JPH03128192A - Soldering method - Google Patents

Abstract

PURPOSE:To improve the reliability of a soldered part by working a cast alloy formed by adding Ag, etc., to essential components of Pb and Sn to a blank material of the form adapted to soldering, disposing this material in the parts to be joined, melting the material and cooling the same in such a manner so as not to solution heat the secondary phase. CONSTITUTION:The alloy, which consists essentially of the Pb and Sn and contains >=1 kinds of Ag, Au, As, Bi, Cu, Ni, In, Ca, Mg, Te, Ti, Zn, Sr, Be, Sb, Bi, Pd, Te, and Tl, at the ratio at which the secondary phase is formed in soldering and at <=30%, is cast and the secondary phase after the casting by the additive elements is parted to work the blank material to the form suitable for soldering. The blank material for soldering is then disposed in the parts to be joined and is melted, then the melt is cooled so as not to solution heat the secondary phase. The reliability of the soldering to be operated under the server conditions of low and high temps. is improved in this way.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a soldering method, and more specifically, it relates to a soldering method for soldering, and more specifically, for soldering, such as electrical components for automobiles, which are constantly exposed to vibration and easily fatigued. The present invention relates to soldering parts and a soldering method suitable for soldering parts used in the environment, particularly for joining electronic parts to printed circuit boards.

(Prior Art) Generally, solder materials have a 5n-Pb binary system as a basic component, and it is known that various components are added to improve the properties.

Japanese Patent Publication No. 40-25885 discloses that copper, silver, nickel, etc. are added to the solder material in order to prevent the copper of the tip of an electric iron for soldering from melting into the solder and damaging the solder. do. It is explained that its anti-wear effect is due to fine and uniform distribution of copper in the solder using silver and nickel.

Japanese Patent Publication No. 45-2093 discloses that the corrosion resistance of solder at the soldered joint with an aluminum alloy is improved by adding Ag or sb, and the fluidity and workability of the solder material are improved by C.
It is disclosed that this can be improved by adding d.

In particular, prior art techniques intended to improve solder materials used in integrated circuits, printed circuit boards, etc. include the following.

Japanese Patent Publication No. 52-30377 discloses the simultaneous addition of Cu and Ag in order to prevent thin copper wires to be soldered from being melted by solder, being damaged by melting, or having a decrease in strength. Cu is used to suppress the solder from eating away the soldering material, while the melting point lowering effect of Ag prevents the melting point of the solder from increasing due to the addition of Cu, which makes the soldering material easier to melt. It is explained that there is an effect of simultaneous addition of and Ag.

JP-A No. 56-144893 eliminates the drawback that silver in the silver lead wire of a ceramic capacitor diffuses into the solder and deteriorates the characteristics of the capacitor or peels off the silver surface, and also enables high-speed soldering. For this purpose, we propose a Sn-3Sn-3b-A solder material.

JP-A-59-70490 discloses Sb1 to 15%-Sn (
In) 1-65%-pb system and Sb-Ag-5n (
In)-Pb based components are proposed.

JP-A-63-313689 discloses Pb62-72%,
The basic composition is 5n28-38%, and this includes Cub, 05
%~1.0%, SbO, 05~1.0%, In0.
05-1. 0%, Cd0. 05-1.0%, Fe
We propose a solder alloy composition characterized by adding one or more types of d.05% to 1.0% to prevent bridging between lead terminals.

(Problem to be Solved by the Invention) Regarding the characteristics of solder materials used for soldering integrated circuits and electronic components mounted on printed circuit boards, in recent years, it has been found that A problem that is attracting attention is that cracks occur in the battery, causing malfunctions due to poor electrical conduction. The reason for this is that stress is generated in the board and mounted components due to periodic changes in the operating temperature, and the solder joint, which is the joining material, carries this stress, so the solder is always under stress, and the solder remains under stress for a long time. It is presumed that fatigue failure will occur after long periods of use. Furthermore, thermal effects such as the rise in temperature of some parts of the solder due to energization, heat generation of electronic components, and even mechanical effects such as vibration of the printed circuit board are believed to accelerate fatigue failure during long-term use. Conceivable. It has become clear that the 5n-Pb binary solder material having the basic composition has a problem in terms of fatigue resistance when used in an environment exposed to long-term thermal and mechanical stress as described above. However, conventionally, Pb-3n
Although it is said that fatigue resistance is improved by adding Cu or Ni to binary alloys, no research has been conducted from the perspective of improving fatigue resistance in an environment where solder is exposed.

(Means for Solving the Problems) As a result of intensive research into methods for improving the fatigue resistance of solder materials, the inventors of the present invention have found that by simultaneously adding In and sb (further adding Ag), these materials can be improved immediately after soldering. We discovered that it is effective to dissolve additive elements in solid solution and precipitate these elements during long-term use of solder parts, and filed a patent application on September 14, 1999 (Patent Application No. 1999). 2388
No. 37). However, some elements are difficult to form into a solid solution immediately after soldering, and it has become necessary to find a means to improve the fatigue resistance of solders containing these elements.

The present invention was made against this background, and The following first to third steps; The main components are pb and Sn, and Ag and Au.

As, Bi, Cu, Ni, In, Ca, Mg.

Te, Ti, Zn, Sr, Be, Sb, Bi.

An alloy containing one or more additive elements of Pd, Te, and Tβ in an amount greater than or equal to the amount at which a secondary phase is generated in the soldering state, but less than 30%, is cast, and (a) the additive element produces a raw acid after casting. (b) Heat treatment is performed to dissolve the secondary phase, which has been acidified by the above-mentioned additive elements after casting, into a solid solution during material processing, or (c) the secondary phase is dissolved into a supersaturated solid solution. The cast alloy is made into a solder material in a form suitable for soldering so as to satisfy any one of conditions (a), (b), and (c), which substantially maintains the solid solution state of the additive elements. a first step of processing the material to be bonded; a second step of placing the solder material on the part to be joined; melting the solder material placed in the part to be joined; When processing,
When processing the material under the conditions (b) or (c) so as not to form a solid solution of the secondary phase, the third step includes cooling so as to form a secondary phase of the additive element. This is a soldering method characterized by the following.

(Example) Hereinafter, the configuration of the present invention will be explained in detail.

The solder used in the present invention is PB like normal solder.
The main components are Sn and Sn. In particular, Pb10-9
In the composition range of less than 5% Sn and the remaining Sn (however, not 0%), the composition does not deviate significantly from the eutectic composition of the 5n-Pb binary system, making it possible to solder at a relatively low temperature.

A g + which is an additive element used in the present invention
A u + A s + B l l Cu * N
i + I n +Ca, Mg, Te, Ti, Zn
, Sr., Be.

One or more of Sb, Bi, Pd, Te, and TJ2 forms a secondary phase of an intermetallic compound or a single element in a soldered state. These additive elements tend to form crystallized intermetallic compounds such as those described below in the soldered state.

(1) Ag: CaAg, MgxAg, Agt
Te, SrAg, TiAg(2)Au: Au
Alt, AuPbx, AuSn, AuTe
*, AuZn.

eAu (3) As: InAs, 5nAs (4) Cu:
CuxSb, Cu5Sn.

(5) In: InNi, InTe, InC
u(6)Pb: PbPd, PbTe, PbT
1(7)Sn: 5nTe, 5nTi, AgS
n These intermetallic compounds that crystallize in the soldered state generally become notches and tend to become starting points for cracks caused by fatigue. Therefore, in the present invention, the notch effect is suppressed by making these crystallized substances as fine as possible. It is intended to reduce In other words, these crystallized substances are Pb, which is a low melting point alloy.
- Various forms peculiar to high melting point intermetallic compounds or simple substances crystallized in the 3n matrix, i.e., thread-like, flake-like, or shapes with V-shaped or U-shaped edges (these shapes are not used in the present invention). This needle-like shape does not change even with miniaturization, and the crystallized substances are only divided, so although notches due to the crystallized substances exist, solder alloys generally have a large elongation. (approximately 50%), the inventors believed that notches of small size would be less harmful because materials with high elongation are generally less sensitive to small notches. moreover,
The idea was that by uniformly dispersing fine secondary phases, it would be possible to prevent the progression of a series of processes from crystal grain coarsening to crack generation. For this, the secondary phase is 100
It is desirable that there be 10 or more, preferably 50 or more, more preferably 300 or more in a μm square.

In order to obtain the effect of the secondary phase described above, it is necessary that the additive element be present in an amount greater than the solid solubility limit. The amount is s
b etc. are 8% or more, and N1 etc. are 3% or more. on the other hand,
The amount of added elements (total amount if two or more types are added) is 30%
Exceeding this is not preferable because the basic properties of the solder, such as low melting point and solderability, deteriorate.

In the first step of the present invention, an alloy having the above-mentioned composition is cast into an arbitrary form such as an ingot, a base metal, or a plate. below,
An example in which this casting is performed as a plate will be explained. The thickness of the plate is not particularly limited as long as industrial casting is possible. Intermetallic compounds and elemental elements are crystallized in the cast plate more coarsely than in normal solder joints. This cast plate is 4
Rolling is carried out using a rolling mill suitable for producing thin sheets of ~6 high, and if necessary, intermediate annealing is performed to break up coarse intermetallic compounds until notch insensitivity and uniform dispersion effect are obtained, preferably 10 to 100 μm. The solder material is rolled into a foil-like solder material with a thickness of . Here, if the thickness of the foil is thinner than 10 μm, the soldering work to be performed later will be difficult;
When it is thicker than μm, crystallized substances such as intermetallic compounds are insufficiently separated. Further, in the present invention, the plate can be obtained by a roll quenching method (a method of injecting molten metal onto a rotating cooling roll), which has been used in recent years to obtain ultra-quenched materials. In this case, the necessary thickness of the solder material can be obtained, and at the same time, most of the additive elements are dissolved in supersaturated solid solution, and a part becomes an ultrafine secondary phase having notch insensitivity.

If necessary, when the roll-quenched plate is further rolled, heat generation due to heating or large reduction rolling must be avoided so that precipitation of solid solution elements does not substantially occur during rolling.

Further, in the present invention, when a rolled plate obtained by rolling an ingot or the like contains a secondary phase, a method may be adopted in which the plate is subjected to solution treatment to dissolve the additional elements in solid solution. The conditions for solution treatment are that the heating temperature is above 90-150℃ and below the melting point, the cooling conditions are an ultra-rapid cooling rate such as pouring into salt water or liquid nitrogen, and the treatment time is as short as possible to avoid deformation of the plate. It is.

The solder material can also be provided as a powder. In this case, the base metal is melted and the molten alloy is made into powder by an atomization method. The most common method for obtaining powder is to grind an ingot, but with this method, intermetallic compounds are produced in the ingot as coarse particles, are hardly refined even by grinding, and the powder is Since solution treatment is virtually impossible, the present invention employs an atomization method that has been used for a long time to obtain powder metal as a solder material.

Next, if the solder material is a plate, if necessary, the foil is cut out in the same pattern as the solder parts of the printed circuit board, so that it has a shape and size that can be easily inserted into the gap existing at the joint part. In addition, if the solder material is a powder, for example, 12
% by weight of rosin-based flux.

In the second step of the present invention, a solder material is placed on the parts to be joined. Specifically, the solder is placed so that the surface to be joined is covered with the solder material.For example, an IC is placed on the part to be joined.
There is a gap between the chip, individual electronic components, etc. and the conductor circuit of the printed circuit board, and this is the place for soldering, so the solder material is inserted in solid form into this gap.

In this case, the solder material is processed in advance to be thin and small, so that it can easily fit into the gap. If necessary, the solder material foil can be cut to make the dimensions even smaller. The solder material only needs to be loosely filled in the gap, and it is desirable to fill it very densely, but it is difficult to work with. ,
That is not needed. Further, even if solder material is placed around the gap, there is no problem as long as the melting efficiency of the solder does not decrease due to an extremely large amount of solder material.

FIG. 1 is an explanatory diagram of an embodiment in which solder material is inserted, and in the figure, 1 is a chip component, 2 is an Au-Pd plating layer, and 3
5 is a solder material, 5 is an Altos board, 6.7 is a conductor pattern baked on 5.1, and 8 is a gap. The solder material 3 is cut from foil and is sandwiched between the chip component 1 and the Al2Og substrate 5. Ultrasonic vibrations are applied to the solder material 3 from the outside.

Furthermore, when joining two plate-shaped parts at an L- or T-shaped surface, solder material is temporarily fixed along the L- or T-shaped surface using a paste or the like if necessary.

In the third step, the foil, powder, etc. are melted.

In order to melt the solder material, it is only necessary to input the maximum amount of heat required to melt the solder material, and unlike conventional methods, a small portion of the solder bath is not poured into the joint.
It has the characteristic that melting, cooling, and solidification can be done in an extremely short time. Therefore, coarsening of crystallized substances is less likely to occur compared to conventional methods. On the other hand, if the cooling rate is extremely high, there is a risk that the added element will become a supersaturated solid solution and the dispersion effect intended by the present invention may not be obtained. Comparing the amount of heat and ■The thermal conductivity coefficient of the board, electronic components, etc. that exist in the joint and take away heat from the solder, it is found that there is no risk of supersaturated solid solution of additive elements due to ultra-rapid cooling, which was adopted in the third process. The melting method used is to apply ultrasonic vibration through a barium titanate vibrator chip, or to rapidly heat the foil etc. at the part to be joined by irradiation with a high energy beam such as a laser beam or electron beam. melt. As the melting method, an ultrasonic method is preferable since there is no risk of malfunctioning the electronic components.The frequency of ultrasonic vibration is 16 kHz to 1.6 MHz.

In particular, around 18 kHz is preferable. In addition, in order to rapidly cool the solder material after heating, it is sufficient to momentarily cut off the energy source at the above-mentioned melting temperature to the solder material.By this means, fine crystallized substances are retained.

(Function) Conventionally, it has been known that intermetallic compounds deteriorate the flow of solder, and for this reason, it is known that the component threads are devised to refine the intermetallic compounds in a crystallized state. (For example, Special Publication No. 40-25885). However, in the above method, the solder is melted and poured into the joint, so the intermetallic compound becomes the usual coarse crystallization state.
The fine and uniform dispersion state intended by the present invention cannot be obtained because the flowability of the melt deteriorates or the coarse crystallized substances cause a decrease in strength. Therefore, in order to miniaturize intermetallic compounds and the like, it is necessary to place a required amount of solder material on the parts to be joined, rapidly heat the solder, keep it in a molten state for a short time, and rapidly cool it. As a result, the average particle size of the crystallized product can be reduced to 10 μm or less. The average particle size of the crystallized product is preferably 5 μm or less, more preferably 3 μm or less.

Furthermore, even if intermetallic compounds existing in the solder material or generated during soldering become undissolved during soldering, they will not remain in the joint as coarse crystallized substances. It is necessary to take such measures. This countermeasure is taken under the conditions of the second step: (a) The secondary phase that is bioacidized after casting is separated by the additive element, (b) The secondary phase that is bioacidized after casting is separated by the additive element during material processing. The heat treatment to form a solid solution, or (c) substantially maintaining the solid solution state of the supersaturated added element dissolved in a solid solution will be explained separately.

In the case of condition (a): In the present invention, if the ingot is prepared under normal casting conditions, intermetallic compounds will grow extremely coarsely, so by dividing it under condition (a), the intermetallic compounds will be made as fine as possible. The material obtained in this way.

Coarsening is avoided by dissolving for a short time in the third step. Note that in the third step, the shape of the intermetallic compound etc. becomes rounded.

In the case of condition (b): Due to the solution treatment, a considerable portion of the added elements become solid solution, and the remaining intermetallic compounds etc. are also reduced. When the solder material having such a structure is melted for a short time in the third step, the additive elements crystallize and precipitate again.

Here, since the time for crystal growth is short, coarsening is avoided, and the dimensions of the intermetallic compound etc. are smaller than in case (a), and the shape tends to be rounded.

Condition (c) is the same as condition (b), but
Because the solution treatment is more thorough in the second step, the intermetallic compounds formed in the third step are limited to those that grow in a very short period of time, and their dimensions are even larger than (b). It becomes smaller and its shape becomes more rounded.

Generally, during use, solder is exposed to elevated temperatures (up to about 100°C) that can lead to grain growth, coalescence, etc. Along with this, fatigue strength also decreases. In addition, electronic devices installed in automobiles range from -10 degrees Celsius to about +80 degrees Celsius.
Since it is used in a temperature range of up to ℃, stress due to thermal expansion and contraction of the solder and element lead terminals is added to the solder.

This is a major factor in fatigue failure. Furthermore, if the solder is constantly exposed to high temperatures, the solder will be subjected to a certain amount of stress and may break due to creep, which is also a major factor in fatigue failure. When heat and stress are applied to the solder during use, mainly the Sn crystal grains gradually become coarser, and the eutectic P particles, which were finely dispersed at the beginning of use, become coarser.
b Coarse particles become continuous. As the crystal grains become coarser, the strength of the solder decreases, and cracks are more likely to occur in the continuous PB phase. Since Pb coarse particle continuity occurs with the movement of the grain boundaries of Sn particles, it is important to prevent the Sn particles from becoming coarse in order to simultaneously prevent a decrease in strength and the occurrence of cracks. The secondary phase such as a fine intermetallic compound utilized in the present invention has the following effects and is effective in preventing the above-mentioned Pb and Sn crystal grains from becoming coarse.

(1) These intermetallic compounds have high melting points, are thermally stable at the operating temperatures of solder parts, and maintain their fine morphology.

(2) These intermetallic compounds are produced and precipitated in the soldered state, so the temperature is lower than the soldering temperature.
Therefore, at the temperature at which solder parts are used, where the solid solubility limit is large, almost no solid solution occurs in the Pb and Sn crystals. Therefore, even if grain boundary movement of Pb and Sn crystals occurs, intermetallic compound crystal grains are not eaten by Pb and Sn crystal grains.

(3) The crystallization positions of these intermetallic compounds are uniform, and they are crystallized both at Pb and Sn crystal grain boundaries and within the grains.

When Pb and Sn crystal grains grow, the intermetallic compound phase present at the grain boundaries hinders grain boundary movement. As a result, Pb,
The average grain size of Sn is 10LLm or less, preferably 6μ
m or less.

(Effect of the invention) The fatigue test is conducted using a test piece in which a chip component l is soldered to an Ag-Pd plating layer 4 formed on one surface of an AlzOs substrate 5 shown in FIG. exists in areas other than the gaps between joints.

The test method was to use a fatigue testing machine on the lead wires at a repetition frequency of 20.
A shear load is applied under the conditions of Hz (one-sided swing) and temperature (80℃, constant), and the number of repetitions at which a crack occurs is determined as the fatigue life.
This occurs within the solder as shown in the figure.

Using this method to calculate the number of repetitions until cracks occur due to fatigue, the improvement in fatigue life due to the effect of making the crystallized parts finer is several tens of percent compared to solder with the same composition but without making the crystallized parts finer. In most cases, the improvement is 20-50%. Specifically, under the above test conditions, the life of 2000 hours is extended by 400 hours (20%) to 1000 hours (50%).

According to the present invention, even when the solder material is used under harsh conditions ranging from low temperatures of minus several tens of degrees Celsius to plus hundreds of degrees Celsius, such as on printed circuit boards mounted in automobiles, conventional solder It can be used stably without cracking unlike other materials, and the reliability of solder joints is improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an example of the second step of the present invention, and FIG. 2 is a diagram of a test piece subjected to a fatigue resistance test. 1-chip parts, 2-Ag-Pd plating layer, 3-solder material, 5"-AI20s board, 6.7-5.1 each
Conductor pattern baked on top, 8-gap

Claims (1)

[Claims] 1. The following first to third steps; Pb and Sn are the main components, Ag, Au, As, Bi, Cu, Ni, In, Ca, Mg, Te, T
i, Zn, Sr, Be, Sb, Bi, Pd, Te, Tl
Casting an alloy containing one or more of the following additive elements in an amount greater than or equal to the amount at which a secondary phase is generated in the soldering state, but not more than 30%, The phase is divided, and (b) the secondary phase generated by the additive element after casting is subjected to a heat treatment during material processing, or (c) the additive element is supersaturated as a solid solution. Conditions (a) and (b) to substantially maintain the solid solution state of
A first step of processing the cast alloy into a solder material in a form suitable for soldering so as to satisfy any one of (c); a second step of placing the solder material on the part to be joined; When melting the solder material placed on the part to be joined and processing the material under the conditions of (a) in the first step, apply the conditions of (b) or (c) to prevent the secondary phase from becoming a solid solution. A soldering method comprising: a third step of cooling to form a secondary phase of the additive element when processing the material.