GB2228618A - Radiation detector - Google Patents

Abstract

The radiation detector, particularly a pyroelectric IR radiation detector, comprises a housing (10) containing a radiation detector element together with additional circuit components if required, which housing consists of a moulded, preferably single piece, three dimensional printed circuit having conductive tracks (18a-f) extending at surface regions thereof through which external electrical connection with the element can be made. The element can be mounted directly on the tracks. An opening (12) in the housing (10) over the detector element is closed by a silicon window. The detector may comprise electrical leads (20-22) either partly embedded in the housing and contacting respective tracks or in engagement with tracks on the surface of the circuit. Alternatively, tracks may define external contact pads. The tracks can be provided in two layers, one of which is at the surface. One track (34) may be of extended area and serve as an electrical screen. <IMAGE>

Description

DESCRIPlZaV I#ADIMT# DETECTOR This invention relates to a radiation detector comprising a radiation detector element mounted in a housing having an opening which is closed by a window transparent to radiation to be detected, and electrical conductors extending from within the housing outside the housing for making external electrical connections with the detector element.

The invention is particularly, although not exclusively, concerned with infra-red radiation detectors comprising a pyroelectric detector element. The invention is, however, applicable also to other kinds of optoelectronic radiation detectors.

Infra-red radiation detectors comprising pyroelectric detector elements may be used for a variety of purposes. For example they may be used in remote switching systems, in intruder alarms, and in movement sensors generally. Such sensors rely on the fact that a person naturally provides a moving source of infra-red radiation when walking about. The radiation the person emits is converted by the pyroelectric detector to an electric signal which can be used, for example, to actuate an alarm or to switch lights on or off.

The pyroelectric detector element is mounted in a housing to shield it from environmental influences. lost commonly, the housing is in the form of a metal can having a standardised To. 5 outline. An example is shown and described in British Patent Application GB-A-2,046,431. The can comprises separate base and cover portions, the base portion providing an internal mounting platform and the cover portion being provided with a window transparent to infra-red radiation. Three leads extend outwardly from the base portion for making external electrical connections to the detector. Two of these leads extend through the base to provide two terminals in the form of short posts which protrude above the mounting platform inside the housing.The third lead is electrically connected to the mounting platform. The detector comprises two differentially connected discrete pyroelectric detector elements mounted in the housing together with associated circuitry which includes an E1 for impedance matching the elements output. The necessary interconnections between the pyroelectric elements, FET and the terminals are provided by bonding wires. The technique of wire bonding is both expensive and difficult to perform accurately.

In GB 2,102,200 there is described an improved form of this detector in which the For and possible other circuit components are provided in the form of a microminiature package having conductive leads which serve to support, and electrically connect with, the detector elements whilst other leads of the package are connected to the terminals on the base portion via thin metal straps or wires. Although in this detector the number of wire bonds necessary is reduced, its manufacture is still relatively complicated.

In GB 2,150,747, there is described an alternative form of pyroelectric detector which does not employ a T0-5 configuration housing and whose assembly can be highly mechanised and automated. In this detector, the conductor leads are arranged in-line and supported in an insulative block with two of the leads extending beyond the block and acting as cantilever supports onto which the detector elements are fastened. A separately formed metal or plastic cover is provided over and around the insulative block to enclose the detector elements.

Four conductor leads are involved, three extending outwardly from the insulative block for establishing external connections, one of which comprises an extension serving as one of the cantilever supports, and another separate lead serving as the other cantilever support. The latter lead also serves to support a semiconductor device comprising an FET and other circuit elements and wire bonds are used to connect the semiconductor device to the other three leads. Whilst this detector enables simplified assembly compared with the previously described kind of detectors and lends itself to automated assembly to a large extent, it is not considered wholly satisfactory from the view of ease of manufacture.

It is an object of the present invention to provide an improved detector whose assembly is relatively simple and can be highly automated.

The present invention provides a detector which uses a minimal number of component parts and whose construction lends itself readily to mechanised assembly.

According to the present invention, a radiation detector of the kind referred to in the opening paragraph is characterised in that the housing comprises a three dimensional circuit having conductive tracks at three dimensional surface regions thereof which tracks constitute at least portions of the electrical conductors.

The use of a three dimensional, 3D, circuit as the housing of a detector offers many significant advantages. Primarily, interconnection between components of the detector is simplified and assembly of the detector is greatly facilitated . The use of bonded wires can be avoided with the conductive tracks of the circuit serving to provide interconnections instead. Because the interconnections are provided by the conductive tracks incorporated in the moulding of the 3D circuit, it becomes unnecessary to provide space within the housing to accatrtodate other forms of interconnections such as wires. This space saving can be utilised to enable other components to be accommodated in the housing or alternatively to allow more compact detectors to be produced. The number of components involved, and the ease with which they can be assembled results in a considerable improvement over kncwn contructional forms of detectors. The need for a housing consisting of a nuttiber of separate parts which have to be fastened together is avoided. Instead the housing can be constituted by a moulding, preferably a singlepiece (unitary) moulding for greatest convenience, with appropriate conductive track configurations and defining a recess in which the detector element, and additional associated circuit elements such as an in inthe case of a pyroelectric detector, if required, are accommodated, which recess is closed by a radiation transparent window.External electrical connections are then established via the conductive tracks.

Three dimensional circuits, or moulded electronic assemblies as they are sometimes called, have been used in different applications for some while and several alternative manufacturing techniques have been proposed. Generally, 3D circuits consist of a pattern of conductive (and possibly resistive) tracking on and/or within a surface of a rigid, contoured, substrate of insulative material onto which components can be fastened.

Compared with conventional printed circuit boards in which conductive tracks extend only in two dimensions, (although interconnections such as plated-through holes may be used between two or more layers of tracks), 3-D circuits comprise tracks extending in three dimensions, whilst still allowing multi-layer track circuits to be used if desired. 3D circuits typically are formed using high temperature injection moulding materials and p -mer thick film (PIE) inks.A number of different processes have been devised by various companies such as General Electric, Dupont, General Hybrid, ICI and Pmoco. Differences relate primarily to the manner in which the circuit tracks are combined with the moulding substrate and the technologies can generally be divided into three categories: a first in which tracks are applied after the moulding operation, for example by direct printing, a second in which the track pattern and the moulded component are combined in the moulding process using a two shot injection moulding machine, and a third in which the track layout, possibly inii1ti-layered, is printed in a flat film which is applied in the mould prior to injection so that after moulding the circuit is part of, and embedded in, the substrate.

The latter technology has been developed by General Hybrid and has been found to be especially attractive in practising the present invention, although the other techniques are also applicable.

Examples of a suitable method of fabricating a three dimensional circuit is described in EP-A-236404 and US 4415067 to which reference is invited for further information.

The detector could be an optoelectronic device such as a light detector using a photoelectric, photoconductive or similar detector element.

Considerable advantages are achieved when the invention is applied to an infra-red detector comprising a pyroelectric detector element. As previously mentioned, it is customary in pyroelectric detectors for additional circuit elements, such as an S and possibly also non-linear devices, to be incorporated in the detector and for this reason the use of a three dimensional circuit is particularly attractive as interconnection of the various components can be accomplished in a particularly simple and convenient manner using conductive tracks of the three dimensional circuit.The number of components, and hence the number of assembly operations, is reduced. Moreover, the detectors can be assembled and mass produced using a high degree of automation.

In one enbodiment, the detector may include electrical leads extending from the housing for making external electrical connections with the detector. These leads may be partly embedded, and hence supported, in the three dimensional circuit moulding and arranged to contact or contact with respective conductive tracks thereof. This can be achieved by moulding the circuit around the leads. Alternatively these leads may be fastened to the circuit after fabrication of the circuit. The leads may be used to mount the detector on a circuit board in conventional fashion.

In the case of three or more such leads being provided, then the leads are preferably arranged in-line, that is, coplanar, which is more convenient for automatic testing procedures during fabrication as temporary electrical connections can be made to the detector more easily. In addition, the leads can then also comprise portions of a unitary lead frame making automated assembly much simpler.

For convenience, the three dimensional circuit may be formed with a shoulder extending around the opening thereof for locating the window. The window itself may be of any suitable material which transmits the radiation to be detected, for example a plain slice of silicon or germanium for an IR detector. The window may comprise a lens, for example in the form of a Fresnel lens, for collecting radiation and directing the radiation onto the detector element. In order to ensure that the detector element is isolated from the environment, the window is preferably sealed to the housing to provide an hermetically sealed enclosure in which the element is contained.

Where the detector is to include within the housing one or more additional circuit element or elements, as would be the case in a pyroelectric detector for which an ~ and possibly also non-linear devices such as a pair of parallel opposed low-leakage diodes producing a gate leakage path for the FET are used in a circuit including the detector element, then the additional circuit element (or elements) is preferably provided in the form of a package, for example as a small block of plastics encapsulating the element provided with projecting contact legs, these legs being directly secured, for example by solder or conductive epoxy adhesive, to appropriate respective parts of the conductive tracks of the three dimensional circuit. Assembly and interconnection of the additional circuit element or elements with the three dimensional circuit can thus be accomplished in a simple manner which lends itself to mechanisation.

The detector element, comprising for example a body of radiation sensitive material such as a pyroelectric ceramic material and planar electrodes on opposing surfaces thereof, may in turn be attached to, and supported by, one or more shoulders formed in the three dimensional circuit and/or one or more legs of the encapsulated package. Using this approach, the detector element can be supported such that a major part of it is in spaced relationship with, and hence isolated thermally fram, the housing surface or the encapsulated package surfaces which is important for optimum performance when pyroelectric detector elements are used.

The detector may include a pair of pyroelectric detector elements which, as is knawn per se in existing detectors, are interconnected in series or parallel opposition so that immunity from common-mode signals, such as those generated by variations in ambient temperature, background radiation and accoustic noise, is provided. The two elements may conveniently be formed in a single body of pyroelectric material.

The three dimensional circuit may further comprise one or more areas of conductive material which is connected electrically to one of the conductors and which serves to screen electrically the detector element or elements. This screening conductive area or areas may be formed simultaneously with the conductive tracks and connected to a track which in operation of the detector is earthed. Furthermore, in the case of a detector having a window of conductive or saniconductive material, for example a silicon or germanium window, the window is preferably electrically coupled with the one conductor via a track of the three dimensional circuit, whereby the window acts as a further screen.To this end, a track extension may be provided which extends over the shoulder on which the window is mounted and which electrically connects with the window via material, such as conductive epoxy adhesive used for bonding and sealing the window to the housing.

In order to enhance screening, the screen area or areas of the three dimensional circuit may be electrodes plated with appropriate material such as copper, silver, nickel or gold.

Alternatively, suitable shielding material may be incorporated in the three dimensional circuit during its fabrication.

ntibodinnnts of radiation detectors in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figures 1 to 4 show schematically at various stages of assembly a first ewtodiment of a pyroelectric detector using a 3D circuit in accordance with the invention; Figure 5 is an equivalent circuit diagram of the detector of Figures 1 to 4; Figure 6 is an equivalent circuit diagram of a modified form of the first ewtodiment of detector;; Figure 7 shows achematically a 3D circuit of a second embodiment of pyroelectric detector in accordance with the invention, and Figure 8 shows achematically a 3D circuit of a third embodiment of pyroelectric detector in accordance with the invention.

For the sake of clarity, the drawings are not to scale.

Referring to Figures 1 to 4, the pyroelectric detector comprises a housing 10 defining a recess 12 in which a pyroelectric element 15 is disposed together with associated circuit elements. The Figures show the detector at successive stages in assembly. More specifically, Figure 1 shows the housing 10 of the detector before installation of the detector element and associated circuit elements, Figures 2 and 3 show the mounting in the housing of the circuit elements and detector element respectively, and Figure 4 shows the detector at a final stage of assembly with a window, 16, covering the opening to the recess in the front wall of the housing.

The housing 10 is a three dimensional circuit comprising a single piece moulding of insulative material and tracks 18 of conductive material embedded in three dimensional surface regions thereof. The moulding, which is formed by a high temperature injection moulding process, defines a right parallelpiped structure having generally flat external surfaces and a generally rectangular recess 12 which opens at just one side through the front wall of the structure. The structure is formed with a pair of generally similar, integral, shoulder portions 17a and 17b at opposite sides of the recess with coplanar surfaces substantially parallel to the front wall of the housing.The conductive tracks, shown shaded in the Figures for ease of identification, extend within the recess over selected parts of these shoulders in a predetermined pattern to provide the necessary interconnections between the pyroelectric detector element, associated circuit elements and three conductive leads, here referenced 20, 21 and 22, through which external electrical connection with the detector is achieved.

The three dimensional circuit of this preferred entodiment is fabricated by a process developed by General Hybrid referred to as their NEA (moulded Electronics Assembly) process in which the circuit layout for the desired tracks is screen printed on a flat thin carrier film, of insulative thernurformable material such as, for example, a thermoset polyimide or unfilled polyetherimide, using polymer thick film ink, for example an epoxy base vehicle loaded with a silver powder or ferric oxide, which is fixed in the mould prior to the injection operation.

The injection moulding material can comprise a thermo-plastic resin and for example may be unfilled or glass-filled polytherimide. This process results in very reliable track adhesion.

Further details of suitable materials and fabrication processes for the 3D circuit are given in EP-A-236404 to which reference is invited. Briefly, the fabrication process involves forming a conductive track pattern on the insulative carrier film, and forming the patterned carrier film into a required three dimensional shape whilst supporting a face of the carrier film. The carrier is then placed into a mould into which the substrate material is injected whereby the track pattern is embedded in or within a three dimensional surface of the moulded substrate. In possible variations, the moulded substrate with the embedded track pattern may be post-formed into a desired shape. Alternatively, the carrier film may be applied to a prenrxllded substrate and heat and pressure applied to embed the track pattern in the substrate.

In possible variants, the carrier film may either be removed after moulding of the substrate, leaving the circuit pattern embedded in the substrate, or is left so as to form a part of the 3D circuit. In the latter case, the free surface of the carrier film can be arranged to face the mould material so that the track pattern lies outermost of the circuit and exposed.

Alternatively, the track-carrying surface of the film may be positioned facing the mould material so that in the eventual 3D circuit the tracks are covered, and protected by the film.

In this particular embodiment a conductive pattern is provided on one side only of the carrier film so that in the finished 3D circuit a single pattern of conductive tracks lies at the surface of the circuit and is exposed.

Of course, other known methods of fabricating 3D circuits could be employed instead.

The tracks, or at least those portions thereof at which connections are to be made, are exposed and substantially flush with immediately adjacent parts of the moulding.

In this embodiment, the leads 20, 21 and 22 are placed in the mould during fabrication of the 3D circuit 10 so that portions thereof are embedded in the circuit and supported thereby. The embedded portions of the leads are configured such that end portions underlie a part of a respective track of the three dimensional circuit 10. These lead portions are connected to their associated track by means of conductive material, for example solder or conductive epoxy adhesive, extending through bores interconnecting the track and the lead.Referring to Figure 1, the leads 20, 21 and 22 in this embodiment are connected respectively to the tracks 18d, 18c and 18a via solder, or conductive epoxy, 23 which contacts the tracks and extends rearwardly through communicating recesses formed in the unitary moulding of the three dimensional circuit 10 to contact with exposed underlying lead portions located within the recesses.

Although not visible in Figure 1, the parts of the leads 20, 21 and 22 embedded in the circuit are suitably configured to extend into the recess in the moulding frame at their associated contact regions.

The leads 20, 21 and 22 are coplanar and may initially be joined together at their ends remote from the circuit 10 by an integral strip which in turn carries further leads, at spaced locations, intended for other detectors. In other words, the leads comprise parts of a unitary lead frame consisting of interconnected groups of three leads.

The lead frame assists in the manufacture of the detectors since it ensures that the leads are accurately positioned with respect to one another and it conveniently enables a plurality of detectors to be fabricated simultaneously. A full lead frame may consist of ten groups of leads. Greater numbers can be accatmated using a continuous reel lead frame. After fabrication of the detectors, the detectors are separated by cutting their leads from the connecting strip of the lead frame.

In order to provide a greater degree of support and rigidity during detector fabrication, one of the leads, for example 22, may include an extension, referenced 25, projecting from the opposite side of the 3D circuit 10 with the lead extensions 25 of the lead frame similarly being interconnected by an integral connection strip.

Those portions of the leads 20, 21 and 22 which are embedded in the moulding of the circuit 10 may be shaped simply in two dimensions, that is, in the plane of the leads, this shaping being accomplished at the same time as the leads are stamped, together with their interconnecting strips, from sheet material.

It may be required that the lead portions be shaped in three dimensions. This can be achieved by a bending operation performed at the same time as the stamping out of the leads from the initial sheet.

Referring to Figure 2, a semiconductor device 26 is disposed within the recess 12 between the pair of shoulders 17 and 17b.

This device 26 comprises a field effect transistor (T) and a pair of parallel opposed diodes (D1 and D2) connected to the gate of the FEIC. The device 26 is in the form of a single encapsulated chip consisting of a plastic encapsulation body and four contact legs 19, respective pairs of which project from opposite sides of the body. The device is mounted within the recess so as to occupy the space between the two shoulders 17a and 17b of the recess and such that the four contact legs bear against, and are electrically bonded by solder or conductive epoxy to the conductive tracks 18a, 18b, 18c and 18d respectively, or the conductive material 23 as the case may be, on the shoulders.

After mounting of the device 26, the pyroelectric detector element 15 is inserted into the recess over the device 26, as can be seen from Figure 3. The pyroelectric element 15 consists of a planar body of poled pyroelectric material such as lanthanum and manganese doped lead zirconate titanate ceramic material having electrodes extending over its opposing major surfaces. In this particular #inent, a single detector element is provided, this element being defined by the areas of overlap between two main electrodes on the front and rear surfaces respectively of the pyroelectric body. In this example, the front electrode is co-extensive with the pyroelectric body. These electrodes may be of any suitable material.The electrode facing the opening in the front wall of the circuit 10, through which radiation to be detected passes in the operative detector, is chosen to be transparent to the wavelength range of interest.

Electrical connection with the two electrodes of the element 15 is achieved respectively via parts of the tracks 18b and 18f, the latter being connected with track 18a (via a conductive area 34) and isolated from adjacent tracks 18c and 18d, which tracks 18b and 18f extend over raised portions of the parallel shoulders 17a and 17b (Figure 1) and act as support surfaces so that the inwardly facing surface of the element is physically spaced by a gap, and hence isolated thermally from, the device 26 and the ranainder of the shoulders.The part of track 18b on the raised portion of the shoulder 17a contacts directly with the inwardly-facing electrode of the detector element. In order to permit electrical interconnection between the electrode on the outwardly facing surface of the body of pyroelectric material and the track 18f on the raised portion of the shoulder 17b, the front electrode is electrically connected around an edge of the pyroelectric body to a further electrode constituting a contact area on the inwardly facing surface of the pyroelectric body corresponding in position of the track 18f on the raised portion, which contact area is separated electrically from the main electrode on the inaardly#facing surface.The required edge connection may be formed using a blob of conductive epoxy or other suitable connection means. The detector element is fixed to the raised portions of the shoulders 17a and 17b by means of conductive epoxy or the like. The pyroelectric body may typically be around 4nrn long by 2.5my wide and have a thickness of approximately 70 micrometres.

The electrical circuit configuration of the detector thus achieved is illustrated in Figure 5. The output fran the detector element 15 is impendance matched by the FET, T, operating in source follower mode. The diodes D1 and D2 connected in parallel opposition are low leakage devices and produce a gate leakage path for the F#. This kind of circuit is described in greater detail in British Patent Specification No. 1580403.

In a modified arrangement, the detector uses a pair of detector elements. These elements are formed in a cation body of uniformly poled pyroelectric material such as lanthamm as manganese doped lead zirconate titanate. The two detector elements are defined by two separate electrodes on one major surface of the body and a single carton electrode on the other major surface overlapping the two separate electrodes.The body, and the individual elements are preferably rectangular as before, although different shapes could be errployed. The body comprising the two detector elements is mounted in a similar manner to that shown in Figure 3 with the two separate electrodes arranged facing inwardly of the housing 10 and contacting respectively the tracks 18b and 18f on the raised portions of the shoulders 17a and 17b. The two detector elements are thus connected in series opposition which, as is well knows, provides immunity from commn-mode signals such as those generated by variations in ambient temperature, background radiation and acoustic noise.

The two separate electrodes may be formed, for example, of nichrone in sufficient thickness so as to be reflective to IR radiation of a wavelength at which the detector is responsive.

The conon, outwardly facing, electrode may comprise a thinner layer of nichrome which is transparent to IR radiation and may cover the entire outwardly-facing surface of the body. This detector element arrangement has the advantage that the two contact regions are on the same side, thus simplifying connection with the tracks 18b and 18d and avoiding the need for conductors extending around an edge of the pyroelectric body. By way of example, the two separate electrodes may each be approximately 2.5my by irtin and spaced apart by around lmm. Figure 6 shows the circuit diagram of this two element detector embodiment.

In another modified form of this embodiment of detector, the two detector elements may be connected in parallel opposition using a single body of pyroelectric material with edgeconnected electrodes as described in G#A-2l4308l.

Referring now to Figure 4, the detector assanbly is completed by disposing the window 16 over the opening in the front wall of the housing 10. The window 16, conprising a rectangular slice of silicon material or other suitable material transmitting radiation to be detected, is mounted on an inwardly recessed shoulder 30 defined in the moulding of the 3D circuit 10 which extends around the periphery of the opening 12 in the circuit and is bonded to this shoulder by conductive epoxy adhesive so that the interior of the housing containing the detector element and associated circuit element package 26, is hermetically sealed. In its sealed position, the window 16 lies substantially parallel to, and is physically spaced from, the facing surface of the detector element 15.

The window 16 is coupled electrically via the conductive epoxy adhesive used on the shoulder 30 with an extension part 18e of the track 18f which extends fram the the raised portion of shoulder 17b up to the shoulder 30. Thus the window 16 in operation of the detector is connected to lead 22 and serves to screen electrically the detector element (or elements). Further screening is provided by a conductor layer 34, shown in Figure 1, formed as an extended area track of the 3D circuit interconnecting the tracks 18a and 18f over the planar rear wall of the recess 12 between the shoulders 17a and 17b and substantially coextensive with the detector element (or elements).The shielding effect provided by the layer 34 may be enhanced by electroless plating of the polymer thick film ink with nickel.

The electrical shielding provided in this manner by the window 16 and layer 34 prevents unwanted electrical pick-up leading to false responses.

If reliable window sealing is likely to be a problem, then a frame could be used which is moulded around the periphery of the window, the window then being mounted by bonding the frame to the shoulder 30.

In a modified form of the detector, the window 16 is replaced by a condensing lens which collects radiation and focuses it onto the detector element or elemerrts. This lens may for example comprise a generally planar Fresnel lens moulded from polyethylene material.

Referring now to Figure 7, there is shown a 3D circuit/housing of another #tibodimeL of detector, prior to mounting the device 26, the detector element(s), and the window 16. In many respects the housing of this detector is similar to that of the previous gnbodiment and, accordingly, the same reference arals are used to designate corresponding parts for simplicity. This emendinent differs principally in the manner in which the leads 20, 21 and 22 are interconnected with the tracks 18a, 18c and 18d. Instead of having extensions connected to these tracks via conductive material 23 disposed in catrnunicating recesses, interconnection is achieved via further tracks formed in the 3D circuit.To simplify this, conductive patterns are provided on both sides of the carrier film so that in the finished 3D circuit one pattern of conductive tracks lies at the surface of the circuit and is exposed whilst a second pattern of conductive tracks underlies in parts the first pattern within the substrate. Thus the two patterns are separated physically by the carrier film.

As shown in Figure 7, the leads 20, 21 and 22 in this emLodirnent are connected respectively to tracks 18c, 18d and 18a via additional tracks formed adjacent the area of the recess 12. Those tracks which are on the outer side of the carrier film, and hence exposed, are shown hatched with solid border lines, whereas tracks on the underside of the carrier film are shown dotted with dashed-line borders. Thus, the lead 20 is connected with the track 18c via a track 71 on the underside of the carrier film, lead 21 is connected via a surface track 72 which extends over the shoulder 30 onto the shoulder 17b to connect with the track 18d, and lead 22 is connected via a surface track 73 to the track extension 18e and thence via 18f and 34 to track 18a. The surface tracks are formed integrally with the tracks 18e and 18d.Interconnection between the tracks on opposing sides of the carrier film, for example between the track 18c and the underlying track 71 in this #tibod#rt is achieved by providing a hole in the carrier film with a laser prior to depositing the conductive ink in the carrier film, the ink then connecting the tracks through the hole.

Because in this particular erbodiment two tracks, 72 and 18e, extend over the shoulder 30 in which the window is subsequently mounted, then conductive epoxy is used only at the region of the track 18e when mounting the window, and a non#onducting sealing material applied to the ruining parts of the shoulder.

The leads 20, 21 and 22 are electrically coupled with their associated tracks 71, 72 and 73 at contact regions 74, 75 and 76 using conductive epoxy in the following manner. After printing the tracks on the carrier film, blobs of conductive epoxy are deposited at the described contact regions on the underside of the film. For a track on the underside of the film, namely track 71, the conductive epoxy is deposited directly in the track at the contact region. For tracks on the upper side of the film, namely tracks 72 and 73, holes are provided at the desired contact region by a laser prior to printing the conductive ink so that, when applied, the ink extends through the film to form a contact pad on the underside, blobs of conductive epoxy then being applied to these pads.

The leadframe comprising the leads 20, 21 and 22, whose end portions are suitably configured having regard to the position of the contact regions in relation to the position at which the leads are to exit the circuit 10 after moulding and are each provided with a protrusion at the intended contact area, is arranged together with the carrier film on a supporting frame and the end portions clamped against the film so as to force the protrusions of the end portions through the blobs of conductive epoxy to contact the conductive ink at the contact regions.

Thereafter, this sub assfflbly is placed in the mould and the substrate material injected so as to encapsulate the protrusions. The heat resulting fram the moulding operation causes the blobs of epoxy to reflow thus encasing, and adhering to, the end portions and tracks.

In an alternative process for obtaining connection between a lead and an outer track, a hole is provided through the film and the track at the intended contact region. The protrusion at the end portion of the lead is allowed to project into this hole and following the moulding operation conductive epoxy is simply deposited over the exposed protrusion and adjacent track area to provide electrical connection.

The abovedescribed methods for achieving contact between leads and tracks can be applied in the fabrication of the earlier ebeedinent of detector (Figures 1 to 4) to interconnect the lead end portions with the tracks.

Referring now to Figure 8, there is shown a three dimensional circuit/housing 10 of another #r(b(#meut of detector prior to mounting of the device 26, the detector element (or elements), and the window 16. In many respects this housing is similar to that of the previous anbodint and the same reference numerals are used to designate corresponding parts. This detector differs however in that it is of a leadless kind, i.e.

it does not have connection leads anbedded in the housing.

Instead, the housing comprises three mutually spaced conductive tracks 40, 41 and 42 defining contact pads and extending over the front outer surface of the housing which are electrically connected respectively to the tracks 18c, 18d and 18a. The tracks 40, 41 and 42 are formed simultaneously with the tracks 18 as parts of the three dimensional circuit, the housing dimensions being slightly increased to accatinodate these additional tracks.

The tracks 40, 41 and 42 are connected to their associated tracks 18c, 18d and 18a using interconnection tracks similar to those described with regard to the embodiment of Figure 7 (i.e. tracks 71, 72 and 73) although these are not shown in Figure 8 for the sake of clarity. In practice, the tracks 41 and 42 can be formed as integral extensions of their respective interconnecting tracks (72, 73) whilst the track 40 can be connected to an underlying track (71) using a prinLed-through hole in the manner described previously.

In order to make external electrical connection with the detector, wires may be bonded to the tracks 40, 41 and 42.

Alternatively, the tracks 40, 41 and 42 may be arranged to extend around the lower edge of the front wall and across the lower surface of the housing such that the detector can be surface mounted on a substrate such as a printed circuit board.

In another connection arrangement, electrical leads can be clipped onto the housing to establish contact with the tracks 40, 41 and 42. To this end, the housing 10 of this #tibodant is formed with a cutout 45 defining a reduced thickness lower part at the region of the tracks 40, 41 and 42. Electrical leads with bifurcated ends for example can then be push fitted over this lower part of the housing.

Whilst particular arbodiments of detectors in accordance with the invention have been described above, it will be appreciated that these are given merely by way of examples and that various modifications can be made within the scope of the invention.For example, the shape of the three dimensional circuit constituting the detector housing and its conductive track pattern can be varied to suit differing requirsments. The shape adopted needs merely to provide such features as are necessary for cxrodating the detector element or elements, the associated circuit element or elements if provided, and for attachment of the window. moreover, fewer or more circuit elements may be provided in the housing. The detector can be provided with more, or less, external connecting leads or tracks as may be required, for example by modifying the lead frame as described above in the case of external connecting leads.

In another anbodiment a simplified ~ chip package is used in which the diode elements are omitted and which, accordingly, has only three legs, engaging respectively the tracks 18c, 18d and 18b. In this arrangement a low leakage path for the #a gate can instead be provided by a conductive track, this track being formed of material having a suitable resistive value.

The detector may alternatively comprise an opt#electronic detector using for example a photoconductive or photovoltaic element as the detector element in which case additional circuit elements within the housing may not be required and only two external leads or tracks provided. For an optoelectronic detector intended for detecting radiation in the visible light region, a plain light transmissive window would suffice.

Whilst in the above described detectors, the 3D circuit/housing 10 is formed as a singlepiece, unitary itoulding for simplicity and carwenience, it is envisaged that it could instead be formed by two, or more, separately moulded capponents which are subsequently fixed together, this arrangement allowing more intricately shaped housings and track configurations to be produced.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the field of radiation detectors and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel caribination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and/or catibinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims (16)

ClAIM(S)

1. A radiation detector canprising a radiation detector element mounted in a housing having an opening which is closed by a window transparent to radiation to be detected, and electrical conductors extending fran within the housing outside the housing for making external electrical connections with the detector element, characterised in that the housing comprises a three dimensional circuit having conductive tracks at three dimensional surface regions thereof which tracks constitute at least portions of the electrical conductors.

2. A radiation detector according to Claim 1, characterised in that the three dimensional circuit ccpnprises a single piece moulding defining a recess in which the detector element is acccawdated and which is closed by the window.

3. A radiation detector according to Claim 1 or Claim 2, characterised in that the detector includes electrical leads extending from the three dimensional circuit for making external connection with the detector.

4. A radiation detector according to Claim 3, characterised in that the electrical leads are partly arrbedded in, and supported by, the housing and are connected respectively to conductive tracks of the three dimensional circuit.

5. A radiation detector according to Claim 4, characterised in that the leads are electrically bonded to tracks of the three dimensional circuit by conductive epoxy or solder.

6. A radiation detector according to Claim 3, characterised in that the electrical leads are fastened to the outer surface of the three dimensional circuit in contact with conductive tracks of the circuit.

7. A radiation detector according to any one of Claims 3 to 6, including at least three conductive leads, characterised in that at least the parts of the leads extending from the three dirr#nsioan1 circuit are coplanar.

8. A radiation detector according to Claim 1 or Claim 2, characterised in that tracks of the three dimensional circuit define surface contact pads through which electrical connection with the detector element can be established.

9. A radiation detector according to any one of the preceding Claims, characterised in that the three dimensional circuit canprises conductive tracks in first and second layers, the first layer being exposed at the surface of the circuit and the second layer underlying the first layer within the surface region of the circuit and being separated fran the first layer by an insulative film.

10. A radiation detector according to any one of the preceding claims, characterised in that the three dimensional circuit is formed with a shoulder extending around the opening thereof for locating the window and against which the window is sealed.

11. A radiation detector according to any one of the preceding claims, and including an additional circuit element within the housing, characterised in that the additional circuit element is encapsulated as a package provided with contact legs, the package being disposed within the housing with its legs connected to parts of the conductive tracks of the three dimensional circuit.

12. A radiation detector according to any one of the preceding claims, characterised in that the detector element is supported within the housing with a surface thereof facing the window by one or more shoulders formed in the three dimensional circuit so as to be spaced from adjacent surfaces, and in that conductive tracks extend on the one or more shoulders for contacting electrically with the detector element.

13. A radiation detector according to any one of the preceding claims, characterised in that a track of the three dimensional circuit comprises an area of conductive material which overlies the detector element and is connected electrically to one of the conductors and which serves as an electrical screen in operation of the detector.

14. A radiation detector according to Claim 13, characterised in that the window is of conductive or semiconductive material and in that the window is electrically coupled with said one conductor via a track of the three dimensional circuit so as to provide further screening during operation of the detector.

15. A radiation detector according to any one of the preceding claims, characterised in that the detector element is a pyroelectric element canprising a body of pyroelectric material and electrodes.

16. A radiation detector substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.