Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-08-28
2001-05-15
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S830000, C029S852000, C029S600000, C029S601000, C174S254000
Reexamination Certificate
active
06230401
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus and a method for the manufacturing of printed circuit boards for use in electronic systems.
DESCRIPTION OF RELATED ART
A simple printed circuit board consists of a number of layers, one of which is normally a carrier made of a dielectric material. Printed circuit boards also comprise an electrically conductive earth plane. Transmission conductors, below also called conductors, are placed on one side of the carrier and covered by a dielectric material.
An electromagnetic field arises in a way known in the art between the conductor and the earth plane, and thus some of the field being lost in the dielectric material. This is valid especially for printed circuit boards used for high frequencies, when great energy losses may occur and large amounts of heat may be developed in the conductor.
A known method of minimizing these losses that arise in the printed circuit board is to use a dielectric material with favourable properties at high frequencies.
A disadvantage with this method is that it is expensive to use such dielectric materials in a printed circuit board.
Another prior art method is to mill out a recess in the dielectric material with air between the conductor and the earth plane. This air recess significantly reduces the loss in the conductor compared to a solid dielectric.
A disadvantage with this method is that it is complicated and that it is time consuming to make the recess.
The Patent Specification FR 2,665,578 discloses a method of optimizing the ratio between the energy loss and the thermal resistance in conductors in connectors. Recesses in two metal units surround a channel, with one layer of dielectric material between the metal units and two conductors each placed on one side of the dielectric layer in the channel. Thus, the channel is formed by the metal units.
One disadvantage of this method is that it takes up a lot of space in the connector.
U.S. Pat. No. 2,800,634 describes a method for minimizing the losses in a waveguide on, for example, a printed circuit board used at high frequencies. In this method an air gap between an earth plane and the waveguide is utilized, with layers of a dielectric material facing the earth plane building up the air gap between the earth plane and the conductor.
SUMMARY OF THE INVENTION
One problem solved by the invention is the inexpensive and simple creation of an air gap across a conductor on a printed circuit board.
Another problem is to minimize losses arising in a conductor on a printed circuit board.
Yet another problem is the inexpensive and simple way of making an air gap across a conductor on a printed circuit board being used for high frequencies.
The object of the present invention is therefore to achieve an inexpensive and simple manufacturing of an air gap across a conductor on a printed circuit board.
Another object is to minimize losses arising in a conductor on a printed circuit board.
To achieve this according to the present invention a photosensitive varnish layer in the printed circuit board is utilized together with Sequential Build Up (SBU) technology well known in the art. A carrier holding the conductor is covered with the photosensitive varnish layer and an opening is made in the varnish layer over the conductor with a photographic method. An electrically conductive earth plane is attached to the varnish layer with an air gap to the conductor. The resulting printed circuit board has an air gap well adapted to the conductor.
More specifically the method is carried out in the following way: A so called intermediate layer, the varnish layer of a dielectric material, is fixed to a first side of the carrier. On this first side the carrier has said conductor, so that the intermediate layer covers the conductor.
A through opening is made photographically through the intermediate layer of the conductor, said opening being a little wider than the conductor.
A metal layer is then placed on the intermediate layer and fixed to this layer. An air gap is formed between the conductor and the metal layer.
In an alternative method according to the invention the above mentioned carrier also comprises a lower conductor on a second side of the carrier, opposite to the first side of the carrier, said lower conductor being provided with an air gap in the same way as described above.
A layer of a dielectric material, below also called laminate, can, according to an alternative embodiment, be fixed to the metal layer to obtain a more rigid construction.
An advantage of the present invention is that the air gap or air gaps in printed circuit board can be obtained in a simple and inexpensive way, since well known standard materials and the SBU technology which is known in the art, are used.
Another advantage is that the manufacturing time is short, since well known methods and standard materials are used which can easily be found in the market. Furthermore, the air gap is made during the manufacturing of the printed circuit board.
Yet another advantage is that the conductors with the air gaps can easily be created in the intended places on the printed circuit board.
Still another advantage is that the printed circuit board has an air gap well adapted to the conductor.
Another advantage is that the conductors with the air gaps have favourable transmission properties.
Yet another advantage is that, according to the present invention, a high precision in the dimensions of the air gap, and in the position of the air gap on the printed circuit board, are achieved.
The invention will be described in more detail in the following by means of preferred embodiments and with reference to the appended drawings.
REFERENCES:
patent: 2800634 (1957-07-01), Grieg et al.
patent: 3893231 (1975-07-01), Anderson
patent: 5956843 (1999-09-01), Mizumoto et al.
patent: 2665578 (1992-02-01), None
patent: WO95/21472 (1995-08-01), None
Bergstedt Leif
Ligander Per
Burns Doane Swecker & Mathis L.L.P.
Chang Rick Kiltae
Telefonaktiebolaget LM Ericsson (publ)
Young Lee
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