JP2008294583A - Crystal oscillator for surface mounting - Google Patents

Abstract

A surface-mount oscillator that facilitates frequency adjustment after sealing a metal cover.
A surface-mount crystal oscillator in which an IC chip 2 and a crystal piece 3 forming an oscillation closed loop are accommodated in a concave container body 1 made of a plurality of ceramic layers, and connected in parallel in the oscillation closed loop. Forming a plurality of pairs of first and second electrodes forming a plurality of capacitances, and extending and exposing a wiring path connected to the first electrode to an outer surface of the container body 1; And the capacitance value of the parallel connection is varied to adjust the oscillation frequency.
[Selection] Figure 1

Description

  The present invention relates to a surface mount crystal oscillator (hereinafter referred to as a surface mount oscillator), and more particularly to a capacitor for adjusting an oscillation frequency.

(Background of the Invention)
Since the surface-mounted oscillator is small and light, for example, it is incorporated in a portable electronic device typified by a cellular phone as a reference source for frequency and time. In recent years, the demand for frequency accuracy has become stricter. For example, a clock having a frequency accuracy of ± 30 ppm to ± 20 ppm is required.

(Example of conventional technology)
FIG. 5 is a diagram of a surface-mount oscillator for explaining a conventional example, in which FIG. 5 (a) is a sectional view and FIG. 5 (b) is an oscillation circuit diagram.

  The surface-mount oscillator includes an IC chip 2 and a crystal piece 3 in a container body 1 and a metal cover 4. The container body 1 has an inner wall step as a concave shape composed of a plurality of ceramic layers, for example, three layers. The container body 1 has a circuit terminal (not shown) on the inner bottom surface, a crystal holding terminal on the inner wall step portion, and an external terminal on the outer bottom surface.

  The circuit terminal consists of a pair of crystal terminals, a power supply, an output, a ground, and a standby terminal. The pair of crystal terminals are electrically connected to the crystal holding terminals, and the other circuit terminals are electrically connected to the corresponding external terminals through the laminated surface and the outer surface. These connections are made by wiring paths including through holes.

  The IC chip 2 integrates at least an oscillation circuit, and the IC terminal on the circuit function surface is fixed to the circuit terminal of the container body 1 by ultrasonic thermocompression bonding using bumps (flip chip bonding). The crystal piece 3 has excitation electrodes (not shown) on both main surfaces, and extends extraction electrodes on both sides of one end. Then, both sides of one end portion of the crystal piece 3 are fixed to the crystal holding terminals of the inner wall step portion by the conductive adhesive 5.

As the oscillation circuit, a resonance circuit is formed by the crystal resonator 3A (crystal piece 3) and the divided capacitors C1 and C2, and the resonance frequency by these is feedback-amplified by an oscillation amplifier 6 formed of, for example, a CMOS inverter. In this case, the oscillation frequency is determined by the resonance frequency of the crystal resonator 3A and the series-side equivalent capacitance (load capacitance) on the circuit side viewed from now. In the figure, symbol R is a feedback resistor, and numeral 7 is a buffer amplifier.
Japanese Patent No. 3479467

(Problems of conventional technology)
However, the surface mount oscillator having the above configuration satisfies the specification within the design range if the frequency deviation (room temperature 25 ° C.) is about 30 ppm, but if it is about 20 ppm, it becomes difficult to satisfy the specification. For this reason, it is necessary to provide a frequency adjusting capacitor after the metal cover 4 is sealed. However, in this case, since it is externally attached, it is not suitable for miniaturization. Moreover, although frequency adjustment by voltage control is also conceivable, there is a problem that the cost is increased for a clock.

(Object of invention)
It is an object of the present invention to provide a surface mount oscillator that facilitates frequency adjustment after sealing a metal cover.

  As described in the claims (Claim 1), the present invention is for surface mounting in which an IC chip that forms an oscillation closed loop and a crystal piece are accommodated in a concave container body made of a plurality of ceramic layers. In the crystal oscillator, a plurality of pairs of first electrodes and second electrodes forming a plurality of adjustment capacitors connected in parallel in the oscillation closed loop are formed, and a wiring path connected to the first electrode is connected to the container body. The configuration is such that the oscillation frequency is adjusted by changing the capacitance value of the adjustment capacitor that extends to the outer side surface and is exposed, cuts the wiring path, and is connected in parallel.

  With such a configuration, the capacitance value of the parallel capacitor can be varied by cutting the wiring path of the first electrode exposed on the outer surface after the metal cover is sealed. Therefore, an external capacitor or the like is not required, and the miniaturization is maintained and the cost is reduced.

(Embodiment section)
According to a second aspect of the present invention, in the first aspect, the first electrode and the second electrode are formed on both main surfaces of the ceramic layer. Thereby, a capacitor can be formed using the ceramic layer as a dielectric.

  In the third aspect of the present invention, in the first aspect, the first electrode and the second electrode are formed adjacent to the surface of the ceramic layer. Thereby, a line capacitance can be formed.

  In the fourth aspect of the invention, in the first aspect, the container main body has an inner wall stepped portion, the IC chip is fixed to the inner bottom surface of the container main body, and the extraction electrode of the crystal piece is extended to the inner wall stepped portion. The outer periphery is fixed. This clarifies the structure of a specific example of the surface mount oscillator.

  FIG. 1 is a diagram of a surface mount oscillator for explaining an embodiment of the present invention. FIG. 1 (a) is a perspective view excluding a metal cover, FIG. 1 (b) is a sectional view of the same part, and FIG. It is the same oscillation circuit diagram. In addition, the same number is attached | subjected to the same part as a prior art example, and the description is simplified or abbreviate | omitted.

  As described above, the surface-mount oscillator is formed by fixing the IC chip 2 to the inner bottom surface of the concave container body 1 made of a plurality of ceramic layers and fixing both ends of one end of the crystal piece 3 to the inner wall step. The container body 1 has a circuit terminal (not shown) to which the IC terminal of the IC chip 2 is fixed, an external terminal on the outer bottom surface, and a crystal holding terminal on the inner wall step. In the figure, reference numeral 8a denotes an excitation electrode, and 8b denotes an extraction electrode.

  Here, a plurality of adjustment capacitors (C1 to Cn) connected in parallel for frequency adjustment are provided between the crystal resonator 3A and the output terminal of the oscillation amplifier 6. The plurality of adjustment capacitors (C1 to Cn) are provided in a plurality of ceramic layers on the inner wall step portion on one end side where the crystal holding terminal of the container body 1 is formed. FIG. 2 is a partial view of one end side of the container body 1 at a portion indicated by a dotted frame in FIG. 1 (a).

  The container body 1 is composed of a ceramic layer having a four-layer structure, and is composed of a bottom wall layer 1a, a first intermediate layer 1b, a second intermediate frame layer 1c, and an upper wall layer 1d in order from the bottom. The bottom wall layer 1a has a flat plate shape, the first and second intermediate frame layers 1 (bc) have the same frame width, and the upper wall layer 1d forms a step portion having a smaller frame width. And the thickness of the 2nd intermediate | middle layer 1c is made thinner than the other layer 1 (abd).

  The pair of crystal holding terminals 9 is formed on the second intermediate frame layer 1c that becomes the step surface. Then, a wiring path extends from one crystal holding terminal 9, and a plurality of first electrodes 10a are provided in parallel on the laminated surface of the second intermediate layer 1c and the upper wall layer 1d. In addition, a plurality of second electrodes 10b facing the first electrode 10a are provided on the first intermediate layer 1b serving as a laminated surface with the second intermediate layer.

  The plurality of second electrodes 10b extend on the bottom wall 1a through the outer surface of the first intermediate layer 1b and are connected in common. Then, it is electrically connected to one crystal terminal of the IC terminals of the IC chip 2. The other crystal holding terminal is electrically connected to the other crystal terminal of the IC chip 2 through a wiring path.

  In such a case, each of the first electrodes 10a and the second electrodes 10b forms a plurality of adjustment capacitors (C1 to Cn) in which the ceramic of the second intermediate frame layer 1c is connected in parallel as a dielectric. The wiring path 10bx from the second electrode 10b is exposed on the outer surface of the container body 1. Therefore, the capacitance value can be adjusted from the larger value to the smaller value by cutting the wiring path 10bx from the second electrode 10b exposed on the outer surface with, for example, a laser.

  In other words, the oscillation frequency can be adjusted from the lower to the higher. Thus, the oscillation frequency can be adjusted after the IC chip 2 and the crystal piece 3 are accommodated in the container body 1 and covered with the metal cover 4. Therefore, even if the frequency deviation is about 20 ppm, it can be sufficiently handled. In this case, if the oscillation frequency is set to a low value in advance, it is possible to prevent the standard deviation on the high frequency side. As a result, an external capacitor is not required, and the miniaturization is maintained. And compared with the case by voltage control, it can be made cheap.

  When the wiring path 10bx from the second electrode 10b extending to the outer surface of the first intermediate layer 1b is cut, a capacitance is formed with the wiring path 10by of the bottom wall layer 1a using the first intermediate layer 1b as a dielectric. However, since the thickness of the first intermediate layer 1b is sufficiently large, this capacity can be ignored. If it cannot be ignored, for example, the line widths of these wiring paths 10bx and 10by may be narrowed.

(Other matters)
In the above embodiment, the wiring path of the second electrode 10b is exposed and cut on the outer surface of the container body 1, and the capacitance value is adjusted from the larger one to the smaller one. For example, as shown in FIG. Good. That is, the wiring path 10bx exposed on the outer surface of the second electrode 10b is divided in advance to be 10b (x1, x2). Then, for example, the capacitance value may be adjusted from a smaller value to a larger value by connecting with a solder or a conductive adhesive 5 (not shown).

  In this case, if both of the wiring paths 10b and 10b (x1, x2) as adjustment means by disconnection and connection are provided, the frequency adjustment can be selected from higher to lower and vice versa. The range of adjustment can be expanded to minimize deviations from the standard.

  The adjustment capacitor C (1 to n) is formed with the first electrode 10a and the second electrode 10b facing each other. For example, as shown in FIG. 4, from the crystal holding terminal 9 to the surface of the intermediate layer 1b ′ and The wiring paths 11 with narrowed lines are simply arranged in parallel on the outer side surface and the surface of the bottom wall layer 1a to form the adjustment capacity (C1 to Cn) by the line capacity. Then, the capacitance value of the adjustment capacitors (C1 to Cn) may be adjusted by cutting the wiring path 11x exposed on the outer surface of the intermediate layer 1b ′.

  Further, the frequency adjusting capacitor is provided between the crystal resonator 3A and the output side of the oscillation amplifier 6, but it may be connected in parallel to, for example, a split capacitor, and is basically applied within the oscillation closed loop. it can. Furthermore, although the container body 1 is a single room type having a concave shape, for example, an H type having concave portions on both main surfaces, or a bonded type in which a mounting substrate containing the IC chip 2 is bonded to the bottom surface of the crystal resonator 3A. Applicable.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure of the surface mount oscillator explaining one Embodiment of this invention, The figure (a) is a perspective view except a metal cover, The figure (b) is the same part sectional drawing, The figure (c) is the oscillation circuit diagram. It is. It is a fragmentary figure of the one end side of the container main body of the part shown with the dotted-line frame of Fig.1 (a). It is a perspective view except a metal cover explaining other examples of one embodiment of the present invention. It is a fragmentary figure of the one end side of the container main body explaining other embodiment of this invention. It is a figure of the surface mount oscillator explaining a prior art example, the figure (a) is a sectional view and the figure (b) is an oscillation circuit diagram.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Container body, 2 IC chip, 3 Crystal piece, 4 Metal cover, 5 Conductive adhesive, 6 Oscillator amplifier, 7 Buffer amplifier, 8a Excitation electrode, 8b Extraction electrode, 9 Crystal holding terminal, 10a 1st electrode, 10b Second electrode, 11 wiring path.

Claims (4)

  In a crystal oscillator for surface mounting that contains an IC chip and a crystal piece that form an oscillation closed loop in a concave container body made of a plurality of ceramic layers, a plurality of adjustment capacitors connected in parallel are formed in the oscillation closed loop. Forming a plurality of pairs of first and second electrodes, extending and exposing a wiring path connected to the first electrode to an outer surface of the container body, cutting the wiring path and connecting in parallel A crystal oscillator for surface mounting, wherein the oscillation frequency is adjusted by changing the capacitance value of the adjustment capacitor.   2. The surface-mount crystal oscillator according to claim 1, wherein the first electrode and the second electrode are formed on both main surfaces of the ceramic layer.   2. The surface-mount crystal oscillator according to claim 1, wherein the first electrode and the second electrode are formed adjacent to a surface of the ceramic layer.   2. The container body according to claim 1, wherein the container body has an inner wall step portion, the IC chip is fixed to the inner bottom surface of the container body, and the outer peripheral portion where the extraction electrode of the crystal piece extends is fixed to the inner wall step portion. Crystal oscillator for surface mounting.