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1. IN5772/DELNP/2007 - CONDUCTIVE PASTE

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[ EN ]
DESCRIPTION CONDUCTIVE PASTE TECHNICAL FIELD The present invention relates to a conductive paste that is favorably used, for example, for filling of via holes in a printed circuit board.Priority is claimed on Japanese Patent Application No. 2005-16965, filed on January 25, 2005, the content of which is incorporated herein by reference. BACKGROUND ARTMaterials containing silver powder, copper powder, and silver-coated copper powder have conventionally been used as conductive particles in conductive pastes used for filling of via holes in printed circuit boards. However, since these conductive particles generally have a high melting point, fusion splice between particles by heat treatment is hindered. As a result, they have the drawback of exhibiting poor conductive connection reliability in thermal shock tests and moisture resistance tests and the like.Patent Document 1 discloses art that increases the conductive connection reliability by forming metallic bonds between alloy layers that are formed on the outer peripheral portions of particles and consist of metallic particles having a low melting point.In addition, Patent Documents 2 to 5 disclose art in which alloy particles are fusion spliced via thermal processing, and by using alloy particles whose melting points change, a conductive paste with stabilized conductivity is achieved. Among these, Patent Document 2 discloses conductive particles that do not substantially contain lead (Pb), exhibit an exothermic peak by differential scanning calorimetry, and have aplurality of melting points that are defined as endothermic peak temperatures by differential scanning calorimetry. The lowest temperature melting point among the plurality of melting points (initial lowest melting point) is considered to be caused by the melting of the surface portion of the particles. Particularly the surface portion of the conductive particles is provided with a component that exhibits this initial lowest melting point. Therefore, when the conductive particles are heated to a temperature of the initial lowest melting point or higher by heat treatment, at least the surface portion thereof melts, and as a result, firm connectability is exhibited between the conductive particles so that conductivity is stabilized.Also, Patent Documents 6 and 7 disclose conductive pastes that employ specified conductive particles and epoxy resins.Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2002-94242Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2004-234900Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2004-223559Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2004-363052Patent Document 5: Japanese Unexamined Patent Application, First Publication No. 2005-5054Patent Document 6: Japanese Patent Granted Publication No. 3038210Patent Document 7: Japanese Patent Granted Publication No. 2603053 DISCLOSURE OF INVENTIONPROBLEM TO BE SOLVED BY THE INVENTIONHowever, the conductive paste that includes the conductive particles disclosed in Patent Document 1 relies on interlayer connections of particles solely with metal bonding without using a thermosetting resin. Therefore, problems in the conductive connection reliability arise due to the generation of cracks etc. in reliability tests caused by the difference in the coefficient of thermal expansion with an insulation material.Also, even when using a conductive paste that includes a thermosetting resin such as those disclosed in Patent Documents 2 to 5 and Patent Documents 6 and 7, conductivity is not sufficiently stabilized when the diameter of the via holes is small, leading to a tendency for the conductive connection reliability to be inadequate.The present invention was achieved in view of the above circumstances, and has as its object to provide a conductive paste with favorable conductivity and excellent conductive connection reliability.MEANS FOR SOLVING THE PROBLEMSThe present inventors have perfected this invention as the result of concerted study, with the discovery that a combination of conductive particles and binder included in a conductive paste imparts an effect on the conductivity of the conductive paste and the reliability thereof.The conductive paste of the present invention includes a binder containing a thermosetting resin and conductive particles, in which the lowest exothermic peak temperature TI (degrees C) among at least one exothermic peak obtained by differential scanning calorimetry of the binder and the lowest endothermic peak temperature t1 (degrees C) among at least one endothermic peak obtained by differential scanning calorimetry of the conductive particles satisfy Equation (1).t1-20