JPH1133774A - Solder alloy, solder paste, and resin flux cored solder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the solder alloy which reduces the crack under the heat cycle condition, the high temperature creep fracture under the high temperature condition, and the tip upright in the time of the reflow by specifying the composition consisting of Sn, Sb, Ag, Cu, Ni and Pb. SOLUTION: The solder alloy consists of 55.0-61.8 wt.% Sn, 0.3-0.7 wt.% Sb, 0.2-1.0 wt.% Ag, 0.05-0.15 wt.% Cu, 0.025-0.07 wt.% Ni, and the balance of Pb, and shows an excellent heat resistant characteristics. The solder alloy absorbs the stress based on the expansion/shrinkage of a substrate by the heat cycle to reduce the crack generated at the soldering part. Further, the solder alloy reduces the creep fracture of the soldering part against the long-hour load under the high temperature condition, and also reduces the upright phenomenon of a tip part in heat-fusing a surface mounting field. The solder alloy can be used for the solder paste or the resin flux cored solder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder alloy used for a printed circuit board or the like, which absorbs stress caused by expansion and contraction of the board due to thermal cycling, reduces cracks generated at a soldered portion, and provides a high-temperature environment. In this case, if a constant load is continuously applied to the soldered part, the high temperature creep destruction, which is the phenomenon that the soldered part will eventually come off, is reduced, and the upright phenomenon of the chip component when it is heated and melted (reflow) in the surface mounting field (chip standing) ).

[0002]

2. Description of the Related Art It has been said that most failures in electronic devices are failures in soldered portions. When the mechanical failure of the soldered portion is classified by form, it can be classified into (1) thermal fatigue fracture, (2) high temperature creep fracture, (3) vibration fracture, and a combination thereof (4) composite fracture. Among them, thermal fatigue destruction is caused by repeated changes in the temperature of the substrate and the rise and fall of the substrate temperature caused by the ON-OFF of the electric circuit, and the soldered part undergoes a thermal cycle and a stress cycle caused by the expansion and contraction of the substrate. Is repeated. Eventually, the soldered portion becomes coarse because the crystal structure of the solder becomes coarse, becomes brittle, becomes unable to absorb stress, and is broken.

In order to reduce such thermal fatigue fracture,
There has been reported a solder alloy in which second and third metal elements are added to a conventional Sn-Pb-based solder to improve thermal fatigue resistance. For example, in JP-A-6-71480, Sb
1% by weight and 0.01 to 0.2% by weight of Te, and in Japanese Patent Application Laid-Open No. 7-11687
A solder to which 0.02% by weight is added is known.
The purpose of the addition is to provide a crystal structure that can withstand thermal cycle stress, or not to impair the spreadability of the solder material.

[0004] Furthermore, the boards of recent electronic devices, especially the boards of portable telephones and in-vehicle electronic devices, are not only capable of high-density mounting, but also have poor heat radiation and large power consumption. In a still higher temperature environment, the soldered portion receives a high load due to thermal expansion and contraction of the substrate, and the soldered portion comes off. This phenomenon is distinguished from destruction due to thermal cycling, and is considered to be due to lack of mechanical strength of the soldered portion under a high temperature environment. This destruction phenomenon is called high-temperature creep destruction and is one of destruction phenomena that have been regarded as important in recent years.

[0005] In order to reduce such high-temperature creep destruction, there has been reported a solder alloy in which second and third metal elements are added to a conventional Sn-Pb-based solder to improve the high-temperature creep characteristics. For example, in JP-A-8-132278, G
e, Ni and the like to which 0.005 to 0.05% by weight is added are known. The reason for the addition is that the high-temperature creep characteristics are improved by refining the crystal structure.

In the field of surface mounting, the technology for reducing the size and weight has been further advanced, and the mounted chip components have been further reduced in size and weight. Recently, the tip shape is 1.0mm ×
The so-called “1005” of 0.5 mm has also been used frequently. Since such a small chip component is light in weight, the phenomenon of chip standing due to surface tension at the time of melting of solder has come to occur frequently.

[0007] When a chip is formed, a solder paste is printed at a position on the substrate where the left and right electrodes of the chip component are joined, and when the chip component is mounted thereon and reflowed, the melting start time of the left and right solder paste slightly shifts. In some cases, the opposite side of the chip is lifted by the surface tension of the solder that has melted earlier.

In order to prevent this chip standing, conventional methods are disclosed in Japanese Patent Application Laid-Open Nos. 8-186367 and 7-27607.
As shown in No. 6, there is a method of mixing two or three kinds of powdered solders having different melting points to increase the time until the solder becomes a complete liquid after heating. If undissolved powder is present in the liquid, its surface tension will be lower than the surface tension of the complete liquid. This is a technique for adjusting the surface tension to such an extent that the chip does not stand up even if the melting start time of the solder of the left and right electrodes of the chip component slightly shifts.

[0009]

One type of solder alloy has the functions of a solder which is conventionally used, which is resistant to heat cycles, a solder which is resistant to high-temperature creep, and a solder which reduces chip standing. With the progress of high-density mounting, the thermal load and miniaturization of the substrate have been advanced at the same time, so that an alloy having both heat resistance and performance of reducing chip standing during reflow is provided.

In the soldering of electronic equipment by the flow or reflow method, Sn63-Pb37 eutectic solder having a low melting point and excellent in solderability and mechanical properties is often used. The present invention has the performance of reducing the occurrence of cracks in the soldered portion in a heat cycle environment and the excellent creep characteristics at high temperatures without impairing the melting temperature characteristics of the Sn63-Pb37 eutectic solder, and It has the ability to widen the melting temperature range and reduce chip standing during reflow.

[0011]

In order to solve the above problems, in the present invention, Sn is 55.0 to 61.8% by weight, Sb is 0.3 to 0.7% by weight, and Ag is 0.2 ~
1.0% by weight, 0.05 to 0.15% by weight of Cu, Ni
Is 0.025 to 0.07% by weight, and the balance is to be solved by a solder alloy having a basic composition of Pb.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, Sn is set to 55.0 to 55.0.
The reason for using 61.8% by weight is that solder having a low melting point near the eutectic which is generally used in the flow and reflow soldering of electronic equipment is required to have the highest thermal fatigue resistance. is there. Further, the reason why the upper limit of the Sn content is set to 61.9% by weight or less, which is the eutectic composition, is to widen the solidification temperature range and reduce chipping.

The reason why 0.3 to 0.7% by weight of Sb is added is that when Sb is added to the solder alloy in this addition range, the tensile strength is improved without impairing the elongation of the material, so that heat resistance is improved. Characteristics are improved. When Sb is 0.3% by weight or less, no effect is obtained, and when Sb is 0.7% or more, the elongation rate of the material is reduced. Therefore, it is difficult for the solder material to absorb the thermal expansion and contraction of the substrate under a heat cycle. This is because the heat cycle resistance decreases.

Although Ag is added in an amount of 0.2 to 1.0% by weight, the addition of Ag can suppress the coarsening of the solder crystal structure due to thermal cycling, and can also provide Sn / Pb / A
By the ternary eutectic reaction, the solidus temperature can be set to 179 ° C. which is about 4 ° C. lower than the Sn / Pb eutectic temperature. As a result, the solidification temperature range is further widened as compared with the Sn / Pb binary system, and it is possible to contribute to a reduction in chip standing. In addition, the reason why the amount of Ag added is limited to 0.2 to 1.0% by weight in the present invention is that when the amount of Ag is 0.2% by weight or less, the amount of the component that undergoes a ternary eutectic reaction is too small to reduce the prevention of chip standing. Less effective,
This is because the effect of reducing the coarsening of the crystal grain size under a thermal cycle environment is small. The reason why the upper limit of the amount of Ag added is set to 1.0% by weight is that if the amount of Ag exceeds 1.0% by weight, the amount of a component that undergoes a ternary eutectic reaction of Sn / Pb / Ag increases, so that the solder melts during reflow. This is because most of the solder becomes liquid at the beginning, so that the surface tension of the liquid is increased and the effect of preventing chip standing is reduced.

The reason for adding 0.05 to 0.15% by weight of Cu is to improve the high-temperature creep characteristics.
When u is 0.05% by weight or less, the characteristics are not observed, and when Cu is added by 0.15% by weight or more, an intermetallic compound such as Cu6Sn5 is easily formed. May form needle-like crystals having a length of 100 μm or more. The needle-like crystal is mixed into the powder for solder paste, and in a fine circuit for surface mounting, the crystal may short-circuit the circuit.

The reason why Ni is added in an amount of 0.025 to 0.07% by weight is to improve the high-temperature creep characteristics for the same reason as that for Cu described above. To further improve the high temperature creep properties by adding only Cu, 0.15% by weight of Cu
Since the addition is made as described above, the improvement of the high-temperature creep characteristics is measured by the synergistic effect of Cu and Ni. The addition amount of Ni is set to 0.025% by weight or more because an effect of improving the high-temperature creep characteristics is not seen below this addition amount. The reason why the addition amount of Ni is set to 0.07% by weight or less is that Ni is composed of Sn, Ni3Sn, Ni3Sn2, and Ni.
It is easy to form an intermetallic compound such as Sn. If the addition amount of Ni exceeds 0.07% by weight, the intermetallic compound may form needle-like crystals as in the case of Cu, and in a fine circuit for surface mounting, this crystal This is because a short circuit may occur.

[0017]

EXAMPLES Examples of the solder alloy of the present invention and its performance will be described below. As shown in Table 1, JIS Z 3
Sn63-Pb37 corresponding to H63S in 282
Solder was adopted as a reference sample (hereinafter referred to as H1), and 17 types of solder alloy samples (hereinafter referred to as G1 to G17) were used.
). Table 1 is a table showing the results of performance tests (thermal analysis test, heat cycle test, high temperature creep test, chip standing test) according to the examples, FIG. 1 is an explanatory diagram showing the state of soldering of the board and the connector, and FIG. FIG. 3 is a diagram showing criteria for cracks and wrinkle defects appearing on a fillet surface, FIG. 3 is a diagram showing a thermal analysis test result of each sample, FIG. 4 is a diagram showing a heat cycle test result, and FIG. 5 is a high temperature creep test result. FIG. 6 and FIG. 6 are diagrams showing the results of the chip standing test. The results of the performance tests (thermal analysis test, heat cycle test, high temperature creep test, chip standing test) of each sample are shown below.

[0018]

[Table 1]

As shown in Table 1, H1 and G1 to G
This was performed on 17 types of samples. DSC was used as a measuring device for the thermal analysis. The molten metal of the sample was dropped on the Fe plate, and about 30 mg of the solidified particles were selected from the solidified particles and used as a measurement sample. Heating rate: 2 ° C / min, measurement sensitivity: 20mC
al / S, chart speed is 10 mm / min. The results are shown in Table 1 and FIG. The difference between the solidus temperature and the liquidus temperature (solidification temperature range) is only 0. 3 for Sn63 / Pb37 of H1.
This is a typical case in which when the solder dissolution portion of the left and right electrode portions of the chip slightly shifts at 9 ° C., the tip of the chip is caused by a difference in surface tension between the left and right solders. From G1 to G17, the solidification temperature range is 3.7 to 10.6 ° C and H
It can be expected that it is wider than 1 and that the chip standing phenomenon is small. Among them, G5, 6, 7, and 14 to 17 are samples to which Ag is added, and the solidus temperature is lower than other samples. Therefore, it is possible to suppress an increase in only the liquidus temperature in order to widen the solidification temperature range.

The chip standing confirmation test was conducted on H1 and G1, and four kinds of samples G5 added with Ag, which gave the most suitable result as a soldering preventing solder alloy in thermal analysis results,
6, 7, and 17 were performed. The chip component is 1005, which is lightweight and easily causes a chip standing phenomenon. The flux is 35% by weight of solid content containing natural rosin as a main component, 0.06% by weight of a halogen component, and the flux mixing ratio is 10.
5% by weight low residue solder paste with a printed thickness of 0.
15mm, reflow peak temperature is 230 ° C, oxygen concentration of reflow furnace is 100ppm, number of chip parts mounted is 1
The test was performed at 000 points.

In the heat cycle test, as shown in Table 1, H
1 and samples G1 to G17. The substrate used was a universal paper phenol single-sided substrate having a 2.54 pitch and a hole diameter of φ0.9. The connector used was a 10-pin Sn-plated phosphor bronze pin having a wire diameter of 0.64. The soldering conditions were as follows: the connector was pickled, washed with water, and dried, then a rosin flux of the RA type was applied to the connector pins and the board, and after drying, 10 connectors were inserted into the board, that is, 100 pins were inserted.
Soldering by immersion was performed at 0 ° C. Temperature cycle is -40 ° C for 30 minutes, room temperature exposure time is 10 minutes, + 80 ° C
For 30 minutes, and the number of cracks generated in the soldered portion was examined using a stereoscopic microscope. FIG.
FIG. 3 is a cross-sectional reference view of a state where a connector is soldered to a substrate. As shown in FIG. 2, cracks were counted as cracks when the cracks were 以上 or more around the periphery of the solder fillet, and solder fillets having wrinkles all over the circumference were also counted as cracks.

For the high temperature creep test, the test was conducted using H1 and G in Table 1.
This was performed on 1 to G17 types of samples. The substrate used was the same as the substrate used in the heat cycle test. The connector used was the same as the ten connectors used in the heat cycle test, one by one with a nipper, and the tip of the pin was bent into a hook shape so that a weight wire rope could be hooked. Cleaning conditions and soldering conditions are the same as in the heat cycle test. In a 100 ° C. environment, a load of 500 g was continuously applied to the soldered connector, and the time during which the solder was removed was set as the creep time, and five measurements were taken for each type of sample. The average value was shown in Table 1 and FIG. It was shown to.

Effect of suppressing chip standing: Effect of Ag: Table 1 and FIG. 6 show the results of the chip standing confirmation test of H1 and G1, 5, 6, 7, and 17. H1 and G1 are the same binary alloy, and it can be seen that G1 having a wider solidification temperature range is more effective in suppressing chipping. G5, 6,
7 is an alloy obtained by adding Ag stepwise to G1. When the added amount of Ag is 0.1% by weight, as shown in the thermal analysis results, the component that undergoes the Sn / Pb / Ag ternary eutectic reaction is formed. Since it is very slight, the effect of suppressing chip standing is hardly seen. And the number of chip standing points of G6 is as low as 19 points,
In G8, the number of chip standing points rises again to 84. The reason is that if Ag exceeds 1.0% by weight, Sn / Pb / Ag
It is thought that the effect of the ternary eutectic reaction increases, so that most of the solder becomes liquid when the solder begins to melt during reflow, and the surface tension of the liquid increases, thereby reducing the effect of preventing chip standing. .

Heat cycle resistance: Effect of Sb: Table 1 and FIG. 4 show the results of the heat cycle test. G1 is a sample to which 0.2% by weight of Sb was added, but no improvement in heat cycle resistance was observed. G3 is a sample to which 0.5% by weight of Sb is added, and it can be seen that the heat cycle resistance is improved. However, the sample to which 1.0% by weight of Sb of G4 was added did not show improvement in heat cycle resistance. This is considered to be because if the amount of added Sb is too large, the elongation rate of the material is reduced, so that it is difficult for the solder material to absorb the thermal expansion and contraction of the substrate in a heat cycle environment.

Effect of Ag: G5 is a sample containing 0.1% by weight of Ag, but no improvement in heat cycle resistance is observed. G6 is a sample to which 0.5% by weight of Ag is added, and it can be seen that the heat cycle resistance is improved. However, when 1.2% by weight of Ag of G7 was added, the heat cycle resistance was worse than that of G6. It is considered that the reason for this is that if the added amount of Ag is too large, the elongation rate of the material is reduced, and it is difficult for the solder material to absorb the thermal expansion and contraction of the substrate in a heat cycle environment.

Regarding high temperature creep characteristics: Effect of Sb and Ag: The higher the amount of Sb and Ag added, the higher the value of the high temperature creep characteristics. G2,
Samples 3 and 4 were samples to which 0.2%, 0.5% and 1.0% by weight of Sb were added, and samples G5, 6 and 7 were 0.1% by weight, 0.5% by weight and 1% by weight of Ag, respectively. This is a sample to which 0.2% by weight is added. The high temperature creep test results of these samples are shown in Table 1 and FIG. These additional elements improve the mechanical strength of the solder alloy. However, Sb
The amounts of Ag and Ag that can be added are limited from investigations of chip standing characteristics, heat cycle resistance characteristics, and the like.

Effect of Cu: The higher the amount of Cu added, the better the high-temperature creep characteristics. The results are shown in Table 1 and FIG.
It was shown to. In the case of 0.03% by weight of Cu in G8,
No change in high temperature creep characteristics. In the case of 0.1% and 0.2% by weight of Cu in G9 and 10, the characteristic value increases in accordance with the added amount. However, Cu tends to grow needle-like crystals, and Table 1 shows the results of observing the presence of needle-like crystals by microscopic observation of the solder powder produced for the solder paste. From this survey, G9 C
While needle-like crystals were not observed from the sample to which 0.1% by weight of u was added, needle-like crystals were observed from the powder of the sample to which 0.2% by weight of Cu of G10 was added. From these investigations, it is determined that the appropriate range of addition of Cu is 0.05 to 0.015% by weight.

Effect of Ni: The high-temperature creep characteristics of Ni and the tendency to form needle-like crystals were almost the same as those of Cu.
The higher the amount of Ni added, the better the high-temperature creep characteristics. The results are shown in Table 1 and FIG. In the case of 0.02% by weight of Ni in G11, no change is observed in the high-temperature creep characteristics. In the case of Ni 0.05 and 0.1% by weight in G12 and G13, the characteristic value increases in accordance with the addition amount. However, Ni tends to grow needle-like crystals. The results of observing the presence of needle-like crystals by microscopic observation of the solder powder produced for the solder paste are shown in Table 1. From this investigation, needle-like crystals were not observed from the sample to which 0.05% by weight of Ni of G12 was added, whereas needle-like crystals were observed to the powder of the sample to which 0.1% by weight of Ni of G13 was added. Was. From these test results, it is judged that the range of addition of Ni is appropriately from 0.025 to 0.07% by weight.

The synergistic effect of Cu and Ni: In the investigation of the addition of Cu, the limit of 0.15 weight, which is the limit of addition of Cu, at which no needle-like crystals are observed, and the limit, at which no needle-like crystals are observed in the test of the amount of Ni added And the addition amounts of Sb and Ag were set to the limit values of 0.3% by weight and 0.2% by weight determined for G2-4 and G5-7, respectively. A solder alloy (G14) and its powder were produced and their characteristics were investigated. G14 of Table 1 shows the characteristics. Needle-like crystals were observed in the powder.

In the investigation of the addition of Cu, it was found that 0.2% by weight of N and N exceeded the limit Cu addition amount at which no needle crystals were observed.
The combination of 0.07% by weight of Ni, which is the limit of addition of Ni in which no needle-like crystals are observed in the test of i
Ag was prepared with a solder alloy (G15) and its powders having respective limit values of 0.3% by weight and 0.2% by weight, and each characteristic was examined. The properties were almost the same as G14, but needle-like crystals were observed in the arrowhead powder.

A solder alloy (G16) and a powder were prepared with a limit addition amount of Cu of 0.15% by weight and Ni of 0.07% by weight at which the needle-like crystals of Cu and Ni did not occur, and the presence or absence of needle-like crystals was examined. Other Sb and Ag addition amounts are the same as G14 and G15). As a result, no needle crystals were observed at all, contrary to the expectation. This means that the synergistic effect of Cu and Ni reaches the respective limit values.

Further, with respect to the above G16, the addition amounts of Sb and Ag were set to the above upper limits of 0.7% by weight and 1.0%, respectively.
A sample (G17) in which the weight% was obtained was prepared, and the characteristic value and the presence or absence of needle-like crystals were similarly examined. As a result, no needle-like crystals were observed, and the high-temperature creep property was significantly improved as compared with the case where each of Cu and Ni alone was added.

The present invention is based on the conditions required for solder alloys,
In particular, in order to deal with the demands for chip standing (heat analysis test), the requirements for high-temperature creep fracture (high-temperature creep test), and the requirements for thermal fatigue fracture (heat cycle test), which have become increasingly severe in recent years, Not only the analysis but also the synergy between these additional elements is considered and solved.

That is, G16, 1 according to the embodiment of the present invention
As is clear from Table 1, FIG. 4 and FIG. 5, No. 7 shows the best results in heat cycle characteristics and high temperature creep characteristics among the samples. The results of the thermal analysis show that the solidus temperature is 179.2 ° C. and the liquidus temperature is 18 as shown in Table 1.
7.5 ° C. At this level of liquidus temperature, H
It can be said that the temperature characteristics of the Sn63 / Pb37 eutectic solder No. 1 are hardly impaired. The number of chip standing points is about 21 as shown in Table 1 and FIG. 6, and Sb, Cu, Ni
It can be seen that the addition of no adverse effect on suppression of chip standing.

The present invention is characterized in that, for various necessary characteristics intricately intertwined with each other, the optimum addition amount and the limit value of each element are determined including the synergistic effect between the elements. Sn 55.0-61.8% by weight, Sb 0.3-
0.7% by weight, Ag 0.2 to 1.0% by weight, Cu 0.0
A solder alloy composed of 5 to 0.15% by weight, 0.025 to 0.07% by weight of Ni, and Pb as the balance is a feature of the present invention.

[0036]

As described above, the solder alloy according to the present invention can solve the problems, such as chip standing, which had been a problem in the past, and supply a stable and economical solder alloy having a stable performance for ICs. It became possible to do.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state of soldering a board and a connector.

FIG. 2 is a diagram showing criteria for determining cracks appearing on a solder fillet surface.

FIG. 3 is a diagram showing the results of a thermal analysis test of each sample.

FIG. 4 is a view showing a heat cycle test result of each sample.

FIG. 5 is a diagram showing the results of a high-temperature creep test of each sample.

FIG. 6 is a diagram showing the results of a chip standing test using samples H1, G1, 5, 6, 7, and 17;

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

Claims (3)

[Claims] 1. Sn55.0 to 61.8% by weight, Sb
0.3-0.7% by weight, Ag 0.2-1.0% by weight, C
u 0.05-0.15% by weight, Ni 0.025-0.0
Solder alloy with 7% by weight and Pb as the balance. 2. A solder paste comprising a powder and a paste of the solder alloy according to claim 1. 3. A cored solder comprising the solder alloy according to claim 1 and a flux.