Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2001-09-18
2004-05-11
Pert, Evan (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S255000, C174S258000, C428S304400, C428S321300
Reexamination Certificate
active
06734375
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a circuit board used for electronic equipment, more specifically, it relates to a circuit board having an interstitial inner via hole structure, a method for manufacturing the same, and a circuit board electrically insulating material used therefor.
BACKGROUND OF THE INVENTION
In recent years, as miniaturization, light weight and high performance of electronic equipment have been required, there has been a strong demand not only for a small size and light weight of a circuit board but also for higher speed for processing signals and high density mounting, and the like. In order to meet such demands, in the field of a circuit board technology, a technology for increasing the number of layers in a laminate structure, a technology of making the diameter of an inner via hole smaller, a technology for making circuit patterns finer, and the like have been developed rapidly, and circuit boards having various structures have been proposed or put into practice. As one example, the present assignee has developed a circuit board having an all-layer IVH (interstitial inner via hole) structure, in which the interlayer electric connection is secured with an inner via hole filled with a conductive paste in place of a through hole structure that has been a usual method in conventional circuit boards (see, for example, JP7 (1995)-14746 4 A). This circuit board has features that no through hole is needed and inner via holes can be arranged at arbitrary positions, and therefore, this circuit board has a high capacity of wiring, a high degree of freedom in design, shortening of wiring, etc. Thus, this circuit board is suitable for signal processing at high speed and high density mounting. In this circuit board, the conductive paste filled in the through hole is compressed and hardened simultaneously with molding of the laminate, thereby providing an inner via hole for securing an interlayer electrical connection. Therefore, this circuit board needs an electrically insulating material having such a compressive performance that permits sufficient compression of a conductive paste and is capable of maintaining the shape of the inner via hole. In general, as a conductive paste, a prepreg obtained by impregnating an aramid non-woven fabric with a thermosetting resin is used. The compressive performance of the aramid prepreg can be achieved by the melt flow of the thermosetting resin and the effect of defoaming of any remaining air foam. The maintenance of the shape of the inner via hole can be achieved by rigid property of the aramid non-woven fabric.
In the future, in a view that a circuit board will increasingly be required to have a finer circuit pattern, a smaller diameter of an inner via hole and an increase in number of the layers of the laminate structure and the like, it is extremely important to make the electrically insulating layer to be homogenized and ultra-thin. However, a non-woven fabric made of an aramid staple fiber having a diameter of 10-20 &mgr;m may cause a non-negligible non-uniformity of the physical property in a micro area depending on the direction of the fiber. Furthermore, a satisfactory thin layer cannot be obtained because there is a limitation to the number of fibers in the thickness direction.
SUMMARY OF THE INVENTION
With the foregoing in mind, it is an object of the present invention to provide a circuit board electrically insulating material and a circuit board, in which an electrically insulating layer is made to be homogenized and ultra-thin and the connection reliability of the inner via hole including a conductive paste is improved so as to achieve higher density mounting, and also provide a method for manufacturing the same.
In order to achieve the above-mentioned objectives, the circuit board electrically insulating material of the present invention is a circuit board electrically insulating material in sheet form, insulating sheet, including a porous sheet; and a resin layer laminated to a surface of the porous sheet, wherein at least a central portion of the porous sheet is not impregnated with resin and the circuit board insulating material has a thickness sufficiently small for use in a circuit board. In other words, the circuit board electrically insulating material of the present invention includes a porous sheet provided with a semi-hardened resin layer on both surfaces or one surface. In the circuit board electrically insulating material, the pores of the porous sheet are hollow. Furthermore, the pores of the porous sheet of the present invention may be formed by continuous holes. Hereinafter, “at least a center of the porous sheet is not impregnated with resin” also is referred to as “pores of the porous sheet are hollow.”
Next, the circuit board of the present invention includes a desired number of electrically insulating layers and wiring layers laminated alternately, and an inner via hole for securing an electrical connection between the wiring layers by compressing and hardening a conductive paste including a conductive particle and a resin; wherein the electrically insulating layer includes a porous sheet in which a resin layer is laminated to at least one surface, and at least a central portion of the porous sheet is not impregnated with a resin; a through hole penetrating the electrically insulating layer in the thickness direction of the electrically insulating layer is filled with a conductive paste including a conductive particle and a resin, and pores that are present inside the porous sheet are filled with the laminated resin; and the average hole diameter of the pores that are present inside the porous sheet is smaller than the average particle size of the conductive particle.
Next, a first method for manufacturing a double-sided circuit board of the present invention includes: providing a through hole at a desired position of a laminate in which mold release films are formed on both surfaces of the above-mentioned circuit board electrically insulating material; filling the through hole with a conductive paste; peeling off the mold release film from the laminate in which the through hole is filled with the conductive paste; superimposing metal foils on both surfaces of the circuit board electrically insulating material from which the mold release films have been peeled off to form a laminate; heating and pressing the laminate to allow hollow pores of the porous sheet to be filled with a resin and allow the metal foils to be adhered to the porous sheet while compressing and hardening the conductive paste filled in the through hole, thereby providing an inner via hole; and forming desired circuit patterns on the metal foil.
Next, a second method for manufacturing a double-sided circuit board of the present invention includes forming a laminate either by superimposing resin sheets on both surfaces of a porous sheet that is not completely impregnated with a resin, further superimposing the mold release films on both surfaces of the laminated resin sheet, and pressing thereof; or by forming a resin layer on one surface of a mold release film, further sandwiching a porous sheet that is not impregnated with a resin by the sides of the resin layer of the mold release films provided with the resin layers; and pressing thereof; providing a through hole in a desired position of the laminate provided with the mold release films; filling the through hole with a conductive paste; peeling off the mold release films from the laminate in which the through hole has been filled with the conductive paste; superimposing the metal foils on both surfaces of the laminate from which the mold release films have been peeled off; heating and pressing the laminate to allow hollow pores of the porous sheet to be filled with a resin and allow the metal foil to be adhered to the porous sheet, and compressing and hardening the conductive paste filled in the through hole, thereby providing an inner via hole; and forming desired circuit patterns on the metal foil.
Next, a third method for manufacturing a double-sided
Andoh Daizo
Echigo Fumio
Kawakita Yoshihiro
Nakamura Tadashi
Alcala José H.
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Pert Evan
LandOfFree
Circuit board having an interstitial inner via hole structure does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Circuit board having an interstitial inner via hole structure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit board having an interstitial inner via hole structure will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3196559