JP3109374B2 - Resin sealing method for thermal recording head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a heating board having a heating element circuit and a driving circuit board having a driving circuit, wherein a driving IC is mounted on the heating board or the driving circuit board. The present invention also relates to a method of sealing the drive IC of the thermal recording head in which the drive IC is connected to the heating element circuit and the drive circuit via wiring portions such as bonding wires, respectively, and to resin-sealing the wiring portions.

[0002]

2. Description of the Related Art A thermal recording head used in a thermal facsimile or the like generally includes a heating substrate having a heating element circuit and a driving circuit substrate having a driving circuit at their ends. A driving integrated circuit (IC) is mounted near the bonding end of the heating substrate surface or the driving circuit substrate surface, and the integrated circuit is bonded to the heating element circuit and the driving circuit with a bonding wire. Etc. are conducted through the wiring parts such as
In this case, a flip chip bonding method or a wire bonding method is generally known as an IC mounting method.

[0003] After these bondings, in order to prevent moisture and conductive foreign substances from entering the exposed portions of the wiring material of the heat-generating substrate and the driving circuit board and the bonding portion of the driving IC, protective sealing with silicone resin is performed. Stopping is being done. Further, it is common to attach a head cover to the silicone-based sealing portion for the purpose of mechanical protection of the protection sealing portion and guide of the recording paper discharged by the platen roller. In particular, in the mounting method in the wire bonding method, the mechanical strength of the bonding wire is extremely weak even after protection and sealing with a silicone resin, so that a head cover is attached to facilitate handling during the manufacturing process, Alternatively, a jig having a head cover function is required. Also, in the flip chip bonding method,
After protection and sealing with a silicone resin or the like, a head cover is also required to mechanically protect the elements of the driving IC itself.

Conventionally, as described above, a silicone resin is mainly used as a resin used for protective sealing of such a driving IC, and the silicone resin has sufficient environmental resistance and electrical insulation. However, the function of mechanical protection is not sufficient, and a head cover must be attached to the protective sealing portion. Therefore, there is a problem that the number of working steps is large and the material cost is high.

For this reason, in order to provide the function of mechanically protecting the driving IC and the bonding wire not in the head cover but in the sealing resin itself, an epoxy having a large hardness is used instead of a silicone resin which has been generally used so far. A method of sealing with a resin composition has been developed.

However, when sealing is performed with the epoxy resin composition, the epoxy resin composition is inferior in defoaming properties as compared with the silicone resin, and therefore, voids are generated on the surface of the cured sealing resin. Such surface voids have the problem of damaging the thermal recording paper.

[0007] The cause of the void generation is caused by the filling of the resin powder below the high-density wire and the generation of the void from the gap at the joint between the heat generating substrate and the driving substrate.

In order to prevent the voids generated from the gaps between the substrate joints, it is effective to use a resin having a relatively high viscosity to suppress the voids generated from the gaps. If such a high-viscosity resin is used, the resin filling property under the high-density wire will be impaired,
Voids are generated and reliability is reduced.

In particular, in recent years, the heating element has been miniaturized more than ever for the purpose of improving printing accuracy, and accordingly, the distance between the wires has been narrowed, and there has been a trend toward higher density wires. For this reason, a sealing method using an epoxy resin that maintains the filling property of the lower part of the high-density wire and does not generate voids on the surface of the sealing material is desired.

In addition, when attention is paid to reliability, the gap at the substrate bonding portion is seen in the entire lengthwise direction of the TPH device and reaches the side surface. Even if the IC is covered with the resin, water is absorbed from the lower part of the resin, and the reliability is reduced. Therefore, a THP device that prevents surface voids and has excellent reliability is desired from this point of view.

[0011]

The inventor of the present invention has conducted intensive studies to meet the above-mentioned demands. As a result, the distance between the driving circuit board and the heating element circuit board is usually 50 to 200 μm.
Note that there is a large gap, and there is a large variation in the gap depending on the location. This gap is previously sealed and filled with an epoxy resin composition having a flowability of an aspect ratio of 0.1 or less. When the entire IC and each wiring section are sealed with epoxy resin sealing material, epoxy resin sealing material with relatively low viscosity that emphasizes the filling property under the high-density wire can be used, and voids on the surface of the sealing material It has been found that it is possible to prevent the occurrence of water vapor from the lower part of the substrate and to obtain a TPH device with further improved reliability, which has led to the present invention.

Accordingly, the present invention comprises a heating board having a heating element circuit and a driving circuit board having a driving circuit. A driving IC is mounted on the heating board or the driving circuit board. The drive IC and the heating element circuit and the drive circuit are connected to each other via a wiring portion such as a bonding wire, respectively, and the drive IC and each wiring portion of the thermal recording head are resin-sealed using an epoxy resin sealing material. When stopping, the joint between the heat-generating substrate and the driving circuit board is sealed in advance with a first epoxy resin composition having an aspect ratio of 0.1 or less, and then the drive is performed using a second epoxy resin sealing material. The present invention provides a resin sealing method for a thermal recording head, which is characterized by performing resin sealing of an IC for use and each wiring portion.

Hereinafter, the present invention will be described in more detail. As shown in FIGS. 1 to 5, the resin sealing method of the present invention comprises, for example, a heating substrate 1 having a heating element circuit (heating element) 1a and a driving board 1a. The driving circuit board 2 having the circuit 2a is joined at one end thereof, and the driving IC 3 is joined to the terminal of the driving IC 3 near the joining end of the heating substrate 1 or the driving circuit board 2 surface. Mounted along the direction, the terminals of the IC 3 and the heating element circuit 1a and the driving circuit 2
a through the wiring portions 4 and 5 such as bonding wires.
After sealing and filling the joint 6 between the circuit board 2 and the driving circuit board 2 with the epoxy resin composition 7 having an aspect ratio of 0.1 or less in advance, the IC 3 and the wiring sections 4 and 5 are each filled with an epoxy resin sealing material. The sealing is performed at 8. In addition, 9 in the figure is a heat dissipation substrate.

In such a thermal recording head, the heat-generating substrate 1 is brought into contact with a platen roller 10 so that the heat-sensitive recording paper 11 is passed between the heat-generating substrate 1 and the platen roller 10.

The IC 3 is either mounted on the drive circuit board 2 as shown in FIGS. 1 to 3 or mounted on the heat generating board 1 as shown in FIGS.

In the present invention, the epoxy resin composition which fills the gaps of the joints 6 and seals the joints 6 has an aspect ratio of 0.1 or less, more preferably 0.08. Use the one with the following high fluidity. When an epoxy resin composition having an aspect ratio of more than 0.1 is used, it is difficult to penetrate the resin into the gap of the joint 6 and the object of the present invention cannot be achieved.

In the present invention, the aspect ratio is
0.1 g of the epoxy resin composition was dropped on a glass plate to obtain 1
A value obtained by dividing the height of a cured product obtained by heating on a hot plate at 20 ° C. for 1 hour by the diameter of the bottom surface.

As such an epoxy resin composition,
Liquid at room temperature is effective. As the curable epoxy resin constituting the liquid epoxy resin composition, a resin having two or more epoxy groups in one molecule can be used, as long as it can be cured by various curing agents as described below. There are no particular restrictions on the molecular structure, molecular weight, and the like, and various conventionally known compounds can be used. Specifically, for example, epoxy resins synthesized from various novolak resins including epichlorohydrin and bisphenol, alicyclic epoxy resins or epoxy resins into which halogen atoms such as chlorine and bromine atoms have been introduced, and the like, Among them, a glycidyl ether derivative of bisphenol A or bisphenol F is preferably used in order to obtain a low-viscosity composition that is liquid at room temperature. In addition, the use of the epoxy resin is not necessarily limited to one type, and two or more types may be mixed and used.

When using the above epoxy resin, a monoepoxy compound may be appropriately used in combination.
Specific examples of the monoepoxy compound include styrene oxide, cyclohexene oxide, propylene oxide, methyl glycidyl ether, ethyl glycidyl ether, phenyl glycidyl ether, allyl glycidyl ether, octylene oxide, dodecene oxide and the like.

Examples of the curing agent include amine curing agents such as diaminodiphenylmethane, diaminophenylsulfone, and metaphenylenediamine; and acids such as phthalic anhydride, pyromellitic anhydride, and benzophenonetetracarboxylic anhydride. Examples thereof include anhydride-based curing agents and phenol novolac curing agents having two or more hydroxyl groups in one molecule, such as phenol novolak and cresol novolak. Among these, an acid anhydride-based curing agent is preferably used to obtain a low-viscosity, low-stress epoxy resin composition.

The amount of the curing agent used can be a usual amount, but is preferably in the range of 50 to 150 equivalent%, particularly preferably 80 to 110 equivalent%, based on the epoxy group equivalent of the epoxy resin.

Further, in the epoxy resin composition, for the purpose of accelerating the reaction between the curing agent and the epoxy resin,
Various curing accelerators, for example, imidazole or a derivative thereof, a tertiary amine derivative, a phosphine derivative, a cycloamidine derivative, and the like can be used in combination.
In addition, the compounding quantity of these hardening accelerators can also be made into a normal range.

Further, an inorganic filler can be blended in the epoxy resin composition. In this case, the kind of the inorganic filler to be used, a single use or a combination of a plurality of kinds is not limited, and is appropriately selected. Examples of the inorganic filler include one or two selected from natural silica such as crystalline silica and amorphous silica, synthetic high-purity silica, synthetic spherical silica, talc, mica, silicon nitride, boron nitride, and alumina. The above can be used.

The amount of the inorganic filler is determined so that the aspect ratio of the epoxy resin composition is in the above-mentioned range.

The epoxy resin composition may further contain a releasing agent such as a stress reducing agent, a carbon-functional silane for improving adhesion, waxes, fatty acids such as stearic acid and metal salts thereof, and a pigment such as carbon black, if necessary. , Dyes, antioxidants,
A surface treatment agent (such as γ-glycidoxypropyltrimethoxysilane), various conductive fillers, and other additives can be blended.

The epoxy resin composition can be obtained by uniformly stirring and mixing predetermined amounts of the above-mentioned components (the order of blending the components is not particularly limited).

The aspect ratio of the epoxy resin composition can be controlled by appropriately selecting the type of the epoxy resin and the curing agent, the type of the filler, and especially the amount of the filler. Further, for example, a syringe or a needle for discharging the epoxy resin is heated, or a substrate is heated before or after application, so that penetration into a gap can be improved.

In the present invention, as a method for sealing using the epoxy resin composition as described above and filling the gap of the joint 6, the epoxy resin composition 7 may be used before the wire bonding on the driving substrate side. Application and filling method,
Alternatively, a method of applying and filling from the wire after wire bonding may be used.

On the other hand, the epoxy resin encapsulant 8 for encapsulating the drive IC and each wiring portion with resin is appropriately selected. The linear expansion coefficient of the cured product and the curing of the epoxy resin composition 7 are determined. Those having a difference from the coefficient of linear expansion of the object within 25% are preferably used. In addition, the viscosity (BH type rotor 7,
(20 rpm, 25 ° C.) is recommended to use one having 2000 poise or less.

That is, in the heat-sensitive recording head, the bonding wires on the heat-generating substrate side have a higher density than the bonding wires on the driving circuit board side. The filled portion remains to lower the reliability, and the voids rise during curing, making it difficult to obtain a sealing surface state that can be used as a paper feed guide.

When the aspect ratio is lower than 0.1,
There is a case where the part that does not need to be sealed is sealed, which may hinder the original operation of the thermal recording head device,
On the other hand, if the aspect ratio exceeds 0.25, the shape of the sealing portion after curing becomes unsuitable as a paper feed guide.

The components and the amounts of the epoxy resin encapsulant 8 are the same as those of the epoxy resin composition 7, except that the types and the amounts of the epoxy resin, the curing agent, and the filler are appropriately selected and the amount of the epoxy resin is set. It is preferable to adjust the viscosity and the aspect ratio. In this case, fine powder spherical silica having an average particle size of 5 μm or less, particularly 2 μm or less can be blended into the epoxy resin sealing material 8 as a thixotropy imparting agent.

As a method for applying the epoxy resin sealing material 8, at least two lines of the epoxy resin composition are applied across the wiring portions of the driving IC, the heating element circuit and the driving circuit. Then, the linear coating portion is continuously integrated by the flow of the epoxy resin sealing material,
It is recommended to cover the entire surface of the driving IC and each wiring portion with an epoxy resin sealing material and cure the same.

More specifically, in FIG. 1, at least the wiring portion 4 on the heat-generating board side and the driving circuit board 2 along the joining direction of the joint portion 6 between the heat-generating substrate 1 and the drive circuit board 2
In this case, two linear coating portions crossing the wiring portion 5 on the side are separately applied to each other. The number of the linear coating portions 6 may be two or more. The linear coating portions 6 may be formed on the IC 3 in addition to the two crossing the wiring portions 4 and 5. In this case, especially when sealing the IC 3 last,
When applying resin linearly between the linear application parts,
It is permissible to use a resin having an aspect ratio of 0.1 or less as this resin.

By coating as described above, each linear coating portion flows in the width direction and spreads, and is integrated with each other to cover the entire surface of the IC and each wiring portion. By using an epoxy resin encapsulant having a specific ratio, it is possible to flow, expand and integrate well before curing, to reduce voids and reduce unfilled portions, and to secure shape controllability.

It should be noted that there are no restrictions on the type, application method, application conditions, application sequence, and the like used for application.

In this case, since the wiring densities of the bonding wires on the heat generating substrate side and the driving side are different, it is also effective to use an epoxy resin encapsulant for covering these wires having different viscosities and the like according to the wiring density. There is also no restriction on the order as described above, and as a method for improving the filling property, after partially or several coatings, leaving at room temperature or heating, or pre-curing, sealing, and remaining after sealing A method of coating and sealing a portion can be adopted.

The curing method and conditions for the epoxy resin composition 7 and the epoxy resin sealing material 8 are not particularly limited.
A method in which the epoxy resin composition 7 is applied and cured in advance, and then the epoxy resin encapsulant 8 is applied and cured, or the epoxy resin composition 7 is applied and the epoxy resin encapsulant 8 is applied.
Next, any method of simultaneously curing both may be used. The curing conditions are about 30-60 at 60-100 ° C.
It is preferable to perform an initial curing for 120 minutes and then a full curing at 120 to 175 ° C. for 2 to 5 hours.

[0039]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In addition, in the following examples, a part shows a weight part. <Preparation of epoxy resin composition> As an epoxy resin, a bisphenol-type epoxy resin (epoxy equivalent: 184, 25)
C. at 160 ° C.) and acid anhydride (4
-Methylhexahydrophthalic anhydride), a silicone-modified epoxy resin represented by the following formula (1) as a low-stress agent, an imidazole-based curing accelerator (trade name: HX3741, manufactured by Asahi Kasei Corporation) as a curing accelerator, and γ as an additive -Glycidoxypropyltrimethoxysilane, fused spherical silica having an average particle diameter of 1 μm or less as a thixotropy imparting agent, and fused spherical silica having an average particle diameter of 15 μm as an inorganic filler are blended in the amounts shown in Table 1, and these are uniformly mixed. The mixture was mixed to obtain an epoxy resin composition and an epoxy resin sealing material.

[0040]

Embedded image

Next, using the epoxy resin composition shown in Table 1, the thermal recording head shown in FIG. 6 was sealed at the needle position shown by the epoxy resin composition among the needles 12 shown in FIG. Then, the epoxy resin sealing material was sealed at the positions of the needles shown in FIG.

The conditions for this sealing are as follows. Thermal recording head: long piece length 5 cm, 6 driving ICs mounted, heating substrate side wire spacing 80 μm, chip spacing 10
00 μm Model used for resin ejection device: Auto shooter (manufactured by Iwashita Engineering Co., Ltd.) Needle inner diameter: 0.34 mm for epoxy resin composition: 1.25 mm for epoxy resin sealing material Distance from needle tip to chip top: 500 μm Application speed: 30 mm / sec Curing conditions: 2 hours on a hot plate at 150 ° C. Curing method A: Performed on a device after wire bonding, apply epoxy resin composition 7, then apply epoxy resin encapsulant 8, , Cured. Curing method B: Performed on a pre-wire bonding apparatus, applied the epoxy resin composition 7, then performed wire bonding, and then sealed the epoxy resin sealing material 8.

The following evaluation was performed on the sealed thermosensitive recording head. The results are shown in Tables 2 and 3. <Surface void generation state> The number of voids generated on the surface of the sealant (including through voids) was observed and evaluated according to the following criteria. ：: 0 ×: 1 or more <Void lower part generation state> The sealant was cut with a slicer, the number of unfilled parts and the generation of voids in the lower part of the heating element side wire were observed, and evaluated according to the following criteria. ：: 0 pieces ×: 1 piece or more <Defective state-moisture resistance test> Observe the electrical characteristics of all wires on the device at 80 ° C. and 90% RH.
Evaluation was made according to the following criteria.

：: No defect until 1000 hours ×: One or more wires disconnected or contact failure within 1000 hours

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

As is clear from the results of the examples and comparative examples, although not noticed so far, the gap between the substrate bonding portions 6 greatly affects the generation of voids and the reliability during resin sealing. According to the present invention, by filling and sealing the joint portion 6 with an epoxy resin composition having an aspect ratio of 0.1 or less in advance, a driving IC using a low-viscosity epoxy resin sealing material that emphasizes the filling property to a high-density wire and Even when resin sealing is performed on each wiring portion, no surface voids are generated, and it is recognized that moisture resistance reliability is further improved.

[0049]

According to the resin sealing method for a thermal recording head of the present invention, a wiring portion such as a bonding wire of an integrated circuit mounted on the thermal recording head does not generate voids on the surface and has high moisture resistance reliability. Can be sealed.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of a thermal recording head to which the present invention is applied.

FIG. 2 is a cross-sectional view illustrating an example of a thermal recording head to which the method of the present invention is applied.

FIG. 3 is a cross-sectional view showing an example of a thermal recording head to which the method of the present invention is applied.

FIG. 4 is a cross-sectional view showing an example of a thermal recording head to which the method of the present invention is applied.

FIG. 5 is a sectional view showing an example of a thermal recording head to which the method of the present invention is applied.

FIG. 6 is a cross-sectional view showing a thermal recording head and needle positions in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat generation board 1a Heating element circuit 2 Drive circuit board 2a Drive circuit 3 Drive IC 4,5 Wiring part 6 Joint part 7 Epoxy resin composition 8 Epoxy resin sealing material 9 Heat radiating substrate 10 Platen roller 11 Thermal recording paper 12 needle

──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazuo Dobashi 1-10 Hitomi, Matsuida-machi, Usui-gun, Gunma Prefecture Inside Silicone Electronics Materials Research Laboratory Shin-Etsu Chemical Co., Ltd. (72) Takayuki Sawada Matsui, Usui-gun, Gunma Prefecture Hitomi Tamachi 1-10 Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory (56) References JP-A-4-267162 (JP, A) JP-A-6-69259 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) B41J 2/335 B41J 2/345 H01L 23/29 H01L 23/31 H01L 49/00

Claims (2)

(57) [Claims] 1. A heating board having a heating element circuit and a driving circuit board having a driving circuit. A driving IC is mounted on the heating board or the driving circuit board. At the time of resin-encapsulating the drive IC and each wiring portion of the thermal recording head in which the heating element circuit and the driving circuit are respectively connected via wiring portions such as bonding wires using an epoxy resin sealing material,
After the joint between the heating substrate and the driving circuit board is sealed in advance with a first epoxy resin composition having an aspect ratio of 0.1 or less, the driving IC is sealed using a second epoxy resin sealing material.
And a resin sealing method for the thermal recording head, wherein the resin sealing of each wiring portion is performed. 2. The method according to claim 1, wherein the second epoxy resin encapsulant has a viscosity at 25 ° C. of 2000 poise or less and an aspect ratio of 0.1 to 0.25.