JPH048559A - Thermal head - Google Patents

Abstract

PURPOSE:To ensure the significant simplification of manufacturing process and reduction of material consumption by using a metal layer to which a drive IC can be directly soldered, as wiring material on a connected conductor. CONSTITUTION:Cr-Si film and Cr/Cu/Cr are laminated on an insulative substrate 1 as a thermal resistor layer 2 and a connected conductor 3 respectively. In this case, a lower layer Cr formed as a diffusion barrier layer 31 is about 0.1mum thick, Cu as a main connected conductor layer 32 is 3.0mum thick and an upper layer Cr as a layer 33 in contact with a protecting film is about 0.05mum. Then this film layer is patterned and SiO2 which acts as a protecting film 4 and concurrently an oxidation preventing layer is formed with a thickness of 4.0 over the entire surface of the substrate and SiN2 which acts as an acti-abrasion layer 6 formed in an area of a thermal resistor element 5 is formed with a thickness of 1.5mum. In addition, a through hole is formed in an area to which a driver IC 7 for switching mounted on the substrate, and the upper layer Cr which becomes a layer 33 to be connected to a protecting film is formed as equivalent to a through hole pattern of the protecting film 4 using etching techique. Finally Cu which acts as a main connected conductor layer 22 on an exposed surface is connected using a solder starting from the driver IC 7 to complete the entire system.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head, particularly a thermal head suitable for use in facsimiles, printers, and the like.

[Conventional technology]

An example of the structure of a conventional thermal head will be explained with reference to FIGS. 3, 4, and 5. Fig. 3 is a cross-sectional view showing the entire thermal head, Fig. 4 is an electrical equivalent circuit diagram of the head, and Fig. 5 is a detailed cross-sectional view of part 7 in Fig. 3 showing the terminal section for making solder connections. . A heating resistor layer 2 is formed on an insulating substrate 1 having a smooth glazed surface. The wiring conductor layer 3 is patterned into a desired shape, and a protective film 4 that also serves as an anti-oxidation layer is formed over the entire wiring conductor layer 3, and a wear-resistant layer 6 against the sliding of the recording paper is laminated in the area of the heating resistor element 5. This configuration is common. These components include, for example, Ta as the heating resistor material.

Silicides such as Cr, nitrides, and materials with relatively low specific resistance such as AQ, Cu, Au, Mo, and W are used as the wiring conductor 32 materials, and in particular, materials with relatively low specific resistance such as AQ, Cu, Au, Mo, and W are used.
Cr is used as the diffusion barrier layer 31 for the purpose of suppressing thermal reaction with
, a laminated wiring structure sandwiching Ti, etc. is used. The protective film 4 is made of silicon oxide (Sin), and the wear-resistant layer 6 is made of tantalum oxide (Ta205), silicon nitride (Si, N, ),
Silicon carbide (SiC) or the like is used, but there are also examples in which a resin layer made of an organic material is formed in the region covering the wiring conductor 3. A switching driver IC 7 for driving and controlling the heating resistor element 5 is mounted on a board having these structures, and considering that there are a large number of connection points, these are connected all at once by soldering. is the mainstream. At this time, a connection metal layer 8 is formed in advance on the substrate in a through-hole section selectively opened in a specific region of the protective film 4, and the terminal section is connected by solder 9 supplied from the driver IC side. be done. The connection metal layer 8 has a structure in which a connection layer 81 with the wiring conductor 3, a solder diffusion prevention layer 82, and an oxidation prevention layer 83 are laminated. done at the same time. The common electrode 10 is required to have the wiring resistance as small as possible in order to improve recording efficiency, and to form a thick film due to the drive current capacity. There are also examples where the surface is coated with solder. These are Tokugai 57-4
As described in No. 781 and Japanese Unexamined Patent Publication No. 182964/1982, the method of forming a terminal film is a thin film method formed by vapor deposition, sputtering, etc., or a method such as electroless or electroplating. Many methods can be found. Typically, the configuration of the metal layer 8 that makes the solder connection is Cr or Ti(81)/Cu or N1(82)/
In the case of Au(83) plating, Cu and Ni are the most common materials used, and in both cases, a thin layer of Au is formed on the surface to prevent oxidation and improve solder wettability. The Cu or Ni layer 82 is required to have excellent solder wettability and low solder diffusivity. In the case of Cu, it is known that approximately 0.5 to 1.0 μm penetrates into the solder after -1 soldering, and considering the replacement of defective driver ICs, approximately 0.5 to 1.0 μm is melted into the solder.
A film thickness of μm is required. On the other hand, Ni has a significantly superior property of diffusing into solder compared to Cu, and therefore the required film thickness can be formed thin. In other words, since solder wettability is poor, a structure in which Au is laminated is generally used to protect the surface.

As in the above configuration, conventionally it has been common to form a dedicated pattern as a connecting metal for the driver IC and external connection terminals (not shown).

Further, the configuration of the common electrode also requires protection such as solder coating, which causes the head to become larger.

In either case, the manufacturing process for the thermal head is complex and varied, which is a major drawback in terms of manufacturing costs.

[Problem to be solved by the invention]

In the above conventional technology, a complicated manufacturing process is applied to form solder connection terminals such as driver ICs, a patterning process is required to form the terminals, and the head is expensive due to the use of expensive materials. Ta.

An object of the present invention is to significantly simplify the manufacturing process, reduce the amount of materials used, improve head performance such as downsizing the head, and at the same time provide an inexpensive thermal head.

[Means to solve the problem]

That is, in the present invention, the driver ■C1 as in the prior art is
Alternatively, the driver IC is configured to be directly connected to the wiring by soldering without providing terminal metallization for external connection, and the driver IC is characterized by using a metal layer that can be directly connected. For its structure, a laminated wiring of Cr (chromium)/Cu (copper)/Cr is applied, and Cr, which is the upper layer of the wiring, is selectively processed only in the open through-hole area of the protective film that will be the solder connection part.・By removing it by nching, it is possible to connect the solder directly to the Cu surface. At this time, the Cr layer pattern removed by machining and sawching has the function of suppressing solder wetting and spreading during solder connection, and by setting the thickness of Cu, which will become the main conductor layer, to 2 to 5 μm, the conductor This structure aims to reduce the wiring resistance of the common electrode section, eliminate the dedicated patterning process, and cover the entire head with a protective film, thereby reducing the size of the head.

Furthermore, in order to improve the solder connection, Au (gold) is selectively applied to the wiring conductor Cu exposed at the through-hole opening.
By creating a structure with a thin layer of plating, the process was significantly simplified and a low-cost thermal head was realized.

[Effect]

The wiring conductor layer has a laminated structure of Cr/Cu/Cr, and the main conductor layer, Cu, has a thickness in the range of 2 to 5 μm, thereby creating a Cu surface with the Cr layer removed in the area where the driver IC is connected. Furthermore, direct solder connection is possible, and the use of low-resistance materials reduces the wiring resistance of the common electrode portion and the wiring portion, thereby improving recording efficiency and head performance. Furthermore, since the common electrode part has the same structure as the wiring conductor layer, patterning processes such as solder coating can be eliminated, and a structure in which the entire structure is covered with a protective film can be adopted, and the position where the heating resistor element is formed is brought closer to the edge of the board. This makes it possible to downsize the head. Also, the C to which the driver IC is connected
When making solder connections on the U-plane, the upper Cr layer pattern suppresses solder wetting and spreading, so a uniform connection state can be obtained at many connection points, and at the same time, by forming a thin Au layer, Connection reliability also improves.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. The basic structure is the thin film method shown in the prior art, and the electrical configuration (equivalent circuit) is the same. 1st
The figure is a cross-sectional structural view showing the entire thermal head, and FIG. 2 is a detailed cross-sectional view of the section ``■'' in FIG. 1 showing the terminal portion for making solder connections. The overall structure of the thermal head consists of a Cr-3i (chromium-silicon) thin film as the heating resistor layer 2 and a Cr/Cu wiring conductor layer 3 on an insulating substrate 1 such as an alumina ceramic substrate with a smooth glazed surface. /C
Stack r. At this time, each film thickness is the diffusion barrier layer 31
The lower layer Cr to be formed is approximately 0.1 μm thick, and the Cu layer forming the main wiring conductor layer 32 is 3.0 μm thick as the adhesive layer 33 with the protective film.
The upper layer Cr has a thickness of about 0.05 μm. This thin film layer is patterned into a desired shape, and SiO□ is formed as a protective film 4 which also serves as an anti-oxidation layer on the entire surface of the substrate so as to cover them, and SiO□ is formed as a wear-resistant layer 6 formed in the region of the heating resistor element 5.
, N, were formed with a film thickness of 4.0/1.5 μm, respectively.

After that, the switching driver I mounted on the board
A through hole is selectively formed in the region where C7 is connected by wet etching, and the upper layer Cr, which will become the adhesive layer 33 with the protective film, is removed by etching into a shape equivalent to the through hole pattern of the protective film 4 (Sin2). . The driver IC 7 is attached to the Cu which becomes the main wiring conductor layer 32 on this exposed surface.
The entire structure is constructed by making connections using solder 9 supplied from the manufacturer. This configuration is also the same for a terminal portion (not shown) that connects with the outside.

In another configuration, a through hole is selectively formed in a region to which a switching driver IC 7 mounted on the substrate is connected, and the upper layer Cr, which becomes the adhesive layer 33 with the protective film, is replaced with the protective film 4Si.
After etching and removing it into a shape equivalent to the through-hole pattern of O□, the C that will become the main wiring conductor layer 32 on this exposed surface is removed.
Connectivity is improved by forming Au, which will become the connection layer 11, to a thickness of about 0.1 μm on the u-plane by electroless plating for the purpose of improving solder wettability and preventing oxidation of the film surface. Basically, it is known that solder has better wettability than Cu, but reliability is further improved by inserting Au. In any connection state, the protective film 4 (S
The upper layer Cr pattern, which has been etched and removed in a shape equivalent to the through-hole pattern of in2), suppresses the wetting and spreading (area) of the solder, and in particular serves to suppress the diffusion of the Cu film surface.

Cr/Cu/Cr as wiring conductor layer 3 of thermal head
The wiring resistance of the wiring conductor 3 can be made extremely small by adopting the laminated structure and using Cu, which has a low specific resistance, as a material that also serves as the main wiring conductor layer and the connection layer. In addition, by applying Cu (copper) to the common electrode 10, it is possible to reduce the resistance to 2Ω or less with a film thickness (3.0 μm) and a recording width of 2561 mm for a B4 size head, for example. In particular, since the common electrode has the same structure as the wiring conductor, the pattern of the heat-generating resistor 5 that is formed separately can be improved. Since it can be formed in a wide area in a solid manner from very close, it is possible to adopt a structure in which the entire surface is covered with a protective film, and the position where the heating resistor element 5 is formed (Q shown in Fig. 3 and Fig. 1) can be adopted. ,Q')
can be brought closer to the end surface of the substrate. This results in
The head can be miniaturized, the manufacturing process can be simplified, and the price of the thermal head can be reduced.

〔Effect of the invention〕

According to the thermal head of the present invention, the wiring conductor is formed using a metal layer made of Cr/Cu/Cr that can be directly connected to the driver IC by soldering, thereby eliminating the need for a dedicated terminal that was previously required. , the manufacturing process could be greatly simplified.

In addition, the solder wetting area is suppressed by the Cr layer pattern on the upper layer of the wiring conductor, which is opened in a shape equivalent to the through hole shape, and the diffusion of Cu is suppressed as much as possible.
Connection reliability was improved by providing a connection layer of u. In addition, by setting the thickness of the Cu layer, which is a material that also serves as the main conductor layer of the wiring conductor and the solder connection layer, to a range of 2 to 5 μm, wiring resistance is reduced and the common electrode area is expanded. By adopting a structure in which the head is covered with a protective film and the position where the heating resistive element is formed is brought closer to the end surface of the substrate, a 15% reduction in size compared to the conventional head was achieved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the entire thermal head of the present invention;
Figure 2 is a detailed cross-sectional view of the terminal part for soldering connections, and the section ■ shown in Figure 1. Figure 3 is a cross-sectional view of a Searl head in the prior art. Figure 4 is an electrical equivalent circuit diagram of the head. Figure 5. 3 is a sectional view of the V portion in FIG. 3, which is a terminal portion for making a solder connection. 1... Insulating substrate 2... Heat generating resistance layer 3...
Wiring conductor 4... Protective film 5... Heat generating resistor element 6... Wear resistant layer 7... Driver IC 8... Connection metal layer 9... Solder 10... Common electrode 11... Connection layer 31...diffusion barrier layer 3
2... Main wiring conductor layer 33... Adhesive layer with protective film 81... Adhesive layer 82... Diffusion prevention layer 83
...Antioxidant layer 41 figure Sanskrit 2 figure (Δ section detailed lees figure)

Claims (1)

[Claims] 1. A wiring conductor for supplying power to a plurality of heating resistors formed on an insulating substrate having a smooth glazed surface, a protective film formed to cover the wiring conductor, and a switching device. A thermal head comprising a driver IC for control on the substrate, wherein the wiring material is a metal layer to which the driver IC can be directly soldered onto the wiring conductor. 2. In claim 1, the wiring conductor metal is Cr (chromium).
A thermal head having a laminated structure of /Cu (copper)/Cr (chromium), with Cu (copper) as the main conductor layer having a film thickness in the range of 2 to 5 μm. 3. In claim 1 or 2, when the driver IC is soldered to a through-hole portion selectively opened in the protective film formed to cover the wiring conductor, Cr( A thermal head in which a Cr layer is removed by etching in a shape equivalent to the shape of an opened through hole in the protective film, and the solder wetting area is suppressed by the opened Cr layer pattern. 4. The thermal head according to claim 1, 2 or 3, wherein a thin layer of Au (gold) is formed by plating on the wiring conductor Cu (copper) in the through-hole opening for solder connection.