JP2013209720A - Method for jointing metal body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for jointing a metal body, which exerts excellent adhesion force.SOLUTION: A method for jointing a metal body includes: a step of providing a first material 1 to be jointed which is a metal body and has a treated layer 11 that has been subjected to a treatment which causes atomic vacancy and/or rearrangement; a step of feeding a metal particulate 3 between the treated layer 11 of the first material 1 to be jointed and a second material 2 to be jointed; and a step of jointing the first material 1 to be jointed and the second material 2 to be jointed to each other.

Description

  The present invention relates to a method for joining metal bodies, and more particularly to a method for joining metal bodies when the metal body is an electrode of a semiconductor element, an electrode of a substrate such as a circuit board or a ceramic substrate, or a lead frame.

  Generally, solder is used to connect a semiconductor element (so-called power semiconductor element) for controlling or supplying power to a circuit board, a substrate such as a ceramic substrate, or a wiring body such as a lead frame. As such solder, cream solder in which flux is added to solder powder to have an appropriate viscosity is mainly used. However, when flux is used, there is a possibility that the surface of the semiconductor element may be contaminated, and there is a problem that a cleaning process is necessary. In recent years, it has been required to use a lead-free solder material that does not contain lead in consideration of the environment. There is Au-Sn solder as a lead-free solder material that can cope with heat generation of power semiconductors, but it is not practical because it is expensive. Sn-Ag-Cu solder is available as a cheaper solder material than Au-Sn solder, but there is a problem that growth of intermetallic compounds due to thermal history leads to a decrease in reliability.

  As a joining member that does not use solder, there is an anisotropic conductive film (ACF) in which a thermosetting resin is mixed with fine conductive metal particles and formed into a film shape. However, ACF is not suitable for connecting power semiconductors that generate a large amount of heat because there is a concern about deterioration of the thermosetting resin due to high heat.

  Therefore, it has been proposed to use an Ag paste in which Ag particles are dispersed in a resin as another joining member that does not use solder. When an Ag paste is applied as a power semiconductor bonding member, high thermal conductivity and high conductivity are required, and therefore it is necessary to increase the Ag content in the paste. However, as the Ag content increases, the ratio of the resin that is easily elastically deformed decreases, so that the rigidity of the bonding layer after the curing treatment increases and the strain absorption capacity of the bonding layer decreases. When a strain exceeding the strain absorption capability is applied to the bonding layer, there is a problem that a defect occurs in the contact interface between the electrode of the semiconductor element or the die pad and the Ag particle or in the connection material, and peeling occurs.

  In addition, when the electrode of the semiconductor element or the electrode of the substrate is Ni, if the Ag paste is used as the bonding member, the bonding strength (adhesion) is low, the interface is broken by an external force during handling, and the required long-term reliability is obtained. Since there is a problem that it cannot be obtained, it is necessary to perform noble metal plating on the electrode of the semiconductor element or the electrode of the substrate. However, when precious metal plating is performed and bonded in this manner, there is a problem in that durability is reduced because thermal stress on the semiconductor chip due to a difference in thermal expansion between members increases.

  Further, recently, metal particles having an average particle diameter of 100 nm or less whose surface is coated with an organic material are supplied between the materials to be bonded, and the organic particles are decomposed by heating to perform bonding by sintering the metal particles. It is known (see, for example, Patent Document 1).

  Furthermore, an oxide layer containing oxygen is formed at the bonding interface of the materials to be bonded, and a bonding material including a metal compound particle having an average particle size of 1 nm to 50 μm and a reducing agent made of an organic substance is disposed at the bonding interface. Then, it has been proposed to join the materials to be joined by heating and pressurizing the materials to be joined (for example, Patent Document 2). In this bonding material, the metal compound particles are reduced at a lower temperature than when the metal compound particles are thermally decomposed, and metal particles having an average particle diameter of 100 nm or less are produced at that time. In addition, after forming an oxide layer on the bonding surface in advance before bonding, the layer is oxidized to generate an oxide layer with a thickness greater than the natural oxide film thickness. It is said that the organic matter can be discharged efficiently, thereby increasing the shear strength of the joint surface.

JP 2004-107728 A JP 2008-208442 A

  However, in the bonding methods described in Patent Document 1 and Patent Document 2, in the bonding with metal fine particles, the diffusion reaction proceeds in the bonding between the metal fine particles and the metal body as the material to be bonded, as compared with the bonding between the metal fine particles. There was a problem that it was difficult and the adhesion was weak.

  Then, the objective of this invention is providing the connection method of the metal body excellent in the adhesive force.

  In order to achieve the above object, a metal body bonding method according to the present invention provides a first material to be bonded made of a metal having a processed layer subjected to processing that causes atomic vacancies and / or dislocations. A step of supplying metal fine particles between the processed layer of the first material to be joined and a second material to be joined, and the first material to be joined and the second through the metal fine particles. And a step of joining the material to be joined.

  In the metal body bonding method according to the present invention, it is preferable that the second material to be bonded is also a metal body having a processed layer subjected to processing for generating atomic vacancies and / or dislocations.

  In the metal body bonding method according to the present invention, it is preferable that the processed layer is formed only on the surface of the material to be bonded.

  In the metal body bonding method according to the present invention, it is preferable that the processed layer is formed only in a portion of the material to be bonded that is bonded by the metal fine particles.

  In the metal body bonding method according to the present invention, the average particle diameter of primary particles of metal fine particles is preferably 1 nm to 500 nm.

  In the metal body joining method according to the present invention, the metal fine particles are one kind of fine particles selected from the metal element group consisting of silver, gold, copper, aluminum, nickel, platinum, tin, antimony and palladium, and the metal element Selected from the group consisting of fine particles mixed with two or more selected from the group, fine particles composed of an alloy of two or more elements selected from the metal element group, one fine particle selected from the metal element group, or 2 selected from the metal element group It is preferable that the fine particles are a mixture of fine particles mixed with at least species and fine particles made of an alloy of two or more elements selected from the metal element group, oxides thereof, or hydroxides thereof.

  In the metal body bonding method according to the present invention, the metal fine particles are preferably pasted with an organic solvent.

  In the metal body joining method according to the present invention, it is preferable that the processing for generating the atomic vacancies and / or dislocations is mechanical processing.

  In the metal body bonding method according to the present invention, it is preferable that the first material to be bonded is made of copper.

  In the metal body bonding method according to the present invention, the processed layer of the first material to be bonded is recrystallized by heating at a recrystallization temperature or higher of the processed layer of the first material to be bonded. It is preferable.

  In the metal body bonding method according to the present invention, the first material to be bonded is a substrate, a lead frame, or an electrode of a semiconductor element, and the second material to be bonded is an electrode of a semiconductor element or a semiconductor element. It is preferable that it is the back surface.

  According to the metal body bonding method of the present invention, when at least a laminate comprising the first material to be bonded, the second material to be bonded, and the metal fine particles is heated, a melting phenomenon occurs locally on the surface of the metal fine particles, A joint (neck) is formed between the metal fine particles and between the metal fine particles and the first material to be joined. At this time, since the first material to be joined, which is a metal body, has a processed layer that has been processed to generate atomic vacancies and / or dislocations on at least the surface, the metal fine particles and the first fine particles as well as the neck between the metal fine particles The adhesion between the workpiece and the material to be bonded is enhanced because the diffusion of the vacancies in the processed layer to the entire material to be bonded and the metal fine particles is promoted, and the metal fine particles and the neck grow. Strength is obtained and bonding at a lower temperature is possible.

It is explanatory drawing for demonstrating typically the joining method of the metal body which concerns on embodiment of this invention. It is explanatory drawing for demonstrating typically the effect | action of the joining method of the metal body which concerns on embodiment of this invention. It is explanatory drawing for demonstrating typically the joining method of the metal body which concerns on other embodiment of this invention. It is explanatory drawing for demonstrating typically the effect | action of the joining method of the metal body which concerns on embodiment of this invention.

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

(First embodiment)
The metal body joining method according to the present embodiment is a metal body having first and second workpieces 1 and 2 having processed layers 11 and 12 on the surface, which are processed to generate atomic vacancies and / or dislocations. The metal fine particles 3 between the step of preparing the workpiece 2 and the processed layer 1 of the first workpiece 1 and the processed layers 11 and 12 of the second workpiece 2 as shown in FIG. The first material to be joined 1 and the second material to be joined by heating at least a laminate comprising the first material to be joined 1, the second material to be joined 2 and the metal fine particles 3. And joining the material 2.

The first material to be bonded 1 is not particularly limited as long as it is a conductive metal body. For example, it is an electrode of a substrate 100 such as a circuit board or a ceramic substrate, and is made of copper or copper alloy, silver plating or gold plating. It is preferable to become. As the substrate 100, a DBC (Direct Bonding Copper) substrate in which a copper plate is bonded to a ceramic (AlN) substrate can be used. Note that alumina (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), or the like may be used as the ceramic.

  In the present embodiment, the second bonded material 2 is also a metal body. The second bonded material 2 is, for example, an electrode of the semiconductor element 200, and is preferably formed by plating an Sn alloy with Ti, Ti alloy, Ni, or Ni alloy.

  In the above example, the electrode of the semiconductor element 200 and the electrode of the substrate 100 are connected. However, instead of the substrate, the die pad of the lead frame and the back surface of the semiconductor element may be connected. You may apply to what is called a chip-on-chip structure which connects with another semiconductor element. The bonding of the electrodes of the semiconductor element may be bonding by bumps or pin bonding as fine bonding.

  In the present embodiment, the surfaces of the first material to be bonded 1 and the second material to be bonded 2 are subjected to processing for generating atomic vacancies and / or dislocations, and processed layers 11 and 12 are formed. Yes. The formation of the processed layers 11 and 12 is not particularly limited as long as atomic vacancies and / or dislocations are generated on the surfaces of the first material to be bonded 1 and the second material to be bonded 2. It is preferable to use mechanical processing such as polishing by buffing, but radiation damage may also be caused by particle beam irradiation. For example, a processed layer of 5 μm can be obtained by processing at a processing speed of 5 mm / sec under a pressure of 0.15 MPa by a wet blasting method using a medium made of alumina and having a polygonal center particle size of 14 μm. In addition, when the 2nd to-be-joined material 2 is a back surface of a semiconductor element, it does not need to have the process layer 1. FIG.

  In addition, the processed layers 11 and 12 may be formed only on the portions to be bonded by the metal fine particles 3 on the surfaces of the first bonded material 1 and the second bonded material 2. For example, when the first material to be bonded 1 is an electrode of the substrate 100, the electrode of the substrate 100 includes not only a die-bonded portion but also a wire-bonded portion. In some cases, a material or the like may be used. When the diffusion is accelerated, defects such as a carkendar void are likely to be formed. Therefore, it is preferable that the processed layer 11 is not formed in the wire-bonded portion.

  The thickness of the processed layers 11 and 12 is not particularly limited, but is preferably 0.5 μm to 10 μm. Further, the degree of processing is preferably such that the hardness of the processed layers 11 and 12 is 15% or more higher than the micro Vickers hardness before processing in order to lower the temperature at which the connection temperature can be achieved. When the thickness of the processed layers 11 and 12 is thin, the substitute index is that the hardness index measured with a nanoindenter or the like similarly shows a value higher by 15% or more.

  The metal fine particles 3 are one kind of fine particles selected from the metal element group consisting of silver, gold, copper, aluminum, nickel, platinum, tin, antimony and palladium, and fine particles obtained by mixing two or more kinds selected from the metal element group, From the metal element group, fine particles made of an alloy of two or more elements selected from the metal element group, one fine particle selected from the metal element group, or fine particles obtained by mixing two or more elements selected from the metal element group It is preferable to be a fine particle obtained by mixing fine particles made of an alloy of two or more kinds of elements selected, an oxide thereof, or a hydroxide thereof.

  Moreover, it is preferable that the average particle diameter (average particle diameter of a primary particle) of the metal microparticle 3 is 1 nm-500 nm, More preferably, it is 5 nm-200 nm. Here, the average particle diameter of the primary particles means the average diameter of the primary particles that are the individual metal fine particles 3 constituting the secondary particles. The primary particle diameter can be measured using an electron microscope. The average particle size means the number average particle size of primary particles. If metal fine particles 3 having an average primary particle size of 1 nm to 500 nm are contained in a predetermined ratio, preferably 30 to 90% of the total mass, other metal fine particles having a particle size of 0.5 to 50 μm are included. You may go out.

  The metal fine particles 3 are preferably pasted with an organic solvent. As the organic solvent, known solvents can be used as appropriate, and preferred examples include alcohols and / or polyhydric alcohols that are liquid at 25 ° C., and alcohols and / or liquids that are liquid at 25 ° C. What mixed polyhydric alcohol and solid alcohol and / or polyhydric alcohol in 25 degreeC is mentioned.

  In addition, a dispersion auxiliary substance and a solvent can be appropriately blended. As the dispersion auxiliary substance, known substances can be used as appropriate. However, in consideration of improvement in dispersibility and sintering property of the metal fine particles 3, it is preferable to use a compound having an amide group, an amine compound, or the like.

  The metal fine particles 3 are supplied onto the processed layer 11 of the first bonded material 1, and the second bonded material 2 is placed thereon so that the processed layer 12 is in contact with the metal fine particles 3. In this state, the metal fine particles 3 are sintered. The sintering of the metal fine particles 3 is desirably performed in a reducing atmosphere or an inert atmosphere. The inert atmosphere is an atmosphere filled with a gas such as nitrogen or a vacuum atmosphere. By doing so, it becomes possible to remove the oxide layer on the surface of the metal fine particles 3 and improve the sinterability of the metal fine particles 3. Further, depending on the nature of the organic solvent blended in the metal fine particles 3, the sintering may be performed while appropriately pressing. Sintering is preferably performed for 30 to 90 minutes by heating at a temperature higher than the recrystallization temperature of the processed layer 12 and pressurizing at 0 to 20 MPa.

  As a case where it is desirable to sinter the metal fine particles 3 by heat treatment while applying pressure, the organic solvent is volatilized by the heat treatment, and there is a case where the volume reduction of the metal fine particles 3 is large. When the occupation area of the metal fine particles 3 is significantly reduced by the heat treatment, the metal density can be increased by pressurization. Moreover, it is possible to prevent cracks from forming in the sintered body of the metal fine particles 3. Furthermore, it becomes possible to join the 1st to-be-joined material 1 and the 2nd to-be-joined material 2 more firmly by pressurizing.

  On the other hand, if the area occupied by the metal fine particles 3 hardly changes even after heat treatment, the metal fine particles 3 can be sintered by heat treatment without applying pressure.

  By heating at least the laminate composed of the first material to be bonded 1, the second material to be bonded 2 and the metal fine particles 3, a melting phenomenon occurs locally on the surface of the metal fine particles 3, as shown in FIG. A joint (neck 4) is formed between the metal fine particles 3 and between the metal fine particles 3 and the first material to be bonded 1 (metal body), and the bonding surfaces of the metal fine particles 3 and the first material to be bonded 1 are joined together. A fusion layer 5 in which the metal fine particles 3 are fused is formed. At this time, since the first material to be bonded 1 has a processed layer 11 that has been processed to generate atomic vacancies and / or dislocations at least on the surface, the space between the metal fine particles 3 and the first material to be bonded 1 is In the neck 4, diffusion accompanied by movement of the atomic vacancies in the processed layer to the whole material to be joined and the metal fine particles is promoted, and the metal fine particles and the neck grow, so that higher adhesion can be obtained, In addition, bonding at a lower temperature becomes possible. Thereby, a recrystallized layer is formed on the surface of the first bonded material 1.

  In addition, since the processed layer 11 is provided on the surface of the first bonded material 1, the efficiency of the diffusion reaction is higher than that in the case of using the bonded material that does not have the processed layer 11 on the normal surface. In order to improve, the recrystallization temperature of the metal fine particles 3 is lower than that in the case of using a material to be joined in which the processed layer 11 is not provided on the normal surface, and joining at a lower temperature is possible. For example, when the metal fine particles 3 are copper, the recrystallization temperature is usually 200 ° C. or higher. However, when the metal fine particles 3 are bonded to the first material 1 having the processed layer 11 on the surface, the recrystallization temperature is 150 ° C. Become. Thus, as a result of being able to sinter at a low temperature, the bonding strength of the connection interface is increased.

  In addition, although the relationship between the 1st to-be-joined material 1 and the metal microparticle 3 was demonstrated above, the relationship between the 2nd to-be-joined material 2 and the metal microparticle 3 is also the same.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIG. In the first embodiment described above, the processed layer 1 is provided only on the surface of the first bonded material 1, whereas in the present embodiment, the entire first bonded material 1 ′ is processed. The same configuration and bonding method as described in the first embodiment can be applied except that the layer 11 ′ is provided and different in the point.

  Hereinafter, differences from the first embodiment will be described. As shown in FIG. 3, the first material to be bonded 1 ′ has been subjected to processing for generating atomic vacancies and / or dislocations throughout the thickness direction, and the first material to be bonded 1 ′ is a processed layer. 11 'only. In order to generate atomic vacancies and / or dislocations across the entire thickness direction of the first bonded material 1 ′, for example, bending may be performed.

  The first material to be bonded 1 ′ is, for example, a die pad of a lead frame. In this case, the second material to be bonded 2 ′ is the back surface of the semiconductor element.

  As shown in FIG. 3, when the metal fine particles 3 are supplied onto the first material to be bonded 1 ′ and heated with the second material to be bonded 2 ′ placed thereon, the first embodiment described above is applied. In the same manner, as shown in FIG. 4, joint portions (neck 4) are formed between the metal fine particles 3 and between the metal fine particles 3 and the first bonded material 1 ′ (metal body). At this time, since the first material to be bonded 1 is a processed layer 11 ′ that has been processed to generate atomic vacancies and / or dislocations, the neck between the metal fine particles 3 and the first material to be bonded 1 ′. 4, diffusion accompanied by movement of the atomic vacancies in the processed layer to the whole material to be joined and the metal fine particles is promoted, and the metal fine particles and the neck grow, so that higher adhesion can be obtained, and , Bonding at a lower temperature becomes possible.

  In addition, since the first material to be bonded 1 ′ is formed of the processed layer 11 ′, the diffusion reaction is faster than the case of using the material to be bonded that is not provided with the normal processed layer 11 ′. The recrystallization temperature of the metal fine particles 3 is lower than that in the case of using a material to be joined in which the processed layer 11 ′ is not provided on the normal surface, and bonding at a lower temperature is possible.

In the first embodiment, since the processed layer 11 is provided only on the surface of the first bonded material 1, as shown in FIG. 2, the first bonded material 1 has atomic vacancies. It diffuses not only on the joining side (surface) but also on the entire first material 1 to be joined.
In contrast, in the second embodiment, the processed layer 11 ′ is provided over the entire thickness direction of the first material to be bonded 1 ′. Therefore, as shown in FIG. In ', the rate at which atomic vacancies diffuse toward the bonding side is relatively increased, and the movement of atomic vacancies toward the bonding side occurs preferentially. Therefore, in the second embodiment, the movement of atomic vacancies is limited to the movement to metal fine particles.
As a result, the diffusion is more efficiently generated in the first embodiment than in the second embodiment, and neck growth between the metal fine particles 3 or between the metal fine particles 3 and the first bonded material 1 Recrystallization proceeds. For this reason, the 1st to-be-joined material 1 in which the process layer 1 was provided only on the surface was used rather than using 1st to-be-joined material 1 'in which the process layer 11' was provided over the thickness direction whole region. In this case, the recrystallization temperature can be lowered. For example, when the metal fine particles 3 are copper, the recrystallization temperature when bonded to the first material to be bonded 1 ′ provided with the processed layer 11 ′ over the entire thickness direction is 180 ° C. or higher, whereas The recrystallization temperature at the time of joining to the first material 1 to be joined provided with the processed layer 11 only was 150 ° C.

DESCRIPTION OF SYMBOLS 1, 1 ': 1st to-be-joined material 11, 11': Processed layer 2, 2 ': 2nd to-be-joined material 22, 22': Processed layer 3: Metal fine particle 4: Neck 5: Fusion layer 6: Atom Hole 100: Substrate 200: Semiconductor element

Claims (9)

Preparing a first material to be joined made of a metal having a processed layer that has been processed to generate atomic vacancies and / or dislocations;
Supplying metal fine particles between the processed layer of the first bonded material and the second bonded material;
A method for joining metal bodies, comprising: joining the first material to be joined and the second material to be joined via the metal fine particles.   The metal body bonding method according to claim 1, wherein the second material to be bonded is a metal body having a processed layer that has been processed to generate atomic vacancies and / or dislocations.   The metal body joining method according to claim 1, wherein the processed layer is formed only on a surface of a material to be joined.   The method for joining metal bodies according to any one of claims 1 to 3, wherein the processed layer is formed only in a portion of the material to be joined that is joined by the metal fine particles.   The metal particle joining method according to any one of claims 1 to 4, wherein the metal fine particles have an average primary particle diameter of 1 nm to 500 nm.   The metal fine particles are one kind of fine particles selected from a metal element group consisting of silver, gold, copper, aluminum, nickel, platinum, tin, antimony and palladium, and a fine particle obtained by mixing two or more kinds selected from the metal element group, From the metal element group, fine particles made of an alloy of two or more elements selected from the metal element group, one fine particle selected from the metal element group, or fine particles obtained by mixing two or more elements selected from the metal element group The fine particles mixed with fine particles made of an alloy of two or more kinds of elements selected, oxides thereof, or hydroxides thereof, according to any one of claims 1 to 5. The joining method of the metal body of description.   The metal body joining method according to any one of claims 1 to 6, wherein the processing for generating the atomic vacancies and / or dislocations is mechanical processing.   The metal body joining method according to claim 1, wherein the first material to be joined is made of copper.   The processing layer of the first bonded material is recrystallized by heating at a recrystallization temperature or higher of the processed layer of the first bonded material. The method for joining metal bodies according to any one of claims 8 to 10.

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