JP2009070724A - Conductive paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive paste for a printed circuit board excellent in conductivity corresponding to reduction of a radius of a through-hole. <P>SOLUTION: The conductive paste used for a printed circuit board comprises metal powder containing copper powder, thermosetting resin, a reducing agent, and metal complex. The thermosetting resin contains epoxy resin or phenol resin, and, with action of the reducing agent, metal is deposited from the metal complex. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a conductive paste used for a printed circuit board.

  Up to now, the electrical connection between the front and back sides of a double-sided printed circuit board having conductor layers on both sides of the base material is so-called by providing a through hole in the substrate using a drill or laser and depositing the plating on the wall surface of the through hole by electroplating Either through-hole plating or a method of filling a through-hole with a conductive paste such as silver or copper by screen printing, which is often found in general-purpose products, is used.

  The conductive paste filling method by the screen printing method is excellent in productivity, but when silver is used as a conductor, the electrical connection is good, but there is a problem that silver migration tends to occur due to high temperature and humidity. . On the other hand, when copper is used as a conductor, the occurrence of migration is suppressed compared to silver, and therefore, the use of conductive paste using copper is widespread.

  In addition, as electronic devices have higher functions and smaller sizes, there is an increasing demand for fine pitch and high conductivity in conductive pastes.

  The conduction mechanism of the conductive paste is due to the pressure bonding between the metal powders due to the curing shrinkage of the thermosetting resin that is the binder, and the conductivity is greatly affected by the oxidation state of the metal powder surface and the curing shrinkage state of the thermosetting resin. receive.

For example, conventionally, an oxide film on the surface of a metal powder that is an insulator has an effect of increasing connection resistance in conduction by pressure bonding between metal powders, which is a conduction mechanism of a conductive paste. Therefore, as a measure for preventing the oxidation of the surface of the metal powder, there has been a report on a technique for blending a substance having a reducing action in a conductive paste (for example, Patent Documents 1 and 2). Therefore, a method of adding a reducing agent to prevent oxidation of the metal surface is taken (for example, Patent Document 3). However, due to the recent refinement, the diameter of through holes tends to be reduced, and the amount of conductive paste filled into the through holes tends to decrease, and as a result, it has been difficult to obtain sufficiently high conductivity.
JP 61-3154 A JP-A 63-286477 JP-A-8-73780

  This invention is made | formed in view of the said situation, and provides the electroconductive paste for printed circuit boards excellent in the electroconductivity corresponding to the diameter reduction of a through-hole.

  The conductive paste according to the present invention is a conductive paste used for a printed circuit board, and includes a metal powder containing copper powder, a thermosetting resin, a reducing agent, and a metal complex. .

  Furthermore, the content of the metal complex is 0.5 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the metal powder, and the addition amount of the reducing agent is 100 parts by weight of the metal complex. On the other hand, it may be 100 parts by weight or more and 1000 parts by weight or less. Thereby, it becomes possible to sufficiently secure the connection point where the deposited metal particles are metal-bonded to the metal powder containing copper at the time of thermosetting.

  ADVANTAGE OF THE INVENTION According to this invention, the electrically conductive paste for printed circuit boards excellent in the electroconductivity corresponding to the diameter reduction of a through-hole can be provided.

  Hereinafter, preferred embodiments of the conductive paste of the present invention will be described in detail.

  The conductive paste of the present invention is a conductive paste used for a printed circuit board, and is composed of a resin composition including a metal powder containing copper powder, a thermosetting resin, a reducing agent, and a metal complex. Has been. As the use of the printed circuit board, a through hole is formed in the laminated board on which the printed circuit is formed using a drill or a laser, and the through hole is filled with a conductive paste using a screen printing method or the like. Create a double-sided printed circuit board by electrically conducting both sides, create a conductive circuit with conductive paste on the surface of the laminate using screen printing, etc., and cover the entire printed circuit board It is used for the purpose of forming a conductive member on a printed circuit board, such as creating an electromagnetic wave shielding layer.

Hereinafter, each component will be described.

  As metal powder containing the copper powder used by this embodiment, what consists of gold | metal | money, silver, and nickel is preferable. Among these, in addition to metal powder made of a single metal, metal powder made of an alloy containing two or more kinds of metals, and those coated with these kinds of metal powders can also be used. From the viewpoint of low cost, it is preferable to use copper powder.

  The shape of the metal powder is not particularly limited, but conventionally used ones such as dendrites, spheres, and flakes can be used. Further, the particle diameter is not particularly limited, but usually, the average particle diameter is preferably 1 μm or more and 50 μm or less.

  It is preferable that content of the said metal powder is 300 to 1000 weight part with respect to 100 weight part of thermosetting resins. Good electroconductivity is acquired as content is in this range.

  The conductive paste of this embodiment uses a thermosetting resin. The thermosetting resin used in the present invention functions as a binder resin for the conductive paste. As the thermosetting resin, epoxy resin, melamine resin, unsaturated polyester resin, phenol resin and the like can be used.

  Examples of the epoxy resin include bisphenol type epoxy resins such as bisphenol A type epoxy resins, bisphenol F type epoxy resins and brominated bisphenol type epoxy resins, biphenyl type epoxy resins, biphenyl aralkyl type epoxy resins, stilbene type epoxy resins, Epichlorohydrin on hydroxyl groups such as phenols, phenol resins and naphthols, such as phenol novolac epoxy resins, cresol novolac epoxy resins, naphthalene epoxy resins, dicyclopentadiene epoxy resins and dihydroxybenzene epoxy resins Epoxy compounds produced by reacting olefins, epoxy resins obtained by oxidizing olefins with peracids, glycidyl ester epoxy resins and glycidyl amides Type epoxy resins and the like may be used singly or in combination of two or more of them. Among these, a glycidylamine type epoxy resin is particularly preferable.

  Moreover, as a phenol resin, the resol type phenol resin which methylated phenol and formaldehyde under the alkali catalyst is preferable. Thereby, the crimping | compression-bonding of the copper powder for providing high electroconductivity can be performed effectively.

  The conductive paste of the present invention uses a reducing agent. The reducing agent is not particularly limited as long as it has a reducing function, but is preferably an alcohol or acid having one or more hydroxyl groups, and examples thereof include glycerin and ethylene glycol. Moreover, you may use the glycidyl amine type epoxy resin used as a thermosetting resin. Thereby, since it has the function as a binder and the function as a reducing agent, it is suitable.

  The glycidylamine type epoxy resin is preferably an epoxy resin having at least three epoxy groups in one molecule. Thereby, since the network-like three-dimensional crosslinked structure is formed by heat curing, the reliability in the temperature cycle test and the heat resistance reliability during reflow can be improved. Examples of the glycidylamine type epoxy resin include those represented by the following general formula (1-1) or general formula (1-2). Since it contains a nitrogen atom, it is possible to obtain a conductive paste having excellent adhesion and excellent through-hole connection reliability.

  The glycidylamine-type epoxy resin preferably further has one or more aromatic groups in one molecule, and a glycidylamine-type epoxy resin represented by the following general formula (2) is particularly preferable.

  When the amount of the reducing agent is 50 parts by weight or more and 1000 parts by weight or less with respect to 100 parts by weight of the metal complex, the metal complex can be sufficiently reduced. More preferably, it is 100 to 1000 weight part. If it is this range, the workability of a paste and a moldability become favorable and are preferable.

  The conductive paste used in the present invention uses a metal complex. The metal complex is preferably a carboxylate containing silver or copper. Specific examples include copper (II) acetylacetonate, copper (II) benzoate, copper (II) acetate, and copper (II) propionate.

  The content of the metal complex is preferably 0.5 parts by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the metal powder, and more preferably 1 part by weight or more with respect to 100 parts by weight of the metal powder, 20 Less than parts by weight. When the metal complex is within this range, metal particles sufficient to connect or bind the metal powder containing copper in the conductive paste between the particles can be precipitated.

  Various methods can be applied as a method for producing the conductive paste, and a kneading apparatus such as a planetary stirrer or a three-roller can be used. It is common to obtain the components after mixing using a mixing and dispersing device. Moreover, it is possible to add various antioxidants, a dispersing agent, fine fused silica, a coupling agent, an antifoaming agent, a solvent, etc. in a composition as needed.

  Further, as a mechanism for improving the conductivity, the conductive paste contains a reducing agent and a metal complex. Thereby, when the conductive paste is cured by heating, fine metal particles are precipitated from the metal complex by the reducing action of the reducing agent contained in the conductive paste. The deposited metal particles are considered to be able to provide a conductive paste having high conductivity by connecting or binding metal powder containing copper in the conductive paste.

  Hereinafter, the present invention will be described using examples and comparative examples, but the present invention is not limited thereto.

  As the metal powder, electrolytic copper produced by Fukuda Metal Foil Powder Industry Co., Ltd. was used. As the thermosetting resin, triglycidyl-p-aminophenol was used as the glycidylamine type epoxy resin, phenol resin PR-54463 manufactured by Sumitomo Bakelite was used as the phenol resin, and bisphenol A type epoxy resin was used as the epoxy resin. . And according to the compounding ratio of Table 1, it knead | mixed with the raikai machine and obtained the copper paste. The copper paste thus prepared was cured at 180 ° C. for 30 minutes, and the volume resistance was measured.

Judgment criteria for measurement results of volume resistance ○: Less than 1 × 10 ⁻⁴ Ω · cm.
Δ: 1 × 10 ⁻⁴ Ω · cm or more and less than 1 × 10 ⁻³ Ω · cm.
×: 1 × 10 ⁻³ Ω · cm or more.

From the above results, all of the conductive pastes of Examples 1 to 6 were conductive pastes having an initial resistance value of less than 1 × 10 ⁻³ Ω · cm.

Claims (8)

A conductive paste used for printed circuit boards,
Metal powder containing copper powder,
A thermosetting resin;
A reducing agent,
A metal complex;
A conductive paste comprising:   The conductive paste according to claim 1, wherein a metal is precipitated from the metal complex by the action of the reducing agent.   The conductive paste according to claim 2, wherein the thermosetting resin includes an epoxy resin.   The conductive paste according to claim 2, wherein the thermosetting resin includes a phenol resin.   The conductive paste according to claim 3 or 4, wherein the metal complex is a carboxylate containing silver or copper.   The conductive paste according to claim 5, wherein the content of the metal complex is 0.5 parts by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the metal powder.   The conductive paste according to claim 6, wherein the reducing agent is an alcohol having one or more hydroxyl groups or an acid. The conductive paste according to claim 7, wherein an amount of the reducing agent added is 50 parts by weight or more and 1000 parts by weight or less with respect to 100 parts by weight of the metal complex.