Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Patent
1996-09-30
1998-09-15
Lam, Cathy F.
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
428615, 428660, 428662, 428671, 428673, 2281221, 22818021, 174259, H01L 2314, H05K 338
Patent
active
058076263
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a ceramic circuit board formed in such a manner that a metal circuit plate is bonded to a ceramic substrate with a brazing material and, more particularly, to a ceramic circuit board in which the bonding strength of a metal circuit plate is high, heat-cycle resistance characteristics are excellent, and reliability is high.
BACKGROUND ART
A conventional ceramic circuit board in which a metal circuit plate having conductivity is integrally bonded to the surface of a ceramic substrate such as an alumina (Al.sub.2 O.sub.3) sintered body having excellent insulating characteristics is popularly used as a constituent part of a semiconductor device.
As a conventional method of integrally bonding a ceramic substrate and a metal circuit board to each other, a refractory metal method (metalize method), a direct bonding method, or an active metal method is employed. The refractory metal method is a method of baking a refractory metal such as Mo or W on a ceramic substrate surface; the direct bonding method is a method of directly heat-bonding a metal circuit plate to a ceramic substrate surface using an eutectic liquid phase between a metal circuit plate component and oxygen as a bonding agent without using a brazing material or the like; and the active metal method is a method of integrally bonding a metal circuit plate and a non-oxide-based ceramic substrate to each other through a brazing material containing an active metal such as Ti. In particular, in order to obtain a ceramic circuit board having high strength, good sealing properties, and good reliability, the active metal method of the above methods is generally used.
The ceramic circuit board requires high bonding strength as the base of structure strength. On the other hand, in order to hold a structure which sufficiently withstands a thermal cycle which repetitively acts under the operation conditions of a semiconductor element serving as a mounted heat-generating part, formation of cracks caused by the linear expansion coefficient difference between the ceramic substrate and the metal circuit plate in a thermal cycle test (TCT) must be suppressed.
However, in a ceramic circuit board in which a metal circuit board is integrally bonded to a ceramic substrate by a brazing material containing an active metal such as Ti, a brittle reaction phase is easily generated on the bonding interface. For this reason, the following problems are posed. That is, sufficient bonding strength cannot be obtained, cracks are easily formed in the bonded portion of the ceramic substrate, and a circuit board having high reliability cannot be obtained.
Even if the ceramic substrate and the metal circuit plate are temporarily bonded to each other at high bonding strength, fine cracks are formed in the stage in which a thermal cycle to be applied is low. When the cracks grows with time, the bonding strength is degraded, and the ceramic substrate is broken or chipped at last. Therefore, reliability cannot be easily maintained for a long period of time.
The present invention has been made to solve the above problems, and has as its object to provide a ceramic circuit board in which cracks are effectively suppressed from being formed even after a thermal cycle is repeatedly applied for a long period of time, i.e., a ceramic circuit board having so-called excellent heat-cycle resistance characteristics and high reliability.
DISCLOSURE OF INVENTION
In order to achieve the above object, the present inventor prepared ceramic substrates with changing the type and amount of element contained in the brazing material for bonding the ceramic substrate and the metal circuit plate, and compared and examined influences of the types of elements contained in the brazing material on the bonding strength of the circuit board, heat-cycle resistance characteristics, and the strength characteristics of the bonded portion.
As a result, the following finding could be obtained. When a substrate and a circuit plate were bonded to each other using a brazin
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Kabushiki Kaisha Toshiba
Lam Cathy F.
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