JPH106077A - High strength solder excellent in thermal fatigue - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the thermal fatigue characteristic of parts, such as electrical equipment for vehicle which is always subject to vibration and heat cycle by adding a specific metal of Sb, etc., in an Sn-Pb solder. SOLUTION: This composition is made made of Sn-Pb solder added with, by weight, 0.3 to 1.0% Sb, 0.001 to 0.1% Ga, 0.3 to 3.0% Ag and 0.1 to 0.5% Cu, and/or 0.3 to 3.0 In. Further, the Sn-Pb solder constituting its base body contains 2 to 95% Sn and the remainder is composed of Sb so as to enable soldering at a comparative low temperature. More preferably, it is of the Sn-Pb eutectic crystal solder containing 63% Sn and 37% Pb. In case of soldering by using the solder of this composition, even in a remarkable severe temperature condition of applying a repeating heat balance from minus scores degree to plus hundreds and scores degree, the excellent durability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength solder having excellent thermal fatigue resistance, and more particularly, to use in an environment which is constantly exposed to vibration and is liable to undergo thermal fatigue, such as electrical components for vehicles. The present invention relates to a solder material suitable for use in soldering components to be used, particularly for joining electronic components to a printed circuit board.

[0002]

2. Description of the Related Art Generally, a solder material has two basic elements of Sn-Pb, and in order to improve its properties,
It is known to add various components. For soldered printed circuit boards used in environments that are constantly exposed to vibration, such as electrical components for vehicles, cracks occur inside the solder, causing problems such as operational errors due to poor current flow. doing.

[0003] This is caused by stresses such as compression, pulling, shearing, and twisting from all directions due to thermal cycling caused by raising and lowering the ambient temperature of the operating environment, and mechanical effects caused by vibration of the printed circuit board. By
It is presumed that strong stress is generated on the board and mounted components, and the solder, which is the joining member, takes over the stress, so that the solder is always placed in a state where strong stress is applied, and as a result, it will be broken by fatigue over a long use. Is done.

In order to solve such a problem, Sn-P
It has been proposed to add various elements to b solder. For example, in JP-A-3-32487,
It is disclosed that Sb and In are added.
No. 480 discloses that Sb and Te are added.

[0005]

The above-mentioned solder to which Sb and In are added has a drawback that when a severe thermal shock stress of −several tens degrees C. to + one hundreds degrees C. is repeatedly applied, the solder joint surface is separated. there were. Further, the solder to which Sb and Te are added has a drawback that when the severe thermal shock stress is repeatedly applied, many wrinkles are generated in the solder fillet and the solder joint surface is peeled off.

[0006] Therefore, none of the above-mentioned conventional methods is practically sufficiently satisfactory in terms of a solder material which does not crack for a long period of time under stress under severe temperature conditions. SUMMARY OF THE INVENTION An object of the present invention is to provide a solder material in which cracks do not occur for a long period of time even under severe temperature condition stress in which cracks easily occur.

[0007]

Means for Solving the Problems The present inventors have conducted a series of basic researches to solve the above-mentioned problems, and have found that Sn-Pb
It has been found that a solder obtained by adding a specific amount of Sb, Ga and Ag, and Cu or In to the solder becomes a high-strength solder excellent in thermal fatigue resistance which does not crack even under severe temperature condition stress. The invention has been reached.

That is, according to the present invention, Sn-Pb solder
b 0.3 to 1.0% by weight, Ga 0.001 to 0.1% by weight and Ag 0.3 to 3.0% by weight, and Cu 0.1 to 0.
5% by weight and / or 0.3 to 2.0% by weight of In are added and mixed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The Sn-Pb solder used in the present invention is preferably Sn2 to 95% by weight, with the balance being Pb. This is because in this composition range, soldering at a relatively low temperature becomes possible. In the above composition range, it is particularly preferable to use a Sn-Pb eutectic solder of 63% by weight of Sn and 37% by weight of Pb.

[0010] The Sb of the present invention plays a role of refining the solid solution structure.
The reason for setting the content to 1.0% by weight is that if the content exceeds the upper limit, a compound containing Sb is generated, and if the content is less than the lower limit, the effect of the addition is not exhibited. The amount of Ga added is 0.00
If it exceeds this upper limit, oxides are formed on the surface of the solder, so-called dripping which deteriorates the adhesion to the metal occurs, and the wetting property deteriorates. The fatigue resistance deteriorates.

The amount of Ag added is 0.3 to 3.0% by weight. If the amount exceeds the upper limit, a compound is formed. If the amount is less than the lower limit, the fatigue resistance of the solder deteriorates. The addition amount of Cu is 0.1 to 0.5% by weight.
If the wettability deteriorates, and if the value falls below this lower limit, the fatigue resistance of the solder deteriorates.

The addition amount of In is 0.3 to 2.0% by weight, and if it exceeds this upper limit, the dripping and wetting properties deteriorate,
Below the lower limit, the fatigue resistance of the solder deteriorates. In the present invention, either Cu or In may be added. However, when both Cu and In are used in combination, the fatigue resistance is further improved.

[0013]

Next, the present invention will be further described with reference to examples, but the present invention is not limited to these examples. In Table 1 below, an example of a solder having an alloy composition of the present invention, an experimental solder not belonging to the present invention, and a commercially available solder are listed for comparison, and each solder was subjected to a thermal shock resistance test. Sn-P
b eutectic alloy is male-Sn (purity: 3N) and same Pb
(Purity: 4N) and Sn-37Pb, and the elements shown in the following Table 1 were added thereto in the amounts shown in the following Table 1. In Table 1, crosses indicate elements that are not blended.

[0014]

[Table 1]

As shown in FIG. 1, each of the solders described in Table 1 above was used as a solder bath 1 at 250 ° C. The capacitor 3 having the lead wire 4 penetrated through the paper phenol substrate 2 was immersed in the solder bath 1 and soldered. The flux is a resin-based post flux (Soldax FR)
-206) and washed by an IPA immersion method (without heating). 5a and 5b are solder fillets. Experiments were conducted on three types of capacitor-3, small (A), medium (B) and (large).

In the thermal shock test, the above soldered product was evaluated as -4
After leaving it at 0 ° C. for 30 minutes, it was left at 120 ° C. for 30 minutes, and this was taken as one cycle. The cycle was repeated 200 times and 500 times, and the appearance of the fillets 5a and 5b was changed to macro and S.
The surface condition and the presence or absence of cracks were determined by EM observation. Table 2 shows the results of 200 cycles, and Table 3 shows the results of 500 cycles.

[0017]

[Table 2]

In Table 2, "Evaluation" was performed according to the following criteria. ◎: No crack or deformation in the fillet portion. ：: Partial interface deformation or peeling, but slight. △: Two or more peeling and interfacial deformation. X: Heavy peeling and deformation.

[0019]

[Table 3]

In Table 3, "Evaluation" was performed according to the following criteria. ◎: No crack or deformation at fillet part ○: Some interface deformation △: Some cracks ×: Two or more cracks or interface deformation Remarks in Tables 2 and 3 above The column is an evaluation by macro observation. A SEM image obtained by SEM observation and a photograph obtained by observing a cross section of a fillet obtained by microstructure observation are attached to the property submission form.

As is clear from Table 2 and the SEM image attached to the property submission, after 200 cycles, commercial products (solders with Sb and In added, solders with Sb and Te added and others) and experimental solders Are capacitors A, B, C
Cracks occurred in one or more places of the fillets 5a and 5b, whereas the solder of the present invention (products 1 to 4 of the present invention)
No cracks occurred in any of them.

As is apparent from Table 3 and the SEM image attached to the property submission, after 500 cycles, many cracks and peeling occurred in all of the commercial products and the experimental solders. No solders (products of the present invention 1 to 4) had no crack at all for the capacitor-large (C). In addition, Sb, Ga, Ag, and Cu have
The invention products 2 and 3 to which n is added are all capacitors.
No cracks occurred in any of the fillets 5a and 5b of (A) to (C).

As can be seen from the attached photographs of the cross section of the fillet, the microstructure of the lead wire of the commercial product and the experimental solder is coarsened.
The interface structure is not coarse at all. This is also consistent with the theoretical grounds that cracks occur due to coarsening of the microstructure.

[0024]

According to the present invention, cracks do not occur even under extremely severe temperature conditions of repeated thermal shock of minus several tens degrees to plus one hundred and several tens degrees, so that vibrations can be continuously generated like electric components for vehicles. When used for components subjected to thermal cycling stresses, the fatigue fracture life can be significantly improved, and the reliability of soldered equipment can be improved.

[0025]

[Brief description of the drawings]

FIG. 1 is a sectional view of a test piece subjected to a fatigue resistance test.

Claims (3)

[Claims] 1. The method according to claim 1, wherein the Sn-Pb solder contains Sb 0.3 to 1.0.
Wt%, Ga 0.001-0.1 wt% and Ag0.3
A high-strength solder excellent in heat fatigue resistance, characterized by adding and mixing 0.1 to 0.5% by weight of Cu and / or 0.3 to 2.0% by weight of In. 2. The solder according to claim 1, wherein the Sn-Pb solder is Sn2 to 95% by weight and the balance is Pb. 3. The solder according to claim 1, wherein the solder is used for soldering a component requiring heat-resistant fatigue characteristics.