Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-06-16
2001-12-25
Gaffin, Jeffrey (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S764000, C361S780000, C361S794000, C361S803000, C257S723000, C257S728000
Reexamination Certificate
active
06333856
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a multilayer printed circuit board, and more specifically to an arrangement for mounting components, preferably chips, more densely in such printed circuit boards.
BACKGROUND OF THE INVENTION
Many different sorts of multilayer printed circuit boards are known to the art. LTCC (Low Temperature Co-fired Ceramic) will be used hereinafter as an example, although it will be understood that the invention can also be applied in other types of multilayer printed circuit boards.
Briefly, multilayer printed circuit boards are manufactured in the following way. There is obtained on the basis of a printed circuit board design a drawing that contains necessary information, such as the number of layers, the appearance and dimensions of the patterns on the various layers, the locations at which different layers shall contact one another, and so on.
Each layer per se is rolled out from a ceramic mass to a predetermined thickness on a plastic film; this is a so-called tape. Different patterns are punched from these tapes in accordance with the design; among other things, the outer edges of the board, the marks that are later used to match the layers together, and holes for binding different layers together with so-called vias.
Subsequent to configuring the layers, the via holes are filled with a suitable conductive material. The patterns are then printed on each of the layers. A common method in this respect is to use screen printing to correctly position the conductors. These conductors may consist of gold, silver or some other suitable conductive material. When the patterns are in place, the various layers are placed one upon the other until all layers are in position.
The whole of the printed circuit board is then placed under pressure, inserted into an oven and baked immediately (Co-fired) at a relatively low temperature, 700-800 degrees centigrade (Low Temperature), wherewith the ceramic mass is sintered and transformed to a ceramic. Subsequent to this curing or hardening process, it is usual to speak of layers instead of tapes.
In the case of applications for high frequency signals, particularly within the microwave field, it is not always possible to use traditional conductors, since this would result in unacceptable losses and disturbances. A normal requirement in the case of microwave signals is the presence of an earth plane above or beneath a conductor, this earth plane following the conductor. When a conductor only has an earth plane on one side it is called a microstrip. These strips are normally arranged so that they have the printed circuit board on one side and air or a similar dielectric on the other side. In other cases, it is desirable that the conductor is surrounded by both an upper and a lower earth plane, this conductor then being called a stripline. When the distances between a stripline and the earth planes are the same on both sides of the conductor, it is said that the stripline is symmetrical. One advantage afforded by striplines is that radiation from the conductors is small when, e.g., transmitting signals in the microwave range in so-called stripline-mode, which is one reason why such signals are often transmitted in this way. Microstrips and striplines can be easily provided in multilayer printed circuit boards, and are consequently often used to this end. In order to enable conductors to be surrounded by earth planes, conductor planes and earth planes are normally disposed alternately in the printed circuit board.
Apart from the possibility of mounting chips, for instance MMIC (Monolithic Microwave Integrated Circuit), on a multilayer printed circuit board, it is also possible to mount chips in said board. This is achieved by placing the chip on the earth plane or some other carrier in a cavity, and connecting the chip to a signal carrying layer by means of bonding wires. This is shown in
FIG. 1
, where the chip is connected to a microstrip in a known manner.
One problem that occurs when a chip is mounted in a multilayer printed circuit board in accordance with the aforesaid method is that the board will contain cavities. A cavity means a loss in board volume. This lost volume cannot then be used effectively in the construction of the board.
JP-07221211 describes an arrangement for mounting two chips in a cavity that enhances the utility of the area of a printed circuit board. This known solution involves mounting a substrate above the cavity. The substrate is connected to the printed circuit board electrically by means of a number of vias, and its underside includes a chip. Only two chips can be mounted in the cavity through the medium of this arrangement. Moreover, the substrate is placed on top of the board, therewith increasing board thickness.
SUMMARY OF THE INVENTION
The present invention addresses the problem of enabling cavities in multilayer printed circuit boards to be utilised more effectively.
One object of the present invention is to provide an arrangement for multilayer printed circuit boards which will enable cavities in the board to be utilised more effectively.
In brief, the present invention provides an arrangement which lies in a cavity and with which components, for instance, chips, can be mounted on at least the underside thereof.
In accordance with an exemplary embodiment of the invention, a substrate includes a chip which is connected to microstrips of the substrate via bonding wires. A multilayer printed circuit board includes a cavity, with a bonding shelf near an edge of the cavity. The substrate is placed on the bonding shelf at the edge of a cavity, with the chip oriented inwards towards the bottom of the cavity, thereby bringing microstrips on the substrate into contact with microstrips on the bonding shelf. An earth plane of the substrate on the opposite side of the substrate from the substrate side on which the chip is located, is connected to an upper earth plane of the multilayer printed circuit board via bonding wires.
One advantage with this solution to the problem resides in a compact method of constructing multilayer printed circuit boards in which the construction height is utilised in a manner that enables chips to be mounted in superimposed relationship instead of juxtaposed relationship. This enables the surface of the board to be utilised more effectively.
The invention will now be described in more detail with reference to preferred embodiments thereof and also with reference to the accompanying drawings.
REFERENCES:
patent: 4751482 (1988-06-01), Fukuta et al.
patent: 5237204 (1993-08-01), Val
patent: 5712767 (1998-01-01), Koizumi
patent: 5874321 (1999-02-01), Templeton, Jr. et al.
patent: 5994983 (1999-11-01), Andersson
patent: 6204442 (2001-03-01), Garland et al.
patent: 7221211 (1995-08-01), None
International-Type Search Report dated Feb. 8, 2000.
Burns Doane Swecker & Mathis L.L.P.
Gaffin Jeffrey
Telefonaktiebolaget LM Ericsson (publ)
Vigushin John B.
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