JP5121534B2 - Crystal oscillator for surface mounting - Google Patents

Description

  The present invention relates to a surface-mount crystal oscillator in which a crystal resonator and an IC (integrated circuit) chip including an oscillation circuit using the crystal resonator are integrated.

  A surface-mount crystal oscillator in which a crystal resonator and an IC chip in which an oscillation circuit using the crystal resonator is integrated is integrated is small and light. Therefore, particularly in a portable electronic device such as a mobile phone. Widely built in as a frequency and time reference source. As one type of crystal oscillator for surface mounting, as shown in Patent Document 1, a crystal resonator is formed by sealing and enclosing a crystal piece in a container, and an IC chip is accommodated in another container. There is a bonded type surface mount crystal oscillator that is integrated with a crystal unit. 6A is a cross-sectional view showing an example of a conventional junction type surface-mount crystal oscillator, FIG. 6B is an assembled cross-sectional view thereof, and FIG. 6C is a side cross-sectional view thereof. 6A corresponds to a cross-sectional view of the long side of the crystal piece 8 viewed from the side, and FIG. 6C corresponds to a cross-sectional view of the short side of the crystal piece 8 viewed from the side.

  The illustrated crystal oscillator includes a mounting substrate 2 containing an IC chip 1 and a crystal resonator 3 in which a crystal piece 8 is hermetically sealed. The mounting substrate 2 is bonded to the bottom surface of the crystal resonator 3. . The mounting substrate 2 is a flat plate member having a substantially rectangular planar shape, and a concave portion for accommodating the IC chip 1 is formed on one main surface thereof.

  The mounting substrate 2 is composed of a laminated ceramic composed of a substantially rectangular flat bottom wall layer 2a and a frame wall layer 2b provided in a frame shape on the bottom wall layer 2a, and is mounted by the frame wall layer 2b. A side wall of the concave portion of the substrate 2 is formed. Bonding for electrically and mechanically bonding the mounting substrate 2 to the bottom surface of the crystal unit 3 at the four corners of the upper surface of the frame wall layer 2b, that is, the four corners of the opening end surface surrounding the recess of the mounting substrate 2 Terminal 5 is formed. The bottom wall layer 2a is formed by laminating a first layer 2a1 constituting the lower side of the figure, that is, the outer bottom surface of the mounting substrate 2, and a second layer 2a2 that comes into contact with the frame wall 2b, etc. An intermediate layer 14 made of a metal film is provided on almost the entire surface where the first layer 2a1 and the second layer 2a2 are laminated. The intermediate layer 14 functions as an electromagnetic shield for the IC chip 1 and the crystal piece 8, and details thereof will be described later. Mounting terminals 4 used when the crystal oscillator is surface-mounted on the set substrate are provided at the bottom surface of the first layer 2a1 of the bottom wall layer 2a, that is, at the four corners of the outer bottom surface of the mounting substrate 1. These four mounting terminals 4 are, for example, a power supply terminal, a ground terminal, an oscillation output terminal, and an AFC (automatic frequency control) terminal. The AFC terminal is a terminal used for supplying an AFC signal to the IC chip 1.

  The IC chip 1 has a substantially rectangular shape, and an electronic circuit including at least an oscillation circuit using the crystal resonator 3 is integrated on a semiconductor substrate. In addition to the oscillation circuit, the IC chip 1 may include a temperature compensation mechanism that compensates for the frequency temperature characteristics of the crystal resonator 3. In the IC chip 1, since electronic circuits such as an oscillation circuit and a temperature compensation mechanism are formed on one main surface of the semiconductor substrate by a normal semiconductor device manufacturing process, these electronic circuits of the pair of main surfaces of the semiconductor substrate are used. The main surface on which is formed is called the circuit function surface of the IC chip. A plurality of IC terminals for connecting the IC chip 1 to an external circuit are also formed on the circuit function surface. The IC terminal includes a power supply terminal, a ground terminal, an oscillation output terminal, an AFC terminal, a pair of crystal connection terminals for connection to a crystal resonator, and the like.

  Circuit terminals 11 are provided corresponding to the IC terminals on the bottom surface of the concave portion of the mounting substrate 2, that is, the exposed surface of the second layer 2a2 by the concave portion. Among the IC terminals, circuit terminals corresponding to the power supply terminal, the ground terminal, the oscillation output terminal, and the AFC terminal are electrically connected to the corresponding mounting terminals 4 through conductive paths (not shown). The circuit terminals corresponding to the pair of crystal connection terminals of the IC chip 2 are electrically connected to, for example, the junction terminals 5 at both ends of one short side of the substantially rectangular mounting substrate 2 through a conductive path (not shown). doing. The remaining two joining terminals 5 are electrically connected to the ground terminal of the mounting terminals 4 through, for example, through holes provided in the mounting substrate 2. The intermediate layer 14 is also electrically connected to the ground terminal of the mounting terminals 4 through a through hole provided in the mounting substrate.

  The IC chip 1 is fixed to the bottom surface of the concave portion of the mounting substrate 2 using a flip chip bonding technique so that the circuit function surface faces the bottom surface of the concave portion of the mounting substrate 2. Specifically, the IC chip 1 is fixed to the bottom surface of the concave portion of the mounting substrate 2 by electrically and mechanically connecting the IC terminal to the circuit terminal 11 by ultrasonic thermocompression using the bump 6.

  On the other hand, the crystal unit 3 accommodates a crystal piece 8 in a container body 7 made of a laminated ceramic having a recess, and a metal cover 9 is bonded to an opening end surface surrounding the recess, whereby the crystal piece 8 is placed in the recess. Is hermetically sealed. In the illustrated example, the metal cover 9 is joined to the metal thick film or the metal ring 15 provided on the opening end face by seam welding or beam welding. External terminals 10 corresponding to the junction terminals 5 of the mounting substrate 2 are provided at the four corners of the outer bottom surface of the container body 7. A pair of crystal holding terminals 12 for holding the crystal piece 8 are provided on the bottom surface of the concave portion of the container body 7.

  The crystal piece 8 is, for example, a substantially rectangular AT-cut crystal piece. Excitation electrodes (not shown) are provided on both main surfaces of the crystal piece 8, and both sides of one end portion of the crystal piece 8 are provided from these excitation electrodes. The extraction electrodes (not shown) extend toward the ends, that is, toward both ends of one short side. The crystal piece 8 is electrically and mechanically connected to the crystal holding terminal 12 by fixing both ends of the crystal piece 8 from which the extraction electrode is extended with the conductive adhesive 13 or the like. Is held in the recess of the container body 7.

  In the container body 7, the pair of crystal holding terminals 12 are electrically connected to the pair of external terminals 10 at both ends of one short side of the outer bottom surface of the container body 7 through a conductive path (not shown). To do. External terminals 10 at both ends of the other short side of the outer bottom surface of the container body 7 are electrically connected to the metal cover 9 through via holes provided in the container body 7.

  In such a configuration, the mounting substrate 2 and the crystal unit 3 are electrically and mechanically connected by connecting the bonding terminal 5 of the mounting unit 2 and the external terminal 10 of the crystal unit 3 using solder or the like. It will be connected and completed as a crystal oscillator for surface mounting. At this time, the crystal holding terminal 12 in the crystal resonator 3 is electrically connected to the IC terminal via the external terminal 10, the junction terminal 5, and the circuit terminal 11. It is electrically connected to the oscillation circuit. Similarly, the metal cover 9 is electrically connected to the ground terminal in the mounting terminal 4, and the intermediate layer 14 formed in the bottom wall layer 2 a is also electrically connected to the ground terminal in the mounting terminal 4.

In this configuration, the crystal piece 8 and the IC chip 1 are sandwiched from above and below by the metal cover 9 and the intermediate layer 14 that are connected to the ground potential when mounted on the set substrate. Since 14 functions as an electromagnetic shield, electromagnetic wave noise from the outside does not enter the crystal piece 8 or the IC chip 1 and the crystal oscillator operates stably.
Japanese Patent No. 2960374

  However, in the conventional junction-type surface-mount crystal oscillator described above, not only the planar size but also the height (part height when mounted on a set substrate) as the equipment on which the crystal oscillator is mounted is reduced in size. It needs to be small. Therefore, in the configuration shown in FIG. 6, the diameter of the bump 6 used for flip chip bonding to the mounting substrate 2 of the IC chip 1 also tends to be reduced. As a result, the circuit function surface of the IC chip 1 and the mounting substrate 2 The distance (gap) from the inner bottom surface of the recess, that is, the exposed surface of the bottom wall layer 2a, is also decreasing, for example, to 30 μm.

  An oscillation circuit or the like is formed on the circuit function surface of the IC chip. However, if the distance between the circuit function surface of the IC chip and the inner bottom surface of the recess becomes small, an electronic circuit such as an oscillation circuit formed on the circuit function surface The distance from the intermediate layer 14 formed in the bottom wall layer 2a is also shortened, and the stray capacitance between them cannot be ignored. If the stray capacitance is too large, the operation of an electronic circuit such as an oscillation circuit in the IC chip 1 is adversely affected.

  Further, the mounting substrate 2 made of a multilayer ceramic is obtained by laminating and firing a plurality of unfired ceramic sheets. In the structure shown in FIG. An intermediate layer 14, which is a metal film, is provided over a wide range on the laminated surface of the first layer 2 a 1 and the second layer 2 a 2. Since the bonding strength between the ceramic and the metal is generally lower than the bonding strength between the ceramics, the mechanical strength of the mounting substrate 2 tends to be insufficient in such a configuration in which the intermediate layer 14 is provided in a wide area. . In addition, when the mounting substrate 2 is formed by firing, the ceramic sheet contracts unevenly, which may result in a partially convex shape on the inner bottom surface of the concave portion of the mounting substrate 2. When such a convex shape occurs when the distance between the IC chip 1 and the inner bottom surface of the concave portion is reduced, the convex shape comes into contact with the circuit functional surface of the IC chip 1 and is formed on the circuit functional surface. It is also possible that the electronic circuit is damaged and does not operate normally.

  Accordingly, an object of the present invention is to maintain the mechanical strength of a mounting substrate that accommodates an IC chip even when it is formed in a small size while maintaining an electromagnetic shield for a crystal piece, and to float an electronic circuit in the IC chip. An object of the present invention is to provide a surface-mount crystal oscillator that is not easily affected by capacitance and that does not damage an electronic circuit in an IC chip due to a convex shape formed on the inner bottom surface of a concave portion of a mounting substrate.

  The crystal oscillator for surface mounting according to the present invention includes a container that hermetically encloses a crystal piece with a metal cover provided on the upper surface, and includes an external terminal that is electrically connected to the crystal piece on an outer bottom surface of the container. A mounting board including a plurality of mounting terminals including a connector, a joining terminal corresponding to an external terminal on one main surface, and at least a grounding terminal on the other main surface; and a recess formed on one main surface of the mounting board And an IC chip in which an oscillation circuit using a crystal piece is integrated, and the mounting substrate is made of a laminated ceramic, and has a bottom wall layer and an opening formed on the bottom wall layer. A frame wall layer formed on the bottom of the recess, and an IC chip is fixed to the bottom surface of the recess by flip chip bonding. The IC chip is electrically connected to a plurality of mounting terminals and joint terminals, The wall layer is the first layer and the second layer An intermediate layer made of a metal film is provided on the laminated surface of the first layer and the second layer, and the intermediate layer has an opening and corresponds to a circuit formation region in the IC chip Is not provided with an intermediate layer, and the metal cover and the intermediate layer are electrically connected to a ground terminal.

  Alternatively, the crystal oscillator for surface mounting according to the present invention has a crystal piece, an IC chip on which an oscillation circuit using the crystal piece is integrated, and a first recess for housing the IC chip on one main surface. A mounting substrate having a second recess for housing the second concave portion on the other main surface, and the mounting substrate is made of a multilayer ceramic and is formed on one main surface of the bottom wall layer with a bottom wall layer and an opening. A first frame wall layer forming a first recess, a second frame wall layer having an opening and formed on the other main surface of the bottom wall layer to form a second recess, A pair of crystal holding terminals are provided on the bottom surface of the two concave portions, the crystal pieces are bonded to each other, a metal cover is bonded to the opening end surface of the two concave portions, and the crystal pieces are placed in the second concave portion by the cover. A plurality of mounting terminals including at least a ground terminal are formed on the opening end surface of the first recess, An IC chip is fixed to the surface by flip chip bonding, the IC chip is electrically connected to a plurality of mounting terminals, and the bottom wall layer is formed by laminating a first layer and a second layer. And the second layer is provided with an intermediate layer made of a metal film, the intermediate layer has an opening and no intermediate layer is provided in a region corresponding to a circuit formation region in the IC chip, The cover and the intermediate layer are electrically connected to a ground terminal.

  In the crystal oscillator for surface mounting according to the present invention, the flip chip bonding is, for example, ultrasonic thermocompression bonding using bumps.

  A position facing the circuit formation region by providing an opening corresponding to the circuit formation region in the IC chip in an intermediate layer provided in the bottom wall layer where the IC chip is fixed by flip chip bonding in the container body. In this case, no intermediate layer is formed, so that stray capacitance between the electronic circuit such as the oscillation circuit and the intermediate layer in the circuit formation region can be suppressed, and the electronic circuit such as the oscillation circuit is stable. In addition, since the area of the portion where the ceramic layer and the metal film are joined decreases, the mechanical strength of the container body increases. Furthermore, since the surface of the bottom wall layer is slightly depressed in the region where the intermediate layer is not formed, even if a convex shape is generated in this region, the convex shape does not contact the circuit formation region of the IC chip.

  FIG. 1 is a side sectional view showing a surface-mount crystal oscillator according to a first embodiment of the present invention, FIG. 2 is a plan view for explaining a circuit function surface of an IC chip, and FIG. 3 is shown in FIG. It is a figure explaining the mounting substrate in a crystal oscillator, (a) is a top view of a mounting substrate, (b) is a top view of a bottom wall layer, (c) is a 1st layer in a bottom wall layer 2 is a plan view showing the arrangement of an intermediate layer formed between the first layer and the second layer, and FIG. In these drawings, the same components as those in FIG. 6 are given the same reference numerals, and description thereof will be omitted or simplified. FIG. 1 corresponds to a view of the short side of the substantially rectangular crystal piece 8 seen from the side, as in FIG.

  The surface-mount crystal oscillator of the first embodiment is the same as the conventional junction-type surface-mount crystal oscillator shown in FIG. 6, except that the first layer 2a1 and the second layer 2a in the bottom wall layer 2a. The shape of the intermediate layer 14 formed as a metal film on the laminated surface with the layer 2a2 is different from that shown in FIG. The structure of the crystal unit 3 in which the crystal piece 8 is hermetically sealed is the same as that shown in FIG.

  FIG. 2 shows a circuit function surface of the IC chip 1. In the present embodiment, the IC chip 1 includes a temperature compensation mechanism that compensates the frequency temperature characteristics of the crystal resonator 3 in addition to the oscillation circuit, and the crystal oscillator of the present embodiment is a temperature compensated crystal oscillator. In the substantially rectangular IC chip 1, electronic circuits such as an oscillation circuit and a temperature compensation mechanism are formed in a substantially central region of the circuit function surface, and these electronic circuits are not formed on the outer periphery of the circuit function surface. Assuming that the area where the electronic circuit is formed in the circuit function plane is a circuit formation area, in the case shown in FIG. 2, the substantially rectangular area at the substantially central portion of the circuit function plane is the circuit formation area 17, and the circuit formation A plurality of IC terminals 16 are arranged so as to surround the region 17. In the illustrated example, eight IC terminals 16 are arranged in two rows, four each per row. The IC terminal 16 is connected to an electronic circuit formed in the circuit forming region 17. In the case shown here, the IC terminal 16 is connected to a power supply terminal, a ground terminal, an oscillation output terminal, an AFC terminal, and a crystal resonator. A pair of crystal connection terminals and a pair of write terminals used to write temperature compensation data to the temperature compensation mechanism are provided as IC terminals 16.

  In the crystal oscillator of this embodiment, when the IC chip 1 is fixed to the inner bottom surface of the concave portion of the mounting substrate 2 by flip chip bonding as in the case shown in FIG. The intermediate layer 14 is not provided. In other words, in the intermediate layer 14 provided as a metal film on the laminated surface of the first layer 2a1 and the second layer 2a2 of the bottom wall layer 2a, as shown in FIG. A substantially rectangular opening corresponding to 17 is provided.

  Next, the mounting substrate 2 used in the surface mount crystal oscillator of the present embodiment will be described in more detail.

  FIG. 3A is a top view of the mounting substrate 2 and shows that the junction terminals 5 are formed at the four corners of the top surface of the frame wall layer 2b. A portion surrounded by the frame wall layer 2b is a recess, and FIG. 3A shows that the IC chip 1 is fixed in the recess. FIG. 3B shows the upper surface of the bottom wall layer 2a, that is, the upper surface of the second layer 2a2. The two-dot chain line in the figure indicates the position where the inner wall of the frame wall layer 2b is formed. As shown in FIG. 3B, eight circuit terminals 11 are arranged in two rows of four in one row on the upper surface of the second layer 2a2. Of these circuit terminals, the two at the left end in the figure correspond to the crystal connection terminals of the IC chip 1, and are joined terminals 5 on the upper surface of the frame wall layer 2b through via holes formed in the frame wall layer 2b. Is electrically connected. The second two circuit terminals 11 from the left end in the figure correspond to the AFC terminal and the power supply terminal of the IC chip 1, and the second two circuit terminals 11 from the right end in the figure are the second circuit terminals 11 of the IC chip 1. This corresponds to a pair of write terminals. Of the two circuit terminals 11 at the right end of the figure, the one on the upper side in the figure corresponds to the output terminal of the IC chip 1, and the one on the lower side in the figure corresponds to the ground terminal. Among these circuit terminals 11, those corresponding to the AFC terminal, the power supply terminal, the oscillation output terminal, and the ground terminal are drawn out to the four corners of the upper surface of the second layer 2 a 2 by the conductive path, and Each of the mounting terminals 4 on the outer bottom surface of the mounting substrate 2 is electrically connected via a conductive path formed on the outer side surface.

  FIG. 3C is a top view of the first layer 2a1 and shows the arrangement of the intermediate layer 14 on the laminated surface of the first layer 2a1 and the second layer 2a2. The hatched portion in the figure is the formation region of the intermediate layer 14. The intermediate layer 14 is provided with an opening corresponding to the circuit formation region 17 of the IC chip 1. The intermediate layer 14 is drawn out to one corner of the upper surface of the first layer 2a1, and is electrically connected to the conductive path for the ground terminal among the conductive paths formed on the outer surface of the mounting substrate 2. , And electrically connected to the ground terminal of the mounting terminals 4. The intermediate layer 14 is also electrically connected to the grounding junction terminal 5 through a via hole formed in the second layer 2a2 and the frame wall layer 2b.

  FIG. 3D shows the outer bottom surface of the mounting substrate 2 and shows that the mounting terminals 4 are provided at the four corners. These mounting terminals 4 are a ground terminal, a power supply terminal, an AFC terminal, and an oscillation output terminal, respectively. As described above, the conductive paths formed on the outer surface of the mounting substrate 2 and the upper surface of the second layer 2a2 are provided. To the corresponding circuit terminal 11. Furthermore, in the crystal oscillator of this embodiment, a data write terminal 18 for writing temperature compensation data to the temperature compensation mechanism in the IC chip 1 is also provided at the center of each long side of the outer bottom surface of the mounting substrate 2. Yes. The data write terminal 18 is electrically connected to the circuit terminal 11 for the write terminal through a via hole formed in the first layer 2a1 and the second layer 2a2.

  Such a mounting substrate 2 is manufactured by laminating and firing unfired ceramic sheets respectively corresponding to the first layer 2a1, the second layer 2a2, and the frame wall layer 2b. On these unfired ceramic sheets, metal film patterns corresponding to the mounting terminals 4, the conductive paths, the junction terminals 5, the circuit terminals 11, the intermediate layer 14, and the like are formed in advance.

  The IC chip 1 is electrically and mechanically connected to the circuit terminals 11 by ultrasonic thermocompression bonding using the bumps 6 so that the circuit function surface faces the bottom surface of the concave portion of the mounting substrate 2 manufactured as described above. By being connected to each other, it is fixed to the bottom surface of the recess of the mounting substrate 2. By bonding the mounting substrate 2 on which the IC chip 1 is mounted to the separately manufactured crystal resonator 3, the surface mount crystal oscillator of this embodiment is completed.

  In the crystal oscillator of the present embodiment, the intermediate layer 14 is not formed at a position facing the circuit formation region 17 of the IC chip 1. Therefore, even if the distance between the circuit function surface of the IC chip 1 and the inner bottom surface of the concave portion of the mounting substrate 2 is reduced, a large stray capacitance may be generated between the intermediate layer 14 in the circuit in the circuit formation region 17. As a result, the electronic circuit such as the oscillation circuit can be reliably operated. Compared to the conventional one shown in FIG. 6, the area of the intermediate layer 14 is reduced, and accordingly, the area of the portion where the first layer 2a1 and the second layer 2a2 are directly joined is increased. Since the bonding between the ceramics is stronger than the bonding between the ceramic and the metal, the crystal oscillator of this embodiment has improved mechanical strength compared to the conventional one.

  Further, the bottom wall layer 2a is formed by laminating and firing the ceramic sheets corresponding to the first layer 2a1 and the second layer 2a2 with the metal film pattern corresponding to the intermediate layer 14 interposed therebetween. At the opening in the intermediate layer 14, the surface of the second layer 2a2 is slightly depressed. If there is such a dent, even if a convex portion is formed in the second layer 2a2 due to non-uniform shrinkage during firing, the height of the convex shape is lowered by the amount of the dent. Thus, the convex shape is prevented from coming into contact with the circuit forming region 17 of the IC chip 1. Therefore, according to the present embodiment, the reliability of the crystal oscillator can be further improved.

  In the configuration described above, among the circuit terminals 11 arranged in two rows on the upper surface of the second layer 2a2, the circuit terminal 11 at the end of the arrangement is used as a circuit terminal corresponding to the oscillation output terminal. A conductive path is extended from the terminal 11 to the nearest corner of the second layer 2a2. As a result, most of the conductive path through which the oscillation output passes passes over the intermediate layer 14, and the influence of external noise on the oscillation output can be prevented.

  FIG. 4 is a diagram for explaining the effect of the electromagnetic shield in the crystal oscillator of this embodiment. 4 corresponds to a cross-sectional view of the long side of the crystal piece 8 as viewed from the side. Since the electronic circuit in the IC chip can be made less susceptible to external electromagnetic noise by devising the circuit configuration or the like, when providing an electromagnetic shield against external noise in the crystal oscillator, The electromagnetic shield for the crystal piece to be constructed should be considered first. In the crystal oscillator according to the present embodiment, an opening is formed in the intermediate layer 14 corresponding to the circuit formation region 17 of the IC chip 1, and an electromagnetic shield by the intermediate layer 14 is not provided at the position of the opening. However, since the IC chip 1 itself made of a semiconductor substrate can function as an electromagnetic shield for the crystal piece 8, as shown in FIG. 4, the crystal piece 8 is shielded by a metal cover 9 from above in the drawing. From the downward direction in the figure, the intermediate layer 14 and the IC chip 1 are shielded. In FIG. 4, thick arrows indicate external noise. In the end, the crystal oscillator according to the present embodiment has the same electromagnetic shielding characteristics as the conventional one shown in FIG. 6 in terms of the crystal piece 8, and is hardly affected by external noise.

  Next, a surface-mount crystal oscillator according to a second embodiment of the present invention will be described.

  As the surface-mount crystal oscillator, in addition to the junction type shown in the first embodiment, a container body or a mounting substrate in which concave portions are formed on both main surfaces is used, and a concave portion on one main surface is used. There is a so-called two-chamber type in which a quartz crystal is configured by sealing and sealing a quartz piece and an IC chip is stored in a recess on the other main surface. The present invention can also be applied to a two-chamber crystal oscillator. FIG. 5 shows a surface-mount crystal oscillator according to a second embodiment of the present invention configured as a two-chamber type. In FIG. 5, the same components as those in the first embodiment described above are given the same reference numerals, and descriptions thereof will be omitted or simplified. In FIG. 5, for the sake of explanation, it is assumed that the IC chip is fixed to the lower surface of the mounting substrate, contrary to that shown in FIG.

  The crystal oscillator shown in FIG. 5 has a mounting substrate 2 made of a laminated ceramic of the crystal oscillator shown in FIG. 1 and has a surface on the side of the two surfaces of the bottom wall layer 2a that is not provided with the frame wall layer 2b. The frame wall layer 2c is provided, and the IC chip 1 is fixed to the bottom surface of the frame wall layer 2b in the same manner as described above, and the crystal 20 is formed in the recess 20b formed by the bottom wall layer 2a and the second frame wall layer 2c. The piece 8 is accommodated. The crystal piece 8 is the same as described above, and a pair of crystal holding terminals 12 for holding the crystal piece 8 are formed on the second frame wall layer 2c on the inner bottom surface of the recess 20b. By joining the metal cover 9 to the opening end face surrounding the recess 20b, the crystal piece 8 is hermetically sealed in the recess 20b. Similar to the above, the metal cover 9 is joined to the metal thick film or the metal ring 15 provided on the opening end face of the recess 20b by seam welding or beam welding.

  The mounting terminals 4 used when the crystal oscillator is surface-mounted on the set substrate are formed on the upper surface of the frame wall layer 2 b, that is, the four corners of the opening end surface of the recess 20 a surrounding the IC chip 1. A circuit terminal 11 is provided on the inner bottom surface of the recess 20a in the same manner as described above, and the circuit terminal 11 corresponding to the crystal connection terminal is held by a crystal via a conductive path (not shown) formed in the bottom wall layer 2a. The terminal 12 is electrically connected. The IC chip 1 is the same as that used in the first embodiment, and is accommodated in the recess 20a by bonding to the circuit terminal 11 by ultrasonic thermocompression using the bump 6. Yes.

  Also in this configuration, the bottom wall layer 2a is composed of the first layer 2a1 and the second layer 2a2, and the laminated surface of the first layer 2a1 and the second layer 2a2 is made of a metal film and is attached to the mounting terminal 4. An intermediate layer 14 electrically connected to the ground terminal is formed. The intermediate layer 14 is provided with an opening corresponding to the circuit formation region 17 of the IC chip 1. Even in this crystal oscillator, since the intermediate layer 14 is not formed at a position facing the circuit formation region 17 of the IC chip 1, the distance between the circuit function surface of the IC chip 1 and the inner bottom surface of the recess 20 a of the mounting substrate 2. However, a large stray capacitance is not generated between the intermediate layer 14 in the circuit in the circuit formation region 17 and the electronic circuit such as the oscillation circuit can be reliably operated. Further, the mechanical strength of the mounting container 2 can be improved while maintaining the effect of the electromagnetic shield on the crystal piece 8 as compared with the case where no opening is provided in the intermediate layer 14. Since the surface of the second layer 2a is slightly depressed at the position of the opening of the intermediate layer 14, that is, at the position of the circuit formation region 17 of the IC chip 1, a convex shape is formed by uneven shrinkage when forming the container body by baking. Even in such a case, this convex shape can be prevented from coming into contact with the circuit forming region 17 of the IC chip.

  As described above, the surface mount crystal oscillator according to the present invention has been described by taking as an example the case of the temperature compensated crystal oscillator in which the temperature compensation mechanism is built in the IC chip. However, the surface using the IC chip without the temperature compensation mechanism is described. Of course, the present invention can also be applied to a mounting crystal oscillator.

1 is a side sectional view showing a surface-mount crystal oscillator according to a first embodiment of the present invention. It is a top view which shows the circuit function surface of an IC chip. (A) is a top view of the mounting substrate, (b) is a plan view of the bottom wall layer, and (c) is an intermediate layer formed between the first layer and the second layer in the bottom wall layer. (D) is a bottom view of the mounting substrate. It is a figure explaining the effect of the electromagnetic shielding in the surface mount crystal oscillator shown in FIG. It is a sectional side view which shows the crystal oscillator for surface mounting of the 2nd Embodiment of this invention. (A), (b), (c) is a sectional view, an assembled sectional view, and a side sectional view, respectively, of a conventional junction type surface mount crystal oscillator.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... IC chip, 2 ... Mounting substrate, 2a ... Bottom wall layer, 2a1 ... 1st layer, 2a2 ... 2nd layer, 2b, 2c ... Frame wall layer, 3 ... Quartz crystal oscillator, 4 ... Mounting terminal, 5 DESCRIPTION OF SYMBOLS Joint terminal, 6 ... Bump, 7 ... Container body, 8 ... Crystal piece, 9 ... Metal cover, 10 ... External terminal, 11 ... Circuit terminal, 12 ... Crystal holding terminal, 13 ... Conductive adhesive, 14 ... Intermediate layer 15 ... Metal ring, 16 ... IC terminal, 17 ... Circuit forming region, 18 ... Data write terminal, 20a, 20b ... Recess, 21 ... Container body.

Claims (3)

A crystal unit including a container that hermetically encloses the crystal piece by a metal cover provided on the upper surface, and an external terminal that is electrically connected to the crystal piece on an outer bottom surface of the container; and
A mounting board including a plurality of mounting terminals including a junction terminal corresponding to the external terminal on one main surface and at least a ground terminal on the other main surface;
An IC chip in which an oscillation circuit using the crystal piece is integrated, housed in a recess formed in the one main surface of the mounting substrate;
Have
The mounting substrate is made of a multilayer ceramic, and includes a bottom wall layer and a frame wall layer having an opening and formed on the bottom wall layer, and the recess includes the opening, and the recess The IC chip is fixed to the bottom surface of the substrate by flip chip bonding, and the IC chip is electrically connected to the plurality of mounting terminals and the joining terminals,
The bottom wall layer is formed by laminating a first layer and a second layer, and an intermediate layer made of a metal film is provided on a laminated surface of the first layer and the second layer. The intermediate layer is not provided in a region corresponding to a circuit formation region in the IC chip having an opening,
The surface-mount crystal oscillator in which the metal cover and the intermediate layer are electrically connected to the ground terminal. A piece of crystal,
An IC chip in which an oscillation circuit using the crystal piece is integrated;
A mounting substrate having a first recess for accommodating the IC chip on one main surface and a second recess for accommodating the crystal piece on the other main surface;
The mounting substrate is made of a multilayer ceramic, and includes a bottom wall layer, a first frame wall layer having an opening and formed on one main surface of the bottom wall layer to form the first recess. A second frame wall layer having an opening and formed on the other main surface of the bottom wall layer to form the second recess,
A pair of crystal holding terminals are provided on the bottom surface of the second recess, and the crystal piece is bonded to the crystal holding terminals,
A metal cover is joined to the opening end surface of the second recess, and the crystal piece is hermetically sealed in the second recess by the metal cover,
A plurality of mounting terminals including at least a ground terminal are formed on the opening end face of the first recess,
The IC chip is fixed to the bottom surface of the first recess by flip chip bonding, and the IC chip is electrically connected to the plurality of mounting terminals and the crystal holding terminals,
The bottom wall layer is formed by laminating a first layer and a second layer, and an intermediate layer made of a metal film is provided on a laminated surface of the first layer and the second layer. The intermediate layer is not provided in a region corresponding to a circuit formation region in the IC chip having an opening,
The surface-mount crystal oscillator in which the metal cover and the intermediate layer are electrically connected to the ground terminal.   The crystal oscillator for surface mounting according to claim 1 or 2, wherein the flip chip bonding is ultrasonic thermocompression bonding using bumps.

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