Radiation imagery chemistry: process – composition – or product th – Imaged product – Multilayer
Patent
1996-07-22
1999-12-21
Nuzzolillo, Maria
Radiation imagery chemistry: process, composition, or product th
Imaged product
Multilayer
430320, 4302861, 430156, 430166, 430167, 430190, 430194, G03C 300
Patent
active
060047054
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a ceramics green sheet suitably used for forming sintered ceramics substrate and the like. More particularly, the present invention relates to a green sheet made of ceramics, which is suitably employed for forming sintered ceramics substrates on which semiconductor devices connected to one another are mounted with a high density, especially for forming multilayer ceramics substrates.
PRIOR ART
Processes for producing multilayer ceramics substrates are largely classified into thick film printing lamination method and green sheet method. In the thick film printing lamination method, electroconductive paste and insulation paste are alternately printed and laminated to form a multilayer structure. After repeating printing and drying, sintering is carried out in one process.
In the green sheet lamination method, electric conductors are printed when the sheets are laminated. A number of green sheets in which via holes (holes which are through each layer) and through holes (holes which are through the entire multilayer sheet)(via holes and through holes are hereinafter collectively referred to as "via holes") are laminated and bonded by heat compression bonding, followed by sintering. This process has, as will be described in detail, a drawback in that the diameter of the via holes cannot be made small and a number of molds and jigs are necessary for forming the via holes.
Conventional ceramics green sheets are produced usually by appropriately blending ceramics powder, an organic binder, plasticizer, solvent and, if necessary, a dispersant, mixing these components to obtain a slurry, and forming green sheets from the obtained slurry by the known doctor blade method or the like, as described in Japanese Laid-open Patent Application (Kokai) Nos. 1-232797 and 2-141458.
After shaping the green sheets into a desired shape by using a cutter or a punching tool, via holes are formed in the green sheets by using a metal mold or a punching die, or by using a laser beam.
For example, in a process for producing a multilayer substrate by green sheet multilayer lamination method, a slurry which is the material for forming the green sheets is continuously and thinly spread on a carrier film to form a green sheet. The green sheet is then punched to a requisite work size and via holes are formed therein. In the via holes, electroconductive paste is embedded by an ordinary screen printing method. In cases where the thickness of the green sheet is as small as 50 .mu.m or less, holes are formed in the green sheet together with the carrier film to provide the via holes.
However, in cases where the via holes are formed in the green sheets by using a conventional punching die made of tungsten carbide, since the strength of the tungsten carbide is low, it is difficult to prepare a punch having a small diameter. Further, the production yield of the green sheets in which via holes are formed by using a punch having a small diameter is extremely low, it is practically impossible to form a hole having a diameter of not more than 0.1 mm. Thus, the practical value of the conventional green sheets produced by this method is extremely low. Since the area occupied by via holes in a substrate is proportional to the square of the diameter of the via holes, a number of advantages such as compaction and high densification of the circuit substrates are expected to be obtained if fine via holes can be formed. However, as long as the via holes are formed by the conventional methods, it is impossible to attain such advantages.
Further, if a tungsten carbide tool is used, the green sheets are contaminated with cut powder which may cause an insulation failure. In addition, in cases where the holes are formed by using a tungsten carbide punch, since the ceramics to be processed is harder than tungsten carbide, the tungsten carbide punch is attrited and must be frequently replaced. The cost for forming the holes is expensive, which is 50% or more of the cost for producing the substrates.
Although holes a
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Iwanaga Keiji
Kitagawa Takao
Masaki Takaki
Yoshimura Akiko
Miller Austin R.
Nuzzolillo Maria
Toray Industries Inc.
Weiner Laura
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