JP5376356B2 - Electronic element mounting method and electronic component mounted by the mounting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joining method by which copper is joined suitably even at a fine junction part without using lead, and a junction section exhibits good mechanical properties. <P>SOLUTION: The mounting method of the electronic element includes a tin thin film forming process for forming tin thin film layers 2 on a copper electrode 1a and copper electrode 1b, and in addition, a heating process in which the tin thin film layers 2 formed on the copper electrode 1a and copper electrode 1b are in contact with each other, and are heated and pressurized at a temperature at which tin is molten and the copper is dissolved in the tin. Thereby, the copper in the copper electrode 1a and copper electrode 1b is dissolved in the tin in the tin thin film layer 2, and the copper electrode 1a and copper electrode 1b are electrically joined by mutual diffusion of the tin in the tin thin film layer 2 and the copper in the copper electrode 1a and copper electrode 1b. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an electronic device mounting method and an electronic component mounted by the mounting method.

  Conventionally, soldering has been used for joining electrodes in mounting electronic devices, and is still used as the mainstream joining method even today. 2. Description of the Related Art In recent years, electronic devices have been increased in density, functionality, and miniaturization. Accordingly, joints, which are spaces that need to be joined when electronic devices are mounted, are further miniaturized. For this reason, there is a need for a joining method in which joining is possible under suitable conditions even if the joining portion is small, and the joining location formed by the alloy after the joining treatment has good mechanical properties.

  In mounting electronic devices, not only circuit wiring connections but also silicon chips are often bonded to a substrate by die bonding. In this case, high-temperature solder containing a large amount of lead is often used. Considering the load applied to the environment, it is not appropriate to use such a high-temperature solder containing lead, and lead-free solder pellets and the like have been developed (see Reference 1).

Here, the preferable condition means that the amount of heat in the vicinity of the joint is small when joining and mounting is possible at a low temperature. In addition, good mechanical properties means that the strength of the joint portion is high and has a certain degree of elongation under the actual use environment of the electronic device. This is because if the elongation is low, when stress is applied to the joint, the joint portion is brittle and easily damaged.
International Publication No. 2005/119755 (December 15, 2005)

  However, the above-described conventional joining method has a problem that even a small joining portion can be joined under suitable conditions, and the joined portion after the joining process cannot satisfy the requirement of having good mechanical properties. Yes.

  Specifically, in the method using the above-described soldering, it is necessary to supply a large amount of solder having a thickness of 15 μm or more to the joint. Moreover, as a space | interval of a junction part, the joining space | interval of 300 micrometers or more is required, and it is difficult to join to a fine junction part. Furthermore, in soldering, a high temperature of about 300 ° C. may be required to melt the solder material, and a large amount of heat is applied to the joint.

  As another bonding method, there is a method of directly bonding electrodes, for example, copper to each other. However, since the flatness of the bonding portion and bonding conditions of high vacuum and high pressure are required, it is not practical. Absent.

  The present invention has been made in view of the above-described conventional problems, and the object thereof is to allow copper to be suitably bonded even if a minute bonding portion without using lead, and the bonding portion is An object of the present invention is to provide a bonding method having good mechanical properties.

  In order to solve the above-described problem, the electronic element mounting method of the present invention joins a circuit electrode made of copper formed on a circuit board and an element electrode made of copper formed on the electronic element, In the electronic element mounting method for mounting the electronic element on the circuit board and the device mounting method such as die bonding of a silicon chip, after performing a tin thin layer forming step for forming a tin thin layer on the circuit electrode and the element electrode The circuit electrode is subjected to a heating step in which tin thin layers formed on the circuit electrode and the element electrode are brought into contact with each other and heated and pressurized at a temperature at which tin can be melted and dissolved in tin. And the copper of the element electrode is dissolved in tin in the tin thin layer, and the circuit electrode and the element electrode are interdiffused by tin in the tin thin layer and the circuit electrode and the copper of the element electrode. It is characterized in that electrically joined.

  According to the above invention, if the tin thin layer can be formed on the circuit electrode and the element electrode made of copper, the method can be carried out, so that the electronic element can be mounted even if the joining portion is fine. Moreover, since tin is used in a thin layer, alloying of tin with copper can be performed efficiently, and the circuit electrode, element electrode, and tin can be integrally formed as an alloy. For this reason, the mechanical property of the alloy layer used as a joining location can be made excellent.

  Furthermore, since heating is performed at a temperature at which tin can be melted and copper can be dissolved into tin, the electronic device can be mounted at a relatively low temperature, and the thermal load on the electronic device can be reduced. Moreover, since the tin thin layer is formed on the circuit electrode and the element electrode made of copper, the formation of an oxide film of copper on the electrode surface can be prevented. For this reason, an electronic element can be mounted without using a flux. In addition, since the copper electrodes can be joined together without using lead, the electronic element mounting method of the present invention is preferable from the viewpoint of the environment.

  In the electronic element mounting method of the present invention, at least one thin layer formed in the order of a copper thin layer and a tin thin layer is formed on at least one of the tin thin layers formed on the circuit electrode and the element electrode. It is preferable to perform a lamination process of laminating layers.

  Thereby, in the heating step, an alloy layer of tin and copper in the laminated body is easily formed. Thereby, the mechanical characteristics of the alloy layer to be formed can be improved.

  In the electronic element mounting method of the present invention, zinc, silver, nickel, germanium, iron, and cobalt are formed on the tin thin layer according to the quality and reliability required in the usage environment of the mounted electronic device. Forming at least one third thin layer made of one element selected from the group consisting of: a step of forming a copper thin layer; and at least one third thin layer on the copper thin layer. After the formation, a third thin layer forming step of performing at least one of the steps of forming the tin thin layer may be further included. These third thin layers have the effect of improving the mechanical properties (toughness, creep resistance, fatigue resistance, etc.) of the joint.

  Further, according to the electronic component of the present invention, the circuit electrode made of copper formed on the circuit board and the element electrode made of copper formed on the electronic device are electrically joined by the electronic element mounting method. Thus, the electronic element is mounted on the circuit board.

  Furthermore, the mounting method according to the present invention can also be applied to a sealing method in die bonding of a silicon chip to a substrate and packaging of an electronic device. In this case, the mounting method of the present invention is a first bonding target member to be bonded in a die bonding method for mounting a silicon chip on a substrate or an electronic element mounting method used for a sealing method in packaging of an electronic device. And after performing the copper thin layer formation process which forms a copper thin layer on the surface of a 2nd joining object member, the tin thin layer formation process which forms a tin thin layer in the said 1st joining object member and a 2nd joining object member Performing a heating step in which the tin thin layers formed on the first joining target member and the second joining target member are brought into contact with each other, and heating and pressurization are performed at a temperature at which tin can be melted and dissolved in copper tin. By performing, the copper formed in the surface of the said 1st joining object member and the 2nd joining object member melt | dissolves in the tin in the said tin thin layer, and the mutual diffusion of the tin and the said copper in a tin thin layer is carried out Ri has the structure for joining the first joining target members and the second joining target members.

  According to the said structure, there can exist an effect similar to the mounting method of the electronic element which mounts an electronic element on the said circuit board. Moreover, it is the same also that it can be set as the structure provided with a lamination process and a 3rd thin layer formation process.

  In the electronic component mounted by the above mounting method, the circuit electrode, the element electrode, and tin are integrally formed as an alloy. For this reason, it is possible to provide an electronic component in which the mechanical properties of the alloy layer serving as a joint location are excellent.

  As described above, the electronic device mounting method of the present invention includes a tin thin layer formed on the circuit electrode and the element electrode after the tin thin layer forming step for forming the tin thin layer on the circuit electrode and the element electrode. The copper of the circuit electrode and the element electrode is changed to tin in the tin thin layer by performing a heating process in which the layers are brought into contact with each other and heated and pressed at a temperature at which tin can be melted and dissolved in tin. The circuit electrode and the element electrode are joined by mutual diffusion of tin in the tin thin layer and the above-mentioned circuit electrode and copper of the element electrode.

  Therefore, an electronic element can be mounted even if the joint portion is fine. Also, since tin is used in a thin layer, the circuit electrode and element electrode can be efficiently dissolved and diffused with copper and tin, and the circuit electrode, element electrode and tin can be integrated as an alloy. Can be formed. For this reason, the mechanical property of the alloy layer used as a joining location can be made excellent. Furthermore, since heating is performed at a temperature at which tin can be melted and copper can be dissolved into tin, the electronic device can be mounted at a relatively low temperature, and the thermal load on the electronic device can be reduced. Moreover, since the tin thin layer is formed on the circuit electrode and the element electrode made of copper, the formation of an oxide film of copper on the electrode surface can be prevented. For this reason, an electronic element can be mounted without using a flux. In addition, since the copper electrodes can be joined without using lead, the electronic element mounting method of the present invention has an effect that it is preferable from the viewpoint of the environment.

  An embodiment of the present invention will be described with reference to FIGS. 1 to 7 as follows. The electronic device mounting method according to the present invention includes a circuit electrode made of copper formed on a circuit board and a device electrode made of copper formed on the electronic element, and the electronic device is attached to the circuit board. How to implement.

  In the electronic element mounting method, after performing a tin thin layer forming step of forming a tin thin layer on the circuit electrode and the element electrode, the tin thin layers formed on the circuit electrode and the element electrode are brought into contact with each other, By heating and pressurizing at a temperature at which melting and dissolution of copper into tin can be diffused, thereby dissolving and diffusing tin in the tin thin layer and copper in the circuit electrode and element electrode. Then, the circuit electrode and the element electrode are joined.

  FIG. 1 is a schematic diagram showing a state in which a thin tin layer 2 is laminated on a copper electrode 1a and a copper electrode 1b in the present invention. (A) of FIG. 1 is for demonstrating the said tin thin layer formation process, and is a schematic diagram which shows the state which formed the tin thin layer 2 in the copper electrode 1a and the copper electrode 1b. The copper electrode 1a shown in FIG. 1A is an element electrode, and the copper electrode 1b is a circuit electrode. For this reason, although not shown in figure, the copper electrode 1a is installed in the electronic element, and the copper electrode 1b is installed in the circuit board.

  Examples of the electronic element include a semiconductor chip, but the electronic element is not limited to the semiconductor chip as long as the electronic element is formed with a copper electrode. Moreover, as a circuit board, wiring boards, such as a conventionally well-known printed circuit board, can be used, and it is not specifically limited. The electronic element and the circuit board are collectively referred to as an electronic component. In addition to mounting for the purpose of electrical connection, a thin layer of copper is formed on the surface of the member to be joined in die bonding to a silicon chip substrate and connection mounting used for sealing electronic elements. But you can. Examples of the bonding target member include a silicon chip, a ceramic substrate, a silicon substrate, and a heat sink.

  The copper electrode 1a and the copper electrode 1b (hereinafter abbreviated as copper electrodes 1a and 1b as appropriate) are made of copper. Examples of the method for forming the copper electrodes 1a and 1b include, but are not limited to, a pattern formation method by a conventionally known vapor deposition method, an etching method, or the like, or a method of forming a copper electrode as a bump.

  In addition, when the surface roughness of copper electrode 1a * 1b is smoother, since a joining state becomes favorable, it is preferable, but the surface roughness Ra of copper electrode 1a * 1b is 0 in the mounting method of the electronic device of this invention. It can be carried out even with a rough surface of 4 μm or more and 10 μm or less.

When the present invention is applied to die bonding or a sealing method, the electronic element and the copper electrode 1a are bonded to the first bonding target member and the copper thin layer, and the circuit board and the copper electrode 1b are bonded to the bonding target member. It can be described by replacing with a certain second joining target member and a copper thin layer. In this case, unlike the case where the electronic element and the circuit board are bonded, a copper thin layer forming step of forming a copper thin layer on the surfaces of the first bonding target member and the second bonding member is performed. The copper thin layer forming step can be performed by a conventionally known pattern forming method such as vapor deposition or etching. The thin copper layer may be formed to a thickness of 1 μm or more.
The tin thin layer forming step, the laminating step, the third thin layer forming step, and the heating step after the copper thin layer forming step are the same as when the copper electrodes 1a and 1b are joined.

(Tin thin layer forming process)
In the electronic element bonding method of the present invention, first, the tin thin layer 2 is formed on the copper electrodes 1a and 1b. The tin thin layer 2 is formed on the opposing surfaces of the copper electrodes 1a and 1b as shown in FIG. As a method for forming the tin thin layer 2, vapor deposition, sputtering, plating, etching, or the like can be used as appropriate. Further, a pattern can be formed as necessary by vapor deposition using a metal mask, etching using a photoresist, or the like.

  The tin thin layer 2 is a thin layer, and when the thin tin layer 2 is formed on the copper electrode, it is preferably 0.5 μm or more and 3 μm or less. The thinnest value of 0.5 μm is the limit thickness at which a non-contact portion does not occur in a wide range when the tin thin layers 2 are brought into contact with each other when the copper electrodes 1a and 1b are displaced by a slight angle from the horizontal. This is due to the accuracy of the mounting machine. The maximum thickness value of 3 μm is a thickness at which it is difficult to form an alloy due to dissolution / diffusion of copper into tin, and this value depends on the mounting temperature, mounting time, and the like. The two tin thin layers 2 formed at two locations of the copper electrodes 1a and 1b may have different thicknesses.

(Lamination process)
In the electronic device mounting method of the present invention, it is preferable to perform a laminating step after the tin thin layer forming step. The lamination step is a step of laminating at least one thin layer formed in the order of a copper thin layer and a tin thin layer on at least one of the tin thin layers 2 formed on the copper electrodes 1a and 1b.

  FIG. 1B is a sectional view showing copper electrodes 1a and 1b in which thin layers are formed in the order of a thin tin layer 2, a thin copper layer 3 and a thin tin layer 2 on the copper electrodes 1a and 1b. (Sn2-Cu1). That is, one layer of the laminated body is formed. Thus, when the tin thin layer 2 and the copper thin layer 3 are formed in a plurality of layers, in the heating step described later, alloying of tin and copper in these thin layers is promoted to form an alloy layer. It becomes easy. This is preferable because the mechanical properties of the formed alloy layer are improved.

  Moreover, the number of laminated bodies formed is not particularly limited. A larger number of laminated bodies is preferable because alloying is facilitated and the mechanical properties of the formed alloy layer are further improved. The increase in the number of formations makes the execution of the laminating process complicated, but if the total of the tin thin layer 2 and the copper thin layer 3 is about 20 layers, the formation can be performed without any problem.

  For example, as shown in FIG. 1C, eight thin tin layers 2 and seven thin copper layers 3 can be formed to form a total of 15 thin layers on the copper electrodes 1a and 1b (see FIG. 1C). Sn8-Cu7). Thus, since the one where the number of formations of the laminated body is larger facilitates the alloying of tin and copper in the laminated body, the alloy can be formed very preferably.

  Further, when the thin tin layer 2 and the thin copper layer 3 are laminated, the total thickness is 0.5 μm or more and 3 μm, as in the case where one thin tin layer 2 is formed (FIG. 1A). It is as follows. Each of the plurality of thin layers is formed with an average film thickness obtained by dividing the total thickness by the number of thin layers formed, but it is of course possible to increase or decrease the film thickness of each thin layer. In addition, although copper electrode 1a * 1b is formed with the same formation number, you may form a laminated body with a different formation number by performing methods, such as vapor deposition, separately with respect to both members.

(Third thin layer forming step)
Further, as shown in FIG. 1 (d), a third thin layer 4 may be formed between the tin thin layer 2 and the copper thin layer 3. The third thin layer 4 is formed in the third thin layer forming step. The third thin layer forming step is a step performed together with the laminating step, and on the tin thin layer 2, a third thin layer made of one element selected from the group consisting of zinc, silver, nickel, germanium, iron and cobalt. Among the steps of forming the thin copper layer 3 after forming at least one layer 4 and forming the thin tin layer 2 after forming at least one third thin layer 4 on the thin copper layer 3 , At least one of the steps.

  In (d) of the figure, each layer is formed in the order of the thin copper layer 1, the thin copper layer 3, the third thin layer 4, the thin tin layer 2, the thin copper layer 3, and the thin tin layer 2 from the copper electrodes 1 a and 1 b. Stacked (Sn3-Cu2-M1). The element M constituting the third thin layer 4 is not particularly limited as long as the solid-liquid diffusion of the tin thin layer 2 and the copper thin layer 3 is not hindered. By forming the third thin layer, there is an effect of improving the mechanical properties (toughness, creep resistance, fatigue resistance, etc.) of the formed alloy layer.

  Examples of elements that hinder solid-liquid diffusion of the tin thin layer 2 and the copper thin layer 3 include Ti and Cr. When a thin layer made of these metals is formed as the third thin layer 4, sufficient solid-liquid diffusion of the tin thin layer 2 and the copper thin layer 3 is prevented, and an alloy formed between the copper electrodes 1a and 1b. Has very poor mechanical properties. Specifically, the formed alloy may have a low shear strength. Further, lead is not selected as an element constituting the third thin layer 4 from the viewpoint of environmental load.

(Heating process)
FIG. 2 is a process diagram illustrating a heating process according to the electronic device mounting method of the present invention. A thin tin layer 2 is formed on the copper electrodes 1a and 1b to be joined with the same configuration as in FIG. In addition, when the laminated body is further formed in the tin thin layer 2 on the copper electrodes 1a and 1b, it can join by the same method.

  First, as shown in FIG. 2A, the copper electrodes 1a and 1b opposed to each other as shown in FIG. In addition, operations such as positioning, movement, and heating / pressing of the electrodes can be performed using a conventionally known mounting facility. Examples of mounting equipment include a flip chip bonder and a die bonder. Further, the positioning of the copper electrodes can be accurately performed by determining coordinates using a camera or the like.

  Next, the tin thin layer 2 is heated and pressurized. Specifically, the heating temperature can be 235 ° C. or higher and the heat resistance temperature (at least 260 ° C.) of the electronic device to be mounted, and more preferably 240 ° C. or higher and 260 ° C. or lower. If it is said temperature range, as shown in the copper-tin two-dimensional phase diagram of FIG. 3, it is more than melting | fusing point of tin, and tin is a liquid at mounting temperature. If it is the said temperature range, an electronic element can be mounted in a comparatively low temperature, and the thermal load to an electronic element can be reduced.

  The pressurizing conditions vary depending on the heating temperature, the number of the thin tin layers 2 and the thin copper layer 3, the surface accuracy of the members to be joined, the surface accuracy of the mounting equipment, and the like, but it is difficult to set uniquely. Generally, it can be performed at 1 MPa or more and 40 or less MPa.

  Heating and pressurization can be performed in an oxygen-containing atmosphere such as an air atmosphere. When it is desired to completely eliminate the influence of oxygen, it can be performed in a vacuum atmosphere, in an atmosphere of an inert gas such as nitrogen or argon, or in a hydrogen reduction atmosphere. The reaction time for heating and pressurization is appropriately changed depending on the number of thin layers formed on the copper electrode and the formation thickness, but is generally from 30 seconds to 10 minutes. If it is said range, it is possible to fully alloy copper of a copper electrode, and tin of a tin thin layer.

  By performing the heating step under the above conditions, as shown in FIG. 2C, tin and copper alloying begins to occur in the tin thin layer 2a in the vicinity of the copper electrodes 1a and 1b. Note that tin and copper are not alloyed in the thin tin layer 2b away from the copper electrodes 1a and 1b.

  Further, by continuing the heating step, as shown in FIG. 2D, alloying of tin and copper proceeds, and the alloy layer 5 is formed. After completion of the heating process, the heating temperature is lowered stepwise to cool the copper electrodes 1a and 1b and the alloy layer 5.

  In the electronic device mounting method of the present invention, the thin tin layer 2 is formed as a thin layer on the copper electrodes 1a and 1b, so that the electronic device can be mounted even if the joining portion is fine. Furthermore, since heating is performed at a temperature at which tin can be melted and copper can be dissolved into tin, the electronic device can be mounted at a relatively low temperature, and the thermal load on the electronic device can be reduced. Moreover, since the tin thin layer is formed on the circuit electrode and the element electrode made of copper, the formation of an oxide film of copper on the electrode surface can be prevented. For this reason, an electronic element can be mounted without using a flux. In addition, since the copper electrodes can be joined together without using lead, the electronic element mounting method of the present invention is preferable from the viewpoint of the environment.

  As described above, the alloy layers 5 are formed and the copper electrodes 1a and 1b are joined. In FIG. 2D, there is a boundary between the copper electrodes 1a and 1b and the alloy layer 5 for convenience of explanation. It is shown as follows. However, in practice, there is no boundary between the copper electrodes 1a and 1b and the alloy layer 5, and the copper content increases as it goes from the alloy layer 5 to the copper electrodes 1a and 1b. . That is, the electrodes 1a and 1b and the alloy layer 5 are alloyed together.

  Since alloying is performed in this way, the alloy layer 5 which is a joining portion has high shear strength. Electronic components are required to have high shear strength, particularly at high temperatures. For this reason, the alloy layer 5 preferably has a shear strength of 50 MPa or more, more preferably 100 MPa or more, under actual use environment temperature conditions.

  Further, the alloy layer 5 is required to exhibit not only high shear strength but also a certain degree of elongation when stress is applied. If the alloy layer 5 does not stretch when stress is applied, that is, it is difficult to deform, the alloy layer 5 is easily broken because it has a brittle structure.

As described above, according to the electronic element mounting method of the present invention, the electronic element on which the copper electrode 1a is installed and the circuit board on which the copper electrode 1b is installed can be mounted. An electronic component composed of the electronic element and the circuit board is obtained by electrically joining a circuit electrode made of copper formed on the circuit board and an element electrode made of copper formed on the electronic element, The electronic element is mounted on the circuit board.
Since the electronic component mounted in this manner has the alloy layer 5, the electronic component has preferable mechanical characteristics at the joint portion. The joint location is preferable because it has the merit that it is very difficult to break.

  Further, according to the electronic element mounting method of the present invention, whether or not an electronic component is mounted on a circuit board can be determined by examining the composition ratio of tin and copper in the joint (alloy layer). Is possible.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the technical means disclosed in different embodiments can be appropriately combined. Such embodiments are also included in the technical scope of the present invention.

  About the copper cylindrical material joined in the present Example and the comparative example, shear strength and elongation were measured under the following conditions. The measuring method is shown below.

<Shear strength>
The shear strength measurement was performed according to JIS Z 3198-5. Specifically, a shear test apparatus (Instron 5582 type, manufactured by Instron Japan Company Limited) was used. FIG. 4 is a cross-sectional view of the shearing device and the joined copper cylinder, showing the state of the shear test. As shown in the figure, the joined copper cylindrical member 10 having a diameter of Φ3 mm and the copper cylindrical member 20 having a diameter of Φ5 mm are installed on a fixed base 30. The shear test apparatus 40 is installed so as to shear the joint surfaces of the copper cylindrical member 10 and the copper cylindrical member 20.

  From this state, shearing was performed by moving the shear testing device 40 vertically downward (arrow direction). The shear strength was measured at a test speed of 5 mm / min in a high temperature environment of 250 ° C.

<Elongation of joint part>
The elongation of the joint was determined from the load-displacement curve in the shear test.

[Example 1]
As a copper electrode, a copper cylindrical material having a diameter of Φ3 mm and a height of 3 mm and a copper cylindrical material having a diameter of Φ5 mm and a height of 5 mm were used as a base material, and both copper cylindrical materials were joined. First, the opposite surfaces of both copper cylinders were buffed with 0.3 μm Al ₂ O, and then a thin tin layer was formed by vapor deposition on the flat part of both copper cylinders in a vacuum environment of about 10 ⁻⁴ Pa. did. The tin thin layer was formed with a layer thickness of 0.7 μm.

  Next, the thin tin layers formed on both the copper cylindrical members were brought into contact with each other using a flip chip bonder. In this state, a load of 40 MPa was applied to both copper cylinders, and the copper cylinders were heated at a temperature of 260 ° C. by resistance pressurization. These heating and pressurization were performed in an air atmosphere. FIG. 5 is a graph showing the temperature change of the copper cylindrical member during heating and pressurization.

  As shown in the figure, the temperature of both copper cylinders reached about 228 ° C., which is the melting point of tin, 270 seconds after the start of heating. Thereafter, the temperature rose to 260 ° C, and again reached 228 ° C after 570 seconds from the start of heating. That is, both copper cylindrical members were heated at a temperature of 228 ° C. or higher and 260 ° C. for 300 seconds.

  Thereafter, the joined copper cylinders were cooled to room temperature to complete the joining. About the joined copper columnar material, the shear strength measurement and the measurement of the elongation of the copper columnar material were performed in a high temperature environment. The results are shown in FIG. FIG. 6 is a graph showing measurement results of shear strength and elongation.

[Example 2]
A thin tin layer was formed on both the copper cylinders, and a thin layer was formed on the tin thin layer in the order of the copper thin layer and the tin thin layer. That is, copper was formed in the same manner as in Example 1 except that three layers of tin thin layer-copper thin layer-tin thin layer were formed, and these three layers were formed at 0.3 μm, 0.1 μm, and 0.3 μm, respectively. The cylindrical members were joined to each other.

  FIG. 6 shows the results of measuring the shear strength and the elongation of the bonded copper cylinders in a high temperature environment.

Example 3
A thin tin layer was formed on both copper cylinders, and the thin layer formation was repeated seven times on the tin thin layer in the order of the copper thin layer and the tin thin layer. That is, in the order of the tin thin layer and the copper thin layer, a total of 15 thin layers of 8 tin thin layers and 7 copper thin layers were formed. The copper columnar members were joined together in the same manner as in Example 1 except that the thickness of tin was 0.1 μm for each layer and the thickness of copper was 0.01 μm for each layer.

  FIG. 6 shows the results of measuring the shear strength and the elongation of the bonded copper cylinders in a high temperature environment.

[Comparative Example 1]
A thin tin layer was formed on both copper cylinders, and a thin copper layer was formed on the tin thin layer. A thin titanium layer was formed on the thin copper layer, and a thin layer was further formed on the thin titanium layer in the order of a tin thin layer, a copper thin layer, and a tin thin layer. The copper cylindrical members were joined in the same manner as in Example 1 except that the thickness of tin was 0.2 μm for each layer, the thickness of copper was 0.1 μm for each layer, and the thickness of titanium was 0.1 μm for each layer. It was.

  FIG. 6 shows the results of measuring the shear strength and the elongation of the bonded copper cylinders in a high temperature environment.

[Comparative Example 2]
The same copper columnar material as in Example 1 was joined using Sn—Ag—Cu solder paste. The joining conditions were the same as in Example 1.

  FIG. 6 shows the results of measuring the shear strength and the elongation of the bonded copper cylinders in a high temperature environment. The shear strength measurement and the elongation measurement were performed at 200 ° C. in consideration of the melting point of the Sn—Ag—Cu solder paste.

  From the measurement results shown in FIG. 6, it can be seen that, in the case of Sn 0.7 μm of Example 1, a good shear strength and elongation measurement result was obtained with a shear strength of 94 MPa and an elongation of 0.27 mm. In addition, the Sn2-Cu of Example 2 has a shear strength of 117 Mpa and an elongation of 0.37 mm, and the Cn8-Cu7 of Example 3 has a shear strength of 120 MPa and an elongation of 0.65 mm. It has been found that as the number of formation increases, very high shear strength and elongation are obtained. This is considered that the alloying of tin and copper in the alloy layer could be improved by increasing the number of formation.

  On the other hand, in Sn3-Cu2-Ti1 of Comparative Example 1, a very low quality alloy layer having a shear strength of about 20 MPa and an elongation of 0.06 mm was formed. This is because a thin titanium layer is formed between the thin tin layer and the thin copper layer. This thin titanium layer hinders the alloying of tin and copper and does not form a good alloy layer. This is probably because Furthermore, in the Sn-Ag-Cu solder paste of Comparative Example 2, similar to Comparative Example 1, the shear strength was 20 MPa and the elongation was 0.18 mm, indicating a low shear strength.

  Furthermore, the fracture surface of the alloy layer after the shear strength measurement in Examples 1 to 3 and Comparative Example 1 was observed with an SEM (scanning electron microscope). FIG. 7 is a photograph showing an SEM image of each fracture surface. 7 corresponds to the fracture surface of the alloy layer of Example 1, (b) of Example 2, (b) of Example 2, (c) of Example 3, and (d) of Comparative Example 1. . When the photographic diagrams of (a) to (c) were compared, a large trace of elongation on the fracture surface was observed in the order of (a), (b), and (c). This is a result consistent with the magnitude of the elongation of the alloy layer. Thus, according to the electronic element mounting method of the present invention, the alloy layer can have high ductility, and even if stress is applied, it can be absorbed to some extent. For this reason, an alloy layer is hard to be destroyed.

  In addition, in the alloy layer containing titanium of (d), almost no evidence of elongation at the fracture surface is observed, and in Comparative Example 1, the alloy layer has almost no ductility against stress and has a very brittle structure. I found out that

  According to the present invention, since the electronic element can be mounted on the circuit board even if the joint portion is fine, it can be suitably used in the field where the electronic element is used.

It is a schematic diagram which shows the state which laminated | stacked the tin thin layer 2 on the copper electrode 1a and the copper electrode 1b in this invention. It is process drawing explaining the mounting method of the electronic device of this invention. It is a two-dimensional state diagram of copper-tin. It is sectional drawing of the shear apparatus and the joined copper cylindrical material which shows the state of a shear test. It is a graph which shows the temperature change of the copper cylinder material at the time of a heating and pressurization. It is a graph which shows the measurement result of the shear strength and elongation of the joined copper cylindrical material. It is a photograph figure which shows the SEM image of the torn surface of the alloy layer which concerns on an Example and a comparative example.

Explanation of symbols

1a copper electrode 1b copper electrode 2 tin thin layer 2a tin thin layer 2b tin thin layer 3 copper thin layer 4 third thin layer 5 alloy layer

Claims (6)

In the mounting method of the electronic element, the circuit electrode made of copper formed on the circuit board and the element electrode made of copper formed on the electronic element are joined, and the electronic element is mounted on the circuit board.
After performing a tin thin layer forming step of forming a tin thin layer on the circuit electrode and the element electrode,
Performing a laminating step of laminating at least one thin layer formed in the order of a copper thin layer and a tin thin layer on at least one of the tin thin layers formed on the circuit electrode and the element electrode;
By performing a heating step in which the tin thin layers formed on the circuit electrode and the element electrode are brought into contact with each other, and heating and pressurization are performed at a temperature at which tin can be melted and copper can be dissolved in tin,
The copper of the circuit electrode and element electrode is dissolved in tin in the tin thin layer,
A method of mounting an electronic element, comprising electrically bonding a circuit electrode and an element electrode by mutual diffusion of tin in the tin thin layer with the circuit electrode and copper of the element electrode.   A third layer composed of one element selected from the group consisting of zinc, silver, nickel, germanium, iron and cobalt on the tin thin layer of the thin layer formed in the order of the copper thin layer and the tin thin layer. Forming the copper thin layer after forming at least one thin layer, and the third thin layer on the copper thin layer of the thin layer formed in the order of the copper thin layer and the tin thin layer The method for mounting an electronic device according to claim 1, further comprising a third thin layer forming step of performing at least one of the steps of forming the tin thin layer after forming at least one layer.   The circuit electrode made of copper formed on the circuit board and the element electrode made of copper formed on the electronic device are electrically joined to each other by the electronic device mounting method according to claim 1 or 2. An electronic component, wherein the electronic element is mounted on the circuit board. In mounting method for electronic devices that need use in Daibondin grayed implementing the silicon chip to the circuit board,
After performing a copper thin layer forming step of forming a copper thin layer on the surface of the silicon chip and circuit board to be bonded,
Performed tin thin layer forming step of forming a tin thin layer on the silicon chip and the circuit board, at least one of tin thin layer formed on the silicon chip and the circuit board, the thin copper layer, in the order of the tin lamina A laminating step of laminating at least one thin layer body to be formed is performed, the tin thin layer formed on the silicon chip and the circuit board is brought into contact with each other, and at a temperature at which tin can be melted and copper can be dissolved in tin. By performing the heating process of heating and pressurization,
The copper formed on the surface of the silicon chip and the circuit board is dissolved in the tin in the tin thin layer, and the silicon chip and the circuit board are joined by mutual diffusion of tin in the tin thin layer and the copper. A method for mounting an electronic device.   A third layer composed of one element selected from the group consisting of zinc, silver, nickel, germanium, iron and cobalt on the tin thin layer of the thin layer formed in the order of the copper thin layer and the tin thin layer. Forming the copper thin layer after forming at least one thin layer, and the third thin layer on the copper thin layer of the thin layer formed in the order of the copper thin layer and the tin thin layer 5. The method of mounting an electronic device according to claim 4, further comprising a third thin layer forming step of performing at least one of the steps of forming the tin thin layer after forming at least one layer. 6. The electronic component according to claim 4, wherein the silicon chip and the circuit board are bonded together by the electronic element mounting method according to claim 4.