Means for assembling a longitudinal body

Abstract: This invention relates to means for assembling a longitudinal body, such as a Surface Acoustic Wave (SAW) component (1,30,60) within a housing or capsule (package) (2,31,66). It includes means (3-11,32-37,61-64) for supporting the component (1,30,60) close to, but not in contact with, the bottom (25,42,79) of the capsule, thereby allowing certain movements of the component or certain parts of the component within the capsule. The supporting means includes a number of clamps (3-11,32-37,61-64) which are fixed to the capsule bottom by means of gluing, soldering, welding, brazing or other fixing method. At least two of the clamps (61-62) are arranged at one end (65) of the component, with an orientation substantially corresponding to the longitudinal direction of the component.

Description: The present invention relates to means for mounting a flat longitudinal body such as a Surface Acoustic Wave (SAW) component within a component housing or capsule. A mount system for surface acoustic wave devices is known (EP 0,185,532) in which the SAW component is resting freely on - and is in full contact with - the bottom of a package cavity. The cavity may be provided with a pad. The component rests upon the pad and there are not indicated, described or provided any means for supporting the component close to, but not in contact with, the bottom of the capsule. In the known device the component is placed on the substrate and the cradle is placed on top of the component, - but only in contact with the substrate. The dimensions of the cradle are kept very close to, but slightly larger than the dimensions of the component. None of the parts of the cradle exerts any pressure against the component. This is also true with the tabs which extend about 0.4 mm over the component. It must be obvious to anyone skilled in the art that these tabs are not meant to - and cannot be calibrated - to exert a certain pressure against the top of the component. The known technique may be suitable for mounting of small components but it is not suitable for mounting larger components (20-200 mm long and 5-15 mm wide). SAW components or devices are characterized by the use of a piezoelectric crystal substrate with electro acoustic transducers, normally a metal film forming an interdigital 'finger' pattern, deposited onto the crystal surface. The transducer produces an electric field over the crystal surface when an electric signal is applied to it. This electric field is transformed into a mechanical force in the crystal, which subsequently launches an acoustic (mechanical) wave in the crystal surface. Conversely, the transducer may convert the acoustic energy back to an electric signal. The most commonly used substrate materials are quartz, lithium niobate and lithium tantalate. These materials are, by their nature, sensitive to mechanical stress. Any mechanical stress will influence the electrical behaviour of the SAW component. SAW components usually have a longitudinal structure, i.e. its length is greater than its width, and they are usually glued along one of its surfaces to the bottom of a housing or capsule. This assembling method can be considered suitable for smaller SAW components, such as those having a length of less than 20-30 mm and for SAW devices with moderate electric performance requirements over the operating temperature range. When larger SAW components are concerned, and when both the electrical performance requirements and the operating temperature range are demanding, other assembling means will prevail, in order to avoid degradation of the electrical performance of the SAW component due to the mechanical stress introduced by the differential coefficient of thermal expansion between the SAW substrate and the capsule. An alternative, well known approach is to isolate the entire SAW component and its capsule thermally, e.g. by use of a temperature controlled heater. This method is however in many cases impracticle or unacceptable for cost or other reasons. Another SAW device (JP 01, 291, 510) is known which is mounted in a housing supported with a flat surface close to but not in contact with the bottom of the capsule. Although parts of the body are fixed to the package base, an appropriate elasticity allows certain movements of the body within the capsule. The object of the present invention is to provide means for mounting a flat longitudinal body such as a SAW component within a component housing or capsule which satisfy electrical performance requirements even under severe environmental conditions (temperature, vibration). One aim of the invention is to provide a mounting technique which allows the SAW crystal to expand and contract with respect to the capsule without being stressed mechanically, and thereby avoid degradation of the electrical behaviour of the SAW component, and simultaneously allows the SAW component to withstand severe mechanical vibration, e g as experienced in satellites during their launch and in missiles and aircraft. The features of the invention are defined by the appended claims. With the invention there is obtained assembling means which is suitable for SAW components having a length exceeding some 20-30 mm up to some 100 to 200 mm. The width and thickness of such components are respectively in the order of 5 - 15 mm and 0.5 - 2 mm. A component having a length of 70 mm, a width of 10 mm and a thickness of 0.8 mm has been verified to withstand random vibration levels exceeding 28 g rms . Above mentioned features and objects of the present invention will clearly appear from the following detailed description of embodiments of the invention taken in conjunction with the drawings, where Fig. 1 and 2 show a SAW component mounted within a capsule, Fig. 3 and 4 show another SAW component mounted within a capsule. Fig. 5 and 6 show details of a supporting clamp, and Fig. 7 and 8 show a preferred embodiment of the invention. It should be noted that the components and parts are not shown to scale in any of the drawings. In Figure 1 is schematically illustrated a SAW component 1 assembled within a housing or capsule 2 having a length of some 100 mm and a width of some 12 mm. This is a delay line component which is supported by a number of clamps 3-11. All the clamps are fixed to the capsule bottom by means of gluing, soldering, welding, brazing or other fixing method. The component is free to move in its longitudinal direction against forces applied by the clamps. The clamps 3 and 4 (and the optional clamps 7 and 8) are socalled 'hard' clamps which are each calibrated to apply a force exceeding 80 grams, to give a resulting force of some 160 grams on each side of the component against longitudinal withdrawal. If the clamps 7 and 8 are omitted the withdrawal force of the clamps 3 and 4 should be in excess of 120 grams. When using the two clamps 7 and 8 these should be placed as close as possible to the clamps 3 and 4. The clamps 5 and 6 are socalled 'loose' clamps which are calibrated to give a force against longitudinal withdrawal of some 60 - 80 grams, to allow longitudinal movements of the right part of the component. It should be noted that the clamps 3 and 7 are arranged somewhat displaced (by 0° to 10°) from the clamps 4 and 8 across the component, and so are the clamps 5 and 6. An optional supporting clamp 9 is arranged on one side of the rather long component. As a rule such side clamps are only required for components longer than some 80 mm. A corresponding clamp on the other side of the component is neither considered desirable nor necessary. Two optional 'loose' clamps 10 and 11 are arranged, one in each end of the component, to prevent excessive longitudinal movement of the component. The clamps 9 - 11 are calibrated to give a force of some 10 - 40 grams against longitudinal movement of the component. As illustrated, the component is provided with recess like end portions 12 and 13 so as to save place within the capsule walls. The distance from the component ends 12, 13 to the clamps 3,4 and 5,6 is in the order of 1/8 to 1/5 of the length of the component. On the upper side, the side edges of the SAW component 1 is provided with a layer of damping material 14. A suitable damping material can be a soft non-conducting glue. The stripe of damping material is interrupted at positions where the clamps are mounted, and where terminations are made at positions 17-18. The capsule 2 is provided with a number of lugs 19-24 for securing the capsule package to some other equipment (not shown). An enlarged crossection of the capsule mounted SAW component taken at line II-II through the clamp 6, is illustrated in Figure 2. This figure shows the component 1 supported by clamps 5 and 6. These clamps are soldered, glued or by other means fixed to the capsule bottom 25. The upper side edge of the component is provided with a conventional stripe of reflection damping material 14. This damping stripe is interrupted at the clamps and it is therefore not shown in connection with clamp 6. A similar crossection could be shown through the clamps 3,4,5,(6),7,8 and 9, and also in principle for the clamps 10 and 11. The end clamps 10 and 11 may be omitted if the risk of excessive longitudinal movements is negligible, or they may be substituted by other stopping means. In Figure 3 is illustrated a different type of SAW component 30 assembled within a capsule 31 having a length of some 60 mm and a width of some 18 mm. This is a chirp filter component 30 which is supported by clamps 32-37, two of which are 'hard' clamps 32, 33 which are calibrated to give a withdrawal force larger than 70 grams. The 'loose' side clamps 34, 35 are calibrated to a force in the order of 10 - 40 grams for allowing defined longitudinal movement of the left part of the SAW component. The optional 'loose' end clamps 36, 37 arranged in recess like end portions 45-46 are calibrated to give 10 - 40 grams, to prevent excessive longitudinal movement of the component. A crossection through the clamp 32 taken along a line IV-IV in Figure 3 is shown in Figure 4. This crossection is similar to that shown in Figure 2, which illustrates a crossection of Figure 1. Similar crossections can in principle also be made through the clamps 33-35 and through clamps 36 and 37. The capsule 31 is provided with lugs 38 and 39. Electrical connections to the SAW component are made through leads 40 and 41. The clamps shown can be of the type having three fingers as illustrated in Figures 1 and 3 (and 7). Two of the fingers are fixed to the capsule bottom 25 and 42 respectively, whereas the third finger, is bent with a calibrating tool to give a desired pressure against the component 1 and 30 respectively. A typical clamp 50 can be made as shown in Figures 5 and 6 for supporting a component 51. The thickness of the clamp is 0.25 mm, the width of the fingers 52,53,54 some 0.5 mm and the length of the fingers some 2.5 mm. The thickness of the component is some 0.5 mm and its contact area 55 with the finger 54 is indicated. The clamps are preferably made of phosphor bronze. Somewhat larger clamps can be used for the long components. The crystal should be supported such that at a resonant frequency of 400-800 Hz, the maximum outswing should be 0.2 mm at a gravity of 5g. After being calibrated by inserting shims of defined thickness between the fingers and measuring the withdrawal force with dummy components, the clamps are cut to correct length and mounted on the component. Thereafter the clamp-component assembly is fixed to the capsule bottom with suitable means. In a preferred embodiment of the invention shown in Figures 7 a band pass filter component 60 is supported by only four clamps 61-64 mounted at the ends of the component, with no side mounted clamps. Preferably the component should be fixed to the capsule bottom in one end by means of glued distance pieces or the glued clamps 63-64, so that the far end 65 of the component is free to move within the clamps 61-62 in the longitudinal direction. The length of this component is some 50 mm, the force of each of the clamps 61-62 is 10-30 grams whereas the force of each of the clamps 63-64 exceeds 60 grams against longitudinal withdrawal. The component is arranged within a capsule 66 through the walls of which there are terminals 67-70 leading to bonding areas 71-74 on the crystal 60. The clamps 61-62 are glued 76 to the bottom 79 of the capsule 66 to hold the crystal 60 in a similar way as shown in Figure 2and 4, whereas the clamps (or distance pieces) 63-64 may be fastened by glue or other fixing means 77 to the capsule bottom 79 and to the crystal as illustrated in Figure 8. The component transducer is indicated at 78. By arranging the clamps at the ends of the crystal only, the capsule can be less wide than when there are arranged clamps along the side of the crystal. Damping material for the SAW crystal is not shown in Figure 7. In Figure 8 is illustrated a crossection through the clamps 62 and 64 in Figure 7, taken along the line VIII-VIII. As an alternative to calibrating the 'hard' clamps 3-4,7-8, Figure 1 and the 'hard' clamps 32 and 33, Figure 3 to some 70 grams or more, the components 1 and 30 respectively, can be glued to these clamps and to the bottom of their capsules 2 and 31 respectively at this position. In this alternative embodiment the clamps 3-4, 7-8 and 32-33 merely function as distance pieces between the lower side of the component and the capsule bottom. Crossections of these alternatives will be similar to the crossection of clamp 64 in Figure 8. If the components 1 and 30 are secured to the capsule bottom at the position of the 'hard' clamps, the end clamps can be omitted, thus saving place in the longitudinal direction. With the invention and the embodiments shown the crystal components will withstand vibrations with 20-30 g rms at 20-2000Hz and temperature cycling from -25°C to +125°C. The operating temperature of the component is from -25°C to +100°C. There is obtained a phase stability of 2° peak-to-peak within the temperature range of 125°C. The above detailed description of embodiments of this invention must be taken as examples only and should not be considered as limitations on the scope of protection.

Claims: Means for mounting a flat longitudinal body such as a SAW component (1, 30, 60) within a component housing or capsule (2, 31, 66), characterized in that it includes means (3-11, 32-37, 61-64) for supporting the body (1, 30, 60) with a flat surface close to, but not in contact with, the bottom (25, 42, 79) of the housing or capsule, thereby allowing certain movements of the body or certain parts of the body within the housing or capsule, the supporting means being constituted by clamps (3-11, 32-37, 61-64) which are fixed to the capsule bottom by means of gluing, soldering, welding, brazing or other fixing method. Means according to claim 1, characterized in that each of the clamps includes lower fingers (52, 53) and an upper finger (54) which are arranged and calibrated to exert a predetermined positive holding pressure on a flat longitudinal body (51) mounted between the two parts. Means according to claim 1, characterized in that at least two of the clamps (10-11, 36-37, 61-62) are end clamps arranged at the end(s) of the body with an orientation substantially corresponding to the longitudinal direction of the body. Means according to claim 1 or 2, characterized in that at least two of the clamps (3-8, 32-35) are side clamps arranged at positions close to one or both ends of the body with an orientation substantially perpendicular to the longitudinal direction of the body. Means according to claim 1, characterized in that at least two of the clamps (32-33, 63-64) are fixed to the body by means of glue, these clamps being arranged in or close to one end of the body. Means according to claim 1, characterized in that at least two of the clamps (5-6, 10-11, 34-35, 36-37, 61- 62) are arranged to allow longitudinal movement of the body against a first defined force. Means according to claim 6, characterized in that at least two clamps (3-4, 7-8, 32-33, 63-64) are arranged to allow longitudinal movement of the body against a second defined force which is greater than the first defined force. Means according to claim 6, characterized in that the first defined force is in the order of 10-80 grams, preferably 10-40 grams. Means according to claim 10, characterized in that the second defined force is greater than 60 grams. Means according to claim 4, characterized in that the distance from the body end(s) to the side clamps (3-8, 32-35) is in the order of 1/8 to 1/5 of the length of the body. Means according to claim 4, characterized in that at least one clamp (10-11, 36-37) is arranged at each end of the body to limit the longitudinal movement of the body, and that the clamps (10-11, 36-37) for limiting the longitudinal movement of the body are arranged at recess like end portions (12-13) of the body. Means according to claim 4, characterized in that clamps (3-8, 32-35) arranged at opposite sides of the body are slightly offset across the body. Means according to claim 1, characterized in that the side edges and end portions on the lower and upper side of the freely supported body (1, 30, 60) are provided with a stripe (14, 44) of damping material, interrupted by the supporting means.

Inventors: HASLEBERG HARALD, HASLEBERG, HARALD
Applicants: ALSTHOM CGE ALCATEL, ALCATEL ALSTHOM COMPAGNIE GENERALE D'ELECTRICITE
Application year: 1992
Main classification: H03H9
IPC codes: H03H9