CA1145425A

CA1145425A - Coil assembly

Info

Publication number: CA1145425A
Application number: CA000335347A
Authority: CA
Inventors: Kaneo Yamamoto; Toshio Konno; Norio Matsuda; Shinya Tominaga; Susumu Kubo; Yasuyuki Mori; Naoki Akiyama; Masaki Murakami
Original assignee: Victor Company of Japan Ltd
Current assignee: Victor Company of Japan Ltd
Priority date: 1978-09-11
Filing date: 1979-09-10
Publication date: 1983-04-26
Also published as: JPS5542311U; JPS622733Y2; GB2032186B; US4532620A; GB2032186A

Abstract

ABSTRACT OF THE DISCLOSURE
A coil assembly comprises a plurality of conductive spiral pattern layers which are piled up via (an) insulating layer(s) on a wafer. The electrical connection between the spiral patterns is established by means of a conductive member, which is a portion of the upper spiral pattern layer, filled in a through-hole which is made in the insulating layer so that the spiral patterns are connected in series to develop a high voltage when the coil assembly is moved in a magnetic field.

Description

~1454ZS

FIELD OF THE INVENTION
This invention generally relates to a coil for picking up vibrations. More particularly, the present invention is related to a coil used in dynamic (moving-coil type) phonograph pickups.

BACKGROUND OF THE INVENTION
Conventional coils used in moving-coil type phonograph pickups ~cartridges) for picking up audio signals from phonograph records (discs) comprises at least one coil which has a winding made of a conductive wire. It is generally known that a coil which is light ln weight is advantageous since li~hter coils have less~influence on the vibrations of the vibratory member, such as a stylus ; ~
arm, to which the coil is secured. In order to provide ~ -15~ a llght coil a fàbricatlng method of an IC ~(lntegrated circuit) was recently adopted and a coil which is made of a microstrip of spiral pattern was developed. This ; ~ newly developed coil comprises a conductive spiral pattern layer formed on a suitable substrate and is~produced by well known photolithographic processes.
Although the above descrlbed newly developed coil ~ -is superior and is advantageous in that the weight of the ;~
coil proper is remarkably reduced compared to the con- ~ -ventional winding type colls, the output voltage of the spiral pattern type coil is in the same level as that of ~S425 the conventional winding type coila. As is well known, the output voltage of a moving-coil type phonograph pick up is much lower than that of the movlng magnet type pickups. Therefore, when a moving-coil type phonograph pickup is employed, a step up transformer is required to raise the output voltage to a sufficient level prior to feeding the output to the input of a preamplifier.
; Provision of a step up transformer causes the input signal of the preamplifier to be deteriorated in the signal to noise ratio. Therefore, it would be advantageous, in view of high fidelity sound reproduction, if such a step up transformer were omitted. In order to directly apply the output voltage of the coil of a dyn~amic phonograph pickup to a preamplifier by omitting a step up transformer,~
the output voltage of the coil has to be high enough so as to meet the requirement of the preamplifier.
Since the output voltage of a coil is in proportion to the number of turns of the winding or conductive element, the number of turns has to be increased to generate a high voltage. However, it is impossible to increase the number of turns when a conventional winding type coil is usecl inasmuch as the increase in the number of turns directly results in the increase in weight deteriorating the frequency characteristic of the pickup.

2 -:

119~5425 When a spiral pattern type coil is used, the number of turns may be readi].y increased without raising such a problem in connection with weight since,a spiral pattern type coil is so light that it widly differs from that of a conventional winding type coil.
However, the increase in the number of turns of a spiral pattern type coil requires the increase in size, such as the diameter, of the coil unless the density of the spiral pattern is increased. The density, i.e.
the number of turns per a given unit area, cannot be increased due to the manufacturing limit defined by the .
nowaday technique of photolithographic process. There-fore one possible way for increasing the number of turns, which has been taken into account hitherto, is to increase :
the diameter of the spiral pattern. However, in case of using a large diameter spiral pattern coll, the plane of .
the spiral pattern is apt to undulate in receipt of vibrations, resulting in the deterioration of the frequency . characteristics of the output signal. Therefore, this . ~ ;
0 method of increasing the diameter of the spiral pattern , for having a large number of turns is not also practical.
SUMMARY OF THE INVENTION : :
The present invention has been developed in order to remove the above described difficulty in increasing the number of turns of a coil used in a dynamic phonograph : :~
pickup.

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~L~459~2S

It is, therefore, a primary object of the present invention to provide a coil for dynamic phonograph pickups, in which the nu~ber of turns is made so'great that the coil generates a high output voltage which is sufficient to be directly applied to the input of a prea~plifier.
Another object of the present invention is to provide a coil for dynamic phonograph pickups in which - the weight of the coil is considerably smaller than that of conventional winding type coils.
A further object of the present invent1on is to provide a coil for dynamic phonograph pickups in which the frequency characterist1c of the output signal is flat over a wide range.
When it is intended to increase the number of turns in the aforementioned spiral pattern type coiI which is ~: :
~ made of a microstripline without increasing the density ~ ~
: ` ::
of the spiral pattern and the diameter thereof, it seems to be possible to place a pa1r of spiral patterns on the~
both sides of a wafer or a film, which serves as the ~20 base of the coil, to connect the spiral patterns in series. However, this arrangement has two disadvantages as follows: The first one is that the thickness of the wafer has to be increased to an exten~ to have sufficient ~ `
strength that the wafer will not be broken during manu-25 - facturing processes in which the wafer has to be turned ~ - 4 - . :~

upside down to form spiral patterns on the both sides thereof. The increase in the thickness of the wafer may result in the increase in weight of~the coil assembly and therefore, this technique is not practical. The second disadvantage is that additional conductlve strip-line layers have to be provided in order to establish :: electrical connection between the terminals at the center . side of the spiral patterns. Provision of additional layers causes the thickness of the coil assembly to be ~ ;
increased resulting in the increase in weight ~:
According to the first feature of the present ~ ~ -.
invention, more than two spiral pattern layers are piled : up via insulating layers on the same side~ of a wafer, :
where the spiral patterns are connected in series.
According to the seco~d feature of the present invention,:the connectlon;be~tween termlnal~of two con~
secutive spiral;patterns lS established by~a conductor ` placed in a through-hole made~in the insulating layer between the two consecutive spiral patterns.
According to the third feature of the present invention, the through-hole is~made~by chemical etching and the through-hole is tapered such that the opening :~
area of the through-hole~;at the upper side:is larger than ;~
: that at the lower side so that the electrical connection :~
between the spiral patterns is easily attained.
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: : ` : ~

:
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1~4~425 In accordance with the present invention there is provided a coil assembly comprising: (a) a nonconductive base; (b) a plurality of spiral pattern~layers made of conductive microstriplines; said spiral pattern layers being piled up on said base and adjacent spiral pattern layers being separated by an insulating layer; and (c) means for establishing electrical connection between said spiral pattern layers.
In accordance with the present invention there is further provided a method of fabricating a coil assembly comprising the steps of: (a) placing a nonconductive wafer on a substrate; (b) placing a first conductive layer on the wafer; (c) etching the first conductlve layer to a desired spiral pattern for forming a first : :~
conductive spiral pattern; (d) placlng an insulating layer on the first conductive spiral pattern; (e) making through-holes in the insulating layer to a desired through-:: - :
~ hole pattern by an etching technique; (f) placing a second ~ -.
conductive layer on the insulating layer, at least one ~20 portion of the second conductive layer being put into one of the through-holes to establish an electrical : ~ connection between the first and second conductive layers;
(g) etching the second conductive layer to a desired spiral pattern for forming a second conductive spiraI
pattern; (h) repeating the steps of (d) to (g) a : -:

, i~ :

ll~S425 predetermined number of times corresponding to the number of spiral pattern layers to be piled up; (i~
fixing connecting leads to the terminals of the coil which is constructed of the series connection of the spiral patterns; and (k) placiny a nonconductive layer on the top most spiral pattern.
In accordance with the present invention there is further provided a dynamic phonograph pickup comprising:
(a) a permanent magnet; (b) a yoke connected to the .
: 10 magnet for having a gap tc) a s~ylus arm supported by ~ -a supporting member at one end thereof; (d) a stylus fixedly secured to the stylus arm at the other end of the -~ ~ stylus arm; (e) a coil assembly fixedly secured to the ;~ ; stylus arm in the vicinity of the stylus, the coiI assembly:
15 ; having at least one coil made:of multi-layers of co~duc~
tive spiral patterns which are piled up on a wafer via :
insulating means, at least two of the;spiral patterns being connected in series~so as to develop a voltage across the terminals of the coil when the coil assembly ~
~20 is moved in the gap. ~ - .
BRIEF DESCRIPTION OP THE:DRAWINGS
These and other objects; and features of the present invention will become more readily apparent from the following detailed description of~the preferred embodiments ; ~ :
taken in conjunction w1th the accompanying drawings in . which~

: - 6 - :

il454Z5 Figs. lA to lM show the manufacturing processes of a two-spiral pattern layer type coil assembly by way of cross sectional views of a coil chip, Fig. 2 is an enlarged view of the through-hole shown in Fig. lH;
Fig. 3 is a perspective view of a coil assembly - corresponding to Fig. lL;
~ igs. 4A and 4B constitùte a single drawing which shows an exploded view of three-spiral pattern layer type coil assembly according to the present invention;
Fig~ 5 shows a pair of coils formed on the same wafer, which coils are used for a stereophonic sound reproducing system; and -~, f .-` ::

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6~

~45425 Fig. 6 shows a dynamic phonograph pick up in which a coil assembly according to the present invention is used.
DETAILED DESCRIPTION OF THE PREFERRED_ EMBODIMENTS
S Referring to Fig. lA to Fig. lM the manu~acturing processes of a coil ass mbly according to~the present invention is shown by way of cross sectional views of a coil chip. Each of the cross sectional views illust-rates a portion of a coil chip for simplicity and actually a single chip includes a larger number of turns of a microstripline than illustrated.
In Fig. lA a reference numeral 1 designates a sub-~ , strate which is made of a suitable màterial~such as -silicone, copper or glass. A reference numeral 2 designates a wafer (base rilm~ which is made of~a nonconductive heat resistive resin. The wafer 2 is, for instance a film made of polyimide resin, and is stuck on the surface of ; the substrate l ~y a suitable technique, such as centri~
fugal atomizing, with the aid of heat reslstive adhesive.
This film 2 wlll serve as~the;base of the coil after the ~;~
coil is completed, and the thickness of the film~2 may be between several microns and several tens of microns. -~
Fig. lB shows that a conductive film 3 which is made of a metallic material, such as Al, Al-Cu, Al-si or Al-Cu-Si, is placed on the surface of the polyimide ::

~:

, ~5~25 .

film 2. The conductive film 3 may be placed on the wafer 2 by means of a suitable coating technique, such as vapour coating or sputtering. After the wafer 2 is coated with the conductive film 3, a film of photoresist

4 is placed on the surface of the conductive film 3 as illustrated in Fig. lC.
A mask (no~ shown) of a desired pattern of a spiral microstripline, is then placed over the surface of the photoresist 4 and then the photoresist 4 will be exposed to ultraviolet light, which will be applied by means of a suitable light source, through the masX. By exposing the photoresist 4 to ultraviolet light through the mask, ;
the photoresist become polymerized under the transparent regions of the mask. The mask is now removed, and the photoresist 4 is developed by using a chemical which - -dissolves the~unexposed (unpolymerized) portions of the photoresist film~and leaves the surface pattern as shown ~; ~ in Fig. lD in case of a negative type photoresist. The photoresist 4' which was not removed in development is now fixed, so that it becomes resistant to the corrosive ; etches used next. A positive type photoresist may be used, if desired, to obtain the same result.
A given kind of gas is applied~to the exposed portions of the conductive film 3 to perform dry etching. -After the exposed portions are totally etched and are ~ ' ~

removed, the fixed photoresist 4' is removed as illustrated in Fig. lE. Now we hàve obtained a conductive spiral pattern layer 3' formed on the wafer 2.- This spiral pattern 3' will be referred to as a first spiral pattern layer hereinafter throughout the specification.
A nonconductive heat resistive film 5, such as a polyimide (an organic insulating matter) film, will be placed on the first spiral pattern layer 3' to perform heat treatment. The nonconductive film 5 will serve as ~10 an insulating layer between the first spiral pattern layer 3' and a second spiral pattern layer~wh1ch will be placed on the nonconductive film 5 in the followlng ~ ;
process. Utilization of a heat reslstive~resin as the insulating layer 5 is advantageous in that the surface of the insulating layer 5~is made flat, because of the flowabillty of the resln, irrespectively of the un-dulations (projections~and recesses) of the etched first spiral pattern layer 3'~. The heat treatment of the~
polyimide resin of~the insulating layer 5 is done for ~20 ~ removing the solvent thereof and for hardening the resin ;
~ ,

5. The final temperature in the~heat treatment process is about 350 degrees centigrade.
With -the insulating layer~5 coated on the conductive ~ ~ -film, i.e. the first spiral pattern layer 3', another photoresist layer 6 lS placed on the insulating layer 5.

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_ 9~

~1~5~5 A second mask (not shown) which corresponds to a desired pattern of through-holes (openings) is put over the photoresist layer 6. The photoresist layer 6 will be processed in the same manner as the first photoresist layer 4 has been etched photolithographically as shown in Fig. lC to Fig. lE. As the result of this process, the photoresist layer 6 is etched partially to the pattern of the through-holes as illustrated in the right-upper part of Fig. lG, while the insulating layer 5 is coated with the photoresist layer 6 except portions at which th,rough-holes are intended to be made in the lnsulating layer 5~
The exposed portions of the insulating layer 5 will ~ be chemically etched. In case that the insula~ing lay~r ;~ 15 5 is made of polyimide,~chemical fluid including hydrazine hydrate as its chief component is most suitable for etching ~; the insulating layer 5 to make through-holes. Pig. lH
:.
` illustrates that a through-hole is made in the insulating layer 5 by the above described process. It is to be ~ ~
noted that the through-hole was made to have reversed ~ -; truncated cone shape rather than a cylindrical shape. ~ -Namely, the cross sectional view of the through-hole is of trapezium, while the length of the base of the trapezium is smaller than-that of the opposite leg.
~5 The through-hole is shown in Fig. 2 by an enlarged :

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11~5~25 view which corresponds to the cross sectional view of Fig. lH. As will be described hereinlater the through-hole will be usea to electrlcally connect a terminal of the first spiral pattern layer 3' with a terminal of the second spiral pattern layer 7 which will be formed on the insulating layer 5. It will be readily understood that such a through-hole of tapered shape is advantageous for ensuring the connection between terminals of the first and second spiral pattern layers. Although the shape of the through-hole shown in Fig. 2 is of reversed truncated cone, other shapes may be selected and if the through-hole is tapered in such a manner that the opening area of the through-hole at the upper side, i.e. the -second spiral pattern layer side, is larger than that of the same at the lower side, i.e. the first layer spiral pattern layer side,~ the electrical connection - between the first and second spiral patterns w~ be established easlly since a portion of the conductive ~ ;
material of the second spiral pattern layer 7 is readily .
inserted therein to reach the surface of the exposed ~ ;
first spiral pattern layer 3'. Furthermore, because of the tapered through-hole the conductive material filled in the through-hole is hardly likely to be broken.
The slope o~the side wall defining the tapered 25 through-hole will be controlled at will by any one of the : : .

1~5425 following methods:
(1) The slope becomes steeper as the percentage of the hydrazine hyarate in the etching~solution decreases;
(2) The slope becomes steeper as the temperature ; 5 in the heat treatment rises; and (3) The upper openlng area of the through-hole will grow larger upon application of a particular kind of a gas when used in surface tre`atment in connection with the exposed areas of the first spiral pattern layer 3'.
Of course more than two of the above three methods , may be used to determine the slope of the tapered through-hole and actually all of the three methods are concurrently ; ~ -used.
15~ After through-holes are made, the photoresist layer ~;

6 is removed and we obtain a first stage intermediate product I as illustrated in Fig. lI. On the insulating polyimide layer~5, a second spiral pattern 7~will be made in the same manner as the flrst spiral pattern 3'.~ ;
In other words, the second spiral pattern layer 7 will be placed in the similar manner as the processes shown .
in Fig. lB to Fig. lE. After~the second spiral pattern layer 7 is formed on the insulating layer 5, we obtain a second stage intermediate product II as illustrated in Fig. lJ.

:;~

5~5 Although the above description of the fabricating processes is made in connection with a single chip of a coil, actually several hundreds of chips are simul-taneously formed on the same substrate 1 in a similar manner as integrated circuits chips are made~ After ~forming the first and second spiral pattern layers 3' , and 7, the entire substrate, on which the first and second spiral pattern layers 3' and 7 are formed, will be divided by means of suitable tools, such as a scriberdicer, , ~ 10 into individual pieces of chips. With the chips separated -from each other, a connecting lead 8 is fixed to a terminal~
- -:
of the second spiral pattern 7, by ultrasonic bondlng, as shown in Fig. lK. Meanwhile, another connecting Iead (not shown) is fixed to a termlnal of the first spiral pattern layer 3' in the same manner. Although the connection of this connecting lead is not shown, it will ;
be understood that the connecting lead reaches the ter-minal of the flrst spiral pattern layer 3' via a through~
hole (not shown) made in the insulating layer 5, which ~20 through-hole was made ln the process of Fig. lI. The substrate 1 is then removed by a suitable method such `~
as etching and we will;have a coil chip, as shown in~
Fig. lL. The surface of the chip shown in Fig. lL lS
coated with a suitable nonconductive surfaoe treatment material, such as varnish or photoresist so as to provide :

:

1145~25 a finished product III as illustrated in Fig. lM.
Fig. 3 illustrates a~perspective view of a single coil chip corresponding to Fig. lL. The coil shown in Fig. 3 comprises first and second spiral pattern layers 3' and 7 which are piled up via the insulating layer 5.
The first spiral pattern layer 3', which is seen as a plurality of strips in the cross sectional view, is of counterclockwise turns when viewed from the~top and has first and second terminals 3'-1 and 3'-2 at both ends thereof. The second spiral pattern layer 7 which is placed over the-flrst spiral pattern layer 3', is of clockwise turns when viewed from the top and~also has first and second terminals 7-1 and 7-2 at~both~ends.
The first terminals 3'-1 and 7-1 of the~flrst and second spiral pattern layers 3'~and 7 are respectlvely located at the periphery of the spiral patterns,~while the second terminals 3'-2 and 7-2 are respectlvely located at the centers of the spiral pstterns. The flrst terminal 3'-1 of the first spiral pat~ern layer 3' is connected to a connecting lead 8', while the first terminal 7-1 of the second spiral psttern layer 7 i~s connected to a connecting ; lead 8. The second terminals 3'-2 and 7-2 of the first - ;~ `
and second spiral patterns 3' ànd 7 are directly connected to each other via a portion of the second splral pattern

7 placed in the through-hole made in the insulating ~
'.:
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- 14 ~

:

54;~5 layer 5. The outer most portion of the first spiral pattern layer 3' is depicted by dotted lines and is shown to be connected to the connecting~lead 8~ which reaches the first termlnal 3'-1 via the through-hole provided at the edge portion of the insulating layer 5.
Although the first and second spiral patterns 3' and 7 are of oval shape, other shapes of spiral patterns may be adapted.
Reference is now made to Figs. 4A and 4B, which constitute a single drawing, showing a second embodiment of the coil assembly according to the present invention.

: ~
The second embodiment coil~assembly comprises three spiral pattern layers 3', 7 and lO which are~pilled~up in ;~
the similar manner as the first embodiment~coil assembly shown in Fig. lM and Fig. 3. For a better;understanding the third embodiment~col1 assembly is shown by way of an exploded view in Figs. 4A and 4B, while the same parts ~ ~ -or elements~which are also used in the first embodiment are designated by the same reference numerals.
Each of the first to thlrd spiral layers 3', 7 and `~
lO has first and second terminals 3'-l, 7-l, lO-l, 3'-2, ~ ;
7-2 and 10-2. Three insulating layers S, 9 and ll are provided in such a manner that the first insulating layer ; 5 is placed between the first and second spiral patterns 3' and 7, the second insulating layer 9 is placed between ~ _ i5 -:
:
,:: ~ . . ~:

1~54Z5 the second and third spiral pattern layers 7 and 10, and the third insulating layer 11 lS pl,aced on the third spiral pattern layer 10. Several throu~h-holes are made in each insulating layer so tha~ electrical contacts .
between the spiral patterns 3', 7 and 10 will be established ~:~ and connecting leads will be connected to terminals of :: .
the coil. All of the above described layers are piled ~.
up on the wafer 2. The spiral patterns 3', 7 and 10 have ~ a shape of heptagon but other shape, such-as any polygon, may be adopted if desired.
:~: The ~irst spiral pattern 3' directly placed on the ~: . wafer 2 has first and second terminals 3'-1 and 3'-2 respectively located at the outer and inner sides. The ~ : first terminal 3'-1 is connected to a connecting lead ::~
`; 15 (not shown) whlch extends through the triangular through~
holes 5C, 9C and llB made in the first,~second and third insulating layers 5, 9~and 11. The second termlnal 3'-2 of the first spiral pattern layer 3' is connected to the ~ first terminal 7-1 of the second spiral pattern layer 7 20 ~::via the triangular through-h:ole 5A made in the first insulating layer 5. The:second terminal 7-2 of the ~ ~ second spiral pattern layer 7 is oonnected via the tri~
: ; ~ angular through-hole 9A to:the first terminal 10-1 af the ~ -third spiral pattern layer 10, the second terminal 10-2 ~ ~, : .
of which is connected to a connecting lead ~not shownj ~ ~
:: ~ ~. ::

~ 16 -: : .
:

5~25 which extends through the pentagonal through-hole llA
made in the third insulating layer 11. The above described connections are implied by three vertical lines with arrows, where the relationship between the lines in Fig. 4A and Fig. 4B is indicated by references X and Y. The pentagonal through-holes 5B and 9B of the first and second insulating layers 5 and 9 are used to connect the second terminal 10-2 of the third spiral pattern layer 10 with pentagonal portions 7-2 and 3'-3 of the second and first spiral pattern layers 7 and 3', These penta~onal portions 7-3 and 3'-3 are not parts of the spiral patterns but~are connected with the second terminal 10-2 of the third spiral pattern layer 10 so `-as to reinforce the termlnal 10-2 preventing the terminal ;~ ~ 15 10-2 from coming off. Arrows are depicted along the : -striplines of the first to third spiral pattern layers 3',~

. 7 and 10 to indicate the~direction of turns of the coil.

The direction of these arrows may indicate the direction of an electric current flow at an instance, where the :
direction is toward the center of the spiral patterns in the first and third spiral pattern layers 3' and lO, and is toward the periphery of the spiral pattern in the second spiral pattern layer 7.
Two embodiments of the coil assembly according to the present invention have been discussed in connection : :

::

~45~5 with double spiral pattern layer type and a triple spiral pattern layer type. However, the number of spiral pattern layers may be increased, if desired, by repeating the processes shown in Fig. ls to Fig. lF.
:
When a dynamic pickup is adapted to a stereophonic sound reproducing system, a pair of moving coils is required as is well known. Fig. 5 shows a pair of coils 16 and 18 formed on the same wafer 2. These two coils 16 and 18 are subjected to generate respective electrical signals corresponding to the left and right channel sounds when moved by means of a stylus arm in a magnetic field. The spiral patterns respectively forming two coils are of hexagonal shape and are arranged on a chip with ;~
a predetermined angle so as to most effectively~pick up the left and right channel audio signals. In this way a single chip including a pair of coils can be fabricated.
- .
By using such a chip of three spiral pattern layers, the dimensions of which is 1 x 2 x 0.04 mm, the thicknèss of -each spiral pattern layer made of aluminum strips being ` 20 approximately 1 micron, the weight of the ohip being approximately 240 micrograms, the number of turns of each coil being 150, i.e. 50 turns for each spiral pattern layer, we have obtained experimentaI results such that the output voltage is approximately 1.6 mV and the fre-quency characteristic is from 10 to 50,000 Hz.
Reference is now made to Fig. 6 which shows a `

~4S4~5 ` -. . .

stereophonic cartridge in wh~ch the moving-coil according to the present invention is disposed. The cartridge 20 comprises a casing generally denoted by~a reference numeral 20, a permanent magnet 30, a yoke 32, a coil assembly 26, a stylus arm 24, a stylus 22, a stylus supporting member including a damper 28, terminals 36, and connecting leads 34. The magnet 30 and~the yoke 32 are fixedly supported by means of a bolt, whlle the stylus arm 24 is supported at one end thereof by the supporting member via the damper 28. The stylus 22 is , disposed at the other end of the stylus arm 2~4 so as to be put in the groove of a phonograph record~(not shown). ~ ;
The coil assembly 26,~which may substantlally~correspond ~ ~ -- to the coil chip illustrated in Fig. 5, is fixedly 15~ ~ secured-to the;stylus-arm 24 l~n the~vlcinity~of the stylus 22. Both ends of the yoke 32 constitute a gap to develop a magnetic field therein.; The coil assembly 26 is interposed in the gap formed by the yoke 32 in such a manner that the coil assembly 26 is freely movable in ~ the gap in accordance wlth the movement of the stylus arm 24. The terminals of the coil assembly 26 are respec~
tively connected by means of the connecting leads 34 to the terminals 36 of the cartridge. ~It will be unders-tood that since the coil assembly 26 is~extremely light in weight, it can be~placed~in the vicinity of the stylus 22 :: : : . : ;:

; ~ , : . . : ' : ~
~:
': ~ : : : : : ~
:

~1454~5 on the stylys ar~ 24. Consequently, the vibratlons picked ;~
up by the stylus 22 is almost directly transmitted to the coil assembly 26 via a short distance so that distortion which may occur in the vibratory system in a phonograph pickup can be considerably reduced compared to conventional pickups.
Although in the above described embodiments a plurality of spiral patterns are connected in series so ~ ;
as to develop a high voltage across the coil terminals, the spiral patterns of multi-layer coil may be connected in parallel resulting in the reduction of the impedance .
` of the coil. For instance, when the number of spiral patterns connected in parallel is "n", the total;impedance of the coil equals one "n"th the impedance of each spiral pattern. The reduction of impedance of a coll is advan-tageous for impedance matching with the following circuit, such as a preamplifier or a step up transformer. Further-::
~ more, when a coil assembly comprises more than three .~
spiral patterns, a series-parallel connection between spiral patterns may be possible so that the voltage developed by the coil is hlgh enough, while the lmpedance of the coil is low enough.
The present invention has been described in con- ;

nection with a moving coil type phonograph pickup by way of various embodiments. However, the application of the :

~45~25 present invention is not llmited to such a phonograph pickup. The coil assembly according to the present invention may be used in other devices and apparatus, such as a vibration pickup for a vibration meter. It will be further recognized that the coil according to - the present invention may be used as a part of an electro-mechanical transducer. Furthermore, the coil according to the present invention may be utilized as a.simple inductace element in an electrical circuit. . ::
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A coil assembly for use with a moving coil stereo pickup, comprising a pair of coils embedded in a unit body, each of said coils comprising:
(a) a nonconductive base;
(b) stacked spiral pattern layers made of conductive microstriplines, said spiral pattern being formed on said nonconductive base;
(c) an insulating material forming a multiple overlay of polyimide films, one of said polyimide films being placed on one of said stacked spiral pattern layers, which is located opposite to said base, each of the remaining polyimide films being interposed between any two consecutive spiral pattern layers, each of said polyimide films being formed through a heat process with which solvent of liquid polyimide is removed to harden the same so as to provide a flat insulating layer; and (d) means for establishing electrical connection between said spiral pattern layers, said means comprising a conductive member connected between any two consecutive spiral pattern layers;
said pair of coils being arranged so that they are symmetrical with a center line which bisects said coil assembly.

2. A coil assembly as claimed in Claim 1, wherein said spiral patterns are formed by etching and photolithography.

3. A coil assembly as claimed in Claim 1, wherein said through-hole is etched in said insulating layer.

4. A coil assembly as claimed in Claim 1, wherein said through-hole is tapered such that the opening area of the through-hole at a side for receiving a second spiral pattern layer is larger than the opening area of the same at the first spiral pattern layer side.

5. A coil assembly as claimed in Claim 1, wherein said insulating layer is a polyimide resin having a thickness of between several microns and several tens of microns.

6. A coil assembly as claimed in Claim 1, wherein said spiral pattern layers are at least three, said spiral pattern layers being electrically connected is series so as to generate a necessary voltage when operating in a magnetic field.

7. A method of fabricating a coil assembly comprising the steps of:
(a) placing a nonconductive wafer on a substrate;
(b) placing a first conductive layer on said wafer;
(c) etching said first conductive layer to a desired spiral pattern for forming a first conductive spiral pattern;
(d) placing an insulating layer on said first conductive spiral pattern;
(e) making through-holes in said insulating layer to a desired through-hole pattern by an etching technique;
(f) placing a second conductive layer on said insulating layer, at least one portion of said second conductive layer being put into one of said through-holes to establish an electrical connection between said first and second conductive layers;
(g) etching said second conductive layer to a desired spiral pattern for forming a second conductive spiral pattern;
(h) repeating said steps of (d) to (g) a prede-termined number of times corresponding to the number of spiral pattern layers to be piled up;
(i) fixing connecting leads to the terminals of the coil which is constructed of the series connection of the spiral patterns; and (k) placing a nonconductive layer on the top most spiral pattern.

8. A method of fabricating a coil assembly as claimed in Claim 7, wherein a number of coil chips are made on the same wafer to be divided into indivisual pieces after a plurality of spiral patterns are formed on said wafer.

9. A dynamic phonograph pickup comprising:
(a) a permanent magnet;
(b) a yoke connected to said magnet to provide a gap;
(c) a stylus arm supported by a supporting member at one end thereof;
(d) a stylus fixedly secured to said stylus arm at the other end of said stylus arm; and (e) a coil assembly comprising a pair of coils embedded in a unit body, each of said coils comprising, a nonconductive base; stacked spiral pattern layers made of conductive microstriplines, said spiral pattern being formed on said nonconductive base; an insulating material forming a multiple overlay of polyimide films, one of said polyimide films being placed on one of said stacked spiral pattern layers, which is located opposite to said base, each of the remaining polyimide films being interposed between any two consecutive spiral pattern layers, each of said polyimide films being formed through a heat process with which solvent of liquid polyimide is removed to harden the same so as to provide a flat insulating layer; and means for establishing electrical connection between said spiral pattern layers, said means comprising a conductive member connected between any two consecutive spiral pattern layers; said pair of coils being arranged so that they are symmetrical with a center line which bisects said coil assembly.