JP2011171473A - Printed wiring board - Google Patents

Abstract

A printed wiring board capable of reducing warpage while maintaining the rigidity of the printed wiring board is provided.
SOLUTION: An insulating base material 11, a first region 21 formed on the base material and formed with a conductor wiring portion 41 having a function as a printed wiring board product, and formed on the base material. In the printed wiring board 10 having the second region 22 formed with the conductor dummy portion 52 that does not function as the product, the conductor of the second region 22 with respect to the conductor remaining rate A of the first region 21 The ratio of the residual rate B ((B / A) × 100 (%)) is 105 to 300%.
[Selection] Figure 7

Description

  The present invention relates to a printed wiring board.

  In the printed circuit board composed of the circuit body part on which the wiring pattern that is the product part is formed and the discarded board part that is outside the product, the remaining copper ratio of the circuit body part and the remaining copper ratio of the discarded board part are made equal. Thus, a printed wiring board is known in which the expansion and contraction behavior of the printed wiring board due to changes in temperature and humidity is made the same throughout the board to reduce warping and twisting of the printed wiring board (Patent Document 1).

JP-A-8-51258

  However, in the above conventional printed wiring board, depending on the design specification of the wiring pattern, the remaining copper ratio of the circuit main body portion is decreased, and accordingly, the remaining copper ratio of the discarded plate portion may be decreased. Therefore, there is a problem that the balance between the rigidity of the entire substrate and the warpage resistance during reflow is poor.

  The problem to be solved by the present invention is to provide a printed wiring board capable of reducing warpage while maintaining the rigidity of the printed wiring board.

  The present invention includes an insulating base material, a first region formed on the base material and formed with a conductor wiring portion having a function as a product of a printed wiring board, and formed on the base material, In a printed wiring board having a second region in which a conductor dummy portion that does not function as a product is formed, the remaining ratio of the conductor remaining rate B in the second region to the conductor remaining rate A in the first region ((B / A) × 100 (%)) is 105 to 300% to solve the above problem. Here, the conductor remaining ratio A in the first region refers to the area ratio of the wiring portion in the total area of the first region on the substrate, and the conductor remaining ratio B in the second region refers to the first region remaining on the substrate. The area ratio of the dummy portion in the total area of the two regions.

  In the above invention, the remaining ratio of the conductor remaining ratio B in the second region to the conductor remaining A in the first region is more preferably 120 to 300%, further preferably 150 to 300%, and further 200 It is more preferable to set it to -300%.

  In the above invention, the first region may be disposed so as to be surrounded by the second region.

  Further, in the above invention, the second region portion is configured such that a plurality of polygonal defect portions where no conductor exists have equal intervals between one side of one polygonal defect portion and the opposite side of another polygonal defect portion adjacent thereto. Can be arranged regularly.

  In the above invention, the conductor dummy portion can be configured as a continuous non-linear conductor pattern having a uniform width.

  According to the present invention, on the insulating substrate, the remaining ratio ((B / A) × 100 (%)) of the conductor remaining ratio B in the second region to the conductor remaining ratio A in the first region is 105 to 300%. Therefore, the performance balance between rigidity and warpage resistance is improved. As a result, it is possible to reduce warpage while maintaining the rigidity of the printed wiring board.

It is a principal part top view which shows the copper clad laminated board of the flexible wiring board which concerns on embodiment of invention. It is sectional drawing which follows the AA line of the copper clad laminated board of FIG. It is a top view which shows the copper clad laminated board after etching the copper clad laminated board of FIG. It is a top view which expands and shows a part of 1st area | region of the copper clad laminated board of FIG. It is a top view which expands and shows a part of 2nd area | region of the copper clad laminated board of FIG. FIG. 6 is an enlarged plan view showing a pattern example of a dummy part in FIG. 5. It is a graph which shows the characteristic of the flatness with respect to a residual ratio shown in Table 1. It is a graph which shows the characteristic of the change rate of the flatness with respect to a residual ratio shown in Table 1. It is a figure which shows the flexible wiring board which concerns on other embodiment of invention, Comprising: It is a top view which shows the positional relationship of each dummy part formed in a some copper foil layer.

<< First Embodiment >>
FIG. 1 is a plan view of an essential part of a flexible printed wiring board 10 (hereinafter also referred to as a single-sided copper-clad laminate 10) to which an embodiment of the present invention is applied, and FIG. 2 is taken along line AA in FIG. It is sectional drawing.
As shown in FIGS. 1 and 2, the copper clad laminate 10 of this example is formed on an insulating base 11 (corresponding to the “base” of the present invention) and the main surface of the insulating base 11, It is a sheet-like member provided with the copper foil 12 for forming the wiring part 41 and the dummy part 52 which are mentioned later.

The insulating base material 11 is composed of a polyimide film having good heat resistance and dielectric properties of the base material, a polyethylene terephthalate film, a polyethylene naphthalate film, a polyester film, or a film obtained by reinforcing these resin films with glass fibers. Can do.

Although the wiring part 41 of this example and the dummy part 52 mentioned later are formed with the copper foil 12, you may comprise from electrically conductive material foil other than copper foil, for example, aluminum foil.

The copper-clad laminate 10 of this example is formed by laminating the copper foil 12 only on one side of the insulating substrate 11, but may be a double-sided copper-clad laminate in which the copper foil is laminated on both sides of the insulating substrate 11. .

  The copper-clad laminate 10 is formed with a wiring portion that functions as a product by etching the copper foil 12. FIG. 3 shows the copper clad laminate 10 after etching the copper foil 12 of the copper clad laminate 10 shown in FIG. As shown in FIG. 3, the copper-clad laminate 10 of this example is a part that functions as a product, and includes a first region 21 in which a wiring part 41 on which an electronic component or the like is mounted, and a product. The second region 22 which does not perform the above function but becomes a part of the product (or is removed before becoming a finished product).

FIG. 4 is an enlarged view showing a part of the first region 21. In the first region 21 of this example, a pad (land) 411 for mounting an electronic component or a connector (not shown) is fitted. A fitting portion or the like is formed. The wiring part 41 is formed on the main surface of the insulating base material 11 and connected to, for example, the pad 411. In addition, the part in which the wiring part 41 and the pad 411 are not formed is in a state where the insulating base material 11 is exposed by etching the copper foil 12.

On the other hand, FIG. 5 is an enlarged view showing a part of the second region 22. The second region 22 does not function as a printed wiring board product, but surrounds the first portion 21 that is rectangular in plan view as shown in FIG. As a function of maintaining rigidity. For this reason, as will be described later, a dummy portion 52 that does not function as a product of a printed wiring board is formed in the second region 22.

The dummy part 52 of the second region 22 is a continuous non-linear copper foil pattern having a uniform width formed simultaneously with the etching process of the wiring part 41. In other words, copper made of the remaining portion of the honeycomb structure of the extraction pattern in which a plurality of regular hexagonal extraction patterns 12 (also referred to as defect portions 12) obtained by etching the copper foil 12 are regularly arranged in the main surface. It is a foil pattern. The regular hexagonal defect portions 51 are arranged at equal intervals in a predetermined direction (120 ° interval), and one regular hexagonal defect portion 51 and one side of the regular hexagonal defect portion 51 adjacent to the regular hexagonal defect portion 51 are arranged. The defect portion 51 is formed so that the distances between the opposite sides of the defect portion 51 are equal, and the insulating base material 11 is exposed in the regular hexagonal defect portion 51.

  The wiring part 41 shown in FIG. 4 and the dummy part 52 shown in FIG. 5 are formed by the following method. First, an etching resist layer is formed on the surface of the copper foil 12 of the copper clad laminate 10 of FIG. 1, and the pattern of the wiring part 41 and the dummy part 52 is exposed and developed. Thereafter, the copper foil 12 exposed on the surface is etched with cupric chloride. Next, the copper-clad laminate 10 shown in FIGS. 3 to 5 is formed by removing the etching resist. In addition, the formation method of the wiring part 41 and the dummy part 52 is not limited to an etching process, For example, the method of printing a conductive paste may be used.

  And the coverlay film which is not shown in figure is laminated | stacked on the main surface of the copper clad laminated board 10 shown in FIG. 3, and the flexible wiring board of this example is formed.

  By the way, since the flexible printed wiring board 10, especially the 1st area | region 21 which show | plays the function as a product is a part in which an electronic component etc. are mounted, it is calculated | required to have the outstanding flatness without a curvature and a twist. However, in the step of reflowing solder by mounting electronic components or the like on the printed wiring board 10, the printed wiring board 10 swells due to gas generated during reflow, or the base material 11 and the copper foil 12 due to heat during reflow There is a possibility that the flatness is lowered due to the difference in the shrinkage rate. On the other hand, in order to improve handling workability in the manufacturing process, the printed wiring board 10 is required to have a certain degree of rigidity. The flatness is defined as the difference between the maximum value and the minimum value of the height of the wiring portion 41 including the pad 411 in the plane of the printed wiring board 10. The smaller the flatness, the more the printed wiring board 10 is warped or twisted. Means small.

Therefore, in this example, in order to suppress the flatness of the printed wiring board 10 within an allowable range while maintaining the rigidity of the printed wiring board 10,
The ratio of the conductor remaining rate B of the second region 22 to the conductor remaining rate A of the first region 21 is defined as follows. By doing so, it is possible to provide the printed wiring board 10 excellent in handling workability by ensuring the rigidity of the printed wiring board 10 while suppressing the decrease in flatness due to the swelling of the printed wiring board 10 after reflow. it can.

  The conductor remaining rate A of the first region 21 indicates the ratio of the area where the copper foil as the conductor remains to the total area of the first region 21 on the main surface of the copper clad laminate 10, from FIG. The conductor remaining rate A of the copper clad laminate 10 shown in FIG. 5 is the ratio of the area of the wiring portion 41 to the total area of the first region 21. The conductor remaining rate B of the second region 22 is the ratio of the area where the copper foil as the conductor remains to the total area of the second region 22 on the main surface of the copper clad laminate 10. The conductor remaining rate B of the copper foil laminate 10 shown in FIG. 3 to FIG. 5 is the ratio of the area of the dummy portion 52 to the area of the second region 22.

  The shape (pattern) of the wiring portion 41 is almost determined by the design specifications of the printed wiring board 10. Therefore, it is not realistic to change the shape of the wiring part 41 and adjust the conductor remaining rate A in the first region 21. Therefore, in this example, the flatness of the flexible printed wiring board 10 falls within a predetermined range by adjusting the conductor remaining rate B in the second region 22 without changing the shape of the wiring portion 41 determined by the design specifications. Adjust to.

  The conductor remaining rate B of the second region 22 can be adjusted by adjusting the area of the regular hexagonal defect 51 where the insulating base material 11 is exposed, for example, as shown in FIG. In other words, the conductor remaining rate B of the second region 22 can be adjusted by adjusting the line width of the dummy portion 52. FIG. 6 is an enlarged view of a main part showing three aspects in which the area of the missing part 51 (the line width of the dummy part 52) is different, and the conductor remaining rate B in FIGS. 6 (a) to 6 (c). 6 (a) shows the mode with the smallest conductor remaining rate B, FIG. 6 (c) shows the mode with the largest conductor remaining rate B, and FIG.

In addition to adjusting the area of the defective portion 51 (line width of the dummy portion 52) while keeping the central arrangement (layout pattern) of each defective portion 51 constant, for example, the arrangement density of the defective portions 51 of the same area ( The conductor remaining rate B may be adjusted by adjusting the density), in other words, by adjusting the layout pattern at the center of each of the defective portions 51.

  In particular, in the printed wiring board 10 of this example, the remaining ratio (B / A × 100 (%)) of the conductor remaining ratio B of the second region 22 to the conductor remaining ratio A of the first region 21 is preferably 105 to 300%. Is 120 to 300%, more preferably 150 to 300%, and even more preferably 200 to 300%, so that the flatness can be enhanced without impairing the rigidity of the printed wiring board 10 itself. As a result, the rigidity of the printed wiring board can be maintained without providing another reinforcing board on the back surface of the printed wiring board 10, thereby preventing warping and twisting due to the reinforcing board even when heat such as reflow is applied. Can do.

  Further, in the printed wiring board 10 of the present example, the second region 22 is formed around the first region 21, and the dummy portion 52 made of the continuous non-linear copper foil pattern shown in FIG. 5 is formed in the second region 22. Therefore, the second region 22 having high rigidity becomes an outer frame and surrounds the first region 21. As a result, the rigidity of the entire printed wiring board 10 can be increased, and handling workability in the manufacturing process and the like is improved.

  Further, compared to a discontinuous (discrete) regular hexagonal dummy pattern as shown in Patent Document 1, the dummy portion 52 made of the continuous copper foil 12 as in this example is more reflowable. Since the stress that leads to warping and twisting of the printed wiring board 10 caused by heat can be evenly distributed in the surface direction, the flatness of the printed wiring board 10 can be suppressed. Furthermore, in this example, as shown in FIG. 5 or FIG. 6, since the line width of the dummy portion 52 (distance between the regular hexagonal missing portions 51) is set equal, the thermal stress acting on the printed wiring board 10. Can be made uniform.

  Further, in the manufacturing process of the printed wiring board 10, the second region 22 serves as a guide for alignment. Since the relatively rigid dummy portion 52 is provided in the second region 22, a reinforcing plate or the like is provided. There is no need to use a separate member for maintaining rigidity.

In addition, in this example, although the shape of the defect | deletion part 51 of the 2nd area | region 22 was made into the regular hexagon, square, a rhombus, and other polygons may be sufficient.
<< Second Embodiment >>
The printed wiring board 10 according to the first embodiment described above is a printed wiring board 10 having a single layer structure including one base material 11 and one copper foil 12, whereas the printed wiring board 10 of this example is This is a printed wiring board 10 having a multilayer structure composed of a plurality of base materials 11 and a plurality of copper foils 12 provided on each base material 11. The present invention can also be applied to the printed wiring board 10 having such a multilayer structure. Hereinafter, a detailed description of the configuration common to the printed wiring board 10 having the single-layer structure described above will be omitted, and a main difference configuration will be described.

FIG. 9 is a plan view for explaining the relative positions of the dummy portions 81, 82, 83 formed on the copper foils 12 in the multilayered flexible printed wiring board 10 of this example. Each dummy portion 81, 82, 83 has a predetermined line width as in the dummy portion 52 shown in FIG. 5, but is shown by a line for convenience in FIG.

The flexible printed wiring board 10 of this example is manufactured in a multilayer structure by bonding a plurality of copper-clad laminates with a thermosetting adhesive or the like. At this time, the dummy portions 81, 82, 83 of the copper foil formed on the main surface of each laminated copper-clad laminate are arranged with a certain period (pitch) shifted in the X-axis direction. That is, as shown in FIG. 9, for example, in the case of a printed wiring board 10 having a four-layer structure, the second-layer dummy portion 82 is shifted by 1/3 period with respect to the position of the first-layer dummy portion 81. The third-layer dummy portion 83 is shifted by 2/3 period. The first-layer dummy portion 81 and the fourth-layer dummy portion (not shown) are at the same position in the X direction. As described above, the positions of the dummy portions 81, 82, and 83 may be adjusted so as to shift the position of the etching mask when the copper foil 12 of each layer is etched, for example.

  The flexible printed wiring board 10 having a multilayer structure of this example is configured so that the dummy portions 81, 82, 83 of the copper foil 12 formed on the main surface of each layer are periodically shifted to overlap each other. The portions 81, 82, and 83 and portions other than the dummy portions (corresponding to the missing portions shown in FIG. 5) overlap, and the step that is likely to occur in the printed wiring board 10 can be suppressed. If the positions of the dummy portions 81, 82, 83 of the copper foil 12 are not shifted in the multilayer printed wiring board 10, the surface of the printed wiring board 10 as a whole may be wavy. In this example, the occurrence of such a step is suppressed. be able to.

  Furthermore, the interlayer adhesive that bonds the copper clad laminate of each layer may swell due to the heat of the reflow process, but in this example, the step between the dummy part and the missing part on the main surface of the copper clad laminate of each layer Thus, the swelling of the interlayer adhesive can be absorbed.

  The number of layers in the multilayer structure is not limited to three, and may be a two-layer structure or a structure of four or more layers. In this example, the period for shifting the positions of the dummy portions 81, 82, and 83 is set to 1/3 period. However, it is not always necessary to set 1/3 of the period, and preferably from 1/4 to 1/2 of the period. If it is.

Examples that further embody the present invention will be described below.
<< Sample preparation >>
A copper-clad laminate in which a 12 μm-thick copper foil is bonded to one side of a 20 μm-thick polyimide film is prepared, and the printed wiring board 10 having a different conductor residual ratio B in each second region is prepared by the etching method described above. Produced. These printed wiring boards 10 having different conductor residual ratios B in the second region were passed through a solder reflow process of 260 ° C. × 1 minute, and the flatness of the obtained printed wiring boards 10 was measured. By patterning the same wiring portion in the first region, the conductor residual ratio A is made equal, and the residual ratio of the conductor residual ratio B to the conductor residual ratio A ((B / A) × 100 (%)) is 105%, Samples with 120%, 150%, 200%, and 300% were designated as Examples 1 to 5, respectively, and samples with remaining ratios of 60%, 80%, and 100% were designated as Comparative Examples 1 to 3, respectively. These evaluation results are shown in Table 1. A graph corresponding to Table 1 is shown in FIG. Moreover, the change rate of the flatness with respect to a residual ratio was computed using the evaluation result of the flatness shown in Table 1. The rate of change was calculated by Δ flatness / Δ remaining ratio. FIG. 8 is a graph showing characteristics of the change rate of flatness with respect to the remaining ratio. In addition, the value attached | subjected to the plot point in FIG. 8 is an intermediate value of the binary of the residual ratio used when calculating a change rate.

<Discussion>
As shown in Table 1 and FIG. 7, in the printed wiring boards of Examples 1 to 5, the flatness is 50 μm or less, and the warping and twisting of the printed wiring board after reflow are suppressed compared to Comparative Examples 1 to 3. It was confirmed that In particular, in the printed wiring boards of Examples 3 to 5, the flatness is 30 μm or less, and warping and twisting of the printed wiring board after reflow are further suppressed.

In addition, when the change rate of the flatness with respect to the remaining rate shown in FIG. 8 is seen, the absolute value of the change rate of the flatness becomes the largest when the remaining rate is 102.5%, but changes when the remaining rate becomes 105% or more. The rate approaches zero and the flatness can be kept small. Accordingly, it is understood that when the remaining ratio is changed in the range of 60 to 300%, the flatness gradually approaches 25 μm with the remaining ratio of 105% as a base point.

From the above results, by setting the remaining ratio of the conductor remaining ratio B to the conductor remaining ratio A to 105 to 300%, warping and twisting of the printed wiring board 10 after reflow can be prevented, and the flatness can be improved. confirmed.

  The handling workability by the rigidity of the printed wiring board 10 is not particularly different as long as the remaining ratio of the conductor remaining ratio B to the conductor remaining ratio A is set to 60 to 300%. Further, in the printed wiring board 10 of this example, the upper limit value of the remaining ratio is defined as 300%. If the remaining ratio exceeds 300%, the area occupied by the copper foil 12 in the second region 22 becomes large, so that gas generated from the insulating base material 11 and the adhesive layer during reflow is generated between the base material 11 and the copper foil 12. It is confined to the surface and is difficult to discharge to the outside, and as a result, warpage may occur. Thereby, the gas generated at the time of reflow can be efficiently discharged, and as a result, warpage of the printed wiring board 10 can be suppressed.

DESCRIPTION OF SYMBOLS 10 ... Copper clad laminated board 11 ... Insulating base material 12 ... Copper foil 21 ... 1st area | region 22 ... 2nd area | region 41 ... Wiring part 411 ... Pad 51 ... Defect part 52, 81, 82, 83 ... Dummy part

Claims (4)

An insulating substrate;
A first region formed on the base material and formed with a conductor wiring portion that functions as a printed wiring board product;
In a printed wiring board having a second region formed on the base material and formed with a conductor dummy portion that does not function as the product,
The printed wiring board, wherein a remaining ratio ((B / A) × 100 (%)) of the conductor remaining ratio B in the second region with respect to the conductor remaining ratio A in the first region is 105 to 300%. .   The printed wiring board according to claim 1, wherein the first region is surrounded by the second region. The second region is
A plurality of polygonal missing portions without conductors are regularly arranged so that the distance between one side of one polygonal missing portion and the opposite side of another adjacent polygon missing portion is equal. The printed wiring board according to claim 1 or 2.   The printed wiring board according to claim 1, wherein the conductor dummy portion is a continuous non-linear conductor pattern having a uniform width.

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