Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1996-12-13
1998-11-17
Lorin, Francis J.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
26427211, 156292, H05K 1300
Patent
active
058370862
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
The present invention relates to a method of injection-moulding plastic elements that will shield against electromagnetic fields of radio frequencies.
In the mass-production of electronics, technical problems often arise in shielding different electronic components so that their functions will not alternate through the effect of high-frequency electromagnetic fields, and so that their functions will not alternate with the functions of other electronic apparatus or be disturbed by surrounding electric apparatus. There is also often the need to produce the electronics cheaply and in a simple manner.
Several different methods of manufacturing shielding casings are known to the art. For instance, the casings may be cast in metal, pressed from sheet metal, cast in plastic that includes an electrically conductive filler, or cast in plastic that is covered with a metal-plated layer.
One problem with all of these methods resides in the provision of joints at those locations where the disparate parts of the casing are contacted with one another, which is a prerequisite for achieving effective screening, particularly in the case of high frequencies or in the case of data signals that have short rise and fall times. Damping requirements are very high, particularly in radio constructions for telecommunications. In the case of the aforesaid plastic-moulding methods, the problem arises of obtaining uniform distribution of effective electrical conductivity. With regard to metallized layers, there is often a problem of providing a metal layer of sufficient thickness in all parts of the construction, with regard to the depth to which electric current will penetrate at the frequency concerned. Furthermore, the application of metal plating to plastic surfaces is a relatively complicated procedure and the number of plastic materials that can be plated with good results is limited.
In the case of metal casings, it is often difficult to obtain a uniformly distributed electric contact function along the casing joints. This problem is normally resolved by using metal fibre packing and closely placed screws, although this solution is neither cheap nor particularly reliable.
State-of-the-art techniques do not enable shielding casings made of metal foil/plastic foil laminates to be formed precisely in an inexpensive manner.
The forming of casings manufactured of pressed sheet metal is relatively limited and the tools used herefor are relatively expensive.
It is known to apply plastic foil in the injection tool of an injection-moulding apparatus when injection moulding apparatus casings, among others. The foil may be provided with decorative print and a surface structure which will have an aesthetic effect on the surfaces of the apparatus. It is also known to use wood veneer inserts to the same end.
When attempting to apply these principles with simple metal foils, it has been found that the plastic moulding material will not adhere to the metal foil or, when using plastic material that is able to bind to the metal foil, the whole workpiece tends to fasten in the mould. Furthermore, metal foils of such thinness as to enable the foils to be formed easily in an injection-moulding operation are too delicate to withstand the large sheer forces that occur during the course of the injection-moulding operation.
In summary, it can be said that none of the established methods is compatible with the desire for uniformly distributed effective electrical conductivity, the establishment of effective electric contact along joints, precise forming of the casings and the desire for a simple and quick method of manufacture.
SUMMARY OF THE INVENTION
The present invention relates to a method of injection-moulding electrically shielding casings, and the object of the method is to solve the aforesaid problems associated with established techniques.
The method comprises injection-moulding a mechanically supporting plastic structure onto a metal-foil/plastic laminate. The injection-moulded plastic structure is applied to one side of the lami
REFERENCES:
patent: 4639341 (1987-01-01), Hanamoto et al.
patent: 5435746 (1995-07-01), Leeb
patent: 5501008 (1996-03-01), Leeb
International Search Report mailed Sep. 27, 1995 corresponding to International Application No. PCT/SE 95/00688.
Dialog Information Services, File 351, Derwent WPI, Dialog accession No. 004379201, WPI accession No. 85-206079/34, Showa Denko KK: "Housing material for shielding electromagnetic radiation is prepd. by laminating metal membrane with thermoplastic resin, inserting in mould and injecting with thermo-plastic resin", JP 60129224, A, 850710, 8534 (Basic).
Patent Abstracts of Japan, vol. 11, No. 356, M-644, Abstract of JP A, 62-135332 (Mitsubishi Monsanto Chem. Co.), Jun. 18, 1987.
Leeb Karl-Erik
Persson Lars
Lorin Francis J.
Telefonaktiebolaget LM Ericsson
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