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Claims  |
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We claim:
1. A method of manufacturing an acoustic surface wave device, in which
acoustic surface waves launched by an input transducer into a
piezoelectric material are transmitted to an output transducer through a
multistrip coupler, comprising the steps of:
forming on said piezoelectric material first and second input transducers,
first and second output transducers diagonally with respect to said first
and second input transducers, respectively, said multistrip coupler
between said input transducers and said output transducers, and lead
patterns between electrodes of each of said second input and second output
transducers;
mounting said piezoelectric material on a package base which has first and
second pairs of pins therethrough;
bonding the electrodes of said first input and first output transducers to
said first and second pairs of pins, respectively, by wires;
testing said device by supplying test signals to said first input
transducer and obtaining output signals from said first output transducer
through said first and second pairs of pins, respectively; and,
when said testing step indicates said device is usable, fixing a cover to
said package base.
2. A method as set forth in claim 1, wherein said forming step further
includes forming lead patterns between the electrodes of each of said
first input and first output transducers and wherein said bonding step
further includes the step of cutting the lead patterns of said first input
and first output transducers.
3. A method as set forth in claim 1 or 2, comprising after the testing step
the further steps of:
cutting the lead patterns between the electrodes of said second input and
second output transducers, removing the wires connecting the electrodes of
said first input and first output transducers to said first and second
pairs of pins, respectively, and bonding the electrodes of said second
input and second output transducers of said first and second pairs of
pins, respectively, by wires;
testing said device by supplying said test signals to said second input
transducer and obtaining said output signals from said second output
transducer through said first and second pairs of pins, respectively; and,
when said testing step indicates said device is usable, fixing said cover
to said package base.
4. The method of claim 3, wherein the electrodes of each of said
transducers are formed with a connecting pad for bonding with said wires.
5. A method of manufacturing an acoustic surface wave device, in which
acoustic surface waves launched by an input transducer into a
piezoelectric material are transmitted to an output transducer through a
multistrip coupler, comprising the steps of:
forming on said piezoelectric material first and second input transducers,
first and second output transducers diagonally with respect to said first
and second input transducers, respectively, said multistrip coupler
between said input transducers and said output transducers, lead patterns
between electrodes of each of said second input and second output
transducers, and external connecting pads connected to electrodes of said
first input and first output transducers;
mounting said piezoelectric material on a package base which has first and
second pairs of pins therethrough;
bonding said external connecting pads to said first and second pairs of
pins, respectively, by wires;
testing said device by supplying test signals to said first input
transducer and obtaining output signals from said first output transducer
through said first and second pairs of pins, respectively; and,
when said testing step indicates said device is usable, fixing a cover to
said package base.
6. A method as set forth in claim 5, comprising after the testing step the
further steps of:
cutting said lead patterns between the electrodes of said second input and
second output transducers and bonding the electrodes of each of said first
input and first output transducers by wires, and connecting said external
connecting pads to electrodes of said second input and second output
transducers, respectively, by wires;
testing said device by supplying said test signals to said second input
transducer and obtaining said output signals from said second output
transducer through said first and second pairs of pins, respectively; and,
when said testing step indicates said device is usable, fixing said cover
to said package base.
7. A method as set forth in claim 1 or 5, wherein each of said lead
patterns is composed of a conductor having an inside surface orthogonal to
the propagation direction of acoustic surface waves.
8. A method as set forth in claim 1 or 5, wherein each of said lead
patterns is composed of a conductor having an inclined reflected surface
with regard to the propagation direction of acoustic surface waves.
9. A method as set forth in claim 1 or 5, wherein each of said lead
patterns is composed of a plurality of parallel and equally spaced
conductors orthogonal to the propagation direction of acoustic surface
waves and spaced apart one quarter of an acoustic surface wave wavelength.
10. A method as set forth in claim 1 or 5, further comprising the step of
coating acoustic absorbent materials on the surface of said piezoelectric
material between said transducers orthogonal to said multistrip coupler
and on the edges of said piezoelectric material.
11. A method of manufacturing an acoustic surface wave device, in which
acoustic surface waves launched by an input transducer into a
piezoelectric material are transmitted to an output transducer through a
multistrip coupler, comprising the steps of:
(a) forming on the piezoelectric material two pairs of input and output
transducers, a multistrip coupler between the input and output
transducers, and lead patterns for electrically shorting at least one pair
of the input and output transducers;
(b) mounting the piezoelectric material on a package base having two pairs
of pins;
(c) bonding electrodes of the non-shorted pair of input and output
transducers to respective pairs of pins by wires; and,
(d) testing the device by supplying signals to the non-shorted input
transducer and obtaining signals from the non-shorted output transducer
through the respectively connected pairs of pins.
12. The method of claim 11 comprising the further steps, when the testing
step indicates said device is not usable, of:
cutting the lead patterns of the first pair of shorted input and output
transducers for non-shorting;
removing the wires connecting the electrodes of the first non-shorted
transducers to the respective pair of pins and bonding the electrodes of
said first non-shorted transducers by wires for electrical shorting;
bonding the electrodes of the non-shorted pair of input and output
transducers to respective pairs of pins by wires; and,
testing the device by supplying signals to the non-shorted input transducer
and obtaining signals from the non-shorted output transducer through said
respectively connected pair of pins.
13. A method of manufacturing an acoustic surface wave device, in which
acoustic surface waves launched by an input transducer into a
piezoelectric material are transmitted to an output transducer through a
multistrip coupler, comprising the steps of:
(a) forming on the piezoelectric material two pairs of input and output
transducers, a multistrip coupler between the input and output
transducers, lead patterns for electrically shorting one pair of the input
and output transducers, and external connecting paths connected to
electrodes of the non-shorted pair of input and output transducers;
(b) mounting the piezoelectric material on a package base having two pairs
of pins;
(c) bonding the external connecting pads of the non-shorted pair of input
and output transducers to respective pairs of pins by wires; and
(d) testing the device by supplying signals to the non-shorted input
transducer and obtaining signals from the non-shorted output transducer
through the respectively connected pairs of pins.
14. The method of claim 13 comprising the further steps, when testing step
indicates said device is not usable, of:
cutting the lead patterns of the first pair of shorted input and output
transducers for non-shorting;
bonding the electrodes of the first non-shorted transducers by wires for
electrical shorting;
bonding the external connecting pads to the electrodes of the non-shorted
pair of input and output transducers by wires; and,
testing the device by supplying signals to the non-shorted input transducer
and obtaining signals from the non-shorted output transducer through said
respectively connected pairs of pins and external connecting pads.
15. The method of claim 11 or 13 comprising the further step of fixing a
cover to said package base when the testing step indicates said device is
usable.
16. The method of claim 1, 5, 6, 11, 12, 13 or 14, wherein the electrodes
of each of said transducers are formed with a connecting pad for bonding
with said wires.
17. The method of claim 16 wherein the lead patterns are formed between the
connecting pads of the electrodes of the respective transducers. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing an acoustic
surface wave device which serves as a band pass filter, a delay line or
the like.
In general, conversion from acoustic surface waves propagating across a
piezoelectric material, such as LiNbO.sub.3 or LiTaO.sub.3, to electrical
energy and vice versa is carried out by a transducer which is
conventionally composed of a pair of separated, interdigitated comb-shaped
electrodes formed on the surface of the piezoelectric material.
One prior art acoustic surface wave device comprises: a piezoelectric
substrate having a planer surface for propagation of acoustic surface
waves; an input transducer formed on the surface for converting electrical
energy into acoustic surface waves; an output transducer formed on the
surface and located diagonally with respect to the input transducer, for
converting the acoustic surface waves into electrical energy, and; a
multistrip coupler (hereinafter referred to as a MSC), including a
plurality of parallel and equally spaced conductive elements, formed on
the surface and interposed between the input and output transducers so as
to be substantially orthogonal to the propagation direction of the
acoustic surface waves launched by the input transducer. The MSC serves as
an acoustic surface wave path changer only for the acoustic surface waves
launched by the input transducer, not for bulk waves which are also
launched by the input transducer and travel through the body of the
substrate. Thus, the bulk waves which reduce the band-pass performance of
the acoustic surface device are prevented from being received into the
output transducer. However, this device requires almost twice as much
piezoelectric material surface area as a conventional acoustic surface
device which has no MSC, and this large surface area results in a higher
manufacturing cost.
Another prior art acoustic surface wave device comprises one more input
transducer and one more output transducer than the above-mentioned prior
art device (see U.S. Pat. No. 3,959,748). In other words, two pairs of
transducers, each of which has two connecting pads, are provided. However,
only one pair of the transducers which satisfies predetermined conditions,
such as time response characteristics and frequency response
characteristics, is used. Therefore, in order to select one of the two
pairs, testing is carried out which examines whether the transducers
satisfy the conditions. First, testing of one pair of transducers is
carried out by applying test signals. In this case, four testing probes
are placed in contact with the four connecting pads of the pair of
transducers. If the first pair of transducers do not satisfy the
predetermined conditions, then, testing of the other pair of transducers
is carried out in the same way. Once one of the pairs of transducers is
selected, the remaining pair of transducers are disabled in order to avoid
undesired reflections, which degrade the performance of the device. For
example, acoustically absorbent material, such as black wax, is deposited
on the remaining pair of tranducers, or dummy impedances are connected
across the connecting pads of the remaining pair of transducers. Thus,
since either pair of transducers may be usable, the production yield of
the acoustic surface devices having two pairs of transducers is improved
over that of devices having one pair of transducers located diagonally to
each other, which results in a lower mass production cost.
However, in the above-mentioned prior art device having two pairs of
transducers, the reliability of testing using a high frequency, such as 30
MHz to 100 MHz, is low because testing can only be carried out by using
probing technology which is not suitable for such a high frequency. In
addition, during testing, the remaining pair of transducers are not
disabled, so that reflections are generated.
SUMMARY OF THE INVENTION
It is a principal object of the present invention to provide a method of
manufacturing an acoustic surface wave device having two pairs of
transducers in which the reliability of testing is high and undesired
reflections during testing are small.
According to the present invention, there is provided a method of
manufacturing an acoustic surface wave device in which acoustic surface
waves launched by an input transducer into a piezoelectric material are
transmitted to an output transducer through a multistrip coupler,
comprising the steps of: forming on said piezoelectric material first and
second input transducers, and first and second output transducers, each of
which is located diagonally with respect to said first and second input
transducers, respectively, said multistrip coupler being interposed
between said input transducers and said output transducers, and also
forming on said piezoelectric material lead patterns between electrodes of
said second input and second output transducers; mounting said
piezoelectric material on a package base which has first and second pairs
of pins therethrough; bonding connecting pads of electrodes of said first
input and first output transducers to said first and second pairs of pins,
respectively, by wires; testing said device by supplying test signals to
said first input transducer and obtaining output signals from said first
output transducer, and; when said test indicates said device is usable,
fixing a cover to said package base. Thus, the acoustic surface wave
device can be tested at an almost completed state without probing
technology, which results in a high reliability of testing. In addition,
undesired reflections during testing are small.
According to the present invention, there is also provided a method of
manufacturing an acoustic surface wave device, in which acoustic surface
waves launched by an input transducer into a piezoelectric material are
transmitted to an output transducer through a multistrip coupler,
comprising the steps of: forming on said piezoelectric material first and
second input transducers, and first and second output transducers, each of
which is located diagonally with respect to said first and second input
transducers, respectively, and said multistrip coupler being interposed
between said input transducers and said output transducers, and also
forming on said piezoelectric material lead patterns between electrodes of
said second input and second output transducers, and external connecting
pads connected to electrodes or said first input and first output
transducers; mounting said piezoelectric material on a package base which
has first and second pairs of pins therethrough; bonding said external
connecting pads to said first and second pairs of pins, respectively, by
wires; testing said device by supplying test signals to said first input
transducer and obtaining output signals from said first output transducer,
and; when said test indicates said device is usable, fixing a cover to
said package base. This method has a further advantage in that the
removing of bonded wires, which is not an easy operation, is not executed.
The present invention will be more clearly understood from the following
description with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view illustrating a conventional acoustic surface
wave device;
FIG. 2 is a perspective view illustrating another conventional acoustic
surface wave device;
FIG. 3A is a graph showing the time response characteristics of the device
of FIG. 2;
FIG. 3B is a graph showing the frequency response characteristics of the
device of FIG. 2;
FIGS. 4A through 4D are plan views used for explaining a first embodiment
of the method of manufacturing an acoustic surface wave device according
to the present invention;
FIGS. 5A through 5D are plan view used for explaining a second embodiment
of the method of manufacturing an acoustic surface wave device according
to the present invention;
FIGS. 6A through 6D are plan views used for explaining a third embodiment
of the method of manufacturing an acoustic surface wave device according
to the present invention;
FIGS. 7A, 7B and 7C are modifications of the embodiment illustrated in FIG.
4C;
FIGS. 8A, 8B and 8C are modifications of the embodiment illustrated in FIG.
5C;
FIGS. 9A, 9B and 9C are modifications of FIG. 6C;
FIGS. 10A through 10D are graphs showing the time response characteristics
of the devices of FIGS. 4C(4D), 5C(6C), 5D(6D) and 7A(7B, 7C, 8A, 8B, 8C,
9A, 9B, 9C), respectively, and;
FIG. 11 is a graph showing the frequency response characteristics of the
devices of the prior art by the broken lines A and B and of the present
invention by the solid line C.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, which illustrates a conventional acoustic surface wave
device, an input transducer 2 and an output transducer 3, each of which is
composed of two separated, interdigitated comb-shaped electrodes, are
formed on the surface of a piezoelectric substrate 1. When an electrical
signal from a tracking generator 4 is applied to the two electrodes of the
input transducer 2, the electrical signal is converted into acoustic
surface waves 6 which are converted into another electrical signal by the
output transducer 3. Transducer 3 is in turn which is connected to a load
impedance 5. In this case, the frequency of the acoustic surface waves 6
is determined by the spacing of the electrodes of the input transducer 2,
which is the same as that of the output transducer 3. Therefore, the
device of FIG. 1 serves as a band-pass filter or a delay line. However, in
this device, bulk waves 7 are also launched by the input transducer 2 and
travel through the body of the substrate 1 to reach the output transducer
3. Accordingly the band-pass characteristics of the device is reduced,
since the transit time of the bulk waves 7 is different from that of the
acoustic surface waves 6.
In order to prevent the bulk waves from reaching the output transducer 3,
an acoustic surface wave device is known wherein an MSC composed of a
plurality of parallel and equally spaced conductors between two
transducers are located diagonally to each other (see U.S. Pat. No.
3,836,876). The MSC serves as a path changer of the acoustic surface
waves, not of the bulk waves. However, this device requires twice as much
piezoelectric substrate surface area as the device of FIG. 1.
FIG. 2 is a perspective view illustrating another conventional acoustic
surface device having two pairs of transducers. First, testing of a pair
of transducers 2-1 and 3-1 is carried out. If the pair of transducers 2-1
and 3-1 are rejected, testing of the pair of transducers 2-2 and 3-2 is
executed. Since either of the two pairs of transducers may be usable, the
mass production yield of the device can be improved over that of the
device of FIG. 1.
In FIG. 2, it should be noted that the electrodes of each of the
transducers 2-2 and 3-2 are not shorted and, hence, reflections from the
transducers 2-2 and 3-2 are large. When an electrical signal S.sub.IN from
the tracking generator 4 is supplied to the input transducer 2-1, acoustic
surface waves are propagated on the surface of the piezoelectric substrate
1. One part of the acoustic surface waves is transmitted via an MSC 8 to
the output transducer 3-1, as indicated by S.sub.OUT, while another part
is reflected by the transducer 3-2 to reach the output transducer 3-1, as
indicated by S.sub.R. As a result, electrical signals S.sub.OUT and
S.sub.R are obtained in the load impedance 5 as illustrated in FIG. 3A,
where .tau. is a transit time of the signal S.sub.OUT and 3.tau. is the
transit time of the signal S.sub.R. Consequently, the frequency response
characteristics of the device of FIG. 2 include a large ripple rate, as
indicated by a dotted line in FIG. 3B, and the band-pass characteristics
of the device of FIG. 2 are reduced. In order to avoid such reduction of
the band-pass characteristics, acousitc absorbent materials are used in
the non-selected pair of transducers after testing. However, since such
acoustic absorbent materials are not used during testing, reflections are
large and the reliability of the testing is low. In addition, such testing
is carried out by using probing technology which causes the reliability of
the testing using high frequencies to become even lower.
In the present invention, an acoustic surface wave device is tested after
the device is mounted on a package. Therefore, testing is carried out
without using probing technology.
FIGS. 4A through 4D are plan views used of describing a first embodiment of
the method of manufacturing an acoustic surface wave device according to
the present invention. As indicated in FIG. 4A, two input transducers 2-1
and 2-2, two output transducers 3-1 and 3-2 and an MSC 8 are formed on a
piezoelectric substrate 1. Referring to FIG. 4A, connecting pads 9 are
formed at the ends of electrodes of the transducers 2-1, 2-2, 3-1 and 3-2,
and in addition, lead patterns 10 are formed between the connecting pads 9
of each of the transducers so that all of the transducers are shorted. As
a result, an impedance between the electrodes in each of the transducers
is nearly equal to a characteristic impedance of an acoustic surface wave
path, and, accordingly, reflections from the transducers are small. Here,
it should be noted that the input transducer 2-1 operates with the output
transducer 3-1, while the input transducer 2-2 operates with the output
transducer 3-2.
Next, as indicated in FIG. 4B, the piezoelectric substrate 1 is mounted on
a package base 11 which has four pins 12-1, 12-2, 13-1 and 13-2.
Then, as indicated in FIG. 4C, the lead patterns 10 of the transducers 2-1
and 3-1 are cut. In addition, wires (W) are bonded to the connecting pads
9 of the transducers 2-1 and 3-1 and the pins 12-1, 12-2, 13-1 and 13-2,
so that wires W.sub.1, W.sub.2, W.sub.3 and W.sub.4 are connected as shown
in FIG. 4C. After that, the device of FIG. 4C is mounted on a testing unit
(not shown) and, in order to examine the characteristics of the
transducers 2-1 and 3-1, testing is carried out. In this case, an
electrical test signal is supplied to the transducer 2-1 through the pins
12-1 and 12-2, while an electrical output signal is obtained from the pins
13-1 and 13-2. If the transducers 2-1 and 3-1 are acceptable, a cover (not
shown) is fixed to the package base 11. Contrary to this, when the
transducers 2-1 and 3-1 are rejected, the following operation is carried
out.
As indicated in FIG. 4D, the lead patterns 10 of the transducers 2-2 and
3-2 are cut. In addition, the wires W.sub.1, W.sub.2, W.sub.3 and W.sub.4
are removed, and after that, wires are bonded to the connecting pads 9 of
the transducer 2-2 and 3-2, and the pins 12-1, 12-2, 13-1 and 13-2, so
that wires W.sub.5, W.sub.6, W.sub.7 and W.sub.8 are connected as shown in
FIG. 4D. Wires W.sub.9 and W.sub.10 can be connected to the pads 9 of the
transducers 2-1 and 3-1, repectively. Then, the device is again mounted on
the testing unit (not shown) and testing is carried out in the same way as
mentioned above. If the transducer 2-2 and 3-2 are acceptable, a cover
(not shown) is fixed to the package base 11. However, if the transducers
2-2 and 3-2 are rejected, the device is also rejected. As can be seen from
the above testing is carried out without using probing technology. In this
embodiment, it should be noted that the first testing could be carried out
for the pair of the transducers 2-2 and 3-2 rather than transducucers 2-1
and 3-1.
FIG. 5A through 5D are plan views used for explaining a second embodiment
of the method of manufacturing an acoustic surface device according to the
present invention. The elements in FIGS. 5A through 5D which are identical
to those of FIGS. 4A through 4D are denoted by the same reference numerals
used in FIGS. 4A through 4D. Referring to FIG. 5A, the transducers 2-1 and
3-1 have no lead patterns. Therefore, first testing must be carried out
for the pair of transducers 2-1 and 3-1. As a result, in the manufacturing
step indicated in FIG. 5C, the cutting of lead patterns is not carried out
in contrast to the operational step carried out in the first embodiment,
of the invention.
FIGS. 6A through 6D are plan views for explaining a third embodiment of the
method of manufacturing an acoustic surface wave device according to the
present invention. The elements in FIGS. 6A through 6D which are identical
to those of FIGS. 5A through 5D are denoted by the same reference numerals
used in FIGS. 5A through 5D. As shown in FIG. 6A, two external connecting
pads 61 and 62, which are connected to each other, are connected to the
connecting pads 9 of the transducers 2-1 and 3-1. In the manufacturing
step as indicated in FIG. 6C, wires W.sub.1 and W.sub.4, and W.sub.2 and
W.sub.3 are placed in contact with the external connecting pads 61 and 62.
After that, first testing for the transducers 2-1 and 3-1 is carried out.
If the transducers 2-1 and 3-1 are rejected, second testing for the
transducers 2-2 and 3-2 is carried out. In this case, as indicated in FIG.
6D, the lead patterns 10 of the transducers 2-2 and 3-2 are cut. In
addition, wires W.sub.9 and W.sub.10 are bonded for shorting the
electrodes of the transducers 2-1 and 3-1, and wires W.sub.11, W.sub.12,
W.sub.13 and W.sub.14 are bonded between the connecting pads 9 of the
transducers 2-2 and 3-2 and the external connecting pads 61 and 62 so that
the transducers 2-2 and 3-2 are connected to the pins 12-1, 12-2, 13-1 and
13-2. After that, the second testing is carried out. Thus, in the
manufacturing steps indicated in FIGS. 6A through 6D, the removing of the
bonded wires (W.sub.1, W.sub.2, W.sub.3 and W.sub.4), which is not an easy
operation, is not carried out.
In any of the above-mentioned embodiments, testing is carried out without
using probing technology, which is not suitable for high frequencies. As a
result, the reliability of the testing becomes higher than with the prior
art.
In the above-mentioned embodiments, the lead patterns 10 are connected to
the connecting pads 9, but the lead patterns 10 can be connected to other
portions of the electrodes of the transducers.
In the present invention, the configuration of the lead patterns for
electrically shorting the transducers is modified as mentioned below, in
order to minimize reflections of acoustic surface waves.
FIGS. 7A through 7C, 8A through 8C and 9A through 9C are modifications of
the embodiments illustrated in FIGS. 4C, 5C and 6C, respectively. As shown
in these figures, connecting pads 9 are located beside the transducers
and, in addition, electrodes which are comb-shaped are modified. In FIGS.
7A, 8A and 9A, each of the lead patterns 10A is composed of a conductor
whose inside surface is inclined with regard to the propagation direction
of acoustic surface waves so that reflections from the lead patterns 10A
are scattered, which means that reflections are substantially small. In
FIGS. 7B, 8B and 9B, each of the lead patterns 10B is also composed of a
conductor whose inside surface is inclined with regard to the propagation
direction, but is bent at the center thereof, so that reflections from the
lead patterns 10B are scattered. In FIGS. 7A, 7B, 8A and 8B, the outside
surfaces of the lead patterns 10A and 10B are also inclined. However, it
should be noted that the outside surface can be orthogonal to the
propagation direction. In FIGS. 7C, 8C and 9C, the lead patterns 10C are
composed of a plurality of parallel and equally spaced conductors
orthogonal to the propagation direction and spaced apart one quarter of an
acoustic surface wave wavelength. When the acoustic surface waves penerate
into the lead patterns 10C, reflected waves from the conductors interfere
with each other so that the reflected waves are neutralized, which means
that reflections are substantially small.
In addition, in order to minimize undesired reflections and electromagnetic
waves and as illustrated in FIG. 7A, an acoustic absorbent material 14,
such as black wax, is coated on the surface of the substrate 1 between the
transducers 2-1, 3-2 and the transducers 2-2, 3-1, and on the edges of the
substrate 1.
The time response characteristics of the devices of FIGS. 4C, 4D, 5C, 5D,
6C, 6D, 7A through 7C, 8A through 8C through 9A and 9C will now be
explained. In the devices shown in these figures, the piezoelectric
material 1 is made of LiNbO.sub.3 crystal whose surface area is 4
mm.times.13 mm, the cross-width, i.e., the width of the transducers, is
1.5 mm, and the transit time .tau. is 2 .mu.sec. As indicated in FIG. 10A,
depicting the case of the device of FIG. 4C (or 4D), when an input signal
S.sub.IN is supplied to the transducer 2-1, a signal S.sub.OUT is received
through the MSC 8 by the transducer 3-1. In addition, reflections S.sub.R1
from the lead pattern 10 of the transducer 3-2 and from the lead pattern
10 of the transducer 2-2 are received by the transducer 3-1. In this case,
the amplitude A.sub.3 of the reflections S.sub.R1 is about -50 dB (=20 log
A.sub.3 /A.sub.1). Further, reflections S.sub.R2 from the cut lead
patterns 10 of the transducer 2-1 and from the cut lead pattern 10 of the
transducer 3-1 are received by the transducer 3-1. In this case, the
amplitude A.sub.4 of the reflections S.sub.R2 is about -45 dB.
Furthermore, a signal S.sub.T which is called a triple transit echo is
received by the transducer 3-1. The amplitude A.sub.2 ' of the signal
S.sub.T is about -43 dB. Any one of the amplitudes A.sub.2 ', A.sub.3 or
A.sub.4 is smaller than the amplitude A.sub.2 of the signal S.sub.R (FIGS.
2, 3A and 3B) which is about -40 dB.
As indicated in FIG. 10B, in the case of the device of FIG. 5C (or 6C),
reflections S.sub.R2 are not present, since the transducers 2-1 and 3-1
have no lead patterns 10. Similarly, as indicated in FIG. 10C, in the case
of the device in FIG. 5D (or 6D), reflection S.sub.R1 are not present,
since the transducers 2-1 and 3-1 have no lead patterns 10. On the other
hand, as indicated in FIG. 10D, in the case of the devices of FIG. 7A (or
7B, 7C, 8A, 8B, 8C, 9A, 9B or 9C), reflections are substantially
eliminated by the lead patterns 10A, 10B and 10C.
The amplitudes of undesired signals, such as S.sub.R1, S.sub.R2, S.sub.T
appearing in the devices of the present invention, are smaller than the
amplitude A.sub.2 of the signal S.sub.R appearing in the device of FIG. 3A
or the prior art. In FIG. 11, the frequency response characteristics,
which include a large ripple, for the prior art device of FIG. 2, are
illustrated by a dot-dash line A or a dotted line B, while the frequency
response characteristics, which include a small ripple, for the device
according to the present invention are illustrated by a solid line C.
As explained hereinbefore, the method for manufacturing an acoustic surface
wave device according to the present invention has the following
advantages, as compared with those of the prior art.
(1) The reliability of testing is high, since testing is carried out
without using probing technology.
(2) Undesired reflections during testing are small, since the non-tested
transducers are electrically shorted by wires or lead patterns.
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