WO2007011567A1

WO2007011567A1 - Coating agent and metal mask

Info

Publication number: WO2007011567A1
Application number: PCT/US2006/026698
Authority: WO
Inventors: Yuji Ino
Original assignee: 3M Innovative Properties Company
Priority date: 2005-07-15
Filing date: 2006-07-11
Publication date: 2007-01-25
Also published as: JP2007023160A

Abstract

A coating agent used in the formation of a thin film on a surface of a metal mask, formed from a metallic material, having opening portions of the predetermined pattern, in which said coating agent comprises a fluorine-containing phosphonic acid compound containing fluorine atoms in a molecule thereof, and a phosphonic acid of the fluorine containing phosphonic acid compound can be bonded to a metal atom of the metal mask to form a salt thereof.

Description

COATINGAGENTAND METAL MASK

Technical Field

The present invention relates to a coating agent, and more particularly, it relates to 5 a metallic mask used as a masking means in the printing process and others, that is, a coating agent useful in the formation of a thin film having an ink repellency on a surface of the metal mask. The present invention also relates to a metal mask having applied on a surface thereof a thin film formed from such a coating agent.

0 Background

As is well-known in the production of electronic devices and others, it is conventional to form wiring patterns or external connection terminals, for example, by printing an electrically conducting material such as solder paste on a surface of the printed wiring board. Further, metal masks consisting of a metallic material and having opening

5 portions of the predetermined pattern are widely used to selectively print the conducting material. The metal mask is formed from a metallic material such as stainless steel and nickel. Using a thin plate of these metallic materials, the desired metal mask can be produced by a method in which openings of the desired pattern are formed through, for example, etching or by a method (so-called electroforming method) in which a metal

>0 plating is applied onto a resist pattern having the previously formed openings and then the used resist is removed to obtain a metal plate with openings.

However, when a conducting material which is generally used as a paste is printed through a metal mask on a surface of the printed wiring boars, there is caused a problem that printing of the paste cannot be printed with the desired pattern, because the paste is

>5 adhered to a side wall of the openings of the metal mask or the openings are closed with the paste. Now, a tendency of such a problem is increasing, because in recent years, there is a tendency of miniaturizing the semiconductor packaging parts and increasing the packaging density, and to satisfy these requirements, the openings of the wiring boar have to be formed with a fine pattern and a high density. Especially, when the metal mask has

SO fine openings, a filling property of the paste in the openings is deteriorated and thus the printing itself becomes difficult. To solve these problems, for example, Japanese Unexamined Patent Publication (Kokai) No. 5-220922 suggests a metal mask characterized in that a fluorine-containing chemical adsorptive monomolecular film originated from a fluorine-based silane coupling agent is formed on a surface of the metal mask, made of a metallic material, having openings of the desired pattern. Further, Japanese Unexamined Patent Publication (Kokai) No. 8-290686 suggests a metal mask for printing in which the metal mask is laminated over a printing screen after formation of through-holes for wiring patterns in the mask, and then a printing paste consisting of a conducting material is printed through the mask, characterized in that a full surface of the metal mask has an applied coating of the fluorine-containing resin. Furthermore, Japanese Unexamined Patent Publication (Kokai) No. 10-250032 suggests a metal mask for printing in which after lamination of a dry resist film to a metallic substrate, a photolithographic plate is applied to the substrate to make a contact expose, and the exposed or unexposed portions of the resist film are removed and the substrate is subjected to the subsequent processing steps to obtain the metal mask, characterized in that any areas of the metal mask other than the areas to be contacted with a printing target have an applied nickel/PTFE plating layer. Moreover, Japanese Unexamined Patent Publication (Kokai) No. 2002-192850 suggests a metal mask for printing characterized by having a cured resin layer, as a layer covering an inner wall of the openings or a layer covering a surface of the substrate, which is produced by coating and curing a silicone-modified fluorine-containing resin onto an inner wall of the openings of the metallic layer and a substrate side of the metallic layer.

Summary of the Invention

As described above, to prevent the problems such as adhesion of the printing paste to the metal mask or clogging of the openings, the prior art technologies suggest surface modification methods such as chemical adsorption of the fluorine-based silane coupling agent to a surface of the metal mask, coating treatment of the fluorine-containing resin, application of the nickel/PTFE plating layer and coating of the silicone-modified fluorine-containing resin. However, as described above, as the semiconductor packaging parts and others are miniaturized and are packaged with an increased density in recent years, the prior art surface modification methods are insufficient to obtain the satisfactory effects. Especially, the prior art modification methods suffer from limited reduction of the surface tension in the openings, thereby becoming impossible to improve a filling property of the printing paste in the openings. Further, as the surface modification layer formed according to the prior art methods has a poor bonding power to the metal mask, there is a drawback that a durability of the metal mask is short. Furthermore, as the surface modification layer formed upon the methods described in Japanese Unexamined Patent Publication (Kokai) No. 5-220922, Japanese Unexamined Patent Publication (Kokai) No. 8-290686, and Japanese Unexamined Patent Publication (Kokai) No. 10-250032 has a thickness of several microns, there is a drawback that a configuration of the openings can be varied due to its thickness. Therefore, an object of the present invention is to provide a novel coating agent for metal masks which can prevent adhesion of a printing paste and others to a metal mask or clogging of the mask openings with the paste, even if the metal mask has finely formed openings and the openings are distributed at a high density, thereby enabling to obtain a sufficiently improved filling property of the paste in the openings and an extended durability.

Further, an object of the present invention is to provide a metal mask for use as a masking means in printing a printing paste and others in a predetermined pattern, which can exhibit an excellent filling property of the printing paste in openings and an extended working durability, even if the openings have a fine size and are distributed in a high density.

These and other objects of the present invention will be easily appreciated from the following detailed description of the present invention.

The inventor of this application has positively studied to attain the above objects, and has found that the application of new bonding embodiment in which metal atoms and

5 phosphonic acid are bonded to form a salt of phosphonic acid is useful to complete the present invention, without relying upon the method in which a chemical adsorptive monomolecular layer is fixed through the -Si-O-Metal bond to a metal atom of the metal mask, as in the above-described use of a fluorine-based silane coupling agent, for example.

) According to one aspect thereof, the present invention resides in a coating agent used in the formation of a thin film on a surface of the metal mask, formed from a metallic material, having opening portions of the predetermined pattern, in which the coating agent comprises a fluorine-containing phosphonic acid compound containing fluorine atoms in a molecule thereof, and a phosphonic acid of the fluorine-containing phosphonic acid compound can be bonded to a metal atom of the metal mask to form a salt thereof

Further, according to another aspect thereof, the present invention resides in a metal mask, formed from a metallic material, having opening portions of the predetermined pattern, in which at least a surface of the opening portions (that is, a surface of the side walls) has applied thereon a thin film of the fluorine-containing phosphonate formed from the coating agent according to the present invention.

As will be understood from the following detailed descriptions, using the coating agent for metal masks according to the present invention, it becomes possible to prevent adhesion of a printing paste and others to a metal mask or clogging of the mask openings with the paste, even if the metal mask has finely formed openings and the openings each is distributed at a high density, and thus realize a sufficiently improved filling property of the paste in the openings. Moreover, a working durability of the metal mask can be remarkably extended in comparison with the prior art products, because the resulting thin film of the fluorine-containing phosphonate can be strongly bonded to the metal mask, and thus the thin film cannot be easily abraded or peeled.

In addition, according to the present invention, it becomes possible to provide a metal mask for use as a masking means in printing a printing paste and others in a predetermined pattern, which can exhibit an excellent filling property of the printing paste in openings and also an extended working durability, even if the openings have a fine size and are distributed in a high density.

The metal mask of the present invention can be advantageously used in the production of electronic devices and others, for example, when a conductive material such as a solder paste is printed onto a surface of the printed wiring board to form wiring patterns, external connection terminals and others. In addition, the metal mask can be advantageously used as a masking means in the general printing technologies such as screen printing, for example, when a printing product is produced using a variety of the printing materials, or when a resist material is deposited with the desired pattern in a photolithographic process. Brief Description of the Drawings

Fig. 1 is a cross-sectional view illustrating one preferred embodiment of the metal mask according to the present invention.

Fig. 2 is a cross-sectional view illustrating, in sequence, the method of printing a solder paste on a printed wiring board using the metal mask of the present invention.

Brief Description of the Preferred Embodiments

The coating agent for metal masks and the metal mask according to the present invention each can be advantageously carried out in different embodiments. Hereinafter, the coating agent and the metal mask of the present invention each is described with reference to its preferred embodiments, but it should be understood that the present invention is not restricted to these embodiments.

The coating agent of the present invention is that designed to be especially used for metal masks. That is, the coating agent of the present invention is used to form a thin film on a surface of the metal mask which was made from a metallic material and has opening portions formed in the predetermined pattern. Here, the metal mask is not restricted to the specific one with regard to its constitution and application, and thus it includes metal masks which are generally used as a masking means in the fields of electronic device production and printing processes as well as a photolithographic process. Accordingly, the metal mask can be freely produced from a wide variety of metallic materials. Suitable metallic material includes, for example, an iron, stainless steel, nickel, chromium and others. If desired, these metallic materials may be used in the form of a metal alloy. Generally, the metal mask can be produced from these metallic materials by using the conventional methods such as etching, electroforming and others. To transfer a printing paste and other materials onto the underlying substrate, the metal mask has opening portions bored at the predetermined pattern therein. A pattern of the opening portions can be freely formed depending upon the transfer pattern of the printing paste and others. It is important in the metal mask of the present invention that the functions and effects of the present invention can be fully realized when the opening portions have a fine size and/or are distributed at a high density, while of course, the metal mask may have opening portions having a relatively large size and a relative low distribution density as is conventional in the prior art metal masks. When the coating agent of the present invention is applied to the opening portions of the metal mask, the coating agent can be firmly adhered to a side wall of the opening portions, even if the opening portions have a fine size and a high density. Moreover, as the coating agent itself can exhibit excellent functions and effects in comparison with the prior art surface modifying agents such as a fluorine-based silane coupling agent, it becomes possible to remarkably increase a filling property of the printing paste and largely extend a working durability of the metal mask.

In the practice of the present invention, the printing paste and others used herein are not restricted to the specific materials, and thus may include any printing materials which can be used for the printing purpose in the metal mask of the present invention. Suitable printing paste and others include, for example, a solder paste such as creamy solder, a paste of the printing ink used in a screen printing and other printing processes, a paste of the resist material used in a resist process, and other pastes. It is difficult to numerically limit the viscosity of these pastes, but it is preferred that the pastes have a viscosity sufficient to pass through the opening portions.

The coating agent of the present invention comprises a fluorine-containing phosphonic acid compound which contains one or more fluorine atoms in a molecule thereof. Further, the fluorine-containing phosphonic acid compound, when the coating agent of the present invention is applied as a surface modifying agent to the predetermined areas of the metal mask, can result in bonding of its phosphonic acid to a metal atom of the metal mask to thereby form a salt of the phosphonic acid. Since it has a very low surface energy, the mask surface covered with the resulting salt of the fluorine-containing phosphonic acid compound can exhibit an excellent paste repellency and releasability. In the practice of the present invention, a wide variety of fluorine-containing phosphonic acid compounds may be used as a coating agent. A molecular weight of the fluorine-containing phosphonic acid compounds is generally about 400 to 5,000, preferably about 1,000 to 3,000. Suitable fluorine-containing phosphonic acid compounds include perfluoropolyetherphosphonic acid, for example, at least one compound selected from the group consisting of the following compound (I), (II) and (III):

In the above formulae, n is an integer of about 3 to 30, preferably an integer of about 3 to 15, more preferably an integer of about 3 to 10. The fluorine-containing phosphonic acid compounds may be synthesized with different methods.

Further, another group of suitable fluorine-containing phosphonic acid compounds include a compound containing an amide bode, for example, at least one compound selected from the group consisting of the following compound (IV) and (V):

O R O

Il

_{R f}_j_C N-R 2. p . -ox ]_. : iv)

O X

O R ¹ O

o x

In the above formulae,

R_f is a monovalent or divalent perfluoropolyether group, y is 1 or 2, X may be the same or different and each represents hydrogen, cycloalkyl group, alkali metal, ammonium, ammonium substituted with an alkyl or cycloalkyl group, or 5- to 7-membered heterocyclic group containing a positive charging nitrogen atom, and generally represents hydorongen,

R¹ is hydrogen or an alkyl group, and

R² represents a divalent group selected from the group consisting of an alkylene group, arylene group, heteroalkylene group or a combination thereof. These compounds generally have a molecular weight of about 400 to 5,000, preferably about 1,000 to 3,000.

More specifically, the fluorine-containing phosphonic acid compounds represented by the above formula (IV) include, for example, the following compounds:

In the above formulae, n has an average value of 0 to 50, 1 to 50, 3 to 30, 3 to 15 or 3 to 10. Note that when these compounds are used as a derivative thereof, it is necessary that the derivative is an acid form. Further, the fluorine-containing phosphonic acid compounds may be synthesized with different methods.

0 When the fluorine-containing phosphonic acid compounds described above are applied as a coating agent to the metal mask, the phosphonic acid compounds may be applied to the metal mask with different methods depending upon the types, amounts, properties and others of the phosphonic acid compounds. Generally, a method including the steps of coating a solution of the fluorine-containing phosphonic acid compound on a

:5 metal mask, followed by drying and reacting the compounds can be used as the application method, but, if possible, a method of depositing the phosphonic acid compound at a desired pattern on the metal mask with vacuum deposition and others may be used. When it is coated from its solution, the phosphonic acid compound can be used after dissolving in or diluting with a solvent such as hydrofluoroether and perfluoropolyether. Of course,

>0 if desired, a spraying method, dipping method and others may be used in place of the coating method.

The coating formed on the metal mask from the fluorine-containing phosphonic acid compounds described above, that is, a thin film of fluorine-containing phosphonate has a paste repellency, i.e., repellency to different pastes such as solder pastes, printing ink pastes and resin pastes filled in the opening portions of the metal mask in the subsequent steps.

Further, the thin film of fluorine-containing phosphonate may be formed with different film thicknesses. According to the present invention, the thin film of fluorine- 5 containing phosphonate can be formed at a remarkably reduced thickness, and also such a reduced thickness of the film does not adversely affect onto the functions and effects of the present invention.

In addition to the coating agent for metal masks, the present invention resides in a metal mask using such a coating agent. That is, the metal mask of the present invention is 0 characterized in that it is a metal mask which is formed from a metallic material and has one or more opening portions formed in the predetermined pattern, and also the metal mask has a thin film of the fluorine-containing phosphonate formed from the coating agent of the present invention in at least a surface of the opening portions.

The metal mask of the present invention can be advantageously carried out with 5 different embodiments. Fig. 1 is a cross-sectional view illustrating one preferred embodiment of the metal mask according to the present invention. A metal mask 10 is constituted from a substrate 1 and openings 2 formed with the desired pattern at any positions of the substrate 1. In the illustrated metal mask 10, the openings 2 have a perpendicularly extending inner wall, but if desired, the inner wall of the openings may be O sloped or chamfered in order to improve filling of the paste into the openings and handling. The metal mask 10 can be formed from, for example, stainless steel or nickel by using any conventional methods such as etching, laser drilling and electroforming. For example, when the metal mask is produced from the stainless steel, a stainless plate having the predetermined thickness is first provided. Then, both of the top and back surfaces of 15 the stainless plate is laminated with a dry film resist. In the laminated dry film resist, the resist appearing in the area corresponding to the openings of the metal mask is selectively dissolved to remove it from the stainless plate. Thereafter, using the remaining dry film resist as a masking means, the exposed stainless plate is dissolved and removed with a suitable etchant. Finally, the used dry film resist is removed to obtain a metal mask 10 \0 with the openings 2.

Next, the metal mask 10 is described with regard to a configuration and dimension thereof. Although it can be used in any configurations, the metal mask 10 is generally rectangular. Further, although it can be widely varied depending upon the factors such as the material and application of the metal mask 10, a thickness of the metal mask 10 is usually about 500μm or less, and generally about 200 to 300μm. Similarly, the openings 2 of the metal mask 10 can be formed at any configurations depending upon the factors such as applications of the metal mask, i.e., profiles of the resulting wiring patterns and printing patterns. Further, although they are finely formed, the openings 2 do not adversely affect the functions and effects of the preset invention. For example, even if the openings 2 are finely formed in the metal mask 10 in such a order of several microns in the minimum size, the effects and functions of the present invention will not be adversely affected. The metal mask 10 of the present invention has a film 3 of fluorine-containing phosphonate, formed from the coating agent of the present invention, in at least a surface of the openings 2 thereof. As illustrated, it is preferred that the film 3 of fluorine-containing phosphonate is applied to an inner peripheral portion (side wall) of the openings 2 and an area adjacent thereto. Further, it is preferred that the film of fluorine-containing phosphonate is formed in a back surface 4 of the metal mask 10, in addition to the inner peripheral portion of the openings 2. Furthermore, if desired, the film of fluorine-containing phosphonate may be applied to a surface 5 of the metal mask 10. As described above, the film of fluorine-containing phosphonate can be formed from the coating agent consisting of a fluorine-containing phosphonic acid compound containing one or more fluorine atoms in the molecule thereof. The details of the usable fluorine-containing phosphonic acid compounds were described in the above paragraphs. In addition, although the method of forming a thin film of the fluorine-containing phosphonate can be optionally changed depending upon the properties of the fluorine-containing phosphonic acid compound used and other factors, as briefly described above, a method of applying a fluorine-containing phosphonic acid compound from its solution onto the metal mask, followed by drying and reacting, and other methods can be used.

The method of forming the film of fluorine-containing phosphonate will be further described. First, the selected fluorine-containing phosphonic acid compound is diluted with a suitable solvent such as hydrofluoroether and polyfluoropolyether to obtain a paste having the viscosity suitable for the coating purpose or, if desired, a solution. Next, the resulting paste or solution is coated over the metal mask having the previously formed openings in accordance with any conventional methods. The coating methods include, for example, spray coating, spin coating and dip coating. After coating, the solvent is removed by air drying, and then the coating is baked in an oven. The baking temperature is generally about 100 to 150°C for about 30 minutes. A bonding strength of the coating to the metal mask can be increased with this baking process.

In the metal mask 10 of the present invention, the thin film 3 of fluorine-containing phosphonate formed in an inner wall of the openings 2 may have any desired thicknesses. The film 3 of fluorine-containing phosphonate of the present invention preferably has a thickness of about lOOnm or less, more preferably a thickness of about 5nm or less, most preferably a thickness of about 3nm or less. The present inventor has found that the film of fluorine-containing phosphonate can be formed at a remarkably lowered thickness which could not be expected in the prior art methods, and moreover, such a thin film does not adversely affect the functions and effects of the present invention. Accordingly, the thickness of the film of fluorine-containing phosphonate particularly suitable in the practice of the present invention is in the range of about 1 to lOOnm, and the most suitable film thickness is in the range of about 1 to 5nm.

The metal mask of the present invention can be advantageously used in a variety of applications. For example, in the production of electronic devices and others, the metal mask of the present invention can be used to form a solder pattern such as a pattern of the solder paste on a substrate such as printed wiring boards. Further, the metal mask of the present invention can be used to form a printing pattern on a substrate with a screen printing method and other methods. Moreover, the metal mask of the present invention can be used to form a resinous pattern on a substrate. For example, the metal mask of the present invention can be used to form a resist pattern in accordance with the photolithographic process.

Fig. 2 is a cross-sectional view showing, in sequence, the method of printing a solder paste on a printed substrate using the metal mask of the present invention.

First, as shown in Fig. 2(B), the metal mask 10 of the present invention is disposed on the printed substrate 11. The metal mask 10 has openings 2 in the positions corresponding to the land portions (not shown) of the printed substrate 11 in conformity with the desired printing pattern. Further, the openings 2 have a thin film 3 of fluorine-containing phosphonate, originated from the coating agent of the present invention, in an inner wall surface of the openings 2. The thin film 3 is firmly bonded to a substrate of the metal mask 10, and also it has a property of repelling a solder paste which will be filled in the openings 2 in the subsequent step.

Next, as shown in Fig. 2(B), a solder paste 12 is provided and is filled in the openings 2. In the illustrated instance, a squeegee 13 was used to assist the paste filling operation. Note that in the practice of the present invention, different types of the solder pastes can be used. Examples of the solder composition include Sn-Pb, Sn-Ag, Sn-Cu, Sn-Ag-Cu and the like.

After filling of the solder paste 12 in the openings 2, the metal mask 10 is removed from the printed substrate 11. As shown in Fig. 2(C), the solder pattern 12 is formed on the land portions of the printed substrate 11. The solder pattern 12 can exactly reproduce a configuration of the openings 2. Especially, for the present invention, as a thin film 3 applied to the metal mask 10 has an excellent releasability, it is possible to avoid the undesirable adhesion of a part of the solder paste to the metal mask 10 and thus the undesirable removal of the solder paste adhered to the metal mask 10. As the printing defects can be avoided, it also becomes to avoid the soldering error after reflowing of the solder paste.

Examples Hereinafter, the present invention is described with reference to the examples thereof. Note, however, that the present invention should not be restricted to these examples.

Example 1 In this example, the fluorine-containing phosphonic acid represented by the following formula was prepared.

A 250ml round-bottomed flask provided with an overhead stirrer and a water condenser was provided, and 1Og (0.041 moles) of dimethyl(4-aminobenzyl)phosphonate, 4.15g (0.041 moles) of triethylamine and 100ml of methyl t-buthylether were added under nitrogen. 41.8g (0.041 moles) Of C₃F₇[CF(CF₃)CF₂O]_nCF(CF₃)COF (Mw=l,017) was dropped in the mixture for about 1.5 hours. After stirring the mixture at the ambient temperature for 16 hours, the resulting solution was diluted with an additional amount of methyl t-buthylether, and then washed with about 5% of aqueous sodium bicarbonate. Thereafter, the solution was once washed with 2N hydrochloric acid. Solvent was removed from the solution in a rotary evaporator, after drying over magnesium sulfate. The resulting product was dissolved in diethylether, and then 17.6g (0.115 moles) of bromotrimethylsilane was once added to the solution. The solution was stirred at the ambient temperature for 24 hours, and then an additional amount (1Og) of silane was added. After several hours, absolute methanol was added to decompose unreacted silane and silylether. After removal of the solvent from the resulting solution, the residue was twice washed with absolute methanol as in the manner described above. After the amount of the solution was reduced in a rotary evaporator, the finally obtained methanol solution was poured into water, and a solid product was obtained upon filtering and dried with air. Analysis of the product indicated that the product is a target fluorine-containing phosphonic acid.

Example 2

In this example, the metal mask of the present invention was produced using as a coating agent the fluorine-containing phosphonic acid prepared in Example 1. Further, the metal mask using no coating agent as the comparative example and the metal mask using the commercially available fluorine-based silane coupling agent represented by the following formula:

₃

(Me=methyl) as the control example were produced at the same time. Production of the Metal Mask (Comparative Example)

Rectangular openings (0.2mm x 0.4mm) were fabricated in a stainless steel film having a thickness of 300μm by using an etching process to produce the metal mask as the comparative example.

Production of the Metal Mask (Present Invention)

After fabrication of rectangular openings (0.2mm x 0.4mm) in a stainless steel film having a thickness of 300μm by using an etching process, the openings of the resulting metal mask were coated with the fluorine-containing phosphonic acid prepared in Example 1, as is described below. The fluorine-containing phosphonic acid was diluted with isopropyl alcohol to a concentration of 5 wt.%, and the solid was dissolved with shaking. After filtering of the resulting solution, the filtrate was diluted with methylperfluorobutylether to obtain a 0.1 wt.% coating solution. The cleaned metal mask was dipped in the coating solution for 20 hours, followed by drying with air.

Production of the Metal Mask (Control Example)

After fabrication of rectangular openings (0.2 mm x 0.4 mm) in a stainless steel film having a thickness of 300μm by using an etching process, the metal mask was dipped in a hydrofluoroether solution of the above-described fluorine-based silane coupling agent for 20 hours, followed by drying with air.

Evaluation of the Filling Property of the Solder Paste

The metal mask produced in each of the above-described methods was laminated to the commercially available printed wiring board, and the solder paste was printed through the metal mask to the underlying wiring board. The solder paste used herein was an alloy solder of Sn-Ag-Cu having a melting point of 217 to 220°C (product code "M705", Senjyu Kinzoku Kogyo). The solder paste was completely filled in the openings of the metal mask using a squeegee. The metal mask was removed from the wiring board to obtain a solder-printed product.

In the printed product in each of the wiring board, the transferred solder pattern was observed with a laser microscope. In the printed product obtained using the metal mask (comparative example), the transferred solder pattern showed a profile of ellipse, i.e., rectangular profile having no corner portion, whereas it should has a rectangular profile. This means that a portion of the solder was removed with the metal mask, because the solder could not be separated from the mask. Further, it was observed that the solder itself suffers from the roughness of the solder grains and thus poor filling property of the paste.

Contrary to the comparative example, in the printed product obtained using the metal mask (control example), a transferred solder pattern suitably reproducing rectangular openings of the metal mask could be obtained. Further, it has been found that there is no problem in the solder grains, the filling property of the paste is good, and the printing characteristic is excellent. In addition, the results comparable to those of the control example could be obtained in the printed product obtained using the metal mask (present invention). That is, a transferred solder pattern suitably reproducing rectangular openings of the metal mask could be obtained. Further, it has been found that there is no problem in the solder grains, the filling property of the paste is good, and the printing characteristic is excellent.

In this example, the metal mask (control example) and the metal mask (present invention) were produced in accordance with the method described in Example 2. However, note that in this example, an iron film, nickel film or chromium film, each having the same thickness, was used in place of the stainless steel film having a thickness of 300μm.

To evaluate the durability of each metal mask, (1) a water contact angle after wiping of a surface of the coating of the metal mask with an acetone-impregnated wiping paper, and (2) a removing power (by wiping paper) of the line images marked with an oil-based marking pen on a surface of the coating of the metal mask were determined in accordance with the following methods. Note that acetone was impregnated in the wiping paper in this example to simulate the practical use of the metal masks, because the solder paste is generally produced by dispersing solder grains in a viscous organic compound such as flux, and thus the metal masks are frequently washed with an organic solvent such as acetone. (1) Determination of a Pure Water Contact Angle at the Coating Surface

In the coating surface of each of the metal masks, the pure water contact angle was determined in a contact angle meter of Kyowa Kagakusha, Contactanglemeter (Type CA-A) in accordance with the following manner.

1. wiping operation, in five reciprocal wiping, with an acetone-impregnated wiping paper (wiping operation: no, once, twice or thrice)

2. application of a syringe containing pure water

3. determination of the contact angle with a liquid dropping method

In this example, the determination was carried out in three times for each metal mask to obtain an average value. The results of the determination are summarized in the following Tables 1 and 2.

(2) Determination of a Removing Power of Line Images

1. marking of black line images with an oil-based marking pen (trade name "Mckee", Zebra Co.)

2. wiping operation, in five reciprocal wiping, with an acetone-impregnated wiping paper (wiping operation: no, once, twice or thrice)

3. visual examination of the coating surface wiped with the wiping paper Presence or absence of the black line image was visually examined in the wiped surface of each metal mask. In this example, the metal mask from which the black line images were completely removed was evaluated as "good", the metal mask having a wiping trace of the black line images was evaluated as "fair", and the metal mask having the unremoved black line images was evaluated as "bad". The results of the evaluation are summarized in the following Tables 1 and 2.

Table 1 : Metal Mask Using F-Containing Phosphonic Acid

Note: "-" means not determined

As can be understood from the measurement results of Tables 1 and 2, the fluorine- containing phosphonic acid suggested in the present invention can improve a durability to the wiping and cleaning using acetone, and also can give a good removing power for the marking stain, in other words, a power of easily cleaning and removing a solder paste and the like, to a wide variety of the substrates constituting the metal mask.

Claims

Claims:

1. A coating agent used in the formation of a thin film on a surface of the metal mask, formed from a metallic material, having opening portions of the predetermined pattern, in which said coating agent comprises a fluorine-containing phosphonic acid compound containing fluorine atoms in a molecule thereof, and a phosphonic acid of the fluorine-containing phosphonic acid compound can be bonded to a metal atom of the metal mask to form a salt thereof.

2. The coating agent according to claim 1 , in which the fluorine-containing phosphonic acid compound is at least one compound selected from the group consisting of the compounds of formulas (I), (II) and (III):

wherein n is an integer of 3 to 30.

3. The coating agent according to claim 1, in which the fluorine-containing phosphonic acid compound is at least one compound selected from the group consisting of the compounds if formulas (IV) and (V):

O X

Q O R ¹ O

_{R f}_L_C N— R²— O P O X ] , ^(V)

I O X in which

5 R_f is a monovalent or divalent perfluoropolyether group, y is 1 or 2,

X may be the same or different and each represents hydrogen, cycloalkyl group, alkali metal, ammonium, ammonium substituted with an alkyl or cycloalkyl group, or 5- to 7-membered heterocyclic group containing a positive charging nitrogen atom, O R¹ is hydrogen or an alkyl group, and

R² represents a divalent group selected from the group consisting of an alkylene group, arylene group, heteroalkylene group or a combination thereof.

4. A metal mask, formed from a metallic material, having opening portions of 5 the predetermined pattern, in which at least a surface of the opening portions has applied thereon a thin film of the fluorine-containing phosphonate formed from the coating agent described in any one of claims 1 to 3.

5. The metal mask according to claim 4, in which the thin film of the fluorine- 0 containing phosphonate has a thickness of 1 to lOOnm.

6. The metal mask according to claim 4 or 5, in which the thin film of the fluorine-containing phosphonate has a thickness of 1 to 5nm.

7. The metal mask according to any one of claims 4 to 6, which is used for forming solder patterns on a substrate.

8. The metal mask according to any one of claims 4 to 6, which is used for forming printing patterns on a substrate.

9. The metal mask according to any one of claims 4 to 6, which is used for forming resinous patterns on a substrate.