US2413579A - Crystal holder - Google Patents

Description

I 1, 1946. M. PENNYBAC-KER 5 2,413,579

- cmgmu. noun-m Filed June 28, 1945 mmvmx.

' Mus PEN/VYBAGKE/P ATTORNEY Patented Dec. 31, 1946 UNITED STATES PATENT OFFICE Claims.

This invention relates to a holding device for piezo-electric crystals, more especially to a holder taking the form of a hermetically sealed unit, containing the crystal therein, and provided with contact pins whereby the unit may be rapidly insei'ted into, or removed from a supporting socket or the like. i

The requirements of the present day electronic art have rendered it necessary to use a relatively large number of quartz crystals, for frequency determining purposes, located in relatively confinedquarters. For example, certain radio transmitters may utilize thirty or mor such crystals, in conjunction with a switching system, in order to 'allow rapid and accurate changes to a similar insulating material, this arrangement giving relatively short leakage paths between the connecting pins.

The body of the crystal holder, in this type, is formed of a single, cup-like body of'metal, designed to be placed over the crystal, after the latter has been mounted on the base. The hermetic seal is then accomplished by soldering the open lip of the metal body to the periphery of the base structure. When such soldering operation is performed, a considerable amount of heat is required, since the metal body, as well as the base structure, are both conducting heat with comparative rapidity away from the point of soldering.

In such operation, the heat conducted by the metal body will be radiated inwardly upon both sides of the crystal, which latter is situated parallel to these walls and only a short distance therefrom. The combined result of these various eil'ects is to elevate the temperature of the crystal to an undesirable extent, frequently resulting in permanent alteration of the frequency characteristics thereof.

Other types of crystal holders hitherto employed have used a one-piece glass cup which is employed in the same manner as the metal can just described, the final sealing againtaking place at the base of the holder, where undesirable temperature rise is produced.

One object of this invention is to provide a crystal holder which shall be very compact, so that a large number of complete units, including the crystals, may be mounted in a relatively small space.

Another object of this invention is to provide an improved unitary structure embodying both a frequency determining crystal and a hermetically sealed enclosure protecting the crystal against deleterious atmospheric conditions, such as high humidity.

Yet another object of this invention is to provide, in improved form, a completely mounted and enclosed quartz crystal to which connection may be made through prong and socket arrangements, so that rapid interchangeability of crystals is readily secured.

Still another object of this invention is to provide a holder in which a piezo-electric crystal may be hermetically sealed without danger of raising the crystal to an unduly high tempera. ture, during the sealing process, which high temperature might deleteriously affect the predetermined frequency at which the crystal hasbeen designed to oscillate.

Another purpose of this invention is to provide a frequency determining unit of the plug-in type wherein the contact pins or prong are separated from one another by a relatively long insulating path of glass or similar material, whereby leakage between the prongs over such separating paths is reduced and whereby the capacity between the prongs is greatly reduced.

Yet another purpose of this invention is to provide a crystal holder into which the crystal may readily be inserted and in which the hermetic sealing of the holder, after insertion of the crystal therewithin, will take place at a point sufliciently removed from the crystal, and in the absence of heat conducting elements extending from the point at which sealing takes place to the vicinity ofthe crystal, so that the heat necessarily used for sealing will not be materially conducted to other points in the vicinity of the crystal itself.

An additional purpose of this invention is to provide a crystal holder wherein the final hermetic scaling is accomplished by soldering a metal cap so as to close one end of the holder, and

wherein the soldering operation takes place sub-- stantially entirely on a single plane surface at one extreme end of the holder, at a point rela- 3 tively distant from the crystal, which has previously been inserted into the holder.

Still another purpose of this invention is to provide a crystal holder which shall be relatively transparent to radiations having a wave-length lying between 0.001 micron and 0.00001 micron, such radiations being useful for efiecting changes in the oscillating frequency of the crystal, after it has once been sealed within the holder.

An additional object of this invention is to provide a crystal holder in which the major portion of the body, and the supporting press through which the contact pins pass, are formed entirely of glass, and in which only the sealing cover is formed of metal, whereby undesired leakage and capacitative effects between the various elements are reduced. 1

Other objects and advantages of this invention may be seen from the following specification and Q the hereunto annexed drawing, in which:

Fig. 1 shows a sectional side elevation of one embodiment of this invention.

Fig. 2 shows an end elevation of the device shown in Fig. 1, on the lines 2-2, with the cap removed, and in section.

Fig. 3 is a plan view of the top of the glass body of a crystal holder according to this invention; and

Fig. 4 is a plan view of one form of metal cover used to seal the body shown in Fig. 3.

meet in a common press M, through at least part of which extend contact pins I5, so as to afiord electrical connections to the interior of the body.

These contact pins may be formed of any suitable material which readily seals into the glass, and which possesses a coeficient of expansion substantially identical with that of glass, over the range of temperatures at which the device is to be employed. V Dumet" alloy .of, 0.04 to 0.05 inch diameter has been found suitable, but other sizes and other materials, such as those known as Sealmet or Kovar, maybe employed.

In Fig. 2 the crystal supporting wires i5 are shown rising from the upper end of each contact pin i5 vertically, so that they extend above the upper lip ll of body it, 58. .The two contact plates 28, located upon opposite sides of the quartz crystal i9, are respectively provided with loop-like portions 20, located at opposite edges of the crystal. These loops to slide along the respective connecting wires it, as the crystal is pushed down into the holder, and the surplus portions of wires in may then be out ofi.

In order to make a permanent connectionbe- 'tween loops 2d and wires 25, after the crystal has been slid along the wires into position, it has been found desirable to employ a soldering material having an extremely low melting point, which may be fused without danger of over-heating the quartz crystal. It has been found desirable to employ platinum-coated molybdenumrigidity, properly to support the crystal, and to minimize possible vibration thereof.

Referring now additionally to Fig. 3, the upper lip ll of body i is made to be substantially planar, so that the sealing cover may readily be fastened thereto. It will be noted that the supporting and connecting wires l6 are oifset toone side of the holder, so that the crystal is held approximately centrally therein, thereby being in a position as remote as possible from any heat radiated thereupon from the lateral walls of the holder.

In Fig. 4 the metal cover 2| is shown to have a shape corresponding to the cross-section of the body and to have an overall linear size such that the edges thereof will not project over the exterior edges of lip H. In practice, it is preferred to make this sealing top slightly smaller than the exterior size of the glass body. The top may be formed of any suitable material. By way of example, and not of limitation, tinned soft copper of 0.005 to 0.015 inch thickness has been found suitable. In order to prevent undue stress upon the seal between the body and the cover, the latter may be'formed of an alloy having the same coefficient of expansion as glass, or a material of different coefficient may be provided with crimps or the like, to take up differences in expansion.

In order to efiect a hermetic seal between the lip i1, and the cover 2|, thelip may be coated, prior to insertion of the crystal in the holder, with a material which will bond to the glass so as to aiford a metallic coating ll', overlying the lip of the glass and hermetically sealed thereto. By way of example, and not of limitation, a colloidal suspension of silver or platinum with other metals has been found suitable. Such preparations are available on the market and known in the art. After coating with such a material, heat is applied, to cause a hermetic bonding of the glass and the metal present in the coating. After completion of these operations, the crystal is inserted'in the holder.

When the sealing cover 2i is placed in position upon lip ll, which has been so coated, the application of solder and then heating sufficiently to fuse the solder along the point of contact, will result in the formation of a hermetic seal between the cover and the metallized glass lip. Since the heat used to bring about this sealing is usually applied from the outside, the glass walls of the holder body will act as heat shields protecting the crystal from an undue rise in temperature, during the time when heat is being applied to seal on cover 2i. Furthermore, the actual point of sealing only approaches a single edge of the quartz crystal, so that direct radiation and heat from thepoint of sealing can only affect a very minor portion of the crystal body is. The fact that the soldering operation is done on a single flat surface reduces heating of the crystal by minimizing the time required.

In lieu of the employment of a coating of metal in suspension form upon the lip ii, there may be provided a metallic collar, formed as an eyelet, and hermetically sealed to lip i'i before the crystal is inserted in the holder. To this collar the cap 2! may readily be sealed, by soldering or otherwise.

After the crystal has been hermetically sealed in, it may still be subjected to radiation of exprior art. It can be seenthat such radiation may readily be projected through the lateral walls of the holdenformed of glass, and that the metal sealing cover will present no substantial obstacle to such radiations since it does not lie in the direct path to the body of the crystal, provided that such radiations are aimed at the sides of the crystal.

While I have described the cap of my holder as metallic, it can be seen that the cover may be formed of another suitable material, for example glass. If a metallic seal is desired, the co-joining surfaces of both lip and cover may be metallized as previously described, or a non-metallic cement or bonding material may be used to yield the desired hermetic seal. Any heat used in forming a seal with such bonding agent will not deleteriously affect the crystal, for the reasons previously pointed out. a

While there have been shown certain embodiments of this invention, other embodiments and modifications thereof will be apparent to those skilled in the art and the scope of this invention is limited only by the hereunto appended claims.

What is claimed is:

1. A glass holder for a piezo-electric crystal, having a press and having at least two parallel conducting pins sealed into said glass press, said holder having the edges of the walls thereof remote from said pins and lying in a single plane substantially perpendicular to the plane of said pins, said edges having a. metal coating thereupon, said holder also including a metallic cover hermetically fastened to said edges of said walls.

2. A containerfor piezo-electric crystals and other similar elements adversely influenced by heating, including a. body portion formed of vitreous material closed at one end and open at another end, means within said body portion for supporting and making connection with a crystal,

crystal connecting means extending through the closed end of said body portion, and a metallic cap covering the open end of said body portion and hermetically sealed thereto.

3. A combination piezo-electric crystal and bolder therefor, including a vitreous container, means locating said crystal within said container in close proximity to the walls thereof, means affording external connection to said crystal, and a metallic cap hermetically closing one end of said container, said cap being sealed thereto by a readily fusible sealing material, whereby the heat engendered by sealing does not adversely affect said crystal.

4. A device according to claim 2, also including a metallic layer substantially covering the open end of said body portion, to which metallic layer said cap is soldered.

5. A device according to claim 2,'also including a metallic collar hermetically sealed to the open" end of said body portion, thereby aflording a metallic surface-to which said cap is soldered.

6. A holder for mounting and enclosing a piezoelectric crystal, including a body portion formed of glass, contact pins extending through a glassseal in said body, whereby electrical contact may be established between said crystal and a circuit external to said holder, the glass wall portion of said body extending from said pins upwardly and being shaped to form a recess only slightly wider than said crystal, and closed at one end, in which said crystal may be mounted, the top edges of said glass wall extending above said crystal, when the latter is mounted therein, and also including a substantially fiat cover plate of metallic material, capable of being hermetically fastened to the upper rim of said walls so as to enclose said crystal within a completely sealed container.

7. A holder according to claim 7, also including two crystal supporting'wires, each connected to a contact pin, and each ofiset to one side of said recess, whereby said crystal is held substantially centrally therein, and means for fastening said crystal to said supporting wires, so as to be held thereby and to be connected thereto.

8. A glass holder for a piezo-electric crystal, having a press and having at least two parallel conducting pins sealed into said glass press, said holder having the edges of the walls thereof remote from said pins and lying in a single plane substantially perpendicular to the plane of said pins, said edges having a metal coating thereupon, whereby a, cover member may readily be hermetically sealed to said edges of said walls, after said crystal is inserted within the holder.

9. A holder for mounting and enclosing a piezoelectric crystal, including a body portion formed of glass, contact pins extending through a glass seal in said body, whereby electrical contact may be established between said crystal and a circuit external to said holder, th glass wall portion of v said body extending fromsaid pins upwardly and being shaped to form a recess only slightly wider than said crystal; and closedat one end, in which said crystal may be mounted, the top edges of said glass wall extending above said crystal,

' when the latter is mounted therein, whereby a fiat cover plate may be hermetically fastened to the upper rim of said walls so as to enclose said crystal within a completely sealed container.

10. A glass holder for a piezo-electrlc crystal,

' having a press and having at least two parallel

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