JP4821710B2 - Printed wiring board - Google Patents

Description

  The present invention relates to a printed wiring board on which electronic components are mounted, and more particularly to a printed wiring board that suppresses the generation of voids in soldered joints with electronic components.

  A printed wiring board is mounted by soldering electronic components having electrodes on the bottom surface to pads on the printed wiring board. FIG. 7 is a top view of a general surface mount component having electrodes on the bottom surface, and FIG. 8 is a top view of a printed wiring board provided with pads for mounting the surface mount component on the substrate.

  In FIG. 7, the surface mount component 1 includes a bottom electrode 2 and leads 3. In FIG. 8, the printed wiring board 104 includes a bottom electrode pad 5 and a lead pad 6 for mounting the surface mounting component 1 on the substrate 4, both of which are surrounded by a solder resist 7.

  In general, the printed wiring board 104 is coated with a small-sized solder containing flux (hereinafter referred to as cream solder) on the bottom electrode pad 5 and the lead pad 6, and the bottom electrode pad 5 and the lead pad. 6, the bottom electrode 2 and the lead 3 of the surface-mounted component 1 are placed, and the solder paste is soldered in such an order that the cream solder is once melted by heating in a reflow furnace or the like and then solidified by natural cooling.

  FIG. 9 shows a DD position (FIG. 9) of the printed wiring board 104 in which the bottom electrode 2 and the lead 3 of the surface mount component 1 are soldered onto the bottom electrode pad 5 and the lead pad 6 on the substrate 4, respectively. It is arrow sectional drawing in 8).

  In FIG. 9, solder joints 8 and 9 connect the bottom electrode 2 and the bottom electrode pad 5, and the lead 3 and the lead pad 6, respectively. The solder joint portion 8 is a bubble (hereinafter referred to as a void) by solidifying the gas generated from the flux contained in the cream solder at the time of melting the solder or a gas such as air engulfed at the time of application while remaining in the melted cream solder. 10 is occurring. FIG. 10 is an X-ray photograph showing a state where the above-described void 10 is generated in an actual machine.

  As a method of suppressing the generation of voids, there is a method of providing a solder resist 7i in a cross shape on the bottom electrode pad 5 as shown in FIG. Reference 1). FIG. 12 is a cross-sectional view taken along the line E-E (FIG. 11) of the printed wiring board 105 on which the surface mounting component 1 is mounted. As shown in FIG. 12, a gap 11 is formed on the solder resist 7i due to the difference in solder wettability between the solder resist 7i and the bottom electrode 2. The gas inside the cream solder is discharged to the outside through the gap 11.

Japanese Patent Laying-Open No. 2006-303392 (stages 0011 to 0014, FIG. 5)

  However, in the conventional printed wiring board 104, the void 10 remains inside the solder joint portion 8, so that the soldering state cannot be kept uniform, and the gap between the bottom electrode 2 and the bottom electrode pad 5 is not maintained. There was a problem that electric characteristics were not stable.

  Moreover, in the printed wiring board 105 described in Patent Document 1, it is difficult to control the amount of the solder portion 8a on the solder resist 7i, and the size of the gap 11 that releases the gas inside the cream solder is adjusted. There was a problem that gas could not be released sufficiently.

  The present invention has been made in order to solve the above-described problems. By suppressing the generation of voids in the soldered joint portion with the electronic component, the soldered state can be kept uniform, and the soldered joint portion. An object of the present invention is to provide a highly reliable printed wiring board.

Printed wiring board according to the present invention includes a substrate, an electronic component and a pad section for mounting the electronic components disposed on the substrate, and the solder joint that connects the electronic component and the pad portion, the pad And a pair of solder resists arranged in parallel from the outer edge of the pad portion on the inside, and a flow path communicating with the outside air is formed by the pair of solder resists and the pad portion .

  According to the present invention, by providing a slit formed of a solder resist on the pad of the printed wiring board, the gas generated at the time of melting the solder escapes from the inside of the solder through the slit. The attached state can be kept uniform, and the electrical characteristics can be stabilized.

Hereinafter, various embodiments of a printed wiring board according to the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a top view showing the configuration of the printed wiring board 101 according to the first embodiment.

  As shown in FIG. 1, a printed wiring board 101 according to the first embodiment has L-shaped solder resists 7a and 7b on a bottom electrode pad 5 as a pad portion of a conventional printed wiring board 104 (FIG. 8). , 7c and 7d are arranged in a cross shape, and slits 12 are formed as flow paths. Other configurations are the same as those of the conventional printed wiring board 104, and the same reference numerals as those in FIG.

  Like the conventional printed wiring board 104, the printed wiring board 101 is coated with cream solder on the bottom electrode pad 5 and the lead pad 6, and each of the electronic components on the bottom electrode pad 5 and the lead pad 6, respectively. The bottom electrode 2 and the lead 3 of the surface mount component 1 (FIG. 7) are placed, heated in a reflow furnace or the like, cooled and soldered.

  In the printed wiring board 101, during heating, a gas such as a gas generated from the flux contained in the cream solder or air entrained during the cream solder application is released to the outside through the slit 12 on the bottom electrode pad 5. FIG. 2 is a cross-sectional view taken along the line AA (FIG. 1) of the printed wiring board 101 after the surface-mounted component 1 is soldered.

  The slit 12 is formed with a predetermined width and secures a passage sufficient to discharge the gas inside the solder to the outside. The slit 12 forms a solder joint 8 where no void remains.

  As described above, in the first embodiment, since the slits 12 are formed in a cross shape with a predetermined width on the bottom electrode pad 5 by the solder resists 7a, 7b, 7c, and 7d, the flux contained in the cream solder is used. Gases such as generated gas and air entrained at the time of cream solder application are escaped, and the generation of voids can be suppressed and the soldering state can be kept uniform, so that the electrical characteristics are stabilized.

  In the first embodiment, the slit 12 is provided on the bottom electrode pad 5 so as to divide the cream solder into four in a cross shape. However, the slit 12 may be divided into any other number, for example, nine in a lattice shape. . The slits may be provided substantially uniformly on the bottom electrode pad 5 from the vicinity of the center of the solder joint to the outside, and the slits may be increased within a range that does not affect the adhesiveness of the solder joint. In this case, the escape route of the gas increases, and the gas can be released efficiently.

Embodiment 2. FIG.
In the printed wiring board 101 of the first embodiment, the case where the slit 12 is provided on the bottom electrode pad 5 is shown. In the second embodiment, a case where a slit is also provided in the bottom electrode pad will be described.

  FIG. 3 is a top view showing the configuration of the printed wiring board 102 according to the second embodiment. 4 is a cross-sectional view taken along the line B-B (FIG. 3) of the printed wiring board 102 after the surface-mounted component 1 is soldered.

  As shown in FIGS. 3 and 4, the printed wiring board 102 according to the second embodiment has an L-shaped solder on the bottom electrode pad 5 of the printed wiring board 101 (FIGS. 1 and 2) according to the first embodiment. Slits 12a, 12b, 12c, and 12d as first groove portions except for the central portion 5a of the cross, having substantially the same width as the slits 12 formed in a cross shape by the resists 7a, 7b, 7c, and 7d. It is formed. The center portion 5a of the cross is not provided with a slit because the bottom electrode pad 5 is connected to be equipotential as one pad.

  Other configurations are the same as those in the first embodiment, and the corresponding parts are denoted by the same reference numerals as those in FIGS. 1 and 2 and description thereof is omitted. Since the printed wiring board 102 has a slit depth larger than that of the printed wiring board 101, the gas in the cream solder at the time of soldering can be easily released, and the gas can be efficiently released.

  As described above, in the second embodiment, the slit 12 made of the solder resist is disposed on the bottom electrode pad 5, and the slit 12a having the same width and the same width except for the central portion in the bottom electrode pad 5. Since 12b, 12c, and 12d are provided, the gas in the cream solder at the time of soldering can be easily released, and the generation of voids can be more efficiently suppressed.

  In the second embodiment, the bottom electrode pad 5 is provided with the slits 12a, 12b, 12c, and 12d except for the central portion. However, the present invention is not limited to this. For example, the slits can be provided up to the center by forming slits halfway and connecting the bottom electrode pads 5 instead of providing slits in the entire thickness direction of the bottom electrode pads 5. In this case, the gas generated in the central part can also be released efficiently.

Embodiment 3 FIG.
In the printed wiring board 102 of the second embodiment, the case where the bottom electrode pad 5 is provided with slits 12a, 12b, 12c, and 12d having the same width at the same position as the slit 12 is shown. In the third embodiment, a case where a groove is provided around a solder resist that forms a slit will be described.

  FIG. 5 is a top view showing the configuration of the printed wiring board 103 according to the third embodiment. FIG. 6 is a cross-sectional view taken along the line C-C (FIG. 5) of the printed wiring board 103 after the surface-mounted component 1 is soldered.

  As shown in FIGS. 5 and 6, the printed wiring board 103 according to the third embodiment is provided with a notch 5b in the bottom electrode pad 5 of the printed wiring board 101 (FIGS. 1 and 2) according to the first embodiment. 5c, 5d, 5e are provided, and solder resists 7e, 7f, 7g, 7h for forming slits 12e, 12f, 12g, 12h are provided on the substrate 1 in the notches 5b, 5c, 5d, 5e, respectively. It has been. Between the notches 5b, 5c, 5d, and 5e and the solder resists 7e, 7f, 7g, and 7h, groove portions 13a, 13b, 13c, and 13d are provided as second groove portions, respectively.

  Other configurations are the same as those in the first embodiment, and the corresponding parts are denoted by the same reference numerals as those in FIGS. 1 and 2 and description thereof is omitted. The printed wiring board 103 is provided with solder resists 7e, 7f, 7g, and 7h, and the slits 12e, 12f, 12g, and 12h are reliably covered with the melted cream solder by the grooves 13a, 13b, 13c, and 13d. Ensure a gas passage.

  As described above, in the third embodiment, the solder resists 7e, 7f, 7g, and 7h in which the slits 12e, 12f, 12g, and 12h are formed are formed in the cutout portions 5b, 5c, 5d, and 5e of the bottom electrode pad 5. Since the groove portions 13a, 13b, 13c, and 13d are provided between the solder resists 7e, 7f, 7g, and 7h and the notches 5b, 5c, 5d, and 5e, the solder is melted into the slit when the solder is melted. A gas passage can be ensured without covering, and generation of voids can be more efficiently suppressed.

It is a top view which shows the structure of Embodiment 1 of the printed wiring board which concerns on this invention. It is sectional drawing which shows the structure of Embodiment 1 of the printed wiring board which concerns on this invention. It is a top view which shows the structure of Embodiment 2 of the printed wiring board which concerns on this invention. It is sectional drawing which shows the structure of Embodiment 2 of the printed wiring board which concerns on this invention. It is a top view which shows the structure of Embodiment 3 of the printed wiring board which concerns on this invention. It is sectional drawing which shows the structure of Embodiment 3 of the printed wiring board which concerns on this invention. It is a top view which shows the structure of the surface mounting components soldered to a printed wiring board. It is a top view which shows the structure of the conventional printed wiring board. It is sectional drawing which shows the structure of the conventional printed wiring board. It is a figure which shows the state of the solder joint part of the conventional printed wiring board and surface mount components. It is a top view which shows the structure of the conventional printed wiring board. It is sectional drawing which shows the structure of the conventional printed wiring board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface mount component 5 Bottom electrode pad 7a, 7b, 7c, 7d, 7e, 7f, 7g, 7h Solder resist 8 Solder joint part 12, 12a, 12b, 12c, 12d, 12e, 12f, 12g, 12h Slit 101, 102, 102 Printed wiring board

Claims (5)

A substrate,
Electronic components,
A pad portion provided on the substrate for mounting the electronic component;
A solder joint that connects the electronic component and the pad portion,
A pair of solder resists arranged side by side from the outer edge of the pad portion on the pad portion;
Printed circuit board, characterized that you passage communicating with the outside air is formed by the pair of solder resist and the pad portion. Printed wiring board according to claim 1, wherein the ambient air is further provided with it a groove communicating with said interposed between a pair of the solder resist position of the pad portion. The printed wiring board according to claim 2, wherein a part of the groove portion penetrates the pad portion. A substrate,
Electronic components,
A pad portion provided on the substrate with a notch directed from the outer edge toward the inside, and mounting the electronic component;
A solder joint for connecting the pad portion and the electronic component;
A pair of solder resists arranged side by side on the substrate corresponding to the notch portion of the pad portion;
The printed wiring board, wherein a flow path communicating with outside air is formed by the pair of solder resists and the substrate. The printed wiring board according to claim 4, wherein a height of the solder resist is higher than a height of the pad portion.

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