JPH04201576A - Thermal head and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture a thermal head at low costs without employing complicated heat treatment and to save the material costs and to improve yield ratio by providing a solder dam on a connecting electrode for a heat-generating resistor-driving device, and by making the solder dam formed of a material same as that of protection film. CONSTITUTION:For a thermal head in which a radiating layer that promotes radiation from copper foils 21a of a double-face copper-plated high heat-resistant resin substrate 20, and a heat accumulating layer formed of polyimide resin 22 in low thermal conductivity are layered on the aforementioned double-face copper-plated high heatresistant resin substrate 20, and a heat-generating resistor 23, electrodes 25, 26, and 27 and a protection film 28 are further formed in layeres one after another, and a control device 24 that controls driving of the heat-generating resistor 23 is mounted, a solder dam 29 that prevent the solder from spreading in the amount more than the specified one is provided on a connecting electrode 27 of the heat-generating resistor-controlling device of the said thermal head. The solder dam 29 is formed of a material same as that of the protection film 28.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a thermal head used as a printing head for facsimile machines, printers, etc. The present invention uses a double-sided copper-clad high heat-resistant resin substrate as the substrate, a polyimide resin as the heat storage layer, and uses a face-down bonding method to control the driving of the heating resistor. It relates to a thermal head that mounts elements. [Conventional technology]

Conventionally, in forming this type of thermal head, a heating resistor film is formed on the entire surface of a double-sided copper-clad high heat-resistant resin substrate coated with polyimide, a conductor film is laminated on top of the heat-generating resistor film, and then the conductor film is patterned. to form a wiring electrode, remove the resistor film so that it has the same pattern as the wiring electrode, and further remove a part of the wiring electrode to expose the heating resistor and form a heating part. 5iAION, 5iPON, 5iBON, or 5i using a sputtering method that enables low-temperature film formation (below 150°C) to form a protective film, leaving only the face-down bonding pad area between the heat-generating resistor drive control element and the
It is formed with a two-layer structure of n2 and T=a2O5, and then a solder dam for face-down bonding is formed using a highly insulating polyimide resin. FIG. 7 shows a cross-sectional view of a face-down bonding portion of a conventional thermal head. In the figure, 1 is a high heat-resistant resin substrate, 2 is copper plating, 3 is nickel plating, 4 is gold plating, 5 is polyimide resin, 9 is a solder dam, and 10 is a control element (driver IC).

[Problem to be solved by the invention]

However, in conventional thermal heads equipped with flip chips as drive control elements, the solder dam formation process is performed using a highly insulating polyimide organic material and a pattern formation process using photolithography. There are various challenges. (1) The shape of the solder dam varies due to the complexity of the heat treatment conditions for imidization and the difference in the imidization rate during the heat treatment. (2) The material cost of polyimide resin is high. (3) The work process increases significantly. As described above, the above-mentioned problems must be solved in the conventional manufacturing method of forming a solder dam using polyimide resin. Further, as a protective film, a film such as 5iA1ON is formed by a sputtering method, but this method has the following problems. (1) The film-forming speed is limited to about 100 to 150 people/min, and it takes a long time to form a protective film with a thickness of 3.0 μm or more, resulting in poor production efficiency and difficulty in mass production. Not suitable for (2) Poor stepping force balance at the stepped portion. (3) The etching rate is slow (and the cost increases when used as a solder dam.) In view of the above, the present invention (1) uses polyimide resin as a solder dam for connection with a driver IC. First, by using a protective film for the thermal head, complicated heat treatment processes and material costs can be omitted, greatly contributing to cost and yield improvements. (2) As a protective film, plasma chemical vapor deposition (P -C
By forming the SiON film using the VD) method, it is possible to increase the film formation rate, improve step coverage, and increase the etching rate during photolithography processing, resulting in a structure with higher productivity and reliability. The purpose of the present invention is to provide a thermal head and a method for manufacturing the same.

[Means to solve the problem]

The means for solving the problem according to claim 1 of the present invention is as shown in FIG. A heat dissipation layer for promoting heat dissipation from the copper foil 21a and a heat storage layer made of polyimide resin 22 with low thermal conductivity covering the heat dissipation layer are laminated, and the heat generating resistor 23, electrodes 25, 26, 27 are laminated. In a thermal head in which a control element 24 for controlling the drive of the heat generating resistor 23 is mounted, and a protective film 28 is sequentially formed, a predetermined amount or more is applied on the connection electrode 27 of the control element 24 for driving the heat generating resistor 23. A solder dam 29 is provided to prevent the solder from spreading, and the solder dam 29 is made of the same material as the protective film 28. Further, the problem solving means according to claim 2 is that in the thermal head according to claim 1, a SiON film is formed as the protective film 28 by a plasma chemical vapor deposition method, and the film forming conditions are a film forming temperature of 250 to 300. °C1 5 as gas used
Using a mixed gas of IH4, N2oSN2, at least S
The ratio of iH4 and N2O is 0.5≦N2O/SiH4≦1
That is.

[Effect]

In the above problem solving means, the solder dam 29 is covered with a protective film (
By forming it from the same material as the SiON film) 28,
The P-CVD method, which is highly suitable for mass production, can be used to form the protective film, and there is almost no thermal damage to the double-sided copper-clad high heat-resistant resin substrate 2O since the maximum temperature is 300°C. In addition, dry etching when forming the solder dam 29 for face-down bonding is performed at a film forming temperature of 250 to 300.
By performing the etching under the conditions of 0.5° C. and a film forming gas ratio of 0.5≦N 2 O/4≦1 on Si, a film with a high etching rate can be formed. Furthermore, since the protective film 28 and the solder dam 29 are formed at the same time, the electrodes 25, 26, 2 are formed after the protective film is formed.
This eliminates the need for a screen printing process for coating 7, which is advantageous in terms of cost. Moreover, the underlying electrode 25.26
．． It also has excellent adhesion with No. 27, and can improve reliability. Furthermore, when forming the protective film 28, the protective film can be formed on the entire surface of the substrate 2O without using a metal mask, thereby preventing a decrease in yield due to dust adhesion and reducing the defective rate. , the work time can be shortened.

【Example】

Hereinafter, one embodiment of the present invention will be described based on the drawings. FIG. 1 is a sectional view of a face-down bonding part of a thermal head showing an embodiment of the present invention, and FIG. 2(a)
~(g) is a diagram showing the structure in the order of the manufacturing process, the third
The figure shows the state in which the common electrode, heat dissipation layer and face-down bonding pad part have been patterned in the step shown in FIG. 2(a), and FIG. 4 shows the state after the step shown in FIG. 2(g) has been completed. FIG. 2 is a plan view of the thermal head shown in FIG. In the figure, 2O is a double-sided copper-clad high heat-resistant resin board, which has high heat resistance and is formed by impregnating glass fiber with epoxy resin. is attached. The copper foils 21a and 21b are etched to form a heat dissipation layer pattern, and the back copper foil 21b is used as is without being etched. The back copper foil 21b improves heat dissipation by quickly diffusing heat from a heat generating resistor 23, which will be described later, and then transmitting the heat to a heat sink (not shown) bonded to the back copper foil 21b. . Further, during the manufacture of the thermal head, it functions as a layer to prevent thermal deformation of the high heat resistant resin substrate 1, and prevents warping and waviness of the substrate 2O. The surface copper foil 21a of the heat dissipation layer is covered with a heat storage layer made of polyimide resin 22. This polyimide resin contains siloxane bonds with a thermal diffusivity of 0.11 (mm"/5ec). Therefore, the heat lost to the substrate 2O side is reduced and the proportion of thermal energy transmitted to the thermal paper is increased. , energy saving can be achieved. Also, a plurality of heating resistors 23 arranged in a line in the main scanning direction are laminated on the polyimide heat storage layer. The heating resistors 23 are made of a TTa-8to film. , a heating resistor driving control element (driver IC) 24 at one end.
Individual wiring electrodes 25 (Fig. 2 (g)
) and a common electrode 26 (see FIG. 2(g)) that is electrically connected to another heating resistor 23 at the other end. On the terminal end of the individual wiring electrode 25, when connecting the driver IC 24 (face-down bonding),
A driver IC connection (face-down bonding) electrode 27 (see FIG. 2(g)) is formed to electrically connect the IC 24 and the individual wiring electrode 25 using solder. A protective film 28 is formed on the face-down bonding electrode 27, the heating resistor 23, the common electrode 26, the individual wiring electrodes 25, and the polyimide heat storage layer 22. Face down bonding electrode 27 of this protective film 28
A solder dam 29 is formed on the top to prevent solder from spreading beyond a predetermined amount. The protective film 28 functions as a moisture-resistant, oxidation-resistant, and wear-resistant film. In addition, in FIG. 1, 40 is a solder bump. Here, the method for manufacturing the above-mentioned thermal head will be described in detail. First, in FIG. 2(a), the part that will serve as the common electrode and the heat dissipation layer, and the part that will become the face-down bonding pad part, are placed on the double-sided steel-clad high heat-resistant substrate 1, as shown in FIG. After photolithography is performed on the surface copper foil 21a having a thickness of 9.0 μm, it is patterned using an etching solution such as ferric chloride. Next, as shown in FIG. 2(b), 1.0 to 1.5 μm of nickel plating 30 is successively coated with gold plating 31 of about 0.07 to 0.1 μm by electroless plating. This is done by coating the face-down electrode surface with gold 3, which is compatible with solder.
It is a process to make it 1, and if you land on Nitsukeno, you will get 3 gold.
This was used to prevent diffusion between the copper foil 1 and the base copper foil 21a. Then, on the entire surface, polyimide resin 22, which is a highly heat-resistant insulating resin, is applied to the entire surface to a thickness of about 15 μm to serve as a heat storage layer and electrical insulation, using a roll coater method or a spin coater method, and immediately at 120° C. for 7 minutes. After curing, 2
Semi-cure at 00°C for 30 minutes. Next, in order to remove the polyimide resin from the contact part of the common electrode and the face-down bonding pad part,
Photolithography is performed and patterning is performed using a mixed etching solution of hirazine and ethylenediamine as shown in FIG. 2(C). After that, main curing was performed at 300°C for 30 minutes, and the surface temperature was raised to about 350°C for 30 minutes while cooling the back side in an infrared heating furnace.
Heating is performed for 0 minutes to perform the process of forming a polyimide heat storage layer. Next, Ta-8i0232 was used as the heating resistor film 33.
It is formed on the entire surface using a sputtering method of about 000 people, and on top of this a conductive thin film is applied as a wiring electrode, and 80% of Al-8t (1%) is applied.
Formed by sputtering method or vapor deposition method.
The structure is shown in figure (d). Then, in order to form a wiring pattern using a conductor thin film,
Patterning is done by wet etching with phosphoric acid or the like using photolithography, and then the thin film resistor pattern under the conductor wiring is patterned with CF4+ using the same pattern as the conductor wiring.
Patterning is performed using an O□-based dry etching method, and a portion of the conductor wiring is wet etched using phosphoric acid or the like using a photolithography method to expose the heating resistor 23 to form a heating section, as shown in FIG. 2 (e). ), the wiring electrode part is connected to the face-down bonding electrode. Thereafter, using a plasma chemical vapor deposition (P-CVD) device, a 5,0% SiON film is deposited on the entire surface as shown in Fig. 2(f).
A protective film 28 is formed by stacking layers of μm. Then, as shown in FIG. 2(g), the solder dam 29 portion of the SiON film is patterned by dry etching of CF4, .O4, N2O, N, and the like using photolithography. The thermal head shown can be obtained. The film formation conditions were as follows: the film formation temperature and N2O/SiH4 ratio were adjusted to form a film that functions as a protective film for the thermal head and has a fast etch rate for processability when forming solder dams. The experiment was conducted as a parameter. Note that conditions other than the above parameters were set based on known techniques. Electrode size 600mm, distance between electrodes 25mm', RF frequency 13.56MHzSRF power2. OKW. Gas pressure 0.9 TorrSN! Flow rate 4750sccm. SiH, flow rate 190 sccm, parameters:
Substrate temperature 200°C to 300°C, N! 0 flow rate 95sec
The film was formed while changing the time from m to 360 sec. Figure 5 shows the SiON film formed using the substrate temperature as a parameter.
The film deposition rate, refractive index, etching rate with Bach's hydrofluoric acid consisting of NH4F+HF, dry etching rate with CF410R gas, and residual stress are shown. - As can be seen, residual stress and compressive stress are at a minimum around 275°C, making it suitable as a protective film. In addition, due to the substrate material, the temperature limit during plasma CVD film formation is 3.
00°C, and considering the temperature variation (±25°C) of the device, the upper limit of the actual temperature setting is 275°C. On the other hand, in SiON films formed at low temperatures, the deposition rate is fast (compressive stress), but the etching rate with Bach's hydrofluoric acid is fast. This indicates that the density of the film is poor; When a SiON film is formed and a printing run test is performed, the abrasion resistance is extremely poor and cracks and peeling occur, making it unsuitable as a protective film for a thermal head.Therefore, the optimum film forming temperature is 275°C. Next, Figure 6 shows the film formation rate, refractive index, Bach hydrofluoric acid etching rate, dry etching rate, and residual stress of the SiON film formed using the Neo flow rate as a parameter.
Shown as in the figure. As shown in the figure, it can be seen that all the characteristics are greatly affected by changing the N,0 flow rate. When these 5iQN films were subjected to a wear resistance test, the one with the smaller Neo flow rate was better in terms of wear amount and crack resistance. Also, the dry etching rate is faster when the N, 0 flow rate is lower (,
Suitable for patterning solder dams by photolithography. Further, if the residual stress is N2O/SiH4≦1, it is on the compressive side and is suitable for a laminated structure of thin films. However, when NzO/S 1) (4<o, 5, the compressive stress becomes large and the warping of the substrate is promoted, which is not preferable. Therefore, a gas ratio of 0.5≦N2O/SiH, ≦1 is good. That is, as in the prior art, after forming the wiring portion and the heat generating portion, the protective film 28 is formed on the entire surface of the substrate 2O, and the face-down pad portion of this protective film 28 is formed so as to become the solder dam 29. Patterned using photolithography technology,
Remove it by dry etching etc. and use the protective film as a solder dam. With the above structure, the protective film 28 can be formed using the P-CVD method, which is highly suitable for mass production, and the thermal damage to the double-sided copper-clad high heat-resistant resin substrate 2O is limited to a maximum of 300°C. rare. In addition, dry etching when forming the solder dam 29 for face-down bonding is performed at a film forming temperature of 250 to 300.
By performing the etching under the conditions of 0.5° C. and a film forming gas ratio of 0.5≦N2O/SiH4≦1, it becomes possible to form a film with a high etching rate. Furthermore, since the protective film 28 and the solder dam 29 are formed at the same time, the single electrode 25.2 is formed after the protective film is formed.
The screen printing process to coat 6.27 is no longer necessary,
It is also advantageous in terms of cost. Moreover, the base lead electrode 25
．． It also has excellent adhesion with 26 and 27, and can improve reliability. Then, when forming the protective film 28, the protective film can be formed on the entire surface of the substrate 2O without using a metal mask, preventing a decrease in yield due to dust adhesion, reducing the defective rate, and improving the workability. It can save time. Note that the present invention is not limited to the above embodiments (
Of course, many modifications and changes can be made to the embodiments described above without departing from the scope of the invention. [Effects of the Invention] As is clear from the above description, according to claim 1 of the present invention, a protective film is used instead of polyimide resin as a solder dam for connection with a control element for driving a heating resistor. This eliminates complicated heat treatment, material costs, etc.
This can greatly contribute to cost and yield improvement. According to claim 2, the protective film is formed at a film forming temperature of 25%.
0-300℃, film-forming gas ratio 05≦N2O/SiH4≦1
By forming a SiON film using the plasma CVD method under the following film-forming conditions, it is possible to increase the film-forming speed, improve step coverage, and increase the etching rate during photolithography processing, resulting in higher productivity and reliability. It can be a structure.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a face-down bonding part of a thermal head showing an embodiment of the present invention, and FIG. 2(a)
~(g) are diagrams showing the structure in the same order of manufacturing steps; FIG. 3 is a diagram showing the state in which the common electrode, heat dissipation layer, and face-down bonding pad portion are patterned in the process shown in FIG. 2(a); Figure 4 is a plan view of the thermal head after the process shown in Figure 2(g) has been completed. Figure 5 is a SiON film formed using the substrate temperature as a parameter.
A diagram showing the film formation rate, refractive index, etching rate with Bach hydrofluoric acid consisting of NH, F + HF, dry etching rate with CF4102 gas, and residual stress. Figure 6 shows the SiO film formed using the N2O flow rate as a parameter.
FIG. 7 is a cross-sectional view of a face-down bonding portion of a conventional thermal head. 2O: double-sided copper-clad high heat resistant resin substrate, 21a, 21b: copper foil, 22: polyimide resin, 23: heating resistor, 24:,
Control element, 25: Individual wiring electrode, 26: Common electrode, 27
: Control element connection electrode, 28: Protective film (S i ON film), 29: Solder dam. Applicant Sharp Corporation

Claims (1)

[Claims] 1. A double-sided copper-clad highly heat-resistant resin substrate is used as the base substrate, and a heat dissipation layer is provided on the base substrate to promote heat dissipation from the copper foil of the double-sided copper-clad highly heat-resistant resin substrate. and a heat storage layer made of polyimide resin with low thermal conductivity that covers the heat dissipation layer are laminated, a heat generating resistor, an electrode and a protective film are sequentially formed, and a control element for controlling the drive of the heat generating resistor is mounted. In the thermal head, a solder dam is provided on the connection electrode of the heating resistor driving control element to prevent solder from spreading beyond a predetermined amount, and the solder dam is made of the same material as the protective film. A thermal head characterized by being formed in. 2. In the thermal head according to claim 1, a SiON film is formed as the protective film by plasma chemical vapor deposition, and the film forming conditions include a film forming temperature of 250 to 300°C, and gases used: SiH_4, N_2O, N_2. The ratio of SiH_4 to N_2O is at least 0.5 using a mixed gas of
A method for manufacturing a thermal head, characterized in that ≦N_2O/SiH_4≦1.