Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2000-07-28
2002-03-19
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S255000, C174S256000, C174S258000, C174S262000, C361S760000, C361S761000, C361S762000, C361S763000, C361S764000, C257S737000, C257S778000
Reexamination Certificate
active
06359235
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrical device mounting wiring board comprising an insulation substrate with electrical devices such as capacitor and semiconductor device mounted on the surface or inside thereof, and a method of producing the same.
2. Description of Related Art
Recently electronics apparatuses have been becoming more compact, and the so-called mobile computing is becoming popular in which people carry hand-held information terminals or computers and operate them away from their homes or offices. To build such compact electronics apparatuses, demands have been growing for a multi-layer wiring board of compact and thin construction with fine patterning.
Semiconductor devices are mounted on the multi-layer wiring board by mounting a package having the semiconductor devices hermetically sealed therein on the multi-layer wiring board. However, this mounting method requires the step of electrically connecting the package with an electrical circuit layer provided on the surface of the multi-layer wiring board. As a result, the production process for completing an electrical apparatus that includes the semiconductor devices includes many steps, leading to a high production cost. Moreover, since the semiconductor devices can be mounted only on the surface of the multi-layer wiring board, there has been a limitation to the size and thickness reduction of the electrical apparatus and to the increase in the packaging density of the semiconductor devices.
Connection between the package and the wiring layer is made, for example, by wire bonding. In this case, connection pads provided on the wiring layer must be arranged at intervals of about 200 &mgr;m. This requirement also hampers the progress of size reduction. Also because terminals of the package must be individually connected to the connection pads, it takes a long time to make connection resulting in low productivity. Furthermore, since the bonding wire connects the package terminal and the connection pad while winding in a loop shape, a clearance of about 0.5 mm must be secured in the direction of thickness of the package. This has also been hampering the progress of size and thickness reduction of the electrical apparatuses.
In order to solve these problems, module construction where a plurality of semiconductor devices are stacked is proposed in, for example, Japanese Unexamined Patent Publication (KOKAI) No. 9-186204 (1997), Japanese Unexamined Patent Publication (KOKAI) No. 9-283697 (1997) and Japanese Unexamined Patent Publication (KOKAI) No. 11-40745 (1999).
This construction makes it possible to reduce the total area of the wiring board. At the same time, however, there is a problem of increasing thickness of the electrical apparatus including the semiconductor devices as a whole. Moreover, a complex step is involved for connecting the stacked devices, thus resulting in an increasing production cost.
With the background described above, such attempts have been made as incorporating semiconductor devices in the wiring board itself. These attempts are roughly divided into techniques that are based on the conventional printed wiring board, and techniques that are based on the build-up wiring board.
The techniques based on the printed wiring board is disclosed, for example, in Japanese Unexamined Patent Publication (KOKAI) No. 8-88471 (1996). With the technique disclosed in this publication, a printed wiring board is made with part thereof being machined to form recesses. Semiconductor devices are housed in the recesses and electrically connected to wiring lines, via wires provided in the wiring board. Then another wiring board is laminated on the wiring board by thermal pressing or the like, thereby forming a multi-layer wiring board.
The techniques based on the build-up wiring board is disclosed, for example, in Japanese Unexamined Patent Publication (KOKAI) No. 9-321408 (1997) and Japanese Unexamined Patent Publication (KOKAI) No. 9-46049 (1997). With the technique disclosed in these publications, a printed wiring board is made with part thereof being machined to form recesses. Semiconductor devices are housed in the recesses and a circuit is formed thereon by build-up technique. Thus the semiconductor devices are incorporated in the wiring board.
However, any of these techniques have a problem in the applicability to mass production. With the technique based on the printed wiring board, the semiconductor device may be subjected to breakage during the thermal pressing step. This is because one of the boards being thermally pressed has already been cured and therefore even slight unevenness in the recesses that have been machined leads to stress concentration in the uneven portions. Also because shrinkage of the resin used for making the board due to curing proceeds differently on the front and back sides of the semiconductor device, there has been a problem of the semiconductor devices to break due also to the stress concentration caused by shrinkage during curing.
With the technique based on the build-up wiring board, on the other hand, stresses described above are less likely to be generated and lead to less occurrence of breakage of the semiconductor devices. However, there are other problems caused by the step of forming the wiring pattern, that is a wet process such as plating, and by the intrinsically highly moisture-absorption property of a photosensitive resin that is used in the build-up wiring board. Specifically, it has been difficult to put the build-up wiring board into commercial operation, because of insufficient heat resistance (causing swell and other defects generated during solder reflow) due to the absorption of moisture, and significant decrease in reliability demonstrated in thermal cycle test and pressure cooker test.
For the build-up wiring board, much attention has been paid to the laser via board wherein via holes are made by means of carbon dioxide gas laser. However, when it is attempted to incorporate the semiconductor devices in the laser via board, there may occur such a problem as the circuit over the semiconductor devices is broken by the heat generated by the laser when forming the via holes. Also because silicon used in the substrate of the semiconductor device has high heat conductivity, heat of laser is absorbed by the silicon substrate. Consequently, residue of resin, called the smear, deposit on the silicon substrate after machining with the laser. The resin residue hampers electrical connection. As a result, it has been also difficult to put the technique based on the laser via board into commercial operation
Problems similar to the above arise also in cases where electrical components other than semiconductor devices such as capacitor and resistor are mounted on the multi-layer wiring board.
SUMMARY OF THE INVENTION
First object of the present invention is to provide an electrical device mounting wiring board with electrical devices incorporated therein, thereby making it possible to decrease the size of electrical apparatuses and to increase the packaging density of component devices.
Second object of the present invention is to provide a method of producing the electrical device mounting wiring board that makes it possible to easily produce a wiring board having electrical devices incorporated inside thereof.
The present inventors have studied intensively to reduce the size of a wiring board incorporating electrical devices and to simplify a method of producing the same. As a result, it has been found that stress concentration on the electrical devices when the electrical devices are incorporated in the wiring board can be mitigated by forming a resin layer having a glass transition point lower than the curing temperature of a thermosetting resin in the wiring board which incorporates the electrical devices, between at least one of top and bottom surfaces of the electrical device and an insulation layer constituting the wiring board, thereby making it possible to drastically improve the productivity of the
Gaffin Jeffrey
Hogan & Hartson L.L.P.
Kyocera Corporation
Patel I. B.
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