PROCESS FOR SECURING A MICROWAVE MODULE TO A SUPPORT

Abstract: The present invention relates to a process for securing to a metal support at least one microwave electronic module made on a substrate one of whose faces forms an earth plane. The process consists in depositing between the face forming the earth plane and the metal support, at least one strip of conducting adhesive (12',14',19',20') at the level of the zones of breakage of the earth plane. The invention applies to the microwave field.

Description: PROCESS FOR SECURING A MICROWAVE MODULE TO A SUPPORT The present invention relates to a process for securing to a metal support at least one microwave electronic module made or. a substrate one of whose faces forms an earth plane. In the field of microwaves, the fabrication cf circuits carrying out electronic functions such as mixers, amplifiers or others, may be carried out on substrates of various kinds by using etched lines. The making of a microwave subassembly consists in putting several functions in series or in parallel, these functions being linked together by interconnection systems such as etched lines or wiring tracks. In general, several functions are carried oαt on one and the same substrate by using printed circuit type technology which has been matched to the materials and to the specific thicknesses for microwave applications. Thus, as represented schematically in Figure 1, a microwave electronic module can consist of an etched circuit 1 made on a substrate 2 of a material such as "Teflon" glass, namely "Teflon" woven with glass fibres. This substrate, generally not very rigid and exhibiting a relatively small thickness with respect to its other dimensions, is coated on its lower face with a metal earth plane 3. Tnese electronic modules are usually mounted on a metal package cr support 4. Various types of assembly are therefore ised to secure the substrate 2 to the ratal package or support 4. However, the use of electronic circuits at near- millimetre frequencies, in particular at frequencies of several gigahertz, demands good electrical contact between the earth plane 3 of the substrate 2 situated on the lower face of the substrate and the metal earth of the support 4. To address this constraint, various methods can be used to assemble the substrate onto the metal package or support. Thus, it is possible to use a screwing process which has the advantage of being very simple, easily automated and inexpensive. However, this process is not applicable to millimetre frequencies, since the thickness of the substrate 2 is very slender with respect tc these other dimensions, this possibly giving rise to problems of deformation of the circuits etched and/or mounted on the substrate possibly inducing cracks in the solder joints. Moreover, the contact between the earth plane of the substrate and the earth plane of the metal support is very localized. The other technique widely used in the field of microwaves is a bonding technique which makes it possible to obtain reliable transfer having good electrical characteristics. Several methods of bonding exist for assembling two materials. Thus, mention may be made of the use of a film which makes it possible to achieve assembly of very high reliability, although its material cost is relatively high and it is complex to implement since it requires the application of pressure throughout the adhesive curing cycle. Another technique consists in employing one- or two-component conducting epoxy adhesives, the conducting particles usually consisting of silver or gold. In this case, the adhesive is deposited using, for example, a syringe. Whereas this technique is less expensive than the previous one, it requires good control of the adhesive so as to deposit a layer which is quasi-uniform in terms of thickness and surface. According to another embodiment, the epoxy adhesive may be deposited by screen printing, thereby making it possible to obtain a uniform layer in terms of thickness and surface. This technique also has the advantage of being fast but uses a considerable quantity of adhesive. In the field of microwaves, one of the abovementioned bonding techniques is used by spreading the paste over the entire surface of the circuit to be bonded so as to obtain good earth transfer, the adhesives being laden with conducting particles of the silver or gold type. The above technique has the drawback of being especially expensive owing to the appreciable quantity of acnesive required. The app----cant, during studies carr_ed out on the bonding of a substrate comprising at least one iicrowave electronic module on a metal oackage or support, has not_ced, contrary to the give' teachings, that it was not necessary to deposit the adhesive on t e entire surface of the substrate. The adhesive can be deposited at specific sites making it possible to avoid non- conouctivity of the signal /ithout giving rise to prcolems in the operation of t~e electronic moαule. Consequently, the s-oηect of the present invention is a process for securing to a metal support at least one microwave electronic module made on a substrate one of whose faces forms an earth plane, characterized in that it cons-sts m depositi n g between the face forming the earth plane and the metal support, at least one strip of conduct_ng adhesive at the level of the zones of breakage of the earth plane. These breakage zones appear most frequently at transitions. The role of the transition _s to allow the signal to switch from one mode of propagation to anotner (e.g.: frcm the TE10 mode of the rectangular guide to the quasi TE mode of the -iicrostnp lire) while guaranteeing good matching of the assembly and minimum losses for the signal crossir: the transition. If earth co n tinuity is not ensured cetween the two modes of propagation: mismatches appear respiting m a loss of energy of the signal by reflection, a part of the signal "^ay propagate outside the transition and disturb other e_ements of the circuit. The use of the above method makes _t possible to minimize the quantity of adhesive deposited on the suostrate and, consequently, tie cost of the process. Furthermore, to ensure effective bonding of the assembly with better resistance of the circuit to environmental constraints (temperature variations, humidity factor, thermal expansion) , according to another characteristic of the present invention, additional strips of conductive adhesive forming a mechanical reinforcement are deposited. Other characteristics a'd advantages of the present invention will become acoarent on reading the description given herembelo of a preferred embodiment, this description beirg given with reference to the appended drawings in which: Figure 1, already described, is a schematic perspective view of a microwa/e electronic module bonded to a support to which the present invention is applied. Figure 2 is a plan v--ew from above of a millimetre receiver made on a s-_ostrate which will be bonded in accordance with the present invention. Figure 3 is a view corresponding to that of Figure 1 showing the necessary bonding zones. Figure 4 is a plan view from below of the circuit of Figure 1 showing the location of the various bonding zones. To simplify the description, in the figures the same elements bear the same references. The application of the present invention to the case of a 40 GHz millimetre receiver will be described with reference to Figures 2, 3 a^d 4. As represented in Figure 2 , on a substrate 10 wrich may be made in a known manner from "Teflon" glass, has firstly been made a transition 11 between a circular guide 12 and a microstrip line 13 for the reception of the millimetre signal, namely the 40 GHz signal. The c-rcuit also comprises a bandpass filter 14 receiving as input the millimetre signal transported oy the microstrip line 13. The bandpass filter 14 is made in suspended microstrip line technology, its purpose being to filter the useful signal and to reject the image frequency and the leaks of the local oscillator. Mounted at the output of the bandpass filter 14 is a mixer 15 connected to the filter by a microstrip line 16. Moreover, a local oscillator (not represented) is connected to the mixer 15 by a microstrip line 17, this involving at the end of the ra.rrostrip line _7 away from the mixer a mιcrostr_t lme/coaxia- line transition dependent on the errt cdiment of the local oscillator. As represented in F__jre 2, the output of the mixer is linked to the _tput of the entire receiver block by a microstπt line 18, t- ~ _s also giving rise in this case to a ~_crostπp lme/coaxial line transition. With the circuit of Figure 2 and as represented in Figure 3, perfect earth cont---uιty must be oDtamed between the various modes of propagation. The zones where this earth continuity must oe obtained ha /e been represented by a thick line. This invoi r es in particular the output of the c.rcular wave gu_de 12, the perimeter of the bandpass filter 14 and the transitions 19 and 20 respecti ely between t^e local oscillator (not represented) and the microstrip line 17 for connection to the mixer ana between the Output of the receiver block and the m--orostrιp line 18 for connection to the output of the r-xer. In accordance with the oresent invention and taking into account the above~entιoned prob_ems of earth continuity, to avoid ar break in ti~e earth plane, the Teflon glass substrate 10 is bonαed to a metal support (not represented) cy depositing strips of adhesive, only n the zones represented by thιc< lines, namely the zones 12', 14', 19' a'd 20'. In accordance with an acoitional characteristic of the present invention, to e'sure better resistance to the constraints, strips of acesive are alsc applied as mechanical reinforcement, n-- ~ ely the strips 21, 22 and 23. In accordance with the oresent invent-,on, the strips of adhesive consist c: a conducti-g epoxy adhesive which may be a one- or two-component adhesive such as the adhesives sold by t"e company Epo-Tek under the reference H20E, this type be--ng given merel by way of example. These adhesives are laden with particles of silver or gold which prov-.de them witn their conductivity. Moreover, in accordance with the present invention, the adhes_ /e is depositeα preferabl y using screen pr_ntιng deposition. However, it is obv.ous to the person skilled -n the art that other tyoes of depositior, m particular deposition oy syringe or any similar ceposition -.sed in the technology of epoxy adhesives may be employed.

Claims: CLAIMS 1. Process for securing to a metal support at least one microwave electronic module made on a substrate one of whose faces forms an earth plane, characterized in that it consists ir. depositing between the face forming the earth plane ana the metal support, at least one strip of conducting adhesive (12 ',14', 19 ',20') at the level of the zones of breakage of the earth plane. 2. Process according to Claim 1, characterized in that additional strips (21, 22, 23) of conducting adhesive forming a mechanical reinforcement are deposited. 3. Process according to Claim 2, characterized in that the strips forming a mechanical reinforcement are deposited around the perimeter (21) of the face of the module forming the earth plane. 4. Process according to any one of Claims 1 to 3, characterized in that the adhesive is a one- or two- component conducting epoxy adhesive. 5. Process according to Claim 4, characterized in that the conducting adhesive is laden with conducting particles such as silver or gold. 6. Process according to any one of Claims 1 to 5, characterized in that the adhesive is deposited by using screen-printing deposition or deposition by syringe .

Inventors: GUGUEN CHARLINE, HAQUET GERARD, NICOLAS CORINNE, GUGUEN, CHARLINE, HAQUET, GERARD, NICOLAS, CORINNE
Applicants: GUGUEN CHARLINE, HAQUET GERARD, NICOLAS CORINNE, THOMSON LICENSING SA, GUGUEN, CHARLINE, HAQUET, GERARD, NICOLAS, CORINNE, THOMSON LICENSING S.A.
Application year: 2001
Main classification: H01P1
IPC codes: H01P1, H05K1, H05K3