JP2002321084A - Soldering alloy for joining electronic parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Sn-Sb based-soldering alloy for joining electronic parts, which substantially includes no Pb, and has a high solid phase melting point, and an improved wettability, heat resistance and thermal fatigue characteristic. SOLUTION: The alloy comprises Sb of 11-15 in mass %, at least one of either Ni or Ge of 0.01-1 in mass % and substantially the remainder of Sn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder alloy for joining electronic components, and more particularly to a Sn--Sb-based solder alloy for joining electronic components which is substantially free of lead.

[0002]

2. Description of the Related Art Conventionally, solder alloys containing Pb and Sn as main components have been used as materials for joining electronic parts.
Taking a power transistor as an example of an electronic component, a large current load is applied to the power transistor.
Solder alloys used for connecting power transistors are required to have stress relaxation properties, heat-resistant fatigue properties, and electrical conductivity.

When joining a power transistor, first, a lead frame and a semiconductor chip are joined inside the power transistor (internal joining), and then the power transistor is joined to a substrate (mounting). When the power transistor is mounted on the substrate, reflow is performed at 220 to 230 ° C. by using a eutectic solder alloy (melting point: 183 ° C.) containing 63% by mass of Sn and the balance being Pb.

If the solid phase melting point of the solder alloy used in the internal bonding step is lower than the temperature of the reflow performed in the mounting step, the solder alloy in the power transistor is re-melted when the reflow is performed. As a result, the reliability of bonding between the lead frame and the semiconductor chip is reduced. In order to prevent this re-melting, it is necessary to use a solder alloy having a solid phase melting point equal to or higher than the reflow temperature at the time of mounting in the internal bonding step. Therefore, a solder alloy containing 5% by mass of Sn and the balance of Pb (solid-state melting point 305
C.) and a solder alloy (solid phase melting point: 315 ° C.) containing 3% by mass of Sn and the balance of Pb.

As described above, a solder alloy containing Pb is used as an effective material in a process for joining electronic components, and its reliability has been established.

However, on the other hand, the harmfulness of such a solder alloy containing Pb has been pointed out. That is,
If the solder alloy containing Pb is used in the electronic equipment that has been disposed of, the Pb component contained in the solder alloy gradually dissolves and flows out due to acid rain, penetrates into the soil, and accumulates in crops and the like, It is harmful to humans.

Therefore, as an alternative to the above-mentioned eutectic solder alloy used in the step of joining an electronic component to a substrate, a solder alloy containing Sn as a main component has been studied. It is considered that this solder alloy has a solid-state melting point higher than that of the above-mentioned eutectic solder alloy, and a reflow temperature at the time of mounting also increases to around 250 to 260 ° C. Therefore, a solder alloy used inside an electronic component is required to have a solid phase melting point higher than this reflow temperature.

Conventionally, Sn—Sb-based solder alloys have been studied as Pb-free (Pb-free) solder alloys (hereinafter, “Sn—Sb-based” is substantially free of Pb (Pb-free). Free)). Sn-
The Sb-based solder alloy has a solid phase melting point of 246 ° C. when Sb is 11% by mass or more, and has the highest practical solid phase melting point with a solder alloy containing Sn as a main component.

[0009]

However, the above S
The n-Sb-based solder alloy has a Sb composition ratio of 11% by mass.
When it exceeds, a structure having coarse crystal grains that is crystallized during solidification is obtained. These crystal grains are an intermetallic compound (Sn-Sb compound) composed of Sn and Sb, and have a hard and brittle property. Therefore, when an external load is applied, cracks are generated along the outline (grain boundaries) of the crystal grains. This is problematic in that the heat resistance and heat fatigue properties decrease. In order to avoid a decrease in the reliability of electronic components due to such a problem, a solder alloy having a composition ratio of Sb of 11% by mass or less has been used.
On the other hand, the above Sn-S in which the composition ratio of Sb is 11% by mass or less.
The b-based solder alloy is (1) a solid-state melting point of 246 ° C. or less, and (2) a Sn—Sb-based solder which is a substitute for the eutectic solder alloy (Pb—Sn-based alloy) for mounting on a substrate. When an alloy is used, it is necessary to raise the reflow temperature, so that there is a risk that the bondability inside the electronic component is impaired.

[0010] Further, the Sn-Sb-based solder alloy has a problem that the wettability at the time of joining is poor and the thermal fatigue properties are not sufficient.

An object of the present invention is to provide an Sn-Sb based solder alloy for joining electronic components, which solves the above problems, has a high solid-state melting point, and has improved wettability, heat resistance and thermal fatigue characteristics. .

[0012]

In order to solve the above-mentioned problems, the present invention comprises 11 to 15% by mass of Sb and 0.01 to 1% by mass of at least one of Ni and Ge, with the balance being the balance. It is a solder alloy for joining electronic components substantially made of Sn.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor has developed a Sn-Sb based solder alloy containing 11% by mass or more of Sb (solid-state melting point: 246 ° C.)
It has been found that by adding Ni and Ge to the alloy, the wettability, heat resistance, and thermal fatigue characteristics of the Sn—Sb-based solder alloy can be improved and the bonding reliability can be ensured.

In the solder alloy for joining electronic parts of the present invention, the Sb content is 11 to 15% by mass. When the Sb content is less than 11% by mass, the solid-state melting point is 2 as described above.
When the temperature is lower than 46 ° C., there is a danger that the bondability inside the electronic component is impaired. On the other hand, when the Sb content exceeds 15% by mass, the difference between the liquidus temperature and the solidus temperature becomes 50 ° C. or more, so that the temperature of the molten solder alloy changes from the liquidus temperature to the solidus temperature. By then, the crystal grains of the Sn—Sb compound crystallized become coarse. Therefore, as described above, cracks easily occur in the solder alloy.

By adding Ni to the Sn—Sb-based solder alloy, Sn—Ni compound crystal grains are finely precipitated, so that coarsening of the Sn—Sb compound crystal grains can be suppressed. As a result, the structure of the solder alloy becomes finer than when no Ni is added, and there is an effect that cracks are less likely to occur. In addition, the Sn-Ni compound contributes to improvement of thermal fatigue characteristics, and the melting point of Ni is 1450 ° C, so that the solder alloy is thermally stable. Furthermore, when a lead frame having a Ni metallized chip bonding surface is used for an electronic component such as a power transistor, the wettability of a solder alloy is further improved.

Further, since Ge crystal grains are finely precipitated by adding Ge, coarsening of the Sn—Sb compound crystal grains can be suppressed. In addition, since Ge is more easily oxidized than Sn, addition of Ge to the solder alloy can also suppress a decrease in wettability due to oxidation of Sn.

The content of at least one of Ni and Ge is 0.01 to 1% by mass. When the content of at least one of the above is less than 0.01% by mass, there is no effect of the addition of the at least one. On the other hand, when the amount of at least one of the above is more than 1% by mass, segregation of the Sn—Ni compound and Ge crystal grains increases.

[0018]

[Examples 1 to 18 and Comparative Examples 1 to 5] A Sn—Sb-based solder alloy having the composition of Sn, Sb, Ni, and Ge shown in Table 1 was used. ), S
After joining the i-chip to the Cu lead frame, a heat resistance test was performed. Note that the heat resistance test was performed by applying a voltage of 5 to the joint.
0 V, current 1A, 230-270 ° C
It was held for 0 seconds, and was performed for 5 joints at each temperature.

[Conventional Example 1] A heat resistance test was conducted in the same manner as in Example 1 except that a Pb-Sn-based solder alloy having the composition of Pb and Sn shown in Table 1 was used.

Table 1 shows the above results. In the table, for example, 0
/ 5 indicates that the number of cracks out of the five joints is zero.

The following can be seen from Table 1.

(1) In Examples 1 to 18 (Sn-Sb type) and Conventional Example 1 (Pb-Sn type), 230 to 270 ° C.
No crack was found in any of the five joints at any of the above temperatures.

(2) In Comparative Examples 1 to 5, cracks occurred in 1 to 3 joints out of 5 at a temperature of 250 ° C. or higher or 260 ° C. or higher. Incidentally, in the structure of the joint in Comparative Example 3, the Sn—Sb compound crystal grains were coarse. In the structure of the joint in Comparative Example 5, segregation of Sn—Ni compounds and Ge crystal grains occurred.

[0024]

[Table 1]

[0025]

According to the present invention, it is possible to provide a Sn-Sb-based solder alloy having a high solid-state melting point and improved wettability, heat resistance, and thermal fatigue properties, and therefore has no environmental pollution.
Moreover, the internal joining of the electronic components can be performed with high reliability.

Claims (1)

[Claims] 1. Sb is 11 to 15% by mass, and at least one of Ni and Ge is 0.01 to 1% by mass.
A solder alloy for joining electronic components, the balance including substantially the Sn.