JPH10180482A - Solder alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solder alloy capable of being substituted for eutectic solder, excellent in mechanical strength and having versatility applicable to a jet-type automatic soldering device. SOLUTION: This high strength solder alloy is formed of two-element alloy of Sn and Pb as the basis, and three elements of Ag, Sb and Cu are added, melted to improve the strength of the solder. The solder alloy has the composition consisting of, by weight, 64-66% Sn, 0.8-1.5% Ag, 0.3-1.0% Sb, 0.1-0.25% Cu, and the balance Pb. The solder alloy can be used for the automatic soldering in which the soldering is performed by bringing parts to be soldered into contact with the surface of the solder jet to be jetted from a soldering tank. Thus the solder alloy in which three kinds of Ag, Sb and Cu are added to the two-element alloy of Sn and Pb is remarkably improved in the mechanical strength, the soldering workability and the strength of the soldered part by adding the respective metallic elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to tin (Sn), lead (P)
The present invention relates to a solder alloy containing a binary alloy as a main component, and particularly to a solder alloy suitable for use in an automatic soldering method by a jet method (wave soldering method).

[0002]

2. Description of the Related Art In general, in electronic equipment, assembly is performed by soldering and mounting various components on a wiring circuit pattern printed on a printed circuit board. The solder used for this soldering is the most widely used metal as an electrical connection means. However, conventional solder has no metallic strength such as iron (Fe), and is not generally used as mechanical fixing means.

However, with the recent development of high-density packaging,
In general, mounting and soldering are performed so as to expect the component fixing ability of the solder, that is, mechanical strength, and the stress on the soldered part increases, which causes the failure of electrical products in the market It has become more and more. Therefore, a solder alloy having stronger mechanical connection strength as well as electrical performance is required. However,
As a prerequisite, it is desired that the soldering operation can be performed in the current mass production process. Under such circumstances, in the past, there have been proposed many types of Sn-based, Pb-based, and ternary to quinary-based synthetic compositions by adding other metal elements in search of strong solder alloys.

[0004] However, although the strength is improved in all cases, there is a poor balance such as a decrease in actual workability, and there is no alloy composition that can be used as a substitute for the eutectic solder. Furthermore, the definition of strength at this time is also one-sided,
For example, even if the fatigue strength against thermal stress is improved, the mechanical impact strength is lowered and it cannot be put to practical use. Further, even with known compositions, the proposed composition range is very wide, and even within this range, the properties of the alloy may be significantly different, and the industrial effective range is unclear.

[0005]

As described above, as a recent solder, not only the electrical performance but also the mechanical strength is stronger, and the soldering operation must be performed in the current mass production process. It is an essential condition that, for example, in a composition in which the solder alloy is hardened and the tensile strength is increased, the brittleness increases and the fatigue strength decreases, and also, the joining performance of the joint which is the basic performance of soldering There is a problem that the ease of metal production, that is, the wettability is extremely poor, and the metal cannot be used in the current production process. In addition, in the case of a solder alloy with a composition that has improved fracture and creep strength due to metal slip,
Since the melting point of the solder increases, the operating temperature for soldering must be increased. For this reason, there is a problem that excessive heat damage is given to the parts, which requires special design and selection of the parts, and is not versatile.

The present invention has been made in view of the above problems, and has as its object to change the joints between components without changing the design conditions of electronic devices currently used or mounting equipment for production. An object of the present invention is to provide a versatile solder alloy capable of improving strength.

[0007]

The solder alloy according to the present invention contains tin (Sn), lead (Pb), silver (Ag), antimony (Sb) and copper (Cu), with Sn being 64 to 66% by weight. , Ag is 0.8-1.5% by weight, Sb is 0.3-1.5% by weight.
The composition is characterized in that 1.0% by weight, Cu has a composition of 0.1 to 0.25% by weight, and Pb has a composition in the remaining range.

The solder alloy according to the present invention is characterized in that three kinds of metal elements of Ag, Sb and Cu are added to a binary alloy of Sn and Pb as a base metal, and the composition of these metal elements is in the above range. Thereby, it can be replaced with a eutectic solder which is widely and generally used, and has high mechanical strength. In addition, this solder alloy has the versatility that soldering work can be performed by a jet-flow type automatic soldering device, and the balance between solderability and strength allows the design conditions currently used to be used. In addition, the strength of the solder joint of the electronic device can be improved while using the mounting equipment as it is.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

The high-strength solder alloy according to the present embodiment is
As shown in Table 1, tin (Sn) and lead (Pb) 2
The strength of the solder is improved by adding and dissolving silver (Ag), antimony (Sb), and copper (Cu) to the base based on an original alloy.

[0011]

[Table 1]

Thus, the binary alloy of Sn and Pb is made of Ag,
In a solder alloy to which three kinds of metal elements of Sb and Cu are added, the addition amount of each metal element itself greatly changes the soldering workability as well as the mechanical strength.
Therefore, in order to determine the optimum value of the ratio of each metal element in the interaction with the additive element, the characteristics (evaluation index) required for the solder are subdivided in accordance with the actual required characteristics, and 11 items are classified. (See FIG. 11) and quantified. By determining the composition as described above with the policy of being an alloy that is excellent in that all of these evaluation items are balanced, it can be replaced with eutectic solder that is widely used in general. Thus, a solder alloy having higher mechanical strength could be obtained. Hereinafter, a test method as a quantification method for expressing solder strength will be described. The following method satisfies the essential condition that the soldering operation can be performed in the current mass production process, and it is possible to determine whether various strength improvements are meaningful.

First, FIGS. 1A to 1C are diagrams for explaining a method for evaluating thermal fatigue characteristics. 1A shows a substrate 10, FIG. 1B shows a resin component 11 for mounting on the substrate 10, and FIG. 1C shows a state where the component 11 is mounted on the substrate 10 by soldering. It is. In this method, the difference between the thermal expansion coefficient of the constituent material (nylon resin) of the component 11 and the thermal expansion coefficient of the constituent material (paper phenol) of the substrate 10 corresponds to the temperature stress pattern applied to the solder joint 12. Repeated lateral bending stress is applied. Here, the number of repetitions until the solder joint 12 is broken is defined as the thermal fatigue strength. Lead pin 11 of component 11
The magnitude of the stress can be changed by changing the distance between parts a and the component pitch. Hereinafter, the test using a large pitch (pitch: 22.5 mm) as the component 11 is referred to as “high strain thermal fatigue”, and the test using a small pitch (pitch: 10 mm) as the component 11 is referred to as “low strain thermal fatigue”. "
Called. The various conditions of the substrate 10 and the component 11 are as shown in FIG. The solder alloy according to the present embodiment has a high strain thermal fatigue property of about 60% and a low strain thermal fatigue property of about 290% as compared with the eutectic solder.
Improvement was observed.

FIGS. 2A to 2C are diagrams for explaining a method for evaluating high-temperature creep characteristics. In this method, the test piece (solder alloy 21) shown in FIG.
As shown in FIGS. 2B and 2C, a pair of chucks 22 are provided.
a, 22b and 10 mm
After applying a load of 1.0 kg at a displacement rate of / min, the decrease behavior is monitored by a damping curve (F (t)) as shown in FIG.
The creep property is evaluated by reading the time (τ _0.3 ) when The test temperature was 10
0 ° C. In the solder alloy according to the present embodiment, an improvement in creep characteristics of about 140% was recognized as compared with the eutectic solder.

FIGS. 4A and 4B and FIGS.
(B) is a figure for demonstrating the method by a mechanical fatigue test. In this mechanical fatigue test, a lead pin 42 shown in FIG. 4B is soldered to a test board 41 shown in FIG. 4A, and then mechanically minutely displaced by a compression / tensile device 50 shown in FIG. By giving a repetition of (0.1 mm), the fatigue strength is evaluated by the number of repetitions up to the fracture in the lead portion and the vertical direction with respect to the repetitive stress.

The compression / tension device 50 includes a base 51 for mounting a test substrate and a compression / tension mechanism 52. A fixing portion 51a is provided on a side surface of the base 51,
The test board 41 is fixed to the fixing portion 51a. The compression / tension mechanism 52 has an eccentric cam 53 disposed above the base 51. The eccentric cam 53 is rotatable about a shaft 53a. An arm 55 having a weight 54 attached to one end thereof is provided above the base 51.
Are arranged. The arm 54 can swing about a shaft 54 a, and one end of the arm 54 can be moved toward and away from the eccentric cam 53. Above the base 51, an arm 56 is further provided.
Are arranged. The arm 56 is swingable about a shaft 56a, and a weight 57 is fixed to one end of the arm 56. An engagement portion 58 is provided on a side of one end of the arm 56, and the upper end of the other end of the arm 55 can be engaged with a lower portion of the engagement portion 58. The other end of the arm 56 is provided with an engagement portion 59. The engaging portion 59 is held by a holding portion 61 provided on a vertically movable vertical bar 60. At the lower end of the vertical bar 60, the board mounting portion 6 is provided.
2 are provided. In the board mounting portion 62, the upper portion of the lead pin 42 is sandwiched between the vertical bar 60 and the fixing plate 62a, and is fixed with the fixing screw 62b.

In the compression / tensile device 50, when the eccentric cam 53 is located at the bottom dead center as shown in FIG. 5A, the eccentric cam 53 is detached from the arm 55. Accordingly, the arm 55 tends to rotate counterclockwise due to the weight of the weight 54, and the other end of the arm 55 pushes up the other end of the arm 56 via the engaging portion 58 against the weight of the weight 57. . As a result, the arm 56 is
Rotate clockwise around a, and push down the vertical bar 60 via the engaging portion 59. Thus, a constant compressive force (here, 5 kgf) is applied to the solder joint 43 between the test board 41 and the lead pin 42. When the eccentric cam 53 further rotates and reaches the position of the top dead center as shown in FIG. 5B, the eccentric cam 53 comes into contact with the arm 55.
As a result, the arm 55 is lifted clockwise against the weight of the weight 54, and as a result, the other end of the arm 55 is separated from the arm 56. In this state, arm 5
6 rotates counterclockwise around the shaft portion 56 a by the weight of the weight 57, and pushes up the vertical arm 60 via the engaging portion 59. As a result, a constant tensile force (5 in this case) is applied to the solder joint 43 between the test board 41 and the lead pin 42.
kgf). Thereafter, a compressive force and a tensile force are similarly applied alternately.

According to the compression / tensile device 50, stress (compressive force and tensile force) can be applied to the above-mentioned thermal fatigue without changing the ambient temperature. The resulting failure mode can be evaluated. In the solder alloy according to the present embodiment, an improvement in mechanical fatigue strength of about 40% as compared with the eutectic solder was recognized.

The test board 41 shown in FIG.
After soldering the lead pins 42 shown in FIG. 4B to FIG. 4B, the strength against mechanical shock load was also evaluated. That is, after the lead pins 42 are soldered, an impact load is applied by dropping steel balls on the lead pins 42 by the impact strength test device 60 shown in FIG.
The applied impact load when the sample No. 3 was broken was defined as the impact resistance load.

The impact strength test apparatus 60 includes an iron support 67 formed on a base 61 in a substantially cylindrical shape. On the support portion 67, a housing portion 62 formed of a transparent plastic material in a cylindrical shape is provided. The support portion 67 is formed with a lead pin receiving portion 67a. The test board 41 is mounted on the upper surface of the support portion 67 such that the upper end of the lead pin 42 is accommodated in the lead pin accommodating portion 67a and the solder joint 43 is on the upper side. At this time, the center of the lead pin 42 is positioned at the center of the housing 62. A measuring instrument (for example, a peak hold type recorder) 66 is connected to the solder joint 43 and the lead pin 42 via lead wires 66a and 66b, respectively, so that the electric resistance between the solder joint 43 and the lead pin 42 can be reduced. It is designed to measure. A horizontal arm 64 is provided at an upper position in the storage section 62. The distal end of the horizontal arm 64 is constituted by an electromagnetic chuck 64a, and the steel ball 63 can be held or dropped by the on / off operation of the electromagnetic chuck 64a. The horizontal arm 64 is attached to a column 65 provided outside the accommodation section 62. The position at which the horizontal arm 64 is mounted on the column 65 can be changed.
Can be changed in height.

In the impact strength test apparatus 60, the support 67
After mounting the test board 41 with the solder joints 43 facing upward, a measuring instrument 66 is connected to the solder joints 43 and the lead pins 42 via lead wires 66a and 66b. Subsequently, the electromagnetic chuck 64a at the distal end of the horizontal arm 64 is turned off, and the steel ball 63 is allowed to freely fall along the center line of the accommodating portion 62 as shown by the arrow, and the upper end of the lead pin 42 is shown by the broken line. The steel ball 63 is made to collide with the steel to give an impact. At this time, the impact load received by the lead pin 42 is transmitted to the solder joint 43, and the electric resistance between the solder joint 43 and the lead pin 42 changes. The change in the electric resistance value is measured by the measuring device 66 and displayed on a display unit (not shown). At this time, the resistance value when an impact load is applied is displayed as an instantaneous peak. Depending on the magnitude of the impact load, the degree of internal destruction of the solder joint 43 also differs, and as a result, a change occurs in the change in the electric resistance value, so that the mechanical strength of the solder joint 43 can be quantitatively evaluated.

The applied impact load was changed by changing the falling height of the steel ball 63. As a result, the solder alloy according to the present embodiment was found to have about 10% improvement in impact resistance as compared with the eutectic solder.

Further, the lead pin 42 and the solder joint 43
The interfacial strength between the two was also examined. That is, after the solder joints 43 are formed on the lead pins 42, the tensile test of the solder joints 43 is performed with a tensile strength of 2 mm / min.
The breaking strength was defined as the interface strength. As a result, it was found that the solder alloy according to the present embodiment exhibited about 25% improvement in interface strength as compared with the eutectic solder.

FIG. 7 is a configuration diagram of a wettability evaluation system for evaluating solder wettability. This system has a solder tank 7 for accommodating an evaluation sample (molten solder) 70a.
0 is provided. The temperature of the evaluation sample 70 a can be adjusted by a heater (not shown) under the control of the controller 72, and the solder tank 70 can be moved up and down by a motor 71. The controller 72 includes an evaluation sample 70.
The temperature control section 721 includes a temperature control section 721 for maintaining the temperature of a at a constant temperature (for example, 240 ° C.) and a drive control section 722 for controlling the drive of the motor 71. A copper wire (diameter: 0.6 mm) 74 for detecting wetting hanging from the load cell 73 is disposed above the solder tank 70.
When the solder bath 70 is raised, the wetting detection copper wire 74 is immersed in the evaluation sample 70a as shown by a two-dot chain line in the figure. After the buoyancy F applied to the wetting detection copper wire 74 at this time is detected by the load cell 73, it is amplified by the buoyancy detection amplifier 75 and then displayed on the recorder 76.

FIG. 8 shows an example of the measurement result displayed on the recorder 76. In this figure, when the wetting detection copper wire 74 is immersed in the evaluation sample 70a from the initial stage (t = 0, buoyancy F = 0), the wetting detection copper wire 74 is directed upward (downward in FIG. 8) with respect to the wetting detection copper wire 74. Force F acts. After the buoyancy F reaches a constant value, the buoyancy F gradually decreases in accordance with the wettability of the solder, and after a predetermined time (t1), the buoyancy F = 0.
Return to the state. The time required to return to the state of buoyancy F = 0 is defined as the wetting time. The shorter the wetting time, the better the wettability. In this system, a so-called wetting balance method is employed, and the speed at which soldering is performed can be evaluated as an index (wettability).

In the following, many conventional alternatives having improved strength of the eutectic solder having the most common composition (Sn: 63% by weight, Pb: 37% by weight) have been proposed in general and put to practical use widely. Solderability (wettability), which will increase the rejection rate during production, taking into account circumstances that have not been done
A study is made to make the composition of the composition within a range in which the reduction of the composition can be minimized as compared with a general eutectic solder, and an improvement in strength can be expected.

FIG. 9 is a graph showing the relationship between the composition ratio of tin (Sn) and lead (Pb) of the base metal in the solder alloy.
This figure shows the result of examining the effect of the mixing ratio on low strain thermal fatigue and wettability, and shows the relationship between the Sn content in the solder alloy composed of Sn and Pb and the crack generation cycle due to low strain thermal fatigue. It represents. According to this figure, S
Although the low strain thermal fatigue is improved with the increase of n, on the other hand,
It can be seen that the wettability deteriorates. In particular, when the composition of Sn is 66% by weight or more, the wettability is greatly deteriorated, and there is a possibility that the same solderability as the eutectic solder cannot be secured. From this, the optimum value of the Sn content is determined to be 64 to 66% by weight, and in the present embodiment, the Sn content is 65 to 66% by weight.
%.

Next, the mixing ratio of the additional element will be described. Table 2 shows the effect of the mixing ratio on the creep characteristics as an effect when silver (Ag) is added.

[0029]

[Table 2]

According to this table, when the amount of Ag added was 0.8% by weight, the effect on the creep characteristics began to appear,
When added up to 1.5% by weight, the creep time increases with the addition amount. On the other hand, when 2% by weight of Ag is added, this increasing effect tends to be slightly saturated. Since Ag is a high-priced metal, it is industrially desired to obtain an effect with a minimum amount of addition. Therefore, the optimal addition amount of Ag is set to 0.8 to 1.5% by weight, and is set to 1.0% by weight in the present embodiment.

Next, as an effect when antimony (Sb) is added, Table 3 shows the effect of the mixing ratio on low strain thermal fatigue, mechanical fatigue and wettability.

[0032]

[Table 3]

According to this table, it can be seen that the low strain thermal fatigue properties are greatly improved with an increase in the amount of Sb added, but the mechanical fatigue and wettability are each deteriorated. From the balance among these three factors, the optimum addition amount of Sb was determined to be 0.3 to 1.0% by weight, and was set to 0.6% by weight in the present embodiment.

As shown in Table 4, the effect of the addition of copper (Cu) is effective in improving the properties of high strain thermal fatigue resistance and mechanical fatigue strength with the addition of 0.1% by weight. And the addition of 0.2% by weight is even better.

[0035]

[Table 4]

In addition, the addition of Cu causes, in particular, an automatic soldering apparatus (wave soldering apparatus) 100 using a jet flow method as shown in FIG. An effect of preventing a change in composition due to a rapid increase in Cu can also be expected. In this automatic soldering apparatus 100, a substrate 101 to be soldered is put into a dip tank 102 by a conveyor 106. First, the flux is applied to the substrate 101 put in the dip tank 102 by the fluxer 102, and then the flux is applied by 100 ° by the preheater 103.
It is heated to around C and adjusted to the optimum condition for soldering. Thereafter, the substrate 101 passes (contacts) the surface of the solder jet (primary jet, secondary jet) blown up from the solder bath 104, and thereby the soldering is performed. The soldered substrate 101 is taken out of the dip tank 102 after being cooled by the cooling fan 105.

In the automatic soldering apparatus 100, generally, when the Cu concentration in the solder in the solder bath 104 becomes 0.29% by weight or more, an Sn-Cu intermetallic compound is precipitated. When such an Sn-Cu intermetallic compound precipitates, the soldering surface becomes rough and the solderability deteriorates. Accordingly, the maximum addition amount is determined to be 0.25% by weight, and the addition range of Cu is determined to be 0.1 to 0.25% by weight.
In the present embodiment, the content is 0.2% by weight.

FIG. 11 summarizes the various characteristics described above and compares the solder alloy A according to the present embodiment with the conventional solder alloy (eutectic solder) B in a radar chart. As is clear from this figure and the above description, the solder alloy A according to the present embodiment has high strain thermal fatigue, low strain thermal fatigue, high temperature creep, mechanical fatigue, interface strength, and impact strength. It is significantly improved as compared with the conventional solder alloy B.
The characteristics of fillet formation, generation of dross (solder oxide), composition stability and migration resistance are almost the same as those of the conventional solder alloy (eutectic solder) B. Therefore, the solder alloy A according to the present embodiment
Has the versatility that can be used for the automatic soldering device by the jet method, and the design conditions currently used,
The strength of the joint between the components can be improved while using the mounting equipment as it is.

[0039]

As described above, according to the solder alloy of the present invention, tin (Sn), lead (Pb), silver (Ag),
A composition containing antimony (Sb) and copper (Cu), Sn is 64 to 66% by weight, and Ag is 0.8 to 1.5%.
Wt%, Sb is 0.3-1.0 wt%, Cu is 0.1-
Since 0.25% by weight of Pb has a composition in the remaining range, it has general versatility that can be used in an automatic soldering apparatus by a jet method, and aims to improve strength without impairing solderability. Thus, it is possible to improve the strength of the joint while using the currently used design conditions and mounting equipment as they are.

[Brief description of the drawings]

FIG. 1 is a view for explaining a thermal fatigue test method as a method for evaluating the characteristics of a solder alloy according to one embodiment of the present invention, where (a) is a plan view of a substrate to be soldered,
(B) is a side view of the lead pin, and (c) is a side view showing a state where the lead pin is soldered to a substrate.

FIGS. 2A and 2B are diagrams for explaining a creep characteristic evaluation method as a method for evaluating solder alloy characteristics according to an embodiment of the present invention, wherein FIG. 2A is a side view of a test piece (solder alloy), and FIG. () Is a side view showing the state of the test apparatus at the start of load application, and (c) is a side view showing the state after the load application is stopped.

FIG. 3 is a characteristic diagram of a solder alloy obtained by the apparatus of FIG.

4A and 4B are diagrams for explaining a mechanical fatigue test as a method for evaluating the characteristics of a solder alloy according to one embodiment of the present invention, wherein FIG. 4A is a plan view of a test board, and FIG. FIG.

5A and 5B show a configuration of a compression / tensile test apparatus used for a mechanical fatigue test, in which FIG. 5A is a side view showing a state at the time of compression, and FIG. 5B is a side view showing a state at the time of tension.

FIG. 6 is a side view showing a partial cross section of a configuration of an impact strength test apparatus used for evaluating the characteristics of a solder alloy according to one embodiment of the present invention.

FIG. 7 is a configuration diagram of a system used for evaluating solderability (wetting property) of a solder alloy according to one embodiment of the present invention.

FIG. 8 is a characteristic diagram for explaining evaluation of solderability (wetability) obtained by the system of FIG. 7;

FIG. 9 shows Sn of a solder alloy according to an embodiment of the present invention.
FIG. 4 is a characteristic diagram for explaining the effect of the content on wettability and thermal fatigue characteristics.

FIG. 10 is a view for explaining the operation of the automatic soldering apparatus using the jet flow method.

FIG. 11 is a radar chart showing characteristics of a solder alloy according to an embodiment of the present invention in comparison with characteristics of a conventional eutectic solder.

[Explanation of symbols]

10 ... board, 11 ... parts, 11a ... lead pin, 12 ...
Solder joint

Continued on the front page (72) Inventor Keiki Fukuda 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation

Claims (2)

[Claims] 1. Tin (Sn), lead (Pb), silver (Ag),
Contains metal elements of antimony (Sb) and copper (Cu), Sn is 64 to 66% by weight, Ag is 0.8 to 1.5% by weight, Sb is 0.3 to 1.0% by weight, Cu is 0 to 0%. .1 to
0.25% by weight, Pb has a composition in the remaining range. 2. The solder alloy according to claim 1, wherein the solder alloy is used in an automatic soldering method for performing soldering by bringing a component to be soldered into contact with a surface of a solder jet blown up from a solder bath.