JP2015100849A - Solder material and bonding structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solder material that can form a solder part having excellent thermal fatigue characteristics.SOLUTION: This invention relates to a solder material. When content (mass%) of Ag, Bi, Cu, and In in the solder material are set as [Ag], [Bi], [Cu], and [In], Ag of 0.3≤[Ag]<4.0 (excluding the case of Ag being 0.5 mass%, 1.0 mass%), Bi of 0≤[Bi]≤1.0, and Cu of 0.2≤[Cu]≤1.2 are contained. In the range of 0.2≤[Cu]<0.5, In in the range of 6.0≤[In]≤6.8 is contained. In the range of 0.5≤[Cu]≤1.0, In in the range of 5.2+(6-(1.55×[Cu]+4.428)≤[In]≤6.8 is contained. In the range of 1.0<[Cu]≤1.2, In in the range of 5.2≤[In]≤6.8 is contained. The balance is only Sn of 87 mass% or more.

Description

  The present invention relates to a solder material in a solder paste or the like mainly used for soldering an electronic circuit board, and a joint structure using the solder material.

  In an electronic circuit board, generally, a Cu substrate electrode whose electrode material is Cu is often used. However, in-vehicle products such as ECUs (Engine Control Units), DC / DC converters, inverters, and headlamps require high bonding reliability. Therefore, Au flash plating is performed by flash processing that performs thin plating in a short time. An applied Au substrate electrode may be used. As an example, in FIG. 14, an electronic circuit board 930 having Au substrate electrodes 931 and 932, an electronic component 920 having a Cu component electrode 921, and an electronic component 940 having an Au component electrode 941 are joined by soldering. Sectional drawing which forms the structure 900 is shown. In this bonded structure 900, the Au substrate electrode 931 of the electronic circuit substrate 930 and the Cu component electrode 921 of the electronic component 920 are bonded by the solder portion 911. Further, the Au substrate electrode 932 of the electronic circuit board 930 and the Au component electrode 941 of the electronic component 940 are joined by the solder portion 912. And said solder part 911,912 is formed of the solder material which has a composition of Sn-Ag-Bi-In.

  Thus, a solder material having a composition of Sn—Ag—Bi—In composed of four kinds of elements is used for soldering the electronic circuit board 930 and the electronic components 920 and 940 (for example, (See Patent Documents 1 and 2). In such a solder material, thermal fatigue characteristics relating to fatigue failure caused by thermal stress accompanying temperature change are enhanced by a technique using a solid solution effect. Here, solid solution is a technique in which a part of metal atoms arranged in a lattice form is replaced with a different kind of metal atom and the lattice material is distorted so that the solder material is hardly deteriorated.

  In the solder material having the above Sn—Ag—Bi—In composition, In is dissolved in the Sn lattice to improve thermal fatigue characteristics. Specifically, a solder material having a composition such as Sn-3.5 mass% Ag-0.5 mass% Bi-6 mass% In is used. Ag and Bi are also added here, but Ag is added to improve the alloy strength and lower the melting point by precipitation strengthening, and Bi is added to lower the melting point.

Japanese Patent No. 3040929 JP 2010-179336 A

  However, in the case of soldering to the Au substrate electrode, it has been found that a solder material having a composition of Sn—Ag—Bi—In does not necessarily have a sufficiently high thermal fatigue characteristic.

  The present inventors have analyzed the reason as follows. That is, in a solder material having a composition of Sn—Ag—Bi—In, the thermal fatigue characteristics change depending on the In content. The thermal fatigue characteristics here are the number of cycles in which the occurrence of cracks is not confirmed by cross-sectional observation of the solder part after the temperature cycle test is carried out under the test conditions of −40 ° C./150° C. (reliability test conditions for in-vehicle products). It shows with. For example, the composition of the solder material after soldering is Sn-3.5 mass% Ag-0.5 mass% Bi-6 mass% In and Sn-3.5 mass% Ag-0.5 mass% Comparing with the case of Bi-5.5 mass% In, the number of cycles in the temperature cycle test is 2300 cycles and 2150 cycles, respectively, and the number of cycles (thermal fatigue characteristics) also decreases as In decreases.

  The alloy strength related to thermal fatigue characteristics increases as the In content increases, but becomes maximum when the In content is approximately 6% by mass, and decreases when the In content exceeds this. That is, when the In content is about 6% by mass, the number of cycles in the temperature cycle test is high, so that the thermal fatigue characteristics are the highest. Therefore, in order to effectively use the solid solution effect of In, it is desirable to control the In content of the solder material more accurately.

  The Au substrate electrode has a structure in which Ni plating with a film thickness of 1 to 5 μm is applied on the Cu electrode, and further Au flash plating with a film thickness of 0.03 to 0.07 μm is applied on the Ni plating. ing. Then, Au is melted into Sn—Ag—Bi—In during soldering with heating, and Ni plating is exposed. Ni plating has a composition of 90 mass% Ni and 10 mass% P, and since In and P are highly reactive, In reacts with P to produce a compound InP having an In-P composition. The As a result, the amount of In dissolved in the Sn lattice, which contributes to the improvement of thermal fatigue characteristics, decreases, and the substantial In content decreases.

  Here, in order to increase the thermal fatigue characteristics of the Au substrate electrode in which the In content after soldering decreases, the In content of the solder material having the Sn-Ag-Bi-In composition before soldering is increased. In such a case, the thermal fatigue characteristics of the Au substrate electrode are enhanced. However, since electronic components mounted on one electronic circuit board are mixed with those having an Au component electrode and those having a Cu component electrode, these two types of In content of solder material The change is different, and in the Cu component electrode, the amount of decrease in In is small, and thermal fatigue characteristics are reduced due to excessive In. As described above, even if the In content of the solder material before soldering is simply increased to prevent the decrease in In after soldering the Au substrate electrode, the thermal fatigue characteristics of the Cu component electrode are decreased. Therefore, it was necessary to examine means other than the addition of In.

  The present invention has been made in view of the above points, and has good thermal fatigue characteristics even when an Au electrode and a Cu electrode are mixed when an electronic circuit board and an electronic component are joined by soldering. An object of the present invention is to provide a solder material and a joint structure capable of forming a solder part.

The solder material according to the present invention is:
When the content (mass%) of Ag, Bi, Cu, and In in the solder material is [Ag], [Bi], [Cu], and [In],
0.3 ≦ [Ag] <4.0 Ag (except when Ag is 0.5 mass% and 1.0 mass%),
Bi of 0 ≦ [Bi] ≦ 1.0,
0.2 ≦ [Cu] ≦ 1.2 and Cu,
Within the range of 0.2 ≦ [Cu] <0.5,
Including In in the range of 6.0 ≦ [In] ≦ 6.8,
Within the range of 0.5 ≦ [Cu] ≦ 1.0,
5.2+ (6- (1.55 × [Cu] +4.428)) ≦ [In] ≦ 6.8 including In,
Within the range of 1.0 <[Cu] ≦ 1.2,
Including In in the range of 5.2 ≦ [In] ≦ 6.8,
The balance is characterized by only 87 mass% or more of Sn.

The bonded structure according to the present invention is
An electronic circuit board having a substrate electrode;
An electronic component having a component electrode,
At least one of the substrate electrode and the component electrode is an Au electrode,
The substrate electrode and the component electrode are joined by the solder material.

  According to the present invention, it is possible to form a solder portion having good thermal fatigue characteristics even when an Au electrode and a Cu electrode are mixed when an electronic circuit board and an electronic component are joined by soldering. is there.

It is explanatory drawing which shows the relationship between Cu content rate and In content rate in the solder material of this invention. It is explanatory drawing which shows the relationship between Cu content rate and In content rate in the solder material of this invention before considering the upper limit of Cu content rate. It is a graph which shows the reliability test result of the alloy with the composition of Sn-3.5 mass% Ag-0.5 mass% Bi with which In was added for demonstrating the solder material of embodiment in this invention. . (A) is typical sectional drawing which shows Au electrode, (b) is typical sectional drawing which shows Cu electrode. It shows a state of measuring the In content after joining the electrode and the solder material, (a) is a schematic explanatory diagram before soldering, (b) is a schematic explanatory diagram after soldering. A Cu electrode using a solder material having a composition of Sn-3.5 mass% Ag-0.5 mass% Bi-6.0 mass% In for explaining the solder material of the embodiment of the present invention. 4 is a graph showing an analysis result of In content in each solder part after soldering to two kinds of Au electrodes. For explaining the solder material according to the embodiment of the present invention, a solder material having a composition of Sn-3.5 mass% Ag-0.5 mass% Bi-6.0 mass% In added with Cu is used. And it is a graph which shows the analysis result of In content rate inside a solder part after soldering with respect to two types of Au electrodes was performed. In order to explain the solder material of the embodiment of the present invention, the solidification of the solder material having a composition of Sn-3.5 mass% Ag-0.5 mass% Bi-6.0 mass% In to which Cu is added. It is a graph which shows a phase line and a liquidus line. It is typical sectional drawing of the joining structure of embodiment in this invention. (A) is sectional drawing which shows typically the mode before soldering of Au board | substrate electrode of an electronic circuit board, and Cu component electrode of an electronic component, (b) is Au board | substrate electrode of an electronic circuit board, electronic It is sectional drawing which shows typically the mode after soldering with Cu component electrodes of components. (A) is sectional drawing which shows typically the mode before soldering with Cu board | substrate electrode of an electronic circuit board, and Au component electrode of an electronic component, (b) is Cu board | substrate electrode of an electronic circuit board, and electronic It is sectional drawing which shows typically the mode after soldering with Au component electrodes of components. (A) is sectional drawing which shows typically the mode before soldering of Au board | substrate electrode of an electronic circuit board, and Au component electrode of an electronic component, (b) is Au board | substrate electrode of an electronic circuit board, and electronic It is sectional drawing which shows typically the mode after soldering with Au component electrodes of components. (A) is sectional drawing which shows typically the mode before soldering of Cu board | substrate electrode of an electronic circuit board, and Cu component electrode of an electronic component, (b) is Cu board | substrate electrode of an electronic circuit board, and electronic It is sectional drawing which shows typically the mode after soldering with Cu component electrodes of components. It is typical sectional drawing of the joining structure using the conventional solder material.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  First, the principle regarding the solder material of this embodiment will be described with reference to FIG.

  FIG. 3 is a graph showing reliability test results of an alloy having a composition of Sn-3.5 mass% Ag-0.5 mass% Bi to which In is added for explaining the solder material according to the embodiment of the present invention. It is a graph to show.

  The In content on the horizontal axis of the graph shown in FIG. 3 is solid solution in the solder portion after soldering, more specifically, the substantial In content of In in solid solution in the Sn lattice. It is.

  The number of test cycles on the vertical axis of the graph shown in FIG. 3 is the FR5 board in which the chip capacitor of 1608 size (1.6 mm × 0.8 mm) is mounted and the FR grade (Flame Retardant Grade) is FR-5 grade. After the temperature cycle test was carried out under the test conditions of −40 ° C./150° C., the number of cycles in which generation of cracks was not confirmed by cross-sectional observation of the solder portion.

  In a reliability test of an in-vehicle product mounted in the vicinity of an automobile engine, a required number of cycles of 2000 cycles or more is required as an in-vehicle standard. Here, it is assumed that the thermal fatigue characteristics are sufficiently satisfied when the number of cycles is 2000 cycles or more.

  According to the graph shown in FIG. 3, the In content dissolved in the solder part after soldering is 5.5 mass% (2150 cycles), 6.0 mass% (2300 cycles), and 6.5 mass% ( 2200 cycles) is 2000 cycles or more, and when the In content is 5.0% by mass or less or 7.0% by mass or more, it is understood that the number is less than 2000 cycles.

  Further, in FIG. 3, the approximate curve is illustrated as a graph of a quadratic function of the following equation obtained by using the above numerical data.

  Therefore, the range of In content that can secure the number of cycles of 2000 cycles or more, which is the vehicle-mounted standard, is approximately 5.2 to 6.8% by mass, and the management width is approximately ± 0.8% by mass.

  Since the variation range of the In content of the solder alloy in mass production is approximately ± 0.5 mass%, the median value of the In content is 5.7 (= 5.2 + 0.5) mass% or more and 6.3. (= 6.8-0.5) It is desirable that it is below mass%.

  Next, the effect of P contained in the Ni plating will be described with reference mainly to FIGS. In order to investigate this influence, samples prepared for measurement as shown in FIGS. 4A and 4B were used as the Au electrode 40 and the Cu electrode 50.

  4A is a schematic cross-sectional view showing the Au electrode 40, and FIG. 4B is a schematic cross-sectional view showing the Cu electrode 50.

  FIGS. 5A and 5B are schematic explanatory views showing a state in which the In content after the electrode 3 and the solder material 1 are joined is measured. The electrode 3 is an Au electrode or a Cu electrode, and the solder material 1 has a composition of Sn-3.5 mass% Ag-0.5 mass% Bi-6.0 mass% In. 5A shows a state before the solder material 1 supplied onto the electrode 3 is heated, and FIG. 5B shows a state where the solder material 1 supplied onto the electrode 3 is heated and melted to spread out. The state of the solder part 2 after having been shown is shown.

  As shown in FIG. 4A, the commonly used Au electrode 40 includes a Cu electrode 10, Ni plating 20 applied on the Cu electrode 10, and further on the Ni plating 20. And Au flash plating 30 applied. In this case, the Cu electrode 10 is formed of a Cu foil having a thickness of 35 μm. The Ni plating 20 has a film thickness of 1 to 5 μm and is applied as electroless plating that does not require energization like electroplating. The Au flash plating 30 has a film thickness of 0.03 to 0.07 μm. On the other hand, as shown in FIG. 4B, the Cu electrode 50 is formed of a Cu foil having a film thickness of 35 μm. The Au electrode 40 and the Cu electrode 50 as described above are used as a substrate electrode of an electronic circuit board or as a component electrode of an electronic component. In this specification, when the Au electrode 40 and the Cu electrode 50 are used as a substrate electrode of an electronic circuit board, they may be referred to as an Au substrate electrode and a Cu substrate electrode, respectively, and when used as a component electrode of an electronic component, They may be referred to as Au component electrodes and Cu component electrodes, respectively.

  There are two types of Au electrodes prepared as samples. The first Au electrode has a Ni plating thickness of 5 μm and an Au flash plating thickness of 0.07 μm. This assumes the case where one of the substrate side or the component side is an Au electrode. The second Au electrode has a Ni plating thickness of 10 μm and an Au flash plating thickness of 0.07 μm. This assumes the case where both the substrate side and the component side are Au electrodes, and the influence of P is maximized. At the time of soldering, if the solder material melts and becomes a liquid, Au and Ni instantaneously diffuse and react with the solder material. Therefore, by doubling the thickness of Ni containing P, the substrate side and the component side The case where both are Au electrodes can be simulated.

  Then, a solder material having a composition of Sn-3.5 mass% Ag-0.5 mass% Bi-6.0 mass% In, as shown in FIG. Were supplied on the electrode 3 in the shape of a circle and a thickness t = 0.15 mm. The electrode 3 is the above-described two kinds of Au electrode and Cu electrode. Thereafter, when the electrode 3 supplied with the solder material 1 is heated on a hot plate at 240 ° C. for 30 seconds and then slowly cooled at room temperature, the solder material 1 has a solder portion 2 having a shape as shown in FIG. It became.

  A sample of the solder part 2 was obtained as described above. Next, it grind | polished so that the vertical cross section of this solder part 2 might appear, and the In content rate was measured by analyzing the center part of this vertical cross section by the method of using EDX (Energy Dispersive X-ray spectroscopy). . Here, the central portion is a portion corresponding to a position of 1/2 of the thickness B of the solder portion 2 and corresponding to a position of 1/2 of the wetting spread width A of the solder portion 2.

  FIG. 6 shows the soldering of a Cu electrode and two kinds of Au electrodes using a solder material having a composition of Sn-3.5 mass% Ag-0.5 mass% Bi-6.0 mass% In. It is a graph which shows the analysis result of In content in the inside of each solder part after performing.

  The substantial In content of In dissolved in the Sn lattice, which contributes to the improvement of thermal fatigue properties, has decreased from the initial In content of 6.0% by mass. It is 5.9% by mass for an Au electrode having a Ni plating film thickness of 5 μm, and 5.1% by mass for an Au electrode having a Ni plating film thickness of 10 μm.

  As for the Au electrode, Au diffuses into the solder material when heated, and Ni plating having a composition of 90 mass% Ni and 10 mass% P formed under the Au flash plating is exposed.

Then, Sn contained in the solder material reacts with Ni to produce a Ni ₃ Sn ₄ compound, so that the Ni content decreases on the Ni plating solder material side and the P content increases. In the portion where P is concentrated, P per unit area in contact with the solder material increases, so the amount of compound InP generated increases, and the amount of In dissolved in the Sn lattice decreases. The substantial In content is greatly reduced as compared with the Cu electrode.

  For this reason, since the range of In content corresponding to the vehicle-mounted standard is approximately 5.2 to 6.8% by mass as described above, the Au electrode does not satisfy the vehicle-mounted standard.

In addition, since the specific gravity of Ni plating is 7.9 g / cm ³ , the mass of P contained in the Ni plating is 7.9 × T × using the Ni plating film thickness T and the Ni plating area S. It can be calculated by S × 0.1, and the mass of P contained in the Ni plating varies in proportion to the film thickness T of the Ni plating.

In light of such a phenomenon, the present inventors have effectively reduced the amount of Ni ₃ Sn ₄ compound produced in order to suppress the concentration of P, which is the cause of the increase in the amount of InP compound produced. I found out.

There are Zn, Co, Mn, and the like as elements that form an intermetallic compound with Sn. Among these elements, those found as effective elements react with Sn as described below. generating a Cu ₆ Sn ₅ compound, a Cu.

  Here, the solder material according to the present embodiment will be described more specifically with reference to FIGS. 7 and 8.

  FIG. 7 has a composition of Sn-3.5 mass% Ag-0.5 mass% Bi-6.0 mass% In to which Cu is added for explaining the solder material of the embodiment of the present invention. It is a graph which shows the analysis result of In content in the inside of a solder part, after soldering with respect to two types of Au electrodes whose film thickness of Ni plating is 5 micrometers and 10 micrometers using a solder material. The film thickness of the Au flash plating of the two types of Au electrodes is 0.07 μm.

  Further, FIG. 8 has a composition of Sn-3.5 mass% Ag-0.5 mass% Bi-6.0 mass% In added with Cu for explaining the solder material of the embodiment in the present invention. 5 is a graph showing a solid phase line 601 and a liquid phase line 602 of the solder material.

  First, the lower limit of the Cu content will be described with reference mainly to FIG.

  Here, the analysis was performed by the same method as described above, and the In content after the soldering with the Au electrode was measured.

  A sample of solder material was produced as follows.

  First, 89.5 g of Sn was put into a ceramic crucible, and the above crucible was left in an electric jacket heater whose temperature was adjusted to 500 ° C.

  Next, after confirming that Sn was melted, 6.0 g of In was put into the crucible and stirred for 3 minutes.

  Next, 0.5 g of Bi was put into the crucible and further stirred for 3 minutes.

  Next, 3.5 g of Ag was put into the crucible and further stirred for 3 minutes.

  Next, a predetermined amount of Cu was put into the crucible and further stirred for 3 minutes.

  Note that each of the elements Sn, Bi, Ag, and Cu used here contains a very small amount of impurities.

  Thereafter, the crucible was taken out from the electric jacket heater and immersed in a container filled with water at 25 ° C. to cool.

  In FIG. 7, “Δ” indicates a plot in the case of an Au electrode having a Ni plating film thickness of 5 μm. The In content after soldering to an Au electrode with a Ni plating film thickness of 5 μm is (1) 5.1 mass% when the Cu content is zero, but (2) Cu As the content increases, the decrease in In is suppressed, so that it increases. (3) When the Cu content is 0.4% by mass, it becomes 5.2% by mass, and (4) the Cu content is If it becomes 0.9 mass%, it will be 5.99 mass%. Thus, when the Cu content varies from zero to 0.9 mass%, the In content varies from 5.1 mass% to 5.99 mass%.

  In FIG. 7, a plot in the case of an Au electrode having a Ni plating film thickness of 10 μm is indicated by “◯”. The In content after soldering to an Au electrode with a Ni plating film thickness of 10 μm is (1) 5.1 mass% when the Cu content is zero, but (2) Cu When the content increases, the decrease in In is suppressed, so that it increases. (3) When the Cu content is 0.5% by mass, it becomes 5.21% by mass, and (4) the Cu content is When it becomes 0.9 mass%, it will be 5.83 mass%. Thus, when the Cu content varies from zero to 0.9 mass%, the In content varies from 5.1 mass% to 5.83 mass%.

  Comparing the case where the Ni plating film thickness is 5 μm and the case where it is 10 μm, it is assumed that both the substrate electrode and the component electrode are Au electrodes, and the Ni plating film thickness is 10 μm. Since the amount of change is large, it is desirable to calculate the lower limit value of the Cu content by a numerical value when the Ni plating film thickness is 10 μm.

  Using the numerical value when the Cu content is 0.5 mass% to 0.9 mass%, when an approximate straight line is drawn with the numerical value when the Ni plating film thickness is 10 μm, the primary expression represented by the following formula: A graph of the function is obtained.

  Therefore, in order to secure the In content of 5.2% by mass or more necessary for satisfying the on-vehicle standard even in combination with the Au electrode, the Cu content is preferably 0.50% by mass or more. . If the Cu content is 0.50% by mass or more, the In content after soldering is 5.2% by mass or more even in combination with the Au electrode, and the reliability of the on-vehicle standard can be satisfied.

  In the above description, the case where the solder material having the composition of Sn-3.5 mass% Ag-0.5 mass% Bi-6.0 mass% In is used has been described. However, the Cu content is 0.50. Since the amount of change in the In content when it is mass% is 0.8 mass%, for example, it has a composition of Sn-3.5 mass% Ag-0.5 mass% Bi-5.5 mass% In. When a solder material is used, the In content after soldering is 4.7% by mass, and the on-vehicle standard reliability cannot be satisfied. Thus, there is a correlation between the Cu content and the In content. That is, as shown in FIG. 7, when the Cu content is 0.5% by mass or more and 1.0% by mass or less, there is a correlation indicated by the above approximate line, but the Cu content is 0%. There is no correlation in the case of less than 0.5 mass% and in the case of exceeding 1.0 mass%.

  FIG. 2 shows the relationship between the Cu content and the In content in the solder material of the present invention. Hereinafter, the content (mass%) of Ag, Bi, Cu, and In in the solder material may be referred to as [Ag], [Bi], [Cu], and [In], respectively.

  The lower limit value of the In content is determined for each range by dividing the range of the Cu content into three.

  That is, 6.0 ≦ [In] in the range of 0 <[Cu] <0.5.

  In the range of 0.5 ≦ [Cu] ≦ 1.0, 5.2+ (6- (1.55 × [Cu] +4.428)) ≦ [In].

  In the range of 1.0 <[Cu], 5.2 ≦ [In].

  On the other hand, the upper limit value of the In content is also determined for each range by dividing the range of the Cu content into three.

  That is, [In] ≦ 7.6 in the range of 0 <[Cu] <0.5.

  In the range of 0.5 ≦ [Cu] ≦ 1.0, [In] ≦ 6.8 + (6- (1.55 × [Cu] +4.428)).

  In the range of 1.0 <[Cu], [In] ≦ 6.8.

As described above, the combination including the Au electrode has been described. However, in the case of the Cu electrode, since a compound that reacts with In does not exist, the In content does not decrease. FIG. 13A is a cross-sectional view schematically showing a state before soldering between the Cu substrate electrode 220 of the electronic circuit board 200 and the Cu component electrode 320 of the electronic component. At this time, a solder material 100 having a composition of Sn—Ag—Bi—In—Cu is interposed between the Cu substrate electrode 220 and the Cu component electrode 320. FIG. 13B is a cross-sectional view schematically showing a state after soldering between the Cu substrate electrode 220 of the electronic circuit board 200 and the Cu component electrode 320 of the electronic component. At this time, a Cu ₆ Sn ₅ compound 120 is generated between the Cu substrate electrode 220 and the solder part 110. A similar compound 120 is also generated between the Cu component electrode 320 and the solder part 110. Since In does not participate in the formation of the Cu ₆ Sn ₅ compound 120, the In content in the solder material 100 does not decrease. In FIGS. 13A and 13B, electronic components are not shown.

  As described above, when the solder material of the present invention is used in a combination that does not include an Au electrode, the In content does not decrease. Therefore, when the Cu content is 1.0% by mass or less, the In content is 6 on the vehicle-mounted standard. When exceeding 8% by mass occurs. Therefore, in order to be able to use the solder material of the present invention for both the combination including the Au electrode and the combination not including the Au electrode, the In content is 6.% within the range where the Cu content is 1.0 mass% or less. It is necessary to limit the amount to 8% by mass or less.

  Next, the upper limit of the Cu content will be described with reference mainly to FIG.

  That is, if the Cu content is too high, the temperature of the liquidus line 602 increases, so that the meltability of the solder material is lowered and the wettability is likely to deteriorate.

  More specifically, although the solidus temperature represented by the solidus 601 is stable in the range of 199 to 201 ° C., the liquidus temperature represented by the liquidus 602 is Cu When the content exceeds 0.7% by mass, the temperature rises. When the Cu content is 1.2% by mass, the temperature is 216 ° C., and when the Cu content is 1.4% by mass, the temperature is 228 ° C.

  Here, the solidus temperature is a temperature at which the solder alloy heated from the solid state starts to melt, and the liquidus temperature is a temperature at which all the solder alloy heated from the solid state finishes melting.

  Table 1 shows the relationship between Cu content and wetting spread in a solder material having a composition of Sn-3.5 mass% Ag-0.5 mass% Bi-6.0 mass% In to which Cu is added. Show. Specifically, Cu content is 0.2 mass%, 0.5 mass%, 0.7 mass%, 1.0 mass%, 1.2 mass%, 1.4 mass%, 1.7 mass%. In the case of the above, the wetting spread on the Au electrode was evaluated.

  As described above, the mass of P contained in the Ni plating varies in proportion to the film thickness T of the Ni plating. Here, it is assumed that the Ni plating film thickness approaches the lower limit, the P content is minimum, and the wetting spreadability is not good from this viewpoint. Therefore, the wet spread rate was measured by the spread test method defined in JIS Z 3197 “Flux Test Method for Soldering” for the sample prepared so that the Ni plating film thickness was 1 μm.

  In Table 1, regarding the wetting spread evaluation, “◯” indicates that the wetting spread ratio is 90% or more, and “△” indicates that the wetting spread ratio is 85% or more and less than 90%. “×” indicates that the wetting spread rate is less than 85%.

  Therefore, in order to guarantee a wetting spread ratio of 90% or more which is important for good soldering, it is desirable that the Cu content is 1.2 mass% or less.

  FIG. 1 shows the relationship between the Cu content and the In content of the solder material of the present invention by adding 1.2% by mass, which is the upper limit of the Cu content, to FIG. That is, in FIG. 1, the shaded area satisfies the Cu content and the In content of the solder material of the present invention. However, the shaded area includes a solid line and does not include a broken line and a white dot (◯).

  Table 2 shows the relationship between various compositions of the solder material before soldering and changes in the In content of the solder material after soldering in the combination of the Au substrate electrode and the Au component electrode. 3, Examples 4 to 8, Reference Example 9, Examples 10 to 13, and Comparative Examples 1 to 4, and the results of reliability determination and strength determination are also shown.

  Regarding strength determination, “○” satisfies 60 MPa or more based on the tensile strength of the solder material, and can be used for chip parts up to 0.9 mm × 0.8 mm, “◎” satisfies 65 MPa or more. It can be used for large semiconductor parts such as QFP (Quad Flat Package) and BGA (Ball Grid Array), and “◎◎” satisfies 70 MPa or more, and can be used for large parts such as aluminum electrolytic capacitors and module parts. “◎◎◎” satisfies 75 MPa or more, and indicates that it can be used for heavy parts such as coils and transformers. In addition, the tensile strength is measured with the No. 4 test piece of JIS Z 2201.

  The remaining amount after the change in the In content was measured by analyzing the In content in the solder portion after soldering to the Au electrode by using EDX.

  Regarding the determination about the change in In content, “◯” indicates that the In content after soldering is included in the range of 5.2 to 6.8% by mass, and “×”. Indicates that the In content is in a range of less than 5.2% by mass.

  Regarding reliability determination, in the reliability test of in-vehicle products, “○” satisfies the standard, based on the fact that the number of cycles of the temperature cycle test satisfies the required specifications of 2000 cycles or more, or 2250 cycles or more. "X" indicates that the standard is not satisfied.

  From the results of reliability determination in Examples 1, 2, Reference Example 3, Examples 4-8, Reference Example 9, and Examples 10-13, a predetermined amount of solder material having a composition of Sn-Ag-Bi-In was used. It can be seen that the reduction of In content was suppressed by containing Cu. Therefore, it was confirmed that Examples 1, 2, Reference Example 3, Examples 4-8, Reference Example 9, and Examples 10-13 all satisfy the required specifications of 2000 cycles or more.

  In Comparative Examples 1 to 4, since an effective element was not added to suppress a decrease in the In content, the In content after soldering was 4.7 to 5.1% by mass (In content The change was -0.8% by mass), and it was confirmed that the required specifications of 2000 cycles or more were not satisfied.

  Next, Table 3 shows the relationship between various compositions of the solder material before soldering and changes in the In content of the solder material after soldering in Examples 14 and 15, in the combination of the Au substrate electrode and the Cu component electrode. Reference Example 16, Examples 17 to 21, Reference Example 22, Examples 23 to 26 and Comparative Examples 5 to 8 are shown, and the results of reliability determination and strength determination are also shown. The various determinations are the same as in Table 2 above.

  From the results of reliability determination in Examples 14 and 15, Reference Example 16, Examples 17 to 21, Reference Example 22 and Examples 23 to 26, a predetermined amount of solder material having a composition of Sn-Ag-Bi-In was used. It can be seen that the reduction of In content was suppressed by containing Cu. Therefore, it was confirmed that Examples 14 and 15, Reference Example 16, Examples 17 to 21, Reference Example 22, and Examples 23 to 26 all satisfy the required specifications of 2000 cycles or more. Examples 14 and 15, Reference Example 16, Examples 17 to 21, Reference Example 22 and Examples 23 to 26 are combinations of an Au substrate electrode and a Cu component electrode. Similar results are expected to be obtained for combinations.

  In Comparative Examples 5 to 8, since an effective element was not added to suppress a decrease in the In content, the In content after soldering was 4.7 to 5.1% by mass (In content The change was -0.8% by mass), and it was confirmed that the required specifications of 2000 cycles or more were not satisfied.

  Next, Table 4 shows the relationship between various compositions of the solder material not containing Bi and the change in In content in the combination of the Au substrate electrode and the Au component electrode in Example 27, Reference Example 28, and Examples 29 to 29. 31, Reference Example 32, Examples 33 to 38, and Reference Example 39 are shown, and the results of reliability determination and strength determination are also shown. The various determinations are the same as in Table 2 above.

  In Example 27, Reference Example 28, Examples 29-31, Reference Example 32, Examples 33-38, and Reference Example 39 in Table 4, the reliability determination results all satisfy the criteria of 2000 cycles or more. From this, it can be seen that even if the solder material does not contain Bi, it does not affect the change in the In content. Bi is added to adjust the melting temperature of the solder material, and the Bi content does not significantly affect the thermal fatigue characteristics of the solder material.

  Examples 1 to 2 in Tables 2 to 4, Reference Example 3, Examples 4 to 8, Reference Example 9, Examples 10 to 15, Reference Example 16, Examples 17 to 21, Reference Example 22, Example 23 to 27, Reference Example 28, Examples 29-31, Reference Example 32, Examples 33-38, and Reference Example 39, reliability evaluation of in-vehicle products in soldering to Au and Cu electrodes In order to satisfy the above, the solder material having the Sn-Ag-Bi-In composition before soldering satisfies the following relationship.

That is, 0.3 ≦ [Ag] ≦ 4.0 Ag,
Bi of 0 ≦ [Bi] ≦ 1.0,
Cu of 0 <[Cu] ≦ 1.2 is included.
And in the range of 0 <[Cu] <0.5,
Including In in the range of 6.0 ≦ [In] ≦ 6.8,
Within the range of 0.5 ≦ [Cu] ≦ 1.0,
5.2+ (6- (1.55 × [Cu] +4.428)) ≦ [In] ≦ 6.8 including In,
Within the range of 1.0 <[Cu] ≦ 1.2,
Including In in the range of 5.2 ≦ [In] ≦ 6.8,
If the balance is only Sn of 87% by mass or more, it becomes possible to satisfy the criteria for reliability determination after soldering (2000 cycles or more).

  Moreover, the content rate of Ag which comprises the solder material in embodiment is determined for the following reasons. As already described, since the thermal fatigue characteristics are improved by the solid solution action of In with Sn, the thermal fatigue characteristics vary greatly depending on the In content. However, since Ag does not dissolve in Sn, thermal fatigue characteristics do not change greatly.

In addition, since the Ag content affects the melting point of the solder material, if the Ag content exceeds 4 mass%, the melting point becomes 235 ° C. or more, and the wetting spread during soldering deteriorates and cannot be used. Therefore, the maximum value of the Ag content is 4% by mass. Further, when the Ag content is decreased, the amount of Ag ₃ Sn deposited on the Sn phase is decreased and the mechanical strength characteristics are lowered. Therefore, the minimum value of the Ag content is set to 0.3% by mass.

  Next, the content rate of Bi which comprises the solder material in embodiment is determined for the following reasons. As described in Table 4, the minimum value can be zero because it does not affect the thermal fatigue characteristics of the solder material. Further, since Bi has a property of segregating inside the solder alloy, if it exceeds 1% by mass, the amount of segregation increases and the alloy becomes brittle and cannot be used. Therefore, the maximum Bi content is set to 1% by mass.

  From the above, since Ag and Bi do not significantly affect the thermal fatigue characteristics of the solder material, the effect of the In content in the solder material having the composition of Sn-Ag-Bi-In is Sn-Ag-In and It is considered that a solder material having a composition of Sn—Bi—In can be handled similarly. However, in a solder material having a composition of Sn—Bi—In, since the Ag content is zero, the mechanical strength may be reduced.

  As is clear from the above description, the solder material of the present invention can be suitably used for soldering an Au electrode having Ni plating containing P. In this case, the Au electrode may be either an Au substrate electrode or an Au component electrode. The Ni plating has a composition of 3 to 15% by mass of P, preferably 5 to 10% by mass of P, and the balance is Ni.

Also, the above solder material is
0.3 ≦ [Ag] ≦ 4.0 Ag,
Bi of 0 ≦ [Bi] ≦ 1.0,
Cu of 0 <[Cu] ≦ 1.2 is included.

And in the range of 0 <[Cu] <0.5,
Including In in the range of 6.0 ≦ [In] ≦ 6.8,
Within the range of 0.5 ≦ [Cu] ≦ 1.0,
5.2+ (6- (1.55 × [Cu] +4.428)) ≦ [In] ≦ 6.8 including In,
Within the range of 1.0 <[Cu] ≦ 1.2,
Including In in the range of 5.2 ≦ [In] ≦ 6.8,
The balance is only 87% by mass or more of Sn.

  When the above-described solder material is used for soldering the Cu electrode, the In content does not decrease. Therefore, said solder material can be used conveniently also for the combination of Cu board | substrate electrode and Cu component electrode. As described above, according to the solder material of the present invention, even when the Au electrode and the Cu electrode are mixed when the electronic circuit board and the electronic component are joined by soldering, the solder portion having good thermal fatigue characteristics. Can be formed.

  The lower limit of the Cu content is only required to contain a small amount of Cu in order to prevent Cu erosion of the electrode, but a large semiconductor component such as QFP or BGA can be used, and 0.5 mass satisfying a tensile strength of 65 MPa or more. % Or more is preferable.

In particular, 0.5 to 3.8% by mass of Ag,
0.2-1.0 mass% Bi;
6.0-6.8% by mass of In,
0.2 to 1.2% by mass of Cu,
The balance is preferably a solder material containing only 87.2% by mass or more of Sn.

  Specific examples of this solder material include, for example, Example 2 in Table 2, Reference Example 3, and Examples 5 to 8 and 11. These solder materials satisfy stricter criteria for reliability determination (2250 cycles or more).

Moreover, 1.8-3.8 mass% Ag,
0.2-1.0 mass% Bi;
6.0 to 6.7% by mass of In;
0.8 to 1.2% by mass of Cu,
The balance is more preferably a solder material containing only 87.3 mass% or more of Sn.

  Specific examples of this solder material include Examples 5, 6, 8, and 11 in Table 2. These solder materials satisfy more stringent criteria for reliability determination (2250 cycles or more) and have a tensile strength of 70 MPa or more.

Moreover, 3.5-3.8 mass% Ag,
0.6-1.0 mass% Bi;
6.0-6.1 mass% In,
1.1 to 1.2% by mass of Cu,
The balance is more preferably a solder material containing only 87.9% by mass or more of Sn.

  Specific examples of this solder material include Examples 5 and 11 in Table 2. These solder materials satisfy stricter criteria for reliability determination (2250 cycles or more) and also have a tensile strength of 75 MPa or more.

If Bi is not included,
0.5-3.2 mass% Ag,
6.0-6.8% by mass of In,
0.6 to 1.1% by mass of Cu,
The balance is preferably a solder material containing only 88.9% by mass or more of Sn.

  Specific examples of this solder material include, for example, Example 30 in Table 4, Reference Example 32, and Examples 34, 37, and 38. These solder materials satisfy stricter criteria for reliability determination (2250 cycles or more).

If Bi is not included,
2.8 to 3.2 mass% Ag,
6.0-6.2 mass% In,
0.85 to 1.1 mass% Cu,
The balance is more preferably a solder material containing only 89.5% by mass or more of Sn.

  Specific examples of this solder material include, for example, Examples 30, 34, and 38 in Table 4. These solder materials satisfy more stringent criteria for reliability determination (2250 cycles or more) and have a tensile strength of 70 MPa or more.

  The bonded structure of the present invention includes an electronic circuit board having a substrate electrode and an electronic component having a component electrode. Here, as an electronic circuit board, what was pattern-formed on the insulation board | substrate of various FR grades (Flame Retardant Grade) is mentioned, for example. Electronic components include, for example, chip components, large semiconductor components such as QFP (Quad Flat Package) and BGA (Ball Grid Array), large components such as aluminum electrolytic capacitors and module components, and weights of coils, transformers, etc. Examples include parts.

  In the above bonded structure, at least one of the substrate electrode and the component electrode is an Au electrode. For example, when the substrate electrode is an Au electrode (Au substrate electrode), the component electrode is a Cu electrode (Cu component electrode), the substrate electrode is a Cu electrode (Cu substrate electrode), and the component electrode is an Au electrode (Au component electrode), The substrate electrode is an Au electrode (Au substrate electrode), and the component electrode is an Au electrode (Au component electrode).

  And in said joining structure, the board | substrate electrode and the component electrode are joined by the solder material of this invention. As described above, the solder material of the present invention includes Examples 1 and 2 in Tables 2 to 4, Reference Example 3, Examples 4 to 8, Reference Example 9, Examples 10 to 15, Reference Example 16, and Examples. 17-21, Reference Example 22, Examples 23-27, Reference Example 28, Examples 29-31, Reference Example 32, Examples 33-38, and the results of reliability determination shown in Reference Example 39 indicate that the Au electrode and Cu In soldering to electrodes, the reliability evaluation of in-vehicle products is satisfied. Therefore, even when the Au electrode and the Cu electrode are mixed when the electronic circuit board and the electronic component are joined by soldering, it is possible to form a solder portion having good thermal fatigue characteristics. In addition, the content rate of Cu contained in the solder material can be appropriately changed according to the content rate of P included in the Ni plating of the Au electrode.

  FIG. 9 is a schematic cross-sectional view of a bonding structure 700 according to an embodiment of the present invention. In the bonding structure 700, an electronic circuit board 730 having Au substrate electrodes 731 and 732, an electronic component 720 having a Cu component electrode 721, and an electronic component 740 having an Au component electrode 741 are bonded by soldering. In this bonded structure 700, the Au substrate electrode 731 of the electronic circuit board 730 and the Cu component electrode 721 of the electronic component 720 are bonded by the solder portion 711. Further, the Au substrate electrode 732 of the electronic circuit board 730 and the Au component electrode 741 of the electronic component 740 are joined by a solder portion 712. And said solder part 711,712 is formed of the solder material of this invention which has a composition of Sn-Ag-Bi-In-Cu or Sn-Ag-In-Cu. Examples 1 to 2 in Tables 2 to 4, Reference Example 3, Examples 4 to 8, Reference Example 9, Examples 10 to 15, Reference Example 16, Examples 17 to 21, Reference Example 22, Example 23 to 27, Reference Example 28, Examples 29 to 31, Reference Example 32, Examples 33 to 38, and Reference Example 39, as is clear from the reliability determination results, It meets the requirements for reliability testing. In the bonding structure 700 described above, the Au substrate electrodes 731 and 732 may be Cu substrate electrodes.

FIG. 10A is a cross-sectional view schematically showing a state before soldering between the Au substrate electrode 210 of the electronic circuit board 200 and the Cu component electrode 320 of the electronic component. The Au substrate electrode 210 includes a Cu electrode 211, a Ni plating 212, and an Au flash plating 213 from the electronic circuit substrate 200 side. At this time, a solder material 100 having a composition of Sn—Ag—Bi—In—Cu is interposed between the Au substrate electrode 210 and the Cu component electrode 320. FIG. 10B is a cross-sectional view schematically showing a state of the solder part 110 after soldering between the Au substrate electrode 210 of the electronic circuit board 200 and the Cu component electrode 320 of the electronic component. The Au substrate electrode 210 has a Ni plating 212 containing P. Between the Au substrate electrode 210 and the solder portion after soldering, (Cu _0.7 , Ni _0.3 ) ₆ Sn _5, etc. (Cu, Ni) Sn compound 130 is produced. This (Cu, Ni) Sn compound 130 is useful for preventing a decrease in the In content in the solder material 100. On the other hand, a Cu ₆ Sn ₅ compound 120 is generated between the Cu component electrode 320 and the solder part 110. Since In does not participate in the formation of the Cu ₆ Sn ₅ compound 120, the In content in the solder material 100 does not decrease. Note that the electronic components are not shown in FIGS.

FIG. 11A is a cross-sectional view schematically showing a state before soldering between the Cu substrate electrode 220 of the electronic circuit board 200 and the Au component electrode 310 of the electronic component. The Au component electrode 310 includes a Cu electrode 311, an Ni plating 312, and an Au flash plating 313 from the electronic component side. At this time, a solder material 100 having a composition of Sn—Ag—Bi—In—Cu is interposed between the Cu substrate electrode 220 and the Au component electrode 310. FIG. 11B is a cross-sectional view schematically showing the state of the solder portion 110 after soldering between the Cu substrate electrode 220 of the electronic circuit board 200 and the Au component electrode 310 of the electronic component. The Au component electrode 310 has an Ni plating 312 containing P. Between the Au component electrode 310 and the solder part 110 after soldering, (Cu _0.7 , Ni _0.3 ) ₆ Sn _{5 is provided.} (Cu, Ni) Sn compound 130 is produced. This (Cu, Ni) Sn compound 130 is useful for preventing a decrease in the In content in the solder material 100. On the other hand, a Cu ₆ Sn ₅ compound 120 is generated between the Cu substrate electrode 220 and the solder part 110. Since In does not participate in the formation of the Cu ₆ Sn ₅ compound 120, the In content in the solder material 100 does not decrease. In FIGS. 11A and 11B, electronic components are not shown.

FIG. 12A is a cross-sectional view schematically showing a state before soldering between the Au substrate electrode 210 of the electronic circuit board 200 and the Au component electrode 310 of the electronic component. The Au substrate electrode 210 includes a Cu electrode 211, a Ni plating 212, and an Au flash plating 213 from the electronic circuit substrate 200 side. The Au component electrode 310 includes a Cu electrode 311, an Ni plating 312, and an Au flash plating 313 from the electronic component side. At this time, a solder material 100 having a composition of Sn—Ag—Bi—In—Cu is interposed between the Au substrate electrode 210 and the Au component electrode 310. FIG. 12B is a cross-sectional view schematically showing the state of the solder part 110 after soldering the Au substrate electrode 210 of the electronic circuit board 200 and the Au component electrode 310 of the electronic component. The Au substrate electrode 210 has a Ni plating 212 containing P, but (Cu _0.7 , Ni _0.3 ) ₆ Sn ₅ between the Au substrate electrode 210 and the solder part 110 after soldering. (Cu, Ni) Sn compound 130 is produced. Similarly, the Au component electrode 310 has a Ni plating 312 containing P. However, between the Au component electrode 310 and the solder part 110 after soldering, (Cu _0.7 , Ni _0.3 ) A (Cu, Ni) Sn compound 130 such as ₆ Sn ₅ is produced. This (Cu, Ni) Sn compound 130 is useful for preventing a decrease in the In content in the solder material 100. In FIGS. 12A and 12B, electronic components are not shown.

  The solder material and the joining structure in the present invention form a solder portion having good thermal fatigue characteristics even when Au electrodes and Cu electrodes are mixed when the electronic circuit board and the electronic component are joined by soldering. Is possible. For example, it can be suitably used for solder paste used for soldering.

Claims (2)

Solder material,
When the content (mass%) of Ag, Bi, Cu, and In in the solder material is [Ag], [Bi], [Cu], and [In],
0.3 ≦ [Ag] <4.0 Ag (except when Ag is 0.5 mass% and 1.0 mass%),
Bi of 0 ≦ [Bi] ≦ 1.0,
0.2 ≦ [Cu] ≦ 1.2 and Cu,
Within the range of 0.2 ≦ [Cu] <0.5,
Including In in the range of 6.0 ≦ [In] ≦ 6.8,
Within the range of 0.5 ≦ [Cu] ≦ 1.0,
5.2+ (6- (1.55 × [Cu] +4.428)) ≦ [In] ≦ 6.8 including In,
Within the range of 1.0 <[Cu] ≦ 1.2,
Including In in the range of 5.2 ≦ [In] ≦ 6.8,
The balance is only 87 mass% or more of Sn,
Solder material. An electronic circuit board having a substrate electrode;
An electronic component having a component electrode,
At least one of the substrate electrode and the component electrode is an Au electrode,
The substrate electrode and the component electrode are joined by the solder material according to claim 1,
Bonding structure.

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