KR102373856B1 - Lead-free solder alloy, electronic circuit board and electronic control unit - Google Patents

Abstract

Crack growth of solder joints can be suppressed even in harsh environments with severe temperature differences and vibration loads Also in the present invention, a lead-free solder alloy capable of suppressing crack propagation in the vicinity of an interface between an electronic component and a solder joint, and an electronic circuit board and an electronic control device having a solder joint formed using the lead-free solder alloy are provided. . 1 wt% or more and 4 wt% or less of Ag, 1 wt% or less of Cu, 3 wt% or more and 5 wt% or less of Sb, 0.01 wt% or more and 0.25 wt% or less of Ni, and the balance contains Sn It is a lead-free solder alloy characterized in that.

Description

LEAD-FREE SOLDER ALLOY, ELECTRONIC CIRCUIT BOARD AND ELECTRONIC CONTROL UNIT

The present invention relates to a lead-free solder alloy, and an electronic circuit board and an electronic control device having a solder joint formed using the lead-free solder alloy.

Conventionally, when bonding electronic components to an electronic circuit formed on a substrate such as a printed wiring board or a silicon wafer, a solder bonding method using a solder alloy is employed. It was common to use lead for this solder alloy. However, in view of the environmental load, the use of lead is restricted by the RoHS directive or the like, so in recent years, a solder joining method that does not contain lead, so-called lead-free solder alloy, has become common.

As this lead-free solder alloy, Sn-Cu type, Sn-Ag-Cu type, Sn-Bi type, Sn-Zn type solder alloy etc. are well known, for example. Among them, Sn-3Ag-0.5Cu solder alloy is often used for consumer electronic devices used for televisions, mobile phones, etc., and vehicle-mounted electronic devices mounted on automobiles.

Although lead-free solder alloys have somewhat inferior solderability compared to lead-containing solder alloys, improvements in flux and soldering equipment have covered this solderability problem. For this reason, for example, even in a vehicle-mounted electronic circuit board, when placed in a relatively mild environment, although there is a temperature difference such as in the interior of an automobile, a solder joint formed using a Sn-3Ag-0.5Cu solder alloy is also a big problem. It's not happening.

However, in recent years, for example, as with electronic circuit boards used in electronic control devices, temperature differences such as engine compartment, engine fabric, and mechanical integration with motors are particularly severe (eg, -30°C to 110°C, - (due to cold temperatures such as 40°C to 125°C and -40°C to 150°C), and also examination and practical use of the arrangement of electronic circuit boards in harsh environments subjected to vibration loads. Under such an environment where the temperature difference is very severe, thermal displacement of the solder joint due to the difference in the coefficient of linear expansion between the mounted electronic component and the substrate and stress accompanying it are likely to occur. In addition, repeated plastic deformation due to cold temperature difference tends to cause cracks in the solder joint, and since the stress applied repeatedly over time is concentrated near the tip of the crack, the crack crosses to the deep part of the solder joint. Easier to progress The cracks that have remarkably advanced in this way cause breakage of the electrical connection between the electronic component and the electronic circuit formed on the substrate. In particular, in an environment in which vibration is applied to the electronic circuit board in addition to severe cold weather, the cracks and their propagation are more likely to occur.

Therefore, while the number of vehicle-mounted electronic circuit boards and electronic control devices placed under the harsh environment described above increases, the demand for a Sn-Ag-Cu-based solder alloy capable of exhibiting a sufficient crack growth suppression effect is expected to increase in the future. It is expected.

In addition, in the lead portion of electronic components such as QFP (Quad Flat Package) and SOP (Small Outline Package) mounted on vehicle-mounted electronic circuit boards, conventionally Ni/Pd/Au plating or Ni/Au plating is applied. has been used However, with the recent reduction in cost of electronic components and downsizing of substrates, electronic components in which lead parts are replaced with Sn plating or electronic components having Sn-plated lower surface electrodes are being studied and put to practical use.

At the time of soldering, the Sn plated electronic component tends to generate interdiffusion of Sn contained in Sn plating and the solder joint and Cu contained in the lead portion or the lower surface electrode. Due to this interdiffusion, the Cu ₃ Sn layer, which is an intermetallic compound, has a large concavo-convex shape in the region near the interface between the solder joint and the lead portion or the lower electrode (hereinafter referred to as “interface vicinity” in this specification). grow up The Cu ₃ Sn layer is inherently hard and brittle, and the Cu ₃ Sn layer grown to a large concavo-convex shape is more brittle. Therefore, especially under the harsh environment described above, cracks are more likely to occur in the vicinity of the interface compared to the solder joint, and the generated cracks rapidly develop from this as a starting point, so that an electrical short is likely to occur.

Therefore, in the future, even in the case of using an electronic component without Ni/Pd/Au plating or Ni/Au plating under the harsh environment described above, a lead-free solder alloy capable of exhibiting the effect of suppressing crack growth in the vicinity of the interface. Demand is also expected to increase.

Until now, there are several methods for improving the strength of the solder joint and accompanying thermal fatigue characteristics by adding an element such as Ag or Bi to the Sn-Ag-Cu-based solder alloy, thereby suppressing crack growth of the solder joint. It is disclosed (refer patent document 1 - patent document 7).

When Bi is added to the solder alloy, Bi enters the lattice of the atomic arrangement of the solder alloy and is replaced with Sn, thereby distorting the lattice of the atomic arrangement. Thereby, since the Sn matrix is strengthened and the alloy strength is improved, a certain improvement of the solder crack propagation characteristic by the addition of Bi is expected.

However, lead-free solder alloys that are strengthened by the addition of Bi have disadvantages in that ductility deteriorates and brittleness becomes stronger. As a result of the applicant using a conventional lead-free solder alloy to which Bi is added to solder the board and the chip resistor component and placing it in an environment with a large temperature difference, in the fillet part on the chip resistor part side, the long side of the chip resistor part A crack was formed in a straight line from a direction of about 45° to the direction, and an electrical short was generated. Therefore, especially in a vehicle-mounted substrate subjected to a severe cold weather environment, the crack growth suppression effect alone by adding Bi or the like as in the prior art is not sufficient.

In addition, when solder bonding is performed using electronic components that are not plated with Ni/Pd/Au or Ni/Au, the Cu ₃ Sn layer, which is an intermetallic compound, grows large in concave-convex shape near the interface. Suppression of crack propagation in the vicinity is difficult.

Japanese Patent Laid-Open No. 5-228685 Japanese Patent Laid-Open No. 9-326554 Japanese Patent Laid-Open No. 2000-190090 Japanese Patent Laid-Open No. 2000-349433 Japanese Patent Laid-Open No. 2008-28413 International open pamphlet WO2009/011341 Japanese Patent Laid-Open No. 2012-81521

The present invention solves the above problems, and it is possible to suppress the crack propagation of the solder joint even in a harsh environment where the difference between cold and cold is severe and vibration is applied, and Ni/Pd/Au plating or Ni/Au plating is not made. A lead-free solder alloy capable of suppressing crack propagation in the vicinity of the interface even when soldering is performed using an electronic component, and an electronic circuit board having a solder joint formed using the lead-free solder alloy, and an electronic device It aims to provide a control device.

(1) The lead-free solder alloy of the present invention contains Ag at 1 wt% or more and 4 wt% or less, Cu at 1 wt% or less, Sb at 3 wt% or more and 5 wt% or less, and Ni at 0.01 wt% or more It is characterized in that it contains 0.25 weight% or less, and the remainder contains Sn.

(2) In the configuration described in (1) above, the lead-free solder alloy of the present invention is characterized in that it further contains 0.001 wt% or more and 0.25 wt% or less of Co.

(3) The structure of said (1) or (2) WHEREIN: It is characterized by the content of Sb being 3.5 weight% or more and 5 weight% or less.

(4) Further, as another configuration of the present invention, the lead-free solder alloy of the present invention contains 1 wt% or more and 4 wt% or less of Ag, 1 wt% or less of Cu, and 3 wt% or more and 5 wt% or less of Sb with Ni in 0.01 wt% or more and 0.25 wt% or less, Co in 0.001 wt% or more and 0.25 wt% or less, and the balance contains Sn, each content (wt%) of Ag, Cu, Sb, and Ni and Co It is characterized by satisfying all of the following formulas (A) to (D).

1.6≤Ag content+(Cu content/0.5)≤5.4... A

0.73≤(Ag content/4)+(Sb content/5)≤2.10... B

1.1≤Sb content/Cu content≤11.9... C

0<(Ni content/0.25)+(Co content/0.25)≤1.19... D

(5) The structure according to any one of (1) to (4) above, wherein the lead-free solder alloy of the present invention further contains 6% by weight or less of In.

(6) In the configuration described in any one of (1) to (5) above, the lead-free solder alloy of the present invention contains at least 0.001% by weight or more and 0.05% by weight or less of at least one of P, Ga, and Ge in total. It is characterized by including.

(7) In the configuration according to any one of (1) to (6), the lead-free solder alloy of the present invention contains at least one of Fe, Mn, Cr, and Mo in a total of 0.001 wt% or more and 0.05 wt% It is characterized in that it further includes the following.

(8) The electronic circuit board of the present invention is characterized in that it has a solder joint formed using the lead-free solder alloy according to any one of (1) to (7) above.

(9) The electronic control device of the present invention is characterized in that it has the electronic circuit board according to (8) above.

The lead-free solder alloy of the present invention, and an electronic circuit board and electronic control device having a solder joint formed by using the lead-free solder alloy have a severe temperature difference and crack propagation in the solder joint even under a harsh environment loaded with vibration can be suppressed, and crack propagation in the vicinity of the interface can be suppressed even when solder bonding is performed using an electronic component not subjected to Ni/Pd/Au plating or Ni/Au plating.

BRIEF DESCRIPTION OF THE DRAWINGS It relates to one Embodiment of this invention, The partial sectional drawing which shows a part of an electronic circuit board.
2 is an electron micrograph showing a cross section in which a void is generated in a fillet portion of a chip component in a test board according to a comparative example of the present invention.
Fig. 3 is a photograph taken from the chip component side using an X-ray transmitting device, showing a region under an electrode of the chip component and a region in which fillets are formed in test boards according to Examples and Comparative Examples of the present invention;

EMBODIMENT OF THE INVENTION Hereinafter, the lead-free solder alloy of this invention, and one Embodiment of an electronic circuit board and an electronic control apparatus are described in detail. In addition, it goes without saying that this invention is not limited to the following embodiment.

(1) Lead-free solder alloy

The lead-free solder alloy of this embodiment can contain 1 weight% or more and 4 weight% or less of Ag. By adding Ag, Ag ₃ Sn compound can be precipitated in the Sn grain boundary of a lead-free solder alloy, and mechanical strength can be provided.

However, when the Ag content is less than 1% by weight, precipitation of the Ag ₃ Sn compound is small, and the mechanical strength and thermal shock resistance of the lead-free solder alloy are lowered, so it is not preferable. In addition, when the Ag content exceeds 4% by weight, the stretchability of the lead-free solder alloy is impaired, and there is a risk that the solder joint formed using the Ag may cause electrode peeling of the electronic component, which is not preferable.

Further, when the Ag content is set to 2% by weight or more and 3.8% by weight or less, the balance between strength and ductility of the lead-free solder alloy can be further improved. More preferably, the content of Ag is 2.5 wt% or more and 3.8 wt% or less.

The lead-free solder alloy of this embodiment can contain 1 weight% or less of Cu. By adding Cu in this range, while exhibiting the effect of preventing Cu erosion to Cu land of an electronic circuit, the thermal shock resistance of a lead-free solder alloy can be improved by precipitating Cu ₆ Sn ₅ compound in Sn grain boundary.

Further, when the content of Cu is set to 0.5% by weight to 1% by weight, a good Cu corrosion prevention effect can be exhibited. In particular, when the content of Cu is 0.7 wt% or less, the effect of preventing Cu erosion on Cu land can be exhibited, and the viscosity of the lead-free solder alloy at the time of melting can be maintained in a good state, and voids at the time of reflow can be maintained. It is possible to suppress the generation of , and improve the thermal shock resistance of the solder joint to be formed. Furthermore, fine Cu ₆ Sn ₅ is dispersed in the Sn grain boundaries of the molten lead-free solder alloy, thereby suppressing the change in the crystal orientation of Sn and suppressing the deformation of the solder joint shape (fillet shape).

In addition, when the content of Cu exceeds 1% by weight, Cu ₆ Sn ₅ compound tends to precipitate in the vicinity of the interface between the electronic component and the electronic circuit board in the solder joint, and there is a risk of impairing the bonding reliability or the elongation of the solder joint. It is not preferable because there is

The lead-free solder alloy of this embodiment can contain 3 weight% or more and 5 weight% or less of Sb. By adding Sb within this range, the crack growth suppression effect of the solder joint can be improved without impairing the ductility of the Sn-Ag-Cu-based solder alloy. When the content of Sb is 3% by weight or more and 5% by weight or less, more preferably 3.5% by weight or more and 5% by weight or less, the effect of suppressing crack growth can be further improved.

Here, in order to withstand the external stress that is exposed for a long time in a harsh environment with a large temperature difference, the toughness (size of the area surrounded by the stress-strain curve) of the lead-free solder alloy is increased to improve elongation, and also to the Sn matrix. It is considered effective to add an element that dissolves in solid solution to strengthen the solid solution. In addition, Sb is an optimal element for solid solution strengthening of a lead-free solder alloy while ensuring sufficient toughness and ductility.

In other words, by adding Sb in the above range to a lead-free solder alloy in which the base material is substantially Sn (referring to the main constituents of the lead-free solder alloy in this specification, the same applies hereinafter), a part of the crystal lattice of Sn becomes Sb , and distortion occurs in the crystal lattice. Therefore, in the solder joint formed using such a lead-free solder alloy, the energy required for transition in the crystal is increased by Sb substitution of a part of the Sn crystal lattice, and the metal structure thereof is strengthened. Furthermore, by precipitating fine SnSb and ε-Ag ₃ (Sn, Sb) compounds at the Sn grain boundaries, sliding deformation at the Sn grain boundaries is prevented, thereby suppressing the growth of cracks occurring in the solder joint.

In addition, compared to the Sn-3Ag-0.5Cu solder alloy, the structure of the solder joint formed using the lead-free solder alloy containing Sb in the above range shows that Sn crystals are fine even after prolonged exposure to a harsh environment with a severe cold temperature difference. The state was secured, and it was confirmed that it is a structure in which a crack is hard to propagate. This is because the SnSb, ε-Ag ₃ (Sn, Sb) compound deposited at the Sn grain boundary is finely dispersed in the solder joint even after exposure to a harsh environment with a large temperature difference for a long time, so Sn crystal coarsening is suppressed. It is thought that there is That is, in a solder joint using a lead-free solder alloy with Sb added within the above range, the solid solution of Sb in the Sn matrix at a high temperature and the precipitation of the SnSb, ε-Ag ₃ (Sn, Sb) compound at a low temperature Therefore, even when exposed for a long time in a harsh environment with a severe cold-difference, the process of solid-solution strengthening under high temperature and precipitation strengthening under low temperature is repeated, so that excellent cold-thermal shock resistance can be ensured.

In addition, since the lead-free solder alloy containing Sb in the above range can improve its strength without lowering the ductility compared to the Sn-3Ag-0.5Cu solder alloy, sufficient toughness against external stress can be secured. and residual stress can be relieved.

Here, when a solder joint formed using a solder alloy having low elongation is placed in an environment with a severe temperature difference, the stress repeatedly generated tends to accumulate on the electronic component side of the solder joint. Therefore, deep cracks often occur in the solder joint in the vicinity of the electrode of the electronic component. As a result, stress is concentrated on the electrode of the electronic component in the vicinity of the crack, and a phenomenon in which the solder joint portion peels the electrode on the side of the electronic component may occur. However, in the solder alloy of the present embodiment, by adding Sb within the above range, even if an element that affects the elongation of the solder alloy such as Bi is contained, the elongation of the solder alloy itself is hardly inhibited. Even when exposed for a long time under the conditions, it is possible to suppress the electrode peeling phenomenon of electronic components.

In addition, when the content of Sb is less than 3%, in a part of the Sn crystal lattice, the energy required for transition in the crystal increases due to Sb substitution, and the metal structure can be strengthened in solid solution, but SnSb, ε-Ag ₃ (Sn, Sb) Such fine compounds cannot be sufficiently precipitated at the Sn grain boundary. Therefore, when a solder joint formed using such a solder alloy is exposed to a harsh environment with a large temperature difference for a long period of time, the Sn crystal becomes enlarged and changes into a structure in which cracks are prone to propagation. it is difficult

In addition, when the content of Sb exceeds 5% by weight, the melting temperature of the lead-free solder alloy increases, and Sb is not re-dissolved under high temperature. Therefore, when exposed for a long time in a harsh environment with a severe cold temperature difference, only precipitation strengthening with SnSb, ε-Ag ₃ (Sn, Sb) compounds is performed, and these intermetallic compounds become coarse with the passage of time. , the effect of suppressing the sliding strain at the Sn grain boundary is lost. Moreover, in this case, since the heat-resistant temperature of an electronic component also becomes a problem by the rise of the melting temperature of a lead-free solder alloy, it is unpreferable.

The lead-free solder alloy in the present embodiment suppresses an excessive rise in the melting temperature of the lead-free solder alloy even when the Sb content is 3% by weight or more and 5% by weight or less due to its configuration, and the solder formed It gives good strength to the joined body. Therefore, in the lead-free solder alloy of the present embodiment, it becomes possible to sufficiently exhibit the crack growth suppression effect of the solder joint to be formed without Bi as its essential element.

The lead-free solder alloy of this embodiment can contain 0.01 weight% or more and 0.25 weight% or less of Ni. In the configuration of the lead-free solder alloy of the present embodiment, by adding Ni within this range, fine (Cu, Ni) ₆ Sn ₅ is formed in the molten lead-free solder alloy and dispersed in the base material. The growth of cracks can be suppressed, and the thermal fatigue resistance can be improved.

Further, in the lead-free solder alloy of the present embodiment, even when soldering electronic components that are not plated with Ni/Pd/Au or Ni/Au, during solder bonding, Ni moves to the vicinity of the interface and a fine ( Since Cu, Ni) ₆ Sn ₅ is formed, the growth of the Cu ₃ Sn layer in the vicinity of the interface can be suppressed, and the crack growth suppression effect in the vicinity of the interface can be improved.

However, when the content of Ni is less than 0.01% by weight, the effect of modifying the intermetallic compound becomes insufficient, so that the crack suppression effect in the vicinity of the interface cannot be sufficiently obtained. In addition, when the content of Ni exceeds 0.25% by weight, overcooling is less likely to occur compared to the conventional Sn-3Ag-0.5Cu alloy, and the timing at which the solder alloy is solidified becomes faster. For this reason, in the fillet of the solder joint to be formed, a case is confirmed in which the gas that has tried to escape during the melting of the solder alloy is solidified while remaining therein, and a hole (void) is generated by the gas in the fillet. The voids in the fillet deteriorate the thermal fatigue resistance properties of the solder joint, especially under the severe cold temperature difference of -40°C to 140°C and -40°C to 150°C.

Further, as described above, although Ni tends to generate voids in the fillet, in the configuration of the lead-free solder alloy of the present embodiment, from the balance of the content of Ni and other elements, even if Ni is contained in 0.25 wt% or less, the voids can prevent the occurrence of

Further, when the Ni content is set to 0.01% by weight or more and 0.15% by weight or less, suppression of void generation can be improved while improving the good crack growth suppression effect in the vicinity of the interface and thermal fatigue resistance properties.

The lead-free solder alloy of this embodiment can contain 0.001 weight% or more and 0.25 weight% or less of Co other than Ni. In the configuration of the lead-free solder alloy of the present embodiment, by adding Co within this range, the above effect by adding Ni is enhanced, and fine (Cu, Co) ₆ Sn ₅ is formed in the molten lead-free solder alloy and the base material Since it is dispersed in the inside, it is possible to improve the thermal fatigue resistance properties of the solder joint, particularly in an environment with a severe temperature difference, while suppressing creep deformation and crack propagation of the solder joint.

Further, in the lead-free solder alloy of the present embodiment, even in the case of soldering electronic components not subjected to Ni/Pd/Au plating or Ni/Au plating, the above effect by adding Ni is enhanced, and Co is a solder Since they move to the vicinity of the interface during bonding to form fine (Cu, Co) ₆ Sn ₅ , the growth of the Cu ₃ Sn layer in the vicinity of the interface can be suppressed, and the effect of suppressing crack growth in the vicinity of the interface is reduced. can be improved

However, when the content of Co is less than 0.001% by weight, the effect of modifying the intermetallic compound becomes insufficient, so that the crack suppression effect in the vicinity of the interface cannot be sufficiently obtained. In addition, when the content of Co exceeds 0.25% by weight, overcooling is less likely to occur compared to the conventional Sn-3Ag-0.5Cu alloy, and the timing at which the solder alloy is solidified is accelerated. For this reason, in the fillet of the solder joint to be formed, a case is confirmed in which the gas that has tried to escape during the melting of the solder alloy is solidified while remaining therein, and voids due to the gas are generated in the fillet. The voids in the fillet deteriorate the thermal fatigue resistance properties of the solder joint, especially in an environment with a large temperature difference.

Further, as described above, Co tends to generate voids in the fillet, but in the configuration of the lead-free solder alloy of the present embodiment, from the balance of the content of Co and other elements, even if Co is contained in 0.25 wt% or less, the voids can prevent the occurrence of

Moreover, when content of Co is 0.001 weight% or more and 0.15 weight% or less, suppression of void generation can be improved, improving the favorable crack growth suppression effect and thermal fatigue resistance characteristic.

Here, when Ni and Co are used together in the lead-free solder alloy of the present embodiment, the respective contents (wt%) of Ag, Cu, Sb, and Ni and Co must satisfy all of the following formulas (A) to (D) desirable.

1.6≤Ag content+(Cu content/0.5)≤5.4... A

0.73≤(Ag content/4)+(Sb content/5)≤2.10... B

1.1≤Sb content/Cu content≤11.9... C

0<(Ni content/0.25)+(Co content/0.25)≤1.19... D

By making the content of Ag, Cu, Sb, Ni and Co within the above ranges, even if Bi is not an essential element, inhibition of extensibility and increase in brittleness of the solder joint is suppressed, the strength and thermal fatigue properties of the solder joint are improved, and during the fillet Suppression of generated voids, suppression of crack propagation in solder joints under harsh environments with severe cold and fluctuating temperature, and near the interface during solder bonding of electronic components that are not plated with Ni/Pd/Au or Ni/Au. All of the crack growth suppression effects can be exhibited in a well-balanced manner, and the reliability of the solder joint can be further improved.

In addition, 6 weight% or less of In can be contained in the lead-free solder alloy of this embodiment. By adding In within this range, the melting temperature of the lead-free solder alloy raised by the addition of Sb can be lowered, and the crack growth suppression effect can be improved. In other words, since In is also dissolved in the Sn matrix like Sb, it is possible to further strengthen the lead-free solder alloy, and by forming AgSnIn and InSb compounds and precipitating them at the Sn grain boundaries, the effect of suppressing the sliding deformation of the Sn grain boundaries is exhibited. do.

When the content of In added to the solder alloy of the present invention exceeds 6% by weight, the ductility of the lead-free solder alloy is inhibited, and γ-InSn ₄ is formed during prolonged exposure to a harsh environment with a severe cold difference. This is not preferable because the lead-free solder alloy is self-deformed.

Moreover, more preferable content of In is 4 weight% or less, and 1 weight% - 2 weight% are especially preferable.

In addition, the lead-free solder alloy of this embodiment can contain 0.001 weight% or more and 0.05 weight% or less of at least 1 sort(s) of P, Ga, and Ge. By adding at least one of P, Ga, and Ge within this range, oxidation of the lead-free solder alloy can be prevented. However, when these content exceeds 0.05 weight%, since the melting temperature of a lead-free solder alloy rises and it becomes easy to generate|occur|produce a void in a solder joint part, it is unpreferable.

In addition, the lead-free solder alloy of this embodiment can contain 0.001 weight% or more and 0.05 weight% or less of at least 1 sort(s) of Fe, Mn, Cr, and Mo. By adding at least one of Fe, Mn, Cr, and Mo within this range, the crack growth suppression effect of the lead-free solder alloy can be improved. However, when these content exceeds 0.05 weight%, since the melting temperature of a lead-free solder alloy rises and it becomes easy to generate|occur|produce a void in a solder joint part, it is unpreferable.

In addition, in the lead-free solder alloy of this embodiment, other components (element), for example, Cd, Tl, Se, Au, Ti, Si, Al, Mg, Zn, Bi, etc. can contain. Incidentally, the lead-free solder alloy of the present embodiment naturally also contains unavoidable impurities.

In addition, it is preferable that the balance of the lead-free solder alloy of this embodiment contains Sn. Moreover, content of preferable Sn is 83.4 weight% or more and less than 95.99 weight%.

For the formation of the solder joint of the present embodiment, any method may be used as long as the solder joint can be formed, such as a flow method, mounting with a solder ball, or a reflow method using a solder paste composition. Moreover, especially the reflow method using a solder paste composition is used especially preferably.

(2) Solder paste composition

Such a solder paste composition is produced, for example, by kneading the powdered lead-free solder alloy and flux to form a paste.

As such a flux, for example, a flux containing a resin, a thixotropic agent, an activator, and a solvent is used.

Examples of the resin include rosin-based resins including rosin such as tall oil rosin, gum rosin and wood rosin, and rosin derivatives such as hydrogenated rosin, polymerized rosin, heterogeneous rosin, acrylic acid-modified rosin, and maleic acid-modified rosin; Acrylic acid, methacrylic acid, various esters of acrylic acid, various esters of methacrylic acid, crotonic acid, itaconic acid, maleic acid, maleic anhydride, esters of maleic acid, esters of maleic anhydride, acrylonitrile, methacrylonitrile , an acrylic resin formed by polymerizing at least one monomer selected from among acrylamide, methacrylamide, vinyl chloride, and vinyl acetate; epoxy resin; A phenol resin etc. are mentioned. These can be used individually or in combination of plurality.

Among these, a rosin-based resin, and in particular, a hydrogenated acid-modified rosin obtained by adding hydrogen to an acid-modified rosin is preferably used. Moreover, the combined use of hydrogenated acid-modified rosin and an acrylic resin is also preferable.

The resin preferably has an acid value of 10 mgKOH/g or more and 250 mgKOH/g or less, and the blending amount thereof is preferably 10 wt% or more and 90 wt% or less with respect to the total amount of the flux.

Examples of the thixotropic agent include hydrogenated castor oil, fatty acid amides, and oxy fatty acids. These can be used individually or in combination of plurality. It is preferable that the compounding quantity of the said thixo agent is 3 weight% or more and 15 weight% or less with respect to the flux whole quantity.

As said activator, amine salts (an inorganic acid salt and an organic acid salt), such as a hydrogen halide salt of an organic amine, an organic acid, an organic acid salt, and organic amine salt can be mix|blended, for example. More specifically, diphenylguanidine hydrobromide, cyclohexylamine hydrobromide, diethylamine salt, acid salt, succinic acid, adipic acid, sebacic acid, etc. are mentioned. These can be used individually or in combination of plurality. It is preferable that the compounding quantity of the said activator is 5 weight% or more and 15 weight% or less with respect to the total amount of flux.

As said solvent, isopropyl alcohol, ethanol, acetone, toluene, xylene, ethyl acetate, ethyl cellosolve, a butyl cellosolve, glycol ether etc. can be used, for example. These can be used individually or in combination of plurality. It is preferable that the compounding quantity of the said solvent is 20 weight% or more and 40 weight% or less with respect to the flux whole quantity.

An antioxidant may be blended with the flux for the purpose of suppressing oxidation of the lead-free solder alloy. As this antioxidant, a hindered phenol type antioxidant, a phenol type antioxidant, a bisphenol type antioxidant, a polymer type antioxidant, etc. are mentioned, for example. Among them, a hindered phenol-based oxidizing agent is particularly preferably used. These can be used individually or in combination of plurality. Although the compounding quantity of the said antioxidant is not specifically limited, Generally, it is preferable that it is 0.5 weight% or more and about 5 weight% or less with respect to the total amount of flux.

Other resins and additives such as halogen, matting agent, defoaming agent and inorganic filler may be added to the flux.

It is preferable that the compounding quantity of the said additive is 10 weight% or less with respect to the flux whole quantity. Further, a more preferable blending amount thereof is 5% by weight or less based on the total amount of the flux.

The mixing ratio of the lead-free solder alloy and the flux is preferably 65:35 to 95:5 in the solder alloy:flux ratio. A more preferable blending ratio is 85:15 to 93:7, and a particularly preferable blending ratio is 87:13 to 92:8.

(3) electronic circuit board

The structure of the electronic circuit board of this embodiment is demonstrated using FIG. The electronic circuit board 100 of this embodiment has the board|substrate 1, the insulating layer 2, the electrode part 3, the electronic component 4, and the solder joint 10. The solder joint 10 has a solder joint 6 and a flux residue 7 , and the electronic component 4 has an external electrode 5 and an end 8 .

As the board|substrate 1, if it is used for mounting and mounting of electronic components, such as a printed wiring board, a silicon wafer, and a ceramic package board|substrate, it can use as the board|substrate 1 without limitation to these.

The electrode part 3 is electrically joined to the external electrode 5 of the electronic component 4 via the solder joint part 6 .

Further, the solder joint portion 6 is formed using the solder alloy according to the present embodiment.

Since the electronic circuit board 100 of the present embodiment having such a configuration has an alloy composition in which the solder joint portion 6 exhibits the crack growth suppression effect, even when a crack occurs in the solder joint portion 6, the crack propagation is prevented. can be suppressed In particular, even when the electronic component 4 is not subjected to Ni/Pd/Au plating or Ni/Au plating, the crack growth suppression effect in the vicinity of the interface between the solder joint portion 6 and the electronic component 4 can also be exhibited. . Moreover, the electrode peeling phenomenon of the electronic component 4 can also be suppressed by this.

Such an electronic circuit board 100 is manufactured as follows, for example.

First, on the substrate 1 provided with the insulating layer 2 and the electrode part 3 formed to have a predetermined pattern, the solder paste composition is printed according to the pattern.

Then, the electronic component 4 is mounted on the board|substrate 1 after printing, and this reflows at the temperature of 230 degreeC - 260 degreeC. An electronic circuit in which the substrate 1 and the electronic component 4 are electrically joined while the solder joint 10 having the solder joint portion 6 and the flux residue 7 is formed on the substrate 1 by this reflow. The substrate 100 is manufactured.

Moreover, by incorporating such an electronic circuit board 100, the electronic control device of this embodiment is produced.

[Example]

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. In addition, this invention is not limited to these Examples.

Flux production

The following components were kneaded to obtain fluxes according to Examples and Comparative Examples.

Hydrogenated acid-modified rosin (product name: KE-604, manufactured by Arakawa Chemical Industries, Ltd.) 51 wt%

6 wt% hydrogenated castor oil

Dodecanedioic acid 10% by weight (Product name: SL-12, manufactured by Okamura Seiyu Co., Ltd.)

Malonic acid 1% by weight

Diphenylguanidine hydrobromide 2 wt%

1 wt% of hindered phenolic antioxidant (product name: Irganox 245, manufactured by BASF Japan)

Diethylene glycol monohexyl ether 29 wt%

Fabrication of Solder Paste Composition

Examples 1 to 24 and Comparative Examples 1 to 19 were mixed with 11.0 wt% of the flux and 89.0 wt% of each lead-free solder alloy shown in Tables 1 to 2 (powder particle size: 20 µm to 38 µm) Each solder paste composition according to the method was prepared.

(1) Solder crack test (-40°C to 125°C)

ㆍ3.2mm×1.6mm chip parts (Chip A)

A chip component (Ni/Sn plating) having a size of 3.2 mm × 1.6 mm, a solder resist having a pattern capable of mounting a chip component of the size concerned, and an electrode (1.6 mm × 1.2 mm) for connecting the chip component are provided. A single glass epoxy substrate and a metal mask having a thickness of 150 µm having the same pattern were prepared.

Each solder paste composition was printed on the glass epoxy substrate using the metal mask, and the chip components were mounted respectively.

Then, each of the glass epoxy substrates is heated using a reflow furnace (product name: TNP-538EM, manufactured by Tamura Seisakusho Co., Ltd.) to form a solder joint that electrically bonds the glass epoxy substrate and the chip component to each other. formed, and the chip component was mounted. Reflow conditions at this time include preheating at 170°C to 190°C for 110 seconds, peak temperature at 245°C, 200°C or higher for 65 seconds, 220°C or higher for 45 seconds, peak temperature to 200°C The cooling rate was set to 3°C to 8°C/sec, and the oxygen concentration was set to 1500±500 ppm.

Next, using a cold and heat shock test apparatus (product name: ES-76LMS, manufactured by Hitachi Appliances Co., Ltd.) set to the conditions of -40 ° C. (30 minutes) to 125 ° C. (30 minutes), 1,000 cold shock cycles, Each of the glass epoxy substrates was exposed in an environment where 1,500, 2,000, 2,500, and 3,000 cycles were repeated, and then this was taken out to prepare each test substrate.

Subsequently, the target part of each test board|substrate was cut out, and this was sealed using the epoxy resin (Product name: Epomount (main and hardening agent), Refinetech Co., Ltd. product). In addition, using a wet polisher (product name: TegraPol-25, manufactured by Marumoto Struers Co., Ltd.), in such a state that the central section of the chip component mounted on each test board is known, cracks occurring in the formed solder joint are removed. It was observed using a scanning electron microscope (product name: TM-1000, Hitachi High-Technologies Co., Ltd. product) whether the solder joint part completely crossed and fracture|rupture was observed, and the following criteria evaluated it. The results are shown in Tables 3 and 4. In addition, the number of evaluation chips in each cooling/heat shock cycle was set to 10.

◎: No cracks completely crossing the solder joint until 3,000 cycles

○: Cracks completely crossing the solder joint occurred during 2, 501 to 3,000 cycles.

Δ: Cracks completely traversing the solder joint occurred during 2,001 to 2,500 cycles

×: Cracks completely traversing the solder joint occurred in less than 2,000 cycles

ㆍ2.0×1.2mm chip component (Chip B)

A chip component (Ni/Sn plating) having a size of 2.0 × 1.2 mm, a solder resist having a pattern capable of mounting a chip component of the size concerned, and an electrode (1.25 mm × 1.0 mm) for connecting the chip component Except having used the glass epoxy board|substrate, the test board|substrate was produced on the conditions same as the 3.2 mm x 1.6 mm chip component, and also the same method evaluated. The same results are shown in Tables 3 and 4.

(2) Solder crack test in Sn plating SON

1.3mm pitch SON (Small Outline Non-leaded Package) component (terminal number: 8 pins, product name: STL60N3LLH5, manufactured by STMicroelectronics) with a size of 6mm×5mm×0.8tmm and a pattern capable of mounting the SON component A glass epoxy substrate provided with a solder resist and an electrode (according to the manufacturer's recommended design) for connecting the SON components, and a metal mask having a thickness of 150 µm having the pattern were prepared.

Each solder paste composition was printed on the glass epoxy substrate using the metal mask, and the SON component was mounted on each. After that, cold and heat shock is applied to the glass epoxy substrate under the same conditions as the solder cracking test (1), except that each glass epoxy substrate is placed under an environment in which the cold and thermal shock cycle is repeated 1,000, 2,000, and 3,000 cycles, and each test The substrate was fabricated.

Subsequently, the target part of each test board|substrate was cut out, and this was sealed using the epoxy resin (Product name: Epomount (main and hardening agent), Refinetech Co., Ltd. product). In addition, using a wet polisher (product name: TegraPol-25, manufactured by Marumoto Struers Co., Ltd.), in such a state that the central section of the SON component mounted on each test board can be seen, cracks occurring in the solder joint are soldered It was observed using a scanning electron microscope (product name: TM-1000, Hitachi High-Technologies Co., Ltd. product) with respect to whether the junction part had crossed completely and had reached|ruptured. Based on this observation, with respect to the solder joint, the solder base material (in this specification, the solder base material refers to a portion of the solder joint other than the interface and vicinity of the electrode of the SON component among the solder joints. The same applies hereafter. Table 3 and Table 4 In , it was divided into cracks generated in the “base material”) and cracks generated at the interface (intermetallic compound) between the solder joint and the electrode of the SON component, and evaluated as follows. The results are shown in Tables 3 and 4. In addition, the number of evaluation SONs in each cooling/heat shock cycle was set to 20, and one terminal of the gate electrode was observed per SON, and the cross section of a total of 20 terminals was confirmed.

Cracks in the solder base material

◎: No cracks completely crossing the solder base material up to 3,000 cycles

○: A crack that completely crosses the solder base material occurs during 2001 to 3,000 cycles.

△: Cracks completely traversing the solder base material occurred during 1,001 to 2,000 cycles.

×: A crack that completely crosses the solder base material occurs in less than 1,000 cycles

ㆍCracks occurring at the interface between the solder joint and the electrode of the SON component

◎: No cracks completely crossing the interface until 3,000 cycles

○: A crack that completely crosses the interface occurs during 2, 001 to 3,000 cycles.

Δ: A crack that completely crosses the interface occurs during 1,001 to 2,000 cycles.

×: cracks that completely cross the interface occur in less than 1,000 cycles

(3) Solder crack test (-40°C to 150°C)

Since vehicle-mounted boards and the like are placed in a harsh environment with a very large temperature difference, the solder alloy used therefor is required to exhibit a good crack growth suppression effect even under such an environment. Therefore, in order to clarify whether the solder alloy according to this embodiment can exhibit the effect even under such more severe conditions, a liquid bath type cold-heat shock test apparatus was used to test the temperature difference between -40°C and 150°C. Solder cracking test was performed. The conditions are as follows.

First, a liquid bath type cold/heat shock test apparatus (product name: ETAC WINTECH LT80, manufactured by Kusumoto Co., Ltd.) which set the conditions of -40 ° C (5 minutes) to 150 ° C (5 minutes) for each glass epoxy substrate after solder joint formation was performed. Under the same conditions as the solder cracking test (1) above, except for exposing them to an environment in which 1,000, 2,000, and 3,000 cycles of cold and thermal shock cycles were repeated using 3.2 × 1.6 mm chip components and 2.0 × 1.2 mm chip components respectively. A test board was prepared.

Subsequently, the target part of each test board|substrate was cut out, and this was sealed using the epoxy resin (Product name: Epomount (main and hardening agent), Refinetech Co., Ltd. product). In addition, using a wet polisher (product name: TegraPol-25, manufactured by Marumoto Struers Co., Ltd.), in such a state that the central section of the chip component mounted on each test board is known, cracks occurring in the formed solder joint are removed. It was observed using a scanning electron microscope (product name: TM-1000, Hitachi High-Technologies Co., Ltd. product) whether the solder joint part fully crosses and fractures|ruptures, and the following criteria evaluated it. The results are shown in Tables 3 and 4. In addition, the number of evaluation chips in each cooling/heat shock cycle was set to 10.

◎: No cracks completely crossing the solder joint until 3,000 cycles

○: Cracks completely crossing the solder joint occurred during 2, 001 to 3,000 cycles.

△: Cracks completely crossing the solder joint occurred during 1,001 to 2,000 cycles.

×: Cracks completely traversing the solder joint occurred in less than 1,000 cycles

(4) Void test

Under the same conditions as the above solder crack test (1), each test board on which a 2.0 x 1.2 mm chip component was mounted (a solder joint was formed) was produced.

Subsequently, the surface state of each test board was observed with an X-ray transmission device (product name: SMX-160E, manufactured by Shimadzu Corporation), and in 40 lands among each test board, the area under the electrode of the chip component. The area ratio of voids (the ratio of the total area of voids, hereinafter the same) to (region (a) surrounded by the broken line in FIG. 3) and the area where the fillet is formed (region (b) surrounded by the broken line in FIG. 3) The average value of the area ratio of the voids occupied was calculated|required, and it evaluated as follows about each. The results are shown in Tables 3 and 4.

(double-circle): The average value of the area ratio of voids is 3 % or less, and the suppression effect of void generation|occurrence|production is very favorable.

(circle): The average value of the area ratio of a void is more than 3 % and 5 % or less, and the suppression effect of void generation|occurrence|production is favorable.

(triangle|delta): The average value of the area ratio of voids is more than 5 % and 8 % or less, and the inhibitory effect of void generation|occurrence|production is sufficient.

x: The average value of the area ratio of a void exceeds 8 %, and the inhibitory effect of void generation|occurrence|production is inadequate.

As described above, in the solder joint formed using the lead-free solder alloy according to the embodiment, even under a harsh environment in which the temperature difference is large and vibration is applied, even if Bi is not an essential element, regardless of the size of the chip. Furthermore, the crack growth suppression effect in the vicinity of the solder joint and the interface can be exhibited irrespective of whether the electrode is plated with Ni/Pd/Au or plated with Ni/Au. In particular, it can be seen that the solder joint of the example exhibits a good crack suppression effect even under a very harsh environment in which the difference between cold temperatures is -40°C to 150°C using a liquid bath type cold-heat shock test apparatus.

In particular, in Examples 13 to 24 in which Ni and Co were used in combination, a good solder joint portion and an effect of suppressing crack growth in the vicinity of the interface can be exhibited under any conditions.

Moreover, even when it contains 0.25 weight% of Ni or Co like Example 12 and Example 15, generation|occurrence|production of the void in a fillet can be suppressed, for example.

Accordingly, the electronic circuit board having a large temperature difference and having such a solder joint can be suitably used for an electronic circuit board requiring high reliability, such as an electronic circuit board for use in a vehicle. Moreover, such an electronic circuit board can be used suitably for the electronic control apparatus which further higher reliability is calculated|required.

1: substrate
2: insulating layer
3: electrode part
4: Electronic Components
5: external electrode
6: Solder joint
7: Flux residue
8 : end
10: solder joint
100: electronic circuit board

Claims (28)

2 wt% or more and 4 wt% or less of Ag, 0.5 wt% or more and 0.7 wt% or less of Cu, 3 wt% or more and 5 wt% or less of Sb, 0.01 wt% or more and 0.03 wt% or less of Ni, and the remainder A lead-free solder alloy comprising additional Sn. According to claim 1,
A lead-free solder alloy further comprising 0.001% by weight or more and 0.008% by weight or less of Co. The method of claim 1,
A lead-free solder alloy having a content of Sb of 3.5 wt% or more and 5 wt% or less. 3. The method of claim 2,
A lead-free solder alloy having a content of Sb of 3.5 wt% or more and 5 wt% or less. 2 wt% or more and 4 wt% or less of Ag, 0.5 wt% or more and 0.7 wt% or less of Cu, 3.5 wt% or more and 5 wt% or less of Sb, 0.01 wt% or more and 0.03 wt% or less of Ni, and Co 0.001% by weight or more and 0.008% by weight or less, and the balance contains Sn,
A lead-free solder alloy characterized in that each content (weight%) of Ag, Cu, Sb, Ni and Co satisfies all of the following formulas (A) to (D).
3≤Ag content+(Cu content/0.5)≤5.4... A
1.2≤(Ag content/4)+(Sb content/5)≤2... B
5≤Sb content/Cu content≤10 ... C
0.124≤(Ni content/0.25)+(Co content/0.25)≤0.152... D 6. The method according to any one of claims 1 to 5,
A lead-free solder alloy further comprising 6 wt% or less of In. 6. The method according to any one of claims 1 to 5,
A lead-free solder alloy characterized by further comprising 0.001 wt% or more and 0.05 wt% or less of at least one of Ga and Ge in total. 7. The method of claim 6,
A lead-free solder alloy characterized by further comprising 0.001 wt% or more and 0.05 wt% or less of at least one of Ga and Ge in total. 6. The method according to any one of claims 1 to 5,
A lead-free solder alloy characterized by further comprising 0.001 wt% or more and 0.05 wt% or less of at least one of Fe, Mn, Cr, and Mo in total. 7. The method of claim 6,
A lead-free solder alloy characterized by further comprising 0.001 wt% or more and 0.05 wt% or less of at least one of Fe, Mn, Cr, and Mo in total. 8. The method of claim 7,
A lead-free solder alloy characterized by further comprising 0.001 wt% or more and 0.05 wt% or less of at least one of Fe, Mn, Cr, and Mo in total. 9. The method of claim 8,
A lead-free solder alloy characterized by further comprising 0.001 wt% or more and 0.05 wt% or less of at least one of Fe, Mn, Cr, and Mo in total. An electronic circuit board having a solder joint formed using the lead-free solder alloy according to any one of claims 1 to 5. An electronic circuit board having a solder joint formed using the lead-free solder alloy according to claim 12. An electronic control device comprising the electronic circuit board according to claim 13 . An electronic control device comprising the electronic circuit board according to claim 14 . delete delete delete delete delete delete delete delete delete delete delete delete

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