JP4901332B2 - Flexible printed wiring board - Google Patents

Description

  The present invention relates to a flexible printed wiring board, and in particular, a flexible printed wiring board that improves the cleaning performance of a flux after soldering while maintaining a shielding property by forming a ground pattern on a copper foil at a lower position of a component. It is about.

  In general, in the manufacturing process of a printed circuit board, oxides on the surface of a copper foil (conductor) are removed using a flux in order to improve the familiarity of solder when mounting components. However, if this flux flows into the gap between the lower surface of the component and the surface of the circuit board and remains as a residue, the influence of atmospheric humidity during use and migration due to the operating voltage occur, and the insulation resistance of the circuit board decreases. It will fall and the function of an electronic device will be impaired. Therefore, it is necessary to remove the flux by cleaning after mounting the components. In addition, with the recent increase in frequency of electronic devices, many circuit boards have improved shield characteristics by forming a ground pattern on the copper foil at the lower part of the component in order to reduce noise generated from the component.

  As a technique for improving the ease of cleaning the flux between the mounted component and the circuit board, for example, as in Patent Document 1, the soldering land is projected to increase the distance between the lower part of the component and the surface of the insulating layer of the printed board. An electronic device is known, but this configuration is not a practical method because it requires many steps for manufacturing a printed circuit board. In addition, when a ground pattern is formed on the surface of the circuit board located below the mounted component to obtain a shielding effect, a step is generated between the protruding part of the component mounting terminal part and the wiring pattern of the circuit board surface. The step may cause disconnection due to thermal shock.

  On the other hand, for example, as in Patent Document 2, a configuration in which a slit such as a groove or a hole is provided in a circuit board at a lower position of a mounted component is also known. Although providing the slit can improve the cleaning property, providing the slit on the circuit board complicates the manufacturing process and increases the manufacturing cost, which increases the manufacturing cost. Further, if a slit is formed in the insulating base material below the circuit component, a ground pattern cannot be formed at that portion, and the shielding effect cannot be improved. Even if the circuit conductor is formed by a metallization method or a plating method, a step is generated as in Patent Document 1, and the step induces disconnection due to thermal shock.

  On the other hand, there are some in which a ground pattern is formed on the lower surface of a component as in Patent Document 3, for example. As described above, when the ground pattern is provided on the lower surface of the component, the shield characteristic is improved and the generation of noise can be suppressed. However, the gap between the component and the circuit board is narrower than that without a ground pattern on the lower surface of the component, and the cleaning performance of the flux is deteriorated.

FIG. 8 shows a pattern of a flexible printed wiring board (hereinafter referred to as “FPC”) when the conventional shield characteristic is given top priority. In the FPC 1, a copper foil (conductor) 4 is provided on a base film 2 via an adhesive 3, and a cover film 5 is covered on the copper foil 4 via an adhesive 3. On the cover film 5, the component 6 is fixed to the land of the copper foil 4 with solder 7.

The copper foil 4 forms a wiring pattern and a land, and also leaves the copper foil 4 at a lower position of the component 6 to form a ground pattern to provide a shielding function. In order to improve the shielding effect, the component 6 should be as close to the copper foil 4 as possible. For this reason, the gap between the lower surface of the component 6 and the surface of the cover film 5 is at most 10 μm.
Japanese Utility Model Publication No. 62-204371 Japanese Utility Model Publication No. 3-62 JP 2002-141739 A

  Conventionally, a fluorocarbon solvent with high permeability (for example, CFC-113 or HCFC-225) has been used as a flux cleaning solution. Even if the gap between the lower part of the component and the circuit board is narrow, it should be several μm or more. As a result, the flux could be removed cleanly. However, the use of chlorofluorocarbon solvents has been restricted due to environmental improvement demands such as the Montreal Protocol and the Kyoto Protocol, and usable detergents have been limited. And since it has the least influence on the environment, the use of cleaning with pure water is increasing. Cleaning with pure water has poor permeability and solubility due to the surface tension of water, and a minimum clearance of 20-30 μm is required to clean and remove the flux remaining at the bottom of the part. It is said.

  As shown in FIG. 8A, the FPC 1 in FIG. 8 is sprayed with a cleaning liquid from above as indicated by an arrow while being conveyed in either of the left and right directions in an upright direction, and the flux is washed. Removed. However, since the gap between the lower surface of the part 6 and the surface of the cover film 5 is very narrow as 10 μm or less, when pure water is used as the cleaning liquid, the cleaning liquid is not in the gap between the part 6 and the cover film 5. As shown in FIG. 9, only the portion close to the outer periphery of the component 6 is cleaned, and the flux 8 remains in the vicinity of the central portion of the component 6 over a wide range.

  Therefore, an object of the present invention is to provide a flexible printed wiring board (FPC) in which the cleaning property of the flux with pure water is improved while maintaining the shielding property to be good.

The present invention has been proposed to achieve the above object, and the invention according to claim 1 is a flexible print in which a copper foil is provided on a base film and a cover film is covered on the copper foil. A wiring board, in which a part having a plurality of terminals is arranged on the upper part of the cover film, and a ground pattern is formed on the copper foil at the lower part of the part, and the flux is removed with a cleaning liquid after soldering the part. In flexible printed wiring board
A copper foil is partially removed by providing a cutout in the ground pattern,
And the said cover film is dented along the said notch part, and the groove-shaped recessed part is formed in the lower part of the said component,
Provided is a flexible printed wiring board characterized in that at least one end of the groove-like recess is protruded outward from the outer periphery of the component corresponding to the notch.

According to this configuration, the cover film is recessed along the notch , and a groove-like recess is formed in the lower part of the part, and at least one end of the groove-like recess is formed in the part corresponding to the notch. Because it protruded outward from the outer periphery,
The cover film bonded on the copper foil is recessed along the notch, and a groove-shaped recess is formed in the lower part of the component. Since one end of the groove-like recess projects outwardly of the part, if spraying cleaning liquid in this state, transmitted a cleaning liquid groove-like recess from the outside of the parts penetrate the bottom parts only the groove-like recess The cleaning liquid penetrates into the gap between the part and the cover film.

  According to a second aspect of the present invention, there is provided the flexible printed wiring board according to the first aspect, wherein the notch portion is provided to be branched in a plurality of different directions below the component.

According to this configuration, since the cutout portion branches in a plurality of different directions at the lower part of the component, the groove-shaped recess also branches in a plurality of different directions along the cutout portion. The cleaning liquid that has entered the groove-shaped recess from the outside of the component branches in a plurality of different directions at the lower part of the component, and the cleaning liquid penetrates not only into the groove-shaped recess but also into the gap between the component and the cover film .

  According to a third aspect of the invention, in the flexible print according to the first or second aspect, at least one end of the notch projecting outward from the outer periphery of the part is formed wider than the lower part of the part. Provide a wiring board.

According to this configuration, the cutout portion has one end protruding to the outside of the component wider than the lower portion of the component, in other words, the cutout portion extends from one end protruding to the outside of the component to the lower portion of the component. Narrow. Accordingly, the groove-shaped recess also has a width that is lower at the bottom of the component than the outside of the component along the notch, and the cleaning liquid that has entered the groove-shaped recess from the outside of the component As a result, the pressure increases, and the cleaning solution penetrates not only into the groove-shaped recesses but also into the gap between the part and the cover film .

In the flexible printed wiring board of the present invention, since the ground pattern is formed on the copper foil at the lower position of the component, the shield characteristics are improved and the generation of noise can be suppressed. Then, by providing a notch in the ground pattern, the cover film is recessed to form a groove-like recess at the lower part of the component, and the sprayed cleaning liquid easily enters the lower part of the component through the groove-like recess. be able to. Therefore, even when the gap between the part and the cover film is very narrow, the cleaning liquid penetrates all over the gap and can be cleaned cleanly without leaving any flux.

Hereinafter, the flexible printed wiring board according to the present invention will be described with reference to preferred embodiments. In order to achieve the object of providing a flexible printed wiring board with improved cleaning properties of flux with pure water while maintaining good shielding properties, the present invention provides an adhesive on a base film. A flexible printed wiring board in which a copper foil is provided and a cover film is covered on the copper foil with an adhesive, and a component having a plurality of terminals is disposed on the cover film. In a flexible printed wiring board that forms a ground pattern on the copper foil at the lower part of the substrate and removes the flux with a cleaning solution after soldering the component, the copper foil is partially removed by providing a cutout in the ground pattern. This is realized by projecting at least one end of the cutout portion outward from the outer periphery of the component.

  FIG. 1 shows an example of a pattern of a flexible printed wiring board (FPC) according to the present invention. The basic structure of the FPC 1 is the same as that shown in FIGS. Duplicate explanation shall be omitted.

  Similar to the FPC 1 of FIGS. 7 to 8, the copper foil 4 is left at the lower position of the component 6 to form a ground pattern in order to improve the shielding characteristics. In the present invention, the notch 11 is provided in the ground pattern to partially remove the thickness of the copper foil 4. At least one notch portion 11 is provided at a lower position of the component 6.

  In the illustrated example, a notch 11 is recessed in the center of the left and right parts 6 along the spray direction of the cleaning liquid. Then, at least one end of the cutout portion 11 on the side to which the cleaning liquid is sprayed protrudes outward from the outer periphery of the component 6 to provide a cutout projection portion 11a.

  Further, the cover film 5 bonded on the copper foil 4 is recessed along the notch 11, and a groove-like recess 12 is formed in the lower part of the component 6. This groove-like recess 12 also protrudes outward from the outer periphery of the component 6 corresponding to the notch 11, and in the same figure, a groove-like recess protrusion 12a is formed on the upper side of the component 6. In parts other than the groove-shaped recess, the lower surface of the component 6 and the surface of the cover film 5 are in close contact with each other.

  As shown in FIG. 1 (a), the FPC 1 formed in this way is placed in an upright direction and conveyed in either the left or right direction. Hereinafter, the cleaning liquid is simply sprayed. Unlike the conventional product, the FPC 1 of the present invention is provided with a notch 11 in the ground pattern, and a groove-like recess 12 is formed in the lower part of the component 6, so that the cleaning liquid is not grooved as in the cleaning process shown in FIG. It is possible to pass through the groove-like concave portion 12 from the protruding portion 12a of the concave portion and enter the lower central portion of the component 6 to wash away the flux 8 at the central portion of the component 6 that has been difficult to remove by conventional cleaning.

  The high-pressure cleaning liquid permeates not only into the groove-shaped recess 12 but also into the gap between the component 6 and the cover film 5, so that the flux 8 near the center of the component 6 is cleaned and removed cleanly. Further, in the central portion of the component 6 provided with the notch portion 11, the flux 8 is washed and removed in a wider range than both the left and right sides of the component 6, and the lower central portion of the component 6 is washed with a high-pressure cleaning liquid. It can be seen that the flux 8 is completely removed from the outer side toward the lower outer side, and the notch 11 improves the cleaning performance. Although illustration is omitted, the flux is completely removed from the gap between the lower surface of the component 6 and the cover film 5 at the end of cleaning.

  FIG. 3 shows a modified example of FIG. 1 and is different from the FPC 1 shown in FIG. 1 in that both ends of the notch portion 11 protrude from the outer periphery of the component 6 to the upper and lower outer sides, and two notch protrusion portions 11a. , 11a. For this reason, the groove-shaped recess 12 formed by the recess of the cover film 5 also protrudes from the outer periphery of the component 6 to the upper and lower sides, and the groove-shaped recess protrusions 12 a and 12 a are formed on both the upper and lower sides of the component 6. Yes.

  Therefore, the spraying direction of the cleaning liquid can be performed from any one of the two upper and lower directions in which the cutout portion 11 protrudes, and the degree of freedom of setting in the transport process and cleaning process of the FPC 1 can be improved.

  The notch portion 11 must be formed so as not to impair the shield characteristics of the ground pattern with respect to the component 6. When the component size in the illustrated example is 4 mm × 5 mm, the notch portion 11 is within about 20% of the area of the ground pattern. Set as follows. Further, the width of the cutout portion 11 may be 0.1 mm or more from the penetration of the cleaning liquid, and the width of the cutout portion 11 and the number of installations can be adjusted within a range that does not adversely affect the shield characteristics. it can.

  FIG. 4 shows another example of the FPC pattern according to the present invention, and redundant description of the same components as those in the first embodiment will be omitted.

  In this embodiment, a notch 11 is recessed in the center of the left and right of the part 6 along the spray direction of the cleaning liquid, and the upper and lower ends of the notch 11 are protruded from the outer periphery of the part 6 to the upper and lower sides. Two notched protrusions 11a and 11a are provided. Further, the notches 11B and 11B are branched from the substantially vertical center of the notch 11 in the left and right direction.

  Thus, the notch 11 in the vertical direction is formed by the recess of the cover film 5 because the notch 11B is branched in a plurality of different directions (left and right in the illustrated example) at the lower position of the component 6. The groove-like recess 12B is also formed to branch in the left and right direction along the notch 11B. That is, the component 6 and the cover are formed by a groove-shaped recess 12 having both upper and lower ends projecting from the outer periphery of the component 6 to the upper and lower outer sides, and a groove-shaped recess 12B branched from the substantially upper and lower central portions of the groove-shaped recess 12 Cross-shaped groove-like recesses 12 and 12 </ b> B are formed in the gaps of the film 5.

  Then, if the cleaning liquid is sprayed from either one of the two upper and lower directions from which the cutout portion 11 protrudes, the cleaning liquid is transferred from the protruding portion 12 a of the groove-shaped recess to the groove-shaped recess 12 to the lower central portion of the component 6. Further, the cleaning liquid branches into the left and right groove-like recesses 12B, and the cleaning liquid penetrates not only into the groove-like recesses 12 and 12B but also into the gaps between the component 6 and the cover film 5.

  Therefore, as in the cleaning process shown in FIG. 5, not only the center portion vertical region of the component 6 but also the periphery of the branched groove-shaped recess 12B, that is, the center portion left-right region of the component 6 is extremely wide. As a result, the flux 8 can be cleaned and removed cleanly. At the end of cleaning, the flux is completely removed from the gap between the lower surface of the component 6 and the cover film 5.

  FIG. 6 shows a modification of FIG. 4. The difference from the FPC 1 shown in FIG. 4 is that both ends of the notch portion 11B protrude from the outer periphery of the component 6 to the left and right sides, and a total of four notches are formed vertically and horizontally. Projecting portions 11a and 11b are provided. For this reason, both ends of both the groove-like recesses 12 and 12B formed by the recesses of the cover film 5 protrude from the outer periphery of the component 6 to the upper, lower, left and right sides, and the protrusions 12a of the groove-shaped recesses in the four directions of the component 6 in the upper, lower, left and right directions. , 12b are formed.

  Therefore, the spraying direction of the cleaning liquid can be performed from any one of a plurality of directions, that is, the four directions of the upper, lower, left, and right sides where the notch 11 protrudes. For example, even when the posture of the component 6 is inclined with respect to the transport direction and the notch 11 does not face the spray direction of the cleaning liquid, the cleaning liquid can enter from the ends of the plurality of notches 11, and the transport process of the FPC 1 and The degree of freedom of setting in the cleaning process can be further improved.

  FIG. 7 shows still another example of the FPC pattern according to the present invention, and redundant description of the same components as those in the first and second embodiments will be omitted.

  In this embodiment, a notch 11 is recessed in the center of the left and right of the part 6 along the spray direction of the cleaning liquid, and the upper and lower ends of the notch 11 are protruded from the outer periphery of the part 6 to the upper and lower sides. Two cutout protrusions 11c and 11c are provided. The protruding part 11 c on the outside of the part 6 is formed wider than the notch part 11 at the lower part of the part 6. That is, the notch 11 becomes narrower when it reaches the lower part of the part 6 from the protruding part 11 c that protrudes to the outside of the part 6.

  Accordingly, the groove-like recess 12 formed by the recess of the cover film 5 is also narrower at the lower part of the component 6 than the outer protrusion 12 c of the component 6 along the notch 11, and the groove-like recess from the outside of the component 6. Since the groove-like recess 12 becomes narrow at the lower part of the part, the cleaning liquid that has entered the pressure increases in pressure, and the cleaning liquid penetrates not only into the groove-like recess 12 but also between the part 6 and the cover film 5.

  It should be noted that the present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

Explanatory drawing which shows an example of the pattern of FPC which concerns on this invention. Explanatory drawing of the washing | cleaning process of FPC shown in FIG. Explanatory drawing which shows the modification of FIG. Explanatory drawing which shows another example of the pattern of FPC which concerns on this invention. Explanatory drawing of the washing | cleaning process of FPC shown in FIG. Explanatory drawing which shows the modification of FIG. Explanatory drawing which shows a further example of the pattern of FPC which concerns on this invention. Explanatory drawing which shows an example of the pattern of the conventional FPC. FIG. 9 is an explanatory diagram showing a cleaning result of the conventional FPC pattern shown in FIG. 8.

Explanation of symbols

1 Flexible Printed Circuit Board (FPC)
2 Base film 3 Adhesive 4 Copper foil 5 Cover film 6 Parts 7 Solder 8 Flux 11, 11B Notch 11a, 11b, 11c Protruding part 12, 12B Grooved concave part 12a, 12b, 12c Protruding part

Claims (3)

A flexible printed wiring board in which a copper foil is provided on a base film and a cover film is covered on the copper foil, wherein a component having a plurality of terminals is disposed on the cover film, and the component In the flexible printed wiring board that forms a ground pattern on the copper foil at the lower position of the solder and removes the flux with a cleaning solution after soldering the component,
A copper foil is partially removed by providing a cutout in the ground pattern,
And the said cover film is dented along the said notch part, and the groove-shaped recessed part is formed in the lower part of the said component,
A flexible printed wiring board, wherein at least one end of the groove-shaped recess is protruded outward from the outer periphery of the component corresponding to the notch.   The flexible printed wiring board according to claim 1, wherein the cutout portion is provided to be branched in a plurality of different directions at a lower portion of the component.   The flexible printed wiring board according to claim 1, wherein the cutout portion has at least one end protruding outward from the outer periphery of the component wider than the lower portion of the component.

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