JPH115189A - Soldering material for package of high density semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a higher fatigue resistance of a solder holding a ball such as a ball grid array or a bump form. SOLUTION: The component of a solder material is at least two of the following three groups; (1) 0.01-10% MA, (at least one of In and Ga), (2) 0.01-8% MB (at least one of Sb and Bi), and (3) 0.01-10% of at least one of Ag and Au, 10-95% Pb, and the balance of Sn (not 0%). The texture of the solder materials MA and MB are substantially dissolved in a Pb phase and a Sn phase under a soldering condition. The secondary phase, which includes or comprises MA and/or MB, mainly exists at the grain boundaries of crystal grains of Pb and Sn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder material, and more particularly, to a solder material used for micro bonding such as ball grid array (BGA), bump bonding, flip chip bonding, and the like. expansion·
The present invention relates to a solder material having a ball or bump shape excellent in fatigue resistance against fatigue caused by repetitive stress caused by shrinkage.

[0002]

2. Description of the Related Art The following method is known as a method for forming a solder bump such as BGA. (A) A method in which a paste is printed on a terminal using a metal mask and then heated and melted. (B) A method of printing a solder paste on a substrate, mounting an LSI package having grid array terminals, and performing reflow. (C) A method in which solder balls are arranged on terminals and heated to form bumps. (D) A method of forming solder balls by plating using a mask such as a resist. (E) Ball bonding method. (F) A method using a solder foil proposed in JP-A-8-197280.

[0003] Since bonding metals such as solder balls formed by these micro-bonding methods, such as copper and nickel, have different coefficients of thermal expansion, distortion occurs on the bonding surface when an LSI is used, and fatigue occurs. It is known that it greatly depends on the shape of the fatigue solder bump ("Surface mounting technology" 1997.
3. See page 20). On the other hand, the fatigue of such micro-joining is also considered from the viewpoint of metal materials, and it is considered that cracks generated by repeated plastic deformation expand and lead to fracture (high reliability micro soldering technology, Industrial Research Committee). (Eds .: pages 247 to 268).

[0004] The inventor's view on the thermal fatigue of micro-joined solder metals such as solder balls and bumps (hereinafter abbreviated as “solder balls”) is that, particularly with the growth of crystal grains due to heat generation at the joints, The cracks once generated due to the coarsening of the fatigue-resistant Pb phase rapidly expand in the Pb phase, and each solder ball restrained between the package and the substrate from above and below, Compression strain and thermal expansion strain in the vertical direction are combined, and strains in the opposite direction are combined during cooling, and the main cause is that cracks are generated by repetition of these. Since the coefficient of thermal expansion of the solder is smaller than that of copper or nickel, the solder undergoes compressive strain during heating and conversely tensile strain during cooling at the joint surface. , The interior of the micro-joined solder is exposed to an extremely severe environment.

[0005] Generally, the wettability of a solder alloy is JISZ3
It can be quantitatively measured by the spread test specified in 197. The effect of a single additive element on the spread rate of the eutectic solder is as follows: when the base material to be joined is copper, brass, or mild steel,
Sb, As, Bi, Cd, Cu, P, Zn, etc. have been investigated (technical literature "Effects of impurity elements on wettability of 60% tin-40% lead solder", published by Nippon Tin Center), all of which are remarkable. No significant effects have been identified. For the combination addition, similarly, Al + Sb, As + S
Very limited combinations such as b, Al + Zn + Cd, etc. have been investigated, and no significant effect has been confirmed. On the other hand, the present inventor has confirmed that when elements such as In and Sb are added to the Pb-Sn-based eutectic solder alloy, poor joining to the copper plate easily occurs.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for improving the fatigue resistance of a solder material. As a result, immediately after soldering, the added element to the Pb-Sn alloy is in a solid solution state. After soldering, by finding this as a secondary phase, it is found that fatigue resistance can be improved, and the following solder material having a ball or bump shape such as a ball grid array, a bump joint, and a flip chip joint is used. Devised.

M _A (however, at least one of In and Ga)
Species) 0.01% to 10% (hereinafter percentages are "wt%" unless otherwise specified), M _B (however, Sb, at least one of Bi) 0.01
And at least two of the group consisting of 0.01 to 10% of at least one of Ag and Au, and 10 to 95% of Pb.
And the remainder (excluding 0%) Sn,
M _A is a soldered state, M _B is the state of being substantially dissolved in the Pb phase and Sn phase, the precipitated after soldering including M _A and / or M _B or M _A and / or M _B
A solder material characterized by having a secondary phase consisting mainly of Pb crystal grains and Sn crystal grains at grain boundaries and having excellent fatigue resistance. The solder material further includes at least one of Ag and Au.
Seeds can be contained from 0.01 to 10%.

However, In and Sb added for the purpose of improving fatigue resistance in these solder materials cause a decrease in wettability. If a joining method that causes the above is not adopted, poor joining occurs, so that the fatigue resistance of the solder alloy cannot be sufficiently brought out. Therefore, the present invention also provides a solder material having excellent wettability and fatigue resistance. Each of the above-mentioned elements can be divided in advance into an element group for improving the spread rate of the Pb-Sn solder alloy and an element group for decreasing the spread rate, and the contribution to the improvement (decrease) of the spread rate of each element is represented by weight%. It has been found that the spreading ratio can be improved when the total amount of the former element group is equal to or greater than the total amount of the latter element group. Therefore,
The present invention relates to a Pb-Sn based solder in which Ag and Bi are used.
And the content (% by weight) of the first element for improving the spreading rate is one or more of In and Sb, and the content of the second element for lowering the spreading rate (%). (Wt.%) Or a solder material having excellent wettability characterized by being equal to or greater than the same. Note that Ni and Cu
(Hereinafter referred to as “third element”) has the same effect as the second element with respect to wettability. However, Ni hardly forms an intermetallic compound, while Cu makes it easier to form an intermetallic compound in a soldered state so that it is difficult to realize a substantially solid solution state. Therefore, the third element can be used for adjusting the spread ratio similarly to the second element after the upper limit is limited to 2%.

In the above-mentioned elements, In, Sb and Ag form intermetallic compounds at the crystal grain boundaries, thereby increasing the crystal structure of the solder alloy structure due to the repetitive stress generated during use after soldering. It is a special element that prevents and improves fatigue resistance. Further, other second elements are effective for improving fatigue resistance by using a soldering method (JP-A-3-128192) in which a secondary phase formed by casting is converted into a fine intermetallic compound by processing and appropriate heat treatment. It is. Therefore, it is preferable to add these elements depending on the use and required characteristics of the joined parts, but the wettability is deteriorated, so that the total amount thereof needs to be less than or equal to the first group element.

[0010]

First, the reasons for limiting the composition in the present invention will be described. In the present invention, with respect to the composition of the Pb-Sn basic system, the composition range of 10 to 95% of Pb and the balance of Sn (excluding 0%) is markedly different from the eutectic composition of the binary system of Sn-Pb in this composition range. This is because soldering can be performed at a relatively low temperature without leaving. However, from the viewpoint of solderability, Sn is preferably 2% or more, and Pb is preferably 10 to 90%, particularly preferably 10 to 80%, and more preferably 20 to 60%.
It is. When Pb is 30 to 50%, preferably 30 to 45%, as a eutectic system, Pb is more excellent in solderability and ease of use, and the solder strength can be increased. When the ratio is about 50% to 45 to 60%, cost is emphasized, which is advantageous for applications in which the soldering strength does not need to be very high. When using at high temperature, P
A solder material having a b content of 60% or more, preferably 70 to 95%, can also be used. In particular, when fatigue resistance at high temperatures is required, it is desirable to reduce the amount of Sn and increase the amount of Pb. For example, Sn 3-9%, Pb 80-
90%. In the first invention, M _A , M _B and Ag
(Au) is used as an additive element, and the reason for limiting the content thereof (in the case of adding two types in each group, the total content) will be described below.

The reason for setting the lower limit of the additive element to 0.01% is as follows.
If the amount is less than this, the fatigue resistance cannot be improved by precipitation, which will be described later in detail. If the contents of M _A and M _B are respectively 10% or more and 8% or more, a large amount of additional elements are precipitated in a state before soldering, and the flowability and solderability of the solder deteriorate. Alternatively, the solder surface becomes cloudy, which tends to cause cracks. Then, in the state at the time of soldering, the precipitates segregate macroscopically, and the fatigue starting point at which fatigue occurs in this portion increases. For this reason, due to the excellent fatigue resistance of the secondary phase precipitated from the solid solution state of the additive element after soldering,
Since the effect of protecting the segregated portion from the fatigue starting point becomes insufficient, the fatigue resistance tends to be remarkably reduced. The content of M _A is preferably 5
%, More preferably 3% or less. The content of M _B is preferably 5% or less, more preferably 3% or less.

The upper limits of Ag and / or Au are determined for the same reason. In particular, if the content of Ag exceeds the upper limit of the content, a large intermetallic compound of Ag-Sn is generated, and a large number of sinkholes, pinholes, blowholes, etc. are generated, and the flowability of the solder decreases. In addition, the fatigue resistance is reduced. Ag and Au cannot be expected to improve performance so much even if they are contained in large amounts, and are also expensive elements. Considering solder performance comprehensively including this economical viewpoint, the total amount of Ag and Au is preferably 5% or less, more preferably 3% or less.

The ranges of the individual addition elements of M _A and M _B are preferably 0.01 to 5%, more preferably 0.03%, respectively, of the In content and the Ga content.
To 1%, more preferably 0.05 to 0.9%.
When increasing the content of M _A , it is more preferable to add both In and Ga than to add only one of In and Ga.

The preferred content of Sb in M _B is 0.1.
It is 0.1 to 3%, more preferably 0.03 to 1%, and still more preferably 0.05 to 0.9%. If Sb is 3% or less, the solderability will be better, but if it exceeds 2%, a very small portion may precipitate even during soldering. This precipitation has little effect on the function of the secondary phase that is subsequently deposited, but in order to obtain a more preferable secondary phase, Sb must be added at 2%.
%. Of M _B, preferable content of Bi is 0.01% to 5%, more preferably from 0.03 to 3%,
More preferably, it is 0.05 to 1%. As with Sb, if Bi also exceeds 3.5%, a very small portion may precipitate during soldering.

[0015] As the component range of the individual additive elements of Ag and Au, the preferable content is 0.01 to 5%, more preferably 0.1 to 4%, and further preferably 0.5 to 3%.

Ag and / or Au added to the solder material of the present invention as an optional additive element have the effect of further improving fatigue resistance. If the content (the total amount when two types are added) is less than 0.01%, there is no effect.
If it exceeds 0%, the effect of the secondary phase will be destroyed and the fatigue resistance tends to be reduced. In particular, if Ag exceeds the upper limit of its content, an intermetallic compound having a large Ag-Sn is generated, and the fatigue resistance is reduced. Considering the solder performance comprehensively from the viewpoint of economy, the total amount of Ag and Au is preferably 5% or less, more preferably 3% or less.

Components other than the above are substantially impurities.
Here, Fe, Mn, Mo, Ti, Cd, Zn, As,
Mg, Ca, Ta, Sr, Be, Tl, Ge, and the like may be mixed in small amounts as impurities, but may be contained for known addition purposes within a range that does not impair the effects of the present invention. Of course. However, As, Ni, Mg, C
a, Ta, Ti, Zn, Sr, Be, Tl, Ge and G
Since a improves the spreading ratio, the amount of Ag and In can be increased in accordance with the abundance of these elements. Cu
If not more than 2%, the action of the secondary phase of the present invention is not destroyed, but a crystallized Cu—Sn-based intermetallic compound is easily generated at the time of soldering.

Next, the organizational features of the present invention will be described.
The structure of the solder material of the present invention is a solid solution structure in which the additive element substantially forms a solid solution in the Sn crystal and the Pb crystal at the time of soldering (hereinafter abbreviated as “solid solution structure”. The solder itself usually has a eutectic structure. Since Pb and Sn are not solid-solution structures but Pb and Sn have a slight solid solubility with respect to each other, they also form a solid solution other than the added elements. These are the characteristics of the “solid solution structure” in the present invention. (Note that there is no relationship). The secondary phase formed at the time of soldering may be effective for improving the static strength, but it is in the form of needles and particles with sharp corners, and such sharp parts become notches and become fatigued. One of the features of the present invention is to avoid the formation of a secondary phase at the time of soldering as much as possible and to form a solid solution structure, since it becomes a starting point of fracture. Then, after soldering, a secondary phase is precipitated from the solid solution structure.

In the fatigue behavior of the Pb-Sn solder, the growth phenomenon of crystal grains, particularly the Pb phase, is dominant. This is because when the Sn phase and the Pb phase gradually grow due to the temperature of the use environment and then the Pb phase is preferentially coarsened, the fatigue progresses from the Pb phase, which is relatively weaker than the Sn phase. It is. Therefore, as a means for stopping the particle growth, a structure generated after soldering the secondary phase can suppress the progress of fatigue at the soldered portion.

In conventional solder materials, it has been recognized that crystallized substances such as intermetallic compounds are harmful, and that the amount of added elements should be restricted so as not to exist as much as possible. In general, the solder is exposed to elevated temperatures (up to about 100 ° C.) during use which can lead to grain growth, coalescence, and the like.

When such crystal grains are exposed to a high temperature, Pb
When the number of phase continuations increases, there are no elements that hinder the propagation of cracks, and thus large cracks and the like occur. Of course, in the solder material of the present invention, the initial strength of the solder is considerably increased by solid solution strengthening, so that it does not lead to rapid fatigue fracture, but crystal grains grow even with solid solution strengthening, And under the conditions of high temperature, long time, and repeated compound stress, significant reorganization of crystal grains occurs.
During use for a long time, the effect of deterioration of fatigue resistance due to coarsening of crystal grains becomes more remarkable than the effect of improving fatigue resistance by solid solution strengthening. Therefore, in the solder material of the present invention, the Pb crystal grains 1 during long-term use after soldering are used.
(See FIG. 1) and the presence of a secondary phase 3 such as an intermetallic compound at the grain boundaries of the Sn crystal grains 2 prevents the crystal grains from growing. Here, the growth of the crystal grains and the generation of the secondary phase do not proceed preferentially on one side but occur simultaneously, so that the competition between the coarsening of the crystal grains and the effect of suppressing the grain growth by the secondary phase may occur. Become. The formation of a secondary phase is promoted at such a high temperature as to cause the coarsening of the crystal grains, and the coarsening of the crystal grains is prevented when some secondary phase is generated.
It should be noted that intermetallic compounds or the like that precipitate during use for a long period of time do not have sharp corners, and are in a lump having substantially the same size in any direction.

In the solder material according to the representative embodiment of the present invention, when the magnification is increased to about 10,000 times with a metallurgical microscope, the secondary phase is actually observed. Of course, a fine secondary phase smaller than this exists, but an expensive measuring instrument is separately required for observation. The size of the secondary phase may be smaller if it is fine and present in a large amount. The substantial solid solution state related to this point can be defined as a state in which the number of secondary phases is 0 to several in a normal field of view of a metal microscope of about 1000 times or more.

According to the present invention, the conventional Pb-Sn-Cu
In a system solder material or the like, almost all of the SnCu intermetallic compound is crystallized at a stage before soldering, and at the time of soldering, the crystallized substance is not substantially dissolved in the matrix. Regarding this point, Japanese Patent Application Laid-Open No. 9-1098 relates to the invention in which the surface of a BGA solder ball is coated with Ni.
No. 6 also mentions the formation of a Sn-Cu intermetallic compound. Such an intermetallic compound becomes coarse due to the heat of soldering. When observing the structure after soldering, the coarse SnCu intermetallic compound is randomly present in the crystal grain boundaries and in the grains, and has substantially no solid solution in the matrix. For this reason, it cannot be precipitated after soldering, and Pb
Grain growth phenomenon was observed to the same degree as that of the Pb-Sn eutectic solder, and no coarse grain Cu intermetallic compound had an effect of suppressing the growth of crystal grains.

Similarly, for Pb-Sn-Ag solder, A
Although the g-Sn intermetallic compound is observed, the structure from immediately after soldering until after long-time use shows that the intermetallic compound is present randomly in the crystal grain boundaries and in the grains, and due to heat during use, the intermetallic compound is present. As a result of the solid solution itself, it grows into a coarse crystal with almost no influence on the grain boundaries of the Pb phase and the Sn phase. Also Ag
The -Sn intermetallic compound may move and grow. For this reason, the Ag-Sn intermetallic compound that existed alone in such a form did not have the effect of suppressing the crystal grain growth on the Pb grain growth phenomenon. As described above, the SnCu intermetallic compound found in conventional soldering and the Ag-Sn intermetallic compound alone cannot not only obtain the effect of extending the fatigue life based on the effect of suppressing crystal grain growth, but also increase the hardness. Pb-S
When a composite strain is applied to a region where a coarse intermetallic compound different from n is present, cracks are likely to occur.

On the other hand, the secondary phase of the present invention can substantially form a solid solution in the Pb phase and / or Sn phase at the time of soldering, and precipitates from this solid solution structure by heat after soldering. As a result, the majority can exist as a result at the grain boundaries of the Pb phase and the Sn phase, whereby an effect of suppressing crystal grain growth can be obtained.

The performance required for the secondary phase, which is a feature of the present invention, is summarized as follows. Immediately after soldering, there is a solid solution that is substantially dissolved in the Pb phase and / or Sn phase, and precipitation occurs due to low-temperature heat treatment after soldering or heat during long-term use. To generate. It has a high melting point and is stable at high temperatures. Alternatively, it must be stable to at least the heat during use so that it does not completely re-dissolve in the matrix.
The intermetallic compound, whether it is a stoichiometric compound, a non-stoichiometric compound, or a compound containing a solid solution element, satisfies this requirement. If a metal (solid solution) is more stable than Pb and Sn, it satisfies this requirement like In or the like. The precipitate is fine and dispersible. A secondary phase formed by precipitation in a low-temperature heat treatment after soldering and a secondary phase formed by precipitation during long-term use of a solder joint part satisfy this requirement. Then, when a large number of fine particles are dispersed and precipitated in the solder structure after soldering, they may be easily arranged at crystal grain boundaries. Most of the dispersed secondary phase is necessary to obtain a high grain growth suppression effect that is present at the crystal grain boundary of the matrix phase, but it is not necessary to precipitate at the crystal grain boundary from the beginning. As a result of the stopping effect, it suffices if it exists at the crystal grain boundary.

A specific example of the secondary phase will be described below. (1) M _A M _B-type intermetallic compound; Sb-In, Sb-Ga , Bi-In, Bi-Ga system intermetallic compound. The intermetallic compound is a binary compound that is generated solder material M _A -M _B -Pb-Sn-based composition. Further, the intermetallic _{compound, M A -M B -Pb-Sn} -Ag (A
In the case of the u) -based composition, it is often produced as a binary compound containing no Ag (Au). In any case, the fatigue strength is remarkably increased by heat precipitation after soldering. Thus, the intermetallic compound precipitated by heat after soldering is fine. When suppressing the growth of particles in the matrix, the intermetallic compound may grow to a very small extent, although this is not a problem. The intermetallic compound (1) is more preferable as the secondary phase. This is because, in addition to the function of the secondary phase of the present invention, the secondary phase itself has a high fatigue strength, a high strength at the contact surface between the secondary phase and the Sn phase / Pb phase, and a growth rate of the secondary phase. Is not so large, the precipitation rate or formation rate from the solid solution is not so large, the secondary phase of an appropriate size is formed sequentially from the ultra-fine secondary phase to enhance the particle growth suppression function If the Sn phase and Pb phase grow slightly, the secondary phase also grows slightly, and it is presumed that there is an additional function such as enhancing the effect of suppressing the movement of the Pb phase. .

[0028] _{(2) M B -Ag (Au} ) type intermetallic compound; Sb-Ag, Bi-Ag , Sb-Au, Bi-Au intermetallic compound. The intermetallic _{compound, M B -Pb-Sn-Ag} (Au)
In the system composition, some of the Ag (Au) is a two-component compound produced in conjunction with M _B. Also, M _A -M _B -P
In the b-Sn-Ag (Au) -based composition, the compound of (1) also exists, and the compound of (2) often exists.
Therefore, in this composition, Ag (Au) is (1)
Tendency to bind with M _B than incorporated into a portion of the intermetallic compound is larger. Due to the coexistence of the intermetallic compounds (1) and (2), the fatigue strength tends to be higher than when only the intermetallic compound (1) is formed.

[0029] _{(3) M A -Ag (Au} ) type intermetallic compound: In-Ag, Ga-Ag , In-Au, Ga-Au intermetallic compound. The intermetallic compound, the M _A -Pb-Sn-Ag based composition, part of the Ag is a two-component compound produced in conjunction with M _A. However, the formation tendency of this compound is weaker than that of the intermetallic compound of (2), and the formation of (3) may not be produced even if the intermetallic compound of (2) is formed.
Here, the generation tendency of the intermetallic compound is described in terms of the tendency of the intermetallic compound generated in the solder preferentially in the component content excluding the vicinity of the upper limit and the lower limit of the composition of the present invention. Therefore, when the composition is near the upper or lower limit,
Intermetallic compounds are generated with a different priority than the generation tendency described here. The intermetallic compound of (3) is Ag
It is easily generated when the content of (Au) and / or the content of Sn is high. The size of the intermetallic compound (3) is usually observed at 0.1 to 1 μm.

[0030] _{(4) M B -Sn-Ag} (Au) type intermetallic compound: Sb-Sn-Ag (Au ), Bi-Sn-Ag (Au)
System intermetallic compound. The intermetallic compound, Ag in M _B -Pb-Sn-based composition
(Au) in the composition with the addition of a Ag, and M _B, compound produced by combining some of the Sn matrix, and the Au, and M _B, generates by combining a part of the Sn matrix Compound. The compound is any of those is M _B were dissolved in the ternary compound a is or Sn-Ag (Au) binary compound. The tendency of formation of this intermetallic compound is stronger than (3) and almost equal to (2).

(5) M _A -Sn-Ag (Au) type intermetallic compound: In-Sn-Ag (Au), Ga-Sn-Ag
This corresponds to the (Au) -based intermetallic compound. The intermetallic compound is M _B (4) corresponds to that replaced by M _A.
It is easy to understand if M _B in the above description (4) is replaced with M _A.

[0032] _{(6) M A M B -Ag} (Au) type intermetallic compound: Sb-In-Ag (Au ), Sb-Ga-Ag (A
u), Bi-In-Ag (Au), Bi-Ga-Ag
(Au) -based intermetallic compounds. This intermetallic compound is a compound containing all the added elements.
M _A M _B type (1), there is a case where the generation tendency than M _A -Ag type intermetallic compound weak, Ag content is generated only when very high (2). The reason that this compound has a weak tendency to form is presumed to be that it is unlikely that the reaction between the added elements having a low concentration is more likely to occur than the matrix component, and that it is originally difficult to form due to the complex composition of the compound. . Similarly, a compound having a simple composition as shown in (1) has a high tendency to be formed even with a compound composed of a dilute concentration element.

The above (1) to (6) may be present as a secondary phase in a single form, but may also be present when the types of added elements are increased. As a whole, fatigue resistance tends to be higher when coexisting. In addition, these precipitated secondary phases are converted into S by heat after soldering.
As a result, the majority is present at the crystal grain boundaries of the n phase and the Pb phase.

The proportion of the precipitated secondary phase existing at the crystal grain boundaries is preferably 60% or more. Preferably, 70%
Or more, more preferably 80% or more, and still more preferably 9% or more.
0% or more. The temperature may be 80 to 100 ° C. in the use environment, and when the environment is exposed to the environment for a long time, the existing ratio can be about 60% or more. If low-temperature heat treatment is performed, it can be easily controlled to about 80 to 95%. When not exposed to such a temperature, this low-temperature heat treatment can be combined and improved.

(7) Ag-Sn type intermetallic compound Although this intermetallic compound alone does not increase the fatigue strength as described above, it has a rather strong tendency to form, and Pb-Sn-
Ag-based solder material is also generated. As described above, in the conventional Pb-Sn-Ag solder, when observing the structure from immediately after soldering to after long-time use, the Ag-Sn intermetallic compound is randomly present in the crystal grain boundaries and grains. In addition, the heat during use causes the intermetallic compound itself to form a solid solution again and grows into a coarse crystal with almost no influence on the grain boundaries of the Pb phase and the Sn phase. Further, the Ag-Sn intermetallic compound sometimes grows by migration. For this reason, the Ag-Sn intermetallic compound present alone in such a form has no effect of suppressing the growth of crystal grains against the glowing phenomenon of Pb grains.

However, the fatigue resistance of the solder is further improved when it coexists with the above intermetallic compounds (1) to (6). This is because the above (1) to (6) are based on the effect of suppressing the particle growth of the Sn phase / Pb phase, and when the particles of the Ag—Sn intermetallic compound move and grow, the movement is suppressed by the pinning effect. The above (1) ~
(6) absorbs Ag and forms or precipitates as a new secondary phase and suppresses movement and growth by a kind of buffer effect. By this buffer effect, movement of Sn phase / Pb phase・ The microscopic working range of the pinning effect of the secondary phase, which suppresses the growth, is substantially increased until the precipitate of the Ag—Sn intermetallic compound, whose migration has been suppressed, is re-dissolved in the matrix by heat in the matrix. Although it is only a short time, Sn phase
An action mechanism such as an auxiliary pinning effect on the phase grain growth can be considered. When a large amount of this intermetallic compound is also formed at the time of soldering, Ag is consumed for the formation of (7), which hinders the formation of the secondary phase, or the above (1) to (5).
It is necessary to pay particular attention to the fact that the secondary phase of (6) cannot be complemented even if it precipitates. Further, regarding (7), it was difficult to selectively exist at the crystal grain boundaries of the Sn phase and the Pb phase even in the low-temperature heat treatment.

(8) Al-Sb intermetallic compound This secondary phase is also converted to Sn phase or Pb by heat after soldering.
The result is a form in which the majority exists at the grain boundaries of the phase.
The size of the intermetallic compound is usually 1 to 5 μm.

Next, what kind of intermetallic compound is actually produced will be described first with reference to the Sn-Pb-Sb-In quaternary composition. In this composition, the matrix phase was an Sn phase and a Pb phase, and the secondary phase was the intermetallic compound phase (1). Most of this secondary phase is Sn
Phase / Pb phase exists at the grain boundaries. Next, Sn-P
In the penta-element composition of b-Sb-In-Ag, the matrix phase is a Sn phase and a Pb phase, and there are seven types of intermetallic compounds that may exist as secondary phases (1) to (7). . When the content of Ag is small, a three-phase structure in which only the intermetallic compound of (1) is dispersed as a secondary phase is formed. However, when the content of Ag is increased, Ag becomes one or both of M _A and M _B. And some also react with Sn. Then, depending on the composition to be blended, one or more intermetallic compounds selected from (1) to (6) exist. Of course, when the Ag content is increased, (7) tends to be relatively increased. In (1), M _A and M _B may be added in predetermined amounts or more. On the other hand, when it is desired to particularly generate (2) and (4), it is only necessary to increase M _B and decrease M _A or not to mix them. If you want to generate (3) and (5) in particular, use M
It suffices to not blended or less large number of _A M _B. Particularly when it is desired to generate (4) and (5), if the Pb content is reduced and the remaining Sn content is relatively increased, it is likely to be generated. In addition, solder is an alloy which has a lot of segregation which has not been subjected to heat treatment such as homogenization as originally cast, and each component locally reacts at a temperature of about 100 ° C., which is the maximum operating temperature, in a solder joint part. Because it is a metastable state, secondary phases that are different from those predicted by the equilibrium diagram theory may coexist.

Further, in the solder alloy of the present invention,
Preferably, the composition has a Pb content of 19.8 to 60% by weight and a Sn content of 40 to 80% by weight.
If the content of Pb exceeds 60% and the content of Sn is less than 40%, the structure of Pb is too large to lower the overall strength, and further the melting point becomes too high to deteriorate the solderability. Conversely, when the content of Pb is less than 19.8% and the content of Sn exceeds 80%, the solderability is significantly reduced. The preferred contents of Pb and Sn are 29.8 to 50% and 70% or less, respectively.

Further, when the content of the first element added to the solder alloy is less than 0.1%, the bonding strength determined by the wettability is reduced due to little improvement in the spreading ratio, and when it exceeds 15%. In addition to the high melting point of the solder, which impairs the workability, the thermal effects of the soldering of the electronic components during soldering cannot be ignored, and there is precipitation of a coarse secondary phase due to segregation, which significantly reduces the solder strength. Such problems occur. On the other hand, if the content of the second element is less than 0.05%, the effect of adding the second element is small, and if it exceeds 15%, the wettability and the bonding strength are reduced. As a countermeasure against this, the amount of the first element added can be increased, but this is not preferable because the total amount of the added elements increases and the melting point of the solder increases at a stroke. The preferable addition amount is 0.15 to 5% for the first element,
The element is 0.05-5%.

The preferred component system of the present invention is In-Sb-A
g or In-Sb-Ag-Cu system. In this component system, most of the two elements, In and Sb, are in solid solution immediately after soldering. However, heat during use of the electronic component forms an intermetallic compound with each other or with each element including Sn. Fatigue can be increased. Ag is mainly S
While forming an intermetallic compound with n and In, the bonding of Ag, Sn and In also occurs during the solidification process after soldering. In general, if an intermetallic compound is generated in a molten or semi-molten solder, the flow of the solder becomes difficult, so the spreading rate should decrease. However, as described above, In and Sb reduce the spreading rate, and Ag It was found that the spreading ratio was improved. Therefore, we researched ways to improve the spread rate, and conducted a study to find the relationship between the amount of each additive element and the wettability for measures to ensure the same solderability as eutectic solder without impairing fatigue resistance. The result shown in FIG. 2 was obtained. Further, the content of each additive element is In:
0.05 to 3.0%, Ag; 0.15 to 10.0%, S
b: 0.05 to 1.5% The total amount of other second elements is A
g or less. Further, Cu can be added instead of or together with Sb. In this case, the added amount or the total amount with Sb is 0.05 to
1.5%.

Further, the same test was performed by changing the amounts of Ag, In and Sb, and the result was expressed as Ag (%) / ΔI
n + Sb + Cu + As + Ni + Mg + Ca + Ta + Ti
+ Zr + Sr + Be + Tl + Ge + Ga (%)} is shown on the horizontal axis, and the spread rate is shown on the vertical axis in FIG. Ag from FIG.
Eliminates the adverse effects of Sb and In and improves the spreading ratio; Ag (%) / (Sb + In + Cu + As + Ni + M
g + Ca + Ta + Ti + Zr + Sr + Be + Tl + Ge
When the (+ Ga) (%) ratio is 1.5 or more, a spreading ratio higher than the eutectic composition is obtained; Ag (%) / (Sb + In + Cu +)
As + Ni + Mg + Ca + Ta + Ti + Zr + Sr + B
When the ratio of (e + Tl + Ge + Ga (%)) is 4 or more, the effect is saturated.

In order to maintain the spread ratio as in the case of the eutectic solder, 90% or more is sufficient.
% Is (In + Sb + Cu + As + Ni + Mg + Ca + T
a + Ti + Zr + Sr + Be + Tl + Ge + Ga)
It can be seen that sufficient wettability is ensured by adding at least one time (%). Desirably, it is 1.25 times or more to secure 91% or more. The content of each additive element is as follows: In: 0.05 to 3.0%, Ag;
0.15 to 10.0%, Sb: 0.05 to 1.5% The total amount of other second elements is preferably not more than the Ag amount. Further, Cu can be added instead of or together with Sb. In this case, the added amount or Sb
Is 0.05 to 1.5%.

[0044]

As described above, according to the present invention, the reliability of a highly integrated electronic device can be improved because cracks due to thermal fatigue of solder at a microjoined portion are less likely to occur.

[Brief description of the drawings]

FIG. 1A is a view schematically showing a structure of a solder material of the present invention after soldering, and FIG. 1B is a view schematically showing a state in which the structure has been changed due to thermal strain. It is.

FIG. 2 is a graph showing an effect of a single element added to a eutectic solder on a spreading rate.

FIG. 3 shows the effect of In, Sb, and Ag added to the eutectic solder on the spread rate, and the horizontal axis is Ag / (In + Sb).
FIG.

Claims (8)

[Claims] 1. The method of claim 1 wherein M _A (In, G
at least one) 0.01% to 10% of a, M _B (however, Sb, at least one) from 0.01 to 8%, and the group consisting of at least one 0.01% to 10% of Ag and Au and Bi At least two kinds of Pb and 10 to 95% of Pb
And the remainder (excluding 0%) Sn,
M _A is a soldered state, M _B is the state of being substantially dissolved in the Pb phase and Sn phase, the precipitated after soldering including M _A and / or M _B or M _A and / or M _B
Solder having a ball or bump shape for mounting a high-density semiconductor, characterized by having a secondary phase consisting mainly of Pb crystal grains and Sn crystal grains at grain boundaries and having excellent fatigue resistance. material. 2. The solder material according to claim 1, further comprising 0.01 to 10% by weight of at least one of Ag and Au. 3. The content (% by weight) of a first element composed of one or two of Ag and Bi is the content (% by weight) of a second element composed of one or more of In and Sb. 3. The solder material according to claim 1, wherein the solder material is equal to or greater than the content of the second element. 4. The method according to claim 1, wherein the total amount of Cu and Ni is 2% or less.
Comprising a third element consisting of one or more of the following,
The solder material according to claim 3, wherein the content (% by weight) of the first element is equal to or greater than the total content (% by weight) of the second element and the third element. 5. The Pb content is 19.8 to 60% by weight, and the Sn content is 40 to 80% by weight.
The solder material described. 6. The content of the first element is 0.1 to 15% by weight.
And the total content of the second element and the third element is 0.05
The solder material according to claim 4, wherein the content is from 15% by weight to 15% by weight. 7. The method according to claim 5, wherein the second element is In and Sb.
The solder material described. 8. The method according to claim 3, further comprising P: 0.001 to 0.1%.
The solder material described in the item.