JP2009275240A - Lead-free sn-ag based solder alloy or solder alloy powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-free Sn-Ag based solder alloy and solder alloy powder, which are applicable under severe atmosphere related to the vibration and the heat. <P>SOLUTION: This lead-free solder alloy is composed of, by weight, 0.10% Ni, 0.08% Al, 0.06% Ge, 0.2% Bi, 0.2% Ag and the balance Sn. The maximum stress of this lead-free solder alloy is 33.00 MPa, the maximum point distortion is 15.53 MPa and the maximum elongation is 64.09%. Further, according to the heat cycle accelerating test, in 1,000 cycle times, the number of broken pieces is 15 based on the 40 measured pieces. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lead-free solder alloy or solder alloy powder, and more particularly to a Sn-Ag alloy or solder alloy powder.

  As is well known, lead (Pb) is subject to regulation in various applications because of concern that it may adversely affect the human body. The same applies to Sn-Pb solder used in electronic equipment. Sn-Pb solder has been fully regulated in Europe since 2006, and the development of lead-free solder alloys and powders has become an urgent issue.

  As a lead-free solder alloy currently recommended and put to practical use by NEDO (New Energy and Industrial Technology Development Organization), etc., Sn-3Ag-0.5Cu alloy and alloys with In and Bi added to it (patents) Document 1) and Sn-9Zn alloys and Sn-0.7Cu alloys are known. Needless to say, the melting point, wettability, and mechanical properties are regarded as important in the case of lead-free solder as in the case of Sn-Pb solder. Sn-3Ag-0.5Cu alloy has excellent melting point and wettability. In addition, Sn-9Zn alloys are being developed for practical use because they include the possibility of lowering the melting point.

  However, regarding mechanical characteristics such as thermal fatigue characteristics and impact characteristics in substrate bonding, it is emphasized that lead-free solder alloys are significantly inferior to Sn-Pb solder alloys.

  In recent years, technological innovations such as miniaturization, weight reduction, and speeding-up of electronic devices such as information and communication fields and digital home appliances have been remarkable, and higher-density, higher-integration, and higher pin count multi-phase circuit boards for electronic circuits. Is progressing. Along with that, electronic device packages have changed from QFP (Quad Flat Package) to BGA (Ball Grid Array) and CSP (Chip Scale Package), and the joints by solder are also miniaturized at the same time.

  In QFP bonding, the lead wire extending from the package and the printed wiring board are joined by soldering, so the mechanical and thermal load applied to the package and the printed wiring board is the lead. It was alleviated by the flexibility of the wire. On the other hand, in area-lay package bonding such as BGA and CSP without lead wire, all the load is applied to the solder, so the mechanical properties required for the joint increase with the miniaturization of the joint. ing. In particular, the trend of board, multiphase integration, and multi-pin combination of materials with different thermal expansion coefficients includes the possibility of solder breakage due to board warpage or direct load on the solder ball. It is out.

  In the automotive industry, it is predicted that the use of metal / ceramic substrates such as aluminum / ceramic substrates having excellent thermal conductivity, heat resistance, and voltage resistance will be generalized in the near future. In fact, metal / ceramic substrates have been adopted as substrates that require high output, and are beginning to be mounted on some vehicles. Electronic boards mounted on automobiles are not only exposed to an environment with a large temperature difference, but also placed in a very harsh environment such as a large thermal cycle load due to ON / OFF of the equipment. Therefore, lead-free solder alloys and solder alloy powders with excellent mechanical properties, including thermal fatigue properties due to stress loading, that can be applied to metal / ceramic substrates used in harsh environments with regard to vibration and heat. The appearance is awaited.

  The inventor of the present application, in Patent Document 2, is a problem of Sn-3Ag-0.5Cu alloy that is put to practical use as a general lead-free solder, particularly regarding crack generation and crack propagation due to thermal cycle load. The cause was clarified.

Specifically, the composition of the Sn-3Ag-0.5Cu alloy is determined so that a eutectic structure can be obtained, as in the case of the Sn-0.7Cu alloy, and Ag ₃ of the intermetallic compound phase in the matrix Sn. Although Sn and Cu ₆ Sn ₅ phases are finely dispersed and have a uniform hardness structure, the structure after solidification does not become a total eutectic structure due to rapid cooling when bonded to the substrate, and is soft. It exhibits a two-phase mixed structure of coarse primary β-Sn phase and hard eutectic phase, and this structure is a factor that promotes deterioration of mechanical properties of Sn-3Ag-0.5Cu alloy. It revealed that.

  As a result of diligent research aimed at refining coarse primary crystal β-Sn phase crystals, as described in Patent Document 2, the present inventor added a small amount of Al to the Sn-Ag binary alloy. And found that a fine sub-grain structure can be formed in the primary β-Sn phase. And since the crystal grain size of the subcrystalline structure crystallized in the β-Sn phase was about 5 μm, by adding a small amount of Al to the Sn-Ag binary alloy, It was found that the grain size of the primary β-Sn phase in Sn-3Ag-0.5Cu solder alloy can be reduced to about 1/6.

International Publication WO 01/080611 Publication JP 2003-211283 A

  The lead-free solder alloy containing a small amount of Al in the Sn-Ag binary alloy disclosed in Patent Document 2 has a large improvement effect in joining large power module substrates, but is a small metal / ceramic substrate. It has been found that further improvement is necessary for practical use in the joining.

  An object of the present invention is to provide a lead-free Sn-Ag solder alloy and a solder alloy powder that can be applied in a severe environment with respect to improvement of thermal fatigue characteristics, particularly vibration and heat.

  It is a further object of the present invention to provide a lead-free Sn-Ag solder alloy and solder alloy powder that contain a small amount of Al and can improve mechanical properties.

  It is a further object of the present invention to provide a lead-free Sn-Ag solder alloy and solder alloy powder that can be adapted for bonding on a flex-rigid substrate (FR substrate).

  It is a further object of the present invention to provide a lead-free Sn-Ag solder alloy and solder alloy powder that can be adapted for bonding with a metal / ceramic substrate having excellent heat resistance.

From the above considerations, the above technical problem is according to the present invention from the viewpoint of balance of strength and structure.
This is achieved by providing a lead-free Sn-Ag solder alloy or solder alloy powder characterized in that the Ag content is 0.1 or more and less than 0.5. When the Ag content is less than 0.1 wt%, the strength improvement effect due to the addition of Ag is diluted.

  As mentioned above, conventional lead-free solder alloy designs are eutectic with the second or third element added to Sn, as seen in Sn-3Ag-0.5Cu solder alloys and Sn-0.7Cu solder alloys. It is added to the composition amount to lower the melting point of the solder alloy and finely disperse the structure characteristics, but the structure changes under the influence of the cooling rate at the time of soldering and can withstand harsh environments There was a fact that mechanical properties could not be obtained. In order to improve this, it is considered that an alloy design based on the following viewpoint is necessary. In other words, in order to alleviate the stress concentration at the bonding interface between the substrate and the solder, the ductility of the solder alloy itself is important, and it is necessary to form a uniform solder structure in which hard and soft phase regions are not mixed. .

  By the way, pure Sn is a metal with excellent ductility, but the biggest drawback of Sn is that the Sn crystal grains are susceptible to brittle fracture, and to solve this, other elements are added to strengthen the grain boundaries. There is a need to. Therefore, in the development of lead-free solder mainly composed of Sn, which is rich in ductility, firstly, it is necessary to reduce the intermetallic compound phase as much as possible, and secondly, a large amount of hardening element is not added. It is considered necessary. In other words, it is considered important to add a small amount of element to Sn that does not adversely affect the structure characteristics and material characteristics.

  Therefore, the inventor of the present application paid attention to the addition amount of silver (Ag) that has an effect of improving the mechanical strength. For example, in the lead-free Sn-Ag solder alloy disclosed in Patent Document 1, 2 to 3 wt% of Ag is added, but when Ag is added to 2 to 3 wt%, as shown in FIG. It can be confirmed that it exhibits a two-phase mixed structure of a primary Sn phase and a relatively hard eutectic.

  Fig. 2 shows the structure of Sn-1Ag-0.5Cu solder alloy (Ag: 1wt%) with reduced Ag addition and solidified on the substrate. Due to the temperature difference in the solidification process at the time of bonding on the substrate, the final solidification (eutectic) is crystallized in the continuous area surrounded by the coarse Sn primary crystal phase. In this continuous eutectic area, Eutectic is formed in the gap between dendrites. When attention is paid to this, by reducing the amount of Ag added, eutectic crystallization can be limited to the gap of dendrites, that is, a narrow region. In other words, by making the addition amount of Ag so small that the eutectic area containing dendrites is not continuous, the factor that promotes cracks can be eliminated.

  3 to 6 show changes in the structure of the lead-free Sn-Ag binary alloy with changes in the amount of Ag added, and FIG. 3 shows a crystal structure in which the amount of Ag added is 0.4 wt%. 4 shows a crystal structure with an Ag addition amount of 0.8 wt%, FIG. 5 shows a crystal structure with an Ag addition amount of 1.0 wt%, and FIG. 6 shows a crystal structure with an Ag addition amount of 2.0 wt%.

  As can be seen from observation of FIGS. 3 to 6, when 0.4 wt% Ag is added, eutectics grow in the shape of needles in the gaps of the dendrites, and the eutectic areas are not continuous (FIG. 3). On the other hand, when 0.8 wt% Ag is added, the eutectic area approaches a chain shape but is not completely connected (FIG. 4). When 1.0 wt% Ag is added, the amount of eutectic increases, and it can be seen that the primary crystals are partially independent like floating islands (Fig. 5). It can be seen that when 2.0 wt% Ag is added, the primary crystal is completely surrounded by the eutectic and is completely in the form of floating islands (Fig. 6).

  Thus, when paying attention to the content of Ag, it is important to limit the content and define the upper limit, and the gist of the present invention, that is, to the extent that the eutectic area containing dendrites is not continuous. By setting the addition amount to a very small amount and setting the upper limit to be in the range of 0.4 to less than 0.5 wt%, the eutectic areas containing dendrites are not continuous with each other, that is, the eutectic areas are scattered in the Sn phase. It can be in a floating island state. Note that if the amount of Ag added is limited, the melting point of the solder alloy tends to increase, but the Ag content should be limited if it is applied to, for example, a metal / ceramic substrate where the substrate itself has excellent heat resistance. An increase in melting point with is allowed.

  It goes without saying that a lead-free solder having excellent thermal cycle characteristics is desirably a solidified structure having a uniform ductility when bonded to a substrate. For this purpose, it is desirable that there is no coarse intermetallic phase in the solidified structure, and most preferably, there is no area of relatively hard eutectic structure.

  From this point of view, we focused on Ni, which can obtain eutectic with a small amount of additive elements in Sn alloys. This Ni has an effect of suppressing dissolution of Cu metallized on the substrate into the solder. Further, the addition of Ni is effective for ductility, wettability, and interface reaction.

  Fig. 7 shows the interfacial reaction phase and solder structure between a lead-free Sn-Ag binary alloy (1 wt% Ag added) without addition of Ni and a Cu substrate, and Fig. 8 shows the Cu substrate with 0.1 wt% Ni added. FIG. 9 shows the interfacial reaction phase and the solder structure with the Cu substrate when 0.5 wt% Ni is added. The bonding conditions were 60 ° C. and 60 seconds.

Referring to FIG. 7, it can be seen that in the Sn-Ag alloy without addition of Ni, Cu on the Cu substrate is eluted in the solder alloy and Cu ₆ Sn ₅ is crystallized in the solder alloy. Referring to FIG. 8, in the 0.1 wt% Ni-added Sn—Ag alloy, the elution of Cu into the solder alloy is suppressed, and the formation of Cu ₆ Sn ₅ structure in the solder alloy is not observed. Referring to FIG. 9, in the Sn-Ag alloy with 0.5 wt% Ni added, the interface reaction phase grows thick, which may impair the bonding strength between the substrate and the solder.

  From the above observations, it is possible to suppress the elution of Cu into the solder by adding Ni, but when the Ni addition amount is increased to 0.5 wt%, the interface reaction phase grows and a thick interface reaction phase is generated. The strength between the substrate and the solder is impaired.

  With reference to FIGS. 10 to 12, further study will be made regarding the amount of Ni added. FIG. 10 is a view showing a structure state of a Sn alloy to which 0.1 wt% of Ni is added, FIG. 11 is a view showing a structure state of a Sn alloy to which 0.5 wt% of Ni is added, and FIG. It is a figure which shows the structure | tissue state of Sn alloy which added 1 wt% Ni. In this experiment, the sample was completely melted at a temperature higher than the melting point of the binary alloy according to the added amount, and then cooled and solidified, and this was used as a base material. A plate material having a thickness of 100 μm was prepared from this sample and bonded to a Cu substrate by setting 300 seconds at 240 to 250 ° C. as reflow conditions. This cross-sectional observation photograph is FIGS.

From the equilibrium binary phase diagram, Sn-Ni alloy does not dissolve in Sn but forms an intermetallic compound phase. In addition, the eutectic is present on the high Sn side (0.14 wt%), and the melting point temperature is rapidly increased in the hypereutectic region. Further, as can be seen from FIGS. 11 and 12, a coarse Ni ₃ Sn ₄ phase is crystallized with the added amount on the hypereutectic side. This Ni ₃ Sn ₄ phase tends to concentrate and crystallize on the solidified cast wall side. From this, it is necessary to raise the temperature to the melting point of the alloy composition in order to suppress the separation of the eutectic and intermetallic compound phases and to uniformly distribute the eutectic and intermetallic compound phases. However, since the melting point rapidly increases as described above with the addition amount on the hypereutectic side, the intermetallic compound phase is not melted and formed in the base material at the reflow temperature (generally 250 ° C.) used for substrate bonding. In this state, the intermetallic compound phase tends to crystallize. From the above consideration, the Ni content is preferably 0.14 wt% or less.

  One intent of adding Ni is to suppress Cu elution from the substrate, but this Cu elution suppression effect dilutes when it is 0.07 wt% or less, and almost 0.05 wt% or less is Cu. The elution suppression effect cannot be expected. Therefore, the Ni content is desirably 0.07 wt% or more.

  The present inventor further paid attention to the sub-grain structure crystallized in the Sn phase in order to suppress the brittle fracture of the Sn crystal grains, and considered the refinement of the sub-crystal structure. It was.

  FIG. 13 is a view showing a structure state when a Sn—Ni binary solder alloy added with 0.1 wt% of Ni is solidified at a mounting cooling rate. FIG. 14 shows the crystal structure of a solder alloy composed of Ni (0.1 wt%)-Al (0.08 wt%)-remaining Sn to which Al is added, although the sub-grain crystal grain size is 40 μm. Further, FIG. 15 shows the crystal structure of a solder alloy composed of Ni (0.1 wt%)-Al (0.08 wt%)-Bi (0.5 wt%)-remaining Sn to which Bi is further added. Although the crystal grain size can be refined to 10 μm or less by adding Al from FIG. 14, the crystal grain size is not uniform. On the other hand, FIG. 15 shows that when Al and Bi are added, the particle size is uniform and further refined.

  FIG. 16 is a diagram showing the relationship between the Al content and the hardness of the Sn alloy. From the figure, it can be seen that the hardness of the alloy rapidly increases when the amount of Al exceeds 0.12 wt%. In addition, from the same figure, the hardness of the alloy increases as the amount of Al added increases, but there is a bending point at about 0.10 wt%, and when the amount exceeds about 0.10 wt%, the degree of increase in the hardness of the alloy increases. Accordingly, the Al content is preferably 0.12 wt% or less, more preferably 0.10 wt% or less.

  FIG. 17 shows the crystal structure when Al is not added, FIG. 18 shows the Sn alloy with 0.02 wt% Al added, and FIG. 19 shows the Sn alloy with 0.08 wt% Al added. As can be seen from FIG. 16 to FIG. 19, the crystal grain size can be refined by adding a small amount of Al, and it is finer when 0.08 wt% Al is added than when 0.02 wt% Al is added. It can be seen that

  According to the above observation regarding the addition of Al, the addition of Al should be 0.02 to 1.2 wt%, preferably 0.02 to 1.0 wt%, more preferably 0.02 to 0.08 wt%. Addition of Al is effective for the strength and ductility of the alloy in addition to the refinement of crystal grains.

  As described above, the addition of Bi is effective for refining crystal grains, but is also effective for the strength of the alloy. 20 to 22 show the relationship between the amount of Bi added and the crystal structure in the Sn—Bi binary alloy. FIG. 20 shows a Sn-0.5Bi alloy with 0.5 wt% Bi added, FIG. 21 shows a Sn-0.5Bi alloy with 1.0 wt% Bi added, and FIG. 22 shows 2.0 wt% Bi added. The added Sn-0.5Bi alloy is shown. Referring to FIGS. 20 to 22, it can be seen that the crystal structure changes greatly with the Bi addition amount of 1.0 wt% as a boundary. That is, in the Sn-0.5Bi alloy, Bi is uniformly dispersed in Sn and the dendrite is not clear. However, it can be seen that when the amount of Bi added is 1.0 wt%, a Bi-rich phase is formed in the gap between the dendrites (FIG. 21). Furthermore, it can be seen that when the amount of Bi added is increased to 2.0 wt%, coarse single Bi precipitates in addition to the Bi-rich phase (FIG. 22). On the other hand, the sub-grain crystal grains crystallized in the dendrite are finely formed when Bi is 0.5 wt% or more, and these crystal grains do not change greatly depending on the amount of Bi added. Therefore, it can be seen that the maximum addition amount of Bi is 1.0 wt% in order to make a uniform structure while suppressing uneven precipitation of Bi.

  Sub-grain refinement by adding Bi is to make the grain size of Sn smaller by adding Bi. However, when 0.2 wt% Bi is added, sub-grain is Sn grain size. Since it cannot be refined to a certain size of 10 μm or less, it is desirable that the addition of Bi is 0.4 wt% or more.

  The Ag—Sn solder alloy and solder alloy powder of the present invention may contain Ge as another trace element. Even if Ge is added to a composition in which fine sub-grains are formed by adding Bi and Al, the addition of Bi and Al will not adversely affect the miniaturization as long as the addition amount is small. I know. It has also been found that the Sn—Ge binary alloy itself further refines the Sn sub-grain crystal grains. In particular, the wettability of the substrate can be improved by adding Ge.

  The Ag—Sn solder alloy and powder thereof of the present invention may contain Pb, Cu, Sb, As, Fe, Zn, Cd, Au, and In as inevitable impurities. The mixing amount of these impurities is preferably limited to the following range.

  That is, Pb is preferably 0.10 wt% or less, and preferably Pb is 0.05 wt% or less. Cu should be 0.05 wt% or less. Further, Sb is preferably 0.10 wt% or less, and preferably 0.05 wt% or less. As should be 0.03 wt% or less. Fe is preferably 0.02 wt% or less. Furthermore, Zn is preferably 0.001 wt% or less. Cd is preferably 0.002 wt% or less, and preferably 0.001 wt% or less. Au should be 0.05 wt% or less. In should be 0.10 wt% or less.

First Example (FIG. 23) :
The composition of the solder alloy is as follows: Ni: 0.10 wt%; Al: 0.08 wt%; Ge: 0.05 wt%; Bi: 0.5 wt%; Ag: 0.3 wt%; Needless to say, the solder alloy or solder alloy powder of the first embodiment contains inevitable impurities.

Second Example (FIG. 24) :
The composition of the solder alloy is as follows: Ni: 0.10 wt%; Al: 0.08 wt%; Ge: 0.05 wt%; Bi: 0.5 wt%; Ag: 0.45 wt%; Needless to say, the solder alloy or solder alloy powder of the second embodiment contains inevitable impurities.

  A reference example (FIG. 25) was prepared for comparison with the first and second examples. In the reference example, the composition of the solder alloy is (Ni: 0.10 wt%; Al: 0.08 wt%; Ge: 0.05 wt%; Bi: 0.5 wt%; Ag: 0.8 wt%; balance Sn). Shown in

  That is, as shown in Table 1 below, Ag is 0.3 wt% in the first embodiment (FIG. 23), Ag is 0.5 wt% in the second embodiment (FIG. 24), and Ag is 0.5 in the reference example. It is 0.8 wt% (FIG. 25), and other elements are common.

Third Example (FIG. 26) :
The composition of the solder alloy is as follows: Ni: 0.10 wt%; Al: 0.08 wt%; Ge: 0.06 wt%; Bi: 0.2 wt%; Ag: 0.2 wt%; Needless to say, the solder alloy or solder alloy powder of the third embodiment contains inevitable impurities. It will be understood from FIG. 26 that uniform and fine crystal grains are present in the entire sample of the third example.

  When a tensile test of the solder alloy of the third example was conducted, the results shown in Table 3 below were obtained. As a comparative example, a conventionally known Sn-3Ag-0.5Cu alloy (SAC) and pure Sn were adopted.

  It has been confirmed that the ductility of the solder that contributes to the improvement of the thermal cycle characteristics is larger than that of pure Sn, and that the maximum point strain for evaluating toughness is also larger than that of pure Sn.

  In addition, when a thermal cycle acceleration test was performed, in the Sn-3Ag-0.5Cu alloy (SAC), the number of fractures was 18 with respect to 20 measured numbers at 500 cycles, whereas In the third example, the number of cycles was 1000, and the number of fractures was 15 for 40 measured. From this, it was confirmed that the thermal cycle characteristics of the third example can be greatly improved as compared with the conventional Sn-3Ag-0.5Cu alloy (SAC).

  In the above first to third embodiments, unavoidable impurities of Pb of 0.10 wt% or less, Cu of 0.05 wt% or less, Sb of 0.10 wt% or less, As of 0.03% or less, Fe of 0.02 wt% or less are inevitable impurities. 0.001 wt% or less of Zn, 0.002 wt% or less of Cd, 0.05 wt% or less of Au, or 0.10 wt% or less of In.

FIG. 6 is a drawing-substituting photograph showing a structure state when Sn-3Ag-0.5Cu solder alloy is solidified at a mounting cooling rate as a conventional example. FIG. 6 is a drawing-substituting photograph showing a structure state when Sn-1Ag-0.5Cu solder alloy is solidified at a mounting cooling rate as a conventional example. FIG. 6 is a drawing-substituting photograph showing a structure state when a Sn—Ag binary alloy containing 0.4 wt% of Ag is solidified at a mounting cooling rate. FIG. 6 is a drawing-substituting photograph showing a structure state when a Sn—Ag binary alloy containing 0.8 wt% of Ag is solidified at a mounting cooling rate. FIG. 6 is a drawing-substituting photograph showing a structure state when a Sn—Ag binary alloy containing 1.0 wt% of Ag is solidified at a mounting cooling rate. FIG. 6 is a drawing-substituting photograph showing a structure state when a Sn—Ag binary alloy containing 2.0 wt% of Ag is solidified at a mounting cooling rate. FIG. 5 is a drawing-substituting photograph showing an interfacial reaction phase and a solder structure state between a Sn—Ag binary alloy without addition of Ni (Ag: 1 wt% addition) and a copper (Cu) substrate. 2 is a drawing-substituting photograph showing an interfacial reaction phase and a solder structure state between a Sn—Ag—Ni alloy (Ag: 1 wt% added, Ni: 0.1 wt% added) and a copper (Cu) substrate. 2 is a drawing-substituting photograph showing an interfacial reaction phase and a solder structure state between a Sn—Ag—Ni alloy (Ag: 1 wt% added, Ni: 0.5 wt% added) and a copper (Cu) substrate. 2 is a drawing-substituting photograph showing an interfacial reaction phase and a solder structure state of a Sn—Ni alloy (Ni: 0.1 wt% added) and a copper (Cu) substrate. 3 is a drawing-substituting photograph showing an interfacial reaction phase between a Sn—Ni alloy (Ni: 0.5 wt% added) and a copper (Cu) substrate and a solder structure state. FIG. 3 is a drawing-substituting photograph showing an interfacial reaction phase and a solder structure state between a Sn—Ni alloy (Ni: 1 wt% added) and a copper (Cu) substrate. FIG. 3 is a drawing-substituting photograph showing a structure state when a Sn—Ni binary alloy containing 0.1 wt% of Ni is solidified at a mounting cooling rate. FIG. 14 is a drawing-substituting photograph showing a structure state when a solder alloy obtained by adding 0.08 wt% of Al to the Sn—Ni binary alloy in FIG. 13 is solidified at a mounting cooling rate. FIG. 15 is a drawing-substituting photograph showing a structure state when a solder alloy obtained by adding 0.5 wt% of Bi to the Sn—Ni (0.1 wt%)-Al (0.08 wt%) alloy in FIG. 14 is solidified at a mounting cooling rate. It is a figure which shows the relationship between content of Al, and the hardness of Sn alloy. 2 is a drawing-substituting photograph showing the structure of pure Sn without addition of Al. FIG. 5 is a drawing substitute photograph showing a structure state when 0.02 wt% Al is added. FIG. 5 is a drawing-substituting photograph showing a structure state when 0.08 wt% Al is added. FIG. 6 is a drawing-substituting photograph showing the structure of a Sn—Bi binary alloy containing 0.5 wt% of Bi when solidified at a mounting cooling rate. FIG. 6 is a drawing-substituting photograph showing the structure of a Sn—Bi binary alloy containing 1.0 wt% Bi solidified at a mounting cooling rate. FIG. 5 is a drawing-substituting photograph showing the structure of a Sn—Bi binary alloy containing 2.0 wt% Bi solidified at a mounting cooling rate. It is a drawing substitute photograph which shows the structure | tissue state when the alloy of 1st Example (Ag: 0.3 wt%) is solidified with the mounting cooling rate. It is a drawing substitute photograph which shows the structure | tissue state when the alloy of 2nd Example (Ag: 0.45 wt%) is solidified with the mounting cooling rate. FIG. 5 is a drawing-substituting photograph showing a structure state when an alloy of a reference example (Ag: 0.8 wt%) is solidified at a mounting cooling rate. It is a drawing substitute photograph which shows the structure | tissue state when the alloy of 3rd Example (Ag: 0.2 wt%) is solidified with the mounting cooling rate.

Claims (7)

  A lead-free Sn-Ag solder alloy or solder alloy powder characterized in that the Ag content is 0.1 or more and less than 0.5.   The lead-free Sn-Ag solder alloy or solder alloy powder according to claim 1, wherein the Ag content is 0.1 to 0.4 wt%.   The lead-free Sn-Ag solder alloy or solder alloy powder according to claim 1, wherein the content of Ag is 0.1 to 0.3 wt%.   The lead-free Sn-Ag binary solder alloy or solder alloy powder according to any one of claims 1 to 3, comprising Ni, wherein the Ni content is less than 0.5 wt%.   The lead-free Sn-Ag binary solder alloy or solder alloy powder according to claim 4, comprising Al, wherein the Al content is 0.12 wt% or less.   The lead-free Sn-Ag binary solder alloy or solder alloy powder according to claim 4, comprising Al, wherein the Al content is 0.10 wt% or less.   The lead-free Sn-Ag binary solder alloy or solder alloy powder according to claim 5 or 6, comprising Bi and having a Bi content of 1.0 wt% or less.