JP2016107343A - Lead-free solder alloy, and on-vehicle electronic circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a solder alloy capable of enduring not only strict temperature characteristics of a low temperature of -40°C and a high temperature of 125°C but also the outside force which occurs at a ride on a curve stone or at a collision against a foregoing vehicle; and an on-vehicle electric circuit using the solder alloy.SOLUTION: A lead-free solder alloy is characterized by comprising Ag: 1 to 4 mass %; Cu: 0.6 to 0.8 mass %; Sb: 3 to 5 mass %; Ni: 0.01 to 0.2%; Bi: 1.5 to 5.5 mass %, and the remainder being made of Sn.SELECTED DRAWING: None

Description

  The present invention relates to a lead-free solder alloy having excellent temperature cycle characteristics and strong against impacts such as a collision, and an in-vehicle electronic circuit device.

  In an automobile, an electronic circuit (hereinafter referred to as an in-vehicle electronic circuit) in which an electronic component such as a semiconductor or a chip resistor component is soldered to a printed circuit board (hereinafter referred to as a printed circuit board) is mounted. In-vehicle electronic circuits are used in devices that electrically control engines, power steering, brakes, and the like, and such devices are very important safety parts for driving a car. In particular, an in-vehicle electronic circuit device called ECU (Engine Control Unit) equipped with an electronic circuit for controlling the driving of an automobile, particularly the operation of an engine with a computer for improving fuel efficiency has been stable and stable for a long period of time. It must be able to operate in a state. In many cases, this ECU is generally installed near the engine, and the usage environment is quite severe. In the present specification, this in-vehicle electronic circuit device is also simply referred to as “ECU” or “ECU electronic circuit device”.

  The vicinity of the engine in which such an in-vehicle electronic circuit is installed becomes a very high temperature of 125 ° C. or more when the engine is rotated. On the other hand, when the rotation of the engine is stopped, the outside air temperature, for example, in a cold region such as North America or Siberia, becomes a low temperature of −40 ° C. or lower in winter. Therefore, the on-vehicle electronic circuit is exposed to a heat cycle of −40 ° C. or lower to + 125 ° C. or higher by repeatedly operating the engine and stopping the engine.

  When an in-vehicle electronic circuit is placed in such an environment where the temperature changes greatly, the electronic component and the printed circuit board will thermally expand and contract, respectively. However, there is a large difference between the coefficient of linear thermal expansion of electronic components mainly made of ceramics and the coefficient of linear thermal expansion of printed circuit boards made of glass epoxy substrates. It occurs in a soldering part (hereinafter referred to as “solder joint part”) that joins a component and a printed circuit board, and stress is repeatedly applied to the solder joint part due to such a temperature change. Then, such a stress eventually breaks the joint interface of the solder joint. In an electronic circuit, even if the solder joint is not electrically ruptured even if it is electrically conductive, even if the solder joint is cracked even at a crack rate of 99% or less, the resistance value of the circuit increases. A malfunction may also be considered. It must be avoided that cracks occur in the solder joints, causing malfunction of the in-vehicle electronic circuit device, particularly the ECU. Thus, temperature cycle characteristics are particularly important for in-vehicle electronic circuit devices, particularly ECUs, and it is required that solder joints used for them, that is, solder alloys, can be used even under severe temperature conditions.

  As a solder for an on-vehicle electronic circuit device, particularly an ECU, which has severe use conditions, Ag: 2.8 to 4% by mass, Bi: 1.5 to 6% by mass, Cu: 0.8 to 1.2% by mass, In-vehicle lead-free solder (WO2009 / 011341A, Patent Document 1) characterized by comprising at least one selected from the group consisting of Ni, Fe and Co in a total amount of 0.005 to 0.05 mass% and the balance Sn. ) Etc. are disclosed.

  Also, as a simple solder alloy composition, in addition to Sn (tin) as a main component, 10 wt% or less Ag (silver), 10 wt% or less Bi (bismuth), 10 wt% or less A solder material comprising an alloy comprising Sb (antimony) and 3 wt% or less Cu (copper), the alloy further comprising 1.0 wt% or less Ni (nickel) (Japanese translations of PCT publication No. 2006-524572, patent document 2) is also disclosed.

WO2009 / 011341A JP-T-2006-524572

  As seen in the spread of hybrid cars and electric cars, the shift from mechanical parts to electronic parts in automobiles is progressing, and miniaturization is required even in electronic circuits for cars that have room for size. Yes. For this reason, it has become natural that in-vehicle electronic circuits that have been soldered by flow soldering after reflow soldering in the past have been subjected to double-sided reflow soldering in which both sides are surface-mounted by solder paste. This has led to a higher density of on-board electronic circuits, and a crack mode defect that has not been seen before has appeared.

  By the way, although the invention of Patent Document 1 disclosed a solder alloy having a long life in a harsh environment, since an automobile is used as a transportation means, it is rarely left in one place, and roads It is often used by etc. When used on such roads, the on-board electronic circuit device is constantly vibrated due to bad roads, and the on-board electronic circuit device is subjected to external force such as climbing on the curb or colliding with the previous car. Many things happen. If a car crash causes a major accident, the vehicle-mounted electronic circuit device is often replaced, but in a simple contact accident, it is often only necessary to replace the exterior of the vehicle. It must be able to withstand external forces.

  In particular, recent automobiles have been digitized due to the popularization of electric cars and hybrid cars, and on-board electronic circuit devices have also been reduced in size and density. Therefore, the amount of solder at the solder joint of the in-vehicle electronic circuit is also reduced. For example, in the case of a 3216 size chip component, the solder amount of the solder joint is 1.32 mg as standard on one side, whereas for the in-vehicle electronic circuit, one side There is only a fine solder amount of less than 0.28 mg. Therefore, in the conventional electronic circuit, the solder fillet portion protrudes from the side surface of the chip component as shown in FIG. 1, but there is almost no solder fillet on the side surface of the chip component as shown in FIG. Therefore, a new crack mode in which the crack propagates in a substantially straight line as shown in FIG. 2 occurs in the solder joint portion of the on-vehicle electronic circuit, which causes a problem of malfunction.

  The problem to be solved by the present invention is not only able to withstand severe temperature cycle characteristics such as low temperature of −40 ° C. and high temperature of 125 ° C. for a long period of time, but also occurs when climbing on a curb or colliding with the previous car It is to develop a solder alloy capable of withstanding an external force for a long period of time and an in-vehicle electronic circuit device using the solder alloy.

  In order to withstand the external force after a long-term temperature cycle, the inventors of the present invention can effectively add a solid solution element to the Sn phase to form a solid solution strengthened alloy. It is found that Sb is an optimum element for making a reinforced alloy, and that addition of Sb in the Sn matrix forms a fine SnSb intermetallic compound, and also exhibits the effect of precipitation dispersion strengthening. Completed.

As for this invention, Ag is 1-4 mass%, Cu is 0.6-0.8 mass%, Sb is 3-5 mass%, Ni is 0.01-0.2 mass%, Bi is 1.5- The lead-free solder alloy is 5.5% by mass and the balance is Sn.
When Co is contained in an amount of 0.001 to 0.1% by mass, the present invention is such that Ag is 1 to 4% by mass, Cu is 0.6 to 0.8% by mass, and Sb is 3 to 5% by mass. Or less, Ni is 0.01 to 0.2% by mass, Bi is 1.5 to 5.5% by mass, Co is 0.001 to 0.1% by mass, and the balance is Sn.

  Here, the metallurgical structure of the alloy according to the present invention is characterized in that the solder alloy is composed of a structure in which Sb is dissolved in an Sn matrix, and the structure is stable at a high temperature of 125 ° C., for example. As the temperature decreases, Sb gradually dissolves into the Sn matrix in a supersaturated state, and, for example, at a low temperature of −40 ° C., the SnSb intermetallic compound. As a structure in which Sb is precipitated.

Furthermore, the present invention is an in-vehicle electronic circuit obtained by performing soldering using the above-described solder alloy, and an in-vehicle electronic circuit device including such an electronic circuit.
Here, “in-vehicle” or “in-vehicle” means that it is installed in an automobile, and specifically, it is repeatedly exposed to a severe use environment, that is, a temperature environment of −40 ° C. to 125 ° C. Even if it is used, the predetermined characteristics can be secured and it can be mounted on an automobile. More specifically, it can withstand a 3000 cycles heat cycle test even under such a temperature environment, and has resistance to a shear test that evaluates external force even under such conditions.

The reason why the solder alloy of the present invention produces fine Sb precipitates even after being exposed to a temperature cycle and does not cause structural deterioration such as coarsening of the compound is as follows.
A vehicle-mounted solder alloy to be joined by reflow soldering is subjected to a temperature cycle test of −40 ° C. to + 125 ° C., in which the low temperature is a cold region and the high temperature is an engine room. In the solder alloy of the present invention, the added Sb is re-dissolved in the Sn matrix at a high temperature of, for example, 125 ° C., and SnSb intermetallic compound is precipitated at a low temperature of, for example, −40 ° C. The SnSb intermetallic compound stops coarsening, and the SnSb metal compound once coarsened is re-dissolved in the Sn matrix on the high temperature side during the temperature cycle test, so that a fine SnSb intermetallic compound is formed. Precipitation dispersion strengthened solder alloy is maintained.

  However, if the amount of Sb exceeds 5% by mass, for example, 8% by mass, the particle size of the SnSb compound at the initial stage of the temperature cycle test does not become large and fine, and the liquidus temperature rises. The Sb added to the solder alloy does not remelt even on the high temperature side, and remains as the original SnSb crystal grains. Therefore, even if the use under the temperature cycle as described above is repeated, a fine SnSb intermetallic compound is not formed.

Furthermore, if the amount of Sb exceeds 5% by mass, the liquidus temperature of the solder alloy increases, and therefore soldering cannot be performed unless the reflow heating temperature is increased. Thus, when the reflow conditions are raised, Cu wiring on the surface of the printed circuit board is melted in the solder, and the SnCu intermetallic compound layer such as Cu ₆ Sn ₅ is thickened at the soldering portion with the printed circuit board. It becomes easy to be formed, and the printed circuit board and the solder joint are easily broken.

  In the present invention, Sb added to the solder alloy becomes a fine precipitate in the form of a compound called SnSb in the Sn matrix of the solder alloy. Even if the temperature cycle of −40 to + 125 ° C. is repeated nearly 3000 cycles, the Sn matrix In this state, the fine precipitate state of the SnSb intermetallic compound can be maintained. As a result, SnSb precipitates interfere with cracks that are likely to occur at the interface between the electronic component such as ceramics and the solder joint.

  According to the present invention, even after the temperature cycle test described above, the particle size of the SnSb intermetallic compound in the Sn matrix is approximately the same as that of the SnSb intermetallic compound particle having a particle size before the start of the test. The particle size is as follows, with coarsening suppressed. Therefore, even if a crack is partially formed in the solder, the fine SnSb intermetallic compound can inhibit the propagation of such a crack, thereby preventing the crack from spreading inside the solder.

In the solder alloy according to the present invention, even when a temperature cycle test from −40 ° C. to + 125 ° C. is repeated nearly 3000 cycles, no crack is generated in the solder joint portion of a small amount of solder. However, it is possible to exhibit excellent temperature cycle characteristics in which cracks are prevented from propagating in the solder.
The use environment in which the solder alloy according to the present invention is exposed to a temperature cycle of −40 to + 125 ° C. by using the solder alloy according to the present invention for soldering an in-vehicle electronic circuit having a small solder amount and almost no solder fillet and a thin solder joint. Even if it is used underneath, cracks do not occur in the solder joints, and even if cracks occur, propagation through the solder is suppressed, so a highly reliable in-vehicle electronic circuit and in-vehicle electronic circuit device Can be obtained.
In addition, the solder alloy of the present invention is also suppressed in cracks generated at the joint interface, and has characteristics particularly suitable for soldering of ECU devices.

It is a schematic diagram around the solder joint part of the conventional electronic circuit. It is a schematic diagram of the periphery of the solder joint of the in-vehicle electronic circuit of the present application. It is the electron micrograph which took the state of the SnSb intermetallic compound after 3000 cycles in the temperature cycle test of the solder alloy (Example 5) of this invention. It is the electron micrograph which took the state of the SnSb intermetallic compound after 3000 cycles in the temperature cycle test of the solder alloy of the comparative example (comparative example 4). It is the schematic diagram which showed the calculation method of the crack rate. From Table 2, it is the graph which plotted the crack generation rate and the shear strength residual rate with respect to Sb content (there is no Bi). From Table 2, it is the graph which plotted the crack generation rate with respect to Bi content. From Table 2, it is the graph which plotted the shear strength residual rate with respect to Bi content.

When Sb added to the solder alloy of the present invention is less than 1% by mass, the amount of Sb is too small, and a form in which Sb is dispersed in the Sn matrix does not appear, and further, the effect of solid solution strengthening does not appear. Furthermore, the shear strength of the solder joint is also reduced. In addition, when Sb is added such that Sb exceeds 5% by mass, the liquidus temperature rises, so Sb does not remelt at a high temperature exceeding 125 ° C. that appears when the engine is operating under the hot sun. Therefore, it is impossible to suppress the propagation of cracks in the solder. Further, when the liquidus temperature rises, the temperature peak at the time of mounting rises, so that Cu wired on the surface of the printed circuit board melts in the solder, and an SnCu intermetallic compound layer such as Cu ₆ Sn ₅ is printed. It becomes easy to form thickly in the soldering part with a board | substrate, and it becomes easy to destroy a printed circuit board and a solder joint part.
Therefore, the amount of Sb of the present invention is 3 to 5% by mass. The amount of Sb is preferably more than 3 to 5%.

The solder alloy of the present invention suppresses the generation and propagation of cracks in the solder and also suppresses the generation of cracks at the solder joint interface between the ceramic component and the solder joint. For example, when soldering to Cu land, an intermetallic compound of Cu ₆ Sn ₅ is generated at the joint interface with Cu land, but the solder alloy of the present invention contains 0.01 to 0.2% by mass of Ni, This contained Ni moves to the soldering interface portion during soldering to generate (CuNi) ₆ Sn ₅ instead of Cu ₆ Sn ₅ , and the (CuNi) ₆ Sn ₅ intermetallic compound layer at the interface The Ni concentration becomes higher. Thereby, an intermetallic compound layer of (CuNi) ₆ Sn ₅ that is finer than Cu ₆ Sn _{5 and} has a uniform particle size is formed at the soldering interface. The fine (CuNi) ₆ Sn ₅ intermetallic compound layer has an effect of suppressing cracks propagating from the interface. This is because, in an intermetallic compound layer having a large particle size such as Cu ₆ Sn ₅ , the generated crack propagates along the large particle size, so that the crack progresses quickly. However, when the particle diameter is fine, the stress of the generated crack is dispersed in many particle diameter directions, so that the progress of the crack can be delayed.

Thus, in the solder alloy of the present invention, by adding Ni, the intermetallic compound in the intermetallic compound layer generated near the soldering interface is refined to suppress the generation of cracks and once generated It works to suppress the propagation of Therefore, the solder alloy of the present invention can suppress the generation and propagation of cracks from the joint interface.
If the amount of Ni is less than 0.01% by mass, the amount of Ni at the soldering interface is small, so the effect of modifying the solder joint interface is insufficient, so there is no crack suppression effect, and the amount of Ni is 0.2. When the mass% is exceeded, the liquidus temperature rises, so that remelting of Sb added to the present invention does not occur, and the effect of maintaining the particle size of the fine SnSb intermetallic compound is hindered.
Therefore, the amount of Ni of the present invention is preferably 0.01 to 0.2% by mass, more preferably 0.02 to 0.1% by mass. More preferably, it is 0.02 to 0.08%.

Ag added to the present invention improves the wettability of the solder and precipitates a network-like compound of an Ag3Sn intermetallic compound in the solder matrix to produce a precipitation dispersion strengthened type alloy, improving the temperature cycle characteristics The effect of aiming at is demonstrated.
In the solder alloy of the present invention, when the Ag content is less than 1% by mass, the effect of improving the wettability of the solder is not exhibited, the amount of Ag ₃ Sn precipitated is reduced, and the intermetallic compound network is not strengthened. . Further, when the amount of Ag exceeds 4% by mass, the liquidus temperature of the solder rises, and remelting of Sb added according to the present invention does not occur, and the effect of miniaturizing the SnSb intermetallic compound is inhibited. Resulting in.
Therefore, the amount of Ag added to the present invention is preferably 1 to 4% by mass. More preferably, the amount of Ag is 3.2 to 3.8% by mass.

Cu added to the solder alloy of the present invention has an effect of preventing Cu erosion to the Cu land and an effect of improving the temperature cycle characteristics by precipitating a fine Cu ₆ Sn ₅ compound in the solder matrix.
When Cu of the solder alloy of the present invention is less than 0.6% by mass, prevention of Cu erosion to Cu lands does not appear, and when Cu is added in excess of 0.8% by mass, an intermetallic compound of Cu ₆ Sn ₅ is bonded to the bonding interface. Therefore, the growth of cracks due to vibration or the like is accelerated.

In the solder alloy of the present invention, the temperature cycle characteristics can be further improved by adding Bi. Sb added in the present invention not only precipitates SnSb intermetallic compounds to form a precipitation dispersion strengthened type alloy, but also enters the atomic arrangement lattice and distorts the atomic arrangement lattice by replacing it with Sn. Reinforcing the matrix also has the effect of improving temperature cycle characteristics. At this time, if Bi is contained in the solder, Bi is replaced with Sb, so that the temperature cycle characteristics can be further improved. This is because Bi has a larger atomic weight than Sb and has a great effect of distorting the lattice of the atomic arrangement. Further, Bi does not hinder the formation of fine SnSb intermetallic compounds, and a precipitation dispersion strengthened solder alloy is maintained.
If the amount of Bi added to the solder alloy of the present invention is less than 1.5% by mass, substitution with Sb hardly occurs and the amount of fine SnSb intermetallic compound decreases, so that the effect of improving the temperature cycle does not appear, When the amount of Bi exceeds 5.5% by mass, the ductility of the solder alloy itself becomes low and it becomes hard and brittle, so that crack growth due to vibration or the like is accelerated.
The amount of Bi added to the solder alloy of the present invention is preferably 1.5 to 5.5% by mass, and more preferably 3 to 5% by mass. More preferably, it is 3.2-5.0 mass%.

Furthermore, in the solder alloy of the present invention, the effect of Ni of the present invention can be enhanced by adding Co.
When the amount of Co added to the solder alloy of the present invention is less than 0.001% by mass, the effect of preventing the growth of interface cracks by precipitation at the joint interface does not appear. The intermetallic compound layer deposited on the interface becomes thick, and crack growth due to vibration or the like is accelerated.
The amount of Co added to the present invention is preferably 0.001 to 0.1% by mass.

  As apparent from the above description, the solder alloy according to the present invention is excellent in heat cycle performance, and since crack generation and propagation in the solder is suppressed, it is used in a state where it is constantly subjected to vibration. Even when used for automobiles, that is, for automobiles, the growth and progress of cracks are not promoted. Therefore, since it has such a particularly remarkable characteristic, it turns out that the solder alloy concerning this invention is especially suitable for the soldering of the electronic circuit mounted in a motor vehicle.

  As used herein, “excellent in heat cycleability” means that cracks occur after 3000 cycles even when a heat cycle test of −40 ° C. or lower and + 125 ° C. or higher is performed as shown in the examples described later. The rate is 90% or less, and similarly, the shear strength remaining rate after 3000 cycles is 30% or more.

Such characteristics mean that even when used under extremely severe conditions such as the above heat cycle test, the on-vehicle electronic circuit does not break, that is, cannot be used or does not cause malfunction. The solder alloy used for soldering is a highly reliable solder alloy. Furthermore, the solder alloy of the present invention is excellent in the shear strength remaining rate after the temperature cycle. That is, even if it is used for a long period of time, resistance to external forces such as shear strength does not decrease against external forces applied from the outside such as collision and vibration.
As described above, the solder alloy according to the present invention is more specifically used for soldering an in-vehicle electronic circuit or used for soldering an ECU electronic circuit and exhibiting excellent heat cycle performance. It is.

The “electronic circuit” is a system (system) that exerts a target function as a whole by an electronic combination of a plurality of electronic components each having a function.
Examples of electronic components that constitute such an electronic circuit include chip resistor components, multiple resistor components, QFP, QFN, power transistors, diodes, capacitors, and the like. An electronic circuit incorporating these electronic components is provided on a substrate to constitute an electronic circuit device.

  In the present invention, a substrate constituting such an electronic circuit device, for example, a printed wiring board, is not particularly limited. Further, the material is not particularly limited, but a heat-resistant plastic substrate (for example, FR-4 having high Tg and low CTE) is exemplified. The printed circuit board is preferably a printed circuit board having a Cu land surface treated with an organic substance (OSP: Organic Surface Protection) such as amine or imidazole.

  The shape of the lead-free solder according to the present invention is used for joining fine solder parts, so it is used for reflow soldering and is usually used as a solder paste, but it is shaped like a ball, pellet or washer. It may be used as a solder preform.

  In Table 1, for each solder alloy in Table 1, the liquidus temperature, the initial value of the temperature cycle test, the SnSb particle diameter after 1500 cycles, and the crack rate were measured by the following methods.

(Solder melting test)
Each solder alloy of Table 1 was produced and the melting temperature of the solder was measured. The measurement method was performed according to JIS Z3198-1 for the solidus temperature. The liquidus temperature was measured by the same DSC method as the method for measuring the solidus temperature of JIS Z3198-1, without adopting JIS Z3198-1.
The results are shown in the liquidus temperature in Table 1.

(Temperature cycle test)
The solder alloy shown in Table 1 was atomized to obtain solder powder. A solder paste of each solder alloy was prepared by mixing with soldering flux composed of pine resin, solvent, activator, thixotropic agent, organic acid, and the like. Solder paste is printed on a 6-layer printed circuit board (material: FR-4) with a 150 μm metal mask, and then mounted with a 3216 chip resistor using a mounter, under the conditions of a maximum temperature of 235 ° C. and a holding time of 40 seconds. Reflow soldering was performed to prepare a test board.
The test board soldered with each solder alloy is put in a temperature cycle test apparatus set at low temperature −40 ° C., high temperature + 125 ° C. and holding time of 30 minutes, and is taken out from the temperature cycle test apparatus at each initial condition after 1500 cycles. The average particle diameter of the SnSb intermetallic compound particles in the Sn matrix of the solder alloy was measured by observation with an electron microscope of 3500 times.
The results are shown in Table 1 as crack rates and SnSb particle sizes.
Here, * 1 in Table 1 indicates that the SnSb intermetallic compound was not visible and measurement was not possible, and * 2 indicates that the liquidus temperature of the solder was high and soldering could not be performed at the reflow condition of 235 ° C. Indicates.

(Crack rate)
The crack occurrence rate is an indicator of how much the cracked area is with respect to the assumed crack length. After measuring the particle size of SnSb, the state of cracks was observed using an electron microscope of 150 times, and the crack rate was measured assuming the full length of the cracks.
Crack rate (%) = total crack length x 100
Assumed line crack total length Here, "assumed line crack total length" refers to the crack length of complete fracture.
The crack rate is a rate obtained by dividing the total length of the plurality of cracks 7 shown in FIG.
The results are listed in Table 1.

  From Table 1, it can be seen that even after 1500 cycles of the temperature cycle test, the SnSb crystal grains are not coarsened and remain unchanged from the initial values.

  FIG. 3 shows the state of the SnSb intermetallic compound 7 after 3000 cycles in the temperature cycle test, taken with an electron microscope of 3500 times, for the solder alloy of Example 5. The SnSb intermetallic compound of Example 5 is fine and is uniformly distributed in the solder. Therefore, even if a crack occurs, it prevents the SnSb intermetallic compound from cracking.

  FIG. 4 shows the state of the SnSb intermetallic compound 7 after 3000 cycles in the temperature cycle test, taken with an electron microscope of 3500 times, for the solder alloy of Comparative Example 4. The SnSb intermetallic compound of the comparative example is enlarged, and the occurrence of cracks in the SnSb intermetallic compound cannot be suppressed.

  Next, in Table 2, the crack occurrence rate and the shear strength remaining rate after 3000 cycles in the temperature cycle test were measured for each solder alloy in Table 2. The method for measuring the crack occurrence rate was the same as in Table 1, but the number of cycles was 3000. The method of measuring the shear strength residual rate is as follows.

(Share strength remaining rate)
The shear strength remaining rate is an index of how much strength is maintained in the temperature cycle test with respect to the shear strength of the soldered portion in the initial state.
The shear strength test was performed using a joint strength tester STR-1000 at room temperature, at a test speed of 6 mm / min, and at a test height of 50 μm.
The results are summarized in Table 2.

  From Table 2, the graph which plotted the crack generation rate and the shear strength residual rate with respect to Sb content about Sn-Ag-Cu-Ni-Sb series solder alloy is shown in FIG. When the amount of Sb is 1.0 to 5.0% within the range of the present invention, the crack occurrence rate is 90% or less and the shear strength residual rate is 30% or more. By the solder alloy of the present invention, A solder alloy that has excellent temperature cycle characteristics and is resistant to impacts such as collisions can be obtained.

  From Table 2, FIG. 7 shows a graph in which the crack occurrence rate is plotted according to the Sb amount with respect to the Bi content with respect to the Sn—Ag—Cu—Ni—Sb—Bi based solder alloy. When the Bi content is 1.5 to 5.5% within the range of the present invention and the Sb content is 1 to 5%, the crack generation rate is 90% or less, excellent in temperature cycle characteristics, and crack generation. Can be suppressed.

  From Table 2, FIG. 8 shows a graph in which the shear strength remaining ratio is plotted according to the Sb amount with respect to the Bi content with respect to the Sn—Ag—Cu—Ni—Sb—Bi based solder alloy. When the Bi content is in the range of 1.5 to 5.5% within the scope of the present invention and the Sb content is 1 to 5%, the shear strength residual ratio is 30% or more, and it is resistant to impacts such as collisions, and cracks. Occurrence can be suppressed.

  In conclusion, the solder alloy of the present invention is maintained in a state where the SnSb crystal grains do not become coarse and remain unchanged from the initial value even under the severe temperature conditions required for an automobile ECU board of −40 to + 125 ° C. As a result, the occurrence of cracks occurring in the solder can be reduced as compared with other solder alloys.

  The lead-free solder alloy according to the present invention is not limited to reflow soldering, but may be ingot, rod, or wire solder, which is the shape of flow soldering, or greased solder, which is the shape of manual soldering.

DESCRIPTION OF SYMBOLS 1 Chip component 2 Solder alloy 3 Board | substrate 4 Cu land 5 Intermetallic compound layer 6 Crack progress path 7 SnSb intermetallic compound 8 Crack expected progress path

Claims (10)

  Ag: 1-4% by mass, Cu: 0.6-0.8% by mass, Sb: 3-5% by mass, Ni: 0.01-0.2% by mass, Bi: 1.5-5.5% by mass %, The balance is Sn, a lead-free solder alloy.   Ag: 1-4% by mass, Cu: 0.6-0.8% by mass, Sb: 3% by mass or more and less than 5% by mass, Ni: 0.01-0.2% by mass, Bi: 1.5-5 A lead-free solder alloy comprising 5 mass%, Co: 0.001 to 0.1 mass%, and remaining Sn.   The free solder alloy according to claim 1 or 2, wherein the Bi content is 3.2 to 5.0 mass%.   The lead-free solder alloy according to any one of claims 1 to 3, wherein a shear strength residual ratio with respect to an initial value after 3000 cycles of a temperature cycle test is 30% or more.   The lead-free solder alloy according to any one of claims 1 to 4, wherein a crack generation rate after 3000 cycles of a temperature cycle test is 90% or less.   The lead-free solder alloy according to any one of claims 1 to 5, wherein the lead-free solder alloy is bonded to a substrate subjected to Cu-OSP treatment.   An in-vehicle electronic circuit having a solder joint made of the lead-free solder alloy according to claim 1.   An ECU electronic circuit having a solder joint made of the lead-free solder alloy according to claim 1.   An in-vehicle electronic circuit device comprising the electronic circuit according to claim 7.   An ECU electronic circuit device comprising the ECU electronic circuit according to claim 8.