JPH08298375A - Board for solder mounting device and mounting structure - Google Patents

Abstract

PURPOSE: To provide a board for surface mounting a device in which incomplete soldering can be visually determined easily. CONSTITUTION: When a surface mounting device 101 is mounted on a board 105 through an adhesive 103, the electrode 107 of the surface mounting device 101 is spaced apart specifically from a pad 102. A resist 104 is arranged between the pad 102 and the electrode 107. In case of incomplete soldering, solder is repelled by the resist 104 exhibiting low wettability to the solder which is thereby prevented from being left between the electrode 107 and the pad 102. Consequently, incomplete soldering can be visually detected easily based on the fact whether the resist 104 is visible or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board to which surface mount components are attached. Particularly, it relates to a structure of a pad portion to be soldered to an electrode of a surface mount component.

[0002]

2. Description of the Related Art Surface-mounted components have been widely used in recent years because the size of the device can be reduced and the components can be easily mounted on a printed circuit board.

For example, Japanese Patent Laid-Open No. 4-49695 describes a structure of a pad portion to be soldered to a surface mount component. FIG. 10 shows this Japanese Patent Laid-Open No. 4-4.
It is explanatory drawing explaining the pad part structure of the printed circuit board described in 9695 gazette. FIG. 10 is a plan view of a printed circuit board described in the above publication, in which a surface mount component and a pad are normally soldered and an uncompleted solder is not soldered. The combined state is also shown. In FIG. 10, the surface-mounted components are those that accommodate resistors, capacitors, transistors, diodes, etc., and the surface of the electrode part 3 is plated with solder.
have. The electrode portion 3 is soldered to the pad portion of the printed board. The printed circuit board is provided with an electrical connection pattern formed on a base material made of, for example, glass epoxy resin. For this pattern, for example, copper foil is used. The resist 6 is applied to this pattern except where it is connected to the electrode portion. Resist 6 is
It is an insulating layer for covering and protecting the upper surface of the copper foil pattern. In addition, a paste-like solder layer is applied to the pad portion at the tip of the copper foil to be soldered to the surface mount component, so that a so-called solder leveler 5 is formed.

As described above, the upper surface of the copper foil pattern is covered with the resist 6 except for the pad portion provided with the solder leveler 5.

In the invention described in the above publication, in a region where the resist 6 is normally covered, the region where the resist 6 is not applied, that is, the copper foil exposed portion 4 is adjacent to the solder leveler 5. The invention is characterized in that it is provided. As described above, the provision of the copper foil exposed portion 4 from which the resist 6 has been removed makes it possible to easily distinguish between an incompletely soldered state and a normal soldered state. ing.

In the incompletely joined state of the solder, the electrode portion 3, the solder leveler 5, and the copper foil exposed portion 4 are all exposed as shown in FIG. This is shown in the pad portion on the upper side with respect to the paper surface direction shown in FIG. On the other hand, in the normal soldering state, as shown in the lower pad portion with respect to the paper surface direction of FIG.
The electrode portion 3, the solder leveler 5, and the copper foil exposed portion 4 are covered with the solder 7. In this case, the solder leveler 5, the solder 7, and the solder plating on the surface of the electrode portion 3 are made of tin and lead and have a silver color, whereas the copper foil and the copper foil exposed portion 4 are yellow. It has a brown color.

Therefore, although the electrode portion 3 and the solder leveler 5 in the incompletely soldered state and the solder 7 in the normal soldering state have the same silver color, the copper foil exposed in the incompletely soldered state is exposed. Since the part 4 has a yellowish brown color, the color tone of the part 4 is significantly different from that of the solder 7 in the normal soldering state of silver-based color. Therefore, according to the invention described in the publication, by detecting the exposed yellow-brown copper foil portion 4 by visual inspection, it is possible to quickly find an incompletely joined state of the solder. It is described in the official gazette.

[0008]

As described above, according to the prior art, it is possible to determine whether the pad has solder or not by determining the color of the solder leveler (silver-based color) and the color of the exposed portion of the copper foil ( (Yellowish-brown). However, even if solder is attached to the pad and the exposed portion of the copper foil, the so-called solder joint with the surface-mounted component is not always complete.

It is possible to detect the case where the solder does not come into contact with the pad at all due to a defective soldering device. However, in many cases of so-called unsoldered solder, there is often solder on the pad, and there is contact between the solder and the surface mount component, so that there is often electrical conduction. In this case, the pads are provided with solder, but this is not the case where so-called complete solder joining is performed. Therefore, as described in the above publication, if the quality of the soldering is simply judged by the judgment of the color of the exposed portion of the copper foil, the electrical inspection (continuity inspection) will be passed, and the electronic device will be actually used. May be a problem when you run.

That is, when the so-called solder joint is incomplete and the solder is simply in contact with the solder, there is a high possibility that conduction failure will occur due to vibration, thermal expansion or contraction during subsequent use. For example, this thermal expansion
It is considered that shrinkage or the like occurs in the range of -40 ° C to + 80 ° C. However, in Japan, -20 to + 80 ° C is generally considered. This is because the rearview mirror of an automobile often has a high temperature.

As described above, it is empirically known that there is not so much correlation between the fact that the solder is attached to the pad and the fact that the solder joining is completely performed on the electrode. When the solder is simply in contact with the electrodes, it is impossible to detect the incomplete solder joint by an electrical inspection. As described above, in the conventional technology, if solder is attached to the pad, it is not recognized as unsoldered, which is a serious problem.

The present invention has been made in view of the above problems, and an object of the present invention is to recognize that solder is not soldered even when the solder is simply attached to the pad and so-called solder bonding is not made to the electrode. It is to provide a structure of a printed circuit board which is capable.

[0013]

In order to solve the above problems, the first invention has at least a pair of electrodes of a surface mount component and at least a pair of pads to which the pair of electrodes are soldered. A member having poor wettability with respect to solder is provided on the surface of the substrate together with the pair of electrodes and pads so as to be recognizable, and at a portion between the pad and the electrodes of the pair of electrodes and the pair of electrodes. In addition, a solder mounting structure for components is characterized in that each of the pads and the electrodes are soldered.

A second aspect of the present invention is a surface mount component substrate having a pad to be connected to an electrode of a surface mount component to be mounted by soldering, and the electrode and the pad are recognizable on the substrate surface. A board for soldering a component, wherein a member having poor wettability with respect to solder is provided on a part of the pad, and the member having poor wettability is arranged between the electrode and the pad. .

According to a third aspect of the present invention, in the surface mount component substrate of the first or second aspect of the present invention, the color of the member having poor wettability is different from the color of the pad and the electrode. It is a characteristic substrate for surface mount components.

The fourth aspect of the present invention is the above-mentioned first, second or third aspect.
In the substrate for surface mount component of the present invention, the member having poor wettability is a luminous substance substrate.

The luminescent substance includes a luminescent substance, a luminescent substance, etc., but it is the luminescent substance that is considered to be the best mode in practice, and strontium aluminate is considered to be particularly preferable.

[0018]

The pad according to the first aspect of the present invention is arranged at a predetermined distance from the electrode of the surface mount component connected by soldering. Further, a member having poor wettability with respect to solder is arranged on the surface of the substrate in the separated gap. Therefore, when the soldering between the pad and the electrode is incompletely coupled, the solder is repelled by the member having poor wettability, and the connection between the solder on the pad and the electrode is surely cut off.

The member having poor wettability in the second aspect of the present invention is different from the color of the pad or the electrode and the color of the resist. Therefore, in the incompletely bonded state of the solder, it is possible to easily detect the incompletely bonded state of the solder by visually detecting the color of the member having poor wettability.

The pad according to the third aspect of the present invention includes two regions, that is, a copper foil exposed region to be soldered and a non-wettable region having poor wettability to solder. Therefore, when the soldering is unsuccessful and the so-called incompletely joined state of the solder is generated, the solder is repelled by the non-wetting region, and it is easily detectable with the naked eye that the incompletely joined state of the solder is present.

The substrate for surface-mounted components according to the fourth aspect of the present invention uses a luminescent substance as a member having poor wettability. Since this luminescent substance emits light for a certain period of time after being irradiated with a certain amount of light, when the solder is incompletely bonded in a small dark box or dark room, that part emits light. This makes it possible to accurately detect the incompletely bonded state of the solder.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a printed circuit board according to a preferred embodiment of the present invention and a state in which a surface mount component 1 is arranged on the surface thereof. FIG. 1A shows a plan view of such a state, and FIG. 1B shows a cross-sectional view of such a case. As shown in FIG. 1B, the surface mount component 101 is fixed on the resist 104 on the substrate 105 with an adhesive 103. As shown in FIGS. 1A and 1B, the pad 102 for the surface mount component 101 is formed in a portion separated from the surface mount component 101 by a certain distance. A solder fillet 106 is formed between the electrode 107 and the pad 102 of the surface mount component 101. The manner in which the solder fillet 106 is formed is shown in FIG.

In particular, on the right side of FIG. 2, it is shown that the soldering is completely performed. However, the soldering cannot be performed on the left side because the solder amount is insufficient. An example of the case is shown.

Since a constant distance is provided between the electrode 107 of the surface mount component 101 and the pad 102, the electrode 104 of the surface mount component 101 can be seen when the resist 104 is viewed from above the printed circuit board when not soldered. And pad 10
2 between them, and it is possible to easily detect that they are not soldered by visual inspection or optical inspection. In addition, since there is no physical contact between the electrode 107 of the surface mount component 101 and the pad 102, it is possible to detect 100% of this unsoldered by an electrical inspection method.

If the distance between the pad 102 and the electrode 107 of the surface mount component 101 is too large, unsoldered detection is possible, but all the solder on the printed circuit board may be unsoldered. How to choose a certain distance is very important. That is, if the distance is too large, the soldering will fail, and if it is too short, the same problems as before (when the solder is visible but the solder joint is not made) remain. Will end up.

According to the normal solder bath passage speed, when the printed board according to the present embodiment is used, the distance between the pad 102 and the electrode 107 of the surface mount component 101 is larger than that of the currently used printed board. Since the distance is large, the rate of unsoldered solder becomes extremely large. Therefore, in the case of adopting the printed circuit board according to the present embodiment, it was confirmed by the inventor's experiment that the unsolder occurrence rate can be suppressed to an extremely small value by setting the speed of passing through the solder bath to about half of the current speed Has been done.

The pad 102 and the surface mount component 10 when the speed of the printed circuit board passing through the solder bath is reduced by half
FIG. 3 is a graph showing the relationship between the distance between the first electrode 107 and the electrode 107 and the unsolder occurrence rate. In the graph shown in FIG. 3, the vertical axis represents the unsolder occurrence rate (%), and the horizontal axis represents the distance (mm) between the surface mount component and the pad.
As can be seen from the graph shown in this FIG.
When the distance between the pad 102 and the electrode 107 of the surface mount component 101 becomes about 0.25 mm or more, the unsoldered rate increases, so if this distance is about 0.25 mm or less and further considering the mounting accuracy. The pad 102
By setting the distance between the surface mount component 101 and the electrode 107 of the surface mount component 101 to be about 0.15 mm, this gap can be accommodated in a region in which unsolder generation is small. In this case, the mounting accuracy is assumed to be ± 0.1 mm. That is,
If the distance between the pad 102 and the electrode 107 of the surface mount component 101 is 0.15 mm, the mounting accuracy is ± 0.1 mm.
Therefore, the distance is actually 0.05 mm ~
It becomes 0.25 mm. Therefore, the length of this range is shown in FIG.
It can be understood from the graph shown in (1) that this is a region where there is little unsoldered.

FIG. 4 shows an explanatory view of another embodiment of the present invention. FIG. 4 is a plan view of the printed circuit board,
It is shown that the pad 110 is arranged so as to surround the electrode 109 of the surface mount component 108.
In this way, the pad 110 is provided so as to have a certain distance from the electrode 109 of the surface mount component 108, and is arranged so as to surround the periphery of this electrode 109, so that it is possible to prevent unsoldering. Can be prevented.

As described above, according to the present embodiment, the electrode of the surface mount component and the electrode and the pad to be soldered are separated from each other. It is possible to detect the complete binding state. In this case, it is preferable to dispose a member having poor wettability with respect to solder between the electrode and the pad. As a result, even if soldering fails, the solder is repelled by the member having poor wettability, and the solder remains between the pad and the electrode even though the solder is incompletely bonded. Can be prevented.

Further, it is also preferable that the color of the member having poor wettability with respect to the solder is made different from the color of the pad or the electrode and the color of the resist. By making the colors different in this way, it becomes easier to detect the incompletely bonded state of the solder with the naked eye.

As described above, in the above-described embodiment, a member having poor wettability with respect to solder is used, and this member is made to have a different color from that of the pad or the like so that the identification can be facilitated. It was

The different colors are used for easy identification. Another configuration to facilitate identification is:
It is also preferable to use a luminous substance as the member having poor wettability. It is preferable to use, for example, strontium aluminate (SrAl ₂ O ₄ ) as the luminous substance.

This strontium aluminate is about 10
It emits light for about 3 to 5 minutes by irradiating with light for minutes.
Therefore, if this strontium aluminate is used as a member having poor wettability with respect to solder, the incompletely bonded state of solder can be detected more reliably than when different colors are used.

When the color of the pad is different from that of the pad or the like, the substrate to be inspected is irradiated with light, and the reflected light is photographed by the naked eye or a camera to detect the incompletely bonded state of the solder. . On the other hand, when a luminescent substance such as strontium aluminate is used, it emits light by itself, so that the incompletely bonded state of the solder can be detected very easily in a dark box or a dark room. In an inspection in a dark room or the like, since it is only necessary to inspect whether or not light is emitted from the substrate, it is possible to automatically detect an incompletely joined state of solder by a small CCD camera or the like.

Other Configuration Examples In the above-described embodiments , the configuration in which the incompletely bonded state of the solder is detected by using the member having poor wettability with respect to the solder is shown. It is also suitable to provide the silk 111 with an easy color. FIG. 5 shows an explanatory view when such a configuration is adopted. 5A and 5B, a plan view of the substrate is shown in FIG. 5A and a sectional view of the substrate is shown in FIG. With such a configuration, similarly to the above-described embodiment, the incompletely bonded state of the solder can be optically detected, and the incompletely bonded state of the solder can be reliably detected by an electrical test. is there.

Further, FIG. 6 shows a pad 10 similar to the conventional one.
2 is an explanatory view of a case where the silk 113 is placed on the second member to achieve the same action and effect as those of the above embodiment. FIG. 6 shows a plan view (a) and a cross-sectional view (b) as in FIGS. 1 and 2. According to the configuration shown in FIG. 6, the same effect as that of the above-described embodiment can be obtained by changing the design of only the silk plate even for the substrate of the conventional design in which the pad 102 and the electrode 107 are in contact with each other. It is possible.

Further, in the above embodiment, the pad 1
02 and the electrode 107, a member having poor wettability is arranged,
Although the pad 102 and the electrode 107 are separated by a predetermined distance, it is also preferable to provide a member having poor wettability with respect to solder in the region of the pad 102. Such a configuration
It can be realized by appropriately applying a member having poor wettability to solder to a predetermined position on the surface of the pad 102. According to such a configuration, when the soldering has failed or the amount of solder is small, the solder is repelled by the member having poor wettability, and the pad 1 remains with a small amount of solder.
02 can be prevented from remaining on top.

FIG. 7 shows an explanatory view of a case where a member having poor wettability is formed in the pad 102 in the form of a strip in the central portion of the pad 102, for example. As shown in FIG.
The strip-shaped member 115 is provided so as to cross the vicinity of the center of the pad 102.

As shown in FIG. 8, when the amount of solder is insufficient, the central strip-shaped member 115 is not covered with the solder, and as a result, an incompletely joined state of the solder is detected by the naked eye. It is possible. 7 and 8, when the amount of solder is sufficient, a conventional solder fillet is formed. FIG. 9 shows a sectional view taken along line IX-IX ′ of FIG.

As a result, it is possible to detect the condition in which the solder is not completely connected to the pad 10 with the naked eye.
2 It is possible to recognize that a member having poor wettability provided on the surface is exposed by repelling the solder, and it is possible to prevent it.
Even when such a configuration is adopted, if the soldering fails, the solder is completely removed from the pad, so it is possible to easily detect the incomplete joint state of the solder by visual inspection. is there.

In the structure shown in FIGS. 7-9,
One strip member 115 having poor wettability (to solder)
However, this may be a plurality of strip-shaped members. Further, in the structure shown in FIGS. 7 to 9, the strip-shaped member 115 does not completely divide the pad 102, but a structure that completely divides the pad 102 may be used.
That is, the strip-shaped member 115 may completely cross the pad 102. Further, the member 115 having poor wettability provided on the pad 102 is not limited to a strip-shaped member or a linear member, and a dot-shaped member also has the same effect.

Further, in the above-mentioned embodiments and other constitutional examples, an insulator is adopted as a member having poor wettability with respect to solder. By adopting this insulator, it was possible to reliably detect the incompletely bonded state of the solder by an electrical test.

However, it is conceivable that a conductive member (a conductor other than an insulator or a semiconductor) is used as the member having poor wettability (to solder). When the conductive member is used in this way, it is no longer possible to detect the incompletely bonded state of the solder by an electrical test, and only the naked eye can be discriminated. On the other hand, the use of the conductive member brings about an effect of further lowering the electric resistance at the joint portion when the soldering is normally performed. This reduces power loss and enables effective signal voltage propagation. This effect is particularly effective when the power supply voltage is small, and it is possible to reduce power (voltage) loss in a vehicle operating at 12 volts, for example.

As such a conductive member, an oxidizable material having conductivity and a color different from that of the electrodes and solder, such as titanium and copper, is suitable. In the case of copper, the wettability with respect to solder can be deteriorated by oxidizing it. Further, in the case of titanium, the wettability to solder is poor even if it is not oxidized, so that it can be used as it is.

[0046]

As described above, according to the first aspect of the present invention, the solder can be completely removed from the printed circuit board in the case where the solder is in an imperfectly coupled state. An effect is obtained that a substrate for surface mount components capable of detecting an incompletely bonded state of solder is obtained.

According to the second aspect of the present invention, the color of the member having poor wettability is different from the color of the pad or the electrode and the color of the resist. The state can be easily detected by an optical image processing device or the like.

Further, according to the third aspect of the present invention, since the non-wetting area is included in the pad, the solder remaining on the pad can be removed when the solder is not soldered or the amount of solder is small. It will be possible. Therefore, also according to the third aspect of the present invention, it is possible to easily visually detect an incompletely joined state of the solder.

Furthermore, according to the first and second aspects of the present invention, since the pads are separated from the electrodes, the intervals between the pads are generally large. Therefore, the wiring provided on the lower surface of the surface-mounted component can be easily routed. That is, since the area where the wiring is provided is increased, the so-called wiring allowance is increased and the handling is facilitated. In the so-called 2125 size surface mount product, the pad spacing was conventionally 1.0 mm, but according to the present invention, it is suitable to be approximately 2.3 mm. Therefore, the minimum conductor width is 0.3 mm and the minimum conductor spacing is 0.3 m.
In the case of m, the number of wirings under the surface mount component can be increased from 1 line to 3 lines, and the wiring routing margin is improved.

Further, according to the fourth aspect of the present invention, since the light emitting substance is used as the substance having poor wettability to solder,
By observing in a dark box or the like, it is possible to detect the incompletely bonded state of the solder extremely easily. Further, in the inspection in the dark box, since it is only necessary to detect the presence or absence of light emission from the substrate, there is no need for a device such as a lamp, a fluorescent lamp, or an LED for irradiating the detection section with light as in the past. Therefore, it is possible to reduce the size of the inspection device and reduce the cost with an inexpensive device. Therefore, it is possible to realize an apparatus for automatically detecting the incompletely joined state of solder by a small camera or the like.

[Brief description of drawings]

FIG. 1 is a plan view and a cross-sectional view of a surface mount component substrate that is a preferred embodiment of the present invention.

2A and 2B are a plan view and a cross-sectional view in the case where a component is soldered to the surface mount component substrate shown in FIG.

FIG. 3 is a graph showing a relationship between a distance between a pad and an electrode and a non-solder occurrence rate.

FIG. 4 is a plan view showing another embodiment of the present invention.

FIG. 5 is an explanatory diagram illustrating another configuration example.

FIG. 6 is an explanatory diagram illustrating another configuration example.

FIG. 7 is an explanatory diagram in the case where a strip-shaped member having poor wettability is provided in the central portion of the pad.

FIG. 8 is an explanatory diagram showing how solder is applied when the amount of solder is small in the configuration shown in FIG. 7.

9 is a sectional view taken along line IX-IX ′ in FIG.

FIG. 10 is an explanatory diagram showing a state in which surface mount components are attached to a conventional printed circuit board.

[Explanation of symbols]

101 surface mount component, 102 pad, 103 adhesive, 104 resist, 105 substrate, 107 electrode,
108 surface mount components, 109 electrodes, 110 pads.

Claims (4)

[Claims] 1. A surface mount component having at least a pair of electrodes and at least a pair of pads to which the pair of electrodes are soldered, and the pair of electrodes and the pads being recognizable on the surface of the substrate. A member having poor wettability with respect to solder is provided at a portion between the pad and the electrode of the pair of pads and the pair of electrodes, and the pad and the electrode are soldered to each other. Soldering mounting structure for the parts to be. 2. A substrate for a surface mount component, which has a pad connected to an electrode of a surface mount component to be mounted by soldering, wherein the electrode and the pad are visibly arranged on the substrate surface, and the pad is recognizable. A solder mounting board for components, wherein a member having poor wettability with respect to solder is provided in a part of the substrate, and the member having poor wettability is arranged between the electrode and the pad. 3. The substrate for surface-mounted components according to claim 1, wherein the color of the member having poor wettability is different from the colors of the pads and electrodes. . 4. The substrate for surface mount component according to claim 1, 2 or 3, wherein the member having poor wettability is a light emitting substance.