JP4071889B2 - Crystal oscillator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a crystal oscillator that supplies a basic clock signal of an IC element frequently used in electronic equipment, communication equipment, and the like.
[0002]
[Prior art]
The crystal oscillator is a very important component that generates a reference frequency (reference clock signal) for controlling transmission and reception in a mobile communication device or the like. Crystal oscillators used in such mobile communication devices and the like must have a very small volume as the mobile communication devices become smaller.
[0003]
The crystal oscillation circuit is a Colpitts oscillation circuit consisting of a crystal resonator, inverter, feedback resistor, and input / output capacitor, and the inverter, feedback resistor, and input / output capacitor are integrated into a single chip using an IC-IC technology (IC chip). The crystal oscillator is configured such that a rectangular crystal resonator and an IC chip are accommodated in a container such as ceramic.
[0004]
For example, FIG. 7 is a cross-sectional view of a conventional crystal oscillator. Specifically, the rectangular crystal resonator element 62 and the IC chip 63 are accommodated in the cavity portion 64 of the ceramic container 61 formed by laminating ceramic insulating layers having a predetermined shape, and the cavity portion 64 is placed on the metal lid 65. Was hermetically sealed by seam welding or the like.
[0005]
The ceramic container 61 is configured, for example, by laminating four insulating layers, and the second and third insulating layers 61b and 61c from the bottom side are formed on a pair of opposing side surfaces inside the cavity portion 64 on a pair of side surfaces. Element mounting step portions (simply step portions) 66a and 66b and IC connection step portions 67a and 67b are formed. The IC chip 63 is attached to the bottom surface of the cavity portion 64, and the IC chip die attach conductor film 68a is formed on the upper surface of the end portion of the two insulating layers 61b from the bottom surface side. The electrode pad for connection 68b is electrically connected to the crystal resonator 62 on the upper surface of one end of the three insulating layers 61c from the bottom surface side (one element mounting step part 66a serving as the element mounting step part 66a, 66b). The connection electrode pads 68c are electrically formed, and the conductor film 68d for joining the seam ring 69 for sealing the metal lid is formed on the uppermost insulating phase layer.
[0006]
Further, terminal electrodes (not shown) such as a Vcc terminal, a GND terminal, and an output terminal are formed on the exterior surface of the container 61. In addition, an internal wiring 68e for connecting each terminal electrode and each connection pad or the like is formed between the insulating layers 61a to 61d.
[0007]
The IC chip 63 accommodated in the container 61 is bonded to the die attach conductive film 68a and connected to the connection electrode pad 68b by wire bonding W.
[0008]
The strip-shaped crystal resonator 62 is held by a pair of element mounting portions 66a and 66b, and is connected to a connection electrode pad 68c formed on one of the element mounting portions 66a by curing of a conductive paste. .
[0009]
The crystal oscillator having the above-described structure is a very small crystal oscillator in which the crystal resonator 62 and the IC chip 63 are accommodated in the ceramic container 61.
[0010]
When such a crystal oscillator is mounted on a printed circuit board such as an electronic device or a communication device, the crystal oscillator does not operate stably due to electromagnetic noise generated inside the electronic device or communication device or external electromagnetic noise. Sometimes. The influence of the electromagnetic wave noise on the crystal oscillator tends to affect the power supply line supplied to the crystal oscillator from the power supply circuit on the printed wiring board.
[0011]
This crystal oscillator accommodates each element within the dotted line Y in the equivalent circuit diagram shown in FIG. The electromagnetic wave noise that tends to affect the above-described power supply line is to be eliminated by the bypass capacitor C ₀ disposed between the Vcc line and the Vcc terminal of the crystal oscillator.
[0012]
[Problems to be solved by the invention]
However, even if a bypass capacitor is arranged between the power supply line of the power supply circuit and the crystal oscillator, the Vcc (power supply line potential) supplied to the Vcc electrode of the IC chip 63 is a DC power supply as shown in FIG. May change with an amplitude of 29 mV. In the measurement, a crystal oscillator having a Vcc of 3.3 V, a temperature of 25 ° C., and an oscillation frequency of 14.31818 MHz is used.
[0013]
This is considered to be caused by the fact that the high frequency noise affects between the bypass capacitor C ₀ and the Vcc electrode of the IC chip 63 of the crystal oscillator, and the impedance varies due to the variation of the inductance component.
[0014]
If the power supply voltage (Vcc) of the IC chip 63 fluctuates in this way, as a result, a stable IC amplification operation cannot be performed, and stable oscillation cannot be performed.
[0015]
The present invention has been devised in view of the above-mentioned problems, and the object thereof is not to increase the size of the oscillator and to effectively suppress fluctuations in the power supply potential supplied to the Vcc electrode of the IC chip. The present invention provides a crystal oscillator that can be used.
[0016]
[Means for Solving the Problems]
According to the present invention, a rectangular crystal resonator that constitutes an oscillation circuit, an IC chip, and a chip capacitor connected to a power line of the IC chip are accommodated in a container body having a cavity portion having a step portion on the upper surface. The strip-shaped crystal resonator has one end bonded to the stepped portion and the other end positioned on the chip capacitor, and the IC chip is located on the bottom surface of the cavity portion. A crystal oscillator characterized by being arranged at a position overlapping with a child .
[0017]
[Action]
In the present invention, a chip capacitor that operates as a bypass capacitor that removes electromagnetic wave noise from a power supply line is housed in a container having a cavity portion together with a crystal resonator and an IC chip. That is, the bypass capacitor can be arranged as close as possible to the Vcc electrode of the IC chip. For this reason, the influence of the electromagnetic wave noise affecting between the Vcc electrode of the IC chip and the bypass capacitor can be extremely reduced, and a stable power supply potential can be supplied to the IC chip.
[0018]
Moreover, the chip capacitor serving as the bypass capacitor is an alternative to the element mounting portion at the other end of the strip-shaped crystal resonator in the container. Thereby, when one end part of a crystal oscillator is joined to a level difference part, joining becomes possible stably. Even if the chip capacitor that substantially supports the other end of the crystal resonator is accommodated in the container, the crystal oscillator is not increased in size as a whole, and the crystal oscillator can be kept downsized.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The crystal oscillator of the present invention will be described in detail below with reference to the drawings.
[0020]
FIG. 1 is an external perspective view of a crystal oscillator according to the present invention, FIG. 2 is a cross-sectional view, and FIG. 3 is a plan view in a state where a metal lid is omitted.
[0021]
The crystal oscillator includes an approximately rectangular parallelepiped ceramic package (hereinafter referred to as a container body) 1 having a concave cavity portion 11 formed on the upper surface, a strip-shaped crystal resonator 2, an IC chip 3, a chip capacitor 4, and a metal lid. 5 is mainly composed.
[0022]
The container body 1 is configured by sequentially laminating, for example, a substantially rectangular ceramic insulating layer 1a and substantially frame-shaped ceramic insulating layers 1b, 1c, and 1d having an opening at the center, whereby a cavity portion of the container body 1 is formed. 11 is configured. And the electrode pad 40 which joins the die attach conductor film 30 of the IC chip 3 and the capacitor | condenser 4 is formed in the bottom face of the ceramic insulating layer 1a. An IC connection step 12 is formed on a part of the ceramic insulating layer 1b, and an IC connection electrode 31 is formed on the upper surface thereof. Further, an element mounting step portion (simply referred to as a step portion) 13 is formed in a part of the ceramic insulating layer 1c, and an element connection electrode 20 is formed on the upper surface thereof. In addition, a sealing conductor film 50 for connection to the metal lid 5 is formed on the upper surface of the ceramic insulating layer 1d.
[0023]
Further, Vcc, GND, output and oscillation control terminal electrodes 14 to 16 (only two terminal electrodes 14 and 16 appear in FIG. 1) are formed on the outer surface and bottom surface of the container body 1. ing. Between the ceramic insulating layers 1a to 1d, there is formed an internal wiring conductor 17 that connects the electrodes 20, 30, 31, 40 and the terminal electrodes 14 to 16 to form the wiring of the oscillation circuit. .
[0024]
The IC chip 3 is bonded to the die attach conductor film 30 in the cavity portion 11, and each electrode of the IC chip 3 and each electrode 31 of the connection step portion 12 are connected by a bonding wire W.
[0025]
The chip capacitor 4 is connected / disposed to the electrode pad 40 via a conductive paste (cured and conductive adhesive member 41).
[0026]
As shown in FIG. 3, the strip-shaped crystal resonator 2 includes vibration electrodes 22 and 23 formed on both main surfaces of a quartz plate 21 that has been cut by AT, for example, and one end portion of the crystal plate 21 from each of the vibration electrodes 22 and 23. Extraction electrode portions 22a and 23a are formed to extend to the surface. Such a crystal resonator 2 is disposed so as to be laid between the step portion 13 in the cavity portion 11 and the capacitor 4, and the connection electrode 20 of the step portion 13 and the extraction electrode 22 a of the crystal resonator 2 are arranged. The conductive paste (cured and conductive adhesive member 24) is bonded by curing so as to be electrically connected to each other. That is, one end portion side of the strip-shaped crystal resonator 2 is placed on the step portion 13, and the other end portion side is disposed on the chip capacitor 4. The crystal unit 2 joined by a conductive adhesive member that is finally cured of a conductive paste is fixed at one end by a conductive adhesive member and the other end is a free end. . The free end, which is the other end of the crystal resonator 2, is slightly lifted from the upper surface of the chip capacitor 4 due to the shrinkage stress when the conductive paste 24 is cured.
[0027]
In such a container body 1, a crystal resonator 2, an IC chip 3, and a chip capacitor 4 are accommodated, and an opening on the upper surface thereof is covered with a metal lid 5.
[0028]
Specifically, a metal lid 5 such as 42 alloy or kovar with a silver brazing layer deposited on the sealing surface may be placed on the sealing conductor film 50 and subjected to a welding process. Further, a seam ring may be interposed. In FIG. 2, the seam ring is omitted.
[0029]
In the crystal oscillator having such a configuration, the number of accommodating elements is increased by the amount of the chip capacitor 4 as compared with the conventional crystal oscillator. However, actually, since the element placement step portion 66b on which the other end portion of the crystal resonator 2 is placed is substituted, the container body 1 is not substantially enlarged.
[0030]
In the crystal oscillator having the above-described structure, the chip capacitor 4 is bonded to the electrode pad 40 connected to the power supply voltage (Vcc) electrode of the IC chip 2 through the bonding wire W and the connection electrode pad 31. That is, the chip capacitor 4 is provided close to the Vcc electrode of the IC chip 3 and is disposed between the Vcc terminal electrode of the crystal oscillator and the Vcc electrode of the IC chip 3.
[0031]
Such a structure is shown by an equivalent circuit as shown in FIG. In the figure, the elements within the dotted line Z are the accommodating elements of the crystal oscillator.
[0032]
As shown in the above equivalent circuit diagram, the chip capacitor 4 acts as a bypass capacitor C ₀ for an IC, particularly an inverter, and causes electromagnetic wave noise existing on the power supply line to be applied to the Vcc terminal electrode of the IC chip 3. Removed in the vicinity.
[0033]
When the power supply voltage supplied to the Vcc electrode of the IC chip 3 is measured, the change in the power supply voltage has an amplitude of a maximum of 13 mV in the DC potential as shown in FIG. 5, for example. In comparison with the case, the fluctuation can be reduced to 1/3. In the measurement, a crystal oscillator having a Vcc of 3.3 V, a temperature of 25 ° C., and an oscillation frequency of 14.31818 MHz was used.
[0034]
The inventor measured the maximum fluctuation of the power supply voltage supplied to the Vcc electrode of the IC chip 3 by variously changing the capacitance of the chip capacitor 4 under the above-described conditions.
[0035]
As a result, although the maximum fluctuation of the power supply voltage can be reduced by increasing the capacity of the bypass capacitor as shown in FIG. 6, the fluctuation amount of the power supply voltage is minimized at about 1000 pF, and fluctuates as the capacity is further increased. It has been found that increases.
[0036]
That is, in order to effectively suppress the fluctuation of the power supply voltage, the arrangement position and the capacity of the chip capacitor 4 are important. It is important to place the chip capacitor 4 as close as possible to the Vcc electrode of the IC chip, and the capacitance is good in the range of 650 pF to 10,000 pF. That is, in this range, the maximum fluctuation of the power supply voltage can be made smaller than the conventional 29 mV, for example, 25 mV or less. When this range is exceeded, the advantage and the conventional amplitude fluctuation amount (about 29 mV) are exceeded as compared with the conventional case. Also, the bypass capacitor C ₀ is supported at the other end of the crystal unit 2. Since it is used as a mounting member, especially when the crystal resonator 2 is temporarily mounted, the alignment is very stable when the crystal resonator 2 is joined. In particular, the lead electrode 23a of the crystal resonator 2 Stable connection positioning between the connection electrode pads 20 and 20 of the step portions 13 and 13 can be achieved.
[0037]
Further, the conductive paste 24 is bonded to the lead electrodes 23a and 23b of the crystal resonator 2 and the connection electrode pads 20 and 20 of the step portions 13 and 13 by a conductive paste (a mixture of silver and an epoxy resin or a polyimide resin). 24, the shrinkage stress due to curing acts, and the other end of the crystal unit 2 is slightly lifted. The weight is controlled so that the gap between the lower surface of the crystal resonator 2 and the upper surface of the chip capacitor 4 generated as a result of the lifting is set to 20 to 100 μm.
[0038]
This control can be controlled by the thickness of the chip capacitor 4 or by forming a stepped portion having a predetermined thickness and a recessed portion having a predetermined depth on the surface on which the chip capacitor 4 is placed. For example, in order not to generate a gap, when the other end portion of the crystal resonator 2 is temporarily placed on the chip capacitor 4, the inclination decreases from the other end portion of the crystal resonator 2 toward the one end portion. In addition, the height of the chip capacitor 4 may be controlled.
[0039]
Also, when trying to increase the gap at the other end of the crystal unit 2, the height of the chip capacitor 4 is controlled to move from one end of the temporarily held crystal unit 2 to the other end. Try to lower the slope. In this way, when the other end of the crystal unit 2 is lifted by the contraction stress of the conductive paste 23, a large interval can be obtained.
[0040]
Therefore, it is important that this interval is 20 to 100 μm as described above. If it is less than 20 μm, the other end portion of the crystal resonator 2 and the chip capacitor 4 are likely to come into contact with each other due to the thickness of the terminal electrode of the chip capacitor 4 and the stable vibration of the crystal resonator 2 is inhibited. .
[0041]
Further, when an external impact is applied to the container body 1 exceeding 100 μm, the allowable amplitude interval at the other end of the crystal resonator 2 is increased, and the crystal resonator 2 is easily damaged by the collision with the chip capacitor 4. .
[0042]
From the above, it is important to set the distance between the other end of the crystal unit 2 and the chip capacitor 4 in the above-described range.
[0043]
In the above-described embodiment, the IC chip 3 is an IC chip that is bonded by wire bonding, but may be an IC such as a face bonding, for example.
[0044]
【The invention's effect】
According to the present invention, although the crystal resonator, the IC chip, and the chip capacitor connected to the Vcc electrode of the IC chip are accommodated in the container, the IC chip is disposed below the crystal resonator, and the chip capacitor Is positioned to hold the other end of the crystal unit. Accordingly, since the chip capacitor replaces a part of the stepped portion on which the crystal resonator is placed, it can be maintained without changing the external shape of the container.
[0045]
In addition, since the chip capacitor operates as a bypass capacitor connected in close proximity to the Vcc electrode of the IC chip, the influence of high frequency noise on the power supply line can be extremely effectively suppressed, and fluctuations in the DC power supply can be suppressed. The operation of the IC chip is stabilized, and the oscillation operation is thereby stabilized.
[Brief description of the drawings]
FIG. 1 is an external perspective view of a crystal oscillator according to the present invention.
FIG. 2 is a cross-sectional view of a crystal oscillator.
FIG. 3 is a top view of the crystal oscillator in a state where a lid is omitted.
FIG. 4 is an equivalent circuit diagram of a crystal oscillator.
FIG. 5 is a characteristic diagram showing fluctuations in power supply voltage according to the present invention.
FIG. 6 is a characteristic diagram showing fluctuation of the capacity-power supply voltage of the present invention.
FIG. 7 is a cross-sectional view of a conventional crystal oscillator.
FIG. 8 is an equivalent circuit diagram of a conventional crystal oscillator.
FIG. 9 is a characteristic diagram showing fluctuation of a conventional power supply voltage.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Container 2 ... Crystal oscillator 3 ... IC chip 4 ... Chip capacitor 5 ... Metal lid

Claims (1)

A rectangular crystal resonator, an IC chip, and a chip capacitor connected to a power line of the IC chip are accommodated in a container body having a cavity portion having a step portion on the upper surface, and the strip is formed. A position where one end portion of the crystal unit is bonded onto the stepped portion, the other end portion is positioned on the chip capacitor, and the IC chip overlaps the strip-shaped crystal unit on the bottom surface of the cavity Crystal oscillator characterized by being arranged in .

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