Thermosetting flux and solder paste

Abstract

The invention aims to provide a thermosetting flux suitable for solder bonding of a semiconductor element and an electronic part and making solder bonding with a high bonding strength and a high heat resistant strength at a high temperature possible and a paste containing the flux and a non-lead type solder paste and with respect to the thermosetting flux, an epoxy resin, a hardening agent, and at least one of rosin derivatives having functional groups reactive on the epoxy resin and selected from maleic acid-modified rosin, a fumaric acid-modified rosin, and acrylic acid-modified rosin are used. The flux can be used in form of a solder paste while being mixed and kneaded with the non-lead type solder alloy powder.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No.2003-289645, filed on Aug. 8, 2003; the entire contents of which are incorporated herein by reference. FIELD OF THE INVENTION [0002] The invention relates to a thermosetting flux suitable for solder bonding of electronic parts of a semiconductor device and a solder paste using the flux. DESCRIPTION OF THE RELATED ART [0003] In assembly of a semiconductor device, a mounting step of mounting a semiconductor element at a prescribed part on a leadframeoraresinsubstrateisoneofimportantstepsaffecting the long term reliability of elements. Conventionally, as a mounting method, a solder mounting method using a low melting point alloy (solder) and a resin mounting method using a resin paste containing mainly a thermosetting resin such as an epoxy resin have been employed. Especially, in the case of a semiconductor element such as a powe...

AI Technical Summary

Benefits of technology

[0013] The invention has been accomplished in consideration of the above-mentioned problems and aims to provide a thermosetting flux suitable for solder bonding of a semiconductor element and an electronic part and

Problems solved by technology

However, any compositions are unsatisfactory in the processibility and further the compositions contain elements easy to be oxidized, so that they are inferior in the wettability and unsuitability for practical uses.

The Sn—Cu type solders have no problem in oxidation and are excellent in wettability, however they have a problem in the brittleness and are thus unsuitable for practical use.

In such a manner, presently, there is no usable non-lead type solder material as a high temperature solder.

However, in order to attain conductivity by the conductive adhesive as high as that by conventional soldering, those containing nickel or carbon as the conductive filler are unsatisfactory and presently, those containing a noble metal powder of such as silver, gold or the like as the conductive filler have to be used.

However, silver and gold cost very high as compared with the cost of a general solder material (mainly containing tin) and that becomes an obstacle to use of the conductive adhesive besides the technical problems.

Also, to use the conductive adhesive as the mounting material for a power element, there is another problem that the thermal conductivity is insufficient.

In the solder bonding using a common non-lead type solder material with a melting point of 250° C. or lower, the heat resistant strength and the bonding strength are not necessarily sufficient.

Particularly, with respect to a semiconductor element, in the wire bonding after mounting the semiconductor element or the second time or later soldering of a double-mounted type substrate bearing parts, the solder material may be re-melted when it is heated to 250° C. or higher to result in an undesirable consequence that the bonded part of the semiconductor element or the electronic part is separated or dropped.

However, this technique is based only on addition of a conventional rosin to the thermosetting resin and the resin is not reacted with the thermosetting resin but simply mixed with and exists in the thermosetting resin and therefore, the heat resistant strength is not sufficient, so that in the case of carrying out soldering at a high temperature for a non-lead type solder, the bonding part is separated to result in deterioration of the reliability of the electronic apparatuses.