JP2001113387A - Solder alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solder alloy in which cracking is less prone to be generated even in the case of being used for the part applied with thermal stress in an electronic apparatus so as to be applied with a temperature cycle, where cracking progresses in the solder joint part by thermal stress as the lapse of a long time, and, finall, its conduction is made inferior. SOLUTION: This solder alloy excellent in fatigue resistance is obtained by adding, by mass, 0.5 to 3.0% Ag, 0.001 to 0.3% Zn, moreover, 0.1 to 2% Sb, further, 0.05 to 0.5% Cu and/or 0.001 to 0.02% Ni to solder having an Sn-Pb eutectic composition of 60 to 70% 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. More specifically, the CPU is mounted on the printed circuit board.
And solder ball alloys for BGA used when mounting electronic components, and are used for soldering micro-parts of electronic components used in environments where metal fatigue is likely to occur due to repeated stress such as temperature cycles. It concerns a suitable solder alloy.

[0002]

2. Description of the Related Art When mounting electronic components on a printed wiring board or the like, a solder alloy around Sn-Pb eutectic (Sn63-Pb37) is generally widely used, and BGA (Ba
Similar solder components are mainly used in solder balls for (ll Grid Array). In the case of a printed circuit board incorporated in an electronic device or an integrated circuit device substrate using a BGA, the ON / OFF of the device switch causes
It is exposed to a thermal shock cycle environment in which heating and cooling are repeated.

When a solder joint is exposed to a thermal shock cycle environment, a thermal stress is generated due to a difference in thermal expansion coefficient between an electronic component and a printed circuit board. In particular, in micro solder ball connection such as flip chip connection in which an integrated circuit chip is directly mounted on a substrate, since the Si chip element and the mounted printed wiring board are directly connected by solder balls, the difference in thermal expansion coefficient between the silicon chip and the printed wiring board is small. Very large and very large thermal stresses cause cracks in the solder at the flip chip connection, leading to destruction. This is because the thermal stress is concentrated on the joint since the solder material of the joint is weaker in material strength than the other members to be joined.

Conventionally, a solder joint is likely to be broken by thermal stress by using a mounting form design in which a component lead is bent and the thermal stress is relieved by the component, or an electrode pad at the joint is enlarged. That is, measures have been taken such as increasing the amount of solder at the joint and consequently increasing the strength of the joint.

[0005] However, with the recent high-density mounting of electronic components, surface mounting and BGA mounting have been particularly advanced in notebook personal computers, video cameras, cellular phones and the like, and the area of substrate electrode pads has been rapidly reduced. In this situation, the amount of solder at the joint must be reduced. That is,
The strength of the solder joint is reduced. 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. Therefore, demands for higher strength and improved fatigue resistance of the solder material are increasing. Is growing.
In response to the above requirements for solder materials, Sn-
The strength of solder materials has been improved by adding a third element to a Pb-based alloy.

[0006] As a Sn-Pb alloy to which a third element is added, Japanese Patent Application Laid-Open Nos. 1-127192 and 1-1237095 disclose Sb, In, Ag, Cu, Te, Ni and the like. Improves fatigue resistance. In addition to these, various solder alloys have been proposed, but most of them have a Sn—Pb-based alloy containing a third element to add Sn in the solder structure.
The intermetallic compound is precipitated at the grain boundary between the Pb phase and the Pb phase, and the compound suppresses coarsening of crystal grains and functions as a pinning pinning for suppressing plastic deformation, thereby increasing the strength and creep resistance of the alloy. Attempts have been made to improve the properties and fatigue resistance.

[0007]

[0005] Fatigue fracture of solder is caused by the concentration of thermal stress at the connection portion on the solder material. That is, the connection portion has elastic plastic deformation capability and strength enough to maintain the connection, absorbs thermal stress, and reduces stress applied from the connected member. Dispersing and precipitating intermetallic compounds in the solder structure and at the grain boundaries has some effect in suppressing grain boundary slippage and fracture crack propagation, but when a certain amount of intermetallic compounds having brittle and hard properties is present. This impairs the spreadability of the solder and reduces the stress relaxation at the connection. A typical example of the conventional fatigue-resistant solder is a Sn-Pb-based alloy in which a small amount of Ag is added as a third element to improve the fatigue resistance, and a typical example is an Ag ₃ Sn intermetallic compound. Precipitates to suppress grain boundary slip and improve fatigue resistance. However, Sn-
When a small amount of Ag is added as a third element to a Pb-based alloy,
Although the strength is increased by about 20% as compared with the eutectic composition of the Sn-Pb alloy (Sn63-Pb37), the elongation is about 2%.
It is reduced by 0%, and the overall improvement in fatigue resistance is not so large. That is, the solder having excellent fatigue resistance required for a BGA solder ball alloy or the like used when mounting a CPU or an electronic component on a printed wiring board is defined as strength for holding the mounted component, thermal stress and the like. This is a solder alloy having spreadability for alleviating the cracking, and a Sn-Pb-based solder alloy satisfying such strength and spreadability has not been found.

[0008]

Means for Solving the Problems The present inventors have proposed a conventional S
We have worked diligently to improve the fatigue strength of solder alloys, in which a small amount of Ag was added as a third element to the n-Pb alloy to improve fatigue resistance. As a result of searching for a means for improving
The inventors have found that an alloy in which Zn and Ag are simultaneously added to an n-Pb-based alloy improves fatigue resistance, and completed the present invention.

[0009] The present invention provides a method for producing a steel sheet, comprising: 60 to 70% by mass of Sn;
A solder alloy comprising 0.5 to 3.0% by mass, 0.001 to 0.3% by mass of Zn, the balance Pb and unavoidable impurities, or 60 to 70% by mass of Sn;
Ag is 0.5 to 3.0% by mass, Zn is 0.001 to 0.3% by mass, Sb is 0.1 to 2% by mass, and the balance is Pb and unavoidable impurities. Mass%, Ag 0.5-3.0 mass%, Zn 0.001-0.3 mass%, Sb 0.1-2
It is a solder alloy characterized by being composed of 0.05% to 0.5% by mass of Cu and / or 0.001% to 0.02% by mass of Ni, with the balance being Pb and unavoidable impurities.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The solder alloy of the present invention takes into account the lack of ductility, which is inversely proportional to the strength improvement, which is a weak point of the conventional fatigue-resistant solder in which an intermetallic compound is precipitated in a solidified structure of solder. It was done. In other words, it melts uniformly in the liquid state, does not excessively precipitate intermetallic compounds in the solidified structure in the solid state, and has sufficient strength for the solder alloy itself to hold the mounted parts with a small amount of solder. And the ductility for relaxing thermal stress etc. is Sn-
This is a solder alloy having excellent ductility which is equal to or higher than the eutectic composition of a Pb-based alloy and has excellent fatigue resistance.

The feature of the present invention is that Sn—Pb alloy
Alloy with simultaneous addition of n and Ag, Z to Sn-Pb alloy
Alloy with simultaneous addition of n, Ag and Sb, or Sn-Pb
As can be seen from the alloy in which Zn, Ag, Sb, and Cu are simultaneously added to the base alloy, by adding a small amount of Zn together with Ag, the strength can be increased without impairing the previously lacking ductility and comprehensively. The point is that the fatigue resistance is improved. The reason for defining the solder alloy component composition in the present invention will be described below.

When Sn is alloyed with Pb, the eutectic point (Sn
Eutectic temperature (183 mass%) at which the melting point is lowest
° C). In order for the solder alloy of the present invention to be a component suitable for bonding with a BGA solder ball or the like used when mounting a CPU or an electronic component on a printed wiring board, S
n needs to be 60 to 70% by mass.

When Ag is added to a Sn—Pb solder alloy, an intermetallic compound such as Ag ₃ Sn is finely precipitated at a crystal grain boundary or the like at the time of solder solidification, thereby suppressing grain boundary slip and the like and suppressing the progress of fatigue fracture. effective. Addition of less than 0.5% by mass in the Sn-Pb solder alloy does not show remarkable improvement in fatigue resistance, and addition of 3% by mass or more raises the liquidus temperature and increases the printed wiring board. It is not suitable for BGA solder used when mounting CPUs and electronic components.

[0014] A solder alloy obtained by simply adding Ag to Sn-Pb does not result in a solder having both strength and ductility, but by simultaneously adding Zn thereto, a solder having both properties can be obtained. be able to.

[0015] Zn is a harmful element because it generally impairs the finished appearance due to a decrease in the fluidity of the solder and the formation of an oxide film, but Zn has been found to behave differently when added in combination with Ag. That is, in the Sn—Pb solder alloy, Zn does not form a solid solution with Pb but forms a solid solution with the Sn phase to improve the mechanical strength by refining crystal grains and strengthening the solid solution. It acts as a precipitation nucleus of an intermetallic compound and has the effect of dispersing and precipitating the intermetallic compound to improve the ductility of the solder alloy, that is, the fatigue resistance. When Zn is added in an amount of less than 0.001% by mass, the effect is not exhibited. On the other hand, when Zn is added in an amount of 0.3% by mass or more, the fluidity of the solder decreases and the solderability is impaired. Therefore, the Zn content of the present invention is 0.001 to 0.3% by mass. Further, without impairing the solderability, a desirable Zn content for improving ductility by simultaneous addition with Ag is 0.002-0.05.
% By mass.

When Sb is further added to the above alloy composition,
It is effective for improving mechanical properties such as tensile strength and low-temperature fracture toughness, but when the amount is large, the wettability of the solder becomes poor. If the amount of Sb is less than 0.1% by mass in the Sn-Pb solder alloy, no improvement in mechanical properties and low-temperature fracture toughness is observed, while if the amount of Sb is more than 2% by mass, wettability deteriorates and solderability becomes poor. Is inhibited.

In the present invention, when further improvement in component holding strength and creep resistance at a solder joint is required,
Cu and Ni may be added simultaneously or separately.

At this time, Cu refines the crystal in the Sn—Pb solder alloy and improves the mechanical strength. However, if Cu is excessively added to the Sn—Pb solder alloy, the melting point increases. Cu is not effective in improving mechanical strength and fatigue resistance in an Sn-Pb solder alloy at an addition amount of less than 0.05% by mass.
If Cu is added in an amount of not less than mass%, the liquidus temperature rises sharply and becomes unsuitable for BGA solder used when mounting CPUs and electronic components on a printed wiring board.

At that time, Ni is dissolved in Pb in the Sn—Pb solder alloy to improve the mechanical strength. However, the solid solubility limit of Ni to Pb at room temperature is about 0.02% by mass, and Ni exceeds the solid solubility limit.
Is added, the Sn-Ni intermetallic compound precipitates and the ductility of the alloy is impaired.
0.02% by weight is appropriate.

In the solder alloy of the present invention, JIS-Z3
Other ingredients as defined in Class A of 282, Bi:
0.05 or less, Fe: 0.03 or less, Al: 0.005
Hereinafter, even if As: 0.03 or less and Cd: 0.005 or less are mixed as unavoidable elements, the characteristics are not affected. Other elements may be contained as long as they do not affect the properties of the alloy of the present invention.

The liquidus temperature of the solder alloy of the present invention is almost the same as that of the Sn-Pb eutectic solder, even though a high melting point metal is added.
Not only suitable for BGA solder used when mounting electronic components and electronic components, but also suitable for all soldering such as dip soldering, reflow soldering, ironing, etc., with excellent mechanical strength and fatigue resistance Solder alloy.

It is to be noted that a solder ball having a solder alloy component of the present invention is a preferred embodiment as a micro solder ball used for a BGA or the like.

[0023]

EXAMPLE Solder alloys shown in Table 1 were prepared, and for each of them, the following Si chip parts and a substrate were soldered, and these were flip-chip connected to obtain test pieces. In the test, a temperature cycle thermal shock test was performed, and the fatigue resistance was evaluated from the breaking rate of the soldered joint (64 points) after 400 cycles. In this evaluation method, the evaluation solder alloy was made by flip chip bonding a ball with a diameter of 300 μm of the evaluation solder alloy to a Si chip and a glass epoxy resin substrate with a large coefficient of thermal expansion. This is a very severe fatigue property evaluation method suitable for evaluation.

[0024]

[Table 1]

[0025] The Si chip part is φ20 on the Si chip.
64 0 μm electrode lands are arranged around the periphery, and the pitch interval is 0.3 mm. The printed circuit board is a glass epoxy resin substrate with single-sided wiring, placed in the same way as a Si chip,
These were flip-chip connected with a ball of φ300 μm of the solder alloy of the present invention.

The temperature cycle condition is -40 ° C. (30 minutes)
＋ １ + 125 ° C. (30 minutes).

The results of the evaluation are shown in Table 1 below. From Table 1, it was found that all of the examples of the present invention had remarkably small breaking rates and were excellent in fatigue resistance as compared with conventional solder alloys.

[0028]

As described above, the solder alloy of the present invention not only has excellent fatigue resistance, but also has excellent strength and spreadability of the solder itself. It is particularly suitable for BGA solder used when mounting components. Furthermore, the liquidus temperature is almost the same as that of Sn-Pb eutectic solder, and it has many features that it can be used for all existing soldering such as dip soldering, reflow soldering, and ironing.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masamoto Tanaka 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division (72) Inventor Michio Endo 20-1 Shintomi, Futtsu City Nippon Steel Corporation (72) Inventor Shinichi Terashima 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Headquarters (72) Inventor Eiji Hashino 20-1 Shintomi, Futtsu City Nippon Steel Corporation (72) Inventor Kohei Tatsumi 20-1 Shintomi, Futtsu-shi Nippon Steel Corporation Technology Development Headquarters (72) Inventor Masami Fujishima 158-1, Sayamagahara, Iruma-shi, Saitama Nippon Steel Corporation Inside the Micro Metal (72) Inventor Takashi Nakamori 158-1 Sayamagahara, Iruma City, Saitama Prefecture Inside the Nippon Steel Micro Metal Co., Ltd. Nippon Filler Metals Co., Ltd. (72) Inventor Tadashi Sato 487 Motomachi, Sekijuku-cho, Higashi-Katsushika-gun, Chiba Prefecture F-Term in Nippon Filler Metals Co., Ltd. 5E319 BB04 BB08

Claims (3)

[Claims] 1. 60 to 70 mass% of Sn, 0.5 to Ag
3.0% by mass, Zn 0.001 to 0.3% by mass, balance P
b. A solder alloy comprising b and unavoidable impurities. 2. The solder alloy according to claim 1, further comprising 0.1 to 2% by mass of Sb. 3. The solder alloy composition according to claim 1, further comprising 0.05 to 0.5% by mass of Cu and / or 0.001 to 0.02% by mass of Ni. Solder alloy.