JPH0948148A - Flexible printed circuit board and thermal head using that - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent irregurality in shading of a printed image from being generated owing to a bend of a thermal head by a method wherein at least one bend part is provided midway to a wiring conductor of a flexible printed circuit board on which a plurality of terminal conductors each one end of which is connected to the wiring conductor are arranged vertically to one side of the substrate. SOLUTION: A wiring conductor 8a of a flexible printed circuit(FPC) 7, when external force compressing in a length direction of a ceramic substrate 1 is applied, absorbs the external force by being deformed so that an opening part of a bend part A is narrowed. Further, when tensile external force is applied, external force deforming the opening part of the bend part A so as to open is absorbed. Therefore, though heat is applied when the ceramic substrate 1 is soldered to the FPC 7, or heat is generated following operation of a thermal head, stress caused by heat thereof is absorbed by deformation of the bend part A provided to the wiring conductor 8a, and a bend of the thermal head is effectively prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed wiring board used for connecting a plurality of electric circuits and the like and a thermal head using the same.

[0002]

2. Description of the Related Art FIG. 7 is a plan view showing a conventional flexible printed wiring board (hereinafter abbreviated as FPC) applied to a thermal head.

The conventional thermal head shown in FIG. 1 has a heating element array 12 including a large number of heating elements arranged in a straight line.
And a rectangular ceramic substrate 11 to which a plurality of driving ICs 16 for controlling Joule heat generation of the heating element are attached.
And an FPC 13 having a plurality of wiring conductors 14 arranged substantially parallel to the long side of the ceramic substrate 11, and the FPC 1 along the long side of the ceramic substrate 11.
It has a structure in which 3 is connected by solder or the like.

Such a conventional thermal head has a driving I
As the C16 is driven, the heating element is selectively caused to generate Joule heat, and the generated heat is conducted to a recording medium such as thermal recording paper to form a predetermined print image on the recording medium, thereby functioning as a thermal head. .

The FPC 13 has a structure in which a wiring conductor 14 made of copper foil or the like is attached to a flexible substrate made of polyimide resin or the like, and a connector 15 attached to one end of the FPC 13 is provided. Is connected to a connector (not shown) of the printer body so that the thermal head is electrically connected to the printer body.

In the vicinity of one long side of the ceramic substrate 11, a conductive layer as a common electrode for supplying power to all the heating elements, a power supply line for supplying power and control signals to each driving IC 16, A plurality of conductive layers as control signal lines are led out, and these conductive layers are respectively connected to the terminal conductors of the FPC 13 on the long side of the ceramic substrate 11 and have the same function as the wiring conductor 14 in the FPC 13 (to the heating element). Power supply function, drive IC power supply function, control signal supply function, etc.) are commonly connected to each group.

[0007]

However, in such a conventional example, while the thermal expansion coefficient of alumina or the like forming the ceramic substrate 11 is about 7.3 × 10 ⁻⁶ cm · ° C. ⁻¹ , the FPC 13 Since the thermal expansion coefficient of copper or the like forming the wiring conductor 14 in the inside is largely different from about 1.7 × 10 ⁻⁵ cm · ° C. ⁻¹ , when the ceramic substrate 11 and the FPC 13 are soldered or the thermal head is operated. At this time, the ceramic substrate 11 and the FP are heated by the heat applied accordingly.
A large thermal stress is generated between the thermal head and C13, and the thermal head is curved into a shape as shown in FIG. As a result, the heating element array 12 on the ceramic substrate 11 is also curved into a shape similar to that of the thermal head, and it becomes impossible to press the heating element array 12 against the recording medium with a constant strength, so that the recording medium is It had a defect that unevenness in the printed image was formed.

[0008]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks, in which a strip-shaped wiring conductor parallel to one side of the substrate is arranged on a flexible substrate having a rectangular shape. An FPC in which a plurality of terminal conductors, one end of which is connected to the wiring conductor, are arranged in a direction perpendicular to one side of the substrate, wherein at least 1 is provided in the middle of the wiring conductor.
It is characterized by having two curved portions.

Further, the present invention is characterized in that the wiring conductor is made of copper and the curved portion has an arc shape having a radius of 1.5 times or more the width of the wiring conductor.

Further, according to the present invention, the heating element is electrically connected to the long side end of the rectangular ceramic substrate provided with the heating element row, and is arranged substantially parallel to the long side of the ceramic substrate. A thermal head formed by attaching an FPC having a wiring conductor, wherein at least one curved portion is provided in the middle of the wiring conductor of the FPC.

Further, according to the present invention, a strip-shaped wiring conductor parallel to one side of the substrate is arranged on a flexible substrate having a rectangular shape, and a plurality of terminals whose one end is connected to the wiring conductor. An FPC in which conductors are arranged in a direction perpendicular to one side of the substrate, wherein a void is provided in the middle of the wiring conductor to divide the wiring conductor into a plurality of locations,
The divided adjacent wiring conductors are connected by a connecting member having a length longer than the gap width.

Still further, according to the present invention, the heating element is electrically connected to the long side end of the rectangular ceramic substrate provided with the heating element array, and is arranged substantially parallel to the long side of the ceramic substrate. A thermal head formed by attaching an FPC having wiring conductors, wherein a space is provided in the middle of the wiring conductors of the FPC to divide the wiring conductors into a plurality of locations, and the divided adjacent wirings. The conductor is connected by a connecting member having a length longer than the gap width.

[0013]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

(First Embodiment) FIG. 1 is a plan view showing a first embodiment of a thermal head, FIG. 2 is a sectional view taken along line XX of FIG.
FIG. 3 is a partially enlarged view schematically showing a form in which thermal stress is absorbed. 1 is a ceramic substrate, 2 is a heating element array, and 7 is F.
PC, 8a are wiring conductors, 8b is a terminal conductor, and A is a curved portion provided in the middle of the wiring conductor 8a.

The ceramic substrate 1 is made of alumina or the like. For example, a slurry obtained by adding and mixing a suitable organic solvent and an organic binder to a ceramic material powder containing alumina as a main component is prepared by a conventionally known doctor blade method to produce a ceramic green sheet. Is formed, punched into a specified shape, and then fired at a high temperature (about 1600 ° C) to form a specified rectangular shape (length 220 mm × width 8 mm × thickness)
0.6-1.0mm) and its thermal expansion coefficient is about 7.3 ×
It becomes 10 ^-6 cm- ° C ^-1 .

On the upper surface of the ceramic substrate 1, there are arranged a plurality of heating elements in a linear array and a heating element array 2
A conductive layer 3 and an individual lead wire 4 connected to each of these heating elements as a common electrode for supplying electric power for causing Joule heating to the heating elements; A driving IC 5 and a power supply line for supplying driving power and a control signal to each driving IC 5 and a conductive layer 6 as a control signal line are provided.

Since the heating element is made of tantalum nitride or the like and has a predetermined electric resistivity,
When a predetermined electric power is applied, the temperature required to form a printed image on a recording medium such as thermal recording paper, for example, 300 ° C.
Joule heat is generated at a certain temperature.

Further, the conductive layer 3 and the individual lead wires 4 are for supplying a predetermined electric power to the heating element, and the conductive layer 3 is commonly connected to each one end of the heating element and is connected to one side of the ceramic substrate 1. Individual lead wire 4 derived to the vicinity of the long side
Are individually connected to the other ends of the heating elements and led out to the vicinity of the driving IC 5.

The heat generating element, the conductive layers 3 and 6, and the individual lead wires 4 are formed on the upper surface of the ceramic substrate 1 with a predetermined thickness by a thin film method such as a sputtering method and a photolithography technique.

A protective film made of silicon nitride or the like is deposited on the heating element in order to protect the heating element from abrasion due to sliding contact of the recording medium and oxidative corrosion due to contact with moisture in the atmosphere. It

On the other hand, as the driving IC 5, for example, a flip-chip type is adopted, and the driving IC 5 is connected to each of the other ends of the heating elements via the individual lead wires 4 on the lower surface thereof. It has a plurality of output terminals and an input terminal connected to the conductive layer 6, and functions to control Joule heat generation of the heating element based on a control signal supplied from the outside.

An FPC 7 having wiring conductors 8a arranged substantially parallel to the long side of the substrate 1 is attached to one end of the ceramic substrate 1 on the long side.

The FPC 7 comprises a copper foil (coefficient of thermal expansion: 1.7 × 10 ^-5 ) on a rectangular flexible substrate 7a made of a polyimide resin (coefficient of thermal expansion: 7.6 × 10 ^-6 cm · ° C. ^-1 ). cm
℃ ^-1 ) and the like, a plurality of strip-shaped wiring conductors 8a parallel to one side of the substrate 7a are deposited, and a plurality of terminal conductors 8b whose one end is connected to the wiring conductor 8a are attached to one side of the substrate 7a. Has a structure in which they are arranged in a vertical direction with respect to each other, and these are further covered with a cover member. By soldering the plurality of terminal conductors 8b to the conductive layers 3 and 6 on the ceramic substrate 1, the ceramic substrate 1 Is attached to. The FPC board 7 electrically connects the conductive layer 3 and the conductive layer 6 and the like adhered on the ceramic substrate 1 to the printer body through a connector 9 attached to one end of the FPC board 7. Electric power and various control signals are supplied to the heating element and the driving IC 5.

Further, the soldering of the FPC 7 and the ceramic substrate 1 is performed by soldering the end portion of the FPC 7 to the conductive layers 3 and 6 with the terminal conductor 8b on one long side end portion of the ceramic substrate 1. Overlap so that they touch each other, then about 30
It is performed by reflowing at a temperature of 0 ° C. to 400 ° C. and heating and melting the solder. The width of the solder joint portion at this time is set to about 0.5 mm, for example.

Further, F connected to the conductive layers 3 and 6
The terminal conductors 8b of the PC 7 are commonly connected to a plurality of wiring conductors 8a for each group having the same function (power supply function for heating element, power supply function for driving IC5, control signal supply function, etc.). In the middle of the wiring conductor 8a, a curved portion A having various shapes such as an arc shape, a triangle shape, and a quadrangle shape is predetermined so as to reduce the thermal stress applied to the ceramic substrate 1 in the longitudinal direction. It is provided at a plurality of locations at intervals of.

When the curved portion A is formed in an arc shape, for example, as shown in FIG. 3A, the width of the wiring conductor 8a is 1 m.
m, the radius of the arc is more than 1.5 times the width (for example, 1.5mm
) And the arrangement interval of the curved portions A is 18 mm.

A curved portion A provided in the middle of the wiring conductor 8a
If the shape of is to be triangular or quadrangular,
As shown in (a) and (b), the depth W of the curved portion A in the direction orthogonal to the arrangement direction of the wiring conductor 8a is set to the wiring conductor 8a.
The width should be 1.5 times or more.

The wiring conductor 8a of the FPC 7 as described above is
When an external force that compresses the PC 7 in the length direction of the ceramic substrate 1 is applied, as shown in FIG.
When an external force is applied to absorb the external force by deforming the opening portion of the FPC 7 so as to be narrow and to pull the FPC 7 in the longitudinal direction of the ceramic substrate 1, as shown in FIG. It is designed to absorb the external force by deforming so as to open the opening part of.

Therefore, even if heat is applied when the ceramic substrate 1 and the FPC 7 are joined by soldering, or if heat is generated due to the operation of the thermal head, the stress due to these heats causes the wiring conductor to have a stress. The bending portion A provided in 8a is absorbed by being deformed, and the bending of the thermal head is effectively prevented. As a result, it becomes possible to press the heating element array 2 against the recording medium with a constant strength, and it is possible to form a good printed image on the recording medium without uneven density.

At this time, the flexible substrate 7a of the FPC 7
The coefficient of thermal expansion of the polyimide resin that forms the film is 7.6 × 10 ^-6
cm · ° C. ^−1, which is higher than that of the copper forming the wiring conductor 8a (1.7 × 10 ⁻⁵ cm · ° C. ⁻¹ ) and the thermal expansion coefficient of the ceramic substrate 1 (7.3 × 10 ⁻⁶ cm · ° C.). ^-1 ) because it is close to
It has been confirmed that it has almost no effect on the curvature of the thermal head.

Thus, in the above-mentioned thermal head, a predetermined electric power is applied between the conductive layer 3 and the individual lead wire 4 in accordance with the driving of the driving IC 5 to selectively cause the heating elements to generate Joule heat and the generated heat. To a recording medium such as thermal paper to form a predetermined print image on the recording medium, thereby functioning as a thermal head.

The present invention is not limited to those shown in FIGS. 1 to 4, and various modifications and improvements can be made without departing from the scope of the present invention.
The wiring conductor 8a of the FPC 7 may be formed in a meandering shape as shown in FIG. 5, and in this case also, the thermal stress applied to the FPC 7 can be absorbed by the deformation of the wiring conductor 8a, and the bending of the thermal head can be prevented. It can be effectively prevented.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG.

FIG. 6 is a perspective view showing a second embodiment of the present invention. 7'is an FPC, 8a 'is a wiring conductor, 8b' is a wiring conductor, B is a terminal portion of the wiring conductor 8a ', and 10 is a wiring conductor. It is a connecting member.

The FPC 7'is, like the first embodiment described above, a strip-shaped wiring conductor parallel to one side of the substrate 7a 'on a flexible substrate 7a' having a rectangular shape (rectangular shape). 8a 'is arranged and one end is the wiring conductor 8
A plurality of terminal conductors 8b 'connected to a'is arranged vertically to one side of the substrate 7a'.

The difference between the second embodiment and the first embodiment is that a gap of a predetermined width is provided in the middle of the wiring conductor 8a 'to form the wiring conductor 8a' at a plurality of places (for example, 3). This is the point that the adjacent wiring conductors 8a ′ are connected to each other by a connecting member 10 having a length longer than the gap width C.

The wiring conductor 8a 'has a terminal portion formed by applying tin plating or the like to the connection portion of the connection member 10, so that the connection member 10 can be well soldered to the wiring conductor 8a'. I am trying to get it.

The connecting member 10 is composed of the wiring conductor 8a '.
For electrically connecting the respective divided portions of the wiring member, and as the connecting member 10, the gap width C provided in the wiring conductor 8a 'is used.
When is 5 mm, for example, a jumper wire having a length of 6 to 10 mm is used. The jumper wire has a structure in which a copper wire or an iron wire is covered with an insulating material such as vinyl chloride.

The wiring conductor 8a 'is provided on the FPC 7'.
When an external force for compressing is applied in the direction in which is arranged (the length direction in the figure), the external force is absorbed by deforming the gap width C so as to be narrow, and the wiring conductor 8a 'is arranged. When an external force is applied to pull in the direction, the external force can be absorbed by deforming to widen the gap width C.

Therefore, the FPC 7'is connected to the wiring conductor 8
When the thermal head is formed by attaching a'to the long side end of the ceramic substrate such that the a'is arranged substantially parallel to the long side of the ceramic substrate on which the heating element array is provided, the ceramic substrate and the FPC 7 ' Even if heat for soldering the two is applied or if heat is generated due to the operation of the thermal head, the stress due to these heats causes the width C of the void provided in the wiring conductor 8a '. Can be favorably absorbed and the thermal head can be effectively prevented from bending. This makes it possible to press the heating element array against the recording medium with a constant strength,
It is possible to form a good printed image without unevenness in density on the recording medium.

[0041]

According to the present invention, since the wiring conductor of the FPC is provided with the curved portion or the void capable of relieving the thermal stress, the heat is applied when the other wiring board is soldered to the FPC. However, the stress due to the heat is absorbed by the curved portion of the wiring conductor, and deformation such as warpage is effectively prevented.

Therefore, when the above-mentioned FPC is applied to the thermal head, the thermal head does not warp, and the heating element array is pressed against the recording medium with a constant strength, so that there is no uneven density in the recording medium. It becomes possible to form a printed image.

[Brief description of drawings]

FIG. 1 is a plan view showing a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line XX of FIG.

3A is a partially enlarged view of the FPC 7, and FIGS. 3B and 3C are diagrams schematically showing a state in which a predetermined force is applied to the FPC 7 in FIG.

FIG. 4 is a partially enlarged view showing a modified example of the first embodiment.

FIG. 5 is a partially enlarged view showing a modified example of the first embodiment.

FIG. 6 is a perspective view showing a second embodiment of the present invention.

FIG. 7 is a plan view of a conventional thermal head.

FIG. 8 is a plan view showing a state in which the thermal head is curved.

[Explanation of symbols]

 1 ... Ceramic substrate 2 ... Heating element array 3, 6 ... Conductive layer 4 ... Individual lead wire 5 ... Driving IC 8a ... Wiring conductor 8b ... Terminal conductor A ... Curved portion 10 ... Connection member

Claims (5)

[Claims] 1. A strip-shaped wiring conductor parallel to one side of the substrate is arranged on a rectangular flexible substrate, and a plurality of terminal conductors whose one end is connected to the wiring conductor are provided on the substrate. A flexible printed wiring board formed by arranging in a direction perpendicular to one side, wherein at least one curved portion is provided in the middle of the wiring conductor. 2. The flexible according to claim 1, wherein the wiring conductor is made of copper, and the curved portion has an arc shape having a radius of 1.5 times or more the width of the wiring conductor. Printed wiring board. 3. A wiring in which the heating element is electrically connected to a long side end of a rectangular ceramic substrate provided with a heating element array and is arranged substantially parallel to the long side of the ceramic substrate. A thermal head comprising a flexible printed wiring board having a conductor attached thereto, wherein at least one curved portion is provided in the middle of the wiring conductor of the flexible printed wiring board. 4. A strip-shaped wiring conductor parallel to one side of the substrate is arranged on a flexible substrate having a rectangular shape, and a plurality of terminal conductors whose one end is connected to the wiring conductor are provided on the substrate. A flexible printed wiring board arranged in a direction perpendicular to one side, wherein a space is provided in the middle of the wiring conductor to divide the wiring conductor into a plurality of places, and the divided adjacent wiring conductors are A flexible printed wiring board, which is connected by a connecting member having a length longer than the gap width. 5. A wiring in which the heating element is electrically connected to an end portion of a long side of a rectangular ceramic substrate provided with a row of heating elements and which is arranged substantially parallel to the long side of the ceramic substrate. A thermal head formed by attaching a flexible printed wiring board having a conductor, wherein a space is provided in the middle of the wiring conductor of the flexible printed wiring board to divide the wiring conductor into a plurality of places, and the divided adjacent The thermal head is characterized in that the wiring conductors are connected by a connecting member having a length longer than the gap width.