1. Field of the Invention
The present invention relates to a surface mount type quartz crystal oscillator, and a surface mount type crystal device.
2. Description of the Related Art
Surface mount type crystal oscillators, which have a quartz crystal element and an oscillation circuit using this crystal element, both contained in a surface mount package, are widely used as reference sources for frequency and time in compact portable electronic devices including, among others, portable telephones, because of their small size and light weight. An example of such surface mount type crystal oscillators is disclosed in US 2005/0193548A1.
Sealing metal film 9 is disposed on the top surface of second ceramic layer 4b along the outer periphery thereof. A pair of crystal holding terminals 10 are formed on the top surface of second ceramic layer 4b along one side of the opening at positions corresponding to both ends of the side for holding crystal blank 3. Crystal holding terminals 10 are electrically connected to circuit terminals 6 through conductive paths, not shown, formed on ceramic substrate 4.
As illustrated in
IC chip 2, which is substantially rectangular in shape, comprises at least an oscillation circuit, which uses crystal blank 3, integrated on a semiconductor substrate. The oscillation circuit is formed on one main surface of the semiconductor substrate through a general semiconductor device fabrication process. Therefore, a circuit forming surface refers to one of both main surfaces of IC chip 3, on which the oscillation circuit is formed, on the surface of the semiconductor substrate. The circuit forming surface is also formed with a plurality of IC terminals 8 corresponding to the aforementioned circuit terminals 6, as illustrated in
Metal cover 5 is formed in a concave shape, such that its opening end face is bonded to metal film 9 on second ceramic layer 4b, for example, through thermo-compression bonding using brazing metal 11 made, for example, of AuSn (gold-tin) eutectic alloy or the like, thereby bonding metal cover 5 to ceramic substrate 4. In this way, metal cover 5 hermetically seals IC chip 2 placed in the recess of ceramic substrate 4, and crystal blank 3 secured to ceramic substrate 4 within package 1.
In such a surface mount type crystal oscillator, since concave metal cover 5 is bonded to the outer periphery of ceramic substrate 4, the internal volume of package 1 can be made larger, and conversely, the crystal oscillator can be reduced in size while the internal volume of package 1 is maintained constant.
For manufacturing the surface mount type crystal oscillator configured as illustrated in
In this event, as illustrated in
However, when the ceramic sheets are baked after they have been formed with division grooves 16 as described above, a contractive force associated with evaporation of a binder from the ceramic sheets concentrates particularly on upper ends of a frame portion defined by second ceramic layer 4b, resulting in external force P exerted in a direction to reduce the area of the opening formed through second ceramic layer 4b. Such external force P thus produced causes first ceramic layer 4a to curve into a concave form in burned ceramic substrate 4. Resulting ceramic substrate 4 suffers from an exacerbated flatness, i.e., plane accuracy on the bottom of the recess.
Assuming here that IC chip 2 is secured to the bottom of the recess in ceramic substrate 4, which is a mounting substrate, i.e., the surface of first ceramic layer 4a, through ultrasonic thermo-compression bonding using bumps 12, sufficient pressure is not applied to bumps 12 on the concave surface which lacks the flatness, as illustrated in
Further, the surface mount type crystal oscillator configured as illustrated in
Surface mount type crystal devices which have a concave metal cover bonded to a ceramic substrate are not limited to the crystal oscillator described above. Such a concave metal cover bonded to a ceramic substrate can be employed as well in a crystal unit which has a crystal blank encapsulated in a package. Such a surface mount crystal unit is also utilized as a reference source for frequency and time in portable electronic devices.
Metal cover 5 is processed such that an opening end face has a flange, and is bonded to ceramic substrate 4 by thermo-compression bonding through the intervention of eutectic alloy 11 such as AuSn alloy or the like between the flange plane and metal film 9. The flange of metal cover 5 is used to increase the width of a portion of metal cover 5 which is bonded to ceramic substrate 4, i.e., a so-called seal-path to ensure the bonding strength and air-tight sealing.
The crystal unit illustrated in
In the crystal unit illustrated in
Various problems caused by the shift in position between metal cover 5 and ceramic substrate 4 can also be experienced in the surface mount type crystal oscillator as illustrated in
It is an object of the present invention to provide a surface mount type crystal device which facilitates a reduction in size and is manufactured at a lower cost.
It is another object of the present invention to provide a surface mount type crystal device which is capable of increasing a positioning accuracy of a metal cover to a ceramic substrate.
It is a further object of the present invention to provide a surface mount type crystal oscillator which facilitates a reduction in size and is manufactured at a lower cost.
It is a further object of the present invention to provide a surface mount type crystal oscillator which is capable of increasing a positioning accuracy of a metal cover to a ceramic substrate.
It is a further object of the present invention to provide a surface mount type crystal oscillator which excels in the flatness of a ceramic substrate to ensure the boding of an IC chip through ultrasonic thermo-compression bonding using bumps.
According to a first aspect, the present invention provides a surface mount type crystal oscillator which comprises a crystal blank, an IC chip having at least an oscillation circuit using the crystal blank, integrated thereon, and a hermetic package for accommodating the crystal blank and the IC chip therein, wherein the hermetic package comprises a ceramic substrate having a substantially rectangular shape and formed with a metal film which makes a round on one main surface thereof, and a concave metal cover having an open end face bonded to the metal film, the ceramic substrate comprises mounting electrodes at corners on the other main surface thereof for use in mounting the crystal oscillator on a wiring board, the IC chip is secured to the one main surface of the ceramic substrate through ultrasonic thermo-compression bonding using bumps, the crystal blank is disposed above the IC chip, and the one main surface of the ceramic substrate is formed as a flat surface.
In the configuration described above, since the ceramic substrate is substantially flat without recess, the ceramic substrate is prevented from curvature associated with a non-uniform contractive force during burning, thus maintaining the flatness of the ceramic substrate after the burning. As a result, the IC chip can be reliably bonded to the ceramic substrate through ultrasonic thermo-compression bonding using bumps. In such a crystal oscillator, the ceramic substrate may be composed of a first ceramic layer formed with the mounting electrodes, and a second ceramic layer laminated on the first ceramic layer for securing the IC chip thereto, wherein the first ceramic layer may comprise a cutout portion in a central area on at least one side thereof, the cutout portion having an outer periphery open to the side, and an adjustment terminals is formed on a laminated surface of the second ceramic layer exposed by the cutout portion. The adjustment terminal typically includes a write surface terminal used to write temperature compensation data into a temperature compensation mechanism within the IC-chip, and/or a crystal test terminal used to measure oscillation characteristics of the crystal blank.
According to a second aspect, the present invention provides a surface mount type crystal oscillator which comprises a substantially rectangular crystal blank an IC chip having at least an oscillation circuit using the crystal blank, integrated thereon, and a package having at least a substantially rectangular ceramic substrate and adapted to accommodate the crystal blank and the IC chip therein, wherein the ceramic substrate comprises mounting electrodes at corners on a surface thereof which is an outer bottom surface of the package for use in mounting the crystal oscillator on a wiring board, the ceramic substrate comprises a first ceramic layer formed with the mounting electrodes, and a second ceramic layer laminated on the first ceramic layer for securing the IC chip thereto, and the first ceramic layer comprises a cutout portion in a central area on at least one side thereof, where the cutout portion has an outer periphery open to the side, and adjustment terminal is formed on a laminated surface of the second ceramic layer exposed by the cutout portion.
According to this configuration, since a write surface terminal for writing, for example, temperature compensation data is formed in the cutout portion, a probe for writing is more readily accessed to the write surface terminal, as compared with a terminal disposed in a hole formed through a center area of a back surface of a substrate, as shown in Japanese Patent Laid-open application No. 8-307153 (JP, A, 8-307153), by way of example. In this event, the ceramic substrate itself can be made substantially flat, thus making it possible to prevent the ceramic substrate from being curved in association with burning.
Here, the thickness of the first ceramic layer, i.e., a difference in level between the mounting electrodes and adjustment terminals is preferably, for example, in a range of 50 μm to 200 μm, and more preferably in a range of 80 μm to 100 μm.
According to a third aspect, the present invention provides a surface mount type crystal oscillator which comprises a substantially rectangular crystal blank, an IC chip having at least an oscillation circuit using the crystal blank, integrated thereon, and a hermetic package having at least a substantially rectangular ceramic substrate and adapted to accommodate the crystal blank and the IC chip therein, wherein the hermetic package comprises a ceramic substrate having a substantially rectangular shape and formed with a metal film which makes a round on one main surface thereof, and a concave metal cover having an open end face bonded to the metal film, the crystal blank comprises excitation electrodes respectively formed on a pair of main surfaces thereof, and a pair of lead-out electrodes extended from the excitation electrodes to both ends on one side of the crystal blank, the ceramic substrate has at least the one main surface formed as a flat surface, the ceramic substrate comprises mounting electrodes at corners on the other main surface thereof for use in mounting the crystal oscillator on a wiring board, the IC chip has its circuit forming surface secured to the one main surface of the ceramic substrate through ultrasonic thermo-compression bonding using bumps, the crystal blank is held in the hermetic package by securing both ends on the one side thereof to a back surface of the IC chip, and the crystal blank is electrically connected to a relay terminal formed on the one main surface of the ceramic substrate using wire bonding.
According to a fourth aspect, the present invention provides a surface mount crystal device which comprises a crystal blank and a hermetic package for accommodating at least the crystal blank therein, wherein the hermetic package comprises a ceramic substrate having a substantially rectangular shape and formed with a metal film which makes a round on a surface thereof, and a concave metal cover having an open end face bonded to the metal film, and the ceramic substrate includes a step for positioning the metal cover on an inner peripheral side of the metal film on the surface of the ceramic substrate.
Crystal devices of the present invention include, for example, a crystal unit which has a crystal blank placed in a package, and a crystal oscillator which has a crystal element and an oscillation circuit integrated therein.
In
The crystal oscillator illustrated in
The crystal oscillator of the first embodiment differs from the one illustrated in
This crystal oscillator uses a pair of metal supporters 20 for disposing crystal blank 3 above IC chip 2. Supporters 20 each have a height larger than the thickness of IC chip 2, and is made up of a body extending vertically, and L-shaped members disposed at both ends of the body, respectively. The L-shaped members at one end (i.e., proximal end) and the other end (i.e., distal end) of supporter 20 have their leading ends extending in the same direction. The L-shaped member at the proximal end has a side surface bonded to relay terminal 17 formed on the top surface of ceramic substrate 4. The upper end side of supporter 20 protrudes upward from the top surface of IC chip 2. Substantially rectangular crystal blank 3 is horizontally held above IC chip 2 by securing a pair of lead-out electrodes extending from both ends on one side of crystal blank 3 to side surfaces of the L-shaped members at the distal ends of the pair of supporters 20 with a conductive adhesive (not shown) in such a manner that the longitudinal direction of crystal blank 3 matches the longitudinal direction of ceramic substrate 4. Here, crystal blank 3 has a length larger than the length of IC chip 2 in the same direction, so that IC chip 2 is completely covered with crystal blank 3. Of course, crystal blank 3 can be formed smaller than IC chip 2, but larger crystal blank 3 results in a larger plate area which facilitates the designing for accomplishing desired oscillation characteristics.
As described above, circuit terminals 6 and a pair of relay terminals 17 are formed on the top surface of ceramic substrate 4. On illustrated ceramic substrate 4, a total of eight circuit terminals 6 are disposed, four along each of the long sides of ceramic substrate 4. These circuit terminals, which correspond to the IC terminals of IC chip 2, include a pair of connection terminals 6(X1), 6(X2) for connection to crystal blank 3, power supply terminal 6(Vcc), oscillation output terminal 6(Vout), ground terminal 6(E), AFC terminal 6(AFC), and a pair of write terminals 6(W1), 6(W2) for writing temperature compensation data. Among these circuit terminals, connection terminals 6(X1), 6(X2) are electrically connected to relay terminals 17 through conductive paths formed on the surface of ceramic substrate 4. Power supply terminal 6(Vcc), oscillation output terminal 6(Vout), ground terminal 6(E), and AFC terminal 6(AFC) are connected to corresponding mounting electrodes 7 through conductive paths formed on the surface of ceramic substrate 4 and via-holes 19 extending through ceramic substrate 4, respectively.
Write surface terminals 7(W1), 7(W2) are disposed on the back surface of ceramic substrate 4, other than the aforementioned mounting electrodes 7, for electric connection to write terminals 6(W1), 6(W2), respectively. In
Ceramic substrate 4 is formed by burning a green ceramic sheet (i.e., unburned ceramic sheet). Via-holes 19 are formed by providing through-holes through the green ceramic sheet, filling the through-holes with a printing material, and disposing a plating layer on a circuit pattern after burning when a circuit underlying pattern (i.e., circuit terminals 6, relay terminals 17, conductive paths 18, and mounting electrodes 7) is formed on the ceramic sheet by printing. The printing material used herein may be, for example, molybdenum (Mo) or tungsten (W). The plating layer is formed by laminating a nickel (Ni) layer and a gold (Au) layer. By forming the plating layer after the burning, via-holes 19 are completed, and in this event, the through-holes are closed to maintain hermetic package 1 in an air-tight state.
In this crystal oscillator, ceramic substrate 4 has both main surfaces formed flat, and is therefore free from a problem of non-uniform contraction which would be otherwise experienced when a second ceramic layer having an opening is laminated on a flat first ceramic layer, and the resulting laminate is burned. Consequently, in this embodiment, ceramic substrate 4 remains flat even after burning, without being curved. Thus, when IC chip 2 is secured to ceramic substrate 4 through ultrasonic thermo-compression bonding using bumps 12, the IC terminals and circuit terminals 6 establish secure electric connections therebetween. The use of concave metal cover 5 facilitates a reduction in size of the surface mount type crystal oscillator, as is the case with the conventional one illustrated in
It should be noted that write surface terminals 7(W1), 7(W2) disposed on the bottom surface of ceramic substrate 4 can be used as mounting electrodes as required in order to enhance a connection strength to a wiring board.
Next, a surface mount type crystal oscillator according to a second embodiment of the present invention will be described with reference to FIGS. 10 to 12.
In the crystal oscillator illustrated in
As illustrated in
Specifically, second ceramic layer 4b has a flat top surface on which circuit terminals 6, metal film 9, and relay terminals 17 are formed. Mounting electrodes 7 are formed at four corners on the back surface of first ceramic layer 4a. Then, as illustrated in
It should be noted that end face electrodes 7b are disposed at four corners of first ceramic layer 4a on end faces of first ceramic layer 4a in a manner similar to the foregoing, but illustration of end face electrodes 7b is omitted in
Mounting electrodes 7 at the four corners are electrically connected to power supply terminal 6(Vcc), output terminal 6(Vout), ground terminal 6(E), and AFC terminal 6(AFC) disposed on the top surface of second ceramic layer 4b, respectively, through via-holes and conductive paths routed on the laminated surface. Likewise, write surface terminals 7(W1), 7(W2) are electrically connected to write terminals 6(W1), 6(W2), respectively, through via-holes and conductive paths.
In the configuration as described above, even though cutout portions 21 are formed in central areas of both sides of first ceramic layer 4a, cutout portions 21 have a smaller area than the opening formed through the second ceramic layer of the conventional crystal oscillator illustrated in
In the second embodiment, since write surface terminals 7(W1), 7(W2) are formed in dimples defined by cutout portions 21, write surface terminals 7(W1), 7(W2) are prevented from coming into contact with a wiring pattern on a wiring board when this crystal oscillator is mounted on the wiring board. Also, sine write surface terminals 7(W1), 7(W2) are disposed in cutout portions 21 formed along the outer periphery of ceramic substrate 4, a probe for writing temperature compensation data can be more readily accessed to write surface terminals 7(W1), 7(W2) than when write surface terminals 7(W1), 7(W2) are disposed in a recess formed in a central area of a substrate, thus leading to improved operability.
In this embodiment, write surface terminals 7(W1), 7(W2) for writing temperature compensation data are placed in correspondence to cutout portions 21 in first ceramic layer 4a, but write surface terminals 7(W1), 7(W2) may be replaced with a pair of crystal test terminals 7Q1, 7Q2 which are electrically connected to a pair of relay terminals 17 through conductive paths, not shown. The use of crystal test terminals 7Q1, 7Q2 permits the electric characteristics and oscillation characteristics of crystal blank 3, as a crystal element, to be independently measured from another circuit even after crystal blank 3 is encapsulated in hermetic package 1. When a single write terminal is provided in IC chip 2, cutout portion 21 is only required along one long side of first ceramic layer 4a, as a matter of course.
Next, a description will be given of a surface mount type crystal oscillator according to a third embodiment of the present invention. While the crystal oscillator of the second embodiment comprises two write surface terminals, three or more write surface terminals may be required depending on the configuration of IC chip 2, or some IC chips are preferably provided with both write surface terminals and crystal test terminals. The crystal oscillator of the third embodiment can be provided with up to four write surface terminals and/or crystal test terminals in combination.
The crystal oscillator of the third embodiment is similar to the crystal oscillator of the second embodiment but differs in the position of cutout portions in first ceramic layer 4a. As illustrated in
By thus forming four cutout portions 21, it is possible to provide a total of four write surface terminals and/or crystal test terminals in combination. Then, as illustrated in
The third embodiment is similar to the first and second embodiments in that cutout portions 21 are formed in an outer peripheral area of first ceramic layer 4a, and IC chip 2 is mounted on a flat central area, so that ceramic substrate 4 is prevented from being curved even if a contractive force acts thereon during burning. Also, since the cutout portions are located symmetrically about the center line of ceramic substrate 4, no excessive stress will act on ceramic substrate 4.
Next, a description will be given of a surface mount type crystal oscillator according to a fourth embodiment of the present invention. In the surface mount type crystal oscillators of the second and third embodiments, a step is formed on the back surface of ceramic substrate 4 and the mounting electrodes and write surface terminals are disposed with the step intervening therebetween. Such a configuration can be also applied to the conventional crystal oscillator illustrated in
Next, a description will be given of a surface mount type crystal oscillator according to a fifth embodiment of the present invention. The crystal oscillator of the fifth embodiment illustrated in
In the crystal oscillator illustrated in
Like the first embodiment, the crystal oscillator of the fifth embodiment can be manufactured at a reduced cost by virtue of the use of a ceramic substrate made of a single layer. Then, since crystal blank 3 is directly secured on IC chip 2, no step is needed to be formed in the ceramic substrate for holding crystal blank 3, so that ceramic substrate 4 can be reduced in size, as compared with the conventional one illustrated in
Also, since crystal blank 3 has its one side directly secured on IC chip 2 with insulating adhesive 29 so that IC chip 2 additionally serves as a holder for crystal blank 3, the number of parts can be reduced.
While crystal blank 3 is horizontally placed in the crystal oscillator illustrated in
Next, a description will be given of a surface mount type crystal oscillator according to a sixth embodiment of the present invention. In the fifth embodiment described above, crystal blank 3 is directly secured to IC chip 2 with an insulating adhesive, whereas in the crystal oscillator of the sixth embodiment illustrated in
A description will now be given of processes of manufacturing the crystal oscillator as described above. First, IC chip 2 is secured on ceramic substrate 4 through ultrasonic thermo-compression bonding similar to the foregoing, and auxiliary substrate 21 is secured on IC chip 2 with insulating adhesive 19. Next, both ends on one side of crystal blank 3, from which lead-out electrodes 14 extend, are secured to given end areas of crystal holding terminals 10 on auxiliary substrate 22 with conductive adhesive 15. Finally, opposite end areas of crystal holding terminals 10 are connected to relay terminals 17 on ceramic substrate 4 with gold wires 30 for wire bonding, and the opening end face of metal cover 5 is bonded to metal film 9 disposed around the outer periphery of ceramic substrate 4 through thermo-compression bonding using brazing metal 11 for sealing.
In the foregoing configuration, auxiliary substrate 22 is entirely secured on IC chip 2 and is therefore mechanically stable, thus facilitating wire bonding operations for connecting crystal holding terminals 10 to relay terminals 17. The intervening auxiliary substrate 21 causes a relatively large gap between crystal blank 3 and IC chip 2 to facilitate securing operations and the like and to prevent crystal blank 3 from coming into contact with IC chip 2 to maintain good oscillation characteristics. Since auxiliary substrate 22 is made of a crystal plate having the same cutting angle (i.e., AT-cut) as crystal blank 3, auxiliary substrate 22 and crystal blank 3 have the same coefficient of thermal expansion, thus eliminating distortions due to a difference in the coefficient of thermal expansion. Consequently, the crystal element (crystal blank 3) is improved in thermal shock resistance characteristics.
Since the sixth embodiment also employs ceramic substrate 4 made of a single layer, as is the case with the fifth embodiment, the crystal oscillator can be manufactured at a reduced cost. Also, since no step is needed to be formed in the ceramic substrate for holding the crystal blank, ceramic substrate 4 can be reduced in length to increase the effective internal volume of sealed package 1.
In the fifth and sixth embodiments described above, ceramic substrate 4 is made of a single layer, but alternatively may be made of laminated ceramics. In this event, since green ceramic sheets need not be stamped, the manufacturing cost can be restrained from increasing. When laminated ceramics are used, conductive paths can be formed on laminated surface for electrically connecting IC chip 2 to mounting electrodes 7 to ensure the air-tight sealing of the hermetic package. When a temperature compensated crystal oscillator is implemented, ceramic substrate 4 may be formed with terminals for writing temperature compensation data, terminals for testing characteristics of a crystal element, and the like on side surfaces thereof. Electrode patterns for write terminals and characteristic test terminals may not be formed on a lowermost ceramic layer and an uppermost ceramic layer to prevent these terminals from electrically shorting, for example, with a conductor pattern on a wiring board.
In the first to sixth embodiments described above, end face electrodes 7b may not be disposed at four corners of ceramic substrate 4 by through-hole processing, such that metal film 9 is formed correspondingly closer to the edges of ceramic substrate 4 to increase the substantial internal volume of hermetic package 1. Metal film 9 may be slightly spaced apart from the side edges of ceramic substrate 4 in order to facilitate a process of dividing burned laminate of ceramic sheets into individual ceramic substrates 4. Also, in each of the embodiments described above, the crystal oscillator has been described to be a temperature compensated crystal oscillator into which temperature compensation data is written from the outside, the crystal oscillator may be an SPXO (simple packaged crystal oscillator) which is not equipped with the temperature compensation mechanism. Further, crystal blank 3 disposed above IC chip 2 has a free end from which lead-out electrodes 14 do not extend, so that an impact, if applied, would cause the free end to collide with the back surface of IC chip 2, possibly resulting in deteriorated oscillation characteristics. Accordingly, a flexible adhesive may be applied to the back surface of IC chip 2 or to the inner surface of metal cover 5, corresponding to the free end of crystal blank 3, so as to reduce a width over which crystal blank 3 swings when an impact is applied thereto.
Next, a description will be given of crystal devices according to the present invention.
The crystal unit illustrated in
In this example, metal film 9 is also produced by forming underlying electrodes of tungsten (W) or molybdenum (No) on a green ceramic sheet by printing, burning the ceramic sheet, and subsequently laminating an Ni layer and an Au layer on the underlying electrodes by plating. Then, pier 23 is formed when the underlying electrodes are formed, by printing multiple layers of W or Mo, which is the same material as the underlying electrodes, only on the inner peripheral side of the underlying electrodes. After burning, an Ni and an Au layer are laminated on the surface including the side surface of pier 23 by plating in a manner similar to metal film 9.
In this embodiment, after crystal blank 3 has been secured to crystal holding terminals 10, the open end face of metal cover 5 including the flange is brought into contact with eutectic alloy 11 disposed on metal film 9, and metal cover 5 is bonded to ceramic substrate 4 by melting eutectic alloy 11 by heating, thereby hermetically sealing crystal blank 3 and completing the crystal unit.
In the configuration as described above, the step formed by pier 23 on the inner peripheral side of metal film 9 can prevent metal cover 5 from shifting in position when it is bonded by eutectic alloy 11. It is therefore possible to ensure a sufficient seal-path between metal cover 5 and ceramic substrate 4 to increase the bonding strength and air-tight sealing. Particularly, in this example, since the Ni layer and Au layer are laminated on the top and side surfaces of pier 23 in a manner similar to metal film 9, eutectic alloy 11 introduces into a gap between metal cover 5 and pier 23 when it is melted by heating for bonding. In this way, a bonding area with eutectic alloy 11 extends to increase the seal-path, resulting in further increased bonding strength and air-tight sealing. Conversely, since the bonding strength and air-tight sealing can be kept high, the flange may be protruded by a shorter length on metal cover 5 to substantially increase the internal volume of the hermetic package.
Also, since frame width W2 of the opening end face of metal cover 5 is made smaller than W2 in consideration of a clearance for step width W1 of the step, the outer periphery of metal cover 5 will not protrude outward from ceramic substrate 4. Consequently, the surface mount type crystal unit satisfies criteria for outer dimensions without fail.
In the foregoing example, pier 23 for forming the step is created by printing multiple layers of the same materials as the underlying electrodes, but pier 23 may be made of an insulating material such as alumina instead of the materials of the underlying electrodes. While pier 23 is formed to make a round on ceramic substrate 4 along metal film 9, the pier 23 is not necessarily so formed. Pier 23 may be locally formed on each of four sides of ceramic substrate 4. Alternatively, L-shaped piers may be formed at a pair of corners on both sides of one diagonal of ceramic substrate 4. Pier 23 may be disposed in whichever manner as long as it has a height larger than the total thickness of metal film 9 and eutectic alloy 11 to have the ability to position metal cover 5.
From a viewpoint of the positioning of metal cover 5, any step may be formed, and the step need not be created by a pier.
Alternatively, a single green ceramic sheet may be formed with mark-off lines, which run vertically and horizontally, by embossing, burned, and then cut vertically and horizontally along the mark-off lines for formation into ceramic substrates 4, each of which has a step on the outer periphery, as illustrated in
In the configurations illustrated in
The bonding of metal cover 5 to ceramic substrate 4 is not limited to a method which is based on a eutectic alloy. For example, as illustrated in
While the crystal devices based on the present invention have been described in connection of exemplary crystal units, each of which has a crystal blank hermetically sealed in a package, the present invention can also be applied to surface mount type crystal oscillators.
Number | Date | Country | Kind |
---|---|---|---|
2005-346617 | Nov 2005 | JP | national |
2005-365328 | Dec 2005 | JP | national |
2005-352687 | Dec 2005 | JP | national |
2006-100025 | Mar 2006 | JP | national |