JP2722917B2 - High temperature solder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-temperature solder.
More specifically, the present invention relates to a Sn-based high-temperature solder having particularly excellent thermal fatigue resistance.

[0002]

2. Description of the Related Art With the rapid development of electronic equipment, many technological innovations have been rapidly made in various joining techniques, especially in solder joining techniques, and a high use of a solder material for each specific application has been made. It has become For example, materials that are suitable for thinning or grain refinement, materials having high strength, and materials that exhibit high corrosion resistance in a specific environment, and material development are being performed according to the high specifications required each time. Was. In particular, the size of today's electronic devices is increasing, and the requirements for reliability in soldering are particularly strict. Therefore, advanced technologies are also required for material development.

The high-density mounting is used under severe conditions such as space environment (artificial satellites such as communication satellites, weather satellites, and military satellites) and in an environment where vehicles are used. Connected electronic devices are also needed. In such a high-density electronic device, for example, if the soldering portion between the printed circuit board and the electronic component is peeled off even at one place, it leads to a serious accident that conduction is lost and the function of the entire electronic device can not be performed at all. .
Therefore, in these electronic devices, it is necessary to use solder in which a soldered portion is not easily peeled, and therefore, high reliability is required for soldering.

By the way, since there is no air as a heat medium in the space where the artificial satellite flies, the artificial satellite has a very high temperature of, for example, 150 ° C. when directly hit by the sun's light. When it is not hit by the earth, the temperature will be as low as -40 ° C. Moreover, this is repeated on the side facing the sun and the back side each time the satellite rotates.

[0005] As described above, since the artificial satellite is exposed to high and low temperature environments due to its revolution and rotation, solder having excellent thermal fatigue resistance is used for the electronic equipment mounted on the artificial satellite. There must be. Because, when the soldered part is subjected to thermal fatigue, not only the solder itself, but also the leads and printed circuit boards of the soldered electronic components repeatedly undergo thermal expansion and thermal contraction,
This is because, in the case of a solder that is weak against thermal fatigue, cracks occur in the solder itself, and the soldered portion is peeled off.

[0006] Further, even when the artificial satellite is exposed to a high temperature, the solder used for the electronic equipment of the artificial satellite does not melt even at a high temperature such as 150 ° C so that the soldered portion maintains a stable state. In addition, it must be a high-temperature solder having high-temperature characteristics such as strong adhesive strength.

Here, the high-temperature solder means that the solidus temperature is Pb
It refers to a material having a eutectic temperature of -Sn or higher (183 ° C) or higher and a liquidus temperature of 450 ° C or lower, and generally contains Sn, Pb, Cd, or the like as a main component. Pb-based high-temperature solder is inferior in both heat-resistant fatigue properties and high-temperature properties and cannot be used for artificial satellites, etc., and Cd-based high-temperature solder cannot be used because Cd is extremely harmful to the human body .

[0008] The high-temperature solder containing Sn as a main component has better high-temperature characteristics than that of a Pb-main component, and has no pollution problem unlike the high-temperature solder containing Cd as a main component. Things. Hitherto, many high-temperature solders based on Sn have been proposed (refer to JP-A-49-38858, JP-A-51-54056, JP-A-58-55193, and JP-A-63-58193).
No. 13689). Here, JP-A-49-38858 discloses an Ag-Sb-Cu-Bi-Sn high-temperature solder for joining joints. It has been developed exclusively as a substitute for the conventional Cd-Zn-based high-temperature solder, and its high-temperature strength is a problem. However, the case of Bi = 0.1% (hereinafter, "%" means "% by weight" unless otherwise specified) is shown as a comparative example, and the tensile strength of the solder itself is shown. Of 0.5 to 2.0% Bi and 3 to 8%
It is believed that the addition of Sb is essential.

Japanese Patent Application Laid-Open No. 51-54056 discloses an example in which Cu and Ag are mixed with a Pb-Sn solder alloy as a solder alloy for electronic equipment. This is to prevent so-called eating. JP-A-58-55193
Japanese Patent Application Laid-Open Publication No. H11-216, discloses a superconducting conductor solder having a composition of 5% of Ag, 0.1 to 1.2% of Bi, and the balance of Sn in order to couple superconducting wires or a superconducting wire and a normal conducting wire. This solder has the basic performance as a solder, and also reduces the coupling current induced between the superconducting wires even under a pulsed magnetic field. Proposed as solder, Bi is more than 0.1% to change the specific resistance
It must be added below 1.2%.

JP-A-63-13689 discloses Sn: 93-99.
%, Cu: 0.7 to 6%, and Ag: 0.05 to 3%, are disclosed. However, they are used exclusively for joining pipes, and low toxicity and corrosion resistance are a problem. It is disclosed in the above publication that Sn: 95 for cost reduction
%, Ag: provides a cheaper solder equivalent to a 5% solder composition.

These conventional high-temperature solders mainly composed of Sn or Pb are required only to be difficult to melt at high temperatures, which is a necessary condition for general high-temperature solders, and to have excellent high-temperature strength. Was not considered at all. Further, JP-A-61-269998 discloses that Ag: 1 to
30% and Sb: one or two of 0.5% to 25%, the remainder having a composition of Sn and unavoidable impurities, an oxygen content as unavoidable impurities of 5 ppm or less, and an average crystal A Sn alloy solder having a particle size of 3 μm or less has been proposed. In order to improve the thermal fatigue characteristics of the solder used in a semiconductor chip joint under severe thermal fatigue conditions, the content of oxygen is suppressed to 5 ppm or less and the average crystal grain size is 3 μm or less.

[0012]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No. 61-26
The solder proposed in Japanese Patent No. 9998 is designed to reduce the oxygen content in unavoidable impurities to 5 ppm or less. It is necessary to jet the molten metal from a crucible provided with a heating device to the surface of a rotary cooling roll to rapidly cool and solidify. Therefore, the manufacturing cost is significantly increased.

At present, most of high-temperature solders are mostly based on Pb, such as Pb-8Sn-2Ag, Pb
-5Sn-2.5Ag, Pb-5In-2.5Ag and the like. However, since these all have a liquidus temperature exceeding 300 ° C, they do not satisfy the soldering specifications for today's printed wiring boards, which have a soldering temperature upper limit of 230 to 240 ° C, and are hardly used for mounting. It has not been done. In fact, the results of tests on these Pb-based high-temperature solders, which have been widely used as high-temperature solders, have revealed that they do not have the thermal fatigue resistance required for mounting. Therefore, the conventional high-temperature solder containing Sn or Pb as a main component cannot be used for electronic devices such as artificial satellites that are subjected to thermal fatigue.

[0014] Examples of the current specifications are: -55 ° C to 125 ° C as thermal fatigue characteristics, satisfying the characteristics of 1000 cycles or more, and 210 ° C to 230 ° C as high temperature characteristics.
Each is required to satisfy a bonding strength of 1 to ² kgf / mm ² at 150 ° C. Here, a general object of the present invention is to provide a high-temperature solder having not only excellent high-temperature characteristics but also excellent thermal fatigue characteristics. A more specific object of the present invention is to have high-temperature characteristics required for electronic devices mounted on satellites, automobiles, and the like, and further, at -55 ° C.
An object of the present invention is to provide a high-temperature solder having excellent thermal fatigue resistance that can withstand conditions of up to 125 ° C. × 1000 cycles.

[0015]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on improving the high-temperature characteristics and the thermal fatigue resistance of high-temperature solder containing Sn as a main component. As a result, a small amount of Ag was added to Sn.
Add only Bi and / or add small amounts of Ag, Cu and
It has been found that the addition of only Sb has an excellent effect in improving the above characteristics, and the present invention has been completed. The present invention relates to a high-temperature solder for forming a soldered part having an excellent thermal fatigue resistance, comprising an alloy having a composition of Ag: more than 3.0% and 5.0% or less, Bi: more than 1.2% and 3.0% or less, and the balance of Sn. is there.

Further, the present invention relates to a method for producing Ag: more than 3.0% and 5.0% or less;
This is a high-temperature solder for forming a soldered part having excellent thermal fatigue resistance, comprising an alloy having a composition of Cu: 0.5-1.5%, Sb: 0.5-1.5%, and the balance Sn. These high temperature solders may be used as cream solders.

[0017]

Next, the reason why the composition of the solder alloy is limited as described above in the present invention will be described in detail. First, the reasons for limiting the composition of the Sn-Ag-Bi solder in the present invention will be described. Ag has a remarkable effect on improving the thermal fatigue resistance, but if its content is less than 3.0%, the effect of improving the thermal fatigue resistance is not sufficient, while if it exceeds 5.0%, the liquidus temperature increases. Soldering must also be performed at a high temperature, which causes thermal damage to electronic components and printed circuit boards. Therefore, the Ag content is limited to more than 3.0% and 5.0% or less. More preferably, it is not less than 4.0% and not more than 5.0%.

If a small amount of Bi is added to the Sn-based high-temperature solder to which a small amount of Ag is added, the melting point is further reduced and the wettability of the solder is improved, so that the adhesive strength of the solder joint is improved. Bi does not show its effect when added to less than 1.2%, while when it is added more than 3.0%, the brittleness of Bi appears and the elongation is extremely reduced. This results in a decrease in bonding strength, which is inappropriate. Therefore, the amount of added Bi exceeds 1.2%
Limited to 3.0% or less. Preferably, the amount of Bi added is 1.7 to
2.3%.

Next, the reason for limiting the composition of the Sn—Ag—Cu—Sb solder in the present invention will be described. The purpose of addition of Ag and the reason for limiting the amount of addition are the same as in the case of the Sn-Ag-Bi solder alloy.

When a small amount of Cu is added to the Sn-based high-temperature solder to which a small amount of Ag is added, the high-temperature characteristics and the heat-resistant fatigue characteristics are further improved by the synergistic action with Ag. Cu is 0.5%
If the addition is less, the effect will not appear, while if it exceeds 1.5%, the liquidus temperature will rise sharply and, like the large addition of Ag, the soldering temperature will be increased and the electronic parts and printed circuit boards will be damaged thermally. In addition, a large amount of Sn-Cu intermetallic compound is generated and the matrix becomes sandy, which deteriorates the thermal fatigue resistance. Therefore, the added amount of Cu is limited to 0.5% or more and 1.5% or less. Preferably, Cu
The amount added is 0.8-1.3%.

Further, 0.5 to 1.5% of Sb is added for the purpose of further improving the thermal fatigue resistance. When the amount of Sb added is 0.5
When the amount is less than 1.5%, the effect is not exhibited. On the other hand, when the amount is more than 1.5%, similarly to Bi, the deformability is reduced or brittleness occurs, and the thermal fatigue resistance is deteriorated. Therefore, the amount of Sb added is limited to 0.5% or more and 1.5% or less.

As described above, according to the present invention, only by adding a small amount of Ag and Bi with Sn as a main component or by adding a small amount of Ag, Cu and Sb with Sn as a main component, the high temperature of the solder can be obtained. Both properties and thermal fatigue properties can be remarkably improved, and if other metals are added, these properties will be deteriorated. Therefore, other metals do not contain anything other than those mixed as impurities. In one embodiment of the present invention, the solder alloy having the above composition has, for example, an average particle size.
After classifying to about 10 to 75 μm, liquid flux is blended and kneaded to make cream solder.

In the case of the above embodiment of the present invention, the liquid flux is not particularly limited, but RMA flux or residue-free flux is preferably used. As the RMA flux, those having a chlorine content of 0.05% or less are exemplified.
Examples of the residue-free flux include those having 30% or less of solid components such as rosin and activator. Next, the operation and effect of the present invention will be described more specifically with reference to examples.

[0024]

EXAMPLES Each high-temperature solder having an alloy composition shown in Table 1 was prepared, classified into an average particle size of 10 to 75 μm, and kneaded with RMA flux to obtain a solder paste. For each test solder paste prepared in this way,
The solidus temperature, liquidus temperature, thermal fatigue resistance, and high temperature adhesive strength tests were performed, and the tensile strength of the solder alloy was measured. The test results are shown in Table 1 together with the compositions of the solder alloys of Examples and Comparative Examples.

[0025]

[Table 1]

SP: Solidus temperature (° C) LP: Liquidus temperature (° C) HC (Heat resistant fatigue property, cycle): Apply cream solder consisting of powdered high-temperature solder alloy and liquid flux to printed circuit board After mounting various electronic components thereon, the printed circuit board and the electronic components were soldered in a reflow furnace. A thermal shock test was conducted in which the printed circuit board thus soldered was repeatedly placed in an environment of -55 ° C and + 125 ° C for 30 minutes.

HS (high temperature bonding strength, kgf / mm ² ): 1 m thick
Two copper plates with a width of 10 mm and a width of 10 mm are joined with high-temperature solder so that the clearance is 0.05 mm and the joint area is 3 × 10 (mm), and they are pulled in a high-temperature environment of 200 ° C. to measure the joint strength. did. In Table 1, Comparative Example 1: Solder described in JP-A-49-38858 Comparative Example 2: Solder described in JP-A-51-54056 Comparative Example 3: JP-A-58-55193 Comparative Example 4: Solder described in JP-A-63-13689. Comparative Example 5: Solder described in JP-A-61-269998.

As is clear from Table 1, according to the present invention, the melting point is 210-230 ° C., and the bonding strength at 150 ° C.
And high temperature properties is 2 kgf / mm ^2, in the range of -55 ° C. to 125 ° C.
A high-temperature solder forming a soldered portion having a heat fatigue resistance of 1000 cycles or more was obtained.

[0029]

As is apparent from the above description, the high-temperature solder of the present invention is not only excellent in high-temperature properties and tensile strength, but also excellent in heat-resistant fatigue properties, and therefore cannot be repaired. Even when used for soldering satellite electronic devices and automotive electronic devices that may cause serious accidents, cracks do not occur due to thermal fatigue repeatedly applied to electronic devices, and peeling of soldered parts at high temperatures It has an unprecedented superior effect of not occurring.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masataka Nishiura 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Rikiya Kato 405 Yatsukacho, Soka City, Saitama Prefecture Senju Metal Industry Co., Ltd. Inside the business site (72) Inventor Yoshitaka Toyoda 405 Yatsukacho, Soka City, Saitama Prefecture Senju Metal Industry Co., Ltd. Soka Business Site (56) References JP-A-2-34295 (JP, A) JP-A-5-50286 (JP, A) JP-B 39-10877 (JP, B1) JP-B 58-29198 (JP, B2) JP-B 52-7422 (JP, B2) JP-B 51-4193 (JP, B2) WELDING JOURNAL INCLUDING Welding Esearch, 1992, Vol. 71, No. 10, p. 47−49

Claims (2)

(57) [Claims] The solidus temperature is the eutectic temperature of Pb-Sn (1
83 ° C) or higher and a liquidus temperature of 450 ° C or lower
However, the main component is Sn, and the weight%
And a high-temperature solder for forming a soldered part having excellent thermal fatigue resistance, comprising an alloy containing only Ag of more than 3.0% and 5.0% or less and Bi of more than 1.2% and 3.0% or less. Wherein the alloy particles having a composition according to claim 1 Symbol mounting, formed by blending a flux component, cream high temperature solder to form a soldered portion having excellent thermal fatigue resistance.