JP2007194630A - Solder joint layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop a solder joint layer which is highly resistant against creep deformation. <P>SOLUTION: The solder joint layer, which is a joint layer formed in joining members using a solder containing Sn, contains at least one selected from a group consisting of Pb, Cu, Ag, Bi and Zn in addition to Sn and Au, and the joint layer further has intermetallic compounds composed containing Sn and Au as a major component, the intermetallic compounds distributing at the ratio of 5 to 50% in area percentage of a joint cross-section. In addition, in the case when two or more members are joined, the solder joint layer is provided by forming the surface of at least one member to be composed of Au, placing a solder on the at least one member and heating the solder to have the Au solved into the solder. A joined member is provided with such a solder joint layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solder joint layer of a precision element. Specifically, the present invention relates to a solder joint layer of an electronic device, an optical device, a laser module, and a semiconductor device.

  Conventionally, Sn—Pb-based (Sn: 63 wt%) eutectic alloy has excellent wettability and an appropriate melting point, and is therefore suitable for bonding between printed circuit boards, mounting members, and members in precision elements. Has been used. However, since the lead contained in the Sn—Pb eutectic alloy is harmful, it has been converted to a solder that does not use lead (hereinafter referred to as lead-free).

  Accordingly, Sn-Ag-based lead-free solder has come to be used in electronic devices that require high reliability due to its high stability and reliability. However, when this solder is used, the melting point is high (221 ° C.), and the wettability with the electrodes of the printed circuit board is inferior to that of eutectic solder. Currently, in order to lower the melting point, Sn-Ag-based solders with a small amount of Cu and Bi added, and Sn-Zn-based and Sn-Bi-based solders have also been developed.

  By the way, the precision element is required to have high positional accuracy so that the positional relationship between members does not change over a long period of time. However, the solder material has a low creep strength as compared with other members constituting the element, for example, a Cu-W alloy or stainless steel. For this reason, there is a problem in that the soldered portion is deformed and the member to be joined moves during use of the precision element, and the positional relationship between the members changes over time.

  Therefore, in order to give the solder strength, Japanese Patent Application Laid-Open No. 2000-190090 discloses that Sn and Cu are 0.1 to 2.5% by weight, Bi and / or In are 1 to 15% by weight, Ni and Ge. By producing an intermetallic compound of Pd, Au, Ti, Fe and Sn or Cu with respect to an alloy solder containing 0.01 to 2% by weight of any one or more of Pd, Au, Ti, and Fe A technique for preventing the slip at the crystal grain boundary of the matrix and improving the mechanical strength of the bonding layer is disclosed.

Japanese Patent Application Laid-Open No. 7-128550 discloses a technique for avoiding this because a brittle compound of Au weakens the bonding strength.
JP 7-128550 A

The prior art will be described. Sn easily reacts with Au to form, for example, a Sn ₄ Au intermetallic compound. Since this intermetallic compound is brittle, it degrades the mechanical strength of the solder joint layer. Therefore, it has been a problem of the prior art to suppress the formation of this intermetallic compound during soldering. In the present invention, on the contrary, this compound is used.

  That is, since the Sn—Au intermetallic compound is brittle but hard, it is desirable that the Sn—Au-based intermetallic compound does not exist for such a high stress that the bonding layer reaches the failure. However, when a high stress up to that point is required and there is no need to change the position of the member, the hard Sn—Au intermetallic compound acts effectively, and the deformation resistance of the solder Will improve.

  As described above, high precision is required for precision elements so that the positional relationship between members does not change over a long period of time. However, since the solder material has a low creep strength, the solder member is deformed and the member to be joined moves during use of the precision element.

  Accordingly, an object of the present invention is to develop a solder joint layer having a high resistance to creep deformation. In general, since the solder creep curve is greatly displaced at the initial stage of creep, an object is to develop a solder joint layer having a small deformation amount at the initial stage of creep.

In order to solve the above-mentioned problems, a first aspect of the present invention is to join a base on which a Peltier element is mounted and the Peltier element, and between the Peltier element and a package of the laser module using a solder containing Sn. The bonding layer is formed when the bonding layer contains, in addition to Sn and Au, one or more selected from Pb, Cu, Ag, Bi, Zn, The bonding layer contains an intermetallic compound composed of Sn ₄ Au, Sn ₂ Au, SnAu, SnAu ₅ , SnAu ₉ composed mainly of Sn and Au, and exists in the bonding cross section. This is a laser module that does not cause misalignment and is joined via a solder joint layer dispersed in a proportion of more than 5% and up to 50% as the total area fraction of intermetallic compounds.

According to a second aspect of the present invention, a joint formed when a base on which a Peltier element is mounted and the Peltier element and between the Peltier element and a package of the laser module are joined using solder containing Sn. The bonding layer contains, in addition to Sn and Au, one or more selected from Pb, Cu, Ag, Bi, and Zn, and further includes Sn in the bonding layer. And an intermetallic compound composed of any of Sn ₄ Au, Sn ₂ Au, SnAu, SnAu ₅ and SnAu ₉ composed mainly of Au, and the crystal grain size of the intermetallic compound is 30 μm or less. In addition, the sum of the area fractions of the intermetallic compounds present in the cross section of the joint does not cause misalignment that is joined through the solder joint layers dispersed in a proportion of more than 5% and up to 50%. Leh The module is

According to a third aspect of the present invention, there is provided a joining method between a base on which a Peltier element is mounted in a laser module and the Peltier element, and between a package of the Peltier element and the laser module, wherein the surface of at least one member is made of Au. And a solder containing Sn is placed on at least one of the members, the solder containing Sn is heated to dissolve the Au in the solder, and react with the Sn. Solder bonding of at least one intermetallic compound of Sn ₄ Au, Sn ₂ Au, SnAu, SnAu ₅ , SnAu ₉ composed mainly of Au in a proportion of more than 5% and up to 50% This is a joining method that does not cause misalignment in the layers.

According to a fourth aspect of the present invention, there is provided a joining method between a base on which a Peltier element is mounted in a laser module and the Peltier element, and between a package of the Peltier element and the laser module, wherein the surface of at least one member is made of Au. And a solder containing Sn is placed on at least one of the members, the solder containing Sn is heated to dissolve the Au in the solder, and react with the Sn. One or more intermetallic compounds of Sn ₄ Au, Sn ₂ Au, SnAu, SnAu ₅ , SnAu ₉ and having a crystal grain size of 30 μm or less composed of Au as a main component exceeds 50% in total. It is a joining method that does not cause misalignment and is dispersed in the solder joint layer at a ratio of up to%.

  According to a fifth aspect of the present invention, in the bonding method according to claim 3 or 4, wherein the thickness of the layer made of Au on the surface of at least one member is 1.0 to 5.0 μm. The thickness of the member on which at least one of the solder is placed is formed to be 30 to 60 μm, and between the base on which the Peltier element is mounted in the laser module and the Peltier element, and between the Peltier element and the laser module, This is a bonding method between packages.

  By using the bonding layer of the present embodiment, a bonding layer with small creep deformation can be obtained, and the position change of the member to be bonded can be suppressed to a very small level in the bonding of precision elements. In addition, even in a laser module that is likely to be off-axis due to fluctuations in the solder part, a highly reliable bonding layer that does not off-axis can be obtained.

  Embodiments of the present invention will be described below. The solder joint layer of the present invention is a joint layer formed when a member is joined using Sn-containing solder, and the joint layer includes Pb, Cu, Ag, Bi, in addition to Sn and Au. It contains any one or more selected from Zn, and the bonding layer is composed of an intermetallic compound composed mainly of Sn and Au as an area fraction of the bonded cross section of 5 to 50%. Dispersed in proportion and has high deformation strength.

  In the present embodiment, the solder alloy containing Sn may be any alloy containing one or more selected from Sn, Pb, Cu, Ag, Bi, and Zn. The element selected from Pb, Cu, Ag, Bi, and Zn, and the addition ratio can be selected as follows. For example, Sn—Bi alloy, Sn—Zn alloy, Sn—Pb alloy, Sn—Ag alloy, Sn—Ag—Cu alloy, Sn—Ag—Cu—Bi alloy, and other elements described above A combined alloy may be selected as appropriate.

  The joining layer as used in the field of this invention is the area | region fuse | melted at the time of joining, Comprising: The area | region which does not melt | dissolve is not included. For example, when the Au plating melts into the solder layer and the Ni plating layer under the Au and the Cu plate of the member to be joined are not melted, the bonding layer is the entire solder layer containing Au, and the Ni plating layer or the Cu plate Does not enter the bonding layer.

  That is, it is a joint portion formed when the members to be joined are joined using the solder containing Sn, and the joining layer requires Au in addition to Sn, and is made of Pb, Cu, Ag, Bi, Zn. It contains any one or more selected.

  In the present embodiment, an example of a method for containing Au in the bonding layer is described below. The first is a method in which a solder that does not contain Au is used before joining, and Au is contained when the solder is melted during joining. An example is as follows.

  Soldering is performed after Au plating is applied to the bonded portion. At this time, the thickness of the Au plating is desirably 0.05 to 8.0 μm as the total plating thickness of the members to be joined, and the thickness of the solder joint layer is desirably 10 to 100 μm. More desirably, the Au plating thickness is 1.0 to 5.0 μm as the total plating thickness of the members to be joined, and the solder joining layer thickness is preferably 30 to 60 μm.

  Soldering is performed after Au deposition processing is performed on the bonded portion by sputtering or the like. Also in this case, it is desirable that the thickness of the Au vapor deposition layer is 0.05 to 8.0 μm as the total vapor deposition layer thickness of the members to be joined, and the thickness of the solder joint layer is 10 to 100 μm. More preferably, the thickness of the Au vapor deposition layer is 1.0 to 5.0 μm as the total vapor deposition layer thickness of the members to be joined, and the thickness of the solder joint layer is desirably 30 to 60 μm.

  Furthermore, a solder sprinkled with Au powder can be used, or an Au foil, an Au plate, or an Au wire can be placed on the solder.

  Second, it is a method in which Au is previously contained in solder foil, solder paste, solder wire or the like before joining. It is desirable to contain about 3 to 30% by weight of Au. The solder alloy containing Au in advance may be used in accordance with a normal soldering operation.

  Third, the first and second methods are used together.

  In the present embodiment, it is desirable to contain Au when melting the solder at the time of joining. Therefore, examples of the method for heating the solder alloy include the following. First, a solder layer is formed by heating and fixing solder to each of the members to be joined. Next, the positions of the solder layers of the members to be joined are aligned and reheated to join the members together.

  First, a solder layer is formed by heating and fixing solder to one of the members to be joined. Next, the solder layer is aligned with a predetermined position of the other member to be joined, and reheated to join the members together. Solder is placed between the members to be joined and heated to join the members together. As the joining conditions, it is desirable that the melting temperature of the solder is 10 to 60 ° C. higher than the eutectic temperature of the alloy and the melting time of the solder is selected from 10 seconds to 5 minutes.

By the way, with respect to the diffusion of Au into Sn, it is easy to make an intermetallic compound because of the high diffusion rate. Examples of the intermetallic compound containing Sn—Au include Sn ₄ Au, Sn ₂ Au, SnAu, SnAu ₅ , and SnAu ₉ . An intermetallic compound containing Sn—Au is dispersed in the bonding layer. The state in which the intermetallic compound is dispersed is that the bonding layer contains Au, the Au exists in the form of an intermetallic compound with Sn, and the compound is dispersed throughout the solder bonding layer. is there.

  In addition, when Au forms a Sn-Au intermetallic compound with Au, for example, when Au is a plating layer, when the solder is heated and melted, Au diffuses into the melted solder, that is, in the solder. It appears to dissolve and react with Sn to form an intermetallic compound. Therefore, Au can be used even if it is formed of a plating layer on the surface of the joining member, or is previously added to the solder as an alloy component.

In this way, by dispersing an intermetallic compound having a high deformation resistance such as Sn ₄ Au intermetallic compound in the solder joint layer, the deformation resistance of the solder at a high temperature can be improved.

  In the embodiment of the present invention, it is desirable that the intermetallic compound containing Sn—Au is dispersed in the bonding layer at a ratio of 5 to 50% in terms of the area fraction of the bonded cross section. Here, the bonded cross section is a cross section including a bonding layer in which two or more members (bonded bodies) are bonded, and a plurality of interfaces between the bonded body and the bonding layer are in a substantially parallel relationship. A plane perpendicular to the interface is defined as a bonding cross section.

  In the present invention, the area fraction refers to the ratio of the area of the Sn—Au compound phase in the bonding layer in the bonding cross section. The area fraction can be obtained as follows. For example, constituent elements in the bonding cross section including the bonding layer are measured by EDX or EPMA in SEM, and the structure of the Sn—Au compound phase is specified. FIG. 1 shows a backscattered electron image of the cross section of the bonding layer in this embodiment. The black solid line length of the photograph corresponds to a length of 10 μm. Next, in the SEM photograph or backscattered electron image photograph of the bonding layer, the Sn—Au compound phase and other portions are separated by binarization, and the area fraction of the Sn—Au compound phase in the bonding layer is calculated. To do. FIG. 2 shows an image in which the Sn—Au layer region shown in FIG. 1 is expressed in white and the other regions are binarized in black.

  For the SEM or backscattered electron image photograph used to calculate the area fraction, the direction perpendicular to the bonding interface is taken as the vertical axis of the photograph, and the direction parallel to the bonding interface is taken as the horizontal axis of the photograph. In addition, the entire length of the photograph is such that the entire thickness of the joining layer is included, and the plated layer and the material to be joined that were not melted during joining are not included in the photograph. The length of the photo horizontal axis is twice the length of the vertical axis. In addition, when the interface between the molten layer and the non-molten layer at the time of bonding is not flat or the two materials to be bonded are not parallel, a region corresponding to the interface is taken as a photograph.

  The above operation is performed five times or more in total from another part of the same cross section or from another cross section of the same sample, and the average value is defined as the area fraction of the Sn—Au compound phase in the cross section of the sample. .

  Here, the reason why the area fraction is 5 to 50% is as follows. If it is less than 5%, there is no effect, and if it exceeds 50%, the creep resistance increases, but it becomes brittle and breaks with a small amount of strain. In the range of 5 to 50%, the initial creep is small, the creep resistance is large, and the reliability with respect to displacement is high.

  In the present embodiment, the crystal grain size of the intermetallic compound in the bonding layer is desirably 30 μm or less. The size of the crystal grain size can be obtained at the time of observing the above-mentioned junction cross section. Here, the reason for setting the crystal grain size to 30 μm or less is that cracks are likely to propagate through the crystal grain boundary if it exceeds 30 μm.

  A second embodiment of the present invention will be described below. In the present invention, when two or more members are joined, the surface of at least one member is made of Au, solder is placed on the surface of one or more members, the solder is heated, and the Au It is a joining member provided with the joining layer obtained by melt | dissolving in solder.

  In the present embodiment, the outermost surface layer of at least one member is a surface made of an Au layer. In the present embodiment, the method described in the first embodiment may be used so that the bonding layer contains Au.

  In this way, a plated layer is formed on the surface, a solder alloy containing Sn is placed between the members, the solder alloy is heated and melted, and Au on the surface of the member is dissolved in the molten solder. Thus, a bonded product including a bonding layer in which an intermetallic compound containing is dispersed is obtained. For example, a bonded product including the bonding layer of this embodiment can be obtained in an electronic device, an optical device, a laser module, or a semiconductor device.

  Sn—Pb (Sn: 63 wt%) eutectic alloy was used as the solder. As a test method, a copper test piece for a ring-pin shear test as shown in FIG. 3 was prepared, and Ni plating was applied to the joint surface of the test piece, and Au was plated thereon. The other was not plated. Using these two types of samples, the solder joint layer of the ring portion was formed using the solder. A ring-pin test piece 31 in FIG. 3 includes a ring portion 33 and a pin portion 35, and a solder joint layer 37 with the pin portion is formed at the center of the ring portion 33. The thickness of the ring part is 3 mm, the outer shape is 15 mm, the diameter of the pin part is 4 mm, and the length is 20 mm.

  For the bonding layer, the bonding cross section was observed. As a result, an Sn phase and a Pb rich phase were observed in the bonding layer although not plated. In the plated product, the Sn—Au intermetallic compound phase having a crystal grain size of 20 μm was dispersed in addition to the Sn phase and the Pb rich phase. Moreover, the area fraction of the Sn-Au metal compound phase of what was plated was determined. As a result, the area fraction value was 15%.

  Creep tests were performed on the above plated and non-plated. A schematic diagram 41 of the creep test method is shown in FIG. The living pin test piece 43 was tested by applying a load in the upward direction of FIG. 4 and the pin in the downward direction of FIG. Two kinds of test temperatures, room temperature and 100 ° C., were used. FIG. 5 shows the test results obtained when the shear stress was 7.5 MPa at room temperature (25 ° C.), and FIG. 6 shows the test results obtained when the shear stress was 1.7 MPa at 100 ° C.

  The horizontal axis of each figure shows time (standardized by the time to break). The vertical axis represents the shear strain. From this, it can be seen that the plated one has extremely small initial creep and less shear strain than the one not plated.

  Table 1 shown as FIG. 8 shows the results of evaluating the Sn—Au phase distribution state and creep deformation resistance. That is, when the Sn—Au phase is uniformly dispersed over the entire bonding layer, the Au plating does not remain at the interface, and in such a case, the deformation resistance tends to be extremely high. On the other hand, when the Sn—Au phase is unevenly distributed on the interface between the object to be bonded and the bonding layer, the Au plating remains on the interface, and in such a case, it broke early.

  Next, a laser module having a laser wavelength of 1.48 μm was prototyped by applying the present invention. A schematic diagram of the laser module is shown in FIG. The soldering locations of the laser module 71 are the joining location 85 between the base 79 and the Peltier element 81 and the joining location 87 between the Peltier element 81 and the package 83, both of which use the same type of solder. The solder used is shown in Table 2 as FIG.

  In order to change the amount of Au—Sn intermetallic compound in the metal junction, the amount of Au—Sn compound was changed by adjusting the Au plating thickness of the base, Peltier, and package surface of the laser module. In the process of heating and melting the solder, all of the Au plating part was dissolved in the molten solder.

  In addition, as shown in Table 1, 11 modules of a total of 11 types of examples and comparative examples were prototyped, and for each one, the cross-sectional structure of the bonding layer was observed to confirm the amount of intermetallic compound. The area fraction (%) of the Au—Sn compound in the cross section of the bonding layer is shown.

  The remaining 10 prototyped modules were subjected to a high temperature storage test that was held at 85 ° C. for 1000 hours. After the test, the laser output was examined. Samples whose output was reduced to 80% or less compared with those before the test were judged as defective, and those exceeding 80% were judged as good products. The results are also shown in Table 2.

The backscattered electron image of the bonding layer cross section was shown. An image obtained by binarizing the Sn—Au phase region of FIG. 1 to white and the other regions to black is shown. A ring-pin shear specimen was shown. It is a schematic diagram of a ring-pin shear creep test. It is a shear creep test result at room temperature. It is a shear creep test result in 100 degreeC. It is a schematic diagram of a laser module. It is Table 1 shown as FIG. 8, and showed the distribution state and creep deformation resistance of the Sn—Au phase. It is Table 2 shown as FIG. 9, and shows the solder type, the area fraction of the Sn—Au compound phase, and the defect rate after the high temperature standing test.

Explanation of symbols

31 Ring-pin shear test piece 33 Ring part 35 Pin part 37 Solder joint layer 41 Schematic diagram of creep test method 43 Ring-pin shear test piece 71 Laser module 73 Optical fiber 75 Lens 77 Laser 79 Base 81 Peltier element 83 Package 85 Solder joint Layer 87 Solder joint layer

Claims (5)

A bonding layer formed when a base on which a Peltier element is mounted and the Peltier element and between the Peltier element and a package of the laser module are bonded using a solder containing Sn, the bonding layer being In addition to Sn and Au, one or more selected from Pb, Cu, Ag, Bi, and Zn are contained, and the bonding layer is composed mainly of Sn and Au. Including an intermetallic compound composed of any one of Sn ₄ Au, Sn ₂ Au, SnAu, SnAu ₅ , and SnAu ₉ , the total area fraction of the intermetallic compound present in the bonding cross section exceeds 5% and exceeds 50% A laser module that does not cause misalignment and is bonded via solder bonding layers dispersed at a rate of up to%. A bonding layer formed when a base on which a Peltier element is mounted and the Peltier element and between the Peltier element and a package of the laser module are bonded using a solder containing Sn, the bonding layer being In addition to Sn and Au, one or more selected from Pb, Cu, Ag, Bi, and Zn are contained, and the bonding layer is composed mainly of Sn and Au. An intermetallic compound comprising any of Sn ₄ Au, Sn ₂ Au, SnAu, SnAu ₅ , and SnAu ₉ , wherein the intermetallic compound has a crystal grain size of 30 μm or less and is present in a bonding cross section. A laser module that is bonded via a solder bonding layer dispersed in a proportion of more than 5% and up to 50% as a total area fraction of intermetallic compounds, and that does not cause an axis deviation. A joining method between a base on which a Peltier element is mounted in a laser module and the Peltier element and between a package of the Peltier element and a laser module, wherein at least one member has a surface made of Au, and at least one of the members Sn containing Sn is heated, and the solder containing Sn is heated to dissolve the Au in the solder and react with the Sn. ₄ Axis misalignment occurs in which one or more intermetallic compounds of Au, Sn ₂ Au, SnAu, SnAu ₅ and SnAu ₉ are dispersed in the solder joint layer in a proportion of more than 5% and up to 50%. There is no joining method. A joining method between a base on which a Peltier element is mounted in a laser module and the Peltier element and between a package of the Peltier element and a laser module, wherein at least one member has a surface made of Au, and at least one of the members A crystal composed of Sn and Au as main components by placing a solder containing Sn on the substrate and heating the solder containing Sn to dissolve the Au in the solder and reacting with the Sn. At least one intermetallic compound of Sn ₄ Au, Sn ₂ Au, SnAu, SnAu ₅ , SnAu _{9 having} a particle size of 30 μm or less in the solder joint layer in a proportion of more than 5% and up to 50% Bonding method that does not cause misalignment.   5. The joining method according to claim 3 or 4, wherein the thickness of the Au layer on the surface of at least one member is 1.0 to 5.0 [mu] m, and at least one solder is placed thereon. A method of joining between a base on which a Peltier element is mounted in a laser module and the Peltier element, and between a package of the Peltier element and the laser module, wherein the thickness of the member is 30 to 60 μm.