Thermal head

Abstract: A thermal head of a real edge type which includes an insulative substrate (B), a plurality of heat generating resistors (R) provided at one edge on an upper surface of the insulative substrate in a parallel relation to the one edge, and individual lead patterns (Se) and a common lead pattern (Ce) provided at an edge of each of the heat generating resistors (R) to extend in a direction at right angles with an aligning direction of the heat generating resistors, in which the extended length of the respective common lead (Ce) patterns is made longer than those of the individual lead patterns (Se) so as to project beyond bonding pad portions of the individual lead patterns, with a common collective pattern directed in a parallel relation with the aligning direction of the heat generating resistors (R) being provided at the extended projecting end portions of the common lead patterns.

Description: The present invention generally relates to a thermal head construction, and more particularly, to a thermal head to be used in a heat transfer printer or the like. In Fig. 4, there is shown a conventional thermal head of a so-called line type, which includes a substrate B, for example, of alumina ceramic material (insulative substrate), a plurality of pairs of heat generating resistors R provided by forming a heat generating resistant film over an upper surface of said substrate B, a common lead pattern (or common electrode) Ce and individual lead patterns (or separate electrodes) Se respectively formed on the substrate B at the sides along opposite side edges Ra and Rb of the respective heat generating resistors R in a state confronting each other, and a protective film (not particularly shown) further formed over surfaces of said heat generating resistors R, and the lead patterns Ce and Se. The known thermal head as described above is so arranged that, by causing the heat generating resistors R to selectively generate heat through impression of a pulse voltage across the lead patterns Ce and Se (i.e. the common electrode and separate electrodes), information is to be printed on a recording paper fed in a state overlapped under pressure with a thermo-sensitive paper (thermo-sensitive ribbon) with respect to said heat generating resistors R. In the conventional line type thermal head (i.e. a thermal head in which many heat generating dots are arranged in a direction intersecting at right angles with respect to the direction of displacement of the recording paper) as referred to above, the lead patterns Ce and Se are respectively formed at the opposite side edges Ra and Rb of the heat generating resistors R as shown in Fig. 4. In other words, the separate lead patterns Se are provided along the side edge Rb of each of the heat generating resistors R, while the common lead pattern Ce is disposed at the side of the other edge Ra thereof, respectively. Accordingly, between the side edge Ra of the heat generating resistors R and a corresponding side edge Ba of the insulative substrate B, the common lead pattern Ce of the predetermined width is located, and thus, there has been such a disadvantage that in the line type thermal head, a so-called real edge type thermal head in which the heat generating resistors are disposed to be aligned at one side edge of the insulative substrate (i.e. to be closely disposed thereat) can not be constituted. Meanwhile, in the serial type thermal heads, there is one type which adopts an edge type thermal head as shown in Fig. 2, which includes an insulative substrate B′, a plurality of pairs of meander type heat generating resistors R′ aligned at side edges Ra′ thereof with respect to one side edge Ba′ of the substrate B′ in a parallel relation thereto, and individual lead patterns (separate electrodes) Se′ provided at opposite side edge Rb′ of each pair of the resistors R′, with a common lead pattern Ce′ being disposed between said individual lead patterns Se′ as shown. Thus, the common lead pattern Ce′ and the individual lead pattern Se′ are arranged in a so-called return-pattern shape. More specifically, the short common lead pattern Ce′ is drawn out from the central portion at the side edge Rb′ of each meander type heat generating resistor R′ in a direction away from said resistor, while the individual lead patterns Se′ longer in lengths than said common lead pattern Ce′ are also extended in a parallel relation with said individual lead patterns Se′ from the side edge Rb′ of said resistor R′. In the thermal head of Fig. 2 having construction as described above, since the common lead pattern Ce′ is not located between one edge Ra′ of each heat generating resistor R′ and corresponding one edge Ba′ of said insulative substrate B′, it is possible to construct the so-called real edge type head in which the heat generating resistors R′ are located along the side edge Ba′ of said substrate B′. In the thermal head as explained so far, however, it is so arranged that the respective common lead patterns Ce′ of the resistors R′ are bonded to each other by bonding wires W, and connected to a collective pattern Cp formed adjacent to one side edge of said substrate B′. Accordingly, if the construction of such edge type thermal head is employed for the line type thermal head having many heat generating dots, not only the work for the wire bonding is complicated, but there is a possibility that the common drop takes place, and thus, the construction can not be applied thereto. On the other hand, there has also been conceived another arrangement as shown in Fig. 3, which is of the serial type thermal head, and adopts the edge type head construction as explained above with reference to Fig. 2, and in which lead patterns (individual lead patterns and common lead patterns) are connected through a flexible circuit board B″. More specifically, in the arrangement of Fig. 3, conductor patterns, i.e. a common conductor Cc and separate conductors Sc respectively corresponding to the common lead patterns Ce″ and the individual lead patterns Se″ are formed on a flexible circuit board B″, and the respective patterns are connected by overlapping said patterns each other. In the construction of Fig. 3, although the complicated wire bonding work and the disadvantage of the common drop may be eliminated, there have been such disadvantages that the expensive flexible circuit board is required, while a pressing mechanism for contacting under pressure, the respective lead patterns in the overlapped state also becomes necessary. A thermal head according to the preamble part of claim 1 is disclosed in JP-A-6221559. In this thermal head a drive IC is provided besides the collective pattern. Furthermore, the resistors are arranged in a distance from the edge of the substrate. Also in thermal head known from JP-A-61148072 and JP-A-61141572 resistors are arranged distant from the edges of the substrate, and the ICs are arranged on the substrate which necessitates a complicated wiring pattern. It is accordingly an essential object of the invention to provide a thermal head of a line head type which is capable of realizing a real edge type, and facilitated in the connection of common lead patterns thereof. It is another object of the invention to provide a thermal head of the above described type which is simple in construction and stable in functioning and can be readily manufactured on a large scale at low cost. The objects are achieved by a thermal head as defined in claim 1; the remaining claims are related to further developments of the invention. In the thermal head having the construction as described above, a plurality of pairs of meander type heat generating resistors (two heat generating resistors are formed into one pair) are aligned in a parallel relation with respect to one side edge of the insulative substrate. At the other side edge of each pair of the heat generating resistors, the common lead pattern and the individual lead patterns are disposed. In each pair of the heat generating resistors, the common lead pattern and the individual lead pattern are led out in a so-called return pattern. More specifically, the common lead pattern is led out from the central portion of the heat generating resistor pair, while the individual lead patterns are respectively led out from opposite sides (heat generating resistor portions) of said heat generating resistor pair in a parallel relation with said common lead pattern, with said common lead pattern being extended beyond the ends of the individual lead patterns located at its opposite sides. In other words, each common lead pattern is extended in a direction opposite to the heat generating resistor and towards the other side edge of the insulative substrate so as to further extend or project beyond bonding pad portions at the forward ends of the individual lead patterns. At the extended ends of the respective common lead patterns, there is further formed a common collective pattern (or a unified common lead) in a direction parallel to the aligned heat generating resistors. Accordingly, the connection of the respective common lead patterns may be effected in an etching manufacturing stage. Furthermore, since it is not required to connect the respective common lead patterns to the common collective pattern through bonding by wires or to effect the connection under pressure through employment of a flexible substrate, a line type thermal head capable of realizing the real edge type may be provided at low cost. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which; Fig. 1 is a fragmentary top plan view showing construction of a thermal head according to one preferred embodiment of the present invention, Fig. 2 is a fragmentary top plan view showing one example of a serial type thermal head employing a real edge type construction (already referred to), Fig. 3 is also a fragmentary top plan view showing the state where respective common lead patterns are to be connected by a flexible circuit substrate (already referred to), and Fig. 4 is a view similar to Fig. 1, which particularly shows an essential portion of a conventional line type thermal head (already referred to). DETAILED DESCRIPTION OF THE INVENTION Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. Referring now to the drawings, there is shown in Fig. 1, an essential portion of a thermal head according to one preferred embodiment of the present invention, which generally includes an insulative substrate 5, for example, of an alumina ceramic material, a plurality of pairs of heat generating resistors 1, for example, of a meander type each corresponding to two dots, and formed on the upper surface of the substrate 5 along its one side edge 5a, and a common lead pattern 2 (common electrode) and individual lead patterns 3 (separate electrodes) formed on each pair of the heat generating resistors 1, and a protective film (not particularly shown) formed over the surfaces of the substrate 5, the heat generating resistors 1 and the lead patterns 2 and 3. The embodiment in Fig. 1 shows a so-called thin film type line head (i.e. a head in which many heat generating dots are aligned in parallel along one side edge of the substrate). The thermal head according to the present invention as shown in Fig. 1 is characterized in that the plurality of pairs of the meander type heat generating resistors 1 are aligned each in its one edge 1a in a parallel relation along the corresponding one side edge 5a of the insulative substrate 5, while the individual lead patterns 3 and the common lead pattern 2 are led out from the other side edge 1b of each of the resistors 1, with the length of the common lead pattern 2 being set to be longer than those of the individual lead patterns 3. Each pair of the meander type heat generating resistors 1 is formed by providing a notch 11 at a central portion of a resistive plate so as to form heat resistor portions 1R at opposite sides, and open sides of these notches 11 are aligned to be directed towards the one side edge 5a of the substrate 5 to form an edge type head. Meanwhile, in each pair of the resistors 1, the common lead pattern 2 and the individual lead patterns 3 are disposed in a so-called return pattern form. More specifically, the common lead pattern 2 is led out from the other edge 1b of the resistor pair 1 (i.e. the edge 1b thereof remote from the corresponding side edge 5a of the insulative substrate 5), at a position corresponding to the central notch portion 11 in a direction away from said resistor pair 1. The individual lead patterns 3 are led out from the opposite sides of the resistor pair 1, i.e. from the respective heat generating resistor portions 1R in a direction parallel to the common lead pattern 2. Moreover, the above common lead pattern 2 is set to be longer in length than the individual lead patterns 3. In other words, the common lead pattern 3 is extended towards the other side edge of the substrate 5 so that the forward end of the common lead pattern 3 extends longer beyond bonding pad portions 31 and 31′ at the forward ends of the individual lead patterns 3. Furthermore, at extended end portions 21 of said common lead patterns 2, a common collective pattern 4 (or a unified common lead) is formed in a direction parallel to the aligning direction of the meander type heat generating resistor pairs 1. On the above common collective pattern 4, for example, a drive IC 6 is mounted, with pads 61 provided on the drive IC 6 and the bonding pad portions 31 of the individual lead patterns 3 being bonded to each other by bonding wires W as shown. In the thermal head (i.e. line type head) having the construction as described above, many meander type heat generating resistor pairs 1 are aligned along the one side edge 5a of the insulative substrate 5, while the common lead pattern 2 in each resistor pair 1 is extended longer than the individual lead patterns 3, with the common collective pattern 4 being formed at the extended end portions 21 of the common lead patterns 2 as explained above. Therefore, the connection of the respective common lead patterns 3 with the common collective pattern 4 can be effected at the etching manufacturing stage. Moreover, it is not required to bond the respective common lead patterns 3 by bonding wires, or to connect them by the flexible substrate and the like. Accordingly, the line type thermal head capable of realizing the real edge type head may be provided through simple processing. As is clear from the foregoing description, according to the present invention, the thermal head is constituted by the insulative substrate, the plurality of heat generating resistors provided at one edge on the upper surface of the insulative substrate in a parallel relation to said one edge, and the individual lead patterns and common lead pattern provided at the edge of each of said heat generating resistors to extend in a direction at right angles with the aligning direction of said heat generating resistors, wherein the extended length of the respective common lead patterns is made longer than those of the individual lead patterns so as to project beyond the bonding pad portions of said individual lead patterns, with the common collective pattern directed in a parallel relation with the aligning direction of said heat generating resistor being provided at the extended projecting end portions of said common lead patterns. Therefore, even in the line type head having a large number of heat generating dots, it becomes possible to realize the real edge type thermal head. Moreover, since the common lead patterns are made longer to extend beyond the bonding pad portions of the individual lead patterns, the common collective pattern for connection with respective common lead patterns may be disposed at the other side edge portion of the insulative substrate. Accordingly, the connection of the respective common lead patterns may be effected at the etching manufacturing stage, and thus, not only the complicated work for wire-bonding the respective common lead patterns as conventionally required is eliminated, but the disadvantage for connection under pressure through employment of the expensive flexible circuit board, etc. may also be eliminated to achieve the object of the present invention.

Claims: A thermal head of a real edge type which comprises an insulative substrate (5), a plurality of heat generating resistors (1) provided on an upper surface of said insulative substrate (5) in a parallel relation to said one edge (5a), and individual lead patterns (3) and a common lead pattern (2) provided at an edge (1b) of each of said heat generating resistors (1) to extend in a direction at right angles with an aligning direction of said heat generating resistors (1), wherein the extended length of the respective common lead patterns (2) is made longer than those of the individual lead patterns (3) so as to project beyond bonding pad portions (31) of said individual lead patterns (3), each of said bonding pad portions (31,31') being aligned with the corresponding of said resistors in a direction perpendicular to said edge (5a), with a common collective pattern (4) directed in a parallel relation with the aligning direction of said heat generating resistors (1) being provided at the extended projecting end portions of said common lead patterns (2), characterized in that said heat generating resistors (1) are provided at one edge (5a) of said insulative substrate, that a drive IC device is provided above the collective pattern (4), and that all bonding pads (61) of said IC device are arranged parallel to said edge (5a) and being aligned with said bonding pads of said individual lead patterns (3) in said perpendicular direction. A thermal head as claimed in claim 1, wherein said insulative subsrate (5) is of an alumina ceramic material. A thermal head as claimed in claim 1, wherein said heat generating resistors (1) are of meander type. A thermal head as claimed in claim 1, wherein a protective film is further formed over said substrate (5), heat generating resistors (1), and lead patterns (2, 3, 4). A thermal head as claimed in claim 1, wherein the bonding pads (64) of said drive IC device and the bonding pads of said individual lead patterns are bonded to each other by bonding wires.

Inventors: NAKANISHI MASATOSHI, NAKANISHI, MASATOSHI
Applicants: ROHM CO LTD, ROHM CO., LTD.
Application year: 1990
Main classification: B41J2
IPC codes: B41J2