WO2008056676A1 - Lead-free solder paste, electronic circuit board using lead-free solder paste, and method for manufacturing electronic circuit board - Google Patents

Abstract

Disclosed is a lead-free solder paste composed of a solder powder and a flux (13) mixed with the solder powder. The solder powder is composed of a first base alloy powder (11) which is a first alloy in a powder form, and a second base alloy powder (12) which is a second alloy in a powder form having a component composition different from that of the first base alloy powder (11). The solder powder has two or more melting points.

Description

 Specification

 Lead-free solder paste, electronic circuit board using lead-free solder paste, and method of manufacturing electronic circuit board

 Technical field

 The present invention relates to a lead-free solder paste which is mainly used for soldering of an electronic circuit board and is obtained by mixing solder powder in flux, an electronic circuit board using the lead-free solder paste, and a method of manufacturing the electronic circuit board. .

 Background art

 [0002] In recent years, in the field of soldering technology, the density of electronic parts has been increased by increasing the size and increasing the size of surface-mounted parts, and a solder bonding material having a higher function is desired. Solder pastes obtained by mixing Sn (tin) -Pb (lead) -based eutectic solder powder with flux, and Sn (tin) Pb (lead) Bi (bismuth) -based solder powder are used as typical conventional solder pastes. There is a solder paste (melting point control product) etc. mixed with Tas. Thus, the conventional solder contains 35 to 50% by weight of Pb.

 However, when exposed to acid rain, conventional solder-bonded electronic components sometimes cause lead contained in the conventional solder to elute from the electronic components and cause the eluted lead to escape. There was a problem of polluting the environment.

 [0004] To solve this problem, lead-free solder (lead-free solder) has been proposed. Japanese Patent Application Laid-Open No. 2005-5570 discloses a solder or the like based on a Sn (tin) Ag (silver) Cu (copper) based alloy as a lead-free solder.

 However, since this lead-free solder is a solder based on a Sn—Ag—Cu-based alloy, it has a melting point higher than that of conventional leaded solders. Therefore, there is a problem that the electronic parts are damaged by heat because it is necessary to perform soldering while keeping the working temperature at 240 to 250 ° C. In addition, the wettability of this lead-free solder is inferior to that of the Sn Pb eutectic solder, and there is a problem that the tombstone phenomenon (Manhattan phenomenon) or void (air bubble) is generated.

In view of these problems, as a lead-free solder, it is low to prevent thermal damage to electronic components Sn-Bi eutectic solder with a melting point has been proposed! Since this lead-free solder is a low melting point solder, it can prevent heat damage to electronic parts. However, while the mechanical strength of this lead-free solder is inferior to that of conventional solder, this lead-free solder is unreliable.

 Disclosure of the invention

 The present invention, while maintaining the environmental advantages of lead-free solder materials, overcomes the lack of wettability, prevents soldering defects such as the occurrence of tombstone phenomena, the occurrence of voids, and lowers the solder paste at a lower temperature. It is an object of the present invention to provide a lead-free solder paste, an electronic circuit board using the lead-free solder paste, and a method of manufacturing the electronic circuit board, which are permitted to be performed.

 [0008] In order to achieve the above object, the present invention provides a solder powder, a flux (13) mixed with the solder powder, and a lead-free solder paste (10) to be used, The body is composed of a first base alloy powder (11) which is a powdery first alloy, and a powdery second alloy having a component composition different from the component composition of the first base alloy powder (11). A second base alloy powder (12), wherein the solder powder has a melting point of 2 or more, and provides a lead-free solder paste (10).

 In a preferred embodiment of the present invention, the first base alloy powder (11) is a powder of a Sn (tin) -Bi (bismuth) eutectic alloy, and the second base The alloy powder (12) is a powder of a Sn (silver) -Ag (silver) -Bi (bismuth) -In (indium) alloy, and the value of weight percentage of Ag after melting of the solder powder. Takes a value in the range of 0.5-2. 4 and the value of In by weight after melting of the solder powder takes a value in the range of 0.25-1.5.

 In a preferred embodiment of the present invention, the weight percent value of the first base alloy powder takes a value within the range of 70 to 95, and the Ag contained in the second base alloy powder. The value of weight percent of is within the range of 0.3 to 3.5, and the value of weight percent of In contained in the second base alloy powder is within the range of 0.5 to 8.0 Take

 [0011] In order to achieve the above object, the present invention provides a lead-free solder paste (10) printed circuit board

(81), and electronic components (82, 84, 86, 88) are placed on the solder bonding pads, and the reflow operation is performed at a temperature of 205.degree. C. or less in the reflow furnace. Lead-free solder paste (10) is melted to bond the electronic components (82, 84, 86, 88) to the printed circuit board (81), and the lead-free solder paste (10) A flux (13) mixed with the solder powder, and the first base alloy powder (11), which is a powdery first alloy, and the solder powder is a powdery first alloy; and the first base alloy Powder-like second alloy power second base alloy powder (12) having a component composition different from the component composition of powder (11), and the solder powder having two or more melting points A method of manufacturing an electronic circuit board characterized by

 In order to achieve the above object, the present invention provides a printed circuit board (81), the printed circuit board (

 A lead-free solder paste (10) disposed on the solder bonding pad of 81), and an electron disposed on the solder bonding node and joined to the printed circuit board (81) by the lead-free solder paste (10) The component (82, 84, 86, 88) and the force, the lead-free solder paste (10) is a solder powder and a flux (13) mixed with the solder powder, the force, the force, the solder The powder is a powdery second alloy having a component composition different from the component composition of the first base alloy powder (11), which is a powdery first alloy, and the first base alloy powder (11). And a second base alloy powder (12), wherein the solder powder has a melting point of 2 or more. An electronic circuit board using a lead-free solder paste is provided.

 According to the present invention, the lead-free solder paste is one of the first base alloy powder and the second base alloy powder, which has a lower melting point, when the solder powder is melted. The alloy contained in is melted before the alloy contained in the other base alloy powder is melted. When the molten alloy contacts the other base alloy powder, it lowers the melting point of the other base alloy powder. Using this function, the electronic component is joined to the printed circuit board by lead-free solder paste. Therefore, since the melting point of the lead-free solder paste is lower than the melting point of the other base alloy powder, the lead-free solder paste is completely melted within the heat-resistant temperature of the electronic component. Thus, the lead-free solder paste of the present invention has two or more melting points by appropriately arranging two base alloy powders having component compositions different from each other.

Specifically, the first base alloy powder is a powder of a Sn—Bi-based eutectic alloy, and the value of the weight percentage of the first base alloy powder is in the range of 70 to 95. It has a value. Second base combination The gold powder is a powder of a Sn-Ag-Bi-In alloy, and the weight percentage value of the second base alloy powder has a value in the range of 5-30. By mixing and heating the first base alloy powder and the second base alloy powder, the Sn—Bi-based eutectic alloy starts to melt at the eutectic temperature (138 ° C.). Furthermore, when the mixture of the first base alloy powder and the second base alloy powder is heated, the Sn—Ag—Bi—In alloy (melting temperature: 200 to 210 ° C.) is melted, It begins to melt as it is incorporated into the crystal. At this time, the melted Sn--Ag--Bi--In alloy has a non-uniform state in which the weight percentage differs from place to place. In addition, the melted Sn-Bi eutectic alloy also has a non-uniform state in which the weight percentage varies from place to place. The melting temperature of the nonuniform state Sn-Ag-Bi-In alloy is lower than the melting temperature of the first Sn-Ag-Bi-In alloy. In addition, the melting temperature of the nonuniform Sn-Bi eutectic alloy is higher than the melting temperature of the first Sn-Bi eutectic alloy.

In general, the reflow operation temperature needs to be set to a temperature (melting point temperature + 20 ° C.) higher than the melting point temperature of the solder in order to stably perform the soldering. However, the lead-free solder paste of the present invention completely melts even if the reflow operation temperature does not reach the melting temperature (200 to 210 ° C.) of the Sn—Ag—Bi—In alloy. Therefore, even if the reflow operation peak temperature is set to 205 ° C. or lower lower than the conventional reflow operation peak temperature, the melting time of the lead-free solder paste is prolonged and the reflow operation peak temperature is the melting point temperature of the lead-free solder paste. The lead-free solder paste is sufficiently heated because it is sufficiently high. As a result, the fluidity of the molten solder is improved, and the gas trapped inside the lead-free solder paste can be smoothly released to the outside, and a joint surface in which the generation of voids is suppressed can be obtained. By suppressing the occurrence of voids, the internal stress and strain of the lead-free solder paste are reduced. In addition, since the peak temperature of the reflow process is lower than the peak temperature of the conventional reflow process, the lead-free solder paste has the property of preventing the electronic parts from being damaged by heat.

Regarding the alloy composition after melting of the lead-free solder paste of the present invention, for example, the weight percentage of the first base alloy powder (powder of Sn—58Bi-based eutectic alloy) is set to 75 wt%, The percentage by weight of base alloy powder (Sn-3. OAg-0.5 Bi-5. OIn alloy powder) is set to 25% by weight. For this ratio, with regard to the composition of the final alloy: The weight percent of Bi will be 43.6 weight percent, the weight percent of Ag will be 0.75 weight percent, the weight percentage of In will be 1.25 weight percent, and the weight percent of Sn will be the remaining weight percent .

 Brief description of the drawings

 FIG. 1 is a schematic view of a lead-free solder paste according to an embodiment of the present invention.

 [FIG. 2A] FIG. 2A is a binary phase diagram of a Sn—Bi-based eutectic alloy, which is one of the components of a lead-free solder paste according to an embodiment of the present invention.

 [FIG. 2B] FIG. 2B is one of the components of the lead-free solder paste according to the embodiment of the present invention, the amount of added Ag and the amount of Sn-Bi-Ag when Ag is added to a Sn—Bi-based eutectic alloy FIG. 5 is a characteristic diagram showing the ductility relationship of a base alloy.

 [FIG. 3] FIG. 3 is an explanatory view showing the melting and solidification characteristics of the Sn—Bi based eutectic alloy according to the example of the present invention.

 [FIG. 4] FIG. 4 is an explanatory view showing the melting and solidification characteristics of a Sn—Bi based eutectic alloy and a Sn—Ag—Bi—In based alloy lead-free solder according to an embodiment of the present invention.

 [FIG. 5] FIG. 5 is an explanatory view showing the melting behavior of a lead-free solder paste comprising a Sn—Bi-based eutectic alloy and a Sn—Ag—Bi—In-based alloy according to an embodiment of the present invention.

 [FIG. 6] FIG. 6 is an explanatory view showing a cross section of the final alloy in a state where the lead-free solder according to the embodiment of the present invention is melted and solidified.

 [FIG. 7] FIG. 7 is an explanatory view showing the surface of the electronic circuit board in a state where a thermal fatigue test has been performed on the electronic circuit board soldered with the lead-free solder paste according to the embodiment of the present invention. is there.

 [FIG. 8] FIG. 8 is a perspective view of an electronic circuit board according to the present embodiment of the present invention.

 BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments and examples of the present invention will be described in detail with reference to FIGS. 1 to 8.

As shown in FIG. 1, the lead-free solder paste 10 is composed of a flux 13 and a solder powder mixed in the flux 13. The lead-free solder paste 10 is disposed on a base material (for example, a substrate) 14 by transfer molding or the like.

The solder powder comprises a first base alloy powder 11 which is a powdery first alloy, and a first base alloy powder. It comprises a second base alloy powder 12 which is a powdery second alloy having a component composition different from the component composition of the body 11. Solder powder has two or more melting points. The first base alloy powder 11 and the second base alloy powder 12 are produced in the form of spherical powder by atomizing the melted first and second alloys in a powder production apparatus. Ru.

The flux 13 reacts with an oxide film generally having a high melting point formed on the metal surface of the bonding member to clean the metal surface of the bonding member. This facilitates the chemical reaction between the components contained in the flux and the metal of the joining member to form a liquefied metal salt having a generally low melting point. As a result, the solder powder easily reacts with the metal of the bonding member because the bonding surface of the lead-free solder paste 10 and the bonding member is liquefied. The flux 13 is produced by heat-dissolving rosin, an activator, a solvent, a thixotropic agent and the like, and processing it into a paste.

 The first base alloy powder 11 is a powder of a Sn (tin) -Bi (bismuth) eutectic alloy. Second

2 Base alloy powder 12 is a powder of a Sn (tin) Ag (silver) Bi (bismuth) In (indueum) based alloy. In the solder powder, by appropriately supplying Ag and In contained in the second base alloy powder 12 to the melted first base alloy powder 11, the content ratio of Ag and In in the solder powder is desired. It is adjusted to become the content rate of In the present embodiment, in the solder powder, the weight percentage of the first base alloy powder 1 in the solder powder is 70 to 95 wt%, and the weight percentage of the second base alloy powder 2 in the solder powder is 5 It is adjusted to be 30 wt ^_0/0.

 In the binary phase diagram of the Sn—Bi-based eutectic alloy in FIG. 2A, the regions a, b, c, d and e are respectively a solid phase of Sn, a solid-liquid coexistence phase of Sn, Sn and It is a solid phase of Bi, a liquid phase of Sn and Bi, and a solid-liquid coexistence phase of Bi. As shown in FIG. 2A, the first base alloy powder 1 has a eutectic point E having a temperature of 138.5 ° C.

More specifically, in the region a where the weight percent value of Bi takes a minute value and the weight percent value of Sn takes a value close to 100, the melting point of the Sn—Bi-based eutectic alloy is It decreases from 232.2 ° C as the weight percentage of increases. On the other hand, in the region e where the weight percent value of Bi takes a value close to 100 and the weight percent value of Sn takes a minute value, the melting point of the Sn—Bi-based eutectic alloy decreases the weight percent of Bi As low as from 271.4 ° C Lower. Eutectic point E is the point where two lines connecting the melting points of the Sn—Bi-based eutectic alloy continuously intersect. The temperature of the eutectic point is called eutectic temperature.

 At the eutectic point E, when the temperature is raised, the Sn—Bi-based eutectic alloy directly changes from the solid state to the liquid state without passing through the solid-liquid coexistence state. Therefore, a Sn—Bi-based eutectic alloy consisting of a Sn—Bi mixture ratio that produces eutectic point E improves the workability. The eutectic point E occurs when the weight percent value of Bi is around 57. The eutectic temperature of eutectic point E is 138.5 ° C. Regarding the melting point of the second base alloy powder 12, for example, when the second base alloy powder 12 is a powder of Sn-3. OAg-O. 5Bi-5. OIn-based alloy, the second base alloy powder The melting point of 12 has a value in the range of about 200 ° C to about 210 ° C.

 The final alloy (Sn—Bi—Ag—In alloy: quaternary lead-free alloy) is produced by heating the lead-free solder paste 10. Specifically, the final alloy is prepared by heating the solder powder in a reflow furnace (heating furnace), and in the order of the first base alloy powder 11 and the second base alloy powder 12, each alloy powder Is produced by melting gradually.

 [0027] As shown in FIG. 2B, when the value of weight percentage of Ag added to the Sn—Bi-based eutectic alloy takes a value of around 0.8, a Sn—Bi—Ag-based alloy (a ternary lead-free alloy) Growth rate will be about 40%. Therefore, the ductility of the alloy is improved by adding about 0.8% by weight of Ag to the Sn—Bi-based eutectic alloy. The addition of Ag is performed when the second base alloy powder 12 is melted. Also, the addition of In is also performed when the second base alloy powder 12 is melted. The addition of Ag can ensure the ductility of the alloy and can refine the structure of the final alloy. The addition of In can suppress the melting point depression of the alloy and the diffusion of Sn. Therefore, the final alloy can ensure flexibility and suppress the formation of whiskers.

 As shown in FIG. 8, an electronic circuit board (mounted board) 80 is configured by joining a plurality of electronic components to a printed circuit board (printed wiring board) 81 using a lead-free solder paste 10. Ru.

The electronic circuit board 80 has a printed circuit board 81, a ball grid array (BGA) package IC 82, a BGA ball 83 which is an electrode of the BGA package IC 82, a small outline package (SO P) package IC 84, a lead 85 of the SOP package IC 84, It comprises a transistor 86, a lead 87 of a transistor 86, a chip component 88 such as a resistor, and a chip electrode 89 of the chip component 88. Next, a method of mounting these electronic components on a printed circuit board 81 using the lead-free solder paste 10 will be described.

 [0031] First, the lead-free solder paste 10 is disposed on the solder bonding pad of the printed circuit board 81 by a metal mask and a squeegee. Second, surface mount components (SMD) such as BGA package ICs 82, SOP package ICs 84, transistors 86, and chip components 88 are placed on the solder bonding pads. Finally, in a reflow furnace in air or nitrogen atmosphere, for example, by performing soldering under the condition of a reflow operation peak temperature of 205 ° C., BGA ball 83, lead 85, 87, tip electrode 89, etc. The joint of the electronic component is joined to the solder joint pad of the printed circuit board 81 by melting the lead-free solder paste 10. Therefore, by using the lead-free solder paste 10, it is possible to manufacture the electronic circuit board 80 with less environmental load S.

 (Example)

 Examples of lead-free solder paste 10 will now be described in detail with reference to FIGS. In this example, the first base alloy powder 11 comprises a Sn-Bi based eutectic alloy having 70 to 95 wt%, and the second base alloy powder 12 has an Sn to Bi 5 to 30 wt%. — Ag— contains Bi-In alloys. Also, the lead-free solder paste 10 is produced by melting the first base alloy powder 1 1 and the second base alloy powder 12, and the final alloy is the weight percentage value of Ag contained in the final alloy and In. It is adjusted so as to take a value in the range of 0.3 to 2.0 and a value in the range of 0.5 to 1.5, respectively. The melted solder powder containing the final alloy is pasted into the flux to form a lead-free solder paste 10 having the following composition.

 Country

Sn-58Bi (75 weight ^{0 /.) + Sn * 0.5Bi} -3.0Ag-5.0In (25 weight _^0/0)

 → Sn-43.6Bi-0.75Ag-1.2δΙ

FIG. 3 shows the melting and solidification characteristics of the Sn—Bi-based eutectic alloy contained in the first base alloy powder 11. Specifically, Fig. 3 shows the DSC (Differentialial Sacnning Calorimetory) curve showing the relationship between the reflow temperature of Sn— Bi-based eutectic alloy and the solderability, and the Sn at 10 points on the DS C curve. The photograph which observed Bi system eutectic alloy is shown. DSC song in Figure 3 As indicated by the line, the first base alloy powder 11 has a melting point of about 140.degree.

FIG. 4 shows that 75 wt% of Sn—Bi-based eutectic alloy contained in the first base alloy powder 11 and 25 wt% of Sn—Ag— Bi—In contained in the second base alloy powder 12 The DSC curve shows the relationship between the reflow temperature of the lead-free solder and solder melting property, and the photograph of the lead-free solder observed at nine points on the DSC curve is shown. As shown in the DSC curve of FIG. 4, the lead-free solder has a first melting point of about 140 ° C. and a second melting point of about 210 ° C.

The initial state of the lead-free solder paste 10 is shown in the photograph 51 of FIG. From the initial state, when the lead-free solder paste 10 is gradually heated, the first base alloy powder 11 begins to melt at the first melting point (about 140 ° C.) (see photo 52 in FIG. 5). Furthermore, when the lead-free solder paste 10 is heated, the second base alloy powder 12 begins to melt so that the second base alloy powder 12 is gradually taken into the molten first base alloy powder 11. Furthermore, when the lead-free solder paste 10 is heated, the second base alloy powder 12 is completely melted around 160 ° C. before the second melting point (about 210 ° C.) (see photo 53 in FIG. 5). Then, when the lead-free solder paste 10 continues to be heated, the lead-free solder paste 10 gets wet as the heating temperature rises. When the heating temperature reaches about 200 ° C. (reflow operation peak temperature), the lead-free solder paste 10 becomes most suitable for soldering (see photo 54 in FIG. 5).

As shown in FIG. 6, when observing the cross section of the solidified final alloy, large voids do not exist, and Sn and Bi are finely dispersed to form a smooth solidified surface without unevenness. Therefore, the lead-free solder paste 10 can prevent the occurrence of the tomstone phenomenon and the void.

[0037] FIG. 7 is a magnified photograph of the surface of the electronic circuit board in a state where a thermal fatigue test was performed on an electronic circuit board made by bonding a chip to a printed board using the lead-free solder paste 10. Is shown. The conditions of the thermal fatigue test are that the test temperature is −40 to + 110 ° C., and the test time is 10 minutes per cycle.

The initial state of the surface of the electronic circuit board is shown in the photograph 71 of FIG. The wettability of the lead-free solder paste 10 is improved compared to the wettability of the conventional lead-free solder paste! /, So the lead-free solder paste 10 spreads evenly on both sides of the chip, and the tombstone phenomenon Occurred! / 、! Surface of electronic circuit board after 500 cycles of thermal fatigue test The situation is illustrated in the photo 72 of FIG. The condition of the surface of the electronic circuit board after 1000 cycles of the thermal fatigue test is shown in the photograph 73 of FIG. As shown in Photo 7273, even when the thermal fatigue test is repeated, the electronic circuit board maintains a good state without generating a crack or the like on the solder surface.

 As described above, the lead-free solder paste 10 has a solidification surface that melts homogeneously at a low melting point and has a sliding force without unevenness after solidification, as compared to the conventional lead-free solder paste. Therefore, lead-free solder paste 10 has excellent reliability!

 Next, with reference to Table 1, the results of evaluating the melting temperature, bonding characteristics, and economic efficiency of the lead-free solder paste 10 when changing the mixing ratio of the first base alloy powder to In will be described. .

 [table 1]

 [0041] As shown in Table 1, when the weight percentage value of the first base alloy powder is 50, the bonding characteristics of lead-free solder paste 10 (suppression of tombstone phenomenon, suppression of void, fatigue resistance, ductility) In the above, the void suppression and fatigue resistance are somewhat inferior, and the economics are inferior. When the value of weight percent of the first base alloy powder is 50, the value of weight percent of In is 2.5. Here, the economy refers to the material cost for In. For example, “The economy is excellent! /” And “/!” Indicate that “The material cost for In is low! /”. Since In is a rare metal and expensive material, an alloy with a large content of In has a small content of In! /, And the material cost is high compared to the alloy.

When the weight percentage of the first base alloy powder has a value in the range of 75 95, the bonding characteristics and economics of the lead-free solder paste 10 are excellent. When the weight percent of the first base alloy powder has a value in the range of 75 95, the weight percent of In has a value in the range of 0.25-1.25. In particular, when the weight percent value of the first base alloy powder has a value in the range of 75, 82, the bonding characteristics of the lead-free solder paste 10 may be voided. And ductility are excellent. When the weight percent of the first base alloy powder has a value in the range of 75 to 82, the weight percent of In has a value in the range of 0.9 to 1.25.

 When the weight percentage value of the first base alloy powder is 95, the ductility is slightly inferior in the bonding characteristics of the lead-free solder paste 10, and the economic efficiency is excellent. When the value of weight percent of the first base alloy powder is 95, the value of weight percent of In is 0.25. When the weight percentage value of the first base alloy powder is 100, the joining characteristics of the lead-free solder paste 10 are inferior and the economy is excellent. At this time, as shown in FIG. 2B, the ductility of the lead-free solder paste 10 changes as the content of Ag changes, so the weight percentage value of the first base alloy powder takes 100, and the Ag When the weight percentage value is zero, the ductility of the lead-free solder paste 10 is significantly inferior.

 Next, with reference to Table 2, the results of evaluation of the melting temperature when the mixing ratio of the first base alloy powder and In is changed will be described.

[Table 2]

 In general, the value of the reflow operation temperature is preferably a value obtained by adding 40 to the value of the melting temperature of the lead-free solder paste in order to improve the bonding characteristics of the lead-free solder paste. On the other hand, in consideration of the heat resistance temperature of the electronic component, in order to ensure the reliability of the electronic component, the value of the reflow operation temperature is preferably set to a value of 205 or less.

[0046] As shown in Table 2, when the weight percentage value of the first base alloy powder is 70, the melting temperature of the lead-free solder paste 10 is 165 ° C, and the reflow operation temperature is 205 (205 = 165). + 40) ° C is obtained. At this time, the weight percentage value of In is 1.5. On the other hand, when the weight percentage value of the first base alloy powder is 65, the melting temperature of the lead-free solder paste 10 is 170 ° C., and the reflow operation temperature is 210 (210 = 170 + 40). It becomes C. At this time, the weight percent value of In is 1.75. Therefore, it is desirable that the weight percentage value of the first base alloy powder be 70 or more. At this time, the weight percentage value of In takes a value of 1.5 or less. Also, referring to FIG. 2B, the ductility of the lead-free solder paste 10 is The value of weight percentage of Ag to be added to the first base alloy powder in order to make it the same as the ductility of the next Sn-Pb eutectic solder paste, the value of the range of 0. 05-2. 4 It is desirable to take.

 As described above, in the lead-free solder paste 10, the value of the weight percentage of the first base alloy powder is preferably in the range of 70 to 95. In addition, after melting lead-free solder paste 10, the values of weight percentages of In and Ag become values in the range of 0.25-1.5, values in the range of 0.5-2.4, 2 It is preferable to adjust the base alloy powder.

 Industrial Applicability

Lead-free solder paste 10 is contained in one of the first base alloy powder 11 and the second base alloy powder 12 in one of the base alloy powders having a lower melting point when the solder powder is melted. Alloy melts before the alloy contained in the other base alloy powder melts. When the molten alloy comes in contact with the other base alloy powder, it lowers the melting point of the other base alloy powder. Using this action, the electronic component is joined to the printed circuit board by lead-free solder 10 paste. Therefore, since the melting point of the lead-free solder paste 10 is lower than the melting point of the other base alloy powder, the lead-free solder paste 10 is completely melted within the heat-resistant temperature of the electronic component. As a result, lead-free solder paste 10 allows lower temperature soldering while maintaining the environmental benefits of lead-free solder materials. Also, referring to the experimental results, the lead-free solder paste 11 has the property of being able to overcome the lack of wettability and to prevent soldering defects such as the occurrence of the solder stone phenomenon and the occurrence of voids. .

Claims

The scope of the claims  [1] with solder powder,  A flux (13) mixed with the solder powder;  Lead-free solder paste (10)  The solder powder is powdery, having a component composition different from the component composition of the first base alloy powder (1 1), which is a powdery first alloy, and the first base alloy powder (1 1) The second base alloy powder (12) consisting of the second alloy  Lead-free solder paste (10), wherein the solder powder has a melting point of 2 or more.  [2] The first base alloy powder (1 1) is a powder of a Sn (tin) -Bi (bismuth) eutectic alloy,  The second base alloy powder (12) is a powder of a Sn (tin) -Ag (silver) -Bi (bismuth) -In (indium) alloy.  The weight percentage of Ag after melting of the solder powder takes a value within the range of 0.5-4.  The lead-free solder paste (10) according to claim 1, characterized in that the weight percent value of In after melting of the solder powder is a value within the range of 0.25-1.5. [3] The weight percent value of the first base alloy powder is within the range of 70 to 95, and the weight percent value of Ag contained in the second base alloy powder is 0.3-3. Take a value in the range of 5,  The lead-free solder paste (10) according to claim 3, wherein the weight percentage value of In contained in the second base alloy powder takes a value within the range of 0.5 to 8.0. [4] Lead-free solder paste (10) is placed on the solder joint pad of the printed circuit board (81), and electronic parts (82, 84, 86, 88) are placed on the solder joint pad,  In a reflow furnace, lead-free solder paste (10) is melted and electronic parts (82, 84, 86, 88) are joined to a printed circuit board (81) at a reflow operation peak temperature which is a temperature of 205 ° C. or less. And The lead-free solder paste (10) is Solder powder,  A flux (13) mixed with the solder powder;  Consists of  The solder powder is  A first base alloy powder (11) which is a powdery first alloy;  A second base alloy powder (12) made of a powdery second alloy, having a component composition different from the component composition of the first base alloy powder (11);  Consists of  The method for manufacturing an electronic circuit board, wherein the solder powder has two or more melting points.  Printed circuit board (81),  Lead-free solder paste (10) disposed on the solder joint pad of the printed circuit board (81) and the solder joint pad disposed on the solder joint pad and joined to the printed circuit board (81) by the lead-free solder paste (10) Electronic components (82, 84, 86, 88),  Consists of  The lead-free solder paste (10) is  Solder powder,  A flux (13) mixed with the solder powder;  Consists of  The solder powder is  A first base alloy powder (11) which is a powdery first alloy;  A second base alloy powder (12) made of a powdery second alloy, having a component composition different from the component composition of the first base alloy powder (11);  Consists of  The electronic circuit board using a lead-free solder paste, wherein the solder powder has a melting point of 2 or more.