JP4483562B2 - Method for forming conductor wiring - Google Patents

Description

The present invention relates to a method of forming a conductive wiring for producing a conductive composition used for bonding the formed and electronic components of the conductor wiring on the substrate.

  Conventionally, a conductive paste, a conductive adhesive, or the like in which a metal powder such as silver or palladium is dispersed in a resin has been used in forming a conductor wiring by printing or mounting an electronic component. However, in recent years, with the miniaturization and thinning of electronic devices, there has been an increasing demand for circuit miniaturization and high density. In order to solve these problems, developments have been made to reduce the junction resistance of electronic component mounting parts and the sheet resistance of conductor wiring.

  Hereinafter, conventional conductive compositions will be described. FIG. 3 is a cross-sectional view for explaining an example of a conventional conductive composition. FIG. 3A is a state immediately after the conductive composition is applied on the substrate 550, and FIG. The state after heat-processing the electrically conductive composition apply | coated on the board | substrate 550 is shown.

  As shown in FIG. 3A, metal particles 530 in which the surface of a nucleus 510 made of a metal such as copper is coated with a low melting point metal layer 520 are dispersed in a resin binder 540. In this example, the weight ratio of the metal particles 530 to the resin binder 540 is 80 to 99.8% by weight. Further, in FIG. 3, only four metal particles 530 that are close to each other are shown, but in reality, a large number of metal particles 530 are dispersed, and the majority of metal particles 530 are in contact with each other. The metal particles 530 may exist alone.

  Note that the core 510 made of metal is a highly conductive metal such as copper (Cu) or nickel (Ni), which has good wettability to the low melting point metal layer 520 and is not compatible. It is said that it is good. Further, the low melting point metal layer 520 is a metal that melts without changing the material of the resin binder 540, and for example, tin (Sn), indium (In), or the like can be used. Further, the resin binder 540 may be either a thermosetting material or a thermoplastic material. For example, a phenol-based, epoxy-based, or silicone-based material can be used.

  By applying heat treatment after applying such a conductive composition, the low melting point metal layer 520 is melted as shown in FIG. 3B, and the nuclei 510 are connected by the melted low melting point metal layer 520. Thus, it is supposed that the state connected by the low melting point metal layer 520 can substantially improve the conductivity substantially compared with the mere mechanical contact (see, for example, Patent Document 1). .

As another method for improving the conductivity of the conductive paste or conductive adhesive, nickel (Ni) particles having a large number of protrusions on the surface and base metal particles having a spherical surface and lipophilicity are contained in a resin binder. Conductive adhesives blended and kneaded with these materials have also been developed. In this case, first, a large number of nickel (Ni) particles are brought into contact with each protrusion, whereby the frequency of contact between the particles is increased, and the conductivity is increased. Furthermore, the conductivity is further improved by the protrusion of the nickel (Ni) particles being pierced into the base metal particles. In this case, the nickel (Ni) particles having protrusions can be produced, for example, by coating the surface of zinc oxide whisker with a nickel layer (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 5-28829 JP-A-11-92727

  In the first conventional example, metal particles such as copper (Cu) whose surface is plated with a low melting point metal are used, and the contacted metal particles are connected by melting of the low melting point metal layer. However, since there is a resin binder on the surface of the low melting point metal layer, even if the metal particles come into contact with each other and the low melting point metal layer melts, it is relatively difficult to break and bond the resin binder on the surface. However, it seems not to be able to fully melt and join. Therefore, when such a conductive adhesive is used, as a result of a part to be melt-bonded, a part to be melted but not joined, and a part that is not in contact from the beginning and exists alone, the conduction resistance cannot be sufficiently reduced. There seems to be a case.

  The second conventional example is a conductive adhesive in which nickel (Ni) particles having protrusions on the surface and base metal particles are blended and kneaded in a resin, but the protrusions of nickel (Ni) particles are base metal. By piercing the particles and breaking the oxide film on the surface of the base metal particles, they are brought into contact with the internal base metal particles to be connected to each other. As the base metal particles, copper (Cu), zinc (Zn), tin (Sn) and the like are preferable. However, for example, since copper (Cu) has a relatively large hardness, the external force for the protrusion of the nickel (Ni) particle to break the oxide film of the base metal particle made of this copper (Cu) and pierce the base metal particle inside, The curing temperature alone is not sufficient.

  Therefore, in this case as well, the protrusions of the nickel (Ni) particles come into contact with the copper (Cu) particles, and some of them break the oxide film and come into contact with the internal copper (Cu). It is estimated that this phenomenon does not occur. For this reason, it is presumed that the resistance cannot be lowered sufficiently particularly when the curing temperature is low.

The present invention is intended to solve the conventional problems described above, it aims to provide a method for forming a can Ru conductors wiring to improve the overall conductivity by reducing the contact resistance between the conductive particles And

The method for forming a conductor wiring according to the present invention has a first binder particle comprising a first nucleus whose surface is covered with a low melting point metal layer in a resin binder, and a plurality of conductive protrusions on the surface. Second conductive particles composed of second nuclei are dispersed, the melting temperature of the low melting point metal layer is lower than the curing temperature of the resin binder, and the first nuclei and the second nuclei A step of forming a circuit pattern made of the conductive composition on a wiring board using a conductive composition of which one is a ferromagnetic particle; and heating the circuit pattern to a temperature equal to or higher than a curing temperature of the resin binder. Forming a cured wiring pattern, wherein the circuit pattern is heated at a temperature equal to or higher than the curing temperature of the resin binder in a direction perpendicular to the circuit pattern forming surface of the wiring board. Exchange And applying a magnetic field or DC magnetic field.

  In this forming method, either the first nucleus or the second nucleus is a ferromagnetic particle, and in the step of heating the circuit pattern at a temperature higher than the curing temperature of the resin binder, it is perpendicular to the circuit pattern formation surface of the wiring board. Alternatively, an AC magnetic field or a DC magnetic field may be applied in at least one of the horizontal direction and the horizontal direction.

  By this method, it is possible to easily form a highly conductive conductor wiring. Further, by applying an AC magnetic field or a DC magnetic field in at least one of the vertical direction and the horizontal direction to the circuit pattern forming surface of the wiring board, the first conductive particles and the second conductive particles are joined. Can be performed more reliably. That is, when the resin binder is softened, the ferromagnetic particles can be easily moved by the magnetic field, so that the conductive protrusions of the second conductive particles are controlled by controlling the direction and strength of the magnetic field. The ratio of biting into and joining the conductor particles can be greatly improved.

In the method for forming a conductor wiring according to the present invention, the conductive protrusions of the second conductor particles pierce the first conductor particles at the time of heat curing, and are formed on the surfaces of the conductive protrusions and the first conductor particles. Since the low-melting-point metal layer is bonded to the metal, the bonding resistance between the conductor particles can be greatly reduced. As a result, a low-resistance conductor wiring can be obtained at a relatively low heating temperature, and it is possible to produce various circuit boards at a low cost.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected about the same element and description may be abbreviate | omitted.

  FIG. 1 is a schematic diagram for explaining a method of forming a conductor wiring using the conductive composition according to the embodiment of the present invention.

  Fig.1 (a) is a schematic cross section which shows the state printed on the board | substrate 30 by using the electrically conductive composition concerning this Embodiment as a conductor paste. In the printed wiring pattern 24 in a state where the conductive composition of the present embodiment is printed as a conductor paste, the first conductor particles 10 in which the low melting point metal layer 14 is formed on the surface of the first core 12; Second conductive particles 20 having conductive protrusions 18 on the surface of the second nucleus 16 are dispersed in the resin binder 22. That is, as shown in FIG. 1A, the first conductor particles 10 and the second conductor particles 20, the first conductor particles 10 and the second conductor particles 20 are respectively Many are not in direct contact and are not yet conductive in this state.

  FIG. 1B shows a state after the solvent is evaporated and then thermally cured. Due to the heat treatment during the thermosetting, the conductive protrusions 18 of the second conductor particles 20 are formed on the surface of the first conductor particles 10 with the low melting point as the solvent evaporates and the resin binder 22 cures and shrinks. The low melting point metal layer 14 melts after the heating process and bites into the first nucleus 12 through the metal layer 14, and the conductive protrusion 18 and the metal bond are also generated. When curing of the resin binder 22 is completed in a state where such a metal bond is generated, the printed wiring pattern 24 becomes a conductive wiring 240 having conductivity. This conductor wiring 240 can be reduced in resistance as compared with the conventional conductor wiring because the ratio of the conductive particles being metallicly bonded to each other is increased.

  In addition, as a material of the 1st nucleus 12 of the 1st conductor particle 10, the softer metal than the material of the 2nd nucleus 16 of the 2nd conductor particle 20 is desirable. Further, as the low melting point metal layer 14 to be coated on the surface of the first nucleus 12, a layer made of an alloy containing tin (Sn), indium (In), tin (Sn) or indium (In) is formed. preferable. However, it is not limited to these metal materials. For example, an alloy made of indium (In) and gallium (Ga) or the like is not particularly limited as long as it is a material that melts at the curing temperature of the resin binder 22 and is metal-bonded to the second conductor particles 20.

  As the second core 16 of the second conductor particle 20, the protrusion is metal-grown on the surface of a metal such as gold (Au), silver (Ag), copper (Cu), nickel (Ni), or A zinc oxide whisker having a tetrapod shape and the surface plated with the above metal can be used.

  Moreover, as the resin binder 22 which disperse | distributes the 1st conductor particle 10 and the 2nd conductor particle 20, an epoxy-type and an acrylic-type resin material can be used. The resin binder 22 is desirably adjusted so as to have curing shrinkage. By doing in this way, since the conductor particles receive a force approaching due to contraction, the conductive protrusions 18 of the second conductor particles 20 are likely to pierce the first conductor particles 10. Note that the curing shrinkage rate of the resin binder 22 can be adjusted by adjusting the number of functional groups in the components of the resin material constituting the resin binder 22.

  In addition, although the electrically conductive composition of this Embodiment can be manufactured by a normal mixing | blending and kneading method, it can also be set as the following manufacturing methods. That is, the first conductive particles 10 are blended in the resin binder 22 and kneaded to form the first conductive resin binder material. Next, the second conductive particles 20 are blended in the same resin binder 22 and kneaded to form a second conductive resin binder material. Thus, after forming each separately, the 1st conductive resin binder material and the 2nd conductive resin binder material are knead | mixed, and the 1st conductor particle 10 and the 2nd conductor particle 20 are mixed. A conductive composition is obtained. According to such a manufacturing method, the 1st conductor particle 10 and the 2nd conductor particle 20 can be mixed more uniformly compared with the conventional manufacturing method.

  FIG. 2 is a schematic diagram for explaining a method of forming a conductor wiring using the conductive composition according to the modification of the embodiment of the present invention. In the case of the conductive composition of this modification, the first core 120 of the first conductor particle 100 is characterized by being a magnetic particle.

  As the conductive particles having magnetism, a metal or an intermetallic compound that is oriented in the direction of the lines of magnetic force when a magnetic field is applied can be used. For example, iron (Fe), nickel (Ni), or cobalt (Co) can be used. Furthermore, particles of manganese (Mn) magnets or rare earth magnets, or those in which a plating layer made of a conductive metal is formed on the surface of these particles can also be used.

  After the conductor paste made of such a conductive composition is printed on the substrate 30, a magnetic field is applied as shown in the figure from the state of fluidity. It is desirable to apply the magnetic field until the resin binder 22 is cured by the heating process. By applying the magnetic field in this way, the first conductive particles 100 are locally moved by the action of the magnetic field. By this movement, the conductive protrusions 18 of the second conductor particles 20 are likely to pierce the first conductor particles 100, and metal bonds are also likely to occur.

  The direction of the magnetic field to be applied may be only in the direction perpendicular to the substrate 30 (direction indicated by arrow A), or may be only in the horizontal direction (direction indicated by arrow B) with respect to the substrate 30 or alternatively. You may apply. Furthermore, if the direction of the magnetic field is changed at regular intervals, the first conductor particles 100 vibrate, and the number of contacts with the second conductor particles 20 in the vicinity increases. Therefore, the probability that the conductive protrusion 18 of the second conductor particle 20 pierces the first conductor particle 100 increases. As a result, metal bonds are more likely to occur. Note that the direction and magnitude of the magnetic field may be determined experimentally including the conductivity and the coating thickness.

  A low melting point metal layer may also be formed on the surface of the second conductor particles. Thus, by forming the low melting point metal layer on both the first conductor particles and the second conductor particles, it is possible to further facilitate the metal bond.

The method for forming a conductor wiring according to the present invention is a method for producing a conductive composition used for forming a conductor wiring on a substrate or connecting an electronic component, wherein a metal bond between conductor particles dispersed in a resin binder is formed. Therefore, a low-resistance conductor wiring can be realized, which is useful in the field of wiring boards and the field of mounting electronic components.

The schematic diagram for demonstrating the method to form a conductor wiring using the electrically conductive composition concerning embodiment of this invention The schematic diagram for demonstrating the method of forming a conductor wiring using the electrically conductive composition of the modification of the embodiment Sectional drawing for demonstrating an example of the conventional electrically conductive composition

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,100 1st conductor particle 12,120 1st nucleus 14,520 Low melting-point metal layer 16 2nd nucleus 18 Conductive protrusion 20 2nd conductor particle 22,540 Resin binder 24 Printed wiring pattern 30, 550 Substrate 240 Conductor wiring 510 Core 530 Metal particle

Claims (4)

In a resin binder, a first conductive particle composed of a first nucleus whose surface is covered with a low melting point metal layer, and a second conductivity composed of a second nucleus having a plurality of conductive protrusions on the surface. and body particles are dispersed, or one the melting temperature of the low melting point metal layer is rather low than the curing temperature of the resin binder, and any one of the first nucleus and the second nucleus ferromagnetic particles Forming a circuit pattern made of the conductive composition on a wiring board using the conductive composition which is:
Forming a cured wiring pattern by heating the circuit pattern to a temperature equal to or higher than the curing temperature of the resin binder,
A method of forming a conductor wiring, wherein in the step of heating the circuit pattern at a temperature equal to or higher than the curing temperature of the resin binder, an AC magnetic field or a DC magnetic field is applied in a direction perpendicular to the circuit pattern forming surface of the wiring board. In a resin binder, a first conductive particle composed of a first nucleus whose surface is covered with a low melting point metal layer, and a second conductivity composed of a second nucleus having a plurality of conductive protrusions on the surface. and body particles are dispersed, or one the melting temperature of the low melting point metal layer is rather low than the curing temperature of the resin binder, and any one of the first nucleus and the second nucleus ferromagnetic particles Forming a circuit pattern made of the conductive composition on a wiring board using the conductive composition which is:
Forming a cured wiring pattern by heating the circuit pattern to a temperature equal to or higher than the curing temperature of the resin binder,
In the step of heating the circuit pattern at a temperature equal to or higher than the curing temperature of the resin binder, an AC magnetic field or a DC magnetic field is applied in a vertical direction and a horizontal direction to the circuit pattern forming surface of the wiring board. Method. 3. The method of forming a conductor wiring according to claim 2, wherein in applying the magnetic field, the direction of the magnetic field is changed at regular intervals. 3. The method of forming a conductor wiring according to claim 2, wherein in applying the magnetic field, a vertical direction and a horizontal direction are alternately applied.

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