A METHOD OF SHIELDING A PRINTED BOARD ASSEMBLY WITH AT LEAST ONE COMPONENT AND A SHIELDING ELEMENT FOR SHIELDING COMPONENTS ON SUCH A PRINTED BOARD ASSEMBLY

Abstract: In a method of producing a printed board assembly from a printed board (1, 2, 3, 4), components (7) are furnace soldered to the printed board. A string (6) of heat curing, electrically conductive material, elastic after curing, is deposited around the site where the components (7) to be shielded, are to be furnace soldered. That string (6) is cured into a shielding gasket in the furnace soldering step, i.e. in the same production step as the components (7) are furnace soldered to the printed board. The shielding gasket is adapted to cooperate with a shielding housing (8, 9) to shield the components (7).

Description: A METHOD OF SHIELDING A PRINTED BOARD ASSEMBLY WITH AT LEAST ONE COMPONENT AND A SHIELDING ELEMENT FOR SHIELDING COMPONENTS ON SUCH A PRINTED BOARD ASSEMBLY TECHNICAL FIELD The invention relates, generally, to shielding of components on printed board assemblies and, more specifically, to a method of producing a printed board assembly having shielding means as well as to a shielding element cooperating with shielding means on a printed board assembly for electrically shielding components on the printed board assembly. BACKGROUND OF THE INVENTION From GB-2 261 324-A, it is known to shield a printed board assembly by applying a shielding material to a conductor on a printed board and, then, depending on the shielding material, harden it, e.g. by means of UV light. The shielding material on the printed board is intended to cooperate with a shielding housing that may be provided with grooves or other recesses to improve the seal and the contact with the shielding material on the printed board. Applying shielding material to a printed board assembly already produced, requires an additional production step as does hardening of the shielding material in a separate production step. Thus, a printed board assembly in accordance with said GB-2 261 324-A will be quite expensive to produce. SUMMARY OF THE INVENTION The object of the invention is to bring about a method of producing printed board assemblies having shielding means, which is cheaper and simpler than the methods known so far. This is attained by the method according to the invention in that, before the components are soldered to conductors on the printed board in a furnace soldering step, a string of a heat curing, electrically conductive material is deposited around the site where at least one component to be electrically shielded, is to be furnace soldered to the printed board, and that said string is cured in the same step as the components are furnace soldered to the conductors on the printed board to form a shielding gasket. Hereby, great savings in production costs will be made in that the curing and the soldering are carried out in the same process step instead of in two separate process steps. BRIEF DESCRIPTION OF THE DRAWING The invention will be described more in detail below with reference to the appended drawing, on which Figs. 1- 4 illustrate different stages of the method according to the invention of producing a printed board assembly, and Fig. 5 is a sectional view of the printed board assembly in Fig. 4, provided with a shielding element in accordance with the invention. PREFERRED EMBODIMENTS Fig. 1 is a partial cross-sectional view of an embodiment of a printed board 1 having, on its one side, a pattern of conductors 2 and a conductor 3 surrounding the conductors 2, and, on its other side, a layer 4 of conductive material. The conductors 2 and 3 as well as the layer 4 are normally of copper. The conductor 3 is not necessary in the general case, but is preferred. In the embodiment illustrated in Fig. 1, components that need to be shielded are supposed to be soldered to the conductors 2, while the conductors 3 are supposed to be provided with a shielding gasket. In Fig. 2, the conductors 2 on the printed board 1 have been provided with a layer 5 of solder at the sites where electric components to be shielded, are to be soldered to the conductors 2. In Fig. 3, a string 6 of heat curing- electrically conductive material, elastic after curing, has been deposited on the conductor 3 surrounding the conductors 2 provided with the solder layer 5 on the printed board 1. In Fig. 4, two components 7 to be shielded, have been placed on the solder layers 5 to be soldered to the conductors 2. In this connection, it should be pointed out that, as an alternative, the components 7 may equally well be placed on the solder layers 5 before the string 6 is deposited on the conductor 3 on the printed board 1. The printed board 1 as apparent from Fig. 4, is then introduced into a solder furnace in order for the components 7 to be furnace soldered to the conductors 2, and for the string 6 of heat curing material to be cured in one and the same step to transform the latter into an elastic shielding gasket. In Fig. 5, the complete printed board assembly with the cured string or shielding gasket 6, has been provided with a shielding element 8 in accordance with the invention for electrically shielding the components 7 in combination with the shielding gasket 6 and the conductive layer 4 on the printed board 1. As apparent from Fig. 5, the shielding element 8 according to the invention is provided with a compartment for receiving the components 7. The rim 9 of the shielding element 8 is adapted to cooperate with the elastic, electrically conductive shielding gasket 6. To this end, the rim 9, in accordance with the invention, is pointed as apparent from Fig. 5. The rim 9 may be shaped like a knife edge or have a sawtooth-shape or any other pointed shape. It is to be understood that the shielding element 8, of course, may have more than one compartment. The shielding element 8 is either of electrically conductive material or of an insulating material clad with a layer of conductive material. By combining the step of soldering the components to the printed board and the step of curing the shielding gasket deposited on the printed board, the production costs for the complete printed board assemblies will be reduced.

Claims: CLAIMS 1. A method of producing a printed board assembly from a printed board (1, 2, 3, 4), comprising the steps of - depositing solder (5) on conductors (2) on the printed board at spots where electric components are to be soldered to the conductors (2), - placing said components (7) at said spots, and - furnace soldering said components (7) to the conductors (2), characterized by - depositing a string (6) of heat curing, electrically conductive material which is elastic after curing, around the site where at least one component (7) to be shielded, is to be furnace soldered, and - in the same process step as the furnace soldering step of said at least one component to be shielded, curing said string (6) to transform it into an elastic shielding gasket which is intended to cooperate with a shielding element (8, 9) to shield said at least one component (7). 2. The method as claimed in claim 1, characterized in that said string (6) is deposited on a conductor (3) surrounding said site. 3. A shielding element for shielding at least one component (7) on a printed board assembly, the shielding element (8), for receiving said at least one component (7), having at least one compartment, the rim (9) of said at least one compartment being adapted to cooperate with an elastic, electrically conductive gasket (6) deposited on the printed board assembly around the site of said at least one component (7) to be shielded, characterized in that said rim (9) is of pointed shape. 4. The shielding element as claimed in claim 3, characterized in that said rim (9) is shaped like a knife edge. 5. The shielding element as claimed in claim 3, characterized in that said rim (9) is sawtooth-shaped.

Inventors: FRIMAN DANIEL, HOLMBERG PER, SANDEVI TOMMY, FRIMAN, DANIEL, HOLMBERG, PER, SANDEVI, TOMMY
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)
Application year: 1998
Main classification: H05K9
IPC codes: H05K3, H05K9