Next, as shown in FIG. 12E, the leads 10 of the electronic component 9 such as a resistor and a capacitor are inserted into the through holes 4 from the front side of the substrate 2 and penetrated to the back side of the substrate 2. Then, in this state, the cream solder 13 is heated and reflowed, and the leads 10 are completely fixed in the through holes 4 by the solder 11 as shown in FIG.
Mount on top. Appropriate means such as far infrared radiation, laser heating, and VPS (Vapor Phase Soldering) can be adopted for the solder reflow.

At this time, the solder 11 is sufficiently alloyed with the copper pattern 5 in the region where the resist 6 does not exist, and the flux agent in the flux is present in the region of the resist 6.
Only 12 partially remain.

FIG. 13 shows a procedure for joining terminals and wires using a soldering iron.

First, as shown in FIG. 13 (A), the tip of the wire 17 is exposed in advance and wound around the terminal 16, and the thread solder 18 and the heated soldering iron 19 are prepared.

Next, as shown in FIG. 13B, the tip of the heated soldering iron 19 is brought into contact with the wire 17 at the joint.

Next, as shown in FIG. 13 (C), the tip of the thread solder 18 is pressed against the wire 17 or the terminal 16 at the joint to melt it.

Next, as shown in FIG. 13D, when a proper amount of solder has melted, the thread solder 18 is quickly separated in the axial direction, and then the soldering iron 19 is separated.

Then, as shown in FIG. 13E, it waits for the solder to cool and solidify. The timing of this solidification can be judged by the change in the gloss of the solder.

In both examples of FIGS. 12 and 13, the solder is not brittle and the melting temperature characteristics are almost the same as those of the conventional tin-lead alloy solder. Since it does not contain harmful lead, it does not cause environmental pollution.

Although the embodiments of the present invention have been described above, various modifications can be made to the above embodiments based on the technical idea of the present invention.

For example, the solder material according to the present invention can be used for soldering in various fields other than the production of electric products. In particular, since it does not contain lead, which is harmful to the human body, it can be preferably used for the production of canned foods.

Depending on the purpose of use, a small amount of tin
The chemical composition is replaced with a component other than zinc and bismuth, and various properties can be improved by this substituted component.

[0061]

The solder material according to the present invention has a chemical composition in which zinc is 0.5 to 10% by weight, bismuth is 0.5 to 8% by weight, and the balance is substantially tin (provided that zinc exceeds 5% by weight). , Less than 10% by weight, bismuth is more than 3% by weight, less than 8% by weight, and the balance is substantially chemical composition consisting essentially of tin.) Since it is not contained, there is no risk of causing environmental pollution.

Moreover, by having the above chemical composition,
It has sufficient mechanical strength and has the same melting temperature characteristics as conventional tin-
Since it is almost the same as the lead-based solder material and easy to join, the joining reliability is high.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the chemical composition and mechanical strength (L ′ / L) of solder samples according to an example of the present invention.

FIG. 2 is a graph showing changes in mechanical strength depending on the zinc content.

FIG. 3 is a graph showing changes in mechanical strength depending on the bismuth content.

FIG. 4 shows the same solder sample preparation mold, in which FIG. 4 (a) is a sectional view (a sectional view taken along the line aa in FIG. 4 (b)) and FIG. 4 (b) is a plan view.

FIG. 5 is a schematic perspective view showing a procedure for cutting the solder sample.

FIG. 6 is an enlarged front view of a cut surface of the solder sample.

FIG. 7 is a chart showing an example of a DSC test result of the solder sample.

FIG. 8 is a chart showing another example of the result of the DSC test of the solder sample.

FIG. 9 is a graph showing the relationship between the chemical composition of the same solder sample and the number of appearance of absorption peaks in a DSC test.

FIG. 10 is a graph showing changes in absorption peak temperature in a DSC test depending on the zinc content.

FIG. 11 is a graph showing a change in absorption peak temperature in a DSC test depending on the bismuth content.

FIG. 12 is an enlarged partial cross-sectional view showing a procedure for mounting the same printed wiring board.

FIG. 13 is a perspective view showing a procedure for joining a terminal and a wire using the soldering iron.

[Explanation of symbols]

2 ... Substrate, 4 ... Through hole, 5 ... Copper pattern, 6 ... Resist, 7 ... Preflux, 8 ... Liquid flux, 9
… Electronic parts, 10… Lead, 11,18… Solder, 13… Cream solder, 16… Terminal, 17… Wire material, 19… Soldering iron, 20… Solder sample, 21… Ductile fracture surface, 22… Brittle fracture surface, 23 … Flat chisel, 24
… Anvil, 30… Mold, 31, 32… Mold, 34… Cavity, L
... Diameter of solder sample, L '... Width of brittle fracture surface, T _P1 ... Absorption peak temperature

Claims (5)

[Claims] 1. Zinc 0.5 to 10% by weight and bismuth 0.5.
~ 8% by weight, the balance being essentially tin (where zinc is greater than 5% and less than 10% by weight, bismuth is greater than 3% and less than 8% by weight, and the balance is A solder material having a chemical composition substantially excluding tin). 2. The chemical composition according to claim 1, wherein
A solder material having a chemical composition in which zinc is 5 to 10% by weight, bismuth is 0.5 to 3% by weight, and the balance is substantially tin. 3. The chemical composition according to claim 1, wherein
A solder material having a chemical composition in which zinc is 0.5 to 5% by weight, bismuth is 0.5 to 8% by weight, and the balance is substantially tin. 4. The solder material according to claim 2, which exhibits a substantially single absorption peak temperature in differential scanning calorimetry. 5. The solder material according to claim 3, which exhibits a plurality of absorption peak temperatures in differential scanning calorimetry.