JP5573557B2 - Joining method and joined body - Google Patents

Description

  The present invention relates to a bonding method for bonding metal members to each other via a conductive adhesive portion, and a bonded body obtained by using the bonding method.

Conventionally, a method of using a conductive adhesive in which conductive metal fine particles such as silver and copper are dispersed in a resin binder is known for mounting electronic components on a substrate and bonding between electrodes. In this method, metal members are joined to each other through a conductive adhesive portion formed by a conductive adhesive.
In recent years, along with the downsizing and high functionality of various electronic devices, the demand for high mounting density of electronic components is increasing, and in response to this, miniaturization is also required for the above conductive adhesive parts Is increasing. One example is the miniaturization of interlayer connection portions of multilayer printed wiring boards.
A multilayer printed wiring board has a structure in which wiring layers are multi-layered. As a method of electrically connecting the wiring layer and the wiring layer, a via hole is provided between the wiring layer and the wiring layer, and the via hole is electrically conductive. There are known a method of interlayer connection by filling a conductive paste, and a method of interlayer connection by providing a conductive bump penetrating a non-conductive layer existing between the wiring layers (Patent Document 1, 2). The multi-layered wiring layer has been made in response to the demand for higher density, but in order to cope with higher density, miniaturization of the interlayer connection portion has been required. However, when the interlayer connection is miniaturized, the contact area between the interlayer connection and the wiring layer is reduced, the contact resistance at the interface between the interlayer connection and the wiring layer is increased, and sufficient conduction cannot be obtained (connection reliability). May be low).

JP-A-6-268345 Japanese Patent No. 3167840

  The present invention has been made in view of the above-described problems, and a joining method for reducing the contact resistance between a metal member and a conductive adhesive portion when joining the metal members through the conductive adhesive portion, and its The present invention has been made to provide a joined body obtained by using a joining method.

The present invention
A joining method for joining a first metal member and a second metal member via a conductive adhesive portion containing metal fine particles having a particle diameter of 0.5 to 5 μm and a binder resin, the first metal member and the conductive material An average primary particle diameter of 1 to 100 nm composed of at least one metal selected from the group consisting of a metal constituting the metal fine particles of the conductive adhesion portion and a metal constituting the first metal member between the adhesion portion and the adhesion portion. A first joining auxiliary portion comprising the nanoparticles of the metal and / or a metal constituting the metal fine particles of the conductive adhesive portion and the second metal between the second metal member and the conductive adhesive portion. Provided is a joining method in which a second joining auxiliary portion comprising nanoparticles having an average primary particle diameter of 1 to 100 nm composed of at least one metal selected from the group consisting of metals constituting a metal member is provided. .

The present invention further includes a first metal member, a second metal member, a conductive adhesive portion, and at least one of a first joining auxiliary portion and a second joining auxiliary portion obtained by using the above-described joining method. Is to provide.

  According to the present invention, the contact resistance between the conductive adhesive portion and the metal member can be reduced. As a result, sufficient conduction can be obtained even if the conductive adhesive portion is miniaturized.

FIG. 1 is a schematic view showing an example of a laminate formed when the bonding method of the present invention is applied to an interlayer connection using conductive bumps as one embodiment of the present invention.

  Hereinafter, the joining method and joined body of the present invention will be described.

The joining method of the present invention is a joining method for joining a first metal member and a second metal member via a conductive adhesive portion containing metal fine particles having a particle diameter of 0.5 to 5 μm and a binder resin. Between 1 metal member and this electroconductive adhesion part, it is comprised with at least 1 type of metal chosen from the group which consists of the metal which comprises the metal microparticle of this electroconductive adhesion part, and the metal which comprises this 1st metal member A first bonding auxiliary portion comprising nanoparticles having an average primary particle diameter of 1 to 100 nm is provided, and / or metal fine particles of the conductive adhesive portion are provided between the second metal member and the conductive adhesive portion. A second joining auxiliary portion comprising nanoparticles having an average primary particle diameter of 1 to 100 nm composed of at least one metal selected from the group consisting of a metal constituting the metal and a metal constituting the second metal member is provided.
Moreover, the joined body of the present invention is obtained by using the joining method described above, and includes at least one of the first metal member, the second metal member, the conductive adhesive portion, the first joining auxiliary portion, and the second joining auxiliary portion. On the other hand.

In the present invention, the first joining auxiliary portion is provided between the conductive adhesive portion and the first metal member, thereby reducing the resistance between the conductive adhesive portion and the first metal member. Similarly, by providing the second joining auxiliary portion between the conductive adhesive portion and the second metal member, it is possible to reduce the resistance between the conductive adhesive portion and the second metal member. In general, as the number of interfaces on the conduction path increases, the resistance also tends to increase. Surprisingly, in the present invention, the provision of the first joining auxiliary portion and the second joining auxiliary portion contributes to the reduction in resistance. Yes.
In the present invention, it is preferable to provide both the first joining auxiliary part and the second joining auxiliary part. When both are provided, the resistance between the first metal member and the second metal member is greatly reduced as compared with the case where either one is provided.

[First metal member, second metal member]
The metal which comprises the 1st metal member and 2nd metal member of this invention will not be specifically limited if it is an electroconductive metal. For example, metals such as gold, silver, copper and Al, and alloys containing these metals can be used, but it is preferable to use copper in view of both conductivity and cost. Further, the shape is not particularly limited, and any shape such as a sheet shape, a plate shape, or a rod shape may be used.

[Conductive adhesive part]
The conductive adhesive part of the present invention contains fine metal particles having an average particle size of 0.5 to 5 μm and a binder resin.
As the metal fine particles having an average particle size of 0.5 to 5 μm of the present invention, for example, silver powder, gold powder, copper powder, nickel powder, platinum powder, palladium powder, solder powder, metal powder such as the alloy powder of the metal, or the like is used. be able to. Two or more kinds of these conductive powders can be used in combination. In consideration of both conductivity and cost, silver powder is preferable.
The form of the conductive powder is arbitrary as long as it is not contrary to the object of the present invention. In the present invention, for example, dendritic, flaky, spherical, and flaky forms, particularly preferably spherical or a mixture of flaky and spherical shapes can be used.
The average particle diameter of the metal fine particles is 0.5 to 5 μm, but if it is less than 0.5 μm, the conductivity is poor, and if it exceeds 5 μm, it is difficult to print a fine pattern. The average particle size is preferably 0.8 to 4.5 μm, more preferably 1.0 to 4.0 μm.
The average particle diameter is a value measured by a laser diffraction method.

  As the binder resin of the present invention, an appropriate one can be selected from binder resins of conductive adhesives that have been used conventionally. Examples thereof include a polyester resin, a phenol resin, a polyimide resin, a polycarbonate resin, a polysulfone resin, a melamine resin, and an epoxy resin.

The conductive adhesive portion is formed using a conductive adhesive prepared by mixing metal fine particles having an average particle size of 0.5 to 5 μm and a binder resin.
The content of the metal fine particles in the conductive adhesive is preferably 300 parts by mass or more, more preferably 900 parts by mass or more, and still more preferably 1200 parts by mass or more with respect to 100 parts by mass in total of the binder resin component. The resistance of the conductive adhesive portion can be lowered as the amount of metal fine particles is increased. On the other hand, if the content of the metal fine particles is too large, the balance between the other characteristics, for example, the adhesiveness with the first metal member and the second metal member, and the formability of the conductive adhesive portion, becomes worse. The content of the metal fine particles is preferably 6000 parts by mass or less, more preferably 5000 parts by mass or less, and further preferably 4800 parts by mass or less.
The conductive adhesive may further contain a solvent as necessary. In addition, pigments, thixotropy imparting agents, antifoaming agents, dispersants, rust preventives, reducing agents and the like are included as necessary.

[First joining auxiliary part, second joining auxiliary part]
The first joining auxiliary portion of the present invention has an average primary particle diameter of 1 to 1 composed of at least one metal selected from the group consisting of a metal constituting the metal fine particles of the conductive adhesive portion and a metal constituting the first metal member. It comprises 100 nm nanoparticles.
In addition, the second joining auxiliary portion of the present invention has an average primary particle diameter of 1 composed of at least one metal selected from the group consisting of a metal constituting the metal fine particles of the conductive bump and a metal constituting the second metal member. Comprising ˜100 nm nanoparticles.
The average primary particle size is a value measured using a scanning transmission electron microscope (STEM).
The size, shape, and the like of the first joining auxiliary portion and the second joining auxiliary portion are appropriately selected according to the size and shape of the first metal member, the second metal member, and the conductive adhesive portion. For example, if the first metal member and the conductive adhesive portion are layered, the first joining auxiliary portion is also layered between the layers.

A method for forming the first joining auxiliary portion is not particularly limited as long as the first joining auxiliary portion can be formed between the first metal member and the conductive adhesive portion. For example, a paste containing nanoparticles (hereinafter also referred to as “nanoparticle paste”) and a conductive adhesive are sequentially applied to the first metal member, and heated, so that the first metal member and the conductive adhesive portion are heated. And a method of forming the first joining auxiliary portion.
The method for forming the second bonding auxiliary portion is the same as the method for forming the first bonding auxiliary portion.
In the case of forming both the first joining auxiliary part and the second joining auxiliary part, for example, a first metal member / nanoparticle paste / conductive adhesive / nanoparticle paste / second metal member structure is formed. After that, there is a method of heating to obtain a joined body of first metal member / first joining auxiliary part / conductive adhesive part / second joining auxiliary part / second metal member. As another method, for example, a first metal member / nanoparticle paste / conductive adhesive structure is formed, and then heated, whereby the first metal member / first joining auxiliary portion / conductive adhesive portion is formed. The first metal member / first joining auxiliary portion / conductive adhesive portion is formed by heating the nanoparticle paste / second metal member structure in contact with the structure. There is also a method for obtaining a joined body of / second joining auxiliary part / second metal member.

  The nanoparticle paste may contain a solvent or the like as a component other than the nanoparticles, but at the time of forming the first bonding auxiliary portion, at the time of forming the second bonding auxiliary portion, it is substantially formed only of nanoparticles. It is preferable from the viewpoint of the resistance reduction effect. A part or all of the nanoparticles may be a sintered body at the stage where the first bonding auxiliary part and the second bonding auxiliary part are formed.

The reason why the resistance reduction effect is obtained when the first joining auxiliary portion is formed is not clear, but is presumed as follows.
When the first joining auxiliary portion is not provided, from the macro viewpoint, the entire interface between the first metal member and the conductive adhesive portion looks like a conduction path. The metal fine particles are in point contact, and when the binder component (not conductive) contained in the conductive adhesive portion is taken into consideration, it is considered that there are few effective conduction paths.
On the other hand, when the first joining auxiliary portion is provided, the nanoparticles have a much smaller particle size than the metal fine particles of the conductive adhesive portion, so that the number of contact points between the first metal member and the nanoparticles is large and effective. The number of effective conduction paths increases. In particular, when the first joining auxiliary portion is substantially composed only of nanoparticles, since there is no inhibition by the binder component or the like, the effective conduction path becomes large. In addition, at the interface between the first joining auxiliary portion and the conductive adhesive portion, the nanoparticles having a small particle size come into contact with the metal fine particles so as to enter the gap between the metal fine particles in the conductive adhesive portion. There are many contact points between nanoparticles and the effective conduction path becomes large. In addition, since the nanoparticles form a sintered body when heated, the resistance inside the anchor layer also decreases.
Further, the nanoparticle has a metal that is the same as the metal constituting the metal fine particles of the conductive adhesion portion or the metal constituting the first metal member as a constituent component, so that the conductive adhesion portion or the first metal member It is thought that it contributes to resistance reduction.

It is more preferable that the nanoparticles of the first joining auxiliary portion are composed of the metal constituting the metal fine particles of the conductive adhesive portion, and the metal constituting the nano particles and the metal constituting the metal fine particles of the conductive bump are both silver. It is particularly preferred that
The average primary particle diameter of the nanoparticles of the first joining auxiliary part is 1 to 100 nm. If it is less than 1 nm, it is difficult to produce, and if it exceeds 100 nm, low-temperature sintering is difficult. The average primary particle diameter of the nanoparticles of the first joining assistant is preferably 5 to 50 nm.

Regarding the reason why the resistance reduction effect is obtained when the second joining auxiliary portion is formed, the reason described above as the reason why the resistance reduction effect is obtained when the first joining auxiliary portion is formed is similarly estimated.
It is more preferable that the nanoparticles of the second bonding auxiliary portion are made of a metal constituting the metal fine particles of the conductive bump, and the metal constituting the nano particles and the metal constituting the metal fine particles of the conductive bump are both silver. It is particularly preferred.
The average primary particle diameter of the nanoparticles of the second joining auxiliary portion is 1 to 100 nm, and if it is less than 1 nm, it is difficult to produce, and if it exceeds 100 nm, low-temperature sintering is difficult. The average primary particle diameter of the nanoparticles of the second bonding assistant is preferably 5 to 50 nm.
Moreover, although the nanoparticle of a 1st joining auxiliary | assistant part and the nanoparticle of a 2nd joining auxiliary | assistant part may be the same or different, it is more preferable that it is the same from a viewpoint of simplification of a manufacturing process.

  As one embodiment of the bonding method of the present invention, an example applied to interlayer connection by conductive bumps in a multilayer printed wiring board can be given. The present invention will be described in detail below based on the embodiment, but the present invention is not limited to the embodiment. The joining method of the present invention can be widely applied as long as the metal members are joined together through the conductive adhesive portion.

  FIG. 1 schematically shows an example of a laminate in which layers are connected by conductive bumps. In the laminate 1, the non-conductive sheet 4 is sandwiched between the first metal sheet 2 and the second metal sheet 3, and the conductive bumps 5 penetrate the non-conductive sheet 4, thereby the first metal sheet. 2 and the second metal sheet 3 are electrically connected. In the laminated body of FIG. 1, the first joining auxiliary portion 6 is provided between the conductive bump 5 and the first metal sheet 2, and the second joining auxiliary is provided between the conductive bump 5 and the second metal sheet 3. Although the part 7 is provided, it is sufficient that at least one of the first joining auxiliary part 6 and the second joining auxiliary part 7 is provided.

The interlayer connection method by the conductive bump of this embodiment is
(1) On the first metal sheet 2, after applying a conductive paste containing a binder resin and metal fine particles having an average particle size of 0.5 to 5 μm, the conductive paste is cured by heating, Forming a conductive pump 5 on the first metal sheet 2;
(2) A step of passing the conductive bumps 5 through the non-conductive sheet 4 by applying pressure after laminating and arranging the non-conductive sheet 4 on the first metal sheet 2 on which the conductive pump 5 is formed, And (3) an interlayer connection method including a step of laminating and arranging the second metal sheet 3 on the non-conductive sheet 4 penetrated by the conductive bumps 5 and pressurizing while heating. ) Includes a step of providing a first joining auxiliary portion 6 between the first metal sheet 2 and the conductive bump 5, and / or the step (3) includes the second metal sheet 3 and the conductive bump. 5 includes a step of providing the second joining auxiliary portion 7 between the two.
Here, the first joining auxiliary portion has an average primary particle diameter of 1 to 100 nm composed of at least one metal selected from the group consisting of a metal constituting the metal fine particles of the conductive paste and a metal constituting the first metal sheet 2. Average primary particles comprising nanoparticles, wherein the second joining auxiliary part is composed of at least one metal selected from the group consisting of a metal constituting the metal fine particles of the conductive paste and a metal constituting the second metal sheet 4. Nanoparticles having a diameter of 1 to 100 nm are included.

Step (1):
In the step (1), a conductive paste prepared by mixing metal fine particles having an average particle size of 0.5 to 5 μm and a binder resin is coated on the first metal sheet 2 and then heated to apply the conductive paste. The conductive paste is cured to form a conductive pump 5 on the first metal sheet 2.
Although the coating method of an electrically conductive paste is not specifically limited, The method of printing using masks, such as a metal mask, is mentioned. Although the temperature of heat processing, processing time, etc. can be suitably determined in consideration of the kind of conductive paste to be used, it is generally about 150 to 200 ° C. and preferably about 10 to 60 minutes.
When the step (1) includes a step of providing the first joining auxiliary portion 6 between the first metal sheet 2 and the conductive bump 5, for example, a nanoparticle paste is applied on the first metal sheet 2. On top of this, a conductive paste is applied. Then, the 1st joining auxiliary | assistant part 6 can be provided between the 1st metal sheet 2 and the electroconductive bump 5 by heating. The method for applying the nanoparticle paste is not particularly limited, and examples thereof include a printing method using a mask such as a metal mask.

Step (2):
In step (2), after the non-conductive sheet 4 is laminated on the first metal sheet 2 on which the conductive pump 5 is formed, the conductive bumps 5 are penetrated through the non-conductive sheet 4 by applying pressure. .
The pressure in the pressure treatment can be appropriately determined in consideration of the hardness of the conductive bump 5, the type of the non-conductive sheet 4 to be used, and the like, but generally about 0.2 to 0.4 MPa is preferable.

Step (3):
In the step (3), the second metal sheet 3 is laminated on the non-conductive sheet 4 penetrated by the conductive bumps 5 and pressed while heating.
In this step, the first metal sheet 2 and the second metal sheet 3 are bonded via the conductive bumps 5.
The heating and pressurizing conditions can be appropriately determined in consideration of the hardness of the conductive bumps 5 and the four types of non-conductive sheets to be used. In general, while heating to about 100 to 200 ° C., It is preferable to pressurize at about 100 MPa.
In the case where the step (3) includes the step of providing the second joining auxiliary portion 7 between the second metal sheet 3 and the conductive bump 5, for example, in the portion that contacts the conductive bump 5 of the second metal sheet 3. A method of applying a nanoparticle paste in advance is mentioned. The second metal sheet 3 to which the nanoparticle paste has been applied in advance is pressed while being heated so that the nanoparticle paste is in contact with the conductive bump 5, whereby the second metal sheet 3 and the conductive bump are applied. It is possible to provide the second joining auxiliary portion 7 between the two.

  Hereinafter, the present invention will be specifically described with reference to examples. The present invention is not limited to the method described below.

(1) Production of laminated body [Example 1] (Structure provided with first joining assisting part)
Nano silver paste was prepared by the following method.
Silver carbonate (64 g) and laurylamine n-C ₁₂ H ₂₅ NH _{2 (} 79 g) were placed as a solid in a three-necked flask and heated to 120 ° C. in an N ₂ atmosphere. After maintaining at 120 ° C. for 5 hours, the mixture was allowed to stand until the temperature was lowered to 70 ° C., methanol was added at 70 ° C. to wash several times, and the obtained powder was dried under reduced pressure. As a result of observing the obtained powder with a scanning transmission electron microscope (STEM), the average primary particle diameter was 7.5 nm. To the obtained powder, 10 g of terpineol was added and stirred sufficiently to obtain a nano silver paste.
A silver paste was prepared by the following method.
130 parts by mass of butyl carbitol acetate was uniformly mixed with 100 parts by mass of the phenolmelamine resin to obtain a resin solution. This resin solution is mixed with 900 parts by mass of an approximately spherical silver powder having an average particle diameter of 1 μm (AGWA-1C, manufactured by DOWA High-Tech Co., Ltd.). A silver paste was obtained.
The nano silver paste and silver paste thus prepared were used in the manufacturing process of the laminate A as follows.
A nano silver paste and a silver paste were sequentially applied on the copper foil, and heated at 200 ° C. for 20 minutes, thereby forming conductive bumps on the copper foil via the nano silver first joining auxiliary portion. After the prepreg was laminated and disposed thereon, the conductive bumps were passed through the prepreg by pressurizing at 0.3 MPa. Further, a copper foil was laminated thereon, and pressurized at 40 MPa while being heated to 175 ° C. Thus, the laminated body A which has the 1st joining auxiliary | assistant part which contains nano silver was obtained.

[Example 2] (Configuration provided with a first joining auxiliary part and a second joining auxiliary part)
A nano silver paste and a silver paste were prepared in the same manner as in Example 1 and used in the manufacturing process of the laminate B as follows.
On the copper foil, nano silver paste and silver paste were sequentially applied and heated at 200 ° C. for 20 minutes to form conductive bumps on the copper foil via the first joining auxiliary portion made of nano silver. . After the prepreg was laminated and disposed thereon, the conductive bumps were passed through the prepreg by pressurizing at 0.3 MPa. Further, a copper foil coated with nano silver paste in advance was laminated so that the nano silver paste and the conductive bumps were in contact with each other, and pressed at 40 MPa while being heated to 175 ° C. Thus, the laminated body B which has the 1st joining auxiliary | assistance part and 2nd joining auxiliary | assistant part containing nano silver in this way was obtained.

[Comparative Example 1] (Configuration in which neither the first joining auxiliary part nor the second joining auxiliary part is provided)
A silver paste was produced in the same manner as in Example 1, and used in the production process of the laminate C as follows.
The silver paste was apply | coated on copper foil, and the conductive bump was formed on copper foil by heating at 200 degreeC for 20 minutes. After the prepreg was laminated and disposed thereon, the conductive bumps were passed through the prepreg by pressurizing at 0.3 MPa. Further, a copper foil was laminated thereon, and pressurized at 40 MPa while being heated to 175 ° C. Thus, the laminated body C which does not have a 1st joining auxiliary | assistant part and a 2nd joining auxiliary | assistant part was obtained.

(2) Measurement of resistance For the laminates A to C obtained in Examples 1 and 2 and Comparative Example 1, the resistance was measured as follows.
With respect to the exposed surface of the first metal sheet (copper foil) and the second metal sheet (copper foil) of the laminate, using a Milliome high tester (3560 AC milliohm high tester, Hioki Electric Co., Ltd.) +- The resistance was measured by bringing the terminals into contact with each other.

The evaluation results of Examples 1 and 2 and Comparative Example 1 are shown in Table 1 below.

DESCRIPTION OF SYMBOLS 1 Laminated body 2 1st metal sheet 3 2nd metal sheet 4 Nonelectroconductive sheet 5 Conductive bump 6 1st joining auxiliary | assistance part 7 2nd joining auxiliary | assistant part

Claims (8)

A joining method for joining a first metal member and a second metal member via conductive bumps containing metal fine particles having a particle diameter of 0.5 to 5 μm and a binder resin,
On the side of the surface to be bonded to the conductive bump of the first metal member, at least one metal selected from the group consisting of a metal constituting the metal and the first metal member constituting the metal fine particles of the conductive bump A first joining auxiliary portion comprising nanoparticles having an average primary particle diameter of 1 to 100 nm and / or the conductive surface of the second metal member on the side to be joined to the conductive bump. Second junction comprising nanoparticles having an average primary particle diameter of 1 to 100 nm composed of at least one metal selected from the group consisting of metals constituting metal fine particles of the conductive bump and metals constituting the second metal member A joining method in which an auxiliary part is provided.   The joining method according to claim 1, wherein both the first joining assistance part and the second joining assistance part are provided. The joining method according to claim 1 or 2, wherein the nanoparticles contained in the first joining auxiliary part are made of a metal constituting metal fine particles of the conductive bump. The joining method according to any one of claims 1 to 3, wherein the nanoparticles contained in the second joining auxiliary portion are made of a metal constituting metal fine particles of the conductive bump. The joining method according to claim 1, wherein a metal constituting the metal fine particles of the conductive bump is silver.   The joining method according to any one of claims 1 to 5, wherein a metal constituting the first metal member and the second metal member is copper. By disposing a non-conductive sheet between the first metal member and the second metal member and penetrating the non-conductive sheet with the conductive bump, the first metal member and the second metal The joining method according to claim 1, wherein a member is connected by the conductive bump. The obtained using the bonding method according to claim 1 to 7, the first metal member, the second metal member, conductive bumps, and the first auxiliary bonding portion and the second auxiliary bonding portion of the at least one conjugate comprising.