Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2000-06-29
2002-07-02
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S209000, C428S901000, C174S251000, C174S255000
Reexamination Certificate
active
06413620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wiring substrate suited for multi-layer wiring substrate and semiconductor device package, and a method of producing the same.
2. Description of the Related Art
Multi-layer ceramic wiring substrates that allow wiring with a relatively high density have been widely used for multi-layer wiring substrates used in, for example, packaging semiconductor devices. The multi-layer ceramic wiring substrate comprises an insulating substrate made of alumina, glass ceramics or the like, and a wiring conductor made of a metal such as W, Mo, Cu and Ag coated on the surface thereof. A cavity is formed in part of the insulating substrate so that a semiconductor device is housed in the cavity. The cavity is air-tightly encapsulated with a lid.
Semiconductor devices such as IC and LSI are made with increasingly high density. Accordingly, wiring substrates used in semiconductor device packages in which semiconductor devices are mounted are required to allow for increasingly higher density, lower resistance, smaller size and lighter weight. Wiring substrates used for hybrid integrated circuits where various electronics components are mounted are also subjected to the same requirements. For these applications, a glass ceramic wiring substrate that is capable of achieving a lower dielectric constant than the alumina ceramics material and allows for lower resistance of a wiring circuit layer is viewed as promising. Glass ceramics comprises glass or a mixture of glass and a ceramic filler. The glass ceramics can be fired at a temperature lower than 1000° C., and therefore can be fired together with a metal having a low resistance such as copper or silver, thereby making it possible to produce a wiring substrate that has a low-resistance wiring circuit layer.
When forming a wiring conductor layer on the glass ceramic wiring substrate, a metallizing paste including a wiring conductor made of a metal such as Cu or Ag as a principal component is printed by screen printing on an insulating substrate made of glass ceramics. However, with such a process, it is difficult to form wiring lines of width not greater than 100 &mgr;m (particularly 80 &mgr;m or less). As a result, there has been a limitation to the reduction of wiring width, posing a threat of blocking the progress toward higher packaging density, smaller size and lighter weight. There has also been such a problem that there exist many voids and grain boundaries due to the formation of the wiring conductor by means of paste; therefore, it is difficult to decrease the electrical resistance. Also the conductive paste includes a filler such as ceramics or glass added thereto, in order to alleviate the difference in thermal shrinkage between the wiring circuit layer and the insulation layer during firing. This gives rise to another cause of hampering the effort to decrease the resistance of the wiring conductor layer.
As means for solving this problem, such a technique has been known that a wiring circuit layer is formed on the glass ceramic wiring substrate by etching a metal foil (see Unexamined Patent Publication (Kokai) No. 63-14493(1998)). However, this technique has such a problem as firing the metal foil and the glass ceramics causes the substrate to warp or crack, thus making it difficult to make practical use of the technique. This is because the glass ceramics shrinks during firing although the metal foil is a dense material and hardly shrinks.
To solve these problems, such a technique is known as forming layers (restricting sheets) of an inorganic composite, that is not sintered at the sintering temperature of the wiring substrate, on both sides of the glass ceramic wiring substrate whereon the wiring circuit layer of the metal foil is formed (see Unexamined Patent Publication (Kokai) No. 7-86743(1995)). When this laminate is sintered, planar shrinkage of the wiring substrate is restricted by the inorganic composite layers, so that the metal foil and the glass ceramics can be co-fired. Also techniques for firing a green sheet coated with a conductive paste printed on the surface thereof while restricting the planar contraction by similar means are disclosed in Unexamined Patent Publication (Kokai) Nos. 4-293978(1992), 5-28867(1993) and 5-102666(1993)
However, since the wiring circuit layer is made of the dense metal foil having high rigidity, and therefore hardly experiences thermal expansion and contraction, resulting in a significant thermal stress generated in the glass ceramics. As a result, crack would occur in the surface of the glass ceramic wiring substrate having the wiring circuit layer formed thereon in the subsequent cooling process, after the co-firing, and eventually leading to the breakage of the substrate.
There has also been such a problem that the glass ceramics is prone to crack when restricting sheet layer is removed.
The glass ceramic wiring substrate of the prior art has a thermal expansion coefficient within a range from 4 to 7 ppm/° C. at a temperature within a range from 40 to 400° C. Meanwhile printed circuit boards comprising glass-epoxy insulation layer with a Cu wiring circuit layer formed thereon are the most frequently used for the external circuit board whereon the wiring substrate is to be mounted. The printed circuit board has a very high thermal expansion coefficient of 12 to 18 ppm/° C. Heat generated during operation of a semiconductor device mounted on a wiring substrate or in a semiconductor device package is transmitted to both the wiring substrate and the printed circuit board. Thus as the operation of the semiconductor device is activated and stopped repeatedly, significant thermal stress is generated due to the difference in the thermal expansion coefficient between the wiring substrate and the printed circuit board.
This thermal stress acts on the periphery of the pad on the bottom surface of the wiring substrate and on the interface of joining wiring conductors of the external circuit board and terminals. This results in such a problem as the connection pad peels off the insulating substrate or the terminals peel off the wiring conductor. Thus it has been impossible to maintain stable electrical connection between the wiring substrate or the package and the printed circuit board over a long period of time.
The glass ceramics green sheet and the restricting sheet are joined by an organic component such as an organic binder included in these sheets. As a result, when the organic component has been decomposed and evaporated in the sintering process, shrinkage of the green sheet is restricted only by the frictional force between the restricting sheet and the green sheet.
However, the restricting sheet usually consists of only such components that becomes sintered at high temperature as alumina so that the restricting sheet would not be easily sintered. That is, the restricting sheet hardly includes glass component that would be turned into liquid phase, and takes the form of porous body in the sintering process.
The green sheet consists of a mixture of glass powder and ceramics filler powder. In the sintering process, the glass component contained in the green sheet forms liquid phase. The liquid phase component diffuses into the porous restricting sheet laminated on the surface of the green sheet. Consequently, glass content in the surface of the green sheet decreases and the surface whereon the restricting sheet is laminated tends to be insufficiently sintered.
Such a problem as described above is encountered more frequently as the glass ceramics composite includes more amorphous component after sintering the glass ceramics green sheet. As a result, surface of the wiring substrate becomes rough with many voids included therein. This causes such problems as lower strength of the substrate and diffusion of plating metal when the wiring circuit layer on the substrate surface is plated.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a ceramic wiring substrate that does not experience
Hayashi Katsura
Kawai Shinya
Kimura Tetsuya
Nishimoto Akihiko
Onitsuka Katsuhiko
Hogan & Hartson L.L.P.
Kyocera Corporation
Lam Cathy
LandOfFree
Ceramic wiring substrate and method of producing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ceramic wiring substrate and method of producing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ceramic wiring substrate and method of producing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2890396