JP2014110282A - Bonding method using paste containing metal fine particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bonding method which bonds a member to be bonded using a paste containing metal fine particles as a bonding material and is capable of obtaining an assembly with excellent durability, and in which a notch does not occur.SOLUTION: A method for bonding a first member 1 to be bonded and a second member 2 to be bonded using a paste 3 containing metal fine particles includes the steps of: applying a paste containing metal fine particles to the second member to be bonded over an area wider than an area of the first member to be bonded; laminating the first member to be bonded on the paste, pressurizing the first member to be bonded, and pushing the first member to be bonded into the paste at a thickness which is not less than 30% of the thickness of the applied paste; and performing heating.

Description

  The present invention relates to a method for joining members to be joined using a paste containing metal fine particles.

  Conventionally, solder has been used as a bonding material, but it has been difficult to use it for power device elements having a high operating temperature. For this reason, a paste containing metal fine particles having high heat resistance has been used as a bonding material (for example, Patent Document 1).

  In the joining method using solder as the joining material, the solder melts and spreads by the weight of the member to be joined, so that a fillet is formed. However, when the metal fine particle-containing paste is used as a bonding material, the metal fine particle-containing paste does not melt and does not spread out, and the paste shrinks due to vaporization due to the temperature rise of the solvent contained in the paste. For this reason, the notch used as a stress concentration part generate | occur | produces in a paste, and durability of the obtained joined body will fall. FIG. 8 shows a conventional joining method using a paste containing metal fine particles. When the metal particle-containing paste 6 is applied to the member to be bonded 5 in the same area as the member to be bonded 4, the member to be bonded 4 is laminated on the paste 6, and heated to join the member to be bonded 4 and the member to be bonded 5, As the solvent contained in the paste 6 is vaporized, the paste 6 contracts. For this reason, as shown in the enlarged view of the joined portion in FIG. 9, a notch that becomes a stress concentration portion is generated between the joined member 4 and the joined member 5, and the durability of the obtained joined body is lowered.

  Also, in general, when a metal fine particle-containing paste is applied over a larger area than the members to be bonded and bonded without pressure, a temperature gradient occurs in the paste layer during heating, so the paste warps in the opposite direction to the heat source. It is known that a notch that becomes a stress concentration portion is generated between the member to be bonded and the paste, and the durability of the obtained bonded body is lowered.

  Furthermore, it has been reported that when a metal fine particle-containing paste containing a specific metal particle precursor and a reducing agent is used as a bonding material, bonding by metal bonding can be realized at a lower temperature at the bonding interface (patent) Document 2), in this document, when the pressure is applied during bonding, the bonded area ratio of the bonded body is 20% or more, but when the pressure is not applied, the bonded area ratio of the bonded body is 5% or less. In addition, it is described that it is essential to pressurize the member to be joined at the time of joining. For this reason, the conventional soldering equipment that does not require pressurization at the time of joining cannot join the members to be joined, and the equipment needs to be modified in order to join them.

JP 2011-21255 A JP 2012-94873 A

  As described above, when the metal fine particle-containing paste is used as a bonding material, notches are generated between the members to be bonded, and the durability of the resulting bonded body may be reduced.

  In addition, even when the metal fine particle-containing paste is applied to a larger area than the member to be bonded and bonded without pressure, a notch is generated between the member to be bonded and the paste, and the resulting bonded body has durability. May decrease.

  Therefore, an object of the present invention is to provide a joining method for obtaining a joined body having no notch and having excellent durability in a joining method of members to be joined using a metal fine particle-containing paste as a joining material.

The present invention includes the following inventions.
(1) In the joining method of joining the first member to be joined and the second member to be joined with the metal fine particle-containing paste,
Applying the metal fine particle-containing paste to the second bonded member in an area wider than the area of the first bonded member;
The first member to be bonded is laminated on the metal fine particle-containing paste, the first member to be bonded is pressed, and the first member to be bonded is applied to the paste at a thickness of 30% or more of the thickness of the paste applied. Pushing process,
Heating the method.
(2) The joining method according to (1), wherein heating is performed from the first joined member side.
(3) The joining method according to (1) or (2), wherein the metal fine particle-containing paste is applied to the second member to be joined in an area wider by 0.5% or more than the area of the first member to be joined.
(4) The joining method according to any one of (1) to (3), wherein the heating step is performed under no pressure.

  ADVANTAGE OF THE INVENTION According to this invention, in the joining method using a metal microparticle containing paste as a joining material, a notch does not generate | occur | produce but the joining method which can obtain the joining body excellent in durability can be provided.

It is a figure which shows the process of the joining method of this invention. It is an enlarged view of the junction part of the conjugate | zygote obtained by the joining method of this invention. It is a figure which shows the 2nd Embodiment of this invention. It is a figure which shows the ultrasonic microscope image before the thermal shock test of the comparative example of this invention. It is a figure which shows the ultrasonic microscope image before the thermal shock test in the conditions of -55 degreeC / 150 degreeC of Example 1 of this invention. It is a figure which shows the ultrasonic microscope image after the thermal shock test in the conditions of -55 degreeC / 150 degreeC of Example 1 of this invention. It is a figure which shows the ultrasonic microscope image before the thermal shock test in the conditions of -65 degreeC / 175 degreeC of Example 1 of this invention. It is a figure which shows the ultrasonic microscope image after the thermal shock test in the conditions of -65 degreeC / 175 degreeC of Example 1 of this invention. It is a figure which shows the ultrasonic microscope image before the thermal shock test in the conditions of -65 degreeC / 175 degreeC of Example 2 of this invention. It is a figure which shows the ultrasonic microscope image after the thermal shock test in the conditions of -65 degreeC / 175 degreeC of Example 2 of this invention. It is a figure which shows the conventional joining method. It is an enlarged view of the junction part of the conjugate | zygote obtained by the conventional joining method.

  Embodiments of the present invention will be described as follows.

  The present invention relates to a joining method for joining a first member to be joined and a second member to be joined with a metal fine particle-containing paste. According to the method of the present invention, a cutout is not generated, and a bonded body having excellent durability can be obtained.

  The kind of metal used as the metal fine particles contained in the metal fine particle-containing paste is not particularly limited, and any of noble metals and base metals can be used. Examples of the noble metal include gold, silver, ruthenium, rhodium, palladium, iridium, and platinum. Examples of the base metal include copper, aluminum, iron, nickel, and the like. One kind of metal may be used, or two or more kinds may be used in combination. The metal fine particles may be in the form of a metal oxide or a metal salt as long as the electrical / thermal conductivity is maintained. Although it does not specifically limit in this invention, It is preferable to use silver from a viewpoint of electrical conductivity and heat conductivity.

  The average particle diameter of the metal fine particles is, for example, 1 to 60 nm, preferably 1 to 20 nm. The smaller the average particle size, the larger the contact area between the particles and the better the bonding strength and electrical / thermal conductivity. The metal fine particles having a specific average particle diameter may be used alone, or a plurality of metal fine particles having a different average particle diameter may be used in combination. In a preferred embodiment of the present invention, a metal nanoparticle paste is used as a metal fine particle-containing paste.

  The content of the metal fine particles in the metal fine particle-containing paste is, for example, 80 to 99% by weight, preferably 95 to 99% by weight.

The metal fine particle-containing paste of the present invention may contain a solvent or an additive.
The solvent is not particularly limited, and is aprotic polar solvent such as water or alcohol, aprotic polar solvent such as amide (for example, dimethylacetamide), nitrile (for example, acetonitrile), ketone (for example, acetone), or cyclic ether (for example, tetrahydrofuran). A solvent or the like can be used.

The additive is not particularly limited, and examples thereof include a viscosity modifier and a dispersant.
The viscosity modifier is not particularly limited, and examples thereof include cellulose derivatives such as carboxymethyl cellulose (CMC), carboxyethyl cellulose, and hydroxyethyl cellulose, polyoxyethylene or a modified product thereof, polyvinyl alcohol or a modified product thereof, a polysaccharide, and a polar solvent. be able to.

  The dispersant is not particularly limited, and includes phosphoric acid dispersants such as phosphate ester dispersants, polyoxyalkylene alkyl ether phosphate dispersants, polyoxyalkylene alkyl phenyl ether phosphate dispersants, and the like. Can be mentioned.

  The to-be-joined member used for this invention is not specifically limited, A metal material, a plastic material, a ceramic material etc. can be used. Examples of the metal material include a metal substrate such as a copper substrate, a gold substrate, and an aluminum substrate. Examples of the plastic material include polyimide, polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, and polyethylene naphthalate. Examples of the ceramic material include glass and silicon.

  Moreover, an electronic component can also be used as a member to be joined. Examples of electronic components include compound semiconductors such as silicon elements, silicon carbide elements, and gallium nitride elements.

  In the present invention, as will be described later, the metal fine particle-containing paste is applied to the second member to be bonded in an area larger than the bonding area of the first member to be bonded, so the area of the bonding surface of the second member to be bonded is the first. It is wider than the area of the joining surface of one member to be joined.

  In a preferred embodiment of the present invention, the first member to be bonded is an electronic component, and the second member to be bonded is a metal substrate.

  FIG. 1 shows the steps of the joining method of the present invention for joining the first member to be joined and the second member to be joined with the metal fine particle-containing paste. The bonding method of the present invention includes a step (step (i)) of applying the metal fine particle-containing paste 3 to the second member 2 to be bonded in a larger area than the bonding area of the first member 1. The bonding member 1 is laminated on the metal fine particle-containing paste 3, the first bonded member 1 is pressurized, and the paste has a thickness of 30% or more of the thickness of the paste 3 coated with the first bonded member 1. 3 (step (iii)) and a step (step (iii)) of heating and joining the first member 1 and the second member 2 to be joined.

Step (i) In step (i) of the bonding method of the present invention, the metal fine particle-containing paste 3 is applied to the second member 2 to be bonded in an area larger than the area of the first member 1. Thereby, as shown in the enlarged view of the joined portion of the joined body obtained by the joining method of the present invention in FIG. 2, it is possible to prevent notches from being formed due to shrinkage of the paste due to heating, and durability of the obtained joined body. Will improve.

  In the present invention, the “area of the member to be joined” means the area of the surface where the first member to be joined or the second member to be joined is joined to the other member to be joined.

  In a preferred embodiment, the metal fine particle-containing paste 3 has an area that is 0.5% or more larger than the area of the first member to be joined 1 and an area that is less than or equal to the area of the second member to be joined 2. To be applied.

  In the present invention, the thickness of the applied metal fine particle-containing paste is not particularly limited and can be 50 to 150 μm, preferably 100 to 150 μm.

Step (ii) After step (i), the first member 1 is laminated on the metal fine particle-containing paste 3 applied in step (i), the first member 1 is pressurized, 1 to-be-joined member 1 is pushed into paste 3 at a thickness of 30% or more of the thickness of applied paste 3. Thereby, it is prevented that a notch is formed due to shrinkage of the paste due to heating, and durability of the obtained bonded body is improved.

  As described above, the metal fine particle-containing paste 3 is applied to the second bonded member 2 in an area larger than the area of the first bonded member 1. In the present invention, when the first member 1 is laminated on the paste 3, the first member 1 is laminated so as not to protrude from the applied paste 3.

  The pressure at which the first member 1 is pushed into the paste 3 is not particularly limited, and the pressure at which the first member 1 can be pushed into the paste at a thickness of 30% or more of the thickness of the paste 3. If it is.

Next, in the step (iii) , the first member 1 and the second member 2 and the applied paste 3 are heated to bond the first member 1 and the second member 2 to each other. To do. The heating step of the present invention can be carried out under no pressure condition. Here, the “non-pressurized condition” means that it is not necessary to apply a high pressure using a machine or the like, and does not exclude a pressure that presses the member to be joined by a human hand. The joining method of the present invention can firmly join the members to be joined even under no pressure condition as compared with the prior art. Since the joining method of this invention can join a to-be-joined member on non-pressurized conditions, a joined body can be manufactured, without modifying the installation which uses the conventional solder as a joining material.

The heating step is performed at, for example, 200 ° C. or higher, preferably 250 ° C. or higher.
Heating may be performed from either side of the first member to be bonded 1 and the second member 2 to be bonded, but is preferably heated from the side of the first member to be bonded.

  Therefore, the second embodiment of the bonding method of the present invention includes a step of applying the metal fine particle-containing paste to the second member to be bonded in an area larger than the area of the first member to be bonded, and the first member to be bonded. Laminating a metal fine particle-containing paste, pressurizing the first member to be bonded, and pressing the first member to be bonded into the paste at a thickness of 30% or more of the thickness of the applied paste; The first member to be joined and the second member to be joined using a metal fine particle-containing paste.

  FIG. 3 is an enlarged view of the joining method of the joining method of the present invention when heated from the first joined member side. When heated from the first bonded member 1 side, the temperature on the first bonded member 1 side is increased inside the metal fine particle-containing paste 3 during heating, and the temperature is increased toward the second bonded member 2 side. A temperature gradient is produced. Accordingly, the paste 3 on the first bonded member 1 side is sintered first, and then the paste 3 on the second bonded member 2 side is sintered. When the solvent contained in the paste 3 is vaporized by the temperature rise and the paste 3 contracts, the paste on the first bonded member 1 side is sintered faster than the paste 3 on the second bonded member 2 side. Therefore, the paste 3 on the second bonded member 2 side contracts greatly, and as a result, the paste 3 warps toward the second bonded member 2 side. Therefore, the bonding area between the paste 3 and the second member 2 is increased, and no notch is generated. Therefore, when heated from the first member to be bonded side, the bonding area between the metal fine particle-containing paste and the second bonded body is larger than that when heated from the second member to be bonded side, and notches are also formed. Since it does not occur, the durability of the resulting bonded body is improved.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to these Examples.

Example 1
The silver nanoparticle paste shown in Table 1 was used as the metal fine particle-containing paste.

  A silicon element (7.6 mm × 7.6 mm, thickness 0.5 mm) was used as the first member to be bonded, and a copper substrate (30 mm × 15 mm, thickness 1.0 mm) was used as the second member to be bonded. .

  The silver nanoparticle paste was applied to a copper substrate with an area of 8.6 mm × 8.6 mm and a thickness of 110 μm. The silicon element was laminated on the silver nanoparticle paste, and the silicon element was pressurized and pressed into the silver nanoparticle paste by 35 μm. The silicon element, the copper substrate, and the silver nanoparticle paste were heated from the copper substrate side with a hot plate in the air under no pressure and at 250 ° C. for 30 minutes. The obtained thermal shock test of the joined body was performed 500 cycles at −55 ° C./+150° C. and −65 ° C./+175° C., respectively. It calculated and compared by valuation processing.

(Example 2)
The same procedure as in Example 1 was performed except that heating by the hot plate was performed from the silicon element side.

(Comparative example)
The same procedure as in Example 1 was performed except that the silver nanoparticle paste was applied to a copper substrate with a coating area of 7.6 mm × 7.6 mm.

  Ultrasonic microscope images before and after the thermal shock test of the joined bodies of Examples 1 and 2 and the comparative example are shown in FIGS. 4 to 7B. Here, in the ultrasonic microscope images of FIGS. 4 to 7B, the square outline represents the outline of the bonding surface of the silicon element, and the gray portion corresponds to the bonding area. In the bonded body of the comparative example, the bonding area was not ensured in the state before the thermal shock test (FIG. 4), and the silicon element was peeled off when performing the thermal shock test under the condition of −55 ° C./150° C. In the joined body of Example 1, the joining area was secured even after the thermal shock test under the condition of −55 ° C./150° C. (FIGS. 5A and 5B). However, when a thermal shock test was performed under the conditions of −65 ° C./175° C. in a wider temperature range, the bonding area after the test was greatly reduced (FIGS. 6A and 6B). In the joined body of Example 2, the joint area after the thermal shock test did not decrease under any conditions of −55 ° C./150° C. and −65 ° C./175° C. Ultrasonic microscope images of the thermal shock test under the conditions of -65 ° C / 175 ° C in Example 2 are shown in FIGS. 7A and 7B.

Table 2 summarizes the evaluation of the bonding area before and after the thermal shock test in each temperature condition of Examples 1 and 2 and Comparative Example.

  From the above results, the bonding area reduction of the joined body of the comparative example is solved by the bonding method of Example 1, and further, the bonding method of Example 2 solves the problem of the reduction of the bonding area in a wider temperature range. I was able to.

1. 1. First member to be joined 2. Second member to be joined 3. Metal fine particle-containing paste 4. Joined member 5. Joined member Paste containing fine metal particles

Claims (4)

In the joining method of joining the first member to be joined and the second member to be joined with the metal fine particle-containing paste,
Applying the metal fine particle-containing paste to the second bonded member in an area wider than the area of the first bonded member;
The first member to be bonded is laminated on the metal fine particle-containing paste, the first member to be bonded is pressed, and the first member to be bonded is applied to the paste at a thickness of 30% or more of the thickness of the paste applied. Pushing process,
Heating the method.   The joining method according to claim 1, wherein the heating is performed from the first joined member side.   The joining method according to claim 1 or 2, wherein the metal fine particle-containing paste is applied to the second member to be joined in an area that is 0.5% or more wider than the area of the first member to be joined.   The joining method according to any one of claims 1 to 3, wherein the heating step is performed under no pressure.

Images