Thin film magnetic head having Au ultrasonic connection structure

Conductor film terminals of a thin film magnetic head are composed of an Au film while lead terminals of a flexible printed circuit board are covered with an Au layer, so that both of these terminals can be bonded by low temperature ultrasonic bonding directly between Au and Au. The reverse surface of the lead terminals of the flexible printed circuit board is bonded and fixed to a flexible polymer resin cover film so that the dimensional accuracy of the bonded terminal portion can be improved.

BACKGROUND OF THE INVENTION 
This invention relates generally to inductive type and magnetoresistive 
type thin film magnetic heads, and more particularly to connection between 
a conductor film terminal and a flexible printed circuit board. Here, the 
term "conductor film terminal" means an external connection terminal for 
applying a current to a thin film magnetic head and inputting an input 
signal or outputting an output signal, made of a conductor film. 
A thin film magnetic film consists of a head element fabricated by use of 
thin film processing technique such as sputtering, vacuum deposition, 
photoetching, and so forth. Particularly because delicate machining is 
possible, the thin film magnetic head can accomplish high density 
packaging and can realize a magnetic head having a small track width. The 
inductive type thin film magnetic head is produced by forming a lower thin 
magnetic film of permalloy (high permeability Ni-Fe alloy such as Ni-25%Fe 
alloy) or the like on a non-magnetic substrate such as glass by plating or 
vacuum deposition, forming then a conductor film having a predetermined 
pattern in such a manner as to cover the lower thin magnetic film, forming 
an upper thin magnetic film on the conductor film through an insulating 
film and extending the conductor film on the thin magnetic film head 
substrate for external connection. 
Accordingly, the terminal width of the conductor film becomes very small as 
the track width becomes small. When the substrate of the thin film 
magnetic head is made of a magnetic material such as ferrite and is used 
also as the lower thin magnetic film, the terminal width of the conductor 
film becomes very small, too, with miniaturization of the track width. On 
the other hand, a thin film magnetic head of a magnetoresistive type which 
is used for reproduction only employs a magnetoresistive element, but the 
terminal width of the conductor film becomes likewise very small with the 
increase in the number of tracks. It is therefore necessary to improve the 
pitch accuracy between the terminals of adjacent tracks due to external 
connection. Moreover, a connection structure is necessary for external 
connection at the terminal of the conductor film which does not exert 
adverse influences on the thin film formation portion. 
Hereinafter, a prior art example will be explained. Generally, the 
conductor film terminals 3 for external connection are formed on the 
surface of the magnetoresistive element 4 on the non-magnetic substrate 
2', as shown in FIG. 4 and these conductor film terminals 3 are connected 
to a large number of lead terminals 7 exposed at one of the ends of the 
flexible printed circuit board 6 by a wire 12 made of Au, Al or the like. 
A connection method which connects both ends of wire to the counter-part 
is employed for this connection in accordance with wire bonding technique 
or the like. However, since connection is made at both ends of the Al or 
Au wire 12 and between a large number of terminals, bonding connection is 
necessary at a large number of spots. Incidentally, reference numeral 1 in 
FIG. 4 represents the thin film magnetic head and 5 does the insulating 
film. 
The head described in another prior art reference, i.e. Japanese Patent 
Laid Open No. 172106/1984, will be explained. FIG. 5 of the accompanying 
drawings shows the main structural portion of the multi-channel thin film 
magnetic head 1 of this prior art. The magnetoresistive element 4 made of 
Fe-Ni alloy or Ni-Cr alloy is formed on the non-magnetic substrate 2' and 
the conductor film terminal 3 for connection with the flexible printed 
circuit board 6 is formed on the magnetoresistive element 4. The lead 
terminal 7 of the flexible printed circuit board 6 consisting partly of a 
transparent member 8' has Sn-Pb alloy 9' put thereto. After the lead 
terminal 7 is located to the conductor film terminal 3, laser beam is 
radiated through a glass sheet 13 to fuse the Sn-Pb alloy 9' so that a 
large number of connection spots between the lead terminal 7 of the 
flexible printed circuited board 6 and the conductor film terminal 3 can 
be connected exclusively by a reflow soldering method. Incidentally, 
reference numeral 10 in FIG. 5 represents a base film and 5 represents the 
insulating film. 
The structure of the prior art techniques described above wherein the 
flexible printed circuit board and the conductor film of the thin film 
head are connected at both ends of the Al or Au wire involves the problem 
that since the number of connection points is great, workability is low 
and the number of manhour increases. The other prior art reference 
described above, i.e. Japanese Patent Publication No. 172106/1984, 
requires essentially the structure wherein the upper part of the lead 
terminal of the flexible printed circuit board is composed of the 
transparent material in order to fuse the solder of the lead terminal by 
use of the laser beam. Therefore, this technique is not suitable for the 
flexible printed circuit board having an opaque portion and imposes a 
structural limitation to the flexible printed circuit board. In order to 
fuse the solder, the connection portion must be heated to a high 
temperature near 300.degree. C. and not only the conductor film at the 
connection corresponding portion but also the thin film head structure 
itself must have heat resistance to this temperature. Accordingly, the 
structure of the thin film head element is limited by the problem of 
connection. Moreover, accuracy of pitch cannot be kept at the time of high 
density packaging due to non-uniformity of the thickness of the Sn-Pb 
alloy layer on the lead terminal of the flexible printed circuit board or 
due to the thermal deformation of the film on the reverse of the lead 
terminal of the flexible printed circuit board, and adjacent terminals are 
likely to come into contact with one another. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a connection structure 
which does not exert any adverse influences on a thin film head structure 
when connecting the lead terminal of the flexible printed circuit board to 
the terminal of the conductor film of the thin film magnetic head, which 
keeps highly accurate connection, and which makes it possible to carry out 
low temperature bonding with a high level of workability. 
The object of the invention described above can be accomplished by making 
it possible to connect both terminals by an ultrasonic bonding method with 
a low temperature rise by forming an Au film as the terminal of the 
conductor film of the thin film magnetic head and an Au layer of the lead 
terminal of the flexible printed circuit board, and by bonding and fixing 
the lead terminal of the flexible printed circuit board to the flexible 
film of the flexible printed circuit board while keeping the dimensional 
accuracy between the lead terminals at a high level of accuracy. 
Namely, the thin film magnetic head in accordance with the present 
invention includes (i) conductor film terminals for applying a current to 
a head and inputting an input signal or picking up an output signal and 
(ii) a flexible printed circuit board having lead terminals connected to 
the conductor film terminals, wherein at least the surface of the 
conductor film terminal is made of an Au film, the surface of the lead 
terminal is made of an Au layer, the Au film and the Au layer are bonded 
to each other, the surface of the lead terminal on the opposite side to 
the bonded surface to the conductor film terminal is bonded and fixed to a 
flexible film (cover film) and this flexible film covers the bond portion 
between the Au film and the Au layer. 
The thin film magnetic head in accordance with the present invention may 
have the same structure as that of the thin film magnetic head of the 
prior art except that at least the surface of the conductor film terminal 
and the surface of the lead terminal of the flexible printed circuit board 
are made of Au and the lead terminal is fixed to the flexible cover film 
on its surface opposite to the bonded surface to the conductor film 
terminal. 
In the present invention, the Au film is formed as the conductor film 
terminal in order to improve corrosion resistance of the conductor film 
when a large number of conductor film terminals of the thin film magnetic 
head are connected to the lead terminals of the flexible printed circuit 
board, and the Au layer is formed on the surface of a large number of lead 
terminals of the flexible printed circuit board. This structure makes it 
possible to employ the ultrasonic bonding technique for the connection 
between them. Therefore, any adverse influences resulting from the 
temperature rise at the time of the connecting operation upon other 
constituent elements such as the conductor film, the magnetoresistive 
element film, and the like, are not exerted. Moreover, the reverse surface 
of a large number of lead terminals of the flexible printed circuit board 
(that is, the surface opposite to the conductor film terminals) is bonded 
to and fixed by the cover film so that the pitch accuracy of the lead 
terminals of the flexible printed circuit board can be improved and 
troubles such as contact between the adjacent terminals, insulation 
defect, and the like, do not occur due to improvement in the connection 
accuracy with the conductor film terminals. Since the present invention 
does not use the wire connection method, workability is high.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, one embodiment of the present invention will be described with 
reference to FIGS. 1, 2 and 3. As shown in FIG. 1, an insulation film 5 of 
Al.sub.2 O.sub.3 or the like is formed on a magnetic substrate 2 of 
ferrite or the like by sputtering, and a magnetoresistive element 4 made 
of Ni-Fe alloy or the like is formed on the insulation film 5 by vaccum 
deposition, and is shaped by photoetching, or the like technique. 
Furthermore, the same insulation film 5 of Al.sub.2 O.sub.3 as described 
above is again formed on the magnetoresistive element 4 by sputtering and 
photoetching. A block 11 made of the same material as, or a different 
material from, the material of the substrate 2 is bonded and fixed on this 
second insulation film 5 by an adhesive 14. 0n the other hand, a plurality 
of conductor film terminals 3 of the thin film magnetic head 1 are 
positioned on the upper insulation film 5 of Al.sub.2 O.sub.3 and the 
magnetoresistive element 4 and a 0.03 to 0.15 .mu.m-thick Ti film 15 as a 
under film is formed thereon as a connection surface to the outside by 
sputtering, or the like. Furthermore, a 0.5 to 1.0 .mu.m-thick Au film as 
a corrosion-resistant conductor film is formed by sputtering, and, 
thereafter they are shaped. Cr, Ta or Mo film may be used in place of this 
Ti film 15. 
The Au film 17 of the conductor film terminals 3 is from 0.2 to 1.5 .mu.m 
thick. In this embodiment, the Au film 17 is 0.5 to 1.0 .mu.m thick. If 
this thickness is below 0.2 .mu.m, quality of the Au film becomes 
nonuniform and if it is above 1.5 .mu.m, bonding strength of the Au film 
drops, undesirably. 
The conductor film terminal is 0.16 mm wide and the pitch between the 
conductor film terminals is 0.315 mm. These terminals extend on the side 
opposite to the surface facing a magnetic recording medium. 
The flexible printed circuit board 6 to be connected to the conductor film 
terminals 3 as the output port of the thin film magnetic head 1 has the 
structure such as shown in FIG. 3. Namely, a large number of lead 
terminals 7 are bonded to a flexible cover film 8 made of a polymer resin 
together with a base film 10 which is cut away partially, and the 
dimensional errors of the pitch between the lead terminals and the width 
of each terminal are suppressed within about .+-.0.02. Examples of the 
polymer resin constituting the flexible cover film 8 are a polyimide resin 
and a polyester resin. The cover film 8 is from 12.5 to 50 .mu.m thick, 
and it is 25 .mu.m thick in this embodiment. If the thickness of the cover 
film is within this range, ultrasonic bonding can be made between the 
conductor film terminals and the lead terminals by putting the tool of 
ultrasonic bonding from above the cover film. 
Each lead terminal 7 is made of a Cu material having an Au layer 9 
deposited on its surface by plating, or the like. The Au layer 9 is 
preferably from 1 to 10 .mu.m thick, and it is 5 .mu.m .+-.1 .mu.m thick 
in this embodiment. If the thickness of the Au layer is smaller than the 
range described above, the Au layer is likely to become non-uniform and if 
the thickness is above the range, the production cost will become higher, 
undesirably. 
Examples of the adhesive for fixing the lead terminals 7 to the cover film 
8 are epoxy type adhesives and acrylic type adhesives. 
The cover film 8 covers the reverse surface of all the lead terminals 
connected to the conductor film terminals and extends from the upper 
surface of the lead terminal portion to a connector connection portion of 
the flexible printed circuit board (which exists on the opposite side of 
the printed circuit board to the lead terminal side, and is not shown in 
the drawing). The cover film 8 covers also the entire surface of the 
printed circuit board with the exception of holes for connector 
connection. The base film 10 is cut partly and the cover film 8 is 
exposed. This exposed length l is from 0.5 to 1.5 mm. 
In this embodiment, the lead terminal 7 is 0.035 mm high and 0.06 to 0.1 mm 
wide, and the pitch between the lead terminals is 0.315 mm. 
FIG. 2 is a perspective view showing the state where the conductor film 
terminals 3 of the thin film magnetic head 1 having the structure 
described above are bonded to the flexible printed circuit board 6 by an 
ultrasonic bonding method with a small temperature rise, and FIG. 1 shows 
the section of the connection portion between them. The connection portion 
provides the structure suitable for ultrasonic bonding at a low 
temperature between Au and Au by the combination of the Au layer 9 of the 
lead terminals 7 of the flexible printed circuit board 6 and the Au film 
17 of the conductor film teminals 3. The bonding temperature in this case 
is from 10.degree. C. to 100.degree. C. As to location of the connecting 
positions, the positions of the lead terminals 7 can be seen by operator's 
eyes with the cover film 8 is transparent or translucent. Therefore, each 
lead terminal 7 can be located to the center of the width of each 
conductor film terminal 3. If the cover film 8 is opaque, location can be 
made by setting in advance the distance from the end portion of the 
flexible printed circuit board 6 to the outermost lead terminal 7 and 
setting the relation of position between this outermost lead terminal 7 
and the conductor film terminal to be connected by disposing a reference 
guide, or the like. 
Furthermore, connection can be made by putting the bonding tool from above 
the cover film 8 and through this cover film 8. Namely, since the cover 
film 8 can be as thin as about 25 .mu.m, it is crushed to form a push 
trace 16 and to transmit the push force as such to the Cu conductor when 
the bonding tool is pushed from above the cover film 8 to the Cu conductor 
having Au deposited thereto with the push force of about 20 kg/mm.sup.2, 
so that the surface between Au of the conductor film and Au of the lead 
terminal is made flat with ultrasonic oscillation, the frictional 
coefficient between them becomes great, and the lead terminal 7 undergoes 
deformation, that is, it causes plastic flow with the result being the 
increase in the adhesion area and bonding between Au and Au. 
The push force of ultrasonic bonding described above is preferably from 2 
to 60 kg/mm.sup.2. In this embodiment, it is 20 kg/mm.sup.2. In this 
embodiment, ultrasonic bonding is made at the power of 20 W maximum, 
frequency of 35 to 110 KHz and the application time of ultrasonic wave of 
from 0.2 ms to 7 s. 
In this embodiment, the temperature rise around the bond portion by 
ultrasonic bonding is at most about 20.degree. C. 
In FIG. 3, reference numeral 18 represents the adhesive. 
This embodiment provides the following effects. First of all, the conductor 
film terminals 3 and the lead terminals 7 of the flexible printed circuit 
board 6 can be connected without causing any thermal problems of the 
constituent elements such as the conductor film of the thin film magnetic 
head. Second, the dimensional accuracy of the flexible printed circuit 
board 6 itself can be improved by use of the lead terminals 7 equipped 
with the cover film, whether it may be transparent or opaque, so that 
connection accuracy can be improved and the problems such as contact 
between the adjacent terminals at the connection portion can be 
eliminated. Thirdly, since the cover film is attached to the reverse 
surface of the lead terminals, the production yield of the flexible 
printed circuit board 6 can be improved and the cost of production of the 
components can be reduced. 
FIG. 6 shows another embodiment of the present invention, wherein the 
structure of the flexible printed circuit board 6 shown in FIG. 3 is 
changed to the structure shown in FIG. 6 in which the flexible film 8 and 
the flexible base film 10 are bonded and fixed to both surfaces of the 
lead terminals at part of the tip. In this case, too, the structure of the 
connection portion is the same as that of the foregoing embodiment and its 
effect can be regarded as the same, too. 
In FIG. 6, reference numerals 18 and 18' represent the adhesive. 
In the embodiment given above, the present invention is applied to the 
magnetoresistive type thin film magnetic head, but the invention provides 
the same effect when applied to the inductive type thin film magnetic head 
by using the conductor film terminal as the coil terminal. 
In each of the drawings, like reference numerals are used to identify like 
constituents. 
In accordance with the present invention, the structure of the connection 
portion consists of connection between Au and Au. Therefore, low 
temperature bonding becomes possible and the influences of heat on the 
thin film head structure at the time of connection can be almost 
eliminated. Since the flexible printed circuit board having the lead 
terminals, which are equipped with the flexible film, is employed and 
since low temperature bonding connection is possible, pitch accuracy 
between the lead terminals as well as connection accuracy can be improved 
and since connection accuracy can thus be improved, problems such as 
mutual contact of the adjacent terminals and insulation defect, and the 
like, can be eliminated. 
Though the present invention has thus been described in its preferred form, 
it is to be understood that various changes and modifications can be made 
by those skilled in the art without departing from the spirit and scope 
thereof.