AN RF-SHIELDED HYBRID CIRCUIT

Abstract: The invention relates to an RF-shielded hybrid circuit which comprises a printed circuit board (1) of an insulating mate­ rial, with foils on both sides, components placed on one side of the printed circuit board, and an RF-shield housing (5) made of metal sheet and fitted around at least part of the circuit. It is the object of the invention to provide an RF-shield which can be manufactured automatically and which at the same time ensures a relatively simple and compact structure. In order to achieve this, the RF-shield for the circuit is made up on the one hand of a cup-like cover (5) the peripheral area of which extends sub­ stantially around the edge of the printed circuit board (1), with the exception of the area of the connectors (2) of the printed circuit board, and which is placed over the components, and on the other hand of an earth foil (2a) which faces away from the components of the printed circuit board and is soldered by its edge to the peri­ pheral area (5a) of the cover (5).

Description: The present invention relates to an RF-shielded hybrid circuit which comprises a printed circuit board of an insulating material, with foils on both sides, components placed on one side of the printed circuit board, and an RF-shield housing, formed of a metal sheet and fitted around at least part of the circuit. From DE-A-1 441 114 there is known an electrical device in which a printed circuit board is provided with a conducting layer-strip which is connected with the zero potential, said strip serving to contact the borders of a shielding cap. A metal sheet is secured by means of spot welding to the inner side of the borders of the shielding cap so as to provide a groove extending along the border of the shielding cap. In the groove there is provided an elastic foamed material whose surface is provided with a metal layer. A good contact between the conducting layer-strip on the printed circuit board and the border of the cap is obtained by means of the metallized foamed material. It is previously known to form an RF-shield for hybrid circuits by fitting substantially around the whole circuit a profiled housing made of metal sheet, which is secured by mechanical means to the printed circuit board itself. The metal sheet housing may be assembled by, for example, spot welding. As electronics components are becoming less and less expensive owing to advanced manufacturing techniques, it is evident that a mechanical structure such as this, requiring several manufacturing steps, unreasonably increases the price of the circuit. Furthermore, since the housing must envelope the printed circuit board itself and its components, the total structure also becomes considerably large. It is, of course, possible to automate the manufacture of the shield housing to a rather high degree, but securing it to the printed circuit board itself is more cumbersome. Furthermore, since the housing extends around the entire board, the final assembling of the housing must not be done until after the printed circuit board with its components has been placed between the halves of the housing. It is the object of the present invention to eliminate these disadvantages and to provide an RF-shield which makes the manufacture of the entire hybrid circuit simpler than previously and which at the same time ensures a sturdy but considerably small-sized structure and good RF-shielding. In order to achieve this, according to the invention as claimed the RF-shield of the circuit is made up jointly on the one hand of a cup-like cover, the peripheral area of which extends substantially around the edge of the printed circuit board, with the exception of the area of the connectors of the printed circuit board, and which is placed over the components, and on the other hand of an earth foil on the other side of the printed circuit board, the earth foil facing away from the components of the printed circuit board, the foil being soldered by its edge to the peripheral area of the cover. In this manner a very compact and sturdy structure is obtained, and the printed circuit board itself can be secured to the cup-like part by, for example, automatic soldering, whereby at the same time a closed shield housing is formed, one side of it being formed by the earth foil of the circuit. In the peripheral area of the shielding cup or cover there are preferably a number of notches, the depth of which corresponds to the thickness of the printed circuit board and with which the corresponding projections in the printed circuit board will mate in order to determine the position of the printed circuit board in relation to the cover. The invention and its other characteristics and advantages will be described below in greater detail in the form of an example and with reference to the accompanying drawings, in which Figure 1 depicts a diagrammatic front view of the printed circuit board itself, Figure 2 depicts the metal cover, as seen from below, Figure 3 depicts a section of the metal cover, as seen from below, Figure 4 depicts the metal cover, as seen directly from the side, Figure 5 depicts the metal cover, sectioned and seen from the end, Figure 6 is a perspective representation of the entire RF-shielded hybrid circuit, and Figure 7 depicts the connecting of the printed circuit board to the mother board. Figure 1 thus shows the printed circuit board itself, which is, in a known manner, made of an insulating material and provided on one side with an earth foil and on the other side with conductor foils, as will be explained below. The printed circuit board has legs 2 which have been made of the material of the board by drilling holes close to the edge of the board and by grinding off the extra parts, whereupon the inner parts of the legs will be rounded. In the upper edge and ends of the printed circuit board there are additionally small protrusions 3 and 4, which serve to determine the position of the printed circuit board in relation to the shielding cover. The shielding cover is shown in greater detail in Figures 2-5. It is preferably made of metal sheet by stamping it into the correct shape, whereafter notches 6 for the legs 2 are made in the edges of the cover and notches 7 for the protrusions 3, and notches 8 for the protrusions 4. The notches 6 made for the legs are deeper than the others, so that the legs 2 will not touch the edges of the notches 6. Figure 6 is a perspective representation of a finished RF-shielded hybrid circuit. The cover 5 is placed on top of the printed circuit board on its component side so that the protrusions 3 engage the notches 7 and the protrusions 4 engage the notches 8, whereby the mutual position of the board 1 and the cover 5 is determined precisely and the circuit is positioned at the correct depth in relation to the cover. Thereafter the printed circuit board and the cover can be interconnected automatically, even by solder dipping, since the entire back side of the printed circuit board is made up of the earth foil 2a, the edges of which will thereby be soldered to the edge of the cover 5 and will at the same time form one wall of the housing. Figure 7 finally shows how such a hybrid circuit can be suitably connected to the mother board. The legs 2 of the hybrid circuit have on one side the earth foil 2a and on the other side at least one conductor foil 2b. In the mother board there are respectively apertures 9, which correspond in width to the legs 2 of the circuit and are preferably oval and at their edges rounded. This simplifies the making of the apertures. The legs 2 are connected electrically to the foils of the mother board, by soldering on the straight sides of the apertures 9. Since the earth foil extends continuously down along the legs 2 all the way to the mother board, and symmetrically in relation to the conductor strips on the other side, a maximally good and at the same time simple RF-shield is obtained. It is, however, clear that the legs can also be of a different material than the printed circuit board and be secured to it mechanically in a suitable manner.

Claims: An RF-shielded hybrid board which comprises a printed circuit board (1) of an insulating material, with foils on both sides, components placed on one side of the printed circuit board, and an RF-shield housing formed of metal sheet and fitted around at least part of the circuit, wherein the RF-shield of the circuit is made up on the one hand of a cup-like cover (5) the peripheral area of which extends substantially around the edge of the printed circuit board (1), with the exception of the area of the connectors in the printed circuit board, and which is placed over the components, and on the other hand of an earth foil (2a) on the other side of the printed circuit board, the earth foil, facing away from the components of the printed circuit board, the earth foil being soldered by its edge to the peripheral area (5a) of the cover (5). A hybrid circuit according to Claim 1, wherein in the edge (5a) of the peripheral area of the cover (5) there have been made two or more notches (7, 8) which mate with corresponding protrusions (3, 4) in the printed circuit board in order to determine the position of the printed circuit board (1) in relation to the cover (5). A hybrid circuit according to Claim 1, wherein in the area of the connector pins (2) there has been made a notch (6) in the peripheral area of the cover (5), the depth of the notch exceeding the thickness of the printed circuit board (1). A hybrid circuit according to Claim 3, wherein the connectors, i.e. legs, of the circuit consist of projections (2) in the edge of the printed circuit board, the projections extending beyond the cover (5) and having each on one side the earth conductor (2a) and on the other side at least one conducting conductor (2b).

Inventors: VAEISAENEN, RISTO, Väisänen, Risto
Applicants: NOKIA MOBILE PHONES LTD.
Application year: 1988
Main classification: H05K9
IPC codes: H01R12, H05K9, H01L25