Oven-type piezoelectric oscillator

Abstract

To provide a thermostat type piezoelectric oscillator capable of improving a heat insulation effect of a core part by obtaining high reliability in both a mechanical junction of a core substrate to a package and an electrical junction between the core part and the package.SOLUTION: In an OCXO 1 in which a core part 5 is encapsulated inside of a package 2 for heat insulation in a sealed state, the core part 5 includes at least an IC 51 for oscillation, a crystal oscillator 50 and an IC 52 for heaters. The core part 5 is loaded on a core substrate 4. The core substrate 4 is mechanically joined to the package 2 by a nonconductive adhesive agent 7, and the core part 5 and the package 2 are electrically joined by wire bonding. A space 2d is provided between the core substrate 4 and a bottom face of the package 2, and a spacer member 2f is interposed between the core substrate 4 and the bottom face of the package 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an oven-controlled piezoelectric oscillator. [Background technology]

[0002] Piezoelectric oscillators such as quartz crystal oscillators change their oscillation frequency depending on the temperature based on their inherent frequency-temperature characteristics. Therefore, oven-controlled piezoelectric oscillators (hereinafter also referred to as "OCXOs") are known in which the piezoelectric oscillator is enclosed in a thermostatic oven to maintain a constant temperature around the piezoelectric oscillator (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-205093 [Patent Document 2] Japanese Patent Application Publication No. 2018-14705 Summary of the Invention [Problem to be solved by the invention]

[0004] The applicant has already filed a patent application for an oven-controlled piezoelectric oscillator in which a core section, consisting of a stacked oscillation IC, piezoelectric resonator, and heater IC, is supported inside a heat-insulating package via a core substrate (Patent Application No. 2020-130421: unpublished at the time of filing). In such oven-controlled piezoelectric oscillators, the mechanical bonding of the core substrate to the package and the electrical bonding performance between the core section and the package affect the reliability of the device. In addition, there is a need to improve the heat insulation effect of the core section.

[0005] The present invention has been made in consideration of the above-described circumstances, and has as its object to provide an oven-controlled piezoelectric oscillator that can achieve high reliability in both the mechanical connection of the core substrate to the package and the electrical connection between the core and the package, and that can also improve the thermal insulation effect of the core. [Means for solving the problem]

[0006] The present invention provides a means for solving the above-mentioned problems as follows: That is, the present invention provides an oven-controlled piezoelectric oscillator in which a core unit is hermetically sealed inside a heat-insulating package, the core unit including at least an oscillation IC, a piezoelectric resonator, and a heater IC, the core unit is mounted on a flexible substrate, the flexible substrate is mechanically joined to the package by a bonding material, the core unit and the package are electrically joined by wire bonding, and a space is provided between the flexible substrate and the bottom surface of the package.

[0007] According to the above configuration, by separating the mechanical connection of the flexible substrate to the package using a bonding material from the electrical connection between the core and the package using wire bonding, high reliability can be achieved for each. For example, the bonding material connecting the flexible substrate to the package can be flexible so that the mechanical bond strength is not easily weakened even when subjected to external stress. Furthermore, by using metal wires with low electrical resistance for wire bonding between the core and the package, common impedance noise is less likely to occur, thereby improving the CN characteristics of the oven-controlled piezoelectric oscillator. In addition, by connecting the core to the package via the flexible substrate and forming a space below the flexible substrate, the thermal insulation effect for the core can be improved.

[0008] In the above configuration, it is preferable that a bonding region for bonding the flexible substrate to the package does not overlap with a region where the core portion is disposed on the flexible substrate in a plan view. In this case, it is preferable that a spacer member is provided in a region closer to the core portion than the bonding region, and the spacer member is interposed between the flexible substrate and the bottom surface of the package. This allows the thickness of the bonding material applied to the bonding region to be determined, thereby easily determining the width of the space between the flexible substrate and the bottom surface of the package. Furthermore, the spacer member allows the flexible substrate to warp in a direction that increases the width of the space between the flexible substrate and the bottom surface of the package when the bonding material applied to the bonding region contracts, thereby improving the thermal insulation effect on the core portion.

[0009] In the above-described configuration, the flexible substrate is preferably made of a heat-resistant resin material, such as polyimide, and the core is preferably vacuum-sealed inside the package.

[0010] In the above configuration, the flexible substrate preferably has a slit between a mounting area on the upper surface of the flexible substrate where the core unit is mounted and a bonding area for bonding the flexible substrate to the package. The flexible substrate preferably has an opening in a region directly below the core unit. Furthermore, the piezoelectric vibrator is preferably not directly wire-connected to the package, and only the oscillation IC is directly wire-connected to the piezoelectric vibrator. [Effects of the Invention]

[0011] In the oven-controlled piezoelectric oscillator of the present invention, the mechanical connection of the flexible substrate to the package using a bonding material and the electrical connection between the core and the package using wire bonding are separated, thereby achieving high reliability in each connection. For example, the bonding material connecting the flexible substrate to the package can be flexible so that the mechanical bond strength is not easily weakened even when subjected to external stress. Furthermore, the use of metal wires with low electrical resistance in the wire bonding between the core and the package reduces the occurrence of common impedance noise, thereby improving the CN characteristics of the oven-controlled piezoelectric oscillator. In addition, connecting the core to the package via the flexible substrate and forming a space below the flexible substrate enhances the thermal insulation effect for the core. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an OCXO according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the OCXO of FIG. [Figure 3] 2 is a cross-sectional view showing a schematic configuration of a core section and a core substrate of the OCXO of FIG. 1. [Figure 4] 4 is a schematic diagram showing the configuration of the crystal oscillator (crystal resonator and oscillation IC) in the core section of FIG. 3. FIG. [Figure 5] 5 is a schematic plan view of the first main surface side of the first sealing member of the crystal oscillator of FIG. 4. [Figure 6] 3 is a schematic diagram showing a modified example of the crystal oscillator included in the core unit of FIG. 2. FIG. [Figure 7] FIG. 10 is a cross-sectional view showing a schematic configuration of a modified example of an OCXO. [Figure 8] 1(a) to 1(c) are plan views showing examples of the shape of a core substrate. [Figure 9] 10(a) and 10(b) are plan views showing modified examples of the core substrate. [Figure 10] FIG. 10 is a cross-sectional view showing a modified example of an OCXO. [Figure 11] FIG. 11 is a bottom view of the OCXO of FIG. 10. DETAILED DESCRIPTION OF THE INVENTION

[0013] First Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] As shown in FIGS. 1 and 2 , the OCXO 1 according to this embodiment has a core 5 disposed inside a substantially rectangular parallelepiped package (housing) 2 made of ceramic or the like, and hermetically sealed by a lid 3. The package 2 has a recess 2a that opens upward, and the core 5 is hermetically sealed inside the recess 2a. The lid 3 is fixed to the upper surface of a peripheral wall 2b surrounding the recess 2a by seam welding via a sealing material 8, thereby sealing the inside of the package 2 in an airtight state. The sealing material 8 is preferably a metal-based sealing material such as an Au-Su alloy or solder, but a sealing material such as low-melting-point glass may also be used. Furthermore, other sealing member configurations, such as seam sealing using a metal ring, direct seam sealing without a metal ring, and beam sealing, may also be used (seam sealing is preferable to avoid reducing the degree of vacuum). The internal space of the package 2 is preferably a vacuum (for example, a vacuum of 10 Pa or less) or an atmosphere with low thermal conductivity such as low-pressure nitrogen or argon. Note that Figure 2 shows the OCXO 1 with the lid 3 removed, illustrating the internal structure of the OCXO 1.

[0015] A stepped portion 2c is formed on the inner wall surface of the peripheral wall portion 2b of the package 2 along the arrangement of connection terminals (not shown). The core portion 5 is disposed on the bottom surface of the recess 2a between a pair of opposing stepped portions 2c, 2c, via a core substrate (flexible substrate) 4 made of a plate-like flexible material. Alternatively, the stepped portion 2c may be formed so as to surround the bottom surface of the recess 2a on all four sides. The core substrate 4 is bonded to the bottom surface of the recess 2a with a non-conductive adhesive (bonding material) 7, and a space (gap) 2d is formed below the core substrate 4. In addition, external terminals (not shown) formed on each component of the core portion 5 are connected to connection terminals formed on the stepped surface of the stepped portion 2c via wires 6a, 6b by wire bonding. Spacer members 2f, 2f are provided inside the non-conductive adhesives 7, 7.

[0016] Non-conductive adhesives 7, 7 are placed at both longitudinal ends of the core substrate 4, and are arranged linearly along the short side of the core substrate 4 (the direction perpendicular to the plane of FIG. 1). Each spacer member 2f is arranged adjacent to the side of the non-conductive adhesive 7, and is arranged linearly along the short side of the core substrate 4. In this way, the spacer members 2f, 2f are interposed between the core substrate 4 and the bottom surface of the package 2, on the inner side of the non-conductive adhesives 7, 7. The spacer members 2f, 2f support both longitudinal ends of the core substrate 4.

[0017] The core substrate 4 is made of a heat-resistant and flexible resin material such as polyimide. The spacer member 2f is made of a paste material such as molybdenum or tungsten. The core substrate 4 is provided so as not to come into contact with the bottom surface of the package 2. The thickness of the core substrate 4 is 5 to 100 μm, and the width (distance) of the space 2d between the core substrate 4 and the bottom surface of the package 2 is preferably 5 to 50 μm.

[0018] Furthermore, the bonding area A1 (the area where the non-conductive adhesive 7 is applied) for bonding the core substrate 4 to the package 2 is arranged so as not to overlap with the area where the core portion 5 is arranged on the upper surface of the core substrate 4 in a plan view. As shown in Fig. 2, the core portion 5 is arranged in an area on the inner side of the pair of spacer members 2f, 2f in a plan view, and the bonding areas A1, A1 are arranged in an area on the outer side of the pair of spacer members 2f, 2f. The distance from the heater IC 52 on the core substrate 4 to the bonding area A1 is preferably 250 to 1000 µm.

[0019] Next, the core unit 5 will be described with reference to FIG. 3. FIG. 3 illustrates the core unit 5 mounted on the core substrate 4. The core unit 5 is a package containing various electronic components used in the OCXO 1. It has a three-layer structure (laminated structure) in which an oscillation IC 51, a crystal unit (piezoelectric oscillator) 50, and a heater IC 52 are stacked in this order from top to bottom. The areas of the oscillation IC 51, the crystal unit 50, and the heater IC 52 in a plan view gradually decrease upward. The core unit 5 is configured to stabilize the oscillation frequency of the OCXO 1 by adjusting the temperatures of the crystal unit 50, the oscillation IC 51, and the heater IC 52, which have particularly strong temperature characteristics. Although the various electronic components in the core unit 5 are not sealed with sealing resin, sealing with sealing resin may be used depending on the sealing atmosphere.

[0020] The crystal oscillator 100 is composed of the crystal unit 50 and the oscillation IC 51. The oscillation IC 51 is mounted on the crystal unit 50 via a number of metal bumps. The oscillation frequency of the OCXO 1 is controlled by controlling the piezoelectric vibration of the crystal unit 50 using the oscillation IC 51. Details of the crystal oscillator 100 will be described later.

[0021] A non-conductive adhesive 53 is interposed between the opposing surfaces of the crystal unit 50 and the oscillation IC 51, and the opposing surfaces of the crystal unit 50 and the oscillation IC 51 are fixed together by the non-conductive adhesive 53. In this case, the top surface of the crystal unit 50 (the first main surface 201 of the first sealing member 20) and the bottom surface of the oscillation IC 51 are joined via the non-conductive adhesive 53.

[0022] The area of ​​the oscillation IC 51 in a plan view is smaller than that of the crystal unit 50, and the entire oscillation IC 51 is located within the range of the crystal unit 50 in a plan view. The entire bottom surface of the oscillation IC 51 is bonded to the top surface of the crystal unit 50 (the first main surface 201 of the first sealing member 20).

[0023] The heater IC 52 is configured to integrate, for example, a heating element (heat source), a control circuit (current control circuit) for controlling the temperature of the heating element, and a temperature sensor for detecting the temperature of the heating element. By controlling the temperature of the core unit 5 using the heater IC 52, the temperature of the core unit 5 is maintained at a substantially constant temperature, and the oscillation frequency of the OCXO 1 is stabilized.

[0024] A non-conductive adhesive 54 is interposed between the opposing surfaces of the crystal unit 50 and the heater IC 52, and the opposing surfaces of the crystal unit 50 and the heater IC 52 are fixed together by the non-conductive adhesive 54. In this case, the bottom surface of the crystal unit 50 (the second main surface of the second sealing member 30) and the top surface of the heater IC 52 are joined via the non-conductive adhesive 54.

[0025] The crystal unit 50 has a smaller area in plan view than the heater IC 52, and the entire crystal unit 50 is located within the range of the heater IC 52 in plan view. The entire lower surface of the crystal unit 50 (the second main surface of the second sealing member 30) is bonded to the upper surface of the heater IC 52.

[0026] A non-conductive adhesive 55 is interposed between the opposing surfaces of the heater IC 52 and the core substrate 4, and the opposing surfaces of the heater IC 52 and the core substrate 4 are fixed together by the non-conductive adhesive 55. Examples of the non-conductive adhesives 53, 54, and 55 that can be used include a polyimide adhesive and an epoxy adhesive.

[0027] In the core unit 5 shown in FIG. 3, external terminals for wire bonding are formed on the top surfaces of the crystal unit 50 and the heater IC 52. Wire bonding of the crystal unit 50 and the heater IC 52 is not performed before mounting the core unit 5 in the package 2, but is performed after mounting the core unit 5 in the package 2. That is, as shown in FIG. 1, after mounting the core unit 5 in the package 2, the external terminals formed on the top surface of the crystal unit 50 are connected via wires 6a to connection terminals formed on the stepped surface of the stepped portion 2c. Furthermore, the external terminals formed on the top surface of the heater IC 52 are connected via wires 6b to connection terminals formed on the stepped surface of the stepped portion 2c. In this way, by performing wire bonding after mounting the core unit 5 in the package 2, wire bonding can be performed efficiently, making it possible to provide an OCXO 1 that is suitable for mass production.

[0028] Although there are no particular limitations on the type of quartz crystal unit 50 used in the core portion 5, a sandwich-structured device can be preferably used, which allows for easier thinning of the device. A sandwich-structured device is a three-layered device that is composed of first and second sealing members made of glass or quartz crystal, and a piezoelectric diaphragm made of, for example, quartz crystal and having a vibrating portion with excitation electrodes formed on both main surfaces, in which the first and second sealing members are stacked and bonded via the piezoelectric diaphragm, and the vibrating portion of the piezoelectric diaphragm disposed inside is hermetically sealed.

[0029] An example of a crystal oscillator 100 in which such a sandwich-structured crystal resonator 50 and an oscillation IC 51 are integrally provided will be described with reference to Figures 4 and 5. Note that, since the sandwich-structured crystal resonator itself is well known, a detailed description of the internal structure of the crystal resonator 50 will be omitted.

[0030] 4, the crystal oscillator 100 includes a crystal diaphragm (piezoelectric diaphragm) 10, a first sealing member 20, a second sealing member 30, and an oscillation IC 51. In this crystal oscillator 100, the crystal diaphragm 10 and the first sealing member 20 are joined together by an annular sealing joint 41, and the crystal diaphragm 10 and the second sealing member 30 are joined together by an annular sealing joint 42, thereby forming a package with a substantially rectangular sandwich structure. The sealing joints 41 and 42 can be formed, for example, by forming a bonding pattern with an Au layer on the surface of each of the bonding surfaces of the crystal diaphragm 10, the first sealing member 20, and the second sealing member 30 (e.g., a bonding pattern with a Ti layer and an Au layer formed from the bottom layer), and bonding the bonding surfaces together by Au-Au diffusion bonding. According to this configuration, the gap dimension between the quartz crystal vibration plate 10 and each of the sealing members 20, 30 can be made extremely small, about 0.15 μm to 1 μm, which is advantageous for reducing the thickness and the heat capacity of the core portion 5.

[0031] That is, in the crystal oscillator 100, a first sealing member 20 and a second sealing member 30 are bonded to both main surfaces of the crystal oscillating plate 10, on which the vibrating portion (not shown) is formed, to form an internal space (cavity) of the package, and the vibrating portion of the crystal oscillating plate 10 is hermetically sealed in this internal space. The oscillation IC 51 mounted on the first sealing member 20 is a one-chip integrated circuit element that, together with the crystal oscillating plate 10, forms an oscillation circuit.

[0032] 4, the core unit 5 has an oscillation IC 51 mounted on a quartz crystal unit 50 via a plurality of metal bumps 21 (i.e., by flip-chip bonding). However, the present invention is not limited to this, and as shown in FIG. 6, the oscillation IC 51 may be die-bonded onto the quartz crystal unit 50 and electrically connected to the quartz crystal unit 50 by wire bonding. Also, a solid electrode 43 to which a GND potential is applied when the OCXO 1 is operating may be formed on the back surface of the quartz crystal unit 50 (the surface to be bonded to the heater IC 52).

[0033] In a configuration in which the oscillation IC 51 is die-bonded to the crystal unit 50, the contact area between the oscillation IC 51 and the crystal unit 50 is larger than in flip-chip bonding. This allows the heat generated by the oscillation IC 51 to be more easily transmitted via the crystal unit 50 to the heater IC 52, which controls the temperature. This allows the temperature in the core unit 5, i.e., the temperatures of the oscillation IC 51, the crystal unit 50, and the heater IC 52, to be efficiently transmitted to the temperature sensor in the heater IC 52, enabling highly accurate temperature control. While it would be desirable for the crystal unit 50 to be unaffected by the oscillation IC 51, which is a heat source other than the heater, this is difficult in practice. Therefore, if the temperature change in the crystal unit 50 caused by the oscillation IC 51 could be efficiently transmitted to the temperature sensor in the heater IC 52, control would be easier.

[0034] Furthermore, when the oscillation IC 51 and the crystal unit 50 are electrically connected by wire bonding, it is preferable that the core unit 5 and the package 2 are not directly wire-bonded with each other, as shown in FIG. 7, and that only the oscillation IC 51 is directly wire-bonded to the crystal unit 50. In FIG. 7, the crystal unit 50 and the oscillation IC 51 are only connected via wire 6c. This configuration can prevent heat from escaping from the crystal unit 50 to the package 2 through the wire. This results in improved thermal insulation for the crystal unit 50, which has the advantage of improving temperature controllability for the crystal unit 50.

[0035] As shown in Fig. 5, external terminals 22 are formed on the top surface of the crystal unit 50. Two of the external terminals 22, 22 have one end (outer peripheral end) electrically connected to an excitation electrode of the vibrating unit (via wiring or through holes in the crystal unit 50), and the other end (inner peripheral end) is connected to an oscillation IC 51. The remaining four external terminals 22 (external terminals provided at the four corners) have one end (outer peripheral end) used for wire bonding to the package 2, and the other end (inner peripheral end) is connected to the oscillation IC 51. The oscillation IC 51 is connected to the external terminals 22 by the FCB method using metal bumps.

[0036] In this embodiment, in the OCXO1 having the above configuration, the core unit 5 is sealed inside a heat-insulating package 2, the core unit 5 is mounted on a flexible core substrate 4, and the core substrate 4 is mechanically joined to the package 2 by a non-conductive adhesive 7. The core unit 5 and the package 2 are electrically joined by wire bonding, and a space 2d is provided between the core substrate and the bottom surface of the package 2.

[0037] According to this embodiment, by separating the mechanical connection of the core substrate 4 to the package 2 using the non-conductive adhesive 7 from the electrical connection between the core unit 5 and the package 2 using wire bonding, high reliability can be achieved for each. For example, the non-conductive adhesive 7 connecting the core substrate 4 to the package 2 can be made of a flexible material whose mechanical bonding strength is not easily reduced even when subjected to external stress. Furthermore, by using metal wires with low electrical resistance for wire bonding between the core unit 5 and the package 2, common impedance noise is less likely to occur, thereby improving the CN (carrier noise) characteristics of the OCXO 1.

[0038] Specifically, by using a core unit 5 in which an oscillation IC 51, a crystal unit 50, and a heater IC 52 are stacked, the heat capacity of the core unit 5 can be reduced. Reducing the heat capacity of the core unit 5 makes it easier to control the temperature with low power, and also improves the temperature tracking ability of the core unit 5, thereby improving the stability of the OCXO 1. Furthermore, if the heat capacity of the OCXO 1 is reduced, it becomes more susceptible to external temperature changes, but by interposing a core substrate 4 between the core unit and the package 2, stress and heat loss can be reduced.

[0039] Here, consider a case where core substrate 4 mediates the electrical connection between core unit 5 and package 2. In this case, connection between core unit 5 and core substrate 4 is made on the upper surface of core substrate 4, and connection between core substrate 4 and package 2 is made on the lower surface of core substrate 4. Furthermore, to connect core substrate 4 and package 2, it is necessary to use a conductive adhesive to connect the connection terminals on the lower surface of core substrate 4 to the connection terminals on the upper surface of package 2. In other words, electrical and mechanical connection must be made simultaneously between core substrate 4 and package 2 by using a conductive adhesive.

[0040] However, conductive adhesives that contain conductive fillers in the underfill are harder than non-conductive adhesives that do not contain conductive fillers, and the mechanical bond strength may be reduced by the influence of external stress. Furthermore, in terms of electrical bonding, conductive adhesives have higher electrical resistance than metal wires, making them more susceptible to common impedance noise, which reduces the CN characteristics of the OCXO1.

[0041] In contrast, in the OCXO 1 according to this embodiment, the crystal unit 50 and the heater IC 52 in the core unit 5 are directly connected to connection terminals formed in the package 2 via wires 6a and 6b. Therefore, the core substrate 4 does not need to have a function to mediate the electrical connection between the core unit 5 and the package 2.

[0042] As a result, in the OCXO 1 according to this embodiment, the core unit 5 and the package 2 can be connected only by mechanical bonding, and a non-conductive adhesive can be used. Non-conductive adhesives can be used that are more flexible than conductive adhesives, and the mechanical bonding strength is less likely to decrease even when subjected to external stress. Furthermore, the use of metal wires with low electrical resistance for the electrical bond between the core unit 5 and the package 2 reduces the occurrence of common impedance noise, improving the CN characteristics of the OCXO 1.

[0043] Furthermore, since the core substrate 4 only needs to support the core part 5 relative to the package 2, the options for materials for the core substrate 4 can be expanded. It is preferable to use a material with excellent heat insulating properties and heat resistance for the core substrate 4, and it is also preferable to use a substrate that is flexible so as to suppress the effects of external stress. From this perspective, in this embodiment, a flexible substrate made of a resin material such as polyimide is used as the core substrate 4.

[0044] In addition, according to this embodiment, the core unit 5 is connected to the package 2 via the core substrate 4, and a space 2d is formed below the core substrate 4, thereby improving the heat insulating effect for the core unit 5. Furthermore, by providing a pair of step portions 2c in the package 2 and providing connection terminals at the step portions 2c, the connection terminals are brought close to the opening of the package 2, making it easier to perform wire bonding between the core unit 5 and the package 2.

[0045] In this embodiment, spacer members 2f are interposed between the core substrate 4 and the bottom surface of the package 2 at both longitudinal ends of the core substrate 4. The spacer members 2f are provided in regions on the inner side of the bonding region A1 for bonding the core substrate 4 to the package 2, i.e., in regions closer to the core part 5 than the bonding region A1. The spacer members 2f determine the thickness of the non-conductive adhesive 7 applied to the bonding region A1, making it easy to determine the width of the space 2d between the core substrate 4 and the bottom surface of the package 2. The thickness of the spacer members 2f is preferably 5 to 50 μm.

[0046] If the spacer member 2f is not provided, the thickness of the non-conductive adhesive 7 varies greatly depending on the amount of the non-conductive adhesive 7 applied to the bonding area A1, and the width of the space 2d between the core substrate 4 and the bottom surface of the package 2 also varies greatly. Also, the distance from the heater IC 52 on the core substrate 4 to the non-conductive adhesive 7 applied to the bonding area A1 varies. This makes it difficult to stably wire bond the crystal unit 50 and the heater IC 52.

[0047] However, in this embodiment, by using the spacer member 2f to define the thickness of the non-conductive adhesive 7 applied to the bonding area A1, it is possible to suppress variations in the width of the space 2d between the core substrate 4 and the bottom surface of the package 2. Also, it is possible to suppress variations in the distance from the heater IC 52 on the core substrate 4 to the non-conductive adhesive 7 applied to the bonding area A1. Furthermore, by forming the core substrate 4 from a specific material, setting the width of the space 2d between the core substrate 4 and the bottom surface of the package 2 within a predetermined range, and further setting the distance from the heater IC 52 on the core substrate 4 to the non-conductive adhesive 7 applied to the bonding area A1 within a predetermined range, it is possible to stably wire bond the crystal unit 50 and the heater IC 52. That is, by bending the core substrate 4 during wire bonding, the core substrate 4 is brought into contact with the bottom surface of the recess 2a of the package 2, and there is no gap between the core substrate 4 and the bottom surface of the package 2. This ensures reliable application of ultrasonic waves during wire bonding, thereby stably wire bonding the crystal unit 50 and the heater IC 52. Specifically, the core substrate 4 is made of polyimide, the thickness of the core substrate 4 is 5 to 100 μm, the width of the space 2d between the core substrate 4 and the bottom surface of the package 2 is 5 to 50 μm, and the distance from the heater IC 52 on the core substrate 4 to the non-conductive adhesive 7 applied to the bonding area A1 is 250 to 1000 μm.

[0048] Furthermore, if the width of the space 2d between the core substrate 4 and the bottom surface of the package 2 is greater than 50 μm, or if the distance from the heater IC 52 on the core substrate 4 to the non-conductive adhesive 7 applied to the bonding area A1 is greater than 1000 μm, the core substrate 4 will bend too much during wire bonding, making it difficult to perform wire bonding stably.

[0049] Furthermore, according to this embodiment, when the non-conductive adhesive 7, 7 applied to the bonding area A1 contracts, the spacer members 2f, 2f allow the core substrate 4 to bend in a direction that increases the width of the space 2d between the core substrate 4 and the bottom surface of the package 2, thereby improving the insulating effect on the core portion 5.

[0050] The present invention can be embodied in various other forms without departing from its spirit, essence, or main features. Therefore, the above-described embodiments are merely illustrative in all respects and should not be interpreted as limiting. The scope of the present invention is defined by the claims and is not limited to the text of the specification. Furthermore, all modifications and variations within the equivalent range of the claims are within the scope of the present invention.

[0051] For example, in the above embodiment, a crystal oscillator 100 including a sandwich-structured crystal resonator 50 is used, but the present invention is not limited to this, and an oscillator other than a sandwich-structure (for example, an SMD (Surface Mount Device) type oscillator) may also be used.

[0052] Furthermore, the number of heaters included in the OCXO 1 is not particularly limited, and the OCXO 1 may have other heaters in addition to the heater included in the heater IC 52. For example, possible configurations include a configuration in which an additional heater is added above the core unit 5, a configuration in which a heater is added in a mounting area for circuit components arranged outside the core unit 5 within the package 2, and a configuration in which a film-like heater is embedded in the main body of the package 2.

[0053] Second Embodiment In order to improve the temperature controllability of the OCXO 1, it is important to reduce heat dissipation from the core unit 5 to the package 2. Here, heat dissipation from the core unit 5 to the package 2 occurs mainly by heat conduction via the core substrate 4. In other words, by reducing the amount of heat conduction through the core substrate 4, the temperature controllability of the OCXO 1 can be improved. In this second embodiment, an example of the configuration of the core substrate 4 that can reduce the amount of heat conduction from the core unit 5 to the package 2 will be described.

[0054] Fig. 8 is a plan view showing an example of the shape of core substrate 4 according to embodiment 2. In Fig. 8, region R1 is a region on the top surface of core substrate 4 where heater IC 52, which is part of core unit 5, is mounted, and region R2 is a region on the back surface of core substrate 4 that is bonded to package 2 (region where adhesive is applied).

[0055] In core substrate 4 according to the second embodiment, slit 401 is provided between region R1 and region R2, and this slit 401 narrows the heat transfer path between region R1 and region R2. This makes it possible to reduce heat dissipation from core unit 5 to package 2 due to heat conduction through core substrate 4.

[0056] In order to optimally obtain the heat conduction reducing effect (thermal insulation effect) of slits 401, it is preferable that slits 401 have a longitudinal direction that is perpendicular (vertical direction in FIG. 8) to the arrangement direction (horizontal direction in FIG. 8) of regions R2 on both sides of core substrate 4. This allows slits 401 to block heat transferred from region R1 to region R2 over a wide range, improving the thermal insulation effect of slits 401.

[0057] It should be noted that the dimension of slit 401 in the short direction (left-right direction in FIG. 8) does not particularly affect the heat insulating effect of slit 401, and is preferably made as small as possible from the viewpoint of avoiding a decrease in the strength of core substrate 4. If the strength of core substrate 4 decreases, ultrasonic waves will not efficiently contribute to bonding when wire bonding core portion 5 to package 2, making it difficult to perform good wire bonding.

[0058] It is preferable that the slit 401 provided between the region R1 and one region R2 is divided into multiple slits in the longitudinal direction rather than being formed as one long slit (see FIG. 8(a)). By dividing the slit 401 into multiple slits in this way, it is possible to avoid a decrease in the strength of the core substrate 4 compared to when the slit 401 is formed as one long slit.

[0059] Furthermore, the slits 401 are not limited to being formed linearly, and may be formed, for example, in a shape that is curved around the periphery of the region R2 (see FIG. 8(b)). In this way, by making the slits 401 curve around the periphery of the region R2, it is believed that heat conduction to the region R2 can be effectively blocked, and an effective heat insulating effect can be obtained by the slits 401.

[0060] Furthermore, the slit 401 is not limited to being disposed between the regions R1 and R2 and close to the region R2, but may be disposed close to the region R1 (see FIG. 8(c)). In this way, by disposing the slit 401 close to the region R1, it is thought that the heat conduction from the region R1 (i.e., the heat conduction from the heater IC 52, which is the heat source) is effectively blocked from the vicinity of the heat source of the heat radiatively transmitted from the region R1, and an effective heat insulating effect is obtained by the slit 401.

[0061] Third Embodiment In the third embodiment, a description will be given of another example of the configuration of the core substrate 4 that can reduce the amount of heat conducted from the core portion 5 to the package 2. Fig. 9 is a plan view showing an example of the shape of the core substrate 4 according to the third embodiment.

[0062] In the core substrate 4 according to the third embodiment, an opening 402 is provided in a region directly below the heater IC 52, which is part of the core unit 5, i.e., so as to substantially overlap with the region R1. This opening 402 reduces the contact area between the heater IC 52 and the core substrate 4, thereby reducing the amount of heat transferred from the heater IC 52 to the core substrate 4. As a result, heat dissipation from the core unit 5 to the package 2 due to heat conduction via the core substrate 4 can be reduced.

[0063] The opening 402 does not completely include the region R1, and the opening 402 is shaped so as to exclude at least the four corners of the region R1, thereby enabling the heater IC 52 to be adhesively fixed to the core substrate 4 at its four corners.

[0064] 9(a) is formed so that the vertical and horizontal dimensions of the opening 402 are larger than the vertical and horizontal dimensions of the region R1. As a result, the region R1 has a shape in which only the four corners are not included in the opening 402. In this case, the contact area between the heater IC 52 and the core substrate 4 can be minimized, and the heat conduction reduction effect (thermal insulation effect) of the opening 402 can be maximized.

[0065] 9(b), the opening 402 is formed so that its vertical and horizontal dimensions are smaller than those of the region R1. As a result, the region R1 is shaped so that not only the four corners but also the entire periphery of the outer edge is not included in the opening 402. In this case, when the core unit 5 is wire-bonded to the package 2, the opening 402 can be prevented from being located directly below the wire bonding pad of the core unit 5. As a result, the posture of the core unit 5 can be stabilized during wire bonding, allowing ultrasonic waves to efficiently contribute to bonding, and facilitating good wire bonding.

[0066] Fourth Embodiment In the above first to third embodiments, the package 2 is a single package, but the present invention is not limited to this. For example, an H-shaped package or a two-tiered package as shown in FIG. 10 may also be used.

[0067] The H-type package OCXO 1 shown in Fig. 10 has a package 2 that has a recess 2e that is open at the bottom in addition to a recess 2a that is open at the top. The recess 2e is formed on the main surface opposite to the main surface (the main surface on which the recess 2a is formed) that serves as the mounting portion for the core unit 5, and can accommodate circuit components (circuit components attached with a circuit component bonding material (e.g., solder)) such as a capacitor 9 as an adjustment electronic component used in combination with the heater IC 52. Unlike the recess 2a, the recess 2e where the capacitor 9 is placed does not need to be sealed with the lid 3.

[0068] Here, the capacitor 9 can be placed inside the package (in the recess 2a) like the core section 5, but placing the circuit components outside the package as shown in Figure 10 reduces the heat capacity inside the package, enabling temperature control with low power and improving the temperature tracking of the core section 5. It also prevents subsequent gas generation due to solder, flux, etc. in the atmosphere inside the hermetically sealed recess 2a. This prevents the core section 5 from being adversely affected by gas, which is desirable for achieving further stabilization of electrical characteristics.

[0069] In this embodiment, the three capacitors 9 are mounted on the other main surface of the package 2 opposite to the one main surface (in this case, the bottom surface of the recess 2e). As shown in FIG. 11, the capacitors 9 are joined by solder to mounting pads 9a (circuit component mounting pads) formed on the bottom surface of the recess 2e of the package 2. Note that in FIG. 11, the arrangement area of ​​the capacitors 9 is indicated by a dashed dotted line. The pair of mounting pads 9a, 9a are arranged opposite each other along the short side of the package 2, and both ends of each of the three capacitors 9 in the short side direction of the package 2 are joined to the mounting pads 9a, 9a.

[0070] As shown in FIG. 11, three pairs of mounting pads 9a, 9a are arranged at predetermined intervals along the long side of the package 2. The mounting pads 9a are scattered like islands on the bottom surface of the package 2. The package 2 and the three capacitors 9 are each rectangular in a plan view, and the three capacitors 9 are arranged symmetrically with respect to a center line L1 along the short side of the package 2 and a center line L2 along the long side. In this case, it is sufficient that the arrangement locations of the three capacitors 9 are line-symmetric with respect to the center lines L1, L2. The bottom surface of the package 2 also has a plurality of external connection terminals 2g (eight in FIG. 11) formed thereon for electrically connecting the OCXO 1 to an external circuit board (not shown) provided externally via solder or the like.

[0071] In this embodiment, the three capacitors 9 are arranged symmetrically with respect to the center line L1 in the short-side direction and the center line L2 in the long-side direction of the package 2, thereby achieving uniform heat distribution throughout the package 2. This makes it difficult for heat transfer to be uneven throughout the package 2, stabilizing the temperature control and characteristics of the OCXO 1. Furthermore, because the capacitors 9 are arranged in a regular orientation and with regular intervals, there is no wasted space in the mounting positions of the capacitors 9 relative to the mounting area on the other main surface of the package 2, improving mountability.

[0072] Furthermore, the number of capacitors 9 mounted on the other main surface of package 2 is not particularly limited, and the number of capacitors 9 may be other than three. Furthermore, circuit components other than capacitors 9 may be mounted on the other main surface of package 2. Furthermore, the sizes (volume, surface area) of all circuit components do not have to be the same.

[0073] 11, the three capacitors 9 are arranged symmetrically with respect to both the center lines L1 and L2, but it is sufficient if they are symmetrical with respect to at least one of the center lines L1 and L2. For example, the three capacitors 9 may be symmetrical with respect to only the center line L1 in the short side direction of the package 2, or the three capacitors 9 may be symmetrical with respect to only the center line L2 in the long side direction of the package 2. This makes it possible to maintain symmetry in heat transfer in a specific side direction of the package 2, making it less likely that heat transfer will be biased, and stabilizing the temperature control and characteristics of the OCXO 1.

[0074] Furthermore, when capacitor 9 is placed outside the package, it is not necessary to form recess 2e as in package 2 shown in Figure 10, and the other main surface opposite to the main surface on which recess 2a is formed may be made flat, and capacitor 9 may be placed on this flat surface.

[0075] Furthermore, although not shown, a two-tiered package OCXO 1 can also be configured in which packages with a recess on only one side are stacked vertically and electrically and mechanically joined, with the upper package hermetically sealed with a lid. In this case, the upper package can be configured to house the core 5 in the recess, as shown in Figure 1, and the lower package can house only the capacitor. Still another OCXO 1 can be configured in which the capacitor 9 is placed on the lid 3 of Figure 1.

[0076] Furthermore, while the core unit 5 described above has a three-layer structure in which the oscillation IC 51, the crystal unit 50, and the heater IC 52 are stacked in this order from the top, the present invention is not limited to this, and the oscillation IC 51 and the crystal unit 50 may be placed flat (side by side) on top of the heater IC 52. In this configuration, the crystal unit 50 is less susceptible to the heat from the oscillation IC 51, and the temperatures of the crystal unit 50 and the heater IC 52 are more likely to be uniform, allowing the temperature sensor provided in the heater IC 52 to perform more accurate temperature control on the crystal unit 50, which is the temperature control target.

[0077] This application claims priority based on Japanese Patent Application No. 2021-031583, filed on March 1, 2021, the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0078] 1 OCXO (oven-controlled piezoelectric oscillator) 2 packages 2d space 2f Spacer member 4 Core board (flexible board) 5 Core 7 Non-conductive adhesive (bonding material) 50 Quartz crystal oscillator (piezoelectric oscillator) 51 Oscillator IC 52 Heater IC

Claims

1. An oven-controlled piezoelectric oscillator in which a core is sealed in a heat-insulating package, The core part includes at least an oscillation IC, a piezoelectric vibrator, and a heater IC, the core portion is mounted on a flexible substrate, and the flexible substrate is mechanically joined to the package by a joining material; the core and the package are electrically connected by wire bonding; an oven-controlled piezoelectric oscillator, wherein a space is provided between the flexible substrate and the bottom surface of the package, and a spacer member is interposed between the flexible substrate and the bottom surface of the package.

2. An oven-controlled piezoelectric oscillator in which a core is sealed in a heat-insulating package, The core part includes at least an oscillation IC, a piezoelectric vibrator, and a heater IC, the core portion is mounted on a flexible substrate, and the flexible substrate is mechanically joined to the package by a joining material; the core and the package are electrically connected by wire bonding; a space is provided between the flexible substrate and the bottom surface of the package; An oven-controlled piezoelectric oscillator, wherein the flexible substrate has a thickness of 5 to 100 μm, and the space has a width of 5 to 50 μm.

3. 2. The oven-controlled piezoelectric oscillator according to claim 1, a bonding region for bonding the flexible substrate to the package does not overlap with an arrangement region of the core portion on the flexible substrate in a plan view; an oven-controlled piezoelectric oscillator, wherein the spacer member is provided in a region closer to the core portion than the bonding region;

4. 3. The oven-controlled piezoelectric oscillator according to claim 2, 10. An oven-controlled piezoelectric oscillator, wherein a bonding area for bonding the flexible substrate to the package does not overlap, in a plan view, with an area where the core portion is disposed on the flexible substrate.

5. 3. The oven-controlled piezoelectric oscillator according to claim 1, The oven-controlled piezoelectric oscillator is characterized in that the flexible substrate is made of a heat-resistant resin material.

6. 3. The oven-controlled piezoelectric oscillator according to claim 1, The core portion is vacuum-sealed inside the package.

7. 3. The oven-controlled piezoelectric oscillator according to claim 1, the flexible substrate has a slit formed on its top surface between a mounting area where the core unit is mounted and a bonding area where the flexible substrate is bonded to the package.

8. 3. The oven-controlled piezoelectric oscillator according to claim 1, The oven-controlled piezoelectric oscillator is characterized in that the flexible substrate has an opening in a region directly below the core portion.

9. 3. The oven-controlled piezoelectric oscillator according to claim 1, The oven-controlled piezoelectric oscillator is characterized in that the piezoelectric vibrator is not directly wire-connected to the package, and only the oscillation IC is directly wire-connected to the piezoelectric vibrator.

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