METHOD FOR FORMING FIDUCIAL MARK IN RESIN STENCIL AND STENCIL FORMED THEREBY

Abstract: An engraved recess (4) not penetrating a resin stencil (1) is processed as a fiducial mark by a laser (3) at a position on a surface of the resin stencil where the resin stencil when registered with a circuit board agrees with a fiducial mark of the circuit board.

Description: DESCRIPTION METHOD FOR FORMING FIDUCIAL MARK IN RESIN STENCIL AND STENCIL FORMED THEREBY TECHNICAL FIELD The present invention relates to a method for forming a fiducial mark in a resin stencil used in printing of a solder paste onto a wiring pattern of a circuit board, and a stencil formed by the method. BACKGROUND ART A metal mask has been employed as a screen in printing of a solder paste onto a wiring pattern of a circuit board. As the circuit board has been increased in size and mounting density, the metal mask has been required to be large with a precise opening pattern. Recently, the metal mask used is 600mm long, 600mm wide or larger, with a thickness of 0.1-0.l5mm and, the opening pattern is processed precisely with the use of a laser or the like. In order to form a fiducial mark in the metal mask, a through hole is opened at a position of the fiducial mark simultaneously when the opening pattern is processed. A resin is filled in the through hole afterwards or an aluminum adhesive tape is attached to the through hole from the rear side to prevent a solder paste from entering and adhering to the circuit board. The through hole is opened at the position of the fiducial mark in this case, because the laser technique affords only to form the through hole in the metal mask. As such, a processing accuracy for the opening pattern is required to be enhanced furthermore so as to improve the mounting density of the circuit board. However, the laser technique or any other methods cannot eliminate the issue that a peripheral part of the processed opening pattern is tapered in the case of the metal mask, that is, there is a limit in the improvement of the processing accuracy. At the same time, even when the metal mask is thinned to 0.1-0.15mm, the metal mask of stainless or the like is hard and not fit well to the circuit board, inviting adverse influences onto a printing accuracy. For solving the above-described issues, a resin stencil has lately been started to be used. The resin stencil can be similarly made 600mm wide, 600mm long or larger and 0.1-0.15mm thick. The peripheral part of the opening pattern can be processed perpendicularly by an excimer laser, without generating tapers, and therefore the processing accuracy is improved. Moreover, because of the resin, the resin stencil is soft as compared with the metal mask of stainless or the like and conveniently fit to the circuit board. When a fiducial mark is to be formed in the conventional resin stencil, a through hole is formed at a position of the fiducial mark simultaneously when the opening pattern is processed in the resin stencil, in the same manner as in the metal mask, and subsequently the through hole is filled with a resin 11 as shown in Fig. 7 or an aluminum adhesive tape 12 is attached to a rear face of the resin stencil as shown in Fig. 8 to prevent the solder paste from penetrating the through hole and adhering to the circuit board. In other words, one step of filling the through hole with the resin 11 is added according to the prior art method, which takes trouble and costs high. Meanwhile, although attaching the aluminum adhesive tape 12 from the rear side is inexpensive, a gap of a thickness of the aluminum adhesive tape 12 is formed between the resin stencil 10 and the circuit board. This adversely influences the printing accuracy and is consequently not recommended. DISCLOSURE OF INVENTION The present invention has for its object to provide a method for forming a fiducial mark in a resin stencil without adverse influences on a printing accuracy, and a stencil formed by the method. In accomplishing these and other aspects, according to a first aspect of the present invention, there is provided a method for forming a fiducial mark in a resin stencil used in printing of a solder paste onto a wiring pattern of a circuit board, the method comprising: processing an engraved recess not penetrating the resin stencil as a fiducial mark by a laser at a position on a surface of the resin stencil. According to a second aspect of the present invention, there is provided a method for forming a fiducial mark in a resin stencil according to the first aspect, further comprising filling a resin of a different color from that of the resin stencil in the not penetrating engraved recess thereby to form the fiducial mark. According to a third aspect of the present invention, there is provided a method for forming a fiducial mark in a resin stencil according to the first aspect, further comprising forming a metal plating of nickel, SUS, titanium or the like on the surface of the resin stencil. According to a fourth aspect of the present invention, there is provided a method for forming a fiducial mark in a resin stencil according to the first or second aspect, further comprising forming a metal plating of nickel, SUS, titanium or the like on the surface of the resin stencil except on the fiducial mark. According to a fifth aspect of the present invention, there is provided a method for forming a fiducial mark in a resin stencil, the method comprising: forming a metal plating of nickel, SUS, titanium or the like on a surface of the resin stencil except at a position on the surface, so that a no metal plated part is rendered a fiducial mark. According to a sixth aspect of the present invention, there is provided a stencil formed by a method for forming a fiducial mark in a resin stencil used in printing of a solder paste onto a wiring pattern of a circuit board, the method comprising: processing an engraved recess not penetrating the resin stencil as a fiducial mark by a laser at a position on a surface of the resin stencil. According to a seventh aspect of the present invention, there is provided a stencil formed by a method for forming a fiducial mark in a resin stencil according to the sixth aspect, further comprising filling a resin of a different color from that of the resin stencil in the not penetrating engraved recess thereby to form the fiducial mark. According to an eighth aspect of the present invention, there is provided a stencil formed by a method for forming a fiducial mark in a resin stencil according to the sixth aspect, further comprising forming a metal plating of nickel, SUS, titanium or the like on the surface of the resin stencil. According to a ninth aspect of the present invention, there is provided a stencil formed by a method for forming a fiducial mark in a resin stencil according to the sixth or seventh aspect, further comprising forming a metal plating of nickel, SUS, titanium or the like on the surface of the resin stencil except on the fiducial mark. According to a tenth aspect of the present invention, there is provided a stencil formed by a method for forming a fiducial mark in a resin stencil, the method comprising: forming a metal plating of nickel, SUS, titanium or the like on a surface of the resin stencil except at a position on the surface, so that a no metal plated part is rendered a fiducial mark. According to the aspects of the present invention, when the engraved recess which does not penetrate the resin stencil is formed by irradiation of laser lights from the laser when a printing opening pattern is processed in the resin stencil, a step required in the prior art to fill the through hole or attach the aluminum adhesive tape from the rear side is eliminated. A processing efficiency is improved and a printing accuracy for a solder paste is improved. In the aspects, when a resin of a different color from that of the resin stencil is filled in the engraved recess thereby to form the fiducial mark, the filling of the resin of the different color in the engraved recess is simpler and inexpensive as compared with the prior art method filling the resin in the through hole and, the fiducial mark can be recognized easily. Moreover, when a metal plating of nickel, SUS, titanium or the like is formed on the surface of the resin stencil, the resin stencil is improved in strength and abrasion resistance. In the aspects, when the metal plating of nickel, SUS, titanium or the like is formed on the surface of the resin stencil except on the fiducial mark, and the no metal-plated engraved recess not penetrating the resin stencil is used as the fiducial mark, not only the resin stencil is improved in strength and abrasion resistance, but the fiducial mark can be recognized easily. BRIEF DESCRIPTION OF DRAWINGS These and other aspects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Figs. IA and IB are diagrams showing a processing method according to an embodiment of the present invention; Fig. 2 is a diagram showing a processing method according to the embodiment of the present invention; Fig. 3 is a diagram showing a processing method according to the embodiment of the present invention; Fig. 4 is a diagram showing a processing method according to the embodiment of the present invention; Fig. 5 is a diagram showing a processing method according to the embodiment of the present invention; Fig. 6 is a diagram showing a processing method according to an embodiment of the present invention; Fig. 7 is a diagram showing a conventional processing method; and Fig. 8 is a diagram showing a conventional processing method. BEST MODE FOR CARRYING OUT THE INVENTION Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. A method for forming a fiducial mark in a resin stencil according to a first embodiment of the present invention will be described with reference to Figs. 1-5. In Fig. IA, a position A where a resin stencil 1 when registered with a circuit board agrees with a fiducial mark of the circuit board is determined on a surface of the resin stencil 1. In general, when the resin stencil 1 is used in printing of a solder paste onto a wiring pattern of the circuit board, the fiducial mark of the resin stencil 1 is used for positioning the resin stencil 1 on the circuit board. Then, an opening 2a is formed at a part of a laser mask 2 corresponding to the position A. The laser mask 2 is used when an opening pattern is processed by irradiation of laser lights from an exci er laser 3 in the resin stencil 1. When the opening pattern is processed in the resin stencil 1 by the excimer laser 3, the laser mask 2 is positioned over the resin stencil 1 and the opening 2a is positioned at the position A. Subsequently, while the penetrating opening pattern is processed by the excimer laser 3, more specifically, simultaneously with the processing of the opening pattern, an engraved recess 4 is formed through the opening 2a by the laser in a shorter time than the processing time of the opening pattern. As a result of this, an engraved recess 5 not penetrating the resin stencil is obtained as a fiducial mark, as indicated in Fig. IB. The excimer laser 3 is used because, in comparison with other lasers, a temperature rise in the periphery of the opening is small, a taper is hard to generate in the periphery of the opening pattern, and moreover the engraved recess 5 not penetrating the resin stencil is easy to form. As shown in Fig. 2, a resin 6 of a different color from that of the resin stencil 1 is filled in the recess 5 of Fig. IB, thereby forming the fiducial mark. As compared with the conventional example filling the resin in the through hole, this method is simple and inexpensive. The fiducial mark can be recognized easily with the use of the color difference. Thereafter, a metal plating 7 of nickel, SUS, titanium or the like is formed on the surface of the resin stencil 1, as in Fig. 3, resulting in a metal- plated engraved recess 7a not penetrating the resin stencil. Accordingly, the resin stencil is improved both in strength and abrasion resistance. If a metal plating 8 of nickel, SUS, titanium or the like is formed, as shown in Fig. 4, on the surface of the resin stencil 1 except the fiducial mark of Fig. IB, the resin stencil 1 is further enhanced in strength and abrasion quality, and the fiducial mark becomes easy to recognize. If the metal plating of nickel, SUS, titanium, or the like is formed on the surface of the resin stencil 1 as shown in Fig. 5 except the fiducial mark of Fig. 2 filled with the resin 6, the strength and abrasion resistance of the resin stencil 1 are improved and the fiducial mark is turned easy to recognize. A method for forming a fiducial mark in a resin stencil according to a second embodiment of the present invention will be described with reference to Fig. 6. Referring to Fig. 6, first, the position A where the resin stencil 1 when registered with the circuit board agrees with the fiducial mark of the circuit board is determined on the surface of the resin stencil 1. Then, while the position A is masked, the surface of the resin stencil 1 is processed by vapor deposition or the like manner and the metal plating 8 of nickel, SUS, titanium or the like is formed. A part 9 without the metal plating 8 works as the fiducial mark because of a color difference between the resin stencil 1 and metal plating 8. According to the method, a count of steps is reduced, the resin stencil is improved in strength and abrasive resistance, and the fiducial mark can be recognized with ease. According to the formation method, the engraved recess not penetrating the resin stencil is formed as the fiducial mark by the laser. Therefore, the process costs less in comparison with the prior art. Since it is not necessary to attach an aluminum adhesive tape from the rear side, the printing accuracy for the solder paste is advantageously improved. When a resin of a different color from that of the resin stencil is filled in the engraved recess not penetrating the resin stencil, this filling operation is simple and inexpensive as compared with the prior art where the resin is filled in the through hole. Moreover, the fiducial mark can be recognized easily. When the metal plating of nickel, SUS, titanium or the like is formed on the surface of the resin stencil, both the strength and the abrasion resistance of the resin stencil are effectively improved. According to the formation method, the metal plating of nickel, SUS, titanium or the like is formed on the surface of the resin stencil, and a part of the resin stencil without the metal plating is used as the fiducial mark with the utilization of the color difference between the resin and metal plating. Therefore, a count of processing steps is reduced and the resin stencil is improved in strength and abrasion resistance, and at the same time, the fiducial mark can be recognized easily. The entire disclosure of Japanese Patent Application No. 8-97082 filed on April 18, 1996, including specification, claims, drawings, and summary are incorporated herein by reference in its entirety. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

Claims: CLAIMS 1. A method for forming a fiducial mark in a resin stencil used in printing of a solder paste onto a wiring pattern of a circuit board, the method comprising: processing an engraved recess not penetrating the resin stencil as a fiducial mark by a laser at a position on a surface of the resin stencil. 2. A method for forming a fiducial mark in a resin stencil according to claim 1, further comprising filling a resin of a different color from that of the resin stencil in the not penetrating engraved recess thereby to form the fiducial mark. 3. A method for forming a fiducial mark in a resin stencil according to claim 1, further comprising forming a metal plating of nickel, SUS, titanium or the like on the surface of the resin stencil. 4. A method for forming a fiducial mark in a resin stencil according to claim 1 or 2, further comprising forming a metal plating of nickel, SUS, titanium or the like on the surface of the resin stencil except on the fiducial mark. 5. A method for forming a fiducial mark in a resin stencil, the method comprising: forming a metal plating of nickel, SUS, titanium or the like on a surface of the resin stencil except at a position on the surface, so that a no metal plated part is rendered a fiducial mark. 6. A stencil formed by a method for forming a fiducial mark in a resin stencil used in printing of a solder paste onto a wiring pattern of a circuit board, the method comprising: processing an engraved recess not penetrating the resin stencil as a fiducial mark by a laser at a position on a surface of the resin stencil. 7. A stencil formed by a method for forming a fiducial mark in a resin stencil according to claim 6, further comprising filling a resin of a different color from that of the resin stencil in the not penetrating engraved recess thereby to form the fiducial mark. 8. A stencil formed by a method for forming a fiducial mark in a resin stencil according to claim 6, further comprising forming a metal plating of nickel, SUS, titanium or the like on the surface of the resin stencil. 9. A stencil formed by a method for forming a fiducial mark in a resin stencil according to claim 6 or 7, further comprising forming a metal plating of nickel, SUS, titanium or the like on the surface of the resin stencil except on the fiducial mark. 10. A stencil formed by a method for forming a fiducial mark in a resin stencil, the method comprising: forming a metal plating of nickel, SUS, titanium or the like on a surface of the resin stencil except at a position on the surface, so that a no metal plated part is rendered a fiducial mark.

Inventors: NAGASAWA YOUSUKE, NAITO TAKAO, SARASHINA EIGO, TAKAHASHI KEN, NAGASAWA, YOUSUKE, NAITO, TAKAO, SARASHINA, EIGO, TAKAHASHI, KEN
Applicants: MATSUSHITA ELECTRIC IND CO LTD, NAGASAWA YOUSUKE, NAITO TAKAO, SARASHINA EIGO, TAKAHASHI KEN, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD., NAGASAWA, YOUSUKE, NAITO, TAKAO, SARASHINA, EIGO, TAKAHASHI, KEN
Application year: 1997
Main classification: H05K3
IPC codes: B41C1, B41N1, H05K1, H05K3