JPS6228260A - Thermal head - Google Patents

Abstract

PURPOSE:To miniaturize a thermal head by shortening the interval between heating resistors and IC chip for driving by a method in which a recession is formed on a substrate, and driving IC chip for heating resistor is buried in the recession. CONSTITUTION:A driving IC chip 4 for heating resistors is buried in the recession 2a of a substrate 2, and the chip 4 and wires 11 and 12 drawn out of the chip 4 are covered with a resin 5 to form a projection of a height of about 0.3mm from the substrate 2. A fear of mechanically damaging the IC chip 4 can thus be prevented and the needs for protective cover can be eliminated. The IC chip 4 can thus be provided much closer to the resistors 3. The preferred interval between the resistors 3 and the chip 4 is about 5mm in view of the temperature rise of the resistors 3 from experiments. Since the interval can be reduced to less than half of the conventional one, 10-15mm, the thermal head can be miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a thermal head used in a thermal recording device.

(Background of the Invention) Thermal recording devices are easy to downsize, easy to maintain,
It is also characterized by being relatively inexpensive compared to other recording devices, but the most important aspect of miniaturization is the miniaturization of the main component, the thermal head.

As shown in FIG. 3, the conventional thermal head has two dots at a desired interval (e.g. 8 dots/am) on the upper surface of the alumina substrate 2.
dot-shaped heating resistors 3 arranged in parallel, and a plurality of driving IC chips 4 for selectively energizing the heating resistors 3.
The IC chip 4 is sealed with a resin 5 and covered with a metal cover 6 to prevent mechanical damage. In addition, in the figure, the heating resistor 3 and the IC chip 4 are
The electrodes connecting these are omitted.

To perform thermal recording using the thermal head 1 shown in FIG. 3, as shown in FIG. The heating resistor 3 is energized to generate heat, thereby recording on the recording paper.

By the way, as can be seen from FIG. 4, when the thermal head 1 is pressed against the platen 7, the metal cover 6 is pressed against the platen 7.
It is necessary to avoid contact with the
The heating resistor 3 and the metal cover 6 must be spaced sufficiently apart.As shown in FIG.
If the height of the metal cover 6 from the board is H1 and the distance between the heat generating resistor 3 and the metal cover 6 is D, then when the heat generating resistor 3 is pressed against the platen 7, the platen 7 and the metal cover 6
The condition that the two do not collide is as follows: D>Pr[] The distance and the radius of the platen 7 when the height H is varied are as shown in FIG.

Here, the radius R of the platen 7 is determined depending on the conditions for obtaining good contact between the recording paper and the thermal head l, but is usually about 10 to 15 mm.
The height H is approximately 6 to 8 inches. Therefore, if the distance is calculated from the graph of FIG. 5, it will be about 10 to 15+s. The width of conventionally used thermal heads (the length in the direction perpendicular to the arrangement direction of the heating resistors) is about 40 to 70 mm, and if the above-mentioned distance can be shortened, it will greatly contribute to the miniaturization of thermal heads. .

(Object of the Invention) In order to eliminate such conventional drawbacks, an object of the present invention is to provide a thermal head in which a driving IC chip on a substrate is brought close to a dot-shaped heating resistor to achieve miniaturization. be.

(Summary of the Invention) The present invention provides a concave portion in a substrate, and a driving IC in the concave portion.
It is characterized by having a chip embedded in it.

(Embodiment) FIGS. 1 and 2 show an embodiment of the thermal head of the present invention, and the same parts as in FIG. 3 are given the same reference numerals and will be described below.

A common electrode 8 is arranged along the periphery of the alumina substrate 2,
A partially glazed heat storage layer (hereinafter referred to as a glaze layer) 9 extends inside the common electrode 8 . Near the top of the glaze layer 9, a plurality of dot-shaped heating resistors (hereinafter simply referred to as heating resistors) 3 are arranged at predetermined intervals in the longitudinal direction of the glaze layer 9.
are arranged side by side. One end of each heating resistor 3 is a common electrode 8
The other end of the individual electrode 10 is connected to the individual electrode 10. A pad 10a for a wire pad is formed at the end of the individual electrode 10. These are formed in thin or thick films according to normal thermal head manufacturing processes.

As can be clearly seen from FIG. 2, pad 1 of the individual electrode 10
A recess 2a is formed in the substrate 2 along the line 0a, and the recess 2a contains a plurality of built-in switching elements for driving a heating element, a serial-to-parallel converter for converting a serial signal for driving into a parallel signal, etc. A number of IC chips 4 are mounted on each other. Here, the IC chip 4 is, for example, a rectangle with a thickness of 0.6 mm and a layer of 3 m x 4 m (the proportional relationship of the dimensions of each part in FIGS. 1 and 2 is not accurate), and one IC chip usually has a thickness of 3 m It is designed to drive 84 heating resistors, and an A4 size thermal head will have about 50 IC chips.

Further, the width of the recessed portion 2a is 5 mm and the depth is 1.0 mm.

The wire pad 10a of the individual electrode 10 and one electrode (not shown) of the IC chip 4 are connected by a wire 11,
The other electrode (not shown) of the IC chip 4 is connected via a wire 12 to an external lead electrode 13 formed on the substrate z. Wires 11 and 12 are wired using the so-called wire pound method. Here, the external electrode 13 includes a ground electrode and a drive signal electrode, and the drive signal turns on/off the switching element of the IC chip, thereby causing the heating resistor 3 to selectively generate heat. The wires 11 and 12 and the IC chip 4 are covered and protected with a resin 5 as shown in FIG. 2, and the thickness of the resin 5 from the top surface of the substrate 2 is 0.3 m.

Note that the resin 5 is omitted in FIG. 1.

As described above, in this embodiment, the driving IC chip 4 of the heating resistor 3 is embedded in the recess 2a of the substrate 2, and the chip 4 and the wires 11 and 12 drawn out from it are embedded in the resin 5.
The protruding height from the substrate 2 was set to 0.3 mm.

Therefore, the IC chip 4 does not have to be damaged mechanically, and the protective cover 6, which has been indispensable in the past, can be omitted. As a result, it has become possible to provide the IC chip 4 very close to the heating resistor 3.According to the experiments of the present inventor, when the temperature rise of the heating resistor 3 is taken into account,
The distance AID to the C chip 4 was suitably about 5 layers.The arrangement of the common electrode 8 and the individual electrodes 1O is not limited to the above-mentioned embodiment, and any arrangement may be used. may be a groove extending to both ends in the longitudinal direction of the substrate 2.Furthermore, in the above embodiment, the depth of the recess 2a is set to I.
The IC chip 4 is completely buried in the recess 2a by making the thickness larger than that of the C chip 4, but the depth and thickness are such that the surface of the IC chip 4 and the surface of the substrate 2 are in a relationship that is equal to the road surface. It can be any value. Furthermore, as long as the IC chip 4 includes at least a drive circuit for the heating resistor 3, it may also include other control circuits and the like.

(Effects of the Invention) According to the present invention, since the IC chip for driving the heating resistor is embedded in the substrate, there is no need for the IC chip protection cover that was previously essential, and thus the protrusion from the substrate around the IC chip is eliminated. The height can be made extremely small and the distance between the heating resistor and the IC chip can be made shorter than before.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing an embodiment of the present invention, FIG. 2 is a vertical cross-sectional view showing the vicinity of the IC chip of the thermal head shown in FIG. 1, and FIG. 3 is an example of a conventional thermal head. 4 is a diagram for explaining the positional relationship between the platen and the thermal head, and FIG. 5 is a diagram showing the relationship between the distance from the heating resistor to the metal cover and the platen radius R.
It is a graph representing the height H of the metal cover as a parameter. [Explanation of symbols of main parts] 1: Thermal head 2 2 substrates 2a: Recessed portion 3: Heat generating resistor 4: Drive IC chip 5: Resin
6: Metal cover 7 = platen 8:
Common electrode 9: Partial glaze layer IO22 type electrode 10a Wire pad portion 11.12: Wire 13: External lead electrode (ON-￥Castle Q

Claims (1)

[Claims] In a thermal head in which a plurality of dot-shaped heating resistors and an IC chip for driving the resistors are provided on the same substrate, a recess is provided in the substrate, and the IC chip is placed in the recess.
A thermal head characterized by an embedded chip.