JP3496308B2 - Soldering method and printed wiring board - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel soldering method and a printed wiring board for implementing the soldering method. More specifically, it is an object of the present invention to provide a soldering method and a printed wiring board that can effectively prevent a defective foot (electrode) of the electronic component from floating when mounting the electronic component on the surface of the printed wiring board. is there.

[0002]

2. Description of the Related Art In the surface mounting of a printed wiring board, solder is supplied onto a land connecting the leads of an electronic component, for example, by a printing method using a metal screen, and the leads of the electronic component are placed on the land. After mounting the electronic component in a shape, the solder is melted by heating in a reflow furnace, the land on the printed wiring board side and the lead on the electronic component side are joined, and then cooled to complete the soldering.

In such surface mounting, it is indispensable to contact the leads of the electronic component with the solder. If the leads do not make contact, the leads a are fixed to the printed wiring board c by the solder b as shown in FIG. Without floating,
There is a problem that the so-called foot floating defect that is not electrically connected is caused.

In particular, in recent years, the number of ICs is increasing because automatic mounting is performed by using a mounting machine.
In so-called multi-legged parts such as connectors and connectors, when mounting on a printed wiring board, the leads do not become solder when they are mounted on the printed wiring board because the heights of the mounting parts of the leads are not uniform. A foot floating defect that is not in contact is likely to occur, and it is an object to reduce this foot floating defect as much as possible.

[0005]

Therefore, in order to solve the above-described foot floating defect, the structure shown in FIG.
As shown by the broken line in FIG.
The height of the solder e is made higher than that of the conventional solder b. By doing this, the solder a cannot reach the solder a with the conventional amount of the solder b, and the lead a is defective in that the solder does not float.
As shown in FIG. 17, the foot floating defect is prevented.

However, although the method of simply increasing the amount of the solder e as described above brings about the above-described effects in the case of the floating lead a, FIG. 18 and FIG.
As shown in, when the lead f does not float, solder e
Of the lead f in the molten solder e
Solder sunk into and is pushed away by the lead f.
Causes a so-called bridging phenomenon in which it loses its place and mixes with the solders e, e, ... Of the adjacent lands d, d.

Therefore, it suffices not to cause a bridge. Therefore, simply thinking, the land is formed so as to overhang outside the component to secure an escape area for extra solder, and at the same time, for each lead. And it is sufficient to widen the space between the lands.

However, in the above-mentioned method, the interval between the components on the mounting board is widened and the useless area is increased.
Obviously, it was against the densification of mounting, and as a result, it could not be an effective means for eliminating the foot floating defect.

[0009]

Therefore, in order to solve the above-mentioned problems, the soldering method of the present invention solders to a lead mounting portion of a land for soldering a lead of an electronic component or a part in the vicinity thereof. It is a slit-shaped area that does not fuse with
Unfused portion is provided that, wide portion of the width of the land and slit
When the solder is melted, the height of the solder in the lead placement part becomes higher than that in the non-fusion part and its vicinity by dividing the solder into a part having a narrow width divided by a tongue-shaped region.
Of the electronic component leads
The lead of the electronic component is soldered so that a sufficient amount of molten solder flows into the slit-shaped region .

Further, the printed wiring board of the present invention has a land for soldering an electronic component, and a lead mounting portion for mounting and fixing the lead of the electronic component is formed on the land. Along with the lead mounting portion , a non-fusion portion, which is a slit-shaped region so as not to fuse with solder, is formed in the lead mounting portion or in the vicinity thereof to form a land with a wide width portion and a slit.
Divided into narrow width parts divided by
The extra solder that was pushed away by the leads of the electronic components
When the solder is melted, it flows into the slit-shaped region .

[0011]

Therefore, according to the soldering method and the printed wiring board of the present invention, the land is divided into a wide width portion and a slit shape.
To divide into areas with narrow width divided by areas
Allows the solder on the lead placement part to be melted when the solder melts.
Is higher than the non-fusion part and its vicinity, and the electronic part
Excessive melting half pushed away by the descent of the product lead
Let the rice fields flow into the slit-shaped area, and until now,
Since the molten solder reaches the leads of electronic components that did not come into contact with the solder on the land when they were mounted on the mounting board and the solder was soldered to the leads of the electronic components, soldering defects are effectively reduced. When the solder is melted and the height of the solder reaches within the reach, it does not cause the foot to float, so the standard of coplanarity (fluttering of leads of electronic parts, etc.) can be relaxed and the cost can be reduced. Will also contribute.

Further, the solder pushed away by the leads of the electronic parts is prevented from moving to the non-fusion portion and flowing out of the land, and further, in order to increase the height of the solder at the time of melting, the solder is added. I'm not increasing the dose,
It is possible to prevent the so-called bridge from being generated by being mixed with the solder of other neighboring lands.

Further, as described above, since the solder pushed away by the leads of the electronic component or the like moves to the non-fusion portion, the presence or absence of the foot floating defect can be detected by detecting the presence or absence of the solder in the non-fusion portion. Can be detected.

[0014]

The details of the soldering method and the printed wiring board of the present invention will be described below with reference to the illustrated embodiments.

Reference numeral 1 denotes a printed wiring board on which substantially rectangular lands 2, 2, ... For connecting leads of electronic parts are connected as a part of the printed wiring pattern 5 or independently. Is formed. The printed wiring board 1 is covered with a solder resist agent 6 except for the lands 2, 2, ....

Further, each land 2 has slit-shaped regions 2a and 2a covered by application of a solder resist agent 6.
a is formed.

In this embodiment, the slit-shaped regions 2a, 2a are formed by cutting the center of the substantially rectangular land 2 from the left and right sides in the longitudinal direction. The number, shape, and formation position are not limited to this, and various ones are conceivable as shown in each modified example described later.

Further, the slit-shaped regions 2a, 2a are not limited to those formed by applying the solder resist agent 6 on the land 2, but for example,
It is conceivable that the land 2 is formed by cutting out a part of the land 2.

The land 2, 2, ... Has a wide width portion 3 by forming slit-shaped areas 2a, 2a and a narrow width portion 4 divided by the slit-shaped areas 2a, 2a. The wide portion 3 serves as a lead mounting portion for mounting and fixing the leads of the electronic component, as will be described later.

.. are formed on the lands 2, 2, ... Using, for example, a metal screen (not shown) formed in conformity with the shapes of the lands 2, 2 ,. Printed.

Then, as shown in FIGS. 1 to 3, on the printed wiring board 1, a portion other than the portion covered with the solder resist agent 6, that is, a slit-shaped region 2 is formed.
Solders 7, 7, ... Are placed on each land 2 including a and 2a.

However, as described above, the solders 7, 7, ...
The leads 8, 8, ... Of electronic components (not shown) are mounted on the lands 2, 2 ,.

The electronic components are mounted on the leads 8, 8, ...
······················ has a predetermined pressure so as to be embedded in the solder 7, 7, ···, therefore, as shown in FIG. , 7, ...
・ ・ Expanded by being crushed.

By the way, of the leads 8, 8, ...
There are leads 8a that are in a floating state without reaching the positions of the solders 7, 7, .... This is a so-called floating state.

Then, the printed wiring board 1 on which the above-mentioned electronic parts are mounted is put in a reflow furnace and heated, and the solder 7,
Are melted, the lands 2, 2, ... Of the printed wiring board 1 and the leads 8, 8, ... Of the electronic component 8 are joined, and then cooled.

By the way, when the solder 7 on each land 2 is melted by heating in the reflow furnace, the slit-shaped region 2 coated with the solder resist agent 6 as described above.
Since the solder 7 on a and 2a is repelled by the solder resist agent 6, it moves to another portion of the land 2 and the lead mounting portion 3 having a wide width and a portion 4 having a narrow width. There is a difference in the degree of swelling due to the surface tension of the solder 7.

That is, as shown in FIGS. 5 and 6, the height of the solder 7 is lower in the portion 4 having a narrow lateral width of the land 2 and higher in the lead mounting portion 3 having a wider lateral width than in the state before melting.

Here, as described above, the principle of the phenomenon that the height of the solder 7 is low in the portion 4 where the width of the land 2 is narrow and is high in the lead mounting portion 3 where the width is wide is based on the experimental results of the inventor. Explain.

That is, in surface mounting, basically rectangular lands are used. When there is no lead on the land, when the solder melts, the center of the land is the highest in the cross-sectional shape, except in special cases where the amount of solder is too small, there is a foreign substance on the land, etc. Become.

Therefore, if it is possible to raise the maximum point of solder rise or shift the position of the maximum point by increasing the amount of the solder by making a special state on the land, it is possible to improve the conventional method. By increasing the amount of solder, it is possible to bring about the same effect as when trying to eliminate the foot floating defect without causing any adverse effects.Therefore, it is possible to change this by changing the land shape. This is the purpose of the method and the printed wiring board.

Next, the effect of an increase in the amount of solder on the shape after melting will be described step by step with reference to FIG.

When the supply amount of the solders 9, 9 onto the lands 10, 10 is increased, the solders 9, 9 are changed to the ones shown in FIGS.
The height of the solder gradually increases.

Then, as shown in FIG. 13C, when the contact angle θ exceeds 90 degrees (assuming that the cross section of the solder 9, 9 has a shape of a part of a circle, the solder 9, 9). (Where the height of the area exceeds half the width of the land), the state of the solders 9, 9 becomes unstable, and after passing through the state of FIG. 13 (d), finally as shown in FIG. 13 (e). , The lands 10, 10 are connected by the bridge of the solders 9, 9, and the contact angle θ
Is less than 90 degrees, and a stable state is achieved.

FIG. 14 shows the state shown in FIG. 13E, that is, the state in which the lands 10 and 10 are connected by the bridge of the solders 9 and 9 as seen from directly above.

In FIG. 14, the height relationship between the points A and B of the solders 9 and 9 is L1: L2 when the width of the lands 9 and 9 is L1 and the space between the lands 10 and 10 is L2. If it is 3: 1, A: B will be approximately 2: 1. The reason why A: B does not become 3: 1 is that the self-weight acts in addition to the surface tension of the solders 9, 9.

Actually, the actually measured values obtained by causing the bridge phenomenon of the solders 9 and 9 between the lands 10 and 10 are 227 μm, 207 μm and 2 at point A, respectively.
At 20 μm, at point B, 110 μm and 1 respectively
They were 00 μm and 110 μm. This measured value also supports the above-described relationship between the heights of the solders 9 and 9 at the points A and B.

Then, the adjacent land 1 shown in FIG.
The state in which 0 and 10 are connected by the bridge phenomenon of the solders 9 and 9, in other words, the heights of the solders 9 and 9 are partially different from each other is realized on one land. The land 2 has a slit-shaped region 2a. That is, points A and B in FIG. 14 are land 2 respectively.
Corresponding to the lead mounting portion 3 and the portion 4 having a narrow width, and similarly, the land 1 other than the portion connected by the bridge.
The portion between 0 and 10 corresponds to the slit-shaped region 2a.

Therefore, by adjusting the position of the slit-shaped region 2a, the highest point of the height of the solder 7 can be moved and adjusted in accordance with the contact position of the lead 8.

The above is the principle of the soldering method of the present invention.

Returning to the explanation of the embodiment, FIG.
As shown in FIG. 3, the solder 7 that rises higher reaches the leads 8a that are in the floating state, and the land 2 and the leads 8 are joined.

On the other hand, the lead 8 which is not in a floating state
In this case, as shown in FIGS. 8 to 10, the excess solder 7 pushed away by the leads 8 flows into the slit-shaped regions 2a, 2a where the solder 7 was not present when the solder 7 was melted, that is, the excess solder 7 was removed. Since the destination of the solder 7 is secured on the land 2, the excess solder 7 flows out of the land 2 and the solder 7, 7 of the adjacent lands 2, 2, ...
.. Does not mix with and cause a bridge.

As described above, in the soldering method and the printed wiring board of the present invention, the solder 7, which is melted without increasing the amount of the solder 7, 7, ... On the lands 2, 2 ,.
Since the heights of 7, ... Are increased, the leads 8, 8 of the electronic components mounted on the printed wiring board 1 are ...
Of ..., even leads 8a which has a floating feet state, as long as within the molten solder 7 arrives, be joined it to land 2, also the normal state even if the lead 8, the destination of the solder 7 that is displaced by the lead 8 is secured, it can be joined without any trouble in both.

By the way, even when the soldering method and the printed wiring board of the present invention as described above are used, the lead floating defect still occurs.

Therefore, it is necessary to detect the state of the leads of the electronic component and inspect whether or not the foot floating defect has occurred.

Therefore, in the conventional inspection for the foot floating defect, the lead floating defect is detected by detecting the change of the reflectance of the solder on the printed wiring board. In the printed wiring board, for example, as shown in FIGS. 11A and 11B, when the leads 8 are in a floating state, the melted solder 8 is pushed away and is not covered by this. since no slit-shaped region 2a will appear all parts.

However, when the foot floating defect does not occur, as shown in FIG. 12A, the slit-shaped region 2a is barely visible because it is covered with the solder 7 pushed away by the lead 8. .

Therefore, the slit-shaped region 2 is formed by an appropriate method.
By detecting the state of “a”, it is possible to easily detect the foot floating defect.

In addition to the above detection using the slit-shaped area 2a, the detection-dedicated slit-shaped area may be provided at a position visible from above without being hidden by the lead 8 on the land. .

FIGS. 15 (a) to 15 (j) show modifications 2A to 2J of the land 2 in the soldering method and the printed wiring board according to the present invention.

Since these modified examples are different only in the shape of the land and the formation locations and the number of slit-like regions in the land from the above-mentioned embodiments, the same reference numerals as those in the above-mentioned embodiments are used. Therefore, the description thereof will be omitted.

As described above, in order to make the height of the solder 7 at the time of melting of the portion of the electronic component 8 on which the leads 8 are mounted higher than that of the other portions, in principle, the width of the land is set to be smaller. Since it suffices to form a wide portion and a narrow portion, various shapes of the land and the slit-shaped region for realizing this can be considered.

[0052]

As is apparent from the above description, according to the soldering method of the present invention, the slits that do not fuse with the solder are formed in the lead mounting portion of the land for soldering the leads of the electronic component or in the vicinity thereof. The non-fusion area, which is a circular area, is provided, and the land is divided into a wide width portion and a slit area.
Thus the Rukoto divided into a narrow portion of the divided width, Ri of higher than the lead solder height at rest parts unfused portion and the vicinity thereof when the solder is melted, the electronic unit
Excessive melting half pushed away by the descent of the product lead
The field is characterized by flowing into the slit-shaped region .

Further, the printed wiring board of the present invention has a land for soldering an electronic component, and a lead mounting portion for mounting and fixing the lead of the electronic component is formed on the land. Along with the lead mounting portion , a non-fusion portion, which is a slit-shaped region so as not to fuse with solder, is formed in the lead mounting portion or in the vicinity thereof to form a land with a wide width portion and a slit.
Divided into narrow width parts divided by
The extra solder that was pushed away by the leads of the electronic components
It is characterized in that it is made to flow into the slit-like region when the solder is melted .

Therefore, according to the soldering method and the printed wiring board of the present invention, the land is divided into the wide width portion and the slit.
-Shaped area divided into narrow width parts
As a result, when the solder melts,
The height of the solder becomes higher than that of the non-fusion area and its vicinity,
Excessive melt that was pushed away by the descending lead of the child part
The molten solder is allowed to flow into the slit-shaped area, and until now, when the solder is mounted on the mounting board, the solder does not come into contact with the solder on the land, and the solder does not contact the solder on the land. Since it arrives and is soldered, it is possible to effectively reduce the foot floating defect, and the solder within the range where the solder whose height has increased reaches the melt does not become the foot floating defect, so coplanarity (electronic parts etc. The flapping (lead fluttering) standard can be relaxed, which also contributes to cost reduction.

Further, in order to prevent the solder pushed away by the leads of the electronic parts or the like from moving to the non-fusion portion and flowing out of the land, and further, increasing the height of the solder at the time of melting, the solder is applied. I'm not increasing the dose,
It is possible to prevent the so-called bridge from being generated by being mixed with the solder of other neighboring lands.

Further, as described above, since the solder pushed away by the leads of the electronic parts or the like moves to the non-fusion portion, it is possible to detect whether or not the foot floating defect has occurred by detecting the presence or absence of the solder in the non-fusion portion. Can be detected.

It should be noted that the specific shapes and structures shown in the above embodiments are merely examples of the implementation in carrying out the present invention, and the technical scope of the present invention is limited by these. Should not be interpreted as.

[Brief description of drawings]

1 shows an example of implementation of a soldering method and a printed wiring board according to the present invention together with FIGS. 2 to 10, and this drawing is a plan view of the printed wiring board.

FIG. 2 is a sectional view taken along line II-II in FIG.

3 is a sectional view taken along the line III-III in FIG.

FIG. 4 is a vertical sectional view including a state in which a lead of an electronic component is mounted.

FIG. 5 is a cross-sectional view showing a state when solder is melted.

6 is a sectional view taken along line VI-VI in FIG.

FIG. 7 is a vertical cross-sectional view showing a joined state of a lead in a floating state to a land.

FIG. 8 is a vertical cross-sectional view showing a bonded state of a lead in a normal state to a land.

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

FIG. 10 is a plan view showing a bonded state of a lead in a normal state to a land.

FIG. 11 is a view for explaining a method for detecting a foot floating defect together with FIG. 12, and this figure shows the leads in a foot floating defective state from different directions, (a) is a plan view, and (b) is a longitudinal section. It is a figure.

12A and 12B are diagrams showing a lead in a normal state from different directions, FIG. 12A is a plan view, and FIG. 12B is a longitudinal sectional view.

FIG. 13 is a schematic view showing the effect of the amount of solder on the land on the shape after melting in order from (a) to (e).

FIG. 14 is a plan view showing a state of FIG. 13 (e) viewed from above.

FIG. 15 is a schematic view showing a modified example of the land in the soldering method and the printed wiring board according to the present invention.

FIG. 16 is a longitudinal sectional view showing the problems in the conventional soldering method and the printed wiring board together with FIGS. 17 to 19;

FIG. 17 is a vertical cross-sectional view showing a joined state of the lead in a floating state to the land.

FIG. 18 is a vertical cross-sectional view showing a bonded state of a lead in a normal state to a land.

FIG. 19 is a vertical cross-sectional view showing a state where FIG. 18 is viewed from another direction.

[Explanation of symbols]

1 printed wiring board 2 land 2a slit-shaped region (non-fusion part) 3 wide width part ( lead mounting part ) 4 narrow width part (near lead mounting part) 6 solder resist agent 7 solder 8 lead 9 solder 10 land 2A land 2B land 2C land 2D land 2E land 2F land 2G land 2H land 2H land 2I land 2J land

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Claims (4)

(57) [Claims] We claim: 1. The unfused portion is provided with electronic components slit shaped region in a part of the lead mounting portion or near the lands for the lead soldering does not fuse with solder, orchid
Is divided into a wide area and a slit-shaped area.
The Rukoto divided into a narrow width portion which, Ri of higher than the lead solder height at rest parts unfused portion and the vicinity thereof when the solder is melted, under the electronic component leads
The excess molten solder that was pushed away by the falling
A soldering method characterized in that it is made to flow into a dovetail-shaped region . 2. A non-fusion portion different from the non-fusion portion is provided at the end of the land.
Form a fused part and detect the amount of solder on the other non-fused part
To detect defective foot floating of electronic components
Soldering method according to claim 1, characterized in that the the like. 3. A land for soldering an electronic component
Have and fix the leads of electronic parts on the land
And a lead mounting portion for forming
A pickpocket that is designed so that it does not fuse with the solder at or near the mounting part.
Width of the land
Width divided by the wide part of the
Divided into narrow parts and pushed back by the lead of electronic parts
The excess solder that has been scraped off is the slit-shaped area when the solder melts.
Printed wiring characterized by flowing into the area
substrate. 4. The non-fusion portion is coated with a solder resist agent.
Serial to claim 3, characterized in that it is formed by Rukoto
The printed wiring board of the mounting.