JP2006100638A - Metal mask plate for cream solder printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To print cream solder on a pad where, for example, an end edge is partially coated with a protective film without causing the cream solder from oozing out the pad. <P>SOLUTION: A metal mask plate 20 for cream solder printing has in a metal plate 21 opening parts 22 and 23 corresponding to pads 11 and 12 formed on a printed circuit board 10, and is for printing the cream solder 40 on the pads 11 and 12 through the opening parts 22 and 23. The metal plate is provided with an elastic film 27 which absorbs a step present on a substrate surface of the printed circuit board 10 at least along peripheries of the opening parts 22 and 23 on the back of the metal plate 21. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a metal mask plate for cream solder printing. More specifically, the present invention relates to a metal mask plate for cream solder printing suitable for a printed circuit board in which a part of the edge of a soldering pad is covered with a protective film. It is about.

  According to the reflow soldering method, cream solder is printed (applied) on the pads of the circuit board in advance. And after mounting a chip component on it, soldering is performed in a heating atmosphere. In many cases, a metal mask plate is used for printing cream solder, and an example of the printing process will be described with reference to FIG.

  In the reflow soldering method, the printed circuit board 10 may be a hard board or a flexible board. Pads 11 and 12 to which chip components (not shown) are soldered are formed at predetermined positions of the printed circuit board 10. In this case, as shown in FIG. A part of the edge is covered with a protective film 13 such as a solder resist, and the protective film 13 is not formed between the pads 11 and 12.

  The metal mask plate 20 is made of, for example, a metal plate 21 such as stainless steel. As shown in FIG. 4B, the metal plate 21 has two openings 22 and 23 corresponding to the pads 11 and 12 of the printed circuit board 10. Is formed.

  When printing, first, as shown in FIG. 3A, the metal mask plate 20 is positioned with respect to the printed surface of the printed circuit board 10 and brought into close contact with the printed circuit board 10. Cream solder 40 is applied.

  Then, as shown in FIGS. 3B and 3C, the squeegee 30 is moved while applying a predetermined pressure, and the cream solder 40 is filled into the openings 22 and 23 while scraping off excess cream solder. As shown in FIG. 3D, the metal mask plate 20 is raised and separated from the printed circuit board 10.

  In this way, the cream solder 40 is printed. As shown in FIG. 4A, a part of the edges of the pads 11 and 12, that is, the opposite edges of the pads 11 and 12 in this example. 3 are covered with the protective film 13, so that when the metal mask plate 20 is disposed on the printed circuit board 10, the openings 22 and 23 are formed as shown in FIG. The intermediate portion 24 in between is raised from the pads 11 and 12 by the thickness of the protective film 13 covering the edge.

  Therefore, as shown in FIG. 5 (enlarged view of FIG. 3C), a part of the cream solder 40 filled in the openings 22 and 23 is generated between the intermediate portion 24 and the pads 11 and 12. May ooze from the gap. Since this exuded cream solder adheres to the back surface side of the intermediate portion 24, the metal mask plate 20 must be periodically cleaned, which is not preferable from the viewpoint of productivity. In addition, the cream solder that has oozed out grows into solder balls during reflow, and depending on the size, the pads 11 and 12 may be short-circuited.

  Since the cream solder printing process is the first step of the reflow soldering process, the success or failure of this process affects the reliability of the electrical connection. Therefore, for example, in Patent Documents 1 and 2 below, various contrivances have been made to prevent the cream solder from spreading and the cream solder from wrapping around the back side of the metal mask plate. Effective soldering has not been done for cream solder bleeding due to the above. A similar problem occurs when a member (for example, a connection terminal of a through hole) having a thickness corresponding to the thickness of the protective film is disposed in the vicinity of the pad.

JP 2004-209934 A JP 2001-244616 A

  Accordingly, an object of the present invention is to provide a cream solder that can be printed on a pad whose edge is partially covered with a protective film without causing bleeding to the outside of the pad. It is to provide a metal mask plate for printing.

  In order to solve the above problems, the present invention includes an opening corresponding to a soldering pad formed at a predetermined position of a printed circuit board on a metal plate, and the printed circuit is provided on the back side of the metal plate. In a metal mask plate for cream solder printing, which is disposed on a substrate and prints cream solder on the pad through the opening, on the back side of the metal plate, the printed material is at least around the opening. It is characterized in that an elastic film that absorbs a level difference existing on the substrate surface of the circuit board is provided.

  In the present invention, in a case where a part of the edge of the pad is covered with a protective film, the thickness of the elastic film is set to be thicker than the thickness of the protective film in the covered part. .

  According to a preferred aspect of the present invention, the elastic film is provided over the entire back surface of the metal plate including the periphery of the opening. Various elastomer materials can be used for the elastic membrane, and silicone rubber is particularly preferable.

  According to the present invention, since an elastic film such as silicone rubber is integrally formed on the back side of the metal plate, even when a step due to, for example, a protective film is formed on the pad of the printed circuit board, the step Is absorbed by the elastic film, and the metal mask plate adheres to the printed circuit board through the elastic film.

  Accordingly, there is no bleeding (leakage) of the cream solder to the outside of the pad, and the labor required for cleaning the metal mask plate can be saved, so that the production efficiency can be improved. In addition, since no solder balls or solder bridges are generated, the quality of solder printing and the reliability of electrical connection can be improved.

  Next, embodiments of the present invention will be described with reference to FIGS. 1 and 2, but the present invention is not limited thereto. FIG. 1 is a sectional view schematically showing an example of a metal mask plate for cream solder printing according to the present invention, and FIG. 2 shows a state in which cream solder is printed on a printed circuit board with the metal mask plate for cream solder printing of the present invention. It is sectional drawing.

  As described with reference to FIGS. 3 and 4, the printed circuit board 10 has pads 11 and 12 formed in the chip component mounting region, and the edges of the pads 11 and 12 are formed. It is assumed that a part, that is, three edges excluding opposing edges of the pads 11 and 12 are covered with the protective film 13, but the protective film 13 is not formed between the pads 11 and 12.

  Also in the present invention, the metal mask plate 20 for cream solder printing is made of a metal plate 21 such as stainless steel as in the conventional example, and the openings 22 and 23 are located at positions corresponding to the pads 11 and 12 of the printed circuit board 10. However, the elastic film 27 is integrally provided on the back surface of the metal plate 21 (the surface facing the printed circuit board 10).

  The elastic film 27 absorbs the thickness of the portion of the protective film 13 that covers the edges of the pads 11 and 12 and adheres the metal mask plate 20 to the printed surface of the printed circuit board 10. In this example, the metal plate 21 is provided over the entire back surface except for the openings 22 and 23.

  According to this, as shown in FIG. 2, when the metal mask plate 20 is aligned and pressed with a predetermined pressure so that the elastic film 27 is compressed on the printed circuit board 10, the space between the openings 22 and 23 is reduced. The gap between the intermediate portion 24 and the pads 11 and 12 is closed by the elastic film 27, and the cream solder 40 is prevented from oozing out of the pad.

  In order to ensure the prevention of the bleeding, the relationship of t1> t2 may be established, where t1 is the thickness of the elastic film 27 when not compressed and t2 is the thickness of the pad covering portion of the protective film 13. Various elastomers such as cross-linked natural rubber and synthetic rubber may be used for the elastic film 27. Among them, silicone rubber is preferably used.

  Further, by adding the elastic film 27 to the back surface of the metal plate 21, the amount of the cream solder 40 applied to the pads 11 and 12 increases by the thickness, but when this is not preferable, the metal plate 21 is added. Is reduced by a thickness corresponding to the thickness t1 of the elastic film 27.

  In the present invention, the elastic film 27 is not necessarily provided over the entire back surface of the metal plate 21, and may be disposed only around the openings 22 and 23. As an example, when the edges of the pads 11 and 12 are covered with the protective film 13 as shown in FIG. 4A, the pads 11 and 12 may be provided only on the back surface between the openings 22 and 23. .

  The present invention is also applicable to the case where a member (for example, a through-hole connection terminal) having a thickness corresponding to the thickness of the protective film 13 is disposed in the vicinity of the pads 11 and 12. Can do.

Sectional drawing which shows typically an example of the metal mask plate for cream solder printing by this invention. Sectional drawing which shows the state which printed cream solder on the to-be-printed circuit board with the metal mask plate for cream solder printing of this invention. (A)-(d) Explanatory drawing which shows typically a reflow soldering process. (A) The schematic diagram which shows the chip component mounting part of a to-be-printed circuit board, (b) The schematic diagram which shows a part containing the opening part of a metal mask plate. Sectional drawing which shows the state which printed the cream solder on the to-be-printed circuit board with the conventional metal mask plate for cream solder printing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Printed circuit board 11, 12 Pad 13 Protective film 20 Metal mask plate for cream solder printing 21 Metal plate 22, 23 Opening 24 Middle part 40 Cream solder

Claims (3)

The metal plate is provided with an opening corresponding to a soldering pad formed at a predetermined position of the printed circuit board, and the back side of the metal plate is arranged on the printed circuit board and the opening is interposed through the opening. In the cream solder printing metal mask plate for printing cream solder on the pad,
For cream solder printing, an elastic film is provided on the back side of the metal plate to absorb a step existing on the substrate surface of the printed circuit board along at least the periphery of the opening. Metal mask version.   2. The metal mask plate for cream solder printing according to claim 1, wherein a part of the edge of the pad is covered with a protective film, and the thickness of the elastic film is larger than the thickness of the protective film in the covered part. .   The metal mask plate for cream solder printing according to claim 1 or 2, wherein the elastic film is provided over the entire back surface of the metal plate including the periphery of the opening.

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