WO2005041352A1

WO2005041352A1 - Device with integrated antenna for encapsulation of radio electronics and a method for fabrication of such devices

Info

Publication number: WO2005041352A1
Application number: PCT/SE2003/001642
Authority: WO
Inventors: Karl-Erik Leeb; Dag BJÖRKLÖF; Urban Lundgren
Original assignee: Proofcap Ab
Priority date: 2003-10-24
Filing date: 2003-10-24
Publication date: 2005-05-06
Also published as: AU2003280902A1

Abstract

The invention which is before us is assigned to a device with an integrated antenna for encapsulation of radio electronics and a method for fabrication of such devices where a shielding-organ 1 enclosure an electronic circuit 6 and the shielding-organ 1 contains patch antenna 2 which is connected to the circuit 6, thus in this manner form a humidity proof and shielding capsule which is fabricated by a combination of lamination, punching and deep drawing resulting in a simple and effective method for duplicate production.

Description

Device with integrated antenna for encapsulation of radio electronics and a method for fabrication of such devices

TECHNICAL FIELD

The present invention relates to a device with integrated antenna for encapsulation of radio electronics and a method for fabrication of such devices, consisting of a shell with shielding and diffusion proof abilities, enclosing an electronic circuit which only transmit a certain radio frequency and also form a hermetic and humidity protecting envelope. It is also an object in the present invention to describe a rational method for the production. STATE OF THE ART

When information will be transferred with transmitters and receivers via radio frequency radiation, there are expectations for a powerful increase of such applications for transferring measurement data for technical use, so called telemetry. The reason for this increase is a more simple installation, in transferring with radio comparing with wire connection and an essential increase of the flexibility. The telecommunication systems for mobile phones and, so called, short range devises, for example bluetooth, have developed so that they, with minor modifications, can be applied to telemetry for control systems. Such systems will be, on a large scale, used outdoor or in other bad environment.

It will be an advantage to connect sensors via radio transmitters for short or long range communication. Electronics for such purpose is vulnerable both for air humidity and electromagnetic disturbances, for example radio frequency radiation.

Established technique for encapsulation of electronics, often consist of metal can with screwed cap and coaxial through-connection, for the signal, to a wire antenna of mono pole or dipole principle. Difficulty will be available to obtain pressure proof caps and through-puts, which results in that humid air sucks into the capsule, caused by variations in temperature. This will sooner or later result in problems by condensation of water, inside the encapsulation. In tight constructions it will be both lumbering and expensive. This will be a problem particular regarding duplicate production. Very often are metallic through-connections and connectors, vulnerable details depending on corrosion and leak-currents. Such electronics encapsulated by casting of plastic compounds are doubtful because that the compound will interact with the dielectric environment close to the circuit, resulting in malfunction. Casting of plastic compounds are also associated with problems depending to the slow curing process and the risk for hypersensitiveness caused by handling of reactive components used in epoxy, polyurethane or silicone based casting materials. Besides casting is often associated with quality problems depending on variable adhesion between the casting compound and the surface at the circuit An additional problem with this kind of protection is the unnecessary high weight.

Antenna components, which in a fundamental form consists of an aperture in a ground-plate surrounded of a microstrip conductor on one side and a dielectric layer with a metal patch on the other side, are known and are called microstrip antennas or patch antennas.

Those are commonly made in the same fabrication technique which is used for circuit boards. A problem with this kind of technique is that it is relatively slow, depending of the long curing times in the epoxy resins used as dielectric. Another problem is the relatively bad plasticity depending on the metal foils which are commonly used, which not admit a simple and integrated forming method in order to form a capsule. These, so called, patch antennas have therefore only been used as components only with electric connection and they have not been joined for the purpose of forming a hermetic encapsulation in a cheap method, suitable for duplicate production.

Several other principles for encapsulation are established and for example in the Swedish patent SE-55 27989 is an elegant method for shielding and humidity protection in duplicate production described, but this methods, in established technique have to be combined with antennas and connectors, which do not admit hermetically and resistance against corrosion in appropriate quality which cause a problematic complexity and a vulnerable construction in harsh environment. As we can read in the above report of state of the art, there are different methods for how to solve all the different parts of the problems. Knowledge about an integrated solution which provide a combined solution for the different technical requirements and which allow duplicate production in a simple manner and with low prize, is not at hand among men of the craft.

THE SOLUTION It is an object of the present invention to solve, inter alia, the above mentioned problems, which are at hand according to existing devices for encapsulation and also point out an unproblematic way for manufacturing of such capsules.

The invention stated an enclosure for the electronic circuit with a metal shell made of rolled plate with one or more patch antennas in resonance with a microstrip conductor and in between a dielectric against a ground plate. Consequently forming a, so called, patch antenna according to some known principle. This principle is shown, for example, in the book "Microstrip antennas, the analyses and design of microstrip antennas and array" by David M Pozar and Daniel H Schaubert. The most common principle is: Probe fed patch antenna, aperture fed and electromagnetic fed patch antenna. 90 The invention combine two basic functions, on one hand enclose the electronic with grounded "tailor-made" metallic envelope, the shielding-organ, on the other hand that in the mentioned enclosure integrate, a hermetic proof, patch antenna, the radiating-organ.

95 The radiating-organ impart the invention herein the property of shielding for outer electromagnetic influence, and in addition it will bring the device properties which protect the radio electronic against humidity and air pollution's. Because the capsule, in all its surfaces, contains metal layers, is the diffusion 100 negligible and the encapsulation will bring sufficient hermetic protection for the circuit in humid environment. The shielding-organ and the radiating-organ is mainly composed of rolled thin metal foil, for example brass 0,1 mm and as dielectric and sealing material is 105 thermoplastic film used, which has the property to form adhesion against metal. In manufacturing of encapsulations according to the invention are the starting material plain metal foil strips, which are pre-treated by punching, laser-cutting or etching to get apertures, microstrip conductors and patches. These are, in plain

110 form, joined by lamination with thermoplastic film with pressure and heat, for example 0,1 bar and 150 C. At this operation are also other surfaces on the capsule covered with the same thermoplastic film as later will be joined to other parts in the capsule or, for example, an electronic circuit. Thereafter are parts formed, which will be shielding-organ, by plastic deformation, in cold condition, in a press

115 with a tool, creating a cavity aimed to contain the electronic circuit. Thereafter is the circuit connected to the microstrip conductor in the radiation-organ and the shielding-organ is sealed by melt-adhesion by the earlier applied in between thermoplastic films.

120 The starting material is cheap and is not of larger quantity than what is necessary. Both rolled metal foil strips and extruded and blown thermoplastic are of lowest possible prize. Punching of holes is fast. The joining between thermoplastic and metal by apply 125 heat and pressure, is fast. The press forming to bring the form at the capsule, is very fast. The encapsulation is easy and environmental friendly to manufacture.

130 In addition is the metal simple to re-use after burning of the plastic, after the life- cycle. The drawbacks according to established technique are herewith eliminated. 135 DESCRIPTION OF THE DRAWINGS Fig. 1 Shows a cross-section of a device with integrated aperture-fed antenna for encapsulation of radio electronics in a form when the electronic circuit is 140 mounted as a circuit-board and connected to a battery for feeding with energy and formed according to the invention. Fig. 2 Shows a cross-section of another form, according to the invention, where the electric components are mounted on an expanded pattern on the microstrip conductors in the radiation-organ and in this figure are two organs shown. Fig. 3 Shows a schematic picture of different moments in a way to manufacture the device.

150 In the figures 1, 2 and 3 is the thickness of the used materials strongly magnified with the purpose to make the pictures distinct.

155 THE BEST EMBODIMENT Fig. 1 Shows an example of a device with integrated antenna for encapsulation of radio electronics, consisting of a shielding-organ 1 and a radiating-organ 2.

160 The shielding-organ 1 consist of two halves 3,4 one halve 3 is deep-drawn to a form so that a closed cavity 5 is created, which contain a circuit-board 6 with mounted electronic components 7 and a battery 8. The halves 3,4 in the shielding- organ 1 is connected to the circuits 6 grounding-surfaces and in one halve 3 is an aperture 9 which on its inner and outer surfaces is fitted with an adhesion plastic

165 layer 10 and on the inner side, a microstrip conductor 11 and on the outer side a metal patch 12 which together form a patch antenna which is the radiating-organ 2 through connection 13 by the radio signal between the microstrip conductor 11 and the circuit 6. The halves 3,4 in the shielding-organ 1 are sealed with an adhesive plastic layer 14 and form a capsule which protect the circuit-board 6,

170 its components 7 , battery 8 and connector 13 to the microstrip conductor 11, from harmful impact of, for example, humidity, at he same time as these parts also will be protected from induced electromagnetic interference. The radiation-organ 2 in the device, which is formed of the aperture 9, the microstrip conductor 11 and the patch 12 with in between plastic layers 10, which form dielectrics in a

175 resonator which is tuned for the frequency in order to get a good efficiency and in the same time make a effective barrier against humidity-diffusion depending on the metal layers 11,12 which overlap in relation to the aperture 9. In this manner the device form an outdoor and radiation proof unit which is able to communicate with radio-frequency radiation 15 in a particular frequency. 180 Fig. 2 shows a cross-section on a device according to the invention in an alternative form, where one halve 17 in the shielding-organ 16 on its inner side is laminated against a plastic layer 19 with a conductor pattern 20 in microstrip style and with mounted electronic components 21, in this manner form an integrated circuit-board which is able to communicate by radio through two different

185 radiating-organs 22,23 aimed for different frequencies. Besides the examples described in the figures also other variables can exist. For example, still more metal-foils can be adhered, with dielectric laminate in between, on the inner side by the signal conductor, in order to improve the internal shielding. Multiple patterns of patches can be used, with or without any phase difference by the signals, many patches can be placed over each other with dielectric in between, in order to bring effect on band width or lobe geometry. The shielding-organ can be formed with many different cavities in order to separate different centres of the circuit.

195 Fig. 3 shows a schematic example on a combination of manufacturing methods which represent one way to make devices according to the invention. a) shows, in the middle, a metal plate with punched aperture 32 surrounded by 200 an upper laminate 30,31 and a lower laminate 33,34. The laminate consist thermoplastic film, of a kind which sticks and adhere to metal 31,33 and rolled metal-foils 30,34. The laminate is produced by applying heat and pressure. b) shows the same parts but the metal layer in one of the laminate 35 is

205 produced by photo etching through photo resist and contact printing resulting in a patch and in the same way a microstrip conductor has been formed in the laminate 36. The aperture in the metal plate 32, the patch in the laminate 35 and the microstrip conductor in the laminate 36 have been oriented in the lateral plane, to each other in order to form a radiating-organ.

210 c) shows how the just mentioned three parts is laminated by heat and pressure, according to the arrows, resulting in forming of a laminate 37 which adhere to the aperture in the centre 32.

215 d) shows how the just mentioned laminate 37 is deformed to a three dimensional form by pressing, according to the arrows, against a forming tool 38, so called deep drawing or hydrostatic pressing. e) shows how the just mentioned laminate 37 is placed in front of another 220 laminate part 39 to the shielding-organ and an electronic circuit 6 has been enclosed, and heat and pressure has been applied against a sealing area via a pressing tool 40,42. f) shows how the just mentioned laminates 37,39 has been joined by melting 225 the thermoplastic together in the sealing area to a device with a radiating-organ and which form a humidity proof capsule 43 enclosing the circuit 6. The invention is not limited to the above embodiments shown as an example but may undergo modifications within the scope of the subsequent claims and tile inventive idea.

Claims

CLAIMS 1. A device with integrated antenna for encapsulation of radio electronics (6,7,8), containing radiation-organ (2) and shielding-organ (1) for enclosure of the electronic circuits and consist of a first metal plate (3) with at least one aperture (9) and on each side are dielectric layers (10) arranged and on one dielectric is one or more patches (12) arranged, each of them is overlapping an aperture (9), on the dielectric in the other side of the first metal plate are microstrip conductors (11) arranged which is connected to the enclosed electronic circuits (6) arranged for feeding each aperture (9) characterized in a second metal plate (4) which is sealed with the first metal plate (3) with thermoplastic (14) which will be melt- fixated with heat and pressure, at least one of the metal plates (3,4) is formed so that at least one cavity is formed for encapsulation of the electronic circuits when the metal plates is joined, the patches (12) is laminated against the first metal plate (3) by a thermoplastic layer on the side turned out from the cavity which is forming the dielectric layer between the patches (12) and the apertures (9), which will bring about a humidity proof joint.

2. A devise according to claim 1 caracterizedin that the dielectric layer between the microstrip conductors (11) and the apertures (9) in the radiating- organ (2) is composed of thermoplastic.

3. A device according to claim 1 caracterize in that the dielectric layer between the microstrip conductors (11) and the apertures (9) in the radiating- organ (2) is composed of air.

4. A device according to claim 1 caracterizedin that the dielectric layer between the microstrip conductors (11) and the apertures (9) in the radiating- organ (2) is composed of ceramic.

5. A device according to claim 1 caracterizedin that the dielectric layer between the microstrip conductors (11) and the apertures (9) in the radiating- organ (2) is composed of thermoset plastic.

6. A device according to claim 1 caracterizedin that the dielectric layer between the microstrip conductors (11) and the apertures (9) in the radiating- organ (2) is composed of dielectric liquid.

7. A device according to any one of the claims 1-6 caracterize in that the electronic circuits enclosed in the shielding-organ (1) is mounted on a circuit- board.

8. A device according to any one of the claims 1-6 caracterizedin that the electronic circuits enclosed in the shielding-organ (22,23), which is assembled of electronic components (21), is mounted against the microstrip conductors (20) in the radiating-organs (22,23).

9. A device according to claim 1 c ara c t e r i z e d in that the dielectric layer between the microstrip conductors (11) and the first metal plate (3), in the shielding-organ (1), and the seating thermoplastic layer (14) is composed of a continuous thermoplastic film which is laminated against the first metal plate (3).

10. A device according to claim 1 c ara c te r i z e d in that the first metal plate (3) in the shielding-organ (1), on both sides is laminated against a continuous thermoplastic film thus in this manner forming the dielectric layer between patches (12) and apertures (9) and between microstrip conductors (11) and apertures (9).

11. Method for manufacturing the means according to claim 1 c ar a ct e r i z e d by that rolled , plain metal is patterned by punching, laser cutting or etching through a resist pattern and that in this manner formed metal pattern is laminated against adhesive thermoplastic film by heat and pressure thus in this manner forming a patterned laminate with metal patterns in multiple layers is arranged such as patches, shielding-organ with apertures and microstrip conductors is oriented against each other with a dielectric layer, in between, which is formed by deep drawing or hydrostatic pressing to form cavities which brings to enclosure circuits connected to that part in the pattern which form radiation-organ and finally is the edges of the cavities sealed by melt adhesion against the thermoplastic film in those surfaces.