JPH031960A - thermal head - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the structure of a thermal head for a printer used in facsimile machines, etc., and in particular, it uses a common material for all wiring conductors and a metal material for solder connection, and This invention relates to a low-cost, high-performance thermal head with a simplified structure.

[Conventional technology]

An example of the structure of a conventional thermal head is shown in FIG. As shown in the figure, the thermal head patterns a heating resistor layer 3 and a wiring conductor layer 4 formed on a high-resistance base material 2 by 1 m order photoetching to form a heating resistor element 1. Further, a protective film 51 for preventing oxidation and a wear-resistant layer 52 are formed in a specific area on the heating resistor element 1 so as to cover the entire surface of the heating resistor cable 1 and the substrate, and the protective film 51 for preventing oxidation is After opening a through hole 8 for connecting the driver IC element 7 at the location, a metal layer 6 for solder connection is formed, and the driver IC element 7 is connected by a solder melting connection method.
Mount element 7.

The film structure of the solder connection metal layer 6 generally has the same structure as the second layer wiring section, external lead terminal section, etc. (none of which are shown). For example, Hitachi Review rcMOS driver equipped high-definition thermal recording head J
(vol, 67, Nα7゜1985, pp5
3 to 56), the heating resistors M3 and C made of Cr-5i-0
A wiring conductor W14 with a two-layer structure consisting of an r layer 41 and an AQ layer 42, an SiO2 film that also serves as an insulating layer and a protective film 51 for preventing oxidation of the heating resistor element 1, and an SiN film as a wear-resistant layer 52.
A protective insulating layer having a 2M structure is formed in which a protective film (not shown) of polyimide resin is formed only in the region above the film and the wiring conductor layer 4 . Further, the solder connection metal layer 6 formed through the connection through hole 8 is made of a Cr layer as an adhesive metal layer and a CuN layer as a diffusion prevention metal layer 62.
The metal layer 63 for providing wettability and preventing oxidation is composed of a three-layer metallized Au layer (Cr/Cu/Au). This wiring structure employs the same structure for the second m-th wiring part and the external lead-out terminal part (both not shown). These wiring structures include an adhesive metal layer 61 (
The diffusion prevention metal layer 62 (for example, C
The number of man-hours required for film formation is reduced by using a common structure of the metal layer 63 (mainly Au) for imparting solder wettability and preventing oxidation.

Among these, the film thickness and solder wettability are determined by the properties of the metal layer 62 for preventing solder diffusion.

For example, approximately 1 μm of Cu melts into the molten solder in one solder connection, so the film must be at least as thick as this thickness, and when reconnecting defective elements repeatedly, Depending on the number of melting times of the solder, C may be added to the solder.
u melts in. Therefore, the thickness of the diffusion preventing metal layer 62 needs to be three to four times the thickness that is melted in one solder fusion connection. For example, in the case of Cu, a film of 4 μm or more is required.

On the other hand, in the case of the thin film thermal head proposed in JP-A No. 57-4781, a portion of the wiring conductor, especially the joint with the external connection lead, is provided with a connection terminal as in the above-mentioned conventional technology. It has a structure in which metal layers are newly laminated. In this case, a Cu layer or a Ni layer is later formed in the area of the connection terminal on the wiring between the A1 layer and the Cr layer or the Au layer and the Ti layer, and after further patterning, At3115 is plated for the purpose of preventing oxidation. This is a structure formed by adhesion using a method.

In any of the examples of the above-mentioned prior art, it has a complicated structure in which a newly laminated metal layer is provided as a terminal metal layer for external connection, and when Cu is used as the metal layer 6 for solder connection, the necessary film The thickness also needs to be increased for the reasons mentioned above.

Furthermore, it is well known that when Ni is applied, the diffusivity to solder can be significantly improved compared to Cu. However, Ni basically has the drawback of extremely poor solder wettability due to the formation of a strong oxide layer on its surface.

Further, when thick metal scraps are formed as in the case of using Cu, the substrate is likely to be destroyed due to internal stress, and the film itself is likely to be damaged. When Ni is used as a material other than Cu, the required film thickness is small, but the solder wettability deteriorates significantly, resulting in poor wiring connections and the like. Furthermore, in the conventional wiring structure, the number of laminated thin films including wiring conductors is large, which is a big bottleneck in terms of product cost.

[Problem to be solved by the invention]

The configuration of the thermal head in the prior art described above has a large number of laminated metal thin film layers for connection including wiring conductors, and has a structure in which solder connection terminals are provided in specific parts, and the metal layer for preventing solder diffusion is laminated. There are problems in that the wiring structure is complicated, such as the need to be formed thickly, and is inferior in terms of structural cost and reliability.

An object of the present invention is to solve the above-mentioned problems in the prior art, and to reduce the thickness of the wiring structure by using the wiring conductor layer connected to the heating resistor in the thermal head as a metal layer for direct solder connection. The object of the present invention is to improve the reliability of wiring connections of a thermal head by providing a new material structure that can be simplified and simplified, and at the same time to provide a thermal head that is inexpensive to manufacture.

[Means to solve the problem]

In order to achieve the above object of the present invention, it is necessary to have good wettability to molten solder, and to have good wettability with respect to the solder components (Sn, Pb,
It is necessary to use an alloy material with a slow diffusion rate of In, etc., and at the same time, it is necessary to use a material with low electrical resistance as a wiring conductor material in terms of heat generation efficiency of the thermal head. That is, examples of materials having a slow diffusion rate include Cu, Ni, and the like.

However, Cu is susceptible to oxidation and requires careful attention to the thermal processing process.Moreover, the diffusion rate of solder is relatively fast, so it is necessary to form an electrode with a large thickness.

On the other hand, although Ni has a low diffusion rate, it has low solder wettability, causing problems in soldering processing. As the terminal material, it is necessary to adopt a material and structure that meets the conditions of use, but at present no single metal material has been found that satisfies various conditions for soldering suitable for thermal heads. Based on this situation, we focused on various alloy materials and as a result, we found that there was no generation of brittle intermetallic compounds,
In addition, we have discovered a Ni--Cu alloy as an alloy material that has good solder wettability and excellent corrosion resistance.

By optimally adjusting the composition ratio of Ni and Cu in this Ni-Cu alloy in the thickness direction of the wiring conductor layer, we simultaneously satisfy solder connectivity and low resistance as a wiring conductor, and the apparent discovered a method for constructing wiring conductors using a single alloy layer.

That is, an object of the present invention is to provide a thermal head that includes a plurality of heat-generating resistive elements formed using a high-resistance method, a wiring conductor connected to each other, and a protective film, in which the wiring conductor is made of an alloy of Ni and Cu. This is achieved by configuring the alloy composition ratio of the wiring conductor made of a Ni--Cu alloy to be rich in Cu in the intermediate region of the wiring conductor layer and rich in Ni in the upper and lower regions of the wiring conductor layer.

The alloy composition ratio of the wiring conductor made of a Ni-Cu alloy provided in the thermal head of the present invention is 1 mol%, with a maximum of 75% Ni and a minimum of 25% Cu in the lower layer region of the wiring and conductor layers, and a minimum of 25% Ni in the intermediate layer region. The composition ratio is set to change to the optimum within the respective ranges, with a minimum of 10% for Ni and a maximum of 90% for Cu, and in the upper layer region, a maximum of 75% for Ni and a minimum of 25% for Cu, almost the same as in the lower layer region. It is preferable to do so. N
The change in the composition ratio of i and Cu may be continuous, latent, or stepwise. Further, in the thermal head of the present invention, it is desirable that a protective film made of, for example, SiO□ be formed on the upper surfaces of the heating resistive element and the wiring conductor for the purpose of preventing oxidation. Furthermore, Aug is deposited and formed on the through-hole portion selectively opened in the protective film and the surface exposed through the through-hole portion of the wiring conductor and serving as the row portion lead-out terminal portion. Also good.

[Effect]

The Ni-Cu alloy used as a solder connection terminal is different from the conventional C
It has the same solder wettability as u and does not cause connection problems. In addition, the larger the Ni composition ratio of Ni-Cu alloy, the slower the solder diffusion rate (and the greater the diffusion prevention effect. Figure 3 shows the relationship between the solder diffusion rate and melting temperature. Figure 33) The graph shown in is the time taken for solder to diffuse through a metal film having a predetermined film thickness.
The solder has a composition of 63Sn/37Pb (mol %). For example, under a temperature condition of 250°C for normal solder fusion connection, an example of a Ni-Cu alloy with a composition ratio of 72 (mol%) Ni (remaining Cu) has a diffusion rate that is about two orders of magnitude higher than that of Cu single metal. It can be seen that there are differences, and that the characteristics change by controlling the composition ratio. Therefore, N i −C
By using the u alloy, the same performance as conventional Cu can be obtained with a thinner film thickness, thereby achieving a thinner film.

In other words, in the case of conventional Cu, a film thickness of 4 μm was required, whereas with Ni-Cu alloy, a film thickness of about 0.1 μm does not cause any functional problems, and at the same time, high precision in pattern formation is possible. There are advantages such as being able to

In addition, Ni-rich WJ formed in the lower region of the wiring conductor layer
(~75 (mol %) Ni) serves as a diffusion barrier layer having the same role as a Cr layer having a two-layer structure of AQ/Cr, which is a conventional wiring conductor structure. This is formed for the purpose of controlling the thermal reaction between the heating resistor element, which repeatedly generates heat at high temperatures, and the wiring conductor.The results of the life test, which is determined by the rate of change in the resistance value of the heating resistor element, have been good, and the heating resistor layer There are no problems with regard to adhesion with the material.

On the other hand, as for the properties of a wiring conductor, it is desirable that the amount consumed (dropped amount) in the wiring conductor is small in order to improve the heat generation efficiency of one heating resistor element, and from this point of view, it is desirable that the consumption amount (drop amount) in the wiring conductor is small. However, considering the influence of thermal reaction, 10 (mol%) Ni mixed with Ni (remaining Cu
) alloying shows good results, and the film thickness is about 0.4 μm, so there is no problem in increasing the wiring resistance value.

According to the wiring conductor made of the above Ni-Cu alloy,
A rational thermal head with good various characteristics and a simplified wiring structure can be obtained.

[Not implemented]

Hereinafter, one embodiment of the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a sectional view showing an example of the structure of a thermal head according to the present invention. In the figure, a photothermal resistor IF! is placed on a high-resistance base material 2 such as alumina ceramics. 3 and wiring conductor layer 4
It is formed by patterning it into a predetermined shape. On these upper surfaces, an oxidation-preventing protective film 51 made of, for example, Sin is formed, which serves both to prevent oxidation of the heat-generating resistor element 1 and to protect the wiring region IIA. A wear-resistant layer 52 is formed in a specific area of the heat-generating resistor element 1, and the driver IC element 7 is mounted in a through hole 8 opened at a predetermined position in the oxidation-preventing protective film 51 by a solder melt connection method. It has a built-in structure. Each film deterioration is caused by heating resistor layer 3.
A Cr-5i-0 heat generating resistor is formed to a thickness of approximately 800 mm as a wiring conductor layer and a Ni, -Cu alloy layer (wiring conductor layer 4) as a wiring conductor layer and a gold deer layer for solder connection is formed as a lower layer. The composition is 75, which has the role of expanding IF and barrier layer in the area.
Approximately 0.1 μ of Ni/25Cu (mo1%) Suwa alloy
m, an alloy with a composition of 1ONi/90Cu (mo1%), which serves as a wiring conductor layer, is placed in the intermediate layer region.
．． The wiring conductor frI is formed by forming a 1Mi alloy of 75Ni/25Cu (mo1%) with a thickness of about 4μm and a thickness of about 0.5μm in the upper layer region, which serves as a metal layer for solder connection.
4 was formed. In this example, a sputtering device was used to form the film. In forming this wiring conductor M4, Ni
, Cu, and Cu, and by continuously controlling the film forming conditions, Ni-Cu with the above composition was sputtered.
A wiring conductor layer 4 made of an alloy layer is formed. This is achieved when a Ni-Cu alloy layer is formed in a layered manner using a sputtering target (material) having the above-mentioned Ni-Cu alloy composition, or by a vacuum evaporation method.

Even when a Ni-Cu alloy layer is continuously formed by simultaneous vapor deposition of Ni and Cu, Ni with the same composition distribution as above is obtained.
It goes without saying that a configuration of a wiring conductor layer made of a -Cu alloy layer can be obtained.

In addition, the pattern formation of the wiring conductor layer 4 has the advantage that it can be processed using a common etching solution (e.g., iodine-ammonium iodide mixture, phosphoric acid, hydrochloric acid, etc.) without changing the composition of the etching solution. There is also.

A protective film 51 for preventing oxidation (Sin2: 2 μm) is formed as a protective film 5 on the pattern of the heating resistor element 1 having the above structure.
and wear-resistant layer 52 (S i -N: 1.5μr
n) was formed, and the driver IC element 7 was mounted in the through hole 8 selectively opened at a predetermined position by a solder fusion connection method. Before connecting the driver IC element 7, it is desirable to perform pretreatment with a dilute sulfuric acid solution in order to remove the extremely thin oxide film on the Ni--Cu alloy film.

In the solder connection of the driver IC element 7, a sufficient solder connection can be obtained by the above method, but as a means to further improve the solder wettability, forming an Au layer is highly effective, and the connection of the wiring conductor of the thermal head is reliability,
It is also extremely effective for the purpose of preventing oxidation of Ni-Cu alloys.

For the thermal head shown in this example.

Normally, several dozen driver IC elements 7 are mounted on the thermal head substrate. This may occasionally include a defective element, and in this case, the element must be replaced. When replacing the element, it is necessary to re-melt the solder, and in the conventional thermal head, it was necessary to form a film of Cu with a thickness of 4 μm or more as a metal for preventing diffusion, but in this example, In the applied Ni--Cu alloy, the thickness was about one-tenth that of the conventional one, and even if the driver IC element 7 was replaced two or more times, no problem occurred in the properties as a diffusion prevention film.

〔Effect of the invention〕

As explained in detail above (Ni
The thermal head of the present invention, which is made of a -Cu alloy with a specific composition range, has excellent electrical conductivity and solder wettability, which are necessary characteristics for a wiring conductor, and has a large diffusion prevention effect, making it easy to connect wiring conductors. A highly reliable thermal head can be obtained.

The Ni-Cu alloy of the present invention can be used as a metal layer for solder connection with a film thickness that is one-tenth to one-tenth of that of a conventional Cu layer, and has the same characteristics as the conventional one. In addition, the wiring conductor layer including the heating resistor has a compact single-layer structure, which reduces the number of thin film layers, shortens the photo-etching process, improves pattern accuracy, and significantly reduces manufacturing costs. can.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of the structure of the heating resistor and driver IC connection part of the thermal head illustrated in the embodiment of the present invention, FIG. 2 is a cross-sectional view showing the structure of a conventional thermal head, and FIG. is a characteristic diagram showing the diffusibility of solder in a metal for preventing solder diffusion. 1... Heating resistance element 2... Height resistance base material 3...
Heat generating resistor layer 4... Wiring conductor layer 5... Protective film
6... Metal layer for solder connection 7... Driver I
C element 8...Through hole 41...CrM42...A
Q layer 51...Antioxidizing protective film 52...
Wear-resistant layer 61...Metal layer for adhesion 62...Gold yC layer for preventing diffusion 63...Metal layer for providing wettability and preventing oxidation. Hanawa 1 Kuni and...-Hatsuran translation kume)? ...-rLfNT anti" Wakatai Neo 3...-4: Kyourizawa Banbi 4, Hikosen Dotai layer 5...Kagosa 7...-Dry Nogu ICC1 8...Through-ho/L 5r -Ikkin otsusei yo Yogogomo, 3゛z-・Yo4 Mogotomo-ΔI flame 2zu・-ShζノL-ding,-/L.

Claims (1)

[Claims] 1. A thermal head having a plurality of heat generating resistor elements formed of a heat generating resistor layer, a wiring conductor layer connected to the heat generating resistor layer, and a protective film on a high resistance base material, The wiring conductor layer is made of an alloy of Ni (nickel) and Cu (copper) having a predetermined composition range, and the alloy composition ratio of Ni and Cu constituting the wiring conductor layer is set to A thermal head comprising an alloy of Ni and Cu having a composition in which a lower layer region of a wiring conductor layer is Ni-rich, an intermediate layer region is Cu-rich, and an upper layer region is Ni-rich. 2. In the thermal head according to claim 1, the alloy composition ratio (mol %) of Ni and Cu constituting the wiring conductor layer is such that in the intermediate layer region of the wiring conductor layer, Ni is 10% or more and Cu is 9%.
The composition is less than 0% Cu-rich, and the upper and lower regions of the wiring conductor layer contain less than 75% Ni and 25% Cu.
1. A thermal head comprising an alloy of Ni and Cu whose composition is changed so as to have a Ni-rich composition of % or more. 3. The thermal head according to claim 1 or 2,
A thermal head characterized in that the wiring conductor is made of an alloy of Ni and Cu in which the alloy composition ratio of Ni and Cu changes stepwise in a continuous or layered manner. 4. The thermal head according to claim 1 or 2, characterized in that a protective film for preventing oxidation is provided on the upper surface of the heating resistor element and the wiring conductor. 5. The thermal head according to claim 1 or 2,
A protective film for preventing oxidation is formed on the upper surfaces of the heating resistor element and the wiring conductor, and a surface portion of the wiring conductor exposed through a through-hole portion selectively opened in the protective film is formed.
A thermal head characterized in that it is formed by depositing an Au (gold) layer.