JPS628585Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mounting structure for a surface acoustic wave device mounted on a conductive base.

Conventionally, a surface acoustic wave device is mounted on a conductive base by fixing a surface wave substrate 1 to a conductive base 2 with a conductive vent 3 in order to provide a shielding effect as well, as shown in FIG. ing.
The surface wave board 1 has input and output interdigital transducers (hereinafter referred to as
A ground electrode 6 is provided between both IDTs 4 and 5 for the purpose of preventing static electricity between input and output.
is installed. Each IDT 4, 5 consists of a pair of comb-tooth electrodes inserted into each other, one comb-tooth electrode for each IDT is connected to hot terminals 7, 9, and the other comb-tooth electrode is connected to ground terminals 8, 10. The ground electrode 6 is also connected to a ground terminal 11 electrically connected to the base 2 .
Then, between terminals 7 and 8 of each IDT and between terminals 9 and 1
Between 0 and 0, there appears a capacitance formed between a pair of comb-shaped electrodes facing each other with a minute interval, and this capacitance is relatively large, and is even larger when the surface wave substrate is made of a high dielectric constant piezoelectric material such as ceramic. As a result, the impedance between the terminals becomes small, and it may become difficult to achieve impedance matching with the circuits in the preceding and succeeding stages. Moreover, in the actual circuit, the body grounded terminal 11 and the input/output ground terminals 8 and 10 are connected externally, so the terminals 7 and 8 are connected externally.
In addition to the above capacitance, another capacitance is added in parallel between the terminals 9 and 10. The other capacitance is formed between the hot-side comb-shaped electrode connected to the hot terminals 7 and 9 and the conductive vein 3. Therefore, the capacitance between terminals 7 and 8 and between terminals 9 and 10 becomes even larger. Incidentally, its capacity is
It will be about 1.2 to 1.5 times the capacity of IDT itself.

The present invention improves the above-mentioned conventional drawbacks, and provides a mounting structure for a surface acoustic wave device that allows the surface acoustic wave device to be mounted on a conductive base such as a hermetic case without reducing input/output impedance. The purpose is to provide.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In FIG. 2, 20 is a conductive base that forms a part of the hermetic case, and five terminals 21, 22, 23, 24, and 25 are fixed through the base 20, of which terminal 25 is fixed. The remaining terminals 21, 22, 23,
24 is electrically insulated from the base 20. 2
Reference numeral 6 denotes a surface wave device, which includes a surface wave substrate 27 made of a piezoelectric material with a relatively high dielectric constant, such as ceramic.
, input and output IDTs 28 and 29 formed on the surface side of this substrate 27, and a ground electrode 30 disposed between both IDTs 28 and 29. IDTs 28 and 29 are installed on the back side of the surface wave board 27.
Non-conductive films 31 and 32, each made of an epoxy resin adhesive or the like and having a lower dielectric constant than the surface wave substrate 27, are applied at positions facing the surface wave substrate 27 by means of printing or the like. Then, on the back surface of the substrate 27, a non-conductive film 31,
A conductive paint 33 is applied over the conductive paint 32 or the conductive paint 33 is applied on the base 20 in advance, and the surface acoustic wave device 26 is fixed to the conductive base 20 by the conductive paint 33. According to this embodiment, the low dielectric constant non-conductive films 31 and 32 are interposed between each IDT 28 and 29 and the base 20, and the distance between each IDT 28 and 29 and the conductive paint 33 is long, so each IDT 28 , 29 hot side comb tooth electrode and base 20 or conductive paint 33
The capacitance generated between the terminals 21 and 22 and the terminals 23 and 24 when incorporated into an actual circuit becomes significantly higher than in the conventional example.

FIG. 3 shows another embodiment, in which the same parts as in the above embodiment are denoted by the same reference numerals and the explanation thereof will be omitted. In this embodiment, non-conductive adhesives 40 and 41 are applied to the back surface of the surface wave substrate 27 and the parts facing each IDT 28 and 29, and the parts facing between both IDTs 28 and 29, that is, both adhesives 40 , 41 is coated with conductive paint 42, and these adhesives and paints 40, 41, 42 also fix the surface acoustic wave device 26 to the base 20. These adhesives and paints40,41,
42 may be applied on the base 20 side.

In each of the above embodiments, a part of the hermetic case is used as the base, but it may also be a printed circuit board or the like. Further, the ground terminals 22 and 24 may be grounded to the body in advance within the device.

As explained above, the present invention provides a conductive surface wave device by interposing a low dielectric constant non-conductive film at a position facing the transducer on the surface of the surface wave substrate where the transducer is not provided. Since the surface acoustic wave device is attached to the magnetic base, the capacitance appearing between the input and output terminals is reduced, and the input/output impedance of the surface acoustic wave device can be increased.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a conventional mounting structure for a surface wave device, FIGS. 2a and 2b are a plan view and a sectional view taken along line B-B, respectively, showing a mounting structure for a surface wave device based on the present invention, and FIG. FIG. 3 is a sectional view showing another embodiment. 20... Conductive base, 26... Surface wave device,
27...Surface wave board, 28, 29...IDT, 3
1, 32, 40, 41... Non-conductive film.

Claims (1)

[Scope of utility model registration request] In the mounting structure of a surface acoustic wave device that is attached to a conductive base, a non-conductive film with a low dielectric constant is interposed at a position facing the transducer on the surface of the surface wave board where the transducer is not provided to conduct electricity. A mounting structure for a surface acoustic wave device, characterized in that it is mounted on a flexible base.