GB2076221A - Method for the production of casings for electronic components - Google Patents

Abstract

To form the base part of the casing, a window is cut in a conducting plate leaving two tongues extending into the window whose ends 6a, 6'a are bent out of the plane of the plate. An insulating layer 8 is deposited on the plate, filling the window to form an insulating support 10 and embedding the bent ends 6a, 6'a of the tongues. The central portion of the plate is removed so as to leave only a frame 12. The roots of the tongues are also removed to separate the bent ends of forming through connections 6a, 6'a from the frame 12. The cover member is produced from a conducting plate on which a uniform insulating layer is deposited. The central part of the conducting plate is removed, so as to leave only a frame corresponding to the frame on the base member. After mounting a component, in particular a quartz resonator, on the support 10 and connecting to the through connections 6a, 6'a the cover is fitted e.g. by soldering the frames together. <IMAGE>

Description

SPECIFICATION Method for the production of casing for electronic components The present invention concerns a method for the production of insulating casings for electronic components, the casing having two parts which are sealed together so as to permit encapsulation, more particularly but not exclusively, of a quartz oscillator element for forming a resonator, for example for an electronic watch.

It is well known that a resonator essentially comprises a quartz oscillating element (bar or tuning fork) on which there are disposed metal deposits forming electrodes, and a casing which encloses the oscillator element.

When the oscillator element is a tuning fork configuration, it is fixed to the casing by means of the base portion of the tuning fork, and electrical connections which are connected to the electrodes must pass through the wall of the casing. In addition, the casing must be sealed in order to permit a certain degree of vacuum to be produced within the casing, with a view to proper operation of the resonator.

A number of methods for making such casings are already known. In one of these methods, the tuning fork-configuration oscillator element is surrounded by a frame which is cut out at the same time as the oscillator element from a plate of piezoelectric material.

The frame is fixed between the edge portions of a cover and a base member which form the casing. This process is not very advantageous when the oscillator elements must be massproduced. Indeed, the presence of the frame reduces the number of oscillator elements which can be machined at the same time in a plate of given dimensions. The cover member and the base member may each be formed by a flat insulating plate, in which case conducting frames forming a spacer are interposed between the frames of the oscillator element and the plates, to permit the quartz to oscillate. The frames serve at the same time as electrical conductors for connecting the electrodes to the exterior of the casing. However, the size of the metal frames interferes with the electrical signals collected.

Another solution is to produce recesses in the insulating plates which form the base and cover members of the casing. As the plates are made for example of glass, machining thereof is a highly delicate operation. In addition, in such a case, the output connections are formed by piercing one or more passages through the wall of the casing and metalplating the passage or passages; it is then difficult to maintain the vacuum within the casing.

With a view to remedying those disadvantages, a first object of the invention is to provide a method for the production of a casing, which does not require any machining of the insulating material forming the casing.

A second object of the invention is to provide such a method, by means of which the conductive connective elements through the casing are produced without piercing the casing.

A third object of the invention is to provide a method which makes it possible simultaneously to produce a large number of casings.

A fourth object of the invention is to provide a method for the production of casings which are specially adapted to the encapsulation of oscillator elements and which are compatible with oscillator elements such as tuning fork members of standard type.

A fifth object of the invention is to provide a method which permits encapsulation of the oscillator element and an integrated circuit associated therewith, the casing then carrying all the electrical connections required.

With a view to achieving these objects there is provided a method according to the invention as defined in claim 1 below. In particular we may proceed by forming a base member and a cover member, taking a metal conducting plate as the basic starting component for each part of the casing. To produce the base member of the casing, a window which defines a plurality of tongue portions are then bent so as to have an end portion which is perpendicular to the plate. A layer of insulating material of constant thickness is then formed on one face of the metal plate in such a way that the ends of the bent portions of the tongues project out of the insulating layer.

When the insulating layer is deposited, the insulating material also penetrates into the window in the plate. The conducting plate is then etched so as to leave only a raised frame on the insulating layer, separated from the bent ends of the tongue portions. Preferably, the cover member of the casing is produced by depositing a uniform layer of insulating material on a conducting plate and etching the plate so as to leave only a frame corresponding to the frame of the first part of the casing. In the case of a resonator, the base of the oscillator element is fixed on the portion of insulating material which filled the window and connections (direct or via an integrated circuit) are made to the internal ends of the tongue portions, forming conductive connecting elements.The bottom member and the cover member of the casing are assembled by way of the free faces of their frames, to form the casing.

It will be appreciated however that the cover member could be produced in a different manner, provided that it has an edge portion defining a central recess and that its edge portion has an assembly face suitable for co-operating with the assembly face of the casing base member.

In other words, it will be seen that, as regards the base member of the casing, the invention can be carried out by a first operation of machining a metal plate which then serves, so-to-speak, as a 'mould' for producing an insulating layer, then effecting a second operation of machining the conducting plate in order on the one hand to define a central recessed portion and on the other hand to separate the conductive connecting elements which extend through the casing from the conducting frame which defines the recessed portion in the base member of the casing.

The invention also concerns the use of the process for producing quartz resonators.

In any event, the invention will be better appreciated from the following description of a number of embodiments of the method according to this invention. The description is given with reference to the accompanying drawings in which: Figures 1 to 3 show views illustrating the different steps in the production of the first part of the casing (or base member) in accordance with a first embodiment, wherein Figure 2b is a view in vertical section taken along line B-B in Figure 2a and Figures 3b and 3c are views in section taken along lines B-B and C-C in Figs. 3a; Figures 4a and 4b are views illustrating the steps in the production of the second part of the casing (or cover member), in accordance with the first embodiment, Fig 4b being a view in vertical section taken along line B-B in Fig. 4a;; Figure 5 shows a view in vertical section of the finished casing produced by the first embodiment of the process and provided with the oscillator element; Figure 6 shows a view in vertical section illustrating an alternative form of the first embodiment of the process which makes it possible simultaneously to produce a large number of casings; Figures 7 and 8 are two views illustrating the steps of an alternative form of the first embodiment of the process which provides for encapsulation of the oscillator element and the associated integrated circuit; Figures 9 and 10 are views illustrating the machining of the metal plates to form the bottom member and the cover member of the casing, in accordance with a second embodiment of the process; and Figure 11 is a view in longitudinal section of a complete casing produced by the second embodiment of the process according to the invention.

Referring firstly to Figs. 1 to 5, we shall describe a preferred embodiment of the process for the production of a single casing. The following description relates to encapsulation of an oscillator element for producing a resonator. It will be understood that the process could be used for encapsulation of another electronic component such as an integrated circuit.

As can be seen from Fig. 5, the casing comprises a first part or base member A on which the oscillator element B (tuning fork) is fixed, and a second part or cover member C which is assembled to the bottom member A by way of its edge portion. Hereinafter in the description, the terms 'base member' A and cover member' C will be used, it being appreciated that the base member is the part of the casing which carries the oscillator element and that no particular orientation of the casing is implied.

Figs. 1 to 3 more particularly illustrate the production of the base member of the casing.

The starting point is a conducting plate 2 whose peripheral outline is of the external configuration of the casing to be produced.

The plate is for example 0.2 mm in thickness.

An opening is cut out in the plate 2, to define a window 4 into which extend two tongue portions 6 and 6' which are integral with the remainder of the plate. The free end portions 6a and 6'a respectively of the tongue portions 6 and 6' are bent so as to make them substantially perpendicular to the plate 2, as can best be seen from Fig. 2b.

In a second step which is shown in Figs. 2 and 2b, a layer 8 of insulating material is deposited by any suitable process on the face 2a of the plate 2 towards which the tongue portions 6a and 6'a have been bent. The deposited layer is of uniform thickness which is less than the length of the bent portions 6a and 6'a of the tongue portions 6 and 6'. This means that the ends 6b and 6'b of the tongue portions project from the layer 8. In the deposit operation, the insulating material also fills the window 4 in the plate 2, thereby forming a base 10 of insulating material. In the deposit operation, the bent portions 6a and 6'a of the tongue portions are thus embedded in the layer 8 of insulating material. Preferably, the insulating material is glass or a similar material (ceramic, porcelain, some plastics materials, and so on). It is desirable for the insulating material also to be transparent in order to permit adjustment of the frequency of the resonator by means of a laser beam. The conducting plate 2 is made of an electrically conducting material which has the same coefficient of heat expansion as the insulating material used and to which the deposit of glass or similar material firmly adheres. The conducting material may be for example the alloy which is known by the Trade Mark 'Kovar'. This is an alloy of nickel, iron and cobalt. It would also be possible to use iron-nickel alloys. The deposit of glass is formed for example by placing glass powder on the plate and heating it to its melting temperature. Another process would involve casting molten glass directly on the plate.It should be noted that, when glass is deposited in a hot process, surface oxidation of the conducting material occurs, which permits the glass to adhere to the metal by virtue of the presence of the mixed oxides.

In a following step of the process, the conducting plate 2 is locally removed over its entire thickness. This-removal operation leaves only a frame 12 which extends round the periphery of the insulating layer 8. This insu lating layer 8 is therefore exposed in the central region 13. In the operation of remov ing the conducting plate, the non-bent por tions 6c and 6'c of the tongue portions 6 and 6' are also removed, exposing the insulating layer 8 in the regions 14 and 14', as can be seen from Figs. 3a and 3b. The bent portions 6 and 6'a are not affected by the removal operation. Thus, the frame 12 is no longer electrically connected to the portions 6a and 6'a of the tongues, the inner end faces 6d and 6'd of which lie flush with the face 1 Oa of the base 10. The result of these operations is the base member A of the casing.It will be appreciated that in plan view the frame 12 and the faces 6d and 6'd of the tongue portions are the only metal parts which are visible. The rest is formed by insulating mate rial. However, the visible face of the insulating material is at two levels: an upper level (base 10) and a lower lever (regions 13, 14 and 14'). It is for this reason alone that Fig. 3a shows the regions 13, 14 and 14' and the region 10 by different hatchings, although the same material is involved.

Figs. 4a and 4b illustrate the production of the cover member C. In accordance with a preferred embodiment, the starting point is a conducting plate 20 on one face of which there is deposited a layer 22 which adheres to that face, the layer being of constant thick ness and comprising an insulating material.

The plate 20 is also preferably of 'Kovar' (Trade Mark). The central region 24 of the conducting plate 20 is then removed so as to leave only a frame 26. The frame 26 is of the same shape as the frame 12 of the base member A of the casing. The free face 26a of the frame 26, like the free face 1 2a of the frame 12, from the faces for assembly of the casing.

In the case of a resonator, the base of the oscillator element B is fixed on the base 10 of insulating material. Preferably, the ends of the electrodes of the oscillator element (not shown in Figs. 1 to 5) are welded or secured by conductive adhesive to the end faces 6d and 6'd of the conducting connector means formed by the bent portions 6a and 6'a of the tongue portions. A conductive epoxy resin can be used as the adhesive. It will be clearly evident that, since the base of the oscillator element is secured to the base 10, there is a clearance between the base member of the casing and the oscillator element. Then, the cover member C and the base member A are assembled together by way of their assembly faces 1 2a and 26a, by means of a bonding layer 30.The layer 30 may comprises two engagement layers which are deposited on the assembly faces respectively and a soldering layer. It will be appreciated that the thickness of the conducting plate 20 must be greater than the thickness of the oscillator element B.

By way of example, the insulating layers 8 and 22 may be 0.2 mm in thickness, the plate 2 may be 0. 15 mm in thickness, and the plate 20 may be 0.3 mm in thickness.

The cased resonator thus has a total thickness of 0.85 mm.

The above-described process is particularly well suited to the simultaneous production of a large number of cased resonators or more generally casings and it is this that is illustrated in Fig. 6. In this case, the starting point is two plates of 'Kovar' (Trade Mark) which make it possible respectively to define a matrix of base members A1, A2, A3 ..., a plurality of windows identical to the window 4 in Fig.

1 are cut out, and the portions of the tongues 6a1, 6a2, etc are bent over. The insulating layer 8' is then deposited, which also fills the windows to give the bases 10" 102, 103 Portions of the conducting plate are then removed so as to leave only frames 12,, 1 22, 1 . .33the width of which is greater than the width of the frame 12 shown in Fig. 2 since each frame edge is common to two juxtaposed casings.

A uniform layer 22' of insulating material is deposited on the conducting plate for forming the cover members C,, C2, C3 ... Portions of the conducting plate are removed so as to leave only the frames 26" 262, 263 It will be appreciated that in this case also the cover members could be produced by a different process.

After the oscillator elements B,, B2, B3 have been set in place on the bases 101, 102, 103 the assembly of cover members is laid upon the assembly of base members. The insulating layers 8' and 22' are then joined together by means of the frames 1 21, 1 22 and 26" 262 . Finally, the resonators R,, R2, R3 are separated by cutting the resulting assembly at the locations of the edge portions along lines X1, X2, X3 Figs. 7 and 8 show an alternative form of the casing which makes it possible to encapsulate not just the oscillator element but also the integrated circuit which is associated therewith. Fig. 7 shows the portion which is cut out in the conducting plate 102 which comprises 'Kovar' (Trade Mark).As can be clearly seen, the only difference between this Figure and Fig. 1 lies in the shape of the window 1 04 corresponding to the window 4.

The window 104 is of greater dimensions and in particular it defines a larger number of tongue portions as indicated at 106, 106', 106" and 106"'. Of course, the number and configuration of the tongue portions depends only on the number and arrangement of the terminals of the integrated circuit. The tongue portions are bent over in part, as already described hereinbefore. The insulating layer is then deposited, and the operations of removing the metal layer are then performed, as already described above.

Fig. 8 shows the final structure of the bottom member of the casing, the cover member being identical to that shown in Fig. 4.

The final structure comprises the frame 112 of conducting material and the conducting through-connecting means which are formed by the bent portions of the tongues, of which Fig. 8 shows the heads (inner end faces) 106d, 106'd, 106"d and 106"'d. The through-connecting means are separated from the frame 11 2 by removal of the regions 114, 114', 114" and 114"' of the metal plate 102. The insulating material which has passed into the window 104 forms the base 110. The base of the oscillator element B which is in the form of a tuning fork in this example is secured by adhesive to the base 11 2, together with the integrated circuit F.

Conductor wires 130 and 130' connect the electrodes (not shown) of the tuning fork element B to the appropriate inputs of the integrated circuit F. The other connecting pads of the integrated circuit are connected by the conductor wires 132 to the heads 106d, 106cud ... of the conducting through-connecting means. Installing the integrating circuit in the insulating casing makes it possible to save a substantial amount of space. In addition, it will be seen that the number of conducting through-connecting means is limited only by the capacity for defining tongue portions 106 in the window 104. For this Figure, the same convention of illustration is used as in respect of Fig. 3a.

The operation of removing the portions of the conducting plate is preferably performed by etching with masking, in known manner.

The result of this is that it is difficult to provide for a highly accurate definition in respect of the edges and the inward side surface of the frame 12 or 112. When it is necessary for the edge portions to be defined in a more accurate and precise manner, it is possible to use a second embodiment of the process according to the invention.

In this embodiment, the bottom member A of the casing is produced from a 'Kovar' (Trade Mark) plate 202. The window 204 is then cut out in that plate, being similar to the window 4 in Fig. 1, with its tongue portions 206 and 206'. However, L-shaped strips of metal 240 and 240' are also removed, the strips of metal extending parallel to the peripheral outline of the plate 202, leaving an edge which will form the frame 212 similar to the frame 12 or 112. The slots 240 and 240' and the window 204 surround a region 213, corresponding to the region 13 in Fig. 3a.

Metal bridge members 242, 242' and 242" connect the central region 214 to the edge of the plate 202. When the operation of depositing the insulating layer is carried out, as already described hereinbefore, the insulating material penetrates not only into the orifice 204 but also into the slots 240, 240', thus forming 'walls' of insulating material which, with the base 210 which results from the window 204 being filled, surround the central region 213 which is of metal. In the last step of the process, the non-bent parts of the tongue portions are removed, and the central region 213 of the metal plate 202 is removed. It will be appreciated however that, in the removal operation, the portion of metal, which is to be removed is more or less entirely surrounded by insulating material.

There is therefore no longer any problem in regard to definition of the sides of the edge portion in the chemical attack operation, since that edge portion side is defined by the wall 224. In this case, the complete frame of the base member A comprises on the one hand the strip of metal 212 which was not removed, and on the other hand the wall 244 of insulating material.

Operation is similar with regard to the cover member C. Slots 250, 250', 250" and 250"' are machined in the metal plate 202, leaving on the plate a frame between the slots and the outline of the plate. When the uniform layer of insulating material 222 is deposited, the insulating material also passes into the slots 250, ... 250"', to form walls 252 of insulating material around the central region 224. Removal of the central region 224 of the metal plate 220 is therefore defined by the insulating material 'walls' 252. As for the base member of the casing, the edge portion is formed by the juxtaposition of the insulating wall 252 and the metal frame 226 which has not been removed. After the oscillator B has been fixed, the cover member C is fixed on the base member of the casing by the con #necting faces of the conducting edge portions 212 and 226. This embodiment is also suitable for the simultaneous production of a plurality of casings.

It will be seen from the foregoing description that the process, in its various forms, has many advantages over the prior art processes.

There is no machining operation to be performed on insulating material or glass. Indeed, the only machining operations (including etching) are carried out on the metal plates, which is easier, and they only require the machining of two masks for the base member and a single mask for the cover member of the casing. The conducting through-connecting means are formed by the bent portions of the tongues. The connecting means are therefore embedded in the layer of glass when it is deposited. The glass therefore adheres very strongly to the metal, and the seal is perfect. The number of such connecting means is virtually unlimited. In addition, the non-bent portion of the tongue portions positions the bent portion in the operation of depositing the insulating layer, thereby further simplifying production. The different steps of the process are highly suitable for mass production of the cover members and the base members and assembly thereof after the components, for example oscillator elements, have been set in position.

The process makes it possible to produce a casing which is of very small thickness (for example of the order of 0.85 mm). Under these conditions, it will be appreciated that the process is particularly advantageous for producing quartz resonators for use in analog or digital electronic watches in respect of which the aim is to achieve a minimum thickness.

Claims (13)

1. A method of making an insulating casing for an electronic component, comprising the steps of cutting a window in a conducting plate, leaving at least one tongue extending into the window, bending the free end of the or each tongue out of the plate of the plate, forming a layer of insulating material over that face of the plate from which the bent end of the or each tongue projects so as also to fill the window and embed the bent end of the or each tongue, but leaving the bent end(s) exposed at both faces of the insulating layer, removing a central portion of the conducting plate so as to leave a conducting frame and remaining part of the plate between the or each said bent end and the frame, thereby to form a first casing part with at least one conductive connecting element extending through the insulating layer; and forming a second casing part for fixing to the frame to close the casing.

2. A method according to claim 1, wherein the second part is made by forming a layer of substantially uniform thickness of the insulating material on a second conducting plate, and removing a central portion of the second conducting plate so as to leave only a conducting frame of substantially the same shape as the conducting frame of the first part, for closing the casing by joining the frames together.

3. A method according to claim 1, wherein, as well as the window, one or more slots are cut through the plate to separate the central portion from the frame, the slot(s) being also filled by the insulating material.

4. A method according to claim 2 and 3, wherein one or more slots are also cut through the second plate to separate the central portion from the frame thereof, these slot(s) being also filled by the insulating material.

5. A method according to any of claims 1 to 4, wherein the insulating material has substantially the same coefficient of thermal expansion as the material forming the conducting plate(s).

6. A method according to claim 5, wherein the insulating material is transparent.

7. A method according to claim 6, wherein the insulating material is glass.

8. A method according to claim 7, wherein the conducting material is an alloy of iron, nickel and cobalt.

9. A method according to any of claims 1 to 8, wherein there is a plurality of tongues and hence of conductive connecting elements, and comprising the steps of fixing the base of a piezoelectric oscillator element to the part of the insulating layer which filled the window and coupling electrodes of the oscillator element to the connecting elements.

10. A method according to claim 9, wherein the electrodes are directly connected to the connecting elements.

11. A method according to claim 9, wherein an integrated circuit is also mounted on the part of the insulating layer which filled the window and terminals thereof are connected to the electrodes and to the connecting elements.

12. A method according to any of claims 1 to 11, wherein a plurality of adjoining first casing parts are formed on a common conducting plate.

13. A method according to claim 12, insofar as dependent on claim 2, wherein a plurality of adjoining second casing parts are formed on a common second conducting plate, electronic components are mounted on the first parts with connection to the conductive connecting elements, the frames of the first and second casing part are joined and the casings are then separated from each other.

14 A method of making an insulating casing for an electronic component, substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 5 or 6 or 7 and 8 or 9 to 11 of the accompanying drawings.