JPH01196360A - thermal head - Google Patents

Abstract

PURPOSE:To reduce cost involved in the mounting of IC chips by coating an area over a common electrode and an area over an interconnected part between a selective electrode and an IC chip for drive with a solder-plated layer and connecting the selective electrode to the IC chip for drive by a face down bonding method. CONSTITUTION:Thermal resistance elements 3a are aligned on an insulative substrate 1. A common electrode 4-1 which is commonly connected to a plurality of thermal resistance elements 3a and a selective electrode 4-2 connected to an IC circuit device for drive which is provided individually on each thermal resistance element 3a, are formed of an aluminum film. In addition, a solder- plated layer 12-1 is formed on the common electrode 4-1 to work as a current capacity compensation electrode for the common electrode 4-1. On the selective electrode 4-2, an opening is provided on an interconnected part with an IC chip 8 of an abrasion-resistant layer 5, and in the opening, a bump 12-2 of a solder-plated layer is formed. A buffer metal 13 is formed in a pad 9 of the IC chip 8, and the IC chip 8 is bonded by a face down bonding method by a reflow of a flip chip between the bump 12-2 and the IC chip 8.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a thermal head used in printers, facsimile machines, etc., and particularly to a long thermal head in which a large number of heating resistor elements are arranged in a row.

(Conventional technology) FIG. 3 shows an example of a conventional thermal head.

The longitudinal direction of this thermal head is perpendicular to the paper surface.
Heat generating resistor elements are arranged along the longitudinal direction.

1 is a ceramic substrate, the surface of which is covered with a glassy glaze layer 2. A resistor film 3 is formed on the glaze layer 2, and a common electrode 4-1 and a selection electrode 4 are formed on it.
-2 is formed. The common electrode 4-1 is commonly connected to all the heat generating resistor elements, and supplies heating power from the power source to the heat generating resistor elements. A selection electrode 4-2 is provided for each heating resistor element, and is connected by a wire 10 to a pad 9 of a driving semiconductor integrated circuit device (hereinafter referred to as IC) 8 die-bonded onto the ceramic substrate 1.

The exposed portion 3a of the resistor coating 3 between the common electrode 4-1 and the selection electrode 4-2 becomes a heat generating portion of the heating resistor element.

As the electrodes 4-1 and 4-2, an aluminum film with a thickness of about 1 μm is used. The pad 9 of the IC 8 is also made of aluminum, and the connecting wire 1o is made of gold. 5 is a wear-resistant layer that protects the heating element portion 3a.

A metal coating 6 for increasing current capacity is provided on the common electrode 4-1 via a buffer metal coating 11.

7 is a solder resist covering the metal film 6.

Now, if a thermal head with a length of 216 mm (A4 size), a density of 8 dots/mm, and a resistance value of one heating element of 1 Ω is operated at 24 V and driven in a 4-division method, the duty is If it is 50%, a current of about 10 A will flow in the area of the width W1 of the common electrode 4-1.

Therefore, if the metal film 6 for capacity enhancement is not provided, a width of about 10 mm is required to flow a current of IOA through the common electrode 4-1 made of a 1 μm aluminum film. Therefore, the width of the ceramic substrate l becomes wider. In thermal heads manufactured using a thin film manufacturing process, the number of thermal heads manufactured in one manufacturing process is reduced, which increases manufacturing costs.

Further, a voltage drop caused by the resistance of the aluminum film causes variations in printing density in the longitudinal direction of the thermal head.

In order to avoid such problems, in the example shown in FIG. 3, a metal coating 6 is provided on the common electrode 4-1 by plating. The metal coating 6 used is made of copper, gold, or the like and has a thickness of 10 to 20 μm.

Since the metal film 6 is not directly attached to the aluminum film 4-1, it is necessary to interpose a buffer metal film 11 of titanium, tungsten, nickel, or the like.

Other thermal heads include those in which an auxiliary electrode is provided on the common electrode side of the ceramic substrate l to reinforce the current capacity, for example, by plating an insulating material with copper.

Furthermore, as another thermal head, ceramic substrate 1
Some have a common electrode extending through the end surface to the back surface.

However, in the example shown in FIG. 3, in order to plate the metal coating 6, it is necessary to form the buffer metal coating 11 by vapor deposition or the like and to perform selective etching, which requires extra equipment and increases the number of man-hours. Costs increase.

For those with auxiliary electrodes to reinforce current capacity,
There is also the problem that the number of steps such as soldering increases, the cost increases, and distortion occurs due to the difference in coefficient of thermal expansion between the ceramic substrate 1 and the insulating material of the auxiliary electrode.

The method of providing a common electrode on the end surface or back surface of the ceramic substrate 1 has the problem that the number of steps increases, the cost increases, and the degree of integration cannot be increased. That is, normally, multiple thermal heads are manufactured at the same time, for example, three 15 mm wide thermal heads are manufactured from a 45 mm wide ceramic substrate, or four 11.25 mm wide thermal heads are manufactured at the same time. This is because if a common electrode is to be formed on the back surface, only two thermal heads at most can be manufactured from one ceramic substrate.

Further, although the selection electrode 4-2 and the IC 8 are connected by wire bonding or TAB, these mounting methods have poor workability and reliability problems.

(Objective) An object of the present invention is to provide a thermal head in which the cost can be reduced by narrowing the width of the substrate on which the heating resistor element is formed, and in which a driving IC can be mounted using the face-down bonding method. It is something.

(Structure) In the thermal head of the present invention, heating resistor elements are arranged in a row on an insulating substrate, and a common electrode commonly connected to a plurality of mature resistor elements is provided individually to each heating resistor element. The selection electrode connected to the driving semiconductor integrated circuit device is formed of an aluminum thin film, and a solder plating layer is formed on the common electrode and the connecting portion where the selection '4 pole is connected to the driving semiconductor integrated circuit device. The selection electrode and the chip of the driving semiconductor integrated circuit device are connected by face-to-face bonding.

An embodiment will be described in detail below. FIG. 1 shows one embodiment.

Similarly to FIG. 3, 1 is a ceramic substrate, 2 is a glassy glaze layer covering its surface, 3 is a resistor coating, 3a is a heat generating part of a heating resistor element, 4-1 is a common electrode, 4- 2 is a selection electrode, and 5 is a wear-resistant layer. As the resistor film 3, T
A::N, TaSiO2, etc. formed to a thickness of 500 to 2000 layers is used. As the electrodes 4-1 and 4-2, an aluminum vapor-deposited film with a thickness of about 1 μm is used.

As the wear-resistant layer 5, a material with high hardness such as SiC or Si3N4 is used.

In this embodiment, a solder plating layer 12-1 having a thickness of approximately several micrometers is formed on the common electrode 4-1 to serve as a current capacity reinforcing electrode for the common electrode 4-1.

On the selection electrode 4-2, an opening with a width W of about 250 μm is provided in the wear-resistant layer 5 at the connection portion with the IC chip 8, and a bump 12-2 made of a solder plating layer is formed in the opening. A buffer metal 13 is placed on the pad 9 of the IC chip 8.
is formed, and the IC chip 8 is face-down bonded to the bump 12-2 by flip-chip adhesive flow. 7 is a solder resist.

Next, the process of manufacturing this example will be explained.

The layers up to the wear-resistant layer 5 are formed by the same method as in the conventional method.

As shown in FIG. 2, the wear-resistant layer 5 is selectively etched to provide an opening in the common electrode region (width W1 region) and the connection region (width W2 region) between the IC chip 8 and the common electrode 4-
1 and those portions of the selection electrode 4-2 are exposed.

Thereafter, solder is formed directly on the aluminum electrode in the opening by ultrasonic plating. Solder plating layer 12-1.1
The thickness of 2-2 is 20 to 40 μm.

After solder plating, a reflow process is performed in an electric furnace at about 250°C. As a result, the width W2 as shown in FIG.
The solder 12-2 swells in a hemispherical shape at the opening on the selection electrode 4-2 having a height T: of approximately 50 to 60 μm.

(Effects) In the present invention, since the common electrode is covered with a solder plating layer, the current capacity of the common electrode can be reinforced at low cost and with high productivity.

In addition, in the present invention, the connection portion where the selection electrode is connected to the driving IC chip is also covered with a solder plating layer, and the selection electrode and the driving IC chip are connected by face-down bonding, so that the solder bump of the flip chip is can be formed at the same time as the current capacity reinforcing electrode of the common electrode.
The mounting cost of the C chip can be reduced. Furthermore, the reliability of IC chip mounting can be improved by the face-down bonding method.

Since current reinforcement can be performed without increasing the width of the substrate, the number of thermal heads that can be manufactured at one time cannot be reduced, and manufacturing costs can also be kept low in this respect.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment, FIG. 2 is a sectional view showing the same embodiment in the middle of manufacturing, and FIG. 3 is a sectional view showing a conventional thermal head. 1... Ceramic substrate 3... Resistor layer, 3a... Heat generating part, 4-1... Common electrode, 4-2... - Selection electrode, 8...IC chip 12-1.12-2...Solder plating layer.

Claims (1)

[Claims] (1) Heat generating resistor elements are arranged in rows on an insulating substrate,
A common electrode commonly connected to a plurality of heat generating resistor elements and a selection electrode provided individually to each heat generating resistor element and connected to a driving semiconductor integrated circuit device are formed of aluminum thin films. A solder plating layer is coated on the upper part and the connection part where the selection electrode is connected to the driving semiconductor integrated circuit device, and the selection electrode and the driving semiconductor integrated circuit device chip are connected by face-down bonding. head.