Optical waveguides – Integrated optical circuit
Reexamination Certificate
2002-01-16
2004-07-06
Bovernick, Rodney (Department: 2874)
Optical waveguides
Integrated optical circuit
C385S129000, C385S130000, C385S131000, C385S132000
Reexamination Certificate
active
06760497
ABSTRACT:
TECHNICAL BACKGROUND
The present invention relates to the field of circuit board technology. It concerns a circuit board having at least one electrical conduction level for relaying electric signals and/or currents and at least one optical conduction level for relaying optical signals, said conduction levels being interconnected and arranged one above the other in a stack within the printed circuit board.
Such a circuit board is disclosed, for example, in the publication U.S. Pat. No. 5,408,568 A.
This invention also relates to a method of producing such a circuit board.
STATE OF THE ART
In the long run, the demand for higher and higher clock rates and faster and faster signal transmission cannot be met with an adequate quality by using copper lines. Through the use of optical transmission pathways (optical fibers) it is possible to transmit signals at extremely high transmission rates within a backplane and also on system boards. A high interference immunity with respect to electromagnetic interference is a very fortunate side effect which is important especially on an electric backplane. Such a backplane is responsible, for example, for the data exchange between the individual processor cards of a multiprocessor high performance computer.
Various proposals have already been made for integrating optical data transmission pathways into multilayer circuitboards. For example, U.S. Pat. No. 5,230,030 A describes an optical interface for coupling to an electronic circuit in the form of multichip modules. The individual ICs are mounted on a multilayer circuit board consisting of layers that conduct electricity, arranged in alternation with insulating layers in the form of a stack. Channels are created in the insulating layers, which consist of an optically transparent material having a low refractive index, and are then filled with another transparent plastic having a higher refractive index. The fillings then form optical conductors which are connected to the ICs on the one hand and on the other hand are led to the edge of the stack, where they can be connected externally by means of an appropriate plug. This method of integrating optical conductors into a circuit board is not only complicated because the circuit board must be built up and structured layer for layer in succession, but also the quality of the optical conductors produced in this way leaves much to be desired because it is very difficult to achieve a uniform and homogeneous conductor structure when filling the channels with the optically active material.
Another proposal which is disclosed in U.S. Pat. No. 5,408,568 A cited above integrates a whole-area optical layer as an intermediate layer into a multilayer circuit board. The optical layer is coupled to the outside by means of an optical fiber with a blunt connection on one end. Chips placed on the top side of the circuit board are connected through holes beneath the chips, extending to the optical layer. The optical layer acts as a uniform optical databus over which all chips can exchange data with each other or with the outside world. No statements are made in that publication regarding the thickness or material of this optical layer.
FIG. 1
of that publication illustrates the optical layer with the same thickness as the printed circuitboards between which it is arranged. Therefore, this type of design could not be suitable for circuitboards having multiple optical levels and defined optical connections between selected chips.
EXPLANATION OF THE INVENTION
Therefore, the object of this invention is to create a circuit board for electrical and optical signals which is characterized by a high quality of the optical connection, a flexibly adaptable and easily varied design and simple integration into known manufacturing methods for multilayer circuitboards.
This object is achieved with a circuit board of the type defined in the preamble by the fact that the optical conduction level as a conducting element comprises at least one thin glass layer. A thin glass layer is understood to refer to a sheet-like layer of glass with a small thickness (approximately 1 mm thick or less) but at the same time a high optical quality (planarity of the surfaces) such as that used for LCD displays, solar cells or as a cover for a CCD circuit. Due to the use of such thin glass layers, it is possible to provide within the circuit board one or more space-saving optical conduction levels of a high transmission quality which can also be structured easily as needed to implement a localized optical connection within the circuit board,
A first preferred embodiment of the circuit board according to this invention is characterized in that the optical conduction level is formed by an optical sandwich which comprises, in addition to the minimum of one thin glass layer, at least one carrier plate which is connected to the minimum of one thin glass layer over the surface. Due to the combination of the thin glass layer with a carrier plate, it is possible to prefabricate the resulting optical sandwich separately from the fabrication of the actual circuit board and to adapt it in a flexible manner to the prevailing needs of the circuit (e.g. by structuring). The prefabricated optical sandwich can be introduced as an additional conduction level or layer into a traditional manufacturing process for a multilayer circuit board without requiring any significant changes in the process management.
It is possible here for the optical sandwich to comprise at least two carrier plates with the minimum of one thin glass layer arranged between them. The thin glass layer is then completely protected for further processing. However, it is also equally possible for the optical sandwich to comprise at least two thin glass layers which are connected to the minimum of one carrier plate over the area, with either the minimum of two thin glass layers being arranged on one side of the minimum of one carrier plate and joined together over the area or the minimum of two glass layers being arranged on opposite sides of the minimum of one carrier plate. In this way, two different optical conduction levels that can be designed separately can be integrated into the circuit board per optical sandwich. Of course, the number of carrier plates and thin glass layers per optical sandwich can also be increased further within the scope of this invention, although this does make production more complicated.
A second preferred embodiment of the circuit board according to this invention is characterized in that the carrier plates are made of an electrically insulating material which is used as the basic material for the production of electric circuitboards, preferably an Aramid-reinforced resin. This guarantees that the optical sandwich can be introduced especially well into the traditional manufacturing process for multilayer circuitboards.
The thin glass layers preferably have a thickness of less than or equal to 1.1 mm and are made of a borosilicate glass. Such a thin glass which is available under the brand names AF 45 and D 263 from the German company DESAG for use in LCD displays or solar cells, for example, and which is available in thicknesses between 30 &mgr;m and 1.1 mm is especially suitable as the optical conduction layer because of its high optical quality.
Essentially the thin glass layer may remain unstructured, then forming a single, continuous, cohesive optical layer. Another preferred embodiment of the circuit board according to this invention, however, is characterized in that at least individual thin glass layers are structured in such a way as to form individual optical conductors within the layer, separated from one another by interspaces. In this way, a variety of independent optical conductors can be produced in one level and can assume different transmission functions without causing any mutual interference.
The optical properties of the individual optical conductors can be optimized either by covering the exposed surfaces of the individual optical conductors with a reflective layer or by filling the interspaces
Bovernick Rodney
Pak Sung
PPC Electronic AG
Tarolli, Sundheim Covell & Tummino L.L.P.
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