JP2009224678A - Metal mask and printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal mask such that the thickness of solder paste printed on a printed wiring board can be adjusted by openings. <P>SOLUTION: The metal mask 1 has the openings 2a and 2b formed at positions corresponding to soldering pads 5a and 5b formed on the printed wiring board 4. A plurality of protrusions 3 protruding toward the printed circuit board 4 are formed at peripheries of the openings 2a and 2b through punching processing. When the metal mask 1 and printed wiring board 4 are printed one over the other, the opening 2b of the metal mask 1 which corresponds to a gull wing lead 12 flexes downward by being depressed by a squeeze 8 and comes into contact with the printed wiring board 4, so the solder paste 9b is printed by the thickness of the metal mask 1. The opening 2a which corresponds to a bottom surface electrode 11 floats from the printed wiring board 4 because of the protrusion 3 provided at its periphery, so that the solder paste 9a is printed more by the flotation height. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a metal mask for printing a solder paste at an arbitrary position on a printed wiring board.

  Usually, in order to print a solder paste on a printed wiring board, a metal mask provided with an opening for printing a solder paste by etching, laser processing, or the like on a stainless steel metal plate is used. The metal mask opening and the soldering pad provided on the printed wiring board are overlapped so that they coincide with each other. By screen printing, the solder paste moves into the opening while the squeegee moves left and right on the metal mask. Fill. After the solder paste is filled, the metal mask is removed, and the component is mounted on the pad on which the solder paste of the printed wiring board is printed. Then, the component is soldered to the printed wiring board by applying heat in a reflow furnace and melting the solder paste.

  However, in this reflow soldering method, when soldering a SOP (Small Outline Package) or QFP (Quad Flat Package) surface mount component having a gull wing lead and a bottom electrode, the bottom electrode is the top of the gull wing lead. Since it exists in a position higher than the lower part, a bottom electrode will float about 50 micrometers-150 micrometers from a printed wiring board. For this reason, in order to reliably join the solder to the bottom electrode, it was necessary to print the solder paste on the printed wiring board with a metal mask having a thickness of 150 μm or more.

  On the other hand, when the thickness of the metal mask is increased to increase the thickness of the solder printed on the printed wiring board, the solder may be crushed during component mounting. In recent years, when the pitch of leads of surface mount components has been reduced, there is a problem that short-circuit defects called solder bridges are likely to occur between adjacent pads arranged at a narrow pitch due to solder crushing. The thickness of the mask has been reduced to about 100 μm-130 μm.

  In this way, in screen printing using a single metal mask, if a large amount of solder is supplied onto the pad on which the surface mount component is mounted in accordance with the height of the bottom electrode, a solder bridge occurs between narrow pitch gull wing leads. It becomes easy. On the other hand, if the supply of solder to the component lead pads is reduced in order to prevent solder bridges between narrow pitch leads, there is a conflicting problem that an unconnected state called “solder floating” tends to occur at the bottom electrode portion.

  Therefore, Patent Document 1 discloses a method of changing the thickness for printing solder paste for each pad using two types of metal masks. First, using the first metal mask, the solder paste is printed on all pads on the printed wiring board. In the second metal mask, an opening is formed only at a portion corresponding to a pad where the solder paste thickness is to be increased. The printed solder paste thickness was changed for each pad by screen printing again using this second metal mask.

JP 2004-14947 A

  Since the conventional metal mask is configured as described above, two metal masks are required for printing on one side of the printed wiring board, and up to four in the case of a double-sided board that also prints the back side. There existed a subject that manufacturing cost and a man-hour increased.

  The present invention has been made to solve the above-described problems, and is a solder paste for pads that require a large amount of locally supplied solder, such as surface-mounted components, with minimum manufacturing cost and man-hours. An object of the present invention is to provide a metal mask capable of thinly printing a solder paste on a pad that causes a solder bridge problem when a large number of solders such as a component lead pad with a narrow pitch are supplied.

  In the metal mask according to the present invention, an opening is formed at a position corresponding to a pad formed on the printed wiring board for soldering the component electrodes, and a plurality of protrusions projecting toward the printed wiring board around the opening. The protrusions are formed.

  According to the present invention, an opening is formed at a position corresponding to a pad formed on a printed wiring board in order to solder a component electrode, and a plurality of protrusions protruding toward the printed wiring board around the opening. Since the portion is formed, the thickness of the solder paste printed on the printed wiring board can be adjusted for each opening.

Embodiment 1 FIG.
1 is a cross-sectional view showing a configuration of a metal mask according to Embodiment 1 of the present invention. FIG. 2 is a schematic top view showing the configuration of the metal mask according to the first embodiment of the present invention. The metal mask 1 shown in FIGS. 1 and 2 is used for printing a printed wiring board on which a SOP or QFP surface-mounted component having a bottom electrode and a gull wing lead is mounted. In the center of the metal mask 1, an opening 2a for printing a solder paste for the bottom electrode of the surface mount component on the printed wiring board is formed, and solder paste for each gull wing lead of the surface mount component is formed on both sides of the opening 2a. Each opening 2b for printing on a printed wiring board is formed.

  A plurality of protrusions 3 are formed between the opening 2a and the opening 2b for floating the opening 2a from the printed wiring board during solder paste printing. These protrusions 3 are formed by punching from the surface of the metal mask 1 opposite to the printed wiring board side with a punch or the like to create a recess protruding to the printed wiring board side, as shown in FIG. It is arranged at a predetermined interval around the part 2a.

  Next, a printed wiring board printing method and a surface mounting component mounting method using the metal mask 1 will be described. FIG. 3 is a sectional view showing a printing and mounting process using the metal mask according to the first embodiment of the present invention. In FIG. 3, the same or corresponding parts as those in FIG. 1 and FIG.

  FIG. 3A shows a printed wiring board printing process using the metal mask 1. The printed wiring board 4 is provided with soldering pads 5a and 5b for joining each electrode of the surface mount component on the surface thereof. The soldering pad 5a is for the bottom electrode of the surface mount component, and the soldering pad 5b is for the gull wing lead. A solder mask 6 is applied to protect the wiring of the copper foil of the printed wiring board 4. On the printed wiring board 4, the metal mask 1 is overlaid so that the protruding vertex of the protrusion 3 comes into contact with the printed wiring board 4. At this time, the soldering pad 5a and the opening 2a are aligned, and the soldering pad 5b and the opening 2b are aligned.

  By placing the solder paste 7 on the metal mask 1 and moving the squeegee 8 while pressing it, the solder paste 7 is filled in the openings 2 a and 2 b and printed on the printed wiring board 4. When the squeegee 8 moves to the vicinity of the opening 2b of the metal mask 1, the metal mask 1 is lowered due to the weight of the squeegee 8, and the solder paste 7 is in a state where the opening 2b and the printed wiring board 4 are in contact with each other. Printed.

  On the other hand, the opening 2a is supported by the protrusion 3 formed on the periphery, so that the solder paste is filled with the opening 2a floating from the printed wiring board 4. FIG. 3B shows the state of the printed wiring board 4 from which the metal mask 1 has been removed after printing. A solder paste 9b equal to the thickness of the metal mask 1 is printed on the soldering pad 5b for the gull wing lead. A solder paste 9a having a thickness obtained by adding the height of the protrusion 3 to the thickness of the metal mask 1 is printed on the soldering pad 5a for the bottom electrode.

  FIG. 3C shows a process for mounting the surface mount component on the printed wiring board. After printing, the bottom electrode 11 of the surface mount component 10 is disposed on the solder paste 9a of the printed wiring board 4, and the gull wing leads 12 of the surface mount component 10 are disposed on the solder paste 9b. Next, the printed wiring board 4 is put in a reflow furnace and heated to melt the solder pastes 9a and 9b. Thereafter, the solder pastes 9a and 9b are cooled to room temperature to solidify the molten solder, whereby the soldering pad 5a and the bottom electrode 11 are joined, and the soldering pad 5b and the gull wing lead 12 are joined.

  The metal mask 1 used in the description has a structure in which a plurality of protrusions 3 are provided on each of the four sides around the opening 2a for the bottom electrode as shown in FIG. What is necessary is just the structure which protrudes one or more at each of arbitrary two sides around the part 2a facing each other.

  In addition, the metal mask 1 used for the description has an elliptical shape in which the protruding portion 3 protrudes as shown in FIG. 2, but is not limited to this, and other than the elliptical shape, a rectangle, a square, a trapezoid, It may be a circular shape, a hexagonal shape, an octagonal shape, or other polygonal shape, or an irregular shape having a different shape for each protrusion.

  As described above, according to the first embodiment, the metal mask 1 corresponds to the soldering pads 5 a and 5 b formed on the printed wiring board 4 in order to solder the bottom electrode 11 and the gull wing lead 12. The openings 2a and 2b are formed in the substrate, and a plurality of protrusions 3 protruding toward the printed wiring board 4 are formed around the openings 2a and 2b by punching. Therefore, since the opening 2b of the metal mask 1 corresponding to the gull wing lead 12 is in contact with the printed wiring board 4, only the solder paste 9b corresponding to the thickness of the metal mask 1 is printed, whereas it corresponds to the bottom electrode 11. The opening 2a is lifted from the printed wiring board 4 by the protrusions 3 projecting from the periphery, so that it is possible to print a large amount of solder paste for the floating height, and the thickness of the solder paste printed on the printed wiring board is opened. It becomes possible to adjust every part.

  Further, according to the first embodiment, the printed wiring board printed using the metal mask 1 can supply a sufficient amount of solder that does not cause solder floating on the bottom electrode.

Embodiment 2. FIG.
FIG. 4 is a schematic top view showing the configuration of the metal mask according to the second embodiment of the present invention. The metal mask 21 shown in FIG. 4 has an opening 22a for printing a solder paste for the bottom electrode of the surface mount component on the printed wiring board in the center. Moreover, each opening part 22b for printing the solder paste for each gull wing lead of surface mount components on a printed wiring board is formed in the both sides of the opening part 22a.

  The metal mask 21 is formed with a protruding portion 23 protruding toward the printed wiring board so as to surround the opening 2a without being interrupted. Since the projecting method is the same as that of the first embodiment, description thereof is omitted.

  As described above, according to the second embodiment, the metal mask 21 is configured such that the protrusion 23 surrounds the opening 22a without interruption. Therefore, variation in the depth of the protrusion does not occur, and solder paste printing with stable quality is possible.

Embodiment 3 FIG.
FIG. 5 is a cross-sectional view showing a configuration of a metal mask according to Embodiment 3 of the present invention. In FIG. 5, the same or corresponding parts as in FIG. In the metal mask 1 shown in FIG. 5, the peripheral portion of the opening 32 a that has been lifted from the printed wiring board 4 due to the formation of the protrusion 33 is filled with resin or the like, and the partition wall 34 is provided. Thus, the periphery of the opening 32a is surrounded by the partition wall 34 made of resin or the like to prevent the printed solder paste from entering the place other than the soldering pad 5a (the solder mask 6 in FIG. 5).

  As described above, according to the third embodiment, the metal mask 31 is configured so that the partition wall 34 surrounding the periphery of the opening 32a on the printed wiring board 4 side is formed of resin. Therefore, it is possible to prevent a solder bridge that is generated when the solder paste printed at the time of component mounting on the printed wiring board flows into the adjacent lead electrode.

  In the first to third embodiments, the bottom electrode of the surface mount component is described as an example of the electrode that needs to supply a large amount of solder paste. However, the present invention is not limited to this. For example, even if the solder paste is printed on the printed wiring board using the metal mask of the first to third embodiments described above for an electrode that needs to supply a large amount of solder paste such as a large surface mount component, the same effect is obtained. can get.

It is sectional drawing which shows the structure of the metal mask which concerns on Embodiment 1 of this invention. It is a schematic top view which shows the structure of the metal mask which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the printing and mounting process using the metal mask which concerns on Embodiment 1 of this invention. It is a schematic top view which shows the structure of the metal mask which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the structure of the metal mask which concerns on Embodiment 3 of this invention.

Explanation of symbols

  1,21,31 Metal mask, 2a, 2b, 22a, 22b, 32a, 32b Opening, 3, 23, 33 Protrusion, 4 Printed wiring board, 5a, 5b Soldering pad, 6 Solder mask, 7 Solder paste, 8 Squeegee, 9a, 9b Printed solder paste, 10 surface mount component, 11 bottom electrode, 12 gull wing lead.

Claims (6)

In a metal mask in which openings are formed at positions corresponding to pads formed on a printed wiring board in order to solder component electrodes,
A metal mask, wherein a plurality of protrusions protruding toward the printed wiring board are formed around the opening.   2. The metal mask according to claim 1, wherein the protrusion is formed by punching from the metal mask surface side opposite to the printed wiring board side.   3. The metal mask according to claim 1, wherein the protrusions are formed around the opening at regular intervals.   The metal mask according to claim 1, wherein the protrusion is formed so as to surround the opening without being cut.   The metal mask according to any one of claims 1 to 4, wherein a partition wall that surrounds the periphery of the opening on the printed wiring board side is formed of a resin. Using the metal mask according to any one of claims 1 to 5,
A printed wiring board obtained by printing a solder paste by overlaying the metal mask on the printed wiring board so that an opening of the metal mask overlaps a pad on the printed wiring board.

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