TW202026436A - Lead-free solder alloy, solder joining material, electronic circuit packaging substrate and electronic control device capable of suppressing development of cracks generated in a solder joint and preventing deformation of the solder joint - Google Patents

Abstract

The present invention provides a lead-free solder alloy, a solder joining material, an electronic circuit packaging substrate and an electronic control device, even in the state that thermal stress is easily concentrated on electronic parts of the solder joint, or the electronic circuit packaging substrate is mounted in a frame body, development of cracks generated in the solder joining can be suppressed, and even under the condition that a moisture-proof agent penetrates into the cracks generated at the solder joint, deformation of the solder joining can be prevented, when an electrode is joined by a BGA solder material composed of a solder ball made of Sn-3Ag-0.5Cu alloy, good thermal fatigue resistance can still be existed. The lead-free solder alloy of the present invention is characterized is that it includes 2.5 mass% or more and 3.1 mass% or less of Ag, 0.6 mass% or more and 1 mass% or less of Cu, 3 mass% or more and 5 mass% or less of Sb, 3.1 mass% or more and 4.5 mass% or less of Bi, 0.01 mass% or more and 0.1 mass% or less of Ni, 0.0085 mass% or more and 0.1 mass% or less of Co, and a remainder of Sn.

Description

Lead-free solder alloys, solder joint materials, electronic circuit packaging substrates, and electronic control devices

The present invention relates to lead-free solder alloys, solder bonding materials, electronic circuit packaging substrates, and electronic control devices.

As a method of joining a conductor pattern formed on an electronic circuit board called a printed wiring board or a module substrate to an electronic component, there is a solder joining method using a solder alloy. In the past, lead was used in this solder alloy. However, from the viewpoint of environmental load, the use of lead is restricted in accordance with the RoHS directive and the like. Therefore, solder joining methods of so-called lead-free solder alloys that do not contain lead have become popular in recent years.

As this lead-free solder alloy, for example, Sn-Cu-based, Sn-Ag-Cu-based, Sn-Bi-based, and Sn-Zn-based solder alloys are widely known. Among them, in consumer electronic devices such as televisions and mobile phones, electronic circuit packaging substrates that use Sn-3Ag-0.5Cu solder alloy for solder bonding (Sn-3Ag-0.5Cu solder alloy is used to form solder joints) are used in large quantities. Here, the solderability of lead-free solder alloys is still slightly worse than that of lead-containing solder alloys. However, through the improvement of flux and soldering equipment, the solderability problem has been overcome. Therefore, equipment such as consumer electronic equipment placed in a relatively stable environment, even with Sn-3Ag-0.5Cu solder alloy Solder bonding can also maintain the reliability of the electronic circuit package substrate to a certain extent.

However, for example, electronic circuit packaging substrates used in electronic control devices that are packaged in an engine room, etc., or electronic control devices that are packaged in motors, etc. (mechatronics), and electronic circuit packaging substrates directly mounted on engines, such as automotive use Electronic circuit packaging substrates must be exposed to a very harsh environment that withstands drastic cold and heat differences (for example, -40°C to 125°C, -40°C to 150°C) and vibration loads. Then, in such an environment where the difference between heat and cold is very severe, in the electronic circuit packaging substrate, because of the packaged electronic parts and substrates (only referred to as "substrates" in this manual, as the case may be, it also refers to any of the following as appropriate: The board before the conductor pattern is formed, the board that has been formed with the conductor pattern and can be electrically connected to the electronic component, and the electronic circuit package substrate on which the electronic component is mounted does not contain the part of the board. In this case, it means "packaged The electronic circuit package substrate of the electronic component does not include the board part of the electronic component") due to the thermal stress caused by the difference in the coefficient of linear expansion, which places a great load on the solder joint. Especially during the use of the automobile, the engine repeatedly runs and stops, which causes the aforementioned load to be repeatedly applied to the solder joint. In addition, the repeated application of the load causes plastic deformation of the solder joint, which may cause cracks in the solder joint.

In addition, due to the repeated application of the load, stress tends to concentrate near the tip of the solder joint where the crack occurs, so that the crack tends to develop transversely to the depth of the solder joint. Such a markedly developed crack will block the electrical connection (electrical short circuit) between the electronic component and the conductor pattern formed on the substrate. Especially in an environment where vibration is applied to the electronic circuit packaging substrate in addition to the drastic difference in heat and cold, the above-mentioned cracks and their development are more likely to occur.

Here, electronic components with leads, such as the quad flat package (QFP; Quad Flat Package) conventionally packaged on electronic circuit boards for vehicles, can relax the thermal stress applied to the solder joints due to the presence of the leads. It is possible to suppress the occurrence of cracks that cross the solder joints to some extent.

However, due to the trend of digitization in recent years, semiconductor devices such as microcontrollers are required to have higher performance and multi-functionality. Therefore, in addition to QFP electronic components, various forms of electronic components such as ball grid array packages (BGA; Ball Grid Array) or quad flat non-leaded packages (QFN; Quad Flat Non-leaded package) are also used. Moreover, in electronic components such as BGA and QFN, the above-mentioned thermal stress is likely to be concentrated in the solder joints, which is more likely to cause electrical short circuits than QFP.

In addition, when the electronic circuit package substrate on which the above-mentioned electronic components are mounted is assembled into an electronic control device, it is often mounted on a frame made of aluminum alloy or the like by screws or the like. The locking torsion generated during the mounting process causes the electronic circuit package substrate to warp, and thus stress may be applied to the solder joints. Therefore, in the case of electronic circuit packaging substrates in which thermal stresses such as BGA and QFN are particularly likely to be concentrated on electronic components in the solder joints, if the thermal cycle test is carried out in the state of being assembled in the frame, it is not only It is thermal stress, and the stress caused by the above-mentioned locking torque is also applied to the solder joint. Therefore, when comparing the assembled state of the electronic circuit package substrate in the frame with the unassembled state, in the thermal cycle test, the load applied to the solder joint is significantly greater in the former case. As such, in the actual use environment of the electronic circuit package substrate, the load applied to the solder joint is extremely large, and it is expected that there will be an increasing need in the future to suppress the occurrence of cracks and cracks in the solder joint even under such conditions. It is a lead-free solder alloy that can maintain its joint reliability.

Some documents have disclosed a method of adding Sb or Bi to Sn-Ag-Cu solder alloys in order to suppress the development of cracks in the solder joints and improve their thermal fatigue characteristics or strength (see patent Document 1 to Patent Document 7). [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 5-228685 [Patent Document 2] Japanese Patent Application Publication No. 9-326554 [Patent Document 3] Japanese Patent Application Publication No. 2000-190090 [Patent Document 4] Japanese Patent Application Publication No. 2000-349433 No. [Patent Document 5] JP 2008-28413 A [Patent Document 6] International Publication No. WO2009/011341 [Patent Document 7] JP 2012-81521 A

When Bi is added to the solder alloy, Bi enters the atomic arrangement lattice of the solder alloy and replaces Sn, thereby deforming the atomic arrangement lattice. The Sn base material is thus strengthened, so that the strength of the solder alloy is increased. Therefore, the effect of suppressing the crack development of the solder alloy can be improved by adding Bi.

Here, the electrodes of the BGA corresponding to the lead-free solder alloy are generally composed of Sn-3Ag-0.5Cu alloy solder balls. Therefore, when the BGA is solder-joined using the above-mentioned Bi-added solder alloy, the Bi concentration in the solder joint becomes thinner, and there is a doubt that the thermal fatigue resistance of the solder joint cannot be improved as expected.

In addition, Bi is an alloy element that reduces the ductility of the solder alloy. Here, as the main cause of voids in the solder joint formed by the use of solder alloys, in addition to the flux or air that is mixed into the molten solder during soldering but is not discharged, the grain boundary existing in the solder joint can be cited Agglomeration (enlargement) of atomic pores. That is, if it is explained using the first figure, it is as follows. During the formation of the solder joint 100, atomic diffusion occurs in the molten solder, and the resulting atomic pores may remain in the solder joint 100. From low temperature to normal temperature, the concentration of the atomic pores is low and the volume is small, so the influence on the solder joint 100 is very small (because it is a small volume, it is not shown in the first figure (a) Atomic holes). However, when the solder joint 100 is placed in a high temperature environment, the concentration of the above-mentioned atomic pores increases, and its volume also increases. As shown in the first figure (b), in particular, the atomic pores 2 existing in the grain boundary 1 tend to increase in concentration and therefore their volume tends to increase. Next, in the grain boundary where the concentration of atomic pores increases, the atomic pores tend to agglomerate. Therefore, as shown in the first figure (c), the atomic pores 2 agglomerate at the grain boundary 1 to form a grain boundary hole 2'. In the case where the solder alloy forming the above-mentioned solder joint has good ductility, even in the case where thermal stress is applied to the solder joint 100 in a state where grain boundary voids 2'are generated, the solder joint 100 has a property of being easily deformed, so The above-mentioned thermal stress can be relieved by the deformation of the solder joint 100. Thereby, the thermal stress applied to the defects such as the grain boundary voids 2'inside the solder joint is inevitably reduced, and the connection of the grain boundary voids 2'can be suppressed. However, as described above, Bi is an alloy element that reduces the ductility of the solder alloy. Therefore, in the solder joint 100 formed using the Bi-added solder alloy, thermal stress is applied to the solder joint in a state where grain boundary voids 2'are generated. In the case of 100, it is expected that the thermal stress cannot be alleviated by the deformation of the solder joint 100, and the stress applied to the grain boundary holes 2'inside the solder joint becomes larger. Therefore, as shown in the first figure (d), the crystal The boundary holes 2'are connected, and cracks 3 are likely to occur.

In addition, when the grain boundary holes 2'are connected to form the crack 3, as described above, the crack 3 is likely to develop along the grain boundary 1, and therefore, the crack 3 is likely to be related to the cross section of the solder joint 100. In the state where the burden (stress) applied to the solder joint is large, that is, when thermal stress such as BGA and QFN is used, it is particularly easy to concentrate on the electronic parts of the solder joint or the electronic circuit package substrate is assembled in the frame. In the physical state, this phenomenon is more likely to occur.

Next, in order to suppress the above-mentioned phenomenon, the solder joint must be given the property of being easily deformed, and the strength of the solder joint must also be improved. Here, Sb is an alloy element that makes the solder alloy good in ductility and is solid-soluble in the Sn base material of the solder alloy. Therefore, for example, thermal stresses such as BGA and QFN are easily concentrated on electronic parts in the solder joint. In the state or the state where the electronic circuit package substrate is assembled in the frame, the deformation of the solder joint can be dispersed and the burden (stress) applied to it can be reduced, and the cracks caused by the connection of the above-mentioned grain boundary holes can be suppressed The emergence and development of

However, the solid solution strengthening ability of Sb is lower than that of Bi. Therefore, although it is possible to suppress the occurrence and development of cracks due to the combination of the above-mentioned grain boundary holes, it has the physical properties of the solder joints to deform and the solder joints in an environment where the thermal stress is repeatedly applied due to the drastic cold and heat difference. Reduce doubts. Next, in this case, cracks are generated in the solder joints due to repeated deformation, and there is a concern that the solder joints are broken due to the cracks.

That is, in the state where the thermal stress of BGA and QFN is particularly likely to concentrate on the electronic parts of the solder joint or the state where the electronic circuit package substrate is assembled in the frame, use an alloy such as Bi that inhibits ductility In the solder joints formed by the elemental solder alloys, cracks are easily generated and developed due to the connection of the grain boundary holes. On the other hand, solder joints formed using Sb-added solder alloys may have reduced physical properties due to repeated thermal stress, resulting in cracks in the solder joints, and there is a concern that the solder joints may break due to the cracks.

Here, in order to prevent short circuiting of the circuit when moisture adheres to the electronic circuit packaging substrate, a moisture-proof agent may be applied thereon. In this case, especially when using electronic parts such as QFP with multiple lead terminals and narrow lead spacing, when cracks occur in the solder joints, the above-mentioned moisture-proof agent penetrates into the cracks and hardens, and There is a concern that the solder joint is deformed. Next, when the plurality of solder joints are deformed, especially in the adjacent solder joints, the deformed solder joints come into contact with each other and become conductive, which may cause a short circuit. That is, if it is explained using the second figure, it is as follows. In addition, the application range of the moisture-proofing agent varies according to the use environment of the electronic circuit package substrate, the type of the substrate or the electronic component, etc. (for example, it may be applied to the periphery of the solder joint or the entire electronic component (including the solder joint) ), etc.). As shown in the second figure, it is the case where the moisture-proof agent is applied to the periphery of the solder joint. As shown in the second figure (a), the electronic circuit packaging substrate 200 has a substrate 11 and a QFP (only its leads are shown in the figure). On the substrate 11, an insulating layer 13 and a lead 14 connecting the electrode 12 and the QFP are formed. The solder joint 15 for sexual bonding. Next, on the solder joint 15 (flux residue), a moisture-proof layer 16 made of a moisture-proof agent is formed. In addition, the flux residue is not shown in the second figure for convenience.

Next, in the electronic circuit packaging substrate 200, for example, due to the intense heat and cold difference, thermal stress is repeatedly applied to the solder joint 15 and cracks 17 are generated in the solder joint 15 (the second image (b)).

Here, if the electronic circuit packaging substrate 200 is placed in a high-temperature environment in a state where the crack 17 is generated in the solder joint 15, the moisture-proof layer 16 having fluidity due to heating penetrates into the crack 17 (the second image (c) )).

Next, in such a state, if the electronic circuit package substrate 200 is placed in a low temperature environment, the moisture barrier layer 16 that penetrates into the crack 17 hardens, causing the solder joint 15 to be deformed (the second image (d)). As shown in the second figure (d), the expanded and deformed solder joint 15 may come into contact with the adjacent solder joint and become a conductive state, and there is a concern that a short circuit may occur.

[The problem to be solved by the invention]

The object of the present invention is to provide a lead-free solder alloy, a material for solder bonding, an electronic circuit package substrate, and an electronic control device in order to solve the above-mentioned problems, specifically the following problems.・Even in a severe environment where the difference between heat and cold is severe and vibration is applied, and when the thermal stress is particularly likely to be concentrated on the electronic parts of the solder joint or the state where the electronic circuit package substrate is assembled in the frame, it can be suppressed Cracks developed in the solder joints.・Even when the moisture-proof agent penetrates into the cracks generated in the solder joint, it can suppress the deformity of the solder joint.・For example, even in the solder joints of BGAs where the electrodes are made of Sn-3Ag-0.5Cu alloy solder balls, the solder joints can exhibit good thermal fatigue resistance. [Means to solve the problem]

The lead-free solder alloy of the present invention is characterized by containing 2.5 mass% to 3.1 mass% Ag, 0.6 mass% to 1 mass% Cu, 3 mass% to 5 mass%, Sb, 3.1 mass% to 4.5 mass% The following Bi, 0.01% by mass or more and 0.1% by mass or less Ni, and 0.0085% by mass or more and 0.1% by mass or less Co, and the remainder is composed of Sn.

Furthermore, in the lead-free solder alloy of the present invention, the Ag content is preferably 2.8% by mass or more and 3.1% by mass or less.

Furthermore, in the lead-free solder alloy of the present invention, the content of Cu is preferably 0.6% by mass or more and 0.8% by mass or less.

In addition, the lead-free solder alloy of the present invention preferably contains at least one of P, Ga, and Ge in a total amount of 0.001% by mass to 0.05% by mass.

In addition, the lead-free solder alloy of the present invention preferably contains at least one of Fe, Mn, Cr, and Mo in a total amount of 0.001% by mass to 0.05% by mass.

The bonding material for solder of the present invention is characterized by having the above-mentioned lead-free solder alloy and a flux containing a matrix resin, a thixotropic agent, an activator, and a solvent.

The solder paste of the present invention is characterized by having a flux, which contains the above-mentioned lead-free solder alloy in powder form, a matrix resin, a thixotropic agent, an activating agent, and a solvent.

The electronic circuit package substrate of the present invention is characterized by having a solder joint formed using the above-mentioned lead-free solder alloy.

The electronic control device of the present invention is characterized by having the above-mentioned electronic circuit packaging substrate. [Effects of Invention]

The object of the present invention is to provide a lead-free solder alloy, a material for solder bonding, an electronic circuit package substrate, and an electronic control device that can solve the above-mentioned problems, specifically the following problems.・Even in a severe environment where the difference between heat and cold is severe and vibration is applied, and when the thermal stress is particularly likely to be concentrated on the electronic parts of the solder joint or the electronic circuit package substrate is assembled in the frame, it can be suppressed Cracks developed in the solder joints.・Even when the moisture-proof agent penetrates into the cracks generated in the solder joint, it can suppress the deformity of the solder joint.・For example, even in the solder joints of BGAs where the electrodes are made of Sn-3Ag-0.5Cu alloy solder balls, the solder joints can exhibit good thermal fatigue resistance.

Hereinafter, an embodiment of the lead-free solder alloy, solder bonding material, electronic circuit packaging substrate, and electronic control device of the present invention will be described in detail. In addition, the present invention is not limited to the following embodiments. (1) Lead-free solder alloy

The lead-free solder alloy of this embodiment may contain Ag in an amount of 2.5% by mass to 3.1% by mass. By adding Ag to the lead-free solder alloy within this range, the ductility of the lead-free solder alloy can be improved, and the Ag ₃ Sn compound can be precipitated in the Sn grain boundary to impart mechanical strength. In addition, by this, the heat fatigue resistance of the lead-free solder alloy can be improved, and the generation of holes in the solder joint can be suppressed.

The content of Ag is more preferably 2.8% by mass or more and 3.1% by mass or less, and the content is still more preferably 2.9% by mass or more and 3.1% by mass or less. By setting the Ag content within this range, the mechanical strength, ductility, and void discharge properties of the lead-free solder alloy can be more balanced.

The lead-free solder alloy of this embodiment may contain 0.6 mass% to 1 mass% of Cu.

By adding Cu to the lead-free solder alloy within this range, the Cu ₆ Sn ₅ compound is precipitated in the Sn grain boundary, and the heat fatigue resistance of the lead-free solder alloy can be improved. In addition, by setting the Cu content within this range, it is possible to improve the thermal fatigue resistance without hindering the elongation of the lead-free solder alloy and suppress the generation of voids.

The Cu content is more preferably 0.6% by mass or more and 0.8% by mass or less, and a more preferable range is 0.7% by mass or more and 0.8% by mass or less. By setting the content of Cu within this range, the thermal fatigue resistance of the lead-free solder alloy and the dischargeability of voids during melting can be more balanced.

The lead-free solder alloy of this embodiment may contain Bi in an amount of 3.1% by mass to 4.5% by mass. By adding Bi to the lead-free solder alloy within this range, on the one hand, the grain boundary voids in the solder joint formed by using it can be suppressed, and on the other hand, the strength can be improved. In addition, because the Bi content is within this range, the strength of the solder joint can be improved, and even when cracks are generated in the solder joint, it is possible to suppress the penetration of the moisture-proofing agent into the crack and the deforming of the solder joint due to hardening.

The content of Bi is more preferably from 3.2% by mass to 4.5% by mass, and the content is still more preferably from 4% by mass to 4.5% by mass. By adding Bi to the lead-free solder alloy within this range, the effect of suppressing the generation of grain boundary voids in the solder joint and the effect of increasing the strength can be further exhibited.

The lead-free solder alloy of this embodiment may contain 3 mass% or more and 5 mass% or less of Sb. By adding Sb to the lead-free solder alloy within this range, it is possible to further suppress the generation of grain boundary voids caused by adding Bi to the lead-free solder alloy without hindering the ductility of the Sn-Ag-Cu-based solder alloy. In addition, by setting the Sb content within this range, even in an environment where thermal stress is repeatedly applied due to a drastic difference in cold and heat, the deformation of the solder joint can be suppressed, and the decrease in physical properties of the solder joint can be suppressed. Therefore, the lead-free solder alloy of this embodiment can suppress the penetration of the moisture-proofing agent into the cracks and the deformed solder joints caused by hardening even when cracks occur in the solder joints.

The content of Sb is more preferably 3.5% by mass to 5% by mass, and still more preferably 4% by mass to 5% by mass. By adding Sb to the lead-free solder alloy within this range, the effect of suppressing the generation of grain boundary voids in the solder joint, the effect of suppressing deformation of the solder joint, and the effect of suppressing the deformity of the solder joint can be further exhibited.

The lead-free solder alloy of this embodiment may contain 0.01 mass% or more and 0.1 mass% or less of Ni. By adding Ni to the lead-free solder alloy within this range, fine (Cu, Ni) ₆ Sn ₅ can be formed in the lead-free solder alloy melted during soldering and dispersed in the solder joint, so that the solder joint can be suppressed The development of cracks further improves its thermal fatigue resistance. In addition, the Ni contained in the lead-free solder alloy moves to the interface between the electrode of the electronic component and the solder joint (hereinafter referred to as the "interface area") during soldering to form fine (Cu, Ni) ₆ Sn ₅ , which can suppress the alloy The layer grows in the interface area, thereby suppressing the development of cracks in the interface area.

Next, in the lead-free solder alloy of this embodiment, by adding Ni within the above-mentioned range, it is possible to exhibit a good effect of suppressing the development of cracks in the interface region, and further to exhibit an effect of suppressing the generation of voids in the solder joint. In addition, in the case of solder bonding to a BGA whose electrode is made of Sn-3Ag-0.5Cu alloy solder balls, when a certain number of holes or more are formed in the formed solder joint, it is placed in a severe cold and heat difference. Under environmental conditions, there is a concern that the thermal fatigue characteristics of solder joints are likely to be reduced. However, if the lead-free solder alloy of this embodiment has the effect of suppressing the formation of voids in the volatile solder joint as described above, it can also be suitably used for the solder joint of such BGA.

The content of Ni is more preferably 0.02% by mass or more and 0.05% by mass or less. By adding Ni to the lead-free solder alloy within this range, the effect of suppressing the formation of voids in the solder joint can be further exerted. For example, in the solder joint of BGA, good heat fatigue resistance can also be exerted.

The lead-free solder alloy of this embodiment may contain Co in an amount of 0.0085 mass% to 0.1 mass% together with Ni. By further adding Co to the lead-free solder alloy, the above-mentioned effect of the addition of Ni can be improved, and fine (Cu, Co) ₆ Sn ₅ is formed in the lead-free solder alloy melted during soldering and dispersed in the solder joint , And it is possible to suppress creep deformation when a predetermined stress is applied to the solder joint, thereby improving the thermal fatigue resistance of the solder joint. In addition, by adding Co to the lead-free solder alloy of this embodiment, Co moves to the interface region during soldering to form fine (Cu, Co) ₆ Sn ₅ , which can suppress the growth of the alloy layer in the interface region, and more Improve the effect of inhibiting the development of cracks in the interface area.

Next, the lead-free solder alloy of the present embodiment contains Co within the above-mentioned range, so that the modification effect of the intermetallic compound caused by adding Ni to the lead-free solder alloy is further improved, and the formation of holes in the solder joint can be suppressed. Effect. In addition, in the case of solder bonding of a BGA composed of Sn-3Ag-0.5Cu alloy solder balls, when a certain number of holes are formed in the formed solder joint, it is placed in an environment with a drastic cold and heat difference. In the case of solder joints, there is a concern that the thermal fatigue characteristics of the solder joints are likely to be reduced. However, the lead-free solder alloy of this embodiment can exhibit the effect of suppressing the generation of voids in the solder joint as described above, and can also be suitably used for solder joints of such BGAs.

The content of Co is more preferably 0.009% by mass or more and 0.05% by mass or less. By adding Co to the lead-free solder alloy within this range, the effect of suppressing the formation of voids in the solder joint can be further exhibited. For example, even when BGA solder is joined, it can exhibit good thermal fatigue resistance.

In the lead-free solder alloy of this embodiment, at least one of P, Ga, and Ge may be contained at 0.001% by mass to 0.05% by mass. By adding at least one of P, Ga, and Ge within this total amount, the generation of voids in the solder joint can be suppressed, and the oxidation of the lead-free solder alloy can be prevented.

In particular, Ge is concentrated on the fillet surface of the formed solder joint, so that the generation of shrinkage holes can be reduced, and the thermal fatigue resistance of the solder joint can be improved. In addition, the Ge content is particularly preferably 0.001% by mass or more and 0.01% by mass or less. By adding Ge to the lead-free solder alloy within this range, the thermal fatigue resistance of the solder joint can be brought to another level.

The lead-free solder alloy of this embodiment may contain at least one of Fe, Mn, Cr, and Mo from 0.001% by mass to 0.05% by mass. By adding at least one of Fe, Mn, Cr, and Mo within this total amount, the effect of suppressing the development of cracks in the solder joint can be improved.

In addition, the lead-free solder alloy of this embodiment may contain other components (elements), such as In, Cd, Tl, Se, Au, Ti, Si, Al, Mg, Zn, etc., within a range that does not hinder its effect. . In addition, the lead-free solder alloy of this embodiment may of course contain unavoidable impurities.

In addition, in the lead-free solder alloy of this embodiment, the remainder is preferably composed of Sn. In addition, the content of Sn is preferably 86.1% by mass or more and 90.7815% by mass or less.

In the lead-free solder alloy of this embodiment, by balancing the content of Bi and Sb and other alloying elements with their content, even if Bi is added, good ductility can be exhibited, and the development of cracks generated in the solder joint can be suppressed, and Even if Sb is added, good strength can be exhibited, and thereby, good thermal fatigue resistance can be exhibited. Therefore, for example, even in the case where cracks occur in the solder joint formed by using the lead-free solder alloy of this embodiment and the moisture-proofing agent penetrates therein, the deformity of the solder joint can be suppressed, and, for example, even in the electrode system In the solder joint of BGA composed of Sn-3Ag-0.5Cu alloy solder balls, the solder joint can also exhibit good thermal fatigue resistance.

As the method of forming the solder joint of this embodiment, the flow soldering method using the lead-free solder alloy of this embodiment, packaging with solder balls, and the use of solder containing the lead-free solder alloy of this embodiment and flux The joining material, the reflow method of the solder paste, etc. may be any method as long as the solder joint can be formed. In addition, the method using solder paste is preferable among them. (2) Materials for solder bonding

As the solder bonding material of this embodiment, for example, it is preferable to use one containing the lead-free solder alloy and flux.

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

Examples of the matrix resin include tall oil rosin, gum rosin, wood rosin and other rosins, including hydrogenated rosin, polymerized rosin, heterogeneous rosin, acrylic modified rosin, and maleic acid modified rosin. Rosin-based resins of rosin derivatives such as rosin; various esters of acrylic acid, methacrylic acid, acrylic acid, various esters of methacrylic acid, crotonic acid, itaconic acid, maleic acid, maleic anhydride, and esters of maleic acid , Maleic anhydride ester, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl chloride, vinyl acetate, etc. acrylic resin obtained by polymerization of at least one monomer; epoxy resin; phenol Resin etc. These can be used alone or in combination. Among them, it is preferable to use a rosin-based resin, particularly acid-modified rosin, which is hydrogenated acid-modified rosin, and a rosin ester that esterifies rosin. In addition, it is preferable to use hydrogenated acid to modify rosin and acrylic resin in combination.

The acid value of the matrix resin is preferably 10 mgKOH/g or more and 250 mgKOH/g or less. In addition, the blending amount of the matrix resin is preferably 10% by mass or more and 90% by mass or less with respect to the total amount of flux.

Examples of the thixotropic agent include hydrogenated castor oil, fatty acid amides, and oxy fatty acids. These can be used alone or in combination. The blending amount of the thixotropic agent is preferably 3% by mass or more and 15% by mass or less with respect to the total amount of flux.

As the active agent, for example, amine salts (inorganic acid salts or organic acid salts) such as hydrogen halide salts of organic amines, organic acids, organic acid salts, organic amine salts, and the like can be blended. More specifically, dibromobutenediol, diphenylguanidine hydrobromide, cyclohexylamine hydrobromide, diethylamine salt, acid salt, glutaric acid, succinic acid, adipic acid , Azelaic acid, malonic acid, dodecanedioic acid, suberic acid, dimer acid, etc. These can be used alone or in combination. The blending amount of the active agent is preferably 5 mass% or more and 15 mass% or less with respect to the total amount of flux.

As the solvent, for example, isopropanol, ethanol, acetone, toluene, xylene, ethyl acetate, ethyl siloxol, butyl siloxol, glycol ether, etc. can be used. These can be used alone or in combination. The blending amount of the solvent is preferably 20% by mass or more and 40% by mass or less with respect to the total amount of flux.

In this flux, an antioxidant can be blended for the purpose of suppressing the oxidation of the lead-free solder alloy. Examples of the antioxidant include hindered phenol antioxidants, phenol antioxidants, bisphenol antioxidants, polymer antioxidants, and the like. Among them, it is particularly preferable to use hindered phenol-based antioxidants. These can be used alone or in combination. The blending amount of the antioxidant is not particularly limited, but in general, it is preferably 0.5% by mass or more and about 5% by mass or less with respect to the total amount of flux.

Additives such as halogens, matting agents, defoamers, and inorganic fillers can also be added to the flux. The blending amount of the additive is preferably 10% by mass or less with respect to the total amount of flux. With respect to the total amount of flux, the blending amount of these is more preferably 5% by mass or less. (3) Solder paste

As the solder bonding material of this embodiment, it is preferable to use solder paste. For example, the powdered lead-free solder alloy (alloy powder) and the flux can be kneaded into a paste to produce such a solder paste.

In the case of making the solder paste, the blending ratio of the alloy powder and the flux is preferably 65:35 to 95:5. The blending ratio is more preferably 85:15~93:7, and the blending ratio is particularly preferably 87:13~92:8.

In addition, the particle size of the alloy powder is preferably 1 μm or more and 40 μm or less, more preferably 5 μm or more and 35 μm or less, and particularly preferably 10 μm or more and 30 μm or less. (4) Solder joint

For example, the solder joint formed using the solder joint material of this embodiment can be formed by the following method. In addition, printed wiring boards, silicon wafers, ceramic package substrates, etc., as long as they can be used for mounting and packaging electronic components, are not limited to these substrates, and the substrates formed by the solder joints of this embodiment can be used.

That is, for example, a predetermined pattern of electrodes and an insulating layer are formed at a predetermined position on the substrate, and the solder paste as the material for solder bonding is printed in accordance with the pattern. Next, electronic components are mounted on a predetermined position on the substrate, and they are reflow-soldered at a temperature of, for example, 220° C. to 245° C., thereby forming the solder joint of this embodiment. The solder joint formed in this way electrically joins the electrode (terminal) provided on the electronic component and the electrode formed on the substrate.

Next, the solder joint formed using the solder paste (the lead-free solder alloy of this embodiment) can exhibit good ductility and strength, and therefore can exhibit good thermal fatigue resistance. In addition, even when cracks are generated in the solder joint and the moisture-proof agent penetrates into it, it is possible to prevent the solder joint from being deformed. For example, the electrode is made of Sn-3Ag-0.5Cu alloy solder balls. In the case of solder joining, the solder joint can also exhibit good thermal fatigue resistance.

In addition, when the lead-free solder alloy of this embodiment is used as the solder ball, for example, an electrode and an insulating layer of a predetermined pattern are formed at a predetermined position on a substrate, a flux is applied to the pattern according to the pattern, and the solder ball is placed . Next, electronic components are mounted on a predetermined position on the substrate, and are reflow-soldered, for example, at a temperature of 220°C to 245°C, thereby forming the solder joint of this embodiment. The solder joint formed in this way electrically joins the electrode (terminal) provided on the electronic component and the electrode formed on the substrate.

Next, the solder joint formed using the solder ball exhibits good ductility and good strength, and therefore can exhibit good thermal fatigue resistance. In addition, even when cracks are generated in the solder joint and the moisture-proof agent penetrates into the solder joint, it is possible to prevent the solder joint from being deformed.

In this way, the electronic circuit packaging substrate with the solder joints of the present embodiment is particularly suitable for the electronic circuit packaging substrates for automobiles that are placed in an environment with severe cold and heat differences and require high reliability. (5) Electronic control device

Furthermore, by installing such an electronic circuit packaging substrate, a highly reliable electronic control device can be manufactured. Next, such an electronic control device can be used especially for automotive electronic control devices that require high reliability. [Example]

Hereinafter, the present invention will be described in detail with examples and comparative examples. In addition, the present invention is not limited to these embodiments.

Preparation of Flux The following components were kneaded to obtain the flux of the Examples and Comparative Examples. Rosin modified by hydrogenation acid (product name: KE-604, manufactured by Arakawa Chemical Industry Co., Ltd.) 32 mass% Rosin ester (product name: HARITACK F85, manufactured by HARIMA Chemical Co., Ltd.) 12 mass% dodecanedioic acid 5 Mass% suberic acid 1 mass% dibromobutenediol 1.5 mass% dimer acid (product name: UNIDYME14, manufactured by Kraton Corporation) 8 mass% fatty acid amide (product name: SLIPACKS ZHH, Japan Chemical Co., Ltd.) (Product) 4% by mass hardened sesame oil 1.5% by mass diethylene glycol monohexyl ether 33% by mass hindered phenol antioxidant (product name: IRGANOX 245, manufactured by BASF JAPAN) 2% by mass

Preparation of Solder Paste The flux 11.9% by mass, and 88.1% by mass of various lead-free solder alloy powders (powder particle size 20μm~38μm) described in Table 1 and Table 2 were mixed to prepare Examples 1 to 27 and Comparative Example 1. Various solder pastes to Comparative Example 20.

[Table 1] Sn Ag Cu Bi Sb Ni Co other Example 1 The remaining part 2.5 0.7 3.2 3.0 0.04 0.015 - Example 2 The remaining part 2.8 0.7 3.2 3.0 0.04 0.015 - Example 3 The remaining part 3.1 0.7 3.2 3.0 0.04 0.015 - Example 4 The remaining part 3.0 0.6 3.2 3.0 0.04 0.015 - Example 5 The remaining part 3.0 0.8 3.2 3.0 0.04 0.015 - Example 6 The remaining part 3.0 1.0 3.2 3.0 0.04 0.015 - Example 7 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 - Example 8 The remaining part 3.0 0.7 3.2 5.0 0.04 0.015 - Example 9 The remaining part 3.0 0.7 3.1 3.0 0.04 0.015 - Example 10 The remaining part 3.0 0.7 4.5 3.0 0.04 0.015 - Example 11 The remaining part 3.0 0.7 4.5 5.0 0.04 0.015 - Example 12 The remaining part 3.0 0.7 3.2 3.0 0.01 0.015 - Example 13 The remaining part 3.0 0.7 3.2 3.0 0.02 0.015 - Example 14 The remaining part 3.0 0.7 3.2 3.0 0.05 0.015 - Example 15 The remaining part 3.0 0.7 3.2 3.0 0.1 0.015 - Example 16 The remaining part 3.0 0.7 3.2 3.0 0.04 0.0085 - Example 17 The remaining part 3.0 0.7 3.2 3.0 0.04 0.009 - Example 18 The remaining part 3.0 0.7 3.2 3.0 0.04 0.05 - Example 19 The remaining part 3.0 0.7 3.2 3.0 0.04 0.1 - Example 20 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.05P Example 21 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.001Ge Example 22 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.05Ge Example 23 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.05Ga Example 24 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.05Fe Example 25 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.05Mn Example 26 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.05Cr Example 27 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.05Mo

[Table 2] Sn Ag Cu Bi Sb Ni Co other Comparative example 1 The remaining part 3.0 0.5 - - - - - Comparative example 2 The remaining part 2.0 0.7 3.2 3.0 0.04 0.015 - Comparative example 3 The remaining part 3.5 0.7 3.2 3.0 0.04 0.015 - Comparative example 4 The remaining part 3.0 0.5 3.2 3.0 0.04 0.015 - Comparative example 5 The remaining part 3.0 1.5 3.2 3.0 0.04 0.015 - Comparative example 6 The remaining part 3.0 0.7 3.2 2.0 0.04 0.015 - Comparative example 7 The remaining part 3.0 0.7 3.2 6.0 0.04 0.015 - Comparative example 8 The remaining part 3.0 0.7 3.0 3.0 0.04 0.015 - Comparative example 9 The remaining part 3.0 0.7 5.0 3.0 0.04 0.015 - Comparative example 10 The remaining part 3.0 0.7 3.2 3.0 - 0.015 - Comparative example 11 The remaining part 3.0 0.7 3.2 3.0 0.15 0.015 - Comparative example 12 The remaining part 3.0 0.7 3.2 3.0 0.04 0.008 - Comparative example 13 The remaining part 3.0 0.7 3.2 3.0 0.04 0.15 - Comparative example 14 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.1P Comparative example 15 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.1Ge Comparative example 16 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.1Ga Comparative example 17 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.1Fe Comparative Example 18 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.1Mn Comparative Example 19 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.1Cr Comparative example 20 The remaining part 3.0 0.7 3.2 3.0 0.04 0.015 0.1Mo

(1) Welding crack resistance test (A) <Welding crack resistance test when it is not installed in the frame> Prepare the following tools.・QFN parts (pitch width: 0.5mm, length 5mm×width 5mm×thickness 0.8mm, number of terminals: 32 pins) ・Printing with solder resist with patterns that can encapsulate the above QFN parts and electrodes connecting the QFN parts Wiring board (product name: R-1766, manufactured by Panasonic, surface treatment: Cu-OSP, thickness: 1.2mm) ・A metal mask with the above pattern and thickness of 150μm is used on the printed wiring board. Various solder pastes are printed on the mask, and two QFN parts are mounted. Afterwards, each printed wiring board is heated in a reflow furnace (product name: TNV30-508EM2-X, manufactured by Tamura Manufacturing Co., Ltd.) to produce electronic circuit packages with solder joints that electrically join electrodes and QFN parts Substrate. At this time, the reflow conditions are preheating from 170°C to 190°C, so that the peak temperature is 245°C, the time above 220°C is 45 seconds, and the cooling rate from peak temperature to 200°C is 1°C to 8°C /second. The oxygen concentration is set to 1,500 ± 500 ppm. Next, use the thermal shock test device (product name: ES-76LMS, manufactured by Hitachi Appliances) set at -40°C (30 minutes) to 125°C (30 minutes) to repeat the thermal shock cycle 1,000, 1,500, After 2,000 cycles, each printed wiring board was exposed to such an environment, and then it was taken out to produce each test substrate.

Then cut out the target part of each test substrate, and encapsulate it with epoxy resin (product name: EPOMOUNT (main agent and hardener), manufactured by Refine Tec (stock)). Furthermore, a wet polishing machine (product name: TegraPol-25, manufactured by Marumoto Struers Co., Ltd.) was used to make the cross section of the solder joint of the QFN part packaged on each test substrate into an observable state, and scan A type electron microscope (product name: TM-1000, manufactured by Hitachi High-Technologies Co., Ltd.) was used to observe whether cracks occurred in the solder joints of each QFN component, and then evaluated based on the following criteria. The results are shown in Table 3 and Table 4. In addition, for each QFN component, the above observation and evaluation were performed at 8 (places) solder joints. ◎: Cracks completely traversing the solder joints did not occur up to 2,000 cycles ○: Cracks completely traversed the solder joints occurred between 1,501 cycles to 2,000 cycles △: Cracks occurred between 1,001 cycles to 1,500 cycles Cracks that completely cross the solder joints ×: Cracks that completely cross the solder joints occur after 1,000 cycles

(1) Solder crack resistance test (B) <Solder crack resistance test in the state installed in the frame> Under the same conditions as the above (1) solder crack resistance test (A), a printed wiring board with each Each electronic circuit package substrate of the solder joint where the electrode and each QFN component are electrically joined. Next, the respective electronic circuit packaging substrates were assembled to an aluminum alloy frame (hereinafter referred to as a "test frame") with screws to manufacture. Next, the use conditions were set to a thermal shock test device (product name: ES-76LMS, manufactured by Hitachi Appliances) from -40°C (30 minutes) to 125°C (30 minutes), and each test frame After being exposed to an environment that repeated 1,000, 1,500, and 2,000 cycles of thermal shock cycles, it was taken out.

Next, take out each electronic circuit package substrate from each test frame, and cut out the target part of each electronic circuit package substrate, using epoxy resin (product name: EPOMOUNT (main agent and hardener), Refine Tec (stock ) System) package. Then use a wet polishing machine (product name: TegraPol-25, manufactured by Marumoto Struers Co., Ltd.) to make the solder joint section of the QFN component packaged on each electronic circuit package substrate into an observable state, and use a scanning type An electron microscope (product name: TM-1000, manufactured by Hitachi High-Technologies) was used to observe whether cracks occurred in the solder joints of each QFN component. The evaluation criteria and methods were the same as those in the above (1) solder crack resistance test (A) Make an evaluation. The results are shown in Table 3 and Table 4.

(2) The test to confirm the deformity of the solder joints uses the following tools, and each printed wiring board is equipped with 4 QFP parts, except that the same conditions as the above (1) solder crack resistance test (A) are used. Each electronic circuit package substrate having a solder joint for electrically joining the electrode of each printed wiring board and each QFP component was produced.・QFP parts (pitch width: 0.5mm, length 26mm×width 26mm×thickness 1.6mm, number of terminals: 176 pins) ・Printing with solder resist with patterns that can encapsulate the above-mentioned QFP parts and electrodes connecting the QFN parts Wiring board (product name: R-1766, manufactured by Panasonic, surface treatment: Cu-OSP, thickness: 1.2mm) Then, a moisture-proof agent (product name: TUFFY TF-4200, Hitachi Chemical Co., Ltd.), and let it dry at room temperature for 6 hours. After that, each electronic circuit package substrate was assembled to an aluminum alloy frame (hereinafter referred to as a "test frame") with screws. Next, use the thermal shock test device (product name: ES-76LMS, manufactured by Hitachi Appliances) under the conditions of -40°C (30 minutes) to 125°C (30 minutes), and expose the respective test frames Take it out after repeating 1,000 and 2,000 cycles of thermal shock cycles.

Next, each electronic circuit package substrate was taken out from each test frame, and the solder joints on each electronic circuit package substrate were evaluated based on the following criteria to see if the solder joints were deformed, and the adjacent solder joints (formed on adjacent leads in each QFP component) Whether the solder joint on the wire is in contact and short-circuited. The results are shown in Table 3 and Table 4. In addition, the above observations and evaluations were performed at 176 solder joints (places) for each QFP part. ◎: No short circuit occurs until 2,000 cycles ○: Short circuit occurs between 1,001 cycles to 2,000 cycles ×: Short circuit occurs below 1,000 cycles

(3) BGA solder crack resistance confirmation test Prepare the following tools.・BGA parts (pitch width: 0.5mm, length 6mm × width 6mm × thickness 1.2mm, number of solder balls 109, solder ball composition: Sn-3Ag-0.5Cu alloy) ・With a pattern that can encapsulate the above-mentioned BGA parts Solder resistance and printed wiring board of the electrode connecting the BGA part (product name: MCL-E-700G (RL), made by Hitachi Chemical Co., Ltd., surface treatment: Cu-OSP, thickness: 1.2mm) ・With the above pattern In addition, a metal mask with a thickness of 110 μm is used to print various solder pastes on the printed wiring board using the metal mask, and one BGA component is mounted. After that, each printed wiring board was heated in a reflow furnace (product name: TNV30-508EM2-X, manufactured by Tamura Manufacturing Co., Ltd.) to fabricate electronic circuits with solder joints that electrically join electrodes and BGA parts Package substrate. At this time, the reflow conditions are preheated at 170°C to 190°C, so that the peak temperature is 245°C, the time above 220°C is 45 seconds, and the cooling rate from the peak temperature to 200°C is 1°C to 8°C /second. In addition, the oxygen concentration is set to 1,500±500 ppm. Next, the respective electronic circuit packaging substrates were assembled to an aluminum alloy frame (hereinafter referred to as a "test frame") with screws to manufacture. Next, use the thermal shock test device (product name: ES-76LMS, manufactured by Hitachi Appliances) under the conditions of -40°C (30 minutes) to 125°C (30 minutes), and expose the respective test frames After 2,500, 3,000, and 3,500 cycles of thermal shock cycles were repeated, they were taken out to fabricate test substrates.

Next, take out each electronic circuit packaging substrate from each test frame, and cut out the target part of each electronic circuit packaging substrate, using epoxy resin (product name: EOPMOUNT (main agent and hardener), Refine Tec (stock)) System) package. Then use a wet polishing machine (product name: TegraPol-25, manufactured by Marumoto Struers Co., Ltd.) to make the solder joint section of the BGA part packaged on each test substrate into an observable state, and use the scanning type An electron microscope (product name: TM-1000, manufactured by Hitachi High-Technologies Co., Ltd.) was used to observe whether cracks were generated in the solder joints of each BGA component, and the evaluation was performed based on the following criteria. The results are shown in Table 3 and Table 4. In addition, the above observation and evaluation were performed on a total of 15 (places) solder joints, including the four corner solder joints of the BGA part and the 11 (place) solder joints arranged under the semiconductor element inside the package. ◎: No cracks completely traversed the solder joints up to 3,500 cycles ○: Cracks completely traversed the solder joints occurred between 3,001 cycles and 3,500 cycles △: Solder was generated between 2,501 cycles and 3,000 cycles Cracks that completely cross the joints ×: Cracks that completely cross the solder joints occur after 2,500 cycles

[table 3] (1) Welding crack resistance test (2) Deformation confirmation test of solder joint (3) BGA welding crack resistance confirmation test (A) (B) Example 1 ◎ 〇 〇 〇 Example 2 ◎ 〇 ◎ ◎ Example 3 ◎ 〇 ◎ ◎ Example 4 ◎ 〇 ◎ 〇 Example 5 ◎ 〇 ◎ 〇 Example 6 ◎ △ ◎ △ Example 7 ◎ 〇 ◎ 〇 Example 8 ◎ 〇 〇 ◎ Example 9 ◎ 〇 〇 〇 Example 10 ◎ △ ◎ ◎ Example 11 ◎ 〇 ◎ ◎ Example 12 ◎ 〇 ◎ △ Example 13 ◎ 〇 ◎ 〇 Example 14 ◎ 〇 ◎ 〇 Example 15 ◎ 〇 ◎ △ Example 16 ◎ 〇 ◎ △ Example 17 ◎ 〇 ◎ 〇 Example 18 ◎ 〇 ◎ 〇 Example 19 ◎ 〇 ◎ △ Example 20 ◎ 〇 ◎ 〇 Example 21 ◎ 〇 ◎ ◎ Example 22 ◎ 〇 ◎ ◎ Example 23 ◎ 〇 ◎ 〇 Example 24 ◎ 〇 ◎ 〇 Example 25 ◎ 〇 ◎ 〇 Example 26 ◎ 〇 ◎ 〇 Example 27 ◎ 〇 ◎ 〇

[Table 4] (1) Welding crack resistance test (2) Deformation confirmation test of solder joint (3) BGA welding crack resistance confirmation test Comparative example 1 〇 〇 × × Comparative example 2 ◎ 〇 × △ Comparative example 3 ◎ × ◎ × Comparative example 4 ◎ 〇 ◎ × Comparative example 5 ◎ × ◎ × Comparative example 6 ◎ × ◎ × Comparative example 7 ◎ 〇 × 〇 Comparative example 8 ◎ 〇 × 〇 Comparative example 9 ◎ × ◎ 〇 Comparative example 10 ◎ 〇 ◎ × Comparative example 11 ◎ 〇 ◎ × Comparative example 12 ◎ 〇 ◎ × Comparative example 13 ◎ 〇 ◎ × Comparative example 14 ◎ 〇 ◎ × Comparative example 15 ◎ 〇 ◎ × Comparative example 16 ◎ 〇 ◎ × Comparative example 17 ◎ 〇 ◎ × Comparative Example 18 ◎ 〇 ◎ × Comparative Example 19 ◎ 〇 ◎ × Comparative example 20 ◎ 〇 ◎ ×

As shown above, it can be seen that the solder joints formed by using the lead-free solder alloys of the examples are particularly likely to concentrate on the electronic parts (QFN parts) of the solder joints even when the thermal stress is used. In the state where the package substrate is mounted on the frame, the cracks generated in the solder joint can also be suppressed from developing. In addition, it is known that the solder joint formed by using the lead-free solder alloy of the example can suppress the deforming of the solder joint even if cracks are generated in the solder joint and the moisture barrier penetrates into the crack. It is also known that the solder joints formed by using the lead-free solder alloys of the examples can perform solder joints even when solder joints of BGA parts composed of solder balls of Sn-3Ag-0.5Cu alloy are used. Good thermal fatigue resistance, and can inhibit the development of cracks.

In this way, the lead-free solder alloy of the embodiment can be preferably used in an electronic circuit packaging substrate and mounted on an electronic control device for a vehicle.

1: Grain boundary 2: Atomic void 2': Grain boundary hole 3: Crack 11: Substrate 12: Electrode 13: Insulating layer 14: Lead 15: Welding part 16: Moisture barrier 17: Crack 100: Welding part 110: Sn crystal Grain 200: electronic circuit packaging substrate

The first figure is a schematic cross-sectional view of the solder joint, which shows the process of producing grain boundary holes and cracks due to the atomic voids in the grain boundary in the solder joint. The second figure is a schematic cross-sectional view of the electronic circuit package substrate for packaging QFN, which shows the process of the moisture-proof agent penetrates into the cracks generated in the solder joint and hardens to cause the solder joint to be deformed.

1: grain boundary

2: Atomic holes

2’: Grain boundary hole

3: crack

100: Solder joint

110: Sn grain

Claims (13)

A lead-free solder alloy comprising: 2.5 mass% to 3.1 mass% Ag, 0.6 mass% to 1 mass% Cu, 3 mass% to 5 mass%, Sb, 3.1 mass% to 4.5 mass% Bi, 0.01% by mass or more and 0.1% by mass or less of Ni, and 0.0085% by mass or more and 0.1% by mass or less of Co, and the remainder is composed of Sn. For example, the lead-free solder alloy in the first item of the scope of patent application, in which the content of Ag is above 2.8% by mass and below 3.1% by mass. For example, the lead-free solder alloy of item 1 or 2 of the scope of patent application, in which the content of Cu is above 0.6 mass% and below 0.8 mass%. For example, the lead-free solder alloy of item 1 or 2 of the scope of patent application contains at least one of P, Ga, and Ge in a total of 0.001% by mass to 0.05% by mass. For example, the third lead-free solder alloy in the scope of the patent application contains at least one of P, Ga, and Ge in a total of 0.001% by mass or more and 0.05% by mass. For example, the lead-free solder alloy of item 1 or 2 of the scope of the patent application contains at least one of Fe, Mn, Cr, and Mo in a total of 0.001% by mass to 0.05% by mass. For example, the lead-free solder alloy of item 3 in the scope of the patent application contains at least one of Fe, Mn, Cr and Mo in a total of 0.001% by mass to 0.05% by mass. For example, the lead-free solder alloy of item 4 in the scope of patent application contains at least one of Fe, Mn, Cr, and Mo in a total of 0.001% by mass to 0.05% by mass. For example, the lead-free solder alloy of item 5 in the scope of the patent application contains at least one of Fe, Mn, Cr and Mo in a total of 0.001% by mass to 0.05% by mass. A material for solder joining, which has a lead-free solder alloy and flux as in any one of items 1 to 9 in the scope of patent application. A solder paste comprising a powdered lead-free solder alloy and a soldering flux as the lead-free solder alloy of any one of items 1 to 9 in the scope of patent application, wherein the soldering flux comprises a matrix resin, a thixotropic agent, an activating agent, and a solvent . An electronic circuit packaging substrate comprising a solder joint formed by using any one of the lead-free solder alloys in the scope of the patent application from 1 to 9. An electronic control device comprising an electronic circuit packaging substrate as claimed in item 12 of the scope of patent application.

Images