JP2002239780A - Solder alloy, solder ball and electronic member having solder bump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a lead-free solder alloy which has excellent joining reliability and falling impact resistance without using so Ag (<=2 mass%), and can be used as a solder bump of an electronic member, to provide a solder ball having the composition, and to provide an electronic member having the solder bump having the composition. SOLUTION: The lead-free solder alloy has a composition containing, by mass, 1.0 to 2.0% Ag and 0.3 to 1.5% Cu, and the balance Sn with inevitable impurities. The solder alloy further contains one or more kinds selected from 0.005 to 1.5% Sb, 0.05 to 1.5% Zn, 0.05 to 1.5% Ni and 0.005 to 0.5% Fe, and in which the total content of Sb, Zn, Ni and Fe is <=1.5%. The concentration of O is <=10 ppm. The lead-free solder ball for an electronic member consists of the above solder alloy. The electronic member has a solder bump consisting of the above solder alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead-free solder alloy, and more particularly to a solder alloy and a solder ball suitable for a solder bump of an electrode in an electronic member such as a semiconductor substrate or a printed board. Further, the present invention relates to an electronic member having a solder bump using the solder alloy.

[0002]

2. Description of the Related Art With the recent miniaturization and high-density mounting of electronic components, BGA (ball grid array) and CSP (chip size package) technologies are used to mount electronic components on printed wiring boards and the like. It is supposed to be. In addition, the size of the electrodes used in these technologies is also steadily miniaturized.

In these bondings, first, solder bumps are formed on a large number of electrodes arranged on a semiconductor substrate, an electronic component, a printed board, or the like. The formation of solder bumps on the electrodes on the electronic member is performed by adhering a solder ball to each electrode using the adhesive force of the flux, and then heating the electronic member to a high temperature to reflow the solder balls. The semiconductor substrate and the like and the printed circuit board and the like are joined via the solder bumps. Here, the solder bump refers to a solder formed in a hemispherical shape on a plating on a copper or aluminum wiring electrode.

In an electronic device in which a semiconductor element or an electronic component is mounted on a substrate by the above mounting technology, the temperature rises due to heat generated by the semiconductor element itself when the device is operated, and is cooled when the device is turned off. It is exposed to a thermal cycle of repeated heating and cooling in which the temperature drops.
Further, depending on the use environment of the electronic device, the entire device is exposed to an environment in which high and low temperatures are repeated. When the semiconductor element itself generates heat, a temperature difference is generated between the semiconductor element and the printed board, so that a thermal stress is generated at a joint between the semiconductor element and the printed board. Further, even when the entire device is subjected to a thermal cycle, a thermal stress is similarly generated at a joint between the semiconductor element and the printed board due to a difference in thermal expansion coefficient between the semiconductor element and the printed board. Since the bonding between the semiconductor element and the printed circuit board is performed by the solder electrode, if the solder electrode has low strength and low thermal fatigue strength, the solder electrode portion is broken by thermal stress. Therefore, a solder alloy used for such joining is required to have excellent thermal fatigue resistance.

[0005] With the recent high-density mounting of electronic components, particularly in notebook computers, video cameras, mobile phones, etc., surface mounting and BGA mounting have progressed, and the area of substrate electrode pads has been rapidly reduced. There is a situation where the amount of solder at the site must be reduced. That is, the bonding area of the solder bonding portion has decreased, and the stress applied to the bonding portion has increased. In addition, due to the high functionality and miniaturization due to the high-density mounting, the portability of information transmission equipment has also rapidly advanced. In addition, the area of economic activity has reached the global scale, and such devices have come to be used in feverish deserts and polar highlands under extremely cold conditions, which have never been considered before. Under such circumstances, there is a demand for a solder mounting design that takes into account the fact that the solder joint is exposed to a more severe environment, and thus the demand for improved fatigue resistance of the solder material has been further increased. Fortunately, lead-free solders, especially Sn-Ag-Cu
In the system, P which is conventionally found in Sn-Pb eutectic solder
Since no coarse graining of b occurs, the fatigue resistance is at a practically satisfactory level.

On the other hand, with respect to portable digital products such as mobile phones, it is necessary to assume a situation in which the digital products are accidentally dropped or hit on the floor during use due to the characteristics of use. It is required that the solder joint of the electronic component used has such an impact resistance that it does not break even under such an impact. On the other hand, in the conventional fatigue-resistant solder alloy, the fatigue resistance is improved mainly by increasing the strength of the solder, and as a result, the impact resistance tends to decrease. . In order to improve the impact resistance at the solder joint, it is most effective to use an alloy having excellent ductility as the solder alloy at the joint.

On the other hand, in order to minimize the influence on the environment when discarding a discarded electronic device, a lead-free solder alloy is required for a solder alloy used in the electronic device.

[0008] As a lead-free solder alloy, Sn is used in a binary system.
A composition containing 3.5% of Ag is a eutectic composition, has a relatively low melting point of 221 ° C., and is widely used as a lead-free solder. The thermal fatigue properties are also reasonably good.

Regarding solder alloys used for electronic parts,
As described above, it requires excellent thermal fatigue properties. In JP-A-5-50286, as lead-free solder alloys for electronic devices, Ag 3.0 to 5.0%, Cu 0.5 to
A high temperature solder comprising 3.0% and the balance of Sn and having excellent thermal fatigue resistance is disclosed. Regarding the Ag content,
Although g has a remarkable effect on the improvement of the thermal fatigue resistance, it is stated that if the addition amount is 3.0% or less, the effect of improving the thermal fatigue resistance is not sufficient. The melting point of the proposed solder alloy is around 218 ° C. It has been reported that a Sn-Ag-Cu-based solder alloy has a ternary eutectic composition at 4.7% Ag-1.7% Cu. The composition near the eutectic point by containing 3% or more of Ag is reported. As a result, the melting point has been lowered and the usability as a solder alloy has been realized.

[0010]

SUMMARY OF THE INVENTION In lead-free solder for electronic members, particularly in lead-free solder balls for electronic members,
An important factor in joint reliability, particularly in shock resistance and drop resistance, is the ductility of the solder material. Conventionally, it is known that Sn-Ag eutectic composition, Sn-3.5Ag, and Sn3.5Ag-0.7Cu near the Sn-Ag eutectic composition have excellent ductility. Furthermore, Sn-4.7Ag-1.7Cu, which is a Sn-Ag-Cu ternary eutectic composition, is also known to have excellent ductility. However, since these solder alloys contain Ag, which is expensive in terms of raw materials, in an amount of 3.0% by mass or more, it must be very expensive.

The present invention relates to a lead-free solder alloy, comprising Ag
Solder alloy that does not use much (2% by mass or less), can provide a solder alloy excellent in joining reliability and drop impact resistance at low cost, and can be used for solder bumps of electronic members, and a solder ball of the composition. It is another object of the present invention to provide an electronic member having solder bumps having the above composition.

[0012]

That is, the gist of the present invention is as follows. (1) Ag: 1.0 to 2.0% by mass, Cu: 0.3 to
A lead-free solder alloy containing 1.5% by mass, the balance being Sn and unavoidable impurities. (2) Further, Sb: 0.005 to 1.5% by mass, Zn:
Sb, Zn, Ni, Fe containing one or more of 0.05 to 1.5% by mass, Ni: 0.05 to 1.5% by mass, and Fe: 0.005 to 0.5% by mass. Is 1.
The lead-free solder alloy according to the above (1), wherein the content is 5% by mass or less. (3) The lead-free solder alloy according to (1) or (2), wherein the O concentration is 10 ppm or less. (4) A lead-free solder ball for an electronic member, comprising the solder alloy according to any one of the above (1) to (3). (5) An electronic member having solder bumps, wherein a part or all of the solder bumps are made of the solder alloy according to any one of the above (1) to (3). (6) An electronic member in which a plurality of electronic components are joined by a solder electrode, and a part or all of the solder electrode includes:
An electronic member comprising the solder alloy according to any one of the above (1) to (3).

Hitherto, it has been considered that a lead-free solder alloy for electronic components requires a Ag content of 3% or more.
In the present invention, it has been found that there is an Ag component range in which the elongation of the solder alloy is remarkably improved when the Ag content is around 1.5% by mass. Improved impact performance.

The present invention has been made on the basis of the above-mentioned findings, in which Ag: 1.0 to 2.0% by mass, Cu: 0.3 to
By applying an Sn-based solder alloy composition containing 1.5 mass%, an inexpensive lead-free solder alloy is provided, heat resistance and impact resistance are remarkably improved, and surface properties after reflow are simultaneously achieved. Made it possible.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Conventional Sn solder alloys having an Ag content in the range of 0.5 to 3% by mass and a Cu content in the range of 0.3 to 2.0% by mass are known. Sn-Pb
It has the same ductility as solder alloys and Sn solder alloys, and has better fatigue resistance than these. In the present invention, the Ag content is further increased to 1.0 to 2.0% by mass.
Within this range, the elongation of the solder alloy is significantly improved, and the ductility can be increased. When the Ag content is in the range of 1.0 to 1.7% by mass, the effect of improving elongation can be obtained most remarkably.

When Cu is added to a Sn-Ag solder alloy, the solidus temperature (melting point) decreases up to a Cu content of 1.5% by mass, but when it exceeds this, the solidus temperature rises sharply. I do. Therefore, in the present invention, the upper limit of the Cu content is set to 1.
5 mass%.

In the Sn—Ag alloy, a network of Ag ₃ Sn intermetallic compound is formed in the solidified structure,
Improves solder strength and fatigue properties. In an alloy containing only Sn—Ag, the networks of Ag ₃ Sn intermetallic compounds are not sufficiently connected to each other.
g ₃ becomes dense ring network Sn intermetallic compound, the strength of the solder bump, to improve fatigue properties, it is possible to secure the necessary strength and thermal fatigue resistance for the electronic components. Therefore, in the present invention, the lower limit of the Cu content is set to 0.1.
3% by mass.

The present invention is a Sn-based solder alloy. Sn has the property of transforming at 13.2 ° C. At the time of Sn transformation at a low temperature, the fracture is apt to progress. By further containing 0.005 to 1.5% by mass of Sb in the solder alloy of the present invention, Sn transformation at a low temperature can be suppressed, and the thermal fatigue resistance under cold climate conditions can be further improved. it can.

If the Sb content is less than 0.005% by mass, the effect of suppressing the low-temperature transformation of Sn is not sufficient, so the lower limit is made 0.005% by mass. On the other hand, if the content exceeds 1.5% by mass, the solder surface after reflow cannot be suppressed from being roughened, and the effect of improving the thermal fatigue resistance is reduced. Therefore, the upper limit is set to 1.5% by mass.

By further adding Zn, Ni or Fe to the solder alloy of the present invention, the strength of the solder alloy can be improved.

When the Zn content is less than 0.05% by mass, there is no effect on the strength improvement, and when the Zn content is more than 1.5% by mass, the solder surface after reflow begins to have roughness, and the ductility increases. Starts to decrease, so the component range is 0.05 to
1.5 mass%.

When the Ni content is less than 0.05% by mass, there is no effect on the strength improvement, and when the Ni content exceeds 1.5% by mass, the ductility starts to decrease. To 1.5% by mass. Further, 0.05% by mass
With the above Ni addition, the diffusion of the substrate plating Ni due to the concentration gradient difference is suppressed at the time of joining with the Ni plating electrode substrate,
Growth of an intermetallic compound such as Ni ₃ Sn ₄ can be suppressed.

If the Fe content is less than 0.005% by mass, there is no effect on the strength improvement, and if it exceeds 0.5% by mass, the ductility decreases, the solder surface becomes rough, and the wettability deteriorates. The range is 0.005 to 0.5% by mass.

The solder of the present invention contains Sb, Zn, Ni, Fe
When one or more of these are added, the strength is improved, but one or more of these, or S
When the total content of b, Zn, Ni, and Fe exceeds 1.5% by mass, the ductility of the solder starts to decrease, so that the total content of Sb, Zn, Ni, and Fe is 1.5% by mass. The following is assumed.

When melting and kneading the solder alloy of the present invention, if the melting atmosphere is changed to a non-oxidizing atmosphere and the concentration of dissolved oxygen in the solder alloy is reduced, the strength is improved by about 10%. When the material obtained by melting and kneading this solder alloy in the atmosphere is analyzed by glow discharge mass spectrometry (Gdmass), it is found that
m oxygen is detected. On the other hand, the detected amount of oxygen of a solder alloy melt-kneaded in a non-oxidizing atmosphere such as an argon atmosphere is on the order of several ppm. When the amount of detected oxygen is 10 ppm or less, the shear strength is higher than that in the atmosphere,
The 10% strength was improved. Therefore, in the above (3) of the present invention, the oxygen concentration in the solder alloy is set to 10 ppm or less.

In the electronic member using the solder alloy of the present invention, since the solder electrode has excellent ductility and strength, the electronic member can be excellent in thermal fatigue resistance and impact resistance.

Further, the electronic member manufactured by using the solder ball of the present invention can be an electronic member having excellent thermal fatigue resistance and impact resistance because the solder electrode has excellent ductility and strength.

Further, an electronic member having solder bumps of the above composition can be a good quality electronic member even when a large number of fine and fine solder bumps are formed. In particular, in the case of a fine solder bump in which the length of one side of the solder bump is 0.2 mm or less, a good result which cannot be realized by a solder bump having a conventional composition can be obtained. An electronic member in which a plurality of electronic components are joined by a solder electrode having the above composition has an excellent feature that the solder electrode has extremely good thermal fatigue resistance and impact resistance.

[0029]

EXAMPLES Solder alloys having the components shown in Table 1 were prepared, and their mechanical properties were evaluated. Examples 1 to 11 are examples of the present invention, and Comparative Example 1 is such that Ag is equal to or less than the lower limit of the present invention,
In Comparative Example 2, Ag is equal to or more than the upper limit of the present invention, Comparative Example 3 is a conventional expensive 3.5Ag lead-free solder alloy, and Comparative Example 4 has 1.5% by mass of the total addition of Sb, Zn, and Ni. Beyond.

[0030]

[Table 1]

Regarding the ductility and strength characteristics of the solder alloy,
The ductility (%) and the strength (MPa) were evaluated, and the strength (M
Pa) × ductility (%) was calculated. Strength x ductility is 1500
In the above case, the impact resistance was evaluated as “○” as being stable and excellent, and when the strength × ductility was 1300 to 1500, it was evaluated as “△” as being excellent in impact resistance, and the strength × ductility was evaluated. Is less than 1300 was evaluated as "x".

Each of the inventive examples 1 to 11 has good strength.
Achieved ductility results. As is clear from the comparison between Example 4 and Example 6, even if the components other than oxygen are the same, A
Since the oxygen concentration of the Example 6 melt-kneaded in the non-oxidizing atmosphere of the r atmosphere is 5 ppm, the strength is improved by about 10% as compared with the Example 4 melt-kneaded in the oxidizing atmosphere and the oxygen concentration is 16 ppm. ing.

In Comparative Example 1, the Ag content was too low.
Is too high, and in Comparative Example 4, since the total addition of Sb, Zn, and Ni exceeds 1.5% by mass, the ductility decreases, and as a result, the value of strength × ductility becomes less than 1300, Sufficient impact resistance was not obtained.

In order to evaluate the drop impact resistance of the solder alloy, a solder ball for connecting electronic members having a diameter of 300 μm was prepared based on the alloy of the present invention. Each of the following Si chip components and a substrate was soldered (240 balls) and flip-chip connected to obtain a test piece. In the drop impact test, the flip-chip-connected impact test piece was fixed to a metal plate with screws and dropped from a height of 50 cm. After dropping, all solder joints (64 points) around the chip with the largest impact were evaluated for electrical continuity. When a solder joint with no continuity occurred even at one point, it was broken. The impact properties were evaluated. An average drop impact resistance of 40 or more was evaluated as “○” because the drop impact resistance was particularly excellent, and the average drop impact resistance was 3
0 to 40 times were evaluated as “Excellent” as being excellent, and the average number of drop-resistant impacts less than 30 times was evaluated as “X”, and the results are shown in Table 1. Examples 1 to 11, which are examples of the present invention, all exhibited good drop impact resistance.

The Si chip component used in the drop strength test has electrode lands of φ200 μm on the Si chip for a total of two.
There are 40 arrangements, 64 arrangements around the outermost contour. The pitch interval is 0.3 mm. The printed board is a single-sided wiring glass epoxy resin board, which is arranged in the same manner as a Si chip, and is made of φ3 of the solder alloy of the present invention.
Flip chip connection was made with a 00 μm ball.

Examples 1 to 11 of the present invention and Comparative Example 3
Compared with a 5Ag solder alloy, the present invention can provide an inexpensive solder alloy because the content of Ag is small, and furthermore has good impact resistance and drop impact resistance equivalent to or higher than that of Comparative Example 3. I was able to get the sex.

[0037]

By using the lead-free solder alloy having the composition of the present invention, it is possible to provide the lead-free solder alloy at a lower cost as compared with the conventional lead-free solder alloy, and at the same time, to obtain extremely excellent thermal fatigue resistance and impact resistance. Could be realized.

A solder bump can be formed by using a solder ball having the composition of the present invention. Further, the electronic member formed with the solder bump of the composition of the present invention and the electronic member joined between electronic components with the solder electrode of the present invention have an effect that the electrode has excellent heat fatigue properties and impact resistance. It is.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H05K 3/34 512 H05K 3/34 512C (72) Inventor Kohei Tatsumi 20-1 Shintomi, Futtsu Nippon Steel Corporation F-term (reference) in Surgery Development Division 5E319 AA03 AC01 AC16 BB01 BB04 BB08 CC33 CD04 CD26 GG03 GG20

Claims (6)

[Claims] 1. Ag: 1.0 to 2.0% by mass, Cu:
A lead-free solder alloy containing 0.3 to 1.5% by mass, the balance being Sn and unavoidable impurities. 2. Sb: 0.005 to 1.5% by mass,
Zn: 0.05-1.5% by mass, Ni: 0.05-1.
5 mass%, Fe: one or more of 0.005 to 0.5 mass%, and the total content of Sb, Zn, Ni, and Fe is 1.5 mass% or less. The lead-free solder alloy according to claim 1. 3. The lead-free solder alloy according to claim 1, wherein the O concentration is 10 ppm or less. 4. A lead-free solder ball for an electronic member, comprising the solder alloy according to claim 1. 5. An electronic member having solder bumps, wherein a part or all of the solder bumps are provided.
An electronic member comprising the solder alloy according to any one of the above. 6. An electronic member in which a plurality of electronic components are joined by a solder electrode, wherein a part or all of the solder electrode is made of the solder alloy according to any one of claims 1 to 3. Electronic member.