Circuit board soldering method and circuit board

Abstract

To provide a method for soldering a circuit board, which can easily identify a defect in which pads are not connected to each other by solder.SOLUTION: A method of soldering a circuit board 10a includes a solder application step of applying a solder S to a first portion 161a, which is a portion of the two pads 16a that are spaced apart from each other, that is, the portion that is closer to each other, and no solder is applied to a second portion 162a, which is the portion that is farther from each other, and a heating step of heating the circuit board 10a and the applied solder S to melt the solder S applied to the first portion 161a and spread the molten solder S to the second portion 162a.SELECTED DRAWING: Figure 2A

Description

Technical Field

[0001] The present invention relates to a soldering method for a circuit board and a circuit board.

Background Art

[0002] Patent Document 1 discloses a configuration in which solder is used instead of a 0Ω resistance element (chip) for circuit examination and circuit switching. Specifically, the circuit board disclosed in Patent Document 1 includes a pad (first conductive land) provided on an insulating substrate, and another pad (second conductive land) provided spaced apart from this pad. Then, by reflow soldering, the solder is soldered so as to straddle the two pads. According to such a configuration, the two pads are electrically conducted by the solder. And since the solder has the same function as the 0Ω resistance element, the mounting of the 0Ω resistance element can be omitted.

[0003] However, in a configuration where pads are connected to each other by solder, if soldering is not properly performed, a defect (so-called open failure) may occur in which the solder is bonded to only one of the two pads and not bonded to the other pad. When such a defect occurs, if the solder is not in contact with the other pad but appears to overlap the other pad in a top view (that is, the solder is lifted from the other pad), it may not be possible to determine whether soldering has been properly performed by visual inspection or image inspection.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

[0005] (Problem to be Solved by the Invention) In view of the above circumstances, the problems that the present invention aims to solve are to provide a soldering method for a circuit board configured to electrically connect pads together by solder, which allows for easy determination of whether or not the pads are properly connected by solder, and to provide a circuit board suitable for such a soldering method.

[0006] (Means for solving the problem) To achieve the above objective, the soldering method for circuit boards according to the present invention is: A soldering method for a circuit board comprising an insulating substrate, a plurality of conductor patterns provided on the surface of the insulating substrate, and a resist film covering the surface of the insulating substrate and the plurality of conductor patterns, wherein the plurality of conductor patterns include a conductor pattern having pads that are exposed and not covered by the resist film, and other conductor patterns having other pads that are spaced apart from the pads by a linear gap and are exposed and not covered by the resist, A soldering step in which solder is applied to a first portion of each of the pads, which is a part of the side of each pad that is close to each other, and not to a second portion of each of the pads, which is a part of each pad other than the first portion that is far from each other, A heating step in which the circuit board and the applied solder are heated to melt the solder applied to the first portion and spread the molten solder to the second portion, This includes connecting the pad and the other pads by soldering.

[0007] According to the present invention, when soldering two pads (the aforementioned pad and the other pad) together, if the solder properly adheres to each of the two pads, the solder will spread to the second portion of each of the two pads. On the other hand, if the solder does not properly adhere to at least one of the two pads, the solder will not spread to the second portion of that at least one pad. Therefore, by visually inspecting whether or not solder is present on the second portion of each of the two pads, it is possible to determine whether or not the soldering has been done properly. Thus, it becomes easier to determine whether or not the soldering has been done properly.

[0008] A configuration can be applied in which the dimension of the second portion of the pad and the other pad in a direction parallel to the direction of extension of the gap is smaller than the dimension of the first portion in a direction parallel to the direction of extension of the gap.

[0009] With this configuration, it becomes easy to distinguish between the first and second parts, making it easier to determine whether or not the solder has spread to the second part. Furthermore, with this configuration, the amount of solder that spreads to the second part can be reduced compared to a configuration where the dimensions parallel to the direction of extension of the gap between the first and second parts are the same, thus reducing the amount of solder required for soldering.

[0010] The aforementioned pad and the other pad have shapes that are substantially symmetrical with respect to the center line of the gap, and in the soldering process, solder is applied to the region including the first portion of the aforementioned pad and the other pad, which has a shape that is substantially symmetrical with respect to the center line of the gap.

[0011] With this configuration, the amount of solder applied to the two pads can be made nearly equal, thus preventing or suppressing the problem of improper soldering caused by uneven solder application.

[0012] Furthermore, the circuit board according to the present invention is The device comprises an insulating substrate, a plurality of conductive patterns provided on the surface of the insulating substrate, and a resist film covering the insulating substrate and the plurality of conductive patterns. The plurality of conductor patterns include a conductor pattern having pads that are exposed without being covered by the resist film, and other conductor patterns having other pads that are spaced apart from the pads by a linear gap and are exposed without being covered by the resist film. The aforementioned pad and the other pad each comprise a first portion which is a part on the side adjacent to each other, and a second portion which is a part other than the first portion and on the side far from each other. The dimension of the second portion in the direction parallel to the extension direction of the gap is smaller than the dimension of the first portion in the direction parallel to the extension direction of the gap.

[0013] According to the circuit board of the present invention, similarly to the above, it is possible to determine whether or not solder has been properly soldered by visual inspection to check whether or not solder is present in the second portion of each of the two pads. Therefore, it becomes easier to determine whether or not soldering has been properly performed. Furthermore, with the circuit board of the present invention, it becomes easier to distinguish between the first portion and the second portion, making it easier to determine whether or not the solder has spread to the second portion. In addition, with this configuration, the amount of solder that spreads to the second portion can be reduced compared to a configuration in which the dimensions parallel to the direction of extension of the gap between the first portion and the second portion are the same, thus reducing the amount of solder required for soldering.

[0014] The two pads have shapes that are substantially symmetrical with respect to the center line of the gap when viewed from above. This configuration can be applied.

[0015] With this configuration, the amount of solder applied to the two pads can be made nearly equal, thus preventing or suppressing the problem of improper soldering caused by uneven solder application.

[0016] The pad and the other pad have shapes that are substantially line-symmetric to each other with respect to a straight line perpendicular to the extending direction of the gap in a top view, the following configuration can be applied: the second portion extends from a substantially center of the first portion in the extending direction of the gap in a direction perpendicular to the extending direction of the gap.

[0017] With this configuration, when molten solder becomes substantially circular or substantially elliptical in top view due to surface tension, an outer peripheral portion of the molten solder approaches the second portion. This makes it easier for the molten solder to flow to the second portion, thereby further improving the accuracy of determining whether soldering has been properly performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] [Figure 1A] FIG. 1A is a plan view showing the configuration of a circuit board according to a first embodiment. [Figure 1B] FIG. 1B is a cross-sectional view taken along line IB-IB in FIG. 1A. [Figure 2A] FIG. 2A is a plan view showing a solder applying step in the soldering method according to the first embodiment. [Figure 2B] FIG. 2B is a cross-sectional view taken along line IIB-IIB in FIG. 2B. [Figure 3] FIG. 3 is a schematic cross-sectional view showing a properly soldered circuit board. [Figure 4] FIG. 4 is a schematic cross-sectional view showing an improperly soldered state of a conventional circuit board. [Figure 5] FIG. 5 is a schematic cross-sectional view showing a conventional solder applying step. [Figure 6A] FIG. 6A is a plan view showing the configuration of a circuit board according to a second embodiment. [Figure 6B] FIG. 6B is a cross-sectional view taken along line VIB-VIB in FIG. 6A. [Figure 6C] FIG. 6C is a cross-sectional view taken along line VIC-VIC in FIG. 6A. [Figure 6D] FIG. 5D is a cross-sectional view taken along line VID-VID in FIG. 5A. [Figure 7A] Figure 7A is a plan view showing the solder application process of the soldering method according to the second embodiment. [Figure 7B] Figure 7B is a cross-sectional view showing the solder application process of the soldering method according to the second embodiment. [Figure 8] Figure 8 is a schematic cross-sectional view showing a properly soldered circuit board. [Modes for carrying out the invention]

[0019] <First Embodiment> (Circuit board) Figures 1A and 1B show a portion of the circuit board 10a according to the first embodiment. Figure 1A is a plan view (top view), and Figure 1B is a cross-sectional view taken along the IB-IB arrow in Figure 1A. As shown in Figures 1A and 1B, the circuit board 10a comprises an insulating substrate 11, a plurality of conductor patterns 12 provided on the surface of the insulating substrate 11, and a resist film 13 covering the insulating substrate 11 and the plurality of conductor patterns 12. In Figures 1A and 1B, two conductor patterns 12 are shown as the plurality of conductor patterns 12. These two conductor patterns 12 are separated by a linear gap 14 (which can also be called a slit-shaped gap 14). These two conductor patterns 12 are conductor patterns that are electrically connected to each other by soldering, which will be described later, and are not electrically connected to each other before soldering.

[0020] In the following explanation, the "center line C of the gap 14 between the two conductor patterns 12" may be abbreviated as "center line C". The direction of extension of center line C is the direction of extension of the gap 14. Also, in a top view (viewed perpendicular to the surface of the circuit board 10a), the direction parallel to center line C may be referred to as the first direction, and the direction perpendicular to center line C (the width direction of the gap) may be referred to as the second direction. In Figure 1A, the up-down direction is the first direction, and the left-right direction is the second direction.

[0021] The resist film 13 is provided with an opening 15a for soldering two conductor patterns 12 together. Hereinafter, this opening 15a may be referred to as the "resist opening 15a". As shown in Figures 1A and 1B, the resist opening 15a is configured to include a portion of each of the two conductor patterns 12 and a portion of the gap 14 between the two conductor patterns 12. Alternatively, the resist opening 15a can be configured to expose a portion of each of the two conductor patterns 12 and a portion of the gap 14 between the two conductor patterns 12. The portion of each of the two conductor patterns 12 that is exposed through the resist opening 15a is the soldering pad 16a.

[0022] The resist opening 15a has an elongated shape that is longer in the second direction and is substantially symmetrical with respect to the center line C. Therefore, a gap 14 is located approximately at the center of the resist opening 15a in the second direction, and two pads 16a are located on both sides of the gap 14 in the second direction. That is, two pads 16a, which have substantially symmetrical shapes with respect to the center line C, are provided adjacent to each other with the gap 14 in between. Of each of the two pads 16a, a portion on the side closer to each other in the second direction is the first portion 161a, to which paste-like solder S is applied in the soldering process described later, and the remaining portion (the portion further from the gap 14 than the first portion 161a) is the second portion 162a to which paste-like solder S is not applied.

[0023] Each of the two pads 16a has an elongated shape that is longer in the second direction. For example, each of the two pads 16a has a roughly rectangular shape in which the dimension in the second direction is approximately twice the dimension in the first direction. The ratio of the dimensions in the second direction of the first portion 161a to the second portion 162a is not particularly limited, but for example, the dimensions in the second direction of the first portion 161a and the second portion 162b are approximately the same. Note that the first portion 161a and the second portion 162a are a single unit and there is no difference in appearance in this embodiment.

[0024] The width of the gap 14 is not particularly limited, but is set to a size that allows the solder S to flow across the two pads 16a when soldering by the reflow method. For example, the width of this gap 14 is set to approximately 0.2 mm. The specific dimensions of the two pads 16a are also not particularly limited, but for example, the dimension of each of the two pads 16a in the first direction is approximately 0.8 mm, and the dimension in the second direction is approximately 1.4 mm. In this case, the dimension in the second direction of the first part 161a and the second part 162a is approximately 0.7 mm. In Figure 1A, an example is shown where the resist opening 15a is a rectangle that is longer in the second direction, but the shape of the resist opening 15a is not limited to a rectangle. For example, the resist opening 15a may be an oval or elliptical shape that is longer in the second direction.

[0025] (Soldering method for circuit boards) Next, the soldering method for the circuit board 10a will be described. According to this embodiment, the pads 16a of the two conductor patterns 12 are connected by solder S. This allows the solder S to function equivalently to a 0Ω resistor for circuit testing or switching. Therefore, the mounting of a 0Ω resistor can be omitted.

[0026] The reflow soldering method is applied to the soldering of the circuit board 10a. Reflow soldering includes a solder application step and a heating step. The solder application step is the step of applying paste-like solder S to a predetermined area of ​​the circuit board 10a. The heating step is the step of heating the circuit board 10a to melt the solder S and join (connect) the solder S to the conductor pattern 12.

[0027] Figure 2A is a schematic diagram showing the soldering process, a plan view showing the state in which the metal mask 50 is placed on the circuit board 10a. Figure 2B is a schematic diagram showing the soldering process, a schematic cross-sectional view (corresponding to the cross-sectional view taken along the IIB-IIB arrow in Figure 2A) showing the state in which paste-like solder S has been applied. As shown in Figures 2A and 2B, a metal mask 50 is used in the soldering process. The metal mask 50 is provided with an opening 501 for defining the area in which the paste-like solder S is applied. For convenience of explanation, the opening 501 provided in the metal mask 50 may be referred to as the "mask opening 501".

[0028] As shown in Figures 2A and 2B, when the metal mask 50 is placed on the surface of the circuit board 10a, the areas where the paste-like solder S is not applied are covered by the metal mask 50, and the areas where the paste-like solder S is applied are exposed through the mask opening 501. When the metal mask 50 is placed on the circuit board 10a, in a top view, the mask opening 501 is configured to include a portion of the resist opening 15a. Specifically, the mask opening 501 is the central part of the resist opening 15a in the second direction and is configured to include the first portion 161a of each of the two pads 16a and the portion between the two first portions 161a of the gap 14. However, the mask opening 501 is configured not to include the second portion 162a of each of the two pads 16a. In other words, when the metal mask 50 is placed on the circuit board 10a, the first portion 161a of each pad 16a of the two conductor patterns 12 is exposed through the mask opening 501, while the second portion 162a is covered by the metal mask 50 and not exposed. Furthermore, the mask opening 501 is configured to include both outer portions of the two pads 16a in the first direction when viewed from above, so that a predetermined amount of paste-like solder S can be applied.

[0029] Furthermore, the mask opening 501 is configured to have a shape that is approximately symmetrical with respect to the center line C when the metal mask 50 is placed on the circuit board 10a. In other words, the mask opening 501 is configured to expose a region that is approximately symmetrical with respect to the center line C when the mask is placed on the circuit board 10a.

[0030] Then, with the metal mask 50 placed on the circuit board 10a, paste-like solder S is applied as shown in Figure 2B. This applies the paste-like solder S to the first portion 161a of each of the two pads 16a (i.e., the portions of the two pads 16a that are close to each other). Furthermore, the paste-like solder S is also applied to the outer portions of both pads 16a in the first direction. However, the paste-like solder S is not applied to the second portion 162a of each of the two pads 16a (the portions other than the first portion 161a that are farther from each other in the second direction).

[0031] The heating process is performed with the paste-like solder S applied. In the heating process, the circuit board 10a from which the metal mask 50 has been removed and the paste-like solder S applied to the circuit board 10a are heated using a reflow oven or the like. The solder S, melted by heating, flows and spreads in the respective planar directions of the two pads 16a due to its wettability. As described above, the paste-like solder S is applied to the first portion 161a of each of the two pads 16a, but not to the second portion 162a. Therefore, when the solder S becomes wettable to the surface of the pads 16a, the solder S spreads (flows) onto the second portion 162a of the pads 16a. However, when the solder S is not wettable to the pads 16a, the solder S does not spread onto the second portion 162a of the pads 16a and tends to take on a roughly spherical shape due to surface tension.

[0032] Figure 3 is a schematic cross-sectional view of a properly soldered circuit board 10a, corresponding to the cross-sectional view taken along the IIB-IIB arrow in Figure 2A. "Properly soldered state" means that the solder S is bonded to the entire surface of the first portion 161a and the second portion 162b via an alloy layer (intermetallic compound) not shown in the figure. Note that the solder S does not necessarily have to be bonded to the entire surface of the second portion 162b; it may be bonded to an area of ​​the second portion 162b that is greater than or equal to a predetermined proportion. After the heating process, when the solder S solidifies, the two pads 16a become connected to each other by the solidified solder S, as shown in Figure 3. Therefore, when properly soldered, the two pads 16a (i.e., the two conductor patterns 12) become electrically conductive through the solder S.

[0033] With this configuration, it becomes easier to determine by visual inspection or image inspection whether the pads 16a of the two conductor patterns 12 are joined (connected) by solder S (in other words, the accuracy of the determination can be improved). Specifically, when viewed from above, it is determined whether solder S has flowed to the second portion 162a of both pads 16a, or in other words, whether solder S is present on the surface of the second portion 162a of both pads 16a. If solder S is present on the second portion 162a of both pads 16a, it can be determined that they have been properly soldered (i.e., the two pads 16a have been properly connected by solder S).

[0034] Furthermore, if solder S is not present on the second portion 162a of at least one of the two pads 16a, it can be determined that the pads are not properly soldered (i.e., the two pads 16a are not properly connected by solder S). Figure 4 is a cross-sectional view showing an example of improper soldering, more specifically a cross-sectional view showing a state in which solder S is not bonded to the pad 16a on the right side of the figure. If the solder S does not have wettability to the surface of one of the pads 16a (the pad 16a on the right side in Figure 4) during the heating process, the molten solder S will gather on the surface of the other pad 16a (the pad 16a on the left side in Figure 4) due to surface tension and will take on a roughly spherical shape. In this case, a portion of the solder S that has taken on a roughly spherical shape will appear to overlap at least a portion of the first portion 161a of the unbonded pad 16a in a top view, but will not overlap the second portion 162a. Therefore, when viewed from above, if solder S is not present on the second portion 162a of at least one pad 16a, or more specifically, if solder S is not present on the parts of at least one pad 16a that are far apart from each other, it can be determined that the soldering was not done properly (an open fault occurred).

[0035] Figure 5 is a schematic cross-sectional view showing a conventional method of applying paste-like solder S to the entire surface of each of two pads 901 in a soldering process. In the conventional soldering method (i.e., a configuration in which the pad 901 does not have a first portion 161a and a second portion 162a), as shown in Figure 5, even if the solder S does not adhere to at least one of the pads 901, the solidified solder S may appear to be superimposed on the entire surface of the unconnected pad 16a in a top view. Therefore, in such cases, it may be difficult to determine whether the soldering is not done properly by visual inspection. In contrast, in this embodiment, if the soldering is not done properly, there is no solder S on the second portion 162a of the pad 16a, making it easier to determine whether the soldering is done properly by visual inspection. Therefore, according to this embodiment, determining whether the soldering is done properly becomes more important compared to the conventional soldering method.

[0036] Furthermore, in this embodiment, the resist opening 15a (i.e., the two pads 16a) has a shape that is substantially symmetrical with respect to the center line C. With this configuration, it is possible to prevent or suppress unevenness in the amount of solder S flowing to the two pads 16a during the heating process. Specifically, if there is a difference in the area of ​​the first portion 161a of the two pads 16a, when the solder S melts during the heating process, the molten solder S tends to accumulate in the "larger area pad 16a" of the two pads 16a due to surface tension. As a result, there is a risk that the solder S will not adhere to the "smaller area pad 16a". As described above, if the two pads 16a have a shape that is substantially symmetrical with respect to the center line C, it is possible to prevent or suppress unevenness in the amount of solder S flowing to the two pads 16a, and thus it is possible to prevent or suppress the inability to properly solder due to unevenness in the amount of solder S.

[0037] Furthermore, the mask opening 501 (i.e., the portion to which the solder S is applied) also has a shape that is substantially symmetrical with respect to the center line C of the gap 14. With this configuration, a substantially equal amount of paste-like solder S can be applied to the two pads 16a. Therefore, for the same reasons as above, it is possible to prevent or suppress the inability to properly solder due to uneven amounts of solder S.

[0038] <Second Embodiment> (Circuit board) Figures 6A, 6B, 6C, and 6D are diagrams showing a portion of the circuit board 10b according to the second embodiment. Figure 6A is a plan view, Figure 6B is a cross-sectional view taken along the VIB-VIB arrow in Figure 6A, Figure 6C is a cross-sectional view taken along the VIC-VIC arrow in Figure 6A, and Figure 6D is a cross-sectional view taken along the VID-VID arrow in Figure 6A. Compared to the circuit board 10a according to the first embodiment, the circuit board 10b according to the second embodiment differs in the configuration of the resist openings 15b of the resist film 13 (in other words, the configuration of the pads 16b), but otherwise has substantially the same configuration. For this reason, the same reference numerals as in the first embodiment are used for components that are the same as in the first embodiment, and their descriptions are omitted.

[0039] The resist film 13 is provided with resist openings 15b. The resist openings 15b are configured to include a portion of each of the two conductor patterns 12 and a portion of the gap 14 between the two conductor patterns 12. The portions of each of the two conductor patterns 12 that are exposed through the resist openings 15b are soldering pads 16b.

[0040] Specifically, the resist opening 15b comprises a main body 151 and two extensions 152. The two extensions 152 are portions that extend outward in the second direction (to opposite sides of each other) from both ends of the main body 151 in the second direction. The dimension of the extensions 152 of the resist opening 15b in the first direction is smaller than the dimension of the main body 151 in the first direction. Furthermore, the extensions 152 have an elongated shape, being longer in the second direction (in other words, their dimension in the second direction is larger than their dimension in the first direction).

[0041] Furthermore, the portion of the resist opening 15b exposed from the main body portion 151 is the first portion 161b of each of the two pads 16b, and the portion exposed from each of the two extensions 152 of the resist opening 15b is the second portion 162b of each of the two pads 16b. Because the resist opening 15b has the above configuration, each of the two pads 16b comprises a first portion 161b located on the side closer to each other (the side closer to the gap 14), and a second portion 162b located on the side farther from each other (the side farther from the gap 14) and extending from the first portion 161b toward the side farther from each other (the side opposite to the gap 14). The second portion 162b is integrally connected to the first portion 161b. Also, the first-direction dimension B2 of the second portion 162b (see Figure 6D) is smaller than the first-direction dimension B1 of the first portion 161b (see Figure 6C). Furthermore, the second portion 162b has an elongated shape that is longer in the second direction.

[0042] Furthermore, the resist opening 15b has a shape that is approximately symmetrical with respect to the center line C of the gap 14. Therefore, the gap 14 is located approximately at the center of the resist opening 15b in the second direction, and the two pads 16b are located on both sides of the gap 14 in the second direction. That is, the two pads 16b, which have a shape that is approximately symmetrical with respect to the center line C, are provided adjacent to each other with the gap 14 in between. In addition, the resist opening 15b has a shape that is approximately symmetrical with respect to a straight line parallel to the second direction. Therefore, the second portion 162b is located approximately at the center of the first portion 161b in the first direction.

[0043] Figure 6A shows an example where the main body 151 (in other words, the first portion 161b of the pad 16b) and extension 152 (in other words, the second portion 162b of the pad 16b) of the resist opening 15b are rectangles that are elongated in a direction perpendicular to the center line C of the gap 14. However, the shape of the main body 151 of the resist opening 15b is not limited to a rectangle. For example, the main body 151 and extension 152 of the resist opening 15b may be oval or elliptical in shape that are elongated in a direction perpendicular to the center line C of the gap 14. Also, the dimensions of the first portion 161b and the second portion 162b are not particularly limited, but for example, the length of the second portion 162b (dimension in the second direction) is approximately the same as the length of the first portion 161b, and the width of the second portion 162b (dimension in the first direction) is approximately half the width of the first portion 161b. More specifically, the following dimensions can be applied: the length of the first section 161b and the length of the second section 162b are approximately 0.7 mm, the width of the first section 161b is approximately 0.8 mm, and the width of the second section 162b is approximately 0.4 mm.

[0044] (Soldering method for circuit boards) Figures 7A and 7B are schematic diagrams illustrating the soldering process. Figure 7A is a plan view, and Figure 7B is a cross-sectional view taken along the line VIIB-VIIB in Figure 7A. As shown in Figures 7A and 7B, a metal mask 50 with mask openings 501 is used in the soldering process.

[0045] As shown in Figures 7A and 7B, a metal mask 50 is placed on the surface of the circuit board 10b. With the metal mask 50 in place, the areas where the paste-like solder S is not applied are covered by the metal mask 50, while the areas where the paste-like solder S is applied are exposed through the mask opening 501. The mask opening 501 is located in the longitudinal center of the resist opening 15b with the metal mask 50 placed on the circuit board 10b, and includes the first portion 161b of each of the two pads 16b and the portion between the two first portions 161b of the gap 14, but does not include the second portion 162b of each of the two pads 16b. In other words, with the metal mask 50 placed on the circuit board 10b, approximately in the longitudinal center of the resist opening 15b, the first portion 161b of each of the pads 16b of the two conductor patterns 12 is exposed through the mask opening 501, while the second portion 162b is covered by the metal mask 50 and not exposed. Furthermore, the mask opening 501 is configured to include the outer portions of the gap 14 between the two pads 16b in the first direction, so that a predetermined amount of paste-like solder S can be applied.

[0046] Furthermore, the mask opening 501 is configured to expose a region that is substantially symmetrical with respect to the center line C when the mask is placed on the circuit board 10b. In addition, the mask opening 501 is configured to be substantially symmetrical with respect to a straight line parallel to the second direction when the metal mask 50 is placed on the circuit board 10b.

[0047] Then, with the metal mask 50 placed on the circuit board 10b, paste-like solder S is applied. This applies the paste-like solder S to the first portion 161b of each of the two pads 16b (the portion on the side that is close to each other). The paste-like solder S is also applied to the outer portions on both sides in the direction parallel to the center line C of the gap 14 between the two pads 16b. However, the paste-like solder S is not applied to the second portion 162b of each of the two pads 16b (the portion other than the first portion 161b, which is the portion that is farther from each other in the direction perpendicular to the center line C of the gap 14).

[0048] In this state, the heating process is performed. The paste-like solder S is applied to the first portion 161b of each of the two pads 16b, but not to the second portion 162b. Therefore, when the solder S becomes wettable to the pads 16b, the solder S flows to the second portion 162b of the pads 16b. However, if the solder S is not wettable to the pads 16b, the solder S will try to take on a roughly spherical shape due to surface tension and will not flow to the second portion 162b of the pads 16b.

[0049] After the heating process, when the solder S solidifies, the two pads 16b become connected to each other by the solidified solder S, as shown in Figure 8. Therefore, the two conductor patterns 12 become electrically conductive through the solder S.

[0050] The second embodiment can achieve the same effects as the first embodiment. Furthermore, in the second embodiment, since the dimension B2 of the second portion 162b in the first direction is smaller than the dimension B1 of the first portion 161b in the first direction, it is easy to distinguish between the first portion 161b and the second portion 162b. Therefore, the accuracy of the determination can be further improved. In addition, since the dimension B2 of the second portion 162b in the first direction is smaller than the dimension B1 of the first portion 161b in the first direction, the amount of solder flowing to the second portion 162b is less compared to the first embodiment, so the amount of solder S required for soldering can be reduced.

[0051] The second portion 162b is located approximately in the center in the first direction. With this configuration, the molten solder S during the heating process flows more easily into the second portion 162b. That is, surface tension acts on the molten solder S during the heating process, causing it to gather in the center of the resist opening 15b when viewed from above and to form a roughly circular or elliptical shape. When the molten solder S forms a roughly circular or elliptical shape in the center of the resist opening 15b when viewed from above, if the second portion 162b of the pad 16b is located in the center, the outer edge of the molten solder S approaches the second portion 162b compared to a configuration where it is located in a part other than the center (for example, the four corners of the first portion 161b). Therefore, when the molten solder S spreads due to its wettability, it flows more easily into the second portion 162b.

[0052] Although embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the embodiments described above. The present invention can be modified in various ways without departing from its spirit, and these modifications are also included within the technical scope of the present invention. [Explanation of symbols]

[0053] 10a, 10b…Circuit board, 11…Insulating substrate, 12…Conductor pattern, 13…Resist film, 14…Gap between conductor patterns, 15a, 15b…Resist opening, 16a, 16b…Conductor pattern pad, 50…Metal mask, 151…Main body of resist opening, 152…Extended part of resist opening, 161a, 161b…First part of pad, 162a, 161b…Second part of pad, 501…Mask opening, C…Center line of gap, S…Solder

Claims

1. A soldering method for a circuit board comprising an insulating substrate, a plurality of conductor patterns provided on the surface of the insulating substrate, and a resist film covering the surface of the insulating substrate and the plurality of conductor patterns, wherein the plurality of conductor patterns include a conductor pattern having pads that are exposed and not covered by the resist film, and other conductor patterns having other pads that are spaced apart from the pads by a linear gap and are exposed and not covered by the resist, A soldering step in which solder is applied to a first portion of each of the pads, which is a part of the side of each pad that is close to each other, and not applied to a second portion of each of the pads, which is a part of each pad other than the first portion that is far from each other, A heating step in which the circuit board and the applied solder are heated to melt the solder applied to the first portion and spread the molten solder to the second portion, A method for soldering a circuit board, comprising connecting the pad and the other pads by solder.

2. A soldering method according to claim 1, A method for soldering a circuit board, wherein the dimension of the second portion of the pad and the other pad in a direction parallel to the direction of extension of the gap is smaller than the dimension of the first portion in a direction parallel to the direction of extension of the gap.

3. A method for soldering a circuit board according to claim 1 or claim 2, The aforementioned pad and the other pad have shapes that are substantially symmetrical with respect to the center line of the gap, A method for soldering a circuit board, wherein in the soldering step, solder is applied to a region including the first portion of the pad and the other pads, and the region has a shape that is substantially symmetrical with respect to the center line of the gap.

4. The device comprises an insulating substrate, a plurality of conductive patterns provided on the surface of the insulating substrate, and a resist film covering the insulating substrate and the plurality of conductive patterns. The plurality of conductor patterns include a conductor pattern having pads that are exposed without being covered by the resist film, and other conductor patterns having other pads that are spaced apart from the pads by a linear gap and are exposed without being covered by the resist film. The aforementioned pad and the other pad each comprise a first portion which is a part on the side adjacent to each other, and a second portion which is a part other than the first portion and on the side far from each other. A circuit board in which the dimension of the second portion in the direction parallel to the extension direction of the gap is smaller than the dimension of the first portion in the direction parallel to the extension direction of the gap.

5. A circuit board according to claim 4, A circuit board in which the two pads have shapes that are substantially symmetrical to each other with respect to the center line of the gap when viewed from above.

6. A circuit board according to claim 4, The aforementioned pad and the other pad have shapes that are substantially symmetrical with respect to a straight line perpendicular to the direction of extension of the gap when viewed from above. The second portion is configured to extend from approximately the center of the extension direction of the gap of the first portion in a direction perpendicular to the extension direction of the gap.

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