JP3844155B2 - Manufacturing method of thermal head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a thermal head.
[0002]
[Prior art]
Thermal heads are widely used in inexpensive and simple printers, taking advantage of the convenience of thermal paper or thermal transfer paper that does not require refilling with ink or the like. Recently, high-quality printing and high-speed printing have also been demanded for printers used for these thermal heads. Further, there is a demand for a high-density thermal head such as 600 dpi to 1200 dpi, which is miniaturized before being used in a color printer system using a thermal transfer system, an index printer of a photo lab automation minilab that emphasizes high image quality, and the like.
[0003]
However, in the thermal head, it is necessary to consider the temperature increase and heat dissipation so that the heat generating portion of the heat generating resistor is rapidly heated to instantaneously raise the temperature and heat is quickly dissipated to prevent bleeding. For rapid temperature increase, heat concentrates on the heat generating part and does not escape around, and rapid heat dissipation requires a conflicting thermal response characteristic that heat of the heat generating part escapes quickly.
[0004]
That is, the following items are basically required for the thermal head.
1) Light, thin and small 2) Low cost 3) Large screen for A3, etc. 4) Low power consumption 5) High speed 6) High-density, clear, so-called high-definition image print 7) Uniformity without color unevenness Screen 8) Maintenance-free with no dirt remaining Conventional thermal heads are generally configured as shown in FIG. As shown in FIG. 6, a heat storage layer 32 made of glass having a melting point of, for example, about 1000 ° C. is provided on the entire surface of an alumina substrate 31 that also serves as a heat radiator (heat sink), and a heating resistor 33 is formed on the heat storage layer 32. Is provided. Reference numeral 34 denotes an electrode that forms the heat generating portion 35, and a wear resistant layer 37 is formed on the surface of the electrode 34 and the heat generating resistor 33 as a protective layer that prevents abrasion due to the thermal paper 36 or the like. Reference numeral 38 denotes a roller, 39 denotes an IC constituting a peripheral circuit fixed on the substrate 31 via an adhesive layer 40, and 41 denotes a wire connecting the electrode 34 and the IC 39.
[0005]
As described above, when the heat storage layer 32 is formed, a glass powder paste made of a binder is applied onto the substrate 31 and baked. The reason for using high-melting glass as the heat storage layer 32 is as follows. First, when a metal having a low electrical resistance such as aluminum or copper is used as an electrode, it is necessary to fire a glass having a high firing temperature in advance in order to prevent such oxidation and alteration of the heating resistor. It is. Second, when heat treatment is performed to improve TCR (resistance / temperature coefficient), glass having a melting point higher than the heat treatment temperature of the heating resistor 33 needs to be formed in advance. The heat storage layer 32 also has a role of smoothing the surface of the substrate 31 with unevenness.
[0006]
In the case of such a conventional thermal head, glass is used as the heat storage layer 32. For the purpose of high-speed printing, a heat storage effect in the heat storage layer 32 is obtained by using a heat-resistant resin such as a polyimide resin for the heat storage layer 32. Various proposals have been made to improve power consumption and reduce power consumption.
[0007]
In the case of using a polyimide resin or the like as described above, in Japanese Patent Application Laid-Open No. 5-64905, an electrode 34 is formed on the heating resistor 33 at an interval to form a heating stack 42 (this heating stack 42 is The concave portion 43 formed on the surface of the heat storage layer 32, the heating resistor 33, the electrode 34, and the protective layer 37 is eliminated, the contact surface of the thermal paper 36 is smoothed, and the heating resistance is obtained. In order to enable heat treatment to improve the TCR of the body 33, a heat storage composed of a protective layer 37, a heating resistor 33, an electrode 34, and a polyimide resin through a sacrificial layer for peeling on the forming substrate A method of manufacturing a thermal head (hereinafter referred to as a transfer method) is disclosed in which the layer 32 is formed in order, and then the substrate 31 is bonded, and then the both are peeled off at the interface between the forming substrate and the peeling layer. That.
[0008]
According to this transfer method, since the protective layer 37 is formed on the plane of the temporary substrate, the surface in contact with the thermal paper 36 is smooth, and no space is formed between the thermal paper 36, so that the thermal efficiency is improved. To do.
[0009]
[Problems to be solved by the invention]
However, as described in the above publication, in the thermal head using a resin such as polyimide resin for the heat storage layer 32, the resin is exposed to a high temperature due to the heat generated in the heat generating portion 35. When hard particles such as sand are bitten between the two, the resin is deformed, so that there is a problem that the biting portion is easily damaged.
[0010]
Further, in the case where a high-melting glass is used as the heat storage layer 32 as in the prior art, a thermal head cannot be manufactured by using a transfer method as described in the above publication. The formation of the recess 43 on the contact surface is inevitable, and there is a problem that the thermal efficiency is deteriorated.
[0011]
In view of the above problems, an object of the present invention is to provide a method for manufacturing a thermal head in which the heat generating portion has a high mechanical strength and a smooth contact surface with thermal paper or the like can be obtained.
[0012]
[Means for Solving the Problems]
In order to achieve this object, the thermal head manufacturing method of the present invention includes a step of forming a heating resistor,
Forming an electrode made of aluminum connected to the heating resistor before or after forming the heating resistor;
Forming a heat storage layer made of a low melting point glass having a softening point of 300 ° C to 400 ° C so as to cover at least a part of the heating resistor and the electrode by firing at 350 ° C to 400 ° C ;
Removing or separating the temporary substrate. ( Claim 1 )
[0013]
Moreover, the manufacturing method of the thermal head of the present invention includes a step of forming a protective layer on a temporary substrate,
Forming a heating resistor on the protective layer;
Forming an electrode made of aluminum connected to the heating resistor before or after forming the heating resistor;
Interposing a barrier layer for preventing diffusion of a substance contained in the heat storage layer in the heat generating portion composed of the heating resistor and the electrode;
Forming a heat storage layer made of low melting point glass having a softening point of 300 ° C. to 400 ° C. on the barrier layer by firing at 350 ° C. to 400 ° C . ;
Removing or separating the temporary substrate. ( Claim 2 )
[0014]
[Action]
The thermal head manufacturing method of the present invention includes a temporary protective layer, a heating resistor, an electrode made of aluminum, and a heat storage layer made of low-melting glass having a softening point of 300 ° C. to 400 ° C. after forming a barrier layer at 350 ° C. Since it is the method of forming by baking at -400 degreeC, the surface of the protective layer is smooth.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1A is a cross-sectional view showing an embodiment of a thermal head according to the present invention, and FIG. 1B is a cross-sectional view showing the overall configuration. As shown in FIG. 1 (A), the heat-generating laminated portion includes a protective layer 3 that acts as a wear-resistant layer, a heat-generating resistor 4, a common electrode 5a provided on the heat-generating resistor 4 in an overlapping manner, and It is interposed between the individual electrode 5b, the heat storage layer 7, the heat generating part 6 formed by the electrodes 5a, 5b and the heat generating resistor 4 and the heat storage layer 7 to prevent the diffusion of substances from the heat storage layer 7. It consists of a barrier layer 8.
[0016]
As the protective layer 3, a SiC compound, a SiB compound, a SiO compound, a SiON compound, or the like is used. In particular, the surface layer is made of SiB having a low coefficient of friction, high hardness, and chemically stable, and the back layer on the side of the heating resistor 4 is made of SiO ₂ having high electrical resistance. This is preferable in terms of ensuring electrical insulation. As a method of forming the protective layer 3, conventionally used methods such as plasma CVD can be employed.
[0017]
As the heating resistor 4, Nb—SiO ₂ , Ni—Cr, Ta, TiO ₂ , BN, or the like can be used. As a method for forming the heating resistor 4, LPCVD (low pressure CVD), plasma CVD, sputtering, or the like can be used.
[0018]
Each heating resistor 4 needs to be etched so as to be formed for each heating dot. As this etching method, it is preferable to use dry etching such as RIE (reactive ion etching). It is also possible to use etching. Moreover, as an etcher (reactive gas) for dry etching, SF ₆ , CF ₄ , Cl ₂ , O _{2, and the} like are generally used, and these can be mixed and used.
[0019]
The electrodes 5a and 5b are made of aluminum (Al). Al is inexpensive and can easily obtain adhesion to other layers without the need to intervene a special layer. The process is simple and the electrical resistance is low, making it easy to obtain fine patterns. Is preferable. As a film forming method, vapor deposition, sputtering, or the like is used.
[0020]
As an etching method for obtaining the pattern of these electrodes 5a and 5b, dry etching can be used, but wet etching is preferably used. As an etchant (etching solution) for wet etching, H ₂ SO ₄ , HNO _{3 and the} like are generally used. In particular, when Al is etched, a mixed solution in which H ₃ PO ₄ , C ₂ H ₄ O ₂ , and HNO ₃ are mixed may be used.
[0021]
SiO ₂ is used for the barrier layer 8. As a film forming method, LPCVD, plasma CVD, sputtering, or the like can be used. As the etching method, either wet etching or dry etching may be used. When wet etching is performed, HF or a mixed solution of HF and NH ₄ F is generally used as an etchant.
[0022]
As the heat storage layer 7, a low melting point glass is used in the present invention. This low melting point glass has a softening point of 400 ° C. or lower in order to prevent electrode deterioration and reaction when Al is used as an electrode, and also prevents softening due to heating in the manufacturing process after the heat storage layer 7 is formed. In this sense, the softening point is 300 ° C. or higher, more preferably 350 ° C. That is, when Al is used as the electrode, the softening point of the low-melting glass is preferably 300 ° C to 400 ° C , more preferably 350 ° C to 400 ° C.
[0023]
As a method for forming the heat storage layer 7, a screen printing method or a dispenser is used, and this is baked at 350 to 400 ° C. As the composition of the lead glass, it is preferable to use, for example, those of _PbO-B 2 _{O 3} -based or _PbO-B 2 O 3 -ZnO system.
[0024]
FIG. 1B is a cross-sectional view showing an example of a thermal head that follows the heat generation laminated portion of the basic structure of FIG. In FIG. 1B, 9 is a driving IC, 10 is a wiring to the outside, 11 is an electrode connecting the wiring 10 and the driving IC 9, 12a to 12c are driving IC and wiring 10 and electrodes 5a, 5b, 11 and The connecting portion 13 is a heat sink made of Al, and the heat sink 13 is provided with a through hole 13a for accommodating the drive IC 9. Reference numeral 14 denotes an adhesive layer made of an epoxy resin, an acrylic resin, or the like that fixes the heat radiating plate 13 to the heat generating laminated portion.
[0025]
In this way, by using the low melting point glass as the heat storage layer 7, a heat generation laminated portion can be realized by a method shown in FIG. 2 described later, and a smooth thermal paper contact surface (printing surface) can be obtained. Further, by forming the heat storage layer 7 with glass, compared to the case where the heat storage layer is formed with a heat-resistant resin such as polyimide resin, the heat generation laminated portion 2 (protective layer 3, heat generation resistor 5, electrodes 5a, 5b, The strength of the barrier layer 8 and the heat storage layer 7) can be improved, and even when hard particles such as sand are bitten, damage can be avoided.
[0026]
In this embodiment, since the driving IC 9 and the external wiring 10 are arranged on the opposite side of the printing surface, there is no contact between the driving IC 9 and its electrical connection portions 12a to 12c and the thermal paper. It is possible to eliminate the risk of occurrence of problems such as electrical disconnection or short circuit.
[0027]
Further, since the driving IC 9 is on the opposite side of the printing surface, the driving IC 9 can be disposed close to the printing unit, and the size of the thermal head can be greatly reduced as compared with the conventional structure. In addition, this miniaturization can increase the number of thermal heads obtained from one collective substrate. As a result, a large number of films can be formed at one time, and the thermal head manufacturing efficiency can be improved. The cost of the thermal head can be reduced.
[0028]
FIG. 2 is a process diagram for explaining a method of manufacturing the thermal head of the embodiment of FIG. In this embodiment, first, as shown in FIG. 2A, a protective layer 3 is formed on a temporary substrate 1. As the temporary substrate 1, a 0.7 mm thick borosilicate glass plate (manufactured by Nippon Electric Glass Co., Ltd., trade name BLC), which is inexpensive and easily available, was used.
[0029]
As the protective layer 3, a SiB layer and a SiO ₂ layer were sequentially formed in a 400 ° C. atmosphere by plasma CVD. The thickness of the SiB layer was 7 μm, and the thickness of the SiO ₂ layer was 3 μm.
[0030]
After forming the protective layer 3, as shown in FIG. 2B, an Nb—SiO ₂ layer to be the heating resistor 4 is formed to a thickness of 0.1 μm by sputtering at a temperature of 300 ° C. to 350 ° C. The individual heating resistors 4 were separated and formed by RIE. The pitch of the heating resistors 4 was 167 μm, and the spacing between the heating resistors 4 was 10 μm. The Nb—SiO ₂ layer is a mixture of metal Nb, Nb silicide, and oxide in an amorphous SiO ₂ layer. After providing the heating resistor 4 in this manner, heat treatment may be performed at about 400 ° C. in order to improve the TCR.
[0031]
Next, as shown in FIG. 2C, an Al layer as electrodes 5a and 5b is formed by vapor deposition at a temperature of 100 ° C. to a thickness of 0.5 μm, and H ₃ PO ₄ , C ₂ H ₄ O ₂ , HNO ₃ was used as an etchant, a common electrode 5a and an individual electrode 5b were formed by overlapping a part of them on the heating resistor 4, and an electrode 11 was formed at another position.
[0032]
Next, as shown in FIG. 2D, a SiO ₂ layer as the barrier layer 8 was formed to a thickness of 0.3 μm by plasma CVD. Then, by etching the formed SiO ₂ layer using HF as an etchant, a drive IC 9 is provided on the opposite side of the protective layer 3 as shown in FIG. 1B, so that it is connected to the electrodes 5b and 11 by flip chip bonding. The barrier layer 8 was provided with a hole for this purpose.
[0033]
Next, as shown in FIG. 2E, in order to form the heat storage layer 7, a paste in which a glass frit having a low melting point was mixed with a binder was screen-printed on the barrier layer 8 and then fired at 360 ° C. for 2 hours. As the glass paste, a product name of PLS-1301 manufactured by Nippon Electric Glass Co., Ltd. was used.
[0034]
Next, the solder balls on the bottom surfaces of the driving IC 9 and the external connection wiring 10 were fused to the electrodes 5b and 11, and the driving IC 9 was fixed to the heat generation laminated portion. That is, the driving IC 9 and the wiring 10 were fixed by flip chip bonding.
[0035]
Next, the hole 13a of the heat radiating plate 13 made of an Al plate is aligned with the drive IC 9 portion, and the heat radiating plate 13 is adhered to the portion formed as described above with an adhesive 14 made of epoxy resin, and heated at 150 ° C. Especially hardened and fixed together.
[0036]
Thereafter, the portion below the temporary substrate 1 was covered with an etching resist (may be a protective wax) made of Nikka Seiko Co., Ltd. and a product name black mask, and immersed in HF solution to dissolve the temporary substrate 1. Thereby, as shown in FIG. 2 (F), the protective layer 3 having a smooth surface formed on the temporary substrate 1 can be exposed.
[0037]
In the embodiment of FIG. 2, an inexpensive glass plate is used as the temporary substrate 1, the protective layer 3 is directly formed on the temporary substrate, and each layer is formed on the temporary substrate 1 and the driving IC 9. After the mounting, the temporary substrate 1 is removed by dissolving. However, when an expensive plate material is used as the temporary substrate 1, a sacrificial layer such as MgO is formed on the temporary substrate 1, As described above, after the layers are formed and the driving IC is fixed, the sacrificial layer may be dissolved with phosphoric acid or the like to separate the temporary substrate 1 from the heat-generating laminated portion 2, and the temporary substrate 1 may be reused. .
[0038]
Further, the electrodes 5a, 5b, and 11 may be formed before the formation of the heating resistor 4, instead of being formed after the heating resistor 4 is formed.
[0039]
FIG. 3A is a cross-sectional view showing another embodiment of the thermal head of the present invention with respect to the heat-generating laminated portion. In this embodiment, the barrier layer 8 is formed in a limited region immediately below the heat-generating portion 6. In addition, a heat storage layer 7 as a partial glaze layer made of low-melting glass is provided, and a heat storage layer 16 made of a heat-resistant resin such as an epoxy resin or a polyimide resin is provided thereunder.
[0040]
According to the present embodiment, since the heat generating portion 6 is supported by the heat storage layer 7 made of glass having a strength higher than that of the resin layer, a thermal head having a strength higher than that of the heat storage layer made of only the resin layer is used. Can be provided. Further, by superposing the heat storage layer 16 made of resin on the heat storage layer 7 made of glass, the heat storage action is increased, and a thermal head with low power consumption can be provided.
[0041]
In the example of FIG. 3B, the heat storage layer 16 made of the resin is also used as a fixing means for the drive IC 9. According to the present embodiment, the effects of the embodiment of FIG. 1B can be obtained, and furthermore, since the resin layer 16 can be used for fixing the heat storage layer and the drive IC 9, the number of parts and the number of processes can be reduced. The effect is obtained.
[0042]
FIG. 4 is a manufacturing process diagram for realizing the heat generation laminated portion structure of FIG. 3, and the processes of FIGS. 4A to 4D are the same as the processes of FIGS. 2A to 2D. It is. After the barrier layer 8 is formed as shown in FIG. 4 (D), the heat storage layer 7 made of the low melting point glass is slightly wider than the length of the heat generating portion 6 in the left-right direction as shown in FIG. 4 (E). The glass paste was formed by printing or application by a dispenser and baking at 350 ° C. to 400 ° C.
[0043]
Next, in order to form the heat storage layer 16 made of an epoxy resin, as shown in FIG. 4F, a paste containing the resin is printed so as to cover the entire heat storage layer 7 made of the low melting point glass, and 150 It was cured by heating at ° C.
[0044]
As shown in FIG. 3B, since the heat storage layer 16 made of the resin is used to fix the drive IC 9, when the drive IC 9 is fixed, the heat storage layer 7 made of low-melting glass is formed in advance and then the drive IC 9 is fixed. The IC 9 is fixed to the electrodes 5b and 11 with solder, and then the heat storage layer 16 is formed.
[0045]
In this embodiment, the heat storage layer 16 made of resin is also used to fix the drive IC 9 and the wiring 10. However, after the heat storage layer 16 and the fixing adhesive are separated and the heat storage layer 7 is formed in advance, the heat storage layer 16 is The drive IC 9 may be fixed by providing it at a place avoiding the place where the drive IC 9 is arranged. Further, in order to adjust the thermal response characteristics, it is also possible to appropriately disperse and contain metal powder or ceramic powder having high thermal conductivity (for example, AlN, Al ₂ O _3, etc.) in the heat storage layer 16 made of resin.
[0046]
FIG. 5 shows another embodiment of the present invention. This embodiment is a thermal head chip comprising only a heat-generating laminated portion by the heat storage layer 7 made of the low-melting glass and the heat-resistant layer 16 made of a heat-resistant resin such as polyimide resin. 24, and the chip 24 is provided with conductors 21 and 22 extending from the electrodes 5a and 5b to the back surface so that a connection portion with the insulating substrate 17 such as alumina is obtained on the opposite side of the printing surface. The chip 24 and the driving IC 9 are separately fixed to the conductors 19 and 20 provided on the insulating substrate 17 by soldering. Reference numeral 18 denotes a heat radiating plate bonded to the insulating substrate 17, and 23 denotes a resin molded on the driving IC 19.
[0047]
The conductors 21 and 22 provided on the chip 24 are formed by forming holes in the heat-resistant layer 16 made of polyimide resin by a method such as excimer laser and filling the holes with a conductive metal such as Ni or solder. be able to.
[0048]
Even in such a structure, the manufacturing method using the temporary substrate can be adopted, a smooth printing surface can be formed, and the use of low-melting glass as the heat storage layer 7 increases the strength as in the above-described embodiment. Can be planned. Further, by electrically connecting the surface opposite to the printing surface to the substrate 17, the distance between the wiring connection portion (bonding pad) and the heat generating portion is increased to about 10 mm as in the conventional thermal head. Therefore, the width of the thermal head chip 24 can be reduced to about 2 mm. For this reason, compared to the conventional thermal head chip 24, it is possible to obtain about five times the number of thermal head chips from a collective substrate having the same area, and the manufacturing cost can be greatly reduced.
[0049]
【The invention's effect】
According to the invention of claim 1, since the heat storage layer of the thermal head is formed by firing at 350 ° C. to 400 ° C. using a low melting point glass having a softening point of 300 ° C. to 400 ° C. , the melting point is relatively inexpensive. Even when an aluminum electrode having a low temperature is used, the electrode does not oxidize when the low melting point glass is fired, and the heat generating resistor can be heat-treated. For this reason, a thermal head having a smooth printing surface can be obtained.
[0050]
Moreover, compared with the case where heat resistant resin is used for a heat storage layer, mechanical strength improves and it can prevent the damage | wound by sand etc. biting.
[0051]
According to the method for manufacturing a thermal head of claim 2 , in addition to the effect of claim 1 , since a barrier layer is formed between the heat storage layer and the heat generating part, the substance contained in the low melting glass constituting the heat storage layer is It is possible to obtain an effect that a thermal head can be obtained which does not have the possibility of diffusing into the heat generating portion and degrading the characteristics.
[Brief description of the drawings]
1A is a cross-sectional view showing an embodiment of a thermal head according to the present invention, and FIG. 1B is a cross-sectional view showing an example of the overall configuration of a thermal head following the basic configuration of FIG. It is.
FIGS. 2A to 2F are manufacturing process diagrams of the embodiment of FIG.
FIG. 3A is a cross-sectional view showing another example of the heat-generating laminated portion of the thermal head according to the present invention, and FIG. 3B is a cross-sectional view showing an example of the overall configuration of the thermal head following the basic configuration of FIG. FIG.
4A to 4G are manufacturing process diagrams of the embodiment of FIG. 2A.
FIG. 5 is a sectional view showing another embodiment of the thermal head according to the present invention.
FIG. 6 is a cross-sectional view showing another example of a conventional thermal head.
[Explanation of symbols]
1: Temporary substrate, 3: Protective layer, 4: Heat generating resistor, 5a: Common electrode, 5b: Individual electrode, 6: Heat generating part, 7: Heat storage layer made of low melting point glass, 8: Barrier layer, 9: Drive IC: 10: External wiring, 11: Electrode, 12a to 12c: Connection part, 13: Heat sink, 14: Adhesive, 16: Heat storage layer made of resin, 17: Insulating substrate, 18: Heat sink, 19 , 20: conductor, 21, 22: conductor, 23: mold resin, 24: thermal head chip

Claims (2)

Forming a protective layer on a temporary substrate;
Forming a heating resistor on the protective layer;
Forming an electrode made of aluminum connected to the heating resistor before or after forming the heating resistor;
Forming a heat storage layer made of a low melting point glass having a softening point of 300 ° C to 400 ° C so as to cover at least a part of the heating resistor and the electrode by firing at 350 ° C to 400 ° C ;
Removing or separating the temporary substrate. A method for manufacturing a thermal head, comprising: Forming a protective layer on a temporary substrate;
Forming a heating resistor on the protective layer;
Forming an electrode made of aluminum connected to the heating resistor before or after forming the heating resistor;
Interposing a barrier layer for preventing diffusion of a substance contained in the heat storage layer in the heat generating portion composed of the heating resistor and the electrode;
Forming a heat storage layer made of a low melting point glass having a softening point of 300 ° C. to 400 ° C. on the barrier layer by firing at 350 ° C. to 400 ° C . ;
Removing or separating the temporary substrate. A method for manufacturing a thermal head, comprising:

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