JP2013207204A - Wiring mother board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wiring mother board capable of reducing a difference between a thickness of a plated layer on an electrode pattern and a thickness of a plated metal layer deposited on a dummy pattern.SOLUTION: A wiring mother board of a first embodiment comprises: a mother board 1 having a wiring board region 11 and a peripheral region 12 surrounding the wiring board region 11; an electrode pattern 2 provided on a lower surface of the mother board 1 and disposed in the wiring board region 11; a dummy pattern 3 provided in a lower surface of the mother board 1 and disposed in the peripheral region 12; and wiring 6 for plating provided in the mother board 1, disposed in the peripheral region 12, electrically connected to the electrode pattern 2 by first connection wiring 4, and electrically connected to the dummy pattern 3 by second connection wiring 5. The second connection wiring 5 is provided so as to have the same electric resistance value as the first connection wiring 4.

Description

  The present invention relates to a wiring mother board having a mother board including a wiring board region and a surrounding region.

  A wiring mother board such as a multi-cavity wiring board has a mother board including a wiring board region and a peripheral region surrounding the wiring substrate region. An electrode pattern is provided in the wiring substrate region, and a dummy pattern for reducing deformation caused by a difference in contraction in the mother substrate is provided in the peripheral region. (For example, see Patent Document 1). Such electrode patterns and dummy patterns are electrically connected to the plating wiring, and a plating layer is deposited on the surface of the electrode pattern layer and the dummy pattern layer provided on the surface of the mother substrate by electrolytic plating. Has been. Further, for example, in order to resin-encapsulate the upper surface of the wiring mother board, the electrode mother board is placed on the base with the electrode pattern and the dummy pattern facing downward, and then the resin sealing is applied to the upper surface of the wiring mother board. There was a case where a die for stopping was placed.

JP 2002-033555

  However, since the thickness of the plating layer provided on the electrode pattern layer and the thickness of the plating layer provided on the dummy pattern layer are different, the thickness of the wiring mother board may be different in the wiring board region and the surrounding region. It was. In such a case, the pressure when the mold for resin sealing is arranged on the upper surface of the wiring mother board distorts the mother board between the wiring board region and the surrounding region, and the electrode pattern and the dummy pattern There was a possibility that a crack would occur in the mother board between the two.

  For example, when a plating layer thicker than the electrode pattern layer is deposited on the dummy pattern layer, the wiring board region of the wiring mother board bends downward when a mold is placed on the wiring mother board. Cracks occurred at the boundary between the wiring board region and the surrounding region.

  A wiring mother board according to one aspect of the present invention includes a mother board having a wiring board region and a surrounding area surrounding the wiring board area, an electrode pattern arranged in the wiring board area, a dummy pattern arranged in the surrounding area, Plating wiring is provided on the mother board and electrically connected to the electrode pattern and the dummy pattern. The electrode pattern and the dummy pattern are provided on the lower surface of the mother board. The plating wiring is disposed in the peripheral region, and is electrically connected to the electrode pattern by the first connection wiring and is electrically connected to the dummy pattern by the second connection wiring. The second connection wiring has an electric resistance value similar to that of the first connection wiring.

In the wiring mother board according to one aspect of the present invention, the first connection wiring and the second connection wiring have the same electric resistance value, and therefore, in the current paths from the plating wiring to the electrode pattern and the dummy pattern, respectively. Since the difference in electrical resistance value can be reduced, the difference in the thickness of the plated metal layer deposited on the electrode pattern and the dummy pattern can be reduced when depositing the plated metal layer by the electrolytic plating method. The difference in height between the electrode pattern and the dummy pattern can be reduced, and cracks generated in the wiring motherboard can be reduced.

(A) is a bottom view which shows an example of the wiring motherboard in the 1st Embodiment of this invention, (b) is a top view which shows the inside of (a). (A) is sectional drawing in the AA line of Fig.1 (a), (b) is sectional drawing in the BB line of Fig.1 (a). It is a bottom view which shows an example of the wiring mother board in the 2nd Embodiment of this invention. (A) And (b) is an example of the top view which shows the inside of FIG. (A) is sectional drawing in the AA line of Fig.3 (a), (b) is sectional drawing in the BB line of Fig.3 (a). (A) is a bottom view which shows the other example of the wiring motherboard in the 2nd Embodiment of this invention. (A) And (b) is an example of the top view which shows the inside of FIG. 6A is a cross-sectional view taken along the line AA in FIG. 6A, FIG. 6B is a cross-sectional view taken along the line BB in FIG. 6A, and a cross-sectional view taken along the line CC in FIG. FIG.

  Several exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
The wiring mother board according to the first embodiment of the present invention includes a wiring board area 11 and a mother board 1 having a peripheral area 12 surrounding the wiring board area 11 and wiring as in the example shown in FIGS. A plurality of electrode patterns 2 disposed in the substrate region 11, a dummy pattern 3 disposed in the surrounding region 12, and a plating wiring 6 disposed in the surrounding region 12 are provided. Each of the plating wiring 6 and the plurality of electrode patterns 2 is electrically connected by the first connection wiring 4, and the plating wiring 6 and the dummy pattern 3 are electrically connected by the second connection wiring 5. ing.

  The mother board 1 has a plurality of wiring board regions 11 arranged vertically and horizontally in plan view. The mother board 1 has a structure in which a plurality of insulating layers are stacked. The surrounding area 12 surrounds the entire plurality of wiring board areas 11. The wiring board area 11 is an area used as a package on which an electronic component is mounted and sealed and mounted on an external circuit board, for example. The peripheral area 12 is an area used when the wiring mother board is manufactured or transported, and the peripheral area 12 is used for positioning, fixing, etc. during processing or transport of the generated shape or the wiring mother board to be the mother board 1. be able to. The plurality of wiring board regions 11 may be arranged in at least one of the vertical and horizontal directions.

  The material of the mother board 1 is an insulator such as ceramics or resin. When the material of the mother substrate 1 is ceramic, for example, an aluminum oxide sintered body (alumina ceramic), an aluminum nitride sintered body, a mullite sintered body, a glass ceramic sintered body, or the like may be used. it can. Further, when the material of the mother board 1 is a resin, as the material, for example, an epoxy resin, a polyimide resin, an acrylic resin, a phenol resin, a polyester resin, a fluororesin such as a tetrafluoroethylene resin, a glass epoxy resin, or the like Can be used.

When the material of the mother substrate 1 is an aluminum oxide sintered body, organic materials suitable for raw material powders such as alumina (Al ₂ O ₃ ), silica (SiO ₂ ), calcia (CaO), and magnesia (MgO) are used. A ceramic green sheet is obtained by adding a solvent and a solvent to form a slurry, and forming this into a sheet by employing a conventionally known doctor blade method or calendar roll method. The mother substrate 1 is manufactured by performing an appropriate punching process on the sheet, stacking a plurality of sheets as necessary, and firing the sheet at a high temperature (about 1500 to 1800 ° C.).

  When the material of the mother board 1 is a resin, the mother board 1 is manufactured by a transfer molding method, an injection molding method, or the like using a mold that can be molded into a predetermined wiring board shape, for example. Further, for example, when the mother board 1 is a glass epoxy resin, a base material made of glass fiber is impregnated with an epoxy resin precursor, and the epoxy resin precursor is thermally cured at a predetermined temperature to thereby form the mother board 1. Is produced.

  The plurality of electrode patterns 2 are provided in each of the plurality of wiring board regions 11 on the lower surface 1b as in the example shown in FIGS. Such a plurality of electrode patterns 2 become connection electrodes or external terminal electrodes when the wiring board region 11 of the wiring mother board is used as a package. The plurality of electrode patterns 2 are electrically connected to the plating wiring 6 through the first connection wiring 4 provided on the mother board 1. The plurality of electrode patterns 2 are connected in parallel to each other.

The dummy pattern 3 is provided in a frame shape on the lower surface 1 b of the peripheral region 12 of the mother substrate 1. Such a dummy pattern 3 is formed, for example, when a plurality of electrode patterns 2 are arranged on a base with a downward direction and then a mold for resin sealing is arranged on the upper surface of the wiring mother board. This is for buffering the pressure applied to the peripheral region 12 of the substrate 1. The dummy pattern 3 is electrically connected to the plating wiring 6 through the second connection wiring 5 provided on the mother board 1.

  As in the example shown in FIG. 1B, the plating wiring 6 is provided inside the mother board 1 in the peripheral region 12, and has a frame shape. Such plating wiring 6 is provided on the upper surface 1a of the mother substrate 1 or inside thereof. When the plating wiring 6 is provided inside the mother substrate 1, it is not necessary to deposit a plating metal layer on the surface of the plating wiring 6, so that the portion where the plating metal layer is provided is reduced. The plating wiring 6 is for electrically connecting a plating power source to the plurality of electrode patterns 2 and the dummy pattern 3.

  The plating wiring 6 is connected to the first connection wiring 4 and the second connection wiring 5 in plan view. The plating wiring 6 is exposed at the inner surface of a notch or a hole provided at the end of the mother board 1.

  If the material of the mother substrate 1 is ceramic, the plurality of electrode patterns 2, dummy patterns 3, and plating wirings 6 are tungsten (W), molybdenum (Mo), manganese (Mn), silver (Ag), It consists of a metal powder metallization such as copper (Cu), and a plurality of electrode patterns 2 and dummy patterns 3 and a conductor paste for plating wiring 6 are printed in a predetermined shape on a ceramic green sheet for the mother substrate 1 by a screen printing method or the like. Then, by firing simultaneously with the ceramic green sheet for the mother substrate 1, it is formed at a predetermined position on the mother substrate 1. The conductor paste is prepared by adding an organic binder and an organic solvent to the main component metal powder and, if necessary, a dispersant and the like, and mixing and kneading them by a kneading means such as a ball mill, a three-roll mill or a planetary mixer. Further, glass or ceramic powder may be added to match the sintering behavior of the ceramic green sheet or to increase the bonding strength with the mother substrate 1 after firing.

The exposed surfaces of the plurality of electrode patterns 2 and dummy patterns 3 are coated with a plating metal having excellent corrosion resistance such as nickel and gold. Such a plated metal layer can effectively suppress corrosion of the plurality of electrode patterns 2 and the dummy patterns 3. In addition, the plating metal layer firmly bonds the connection electrode and the electronic component, the connection electrode and the bonding wire, and the external terminal electrode and the wiring of the external electric circuit board. For example, a nickel-plated metal layer having a thickness of about 1 to 10 μm and a gold-plated metal layer having a thickness of about 0.1 to 3 μm are sequentially deposited on the exposed surfaces of the plurality of electrode patterns 2 and the dummy pattern 3 by an electrolytic plating method. Is done. Here, the difference in thickness between the plated metal layer on the surface of the plurality of electrode patterns 2 and the plated metal layer on the surface of the dummy pattern 3 is less than 5 μm. In particular, the thickness of the plating metal layer on the surface of the plurality of electrode patterns 2 and the plating metal layer on the surface of the dummy pattern 3 provided so as to be adjacent to the dummy pattern 3 across the boundary between the wiring board region 11 and the surrounding region 12. It is preferable that the difference is small.

  Note that the dummy pattern 3 is provided in the peripheral region 12 that is discarded when divided along the outer edge of the wiring board region 11. Therefore, if the plating metal layer deposited on the dummy pattern 3 is deposited to be thinner than the plating metal layer deposited on the plurality of electrode patterns 2 within the above range, the plating metal material The amount used can be reduced.

  In the example shown in FIGS. 1 and 2, the plurality of first connection wirings 4 are a plurality of electrode patterns 2 provided on the lower surface 1 b of the mother board 1 and plating wirings provided inside the mother board 1. 6 is electrically connected. As in the example shown in FIG. 1B, the first connection wiring 4 connects a plurality of electrode patterns 2 provided side by side in the vertical direction. In addition, a plurality of first connection wires 4 are provided in the horizontal direction. Such first connection wiring 4 is provided inside the mother board 1 and is used as a wiring conductor when the wiring board region 11 is used as a package. As the material of the first connection wiring 4, the same material as that of the electrode pattern 2, the dummy pattern 3 and the plating wiring 6 can be used.

  The first connection wiring 4 includes a conductor layer disposed between the insulating layers of the mother board 1 and a through conductor that penetrates the insulating layer and electrically connects the conductors positioned above and below the insulating layer. is there. The conductors electrically connected by the through conductors are the electrode pattern 2 and the plating wiring 6.

  When the material of the mother board 1 is ceramic, the conductor layer disposed between the insulating layers is obtained by printing and applying a conductor paste for the conductor layer to the ceramic green sheet for the mother board 1 by printing means such as a screen printing method. It is formed by firing together with a generated shape for the mother substrate 1. In addition, the through conductor is penetrated for the through conductor by a processing method such as punching by die or punching or laser processing on the ceramic green sheet for the mother substrate 1 prior to printing and applying the conductive paste for forming the conductor layer. A hole is formed, and a conductive paste for a through conductor is filled in the through hole by a printing means such as a screen printing method, and is fired together with a generated shape to be the mother substrate 1. As the conductive paste, the same paste as the electrode pattern 2, the dummy pattern 3, and the plating wiring 6 is used. The conductor paste for the through conductor is generally adjusted to have a higher viscosity than the conductor paste for the conductor layer depending on the kind or addition amount of the organic binder or organic solvent.

  In the example shown in FIGS. 1 and 2, the second connection wiring 5 electrically connects the dummy pattern 3 provided on the lower surface 1 b of the mother board 1 and the plating wiring 6 provided inside the mother board 1. Connected. The second connection wiring 5 is manufactured by the same method as the first connection wiring 4.

The second connection wiring 5 has the same electrical resistance value as that of the first connection wiring 4. The electrical resistance value of the first connection wiring 4 indicates the electrical resistance value of the first connection wiring 4 between the plating wiring 6 and each of the plurality of electrode patterns 2. As in the example shown in FIGS. 1 and 2, the length of the second connection wiring 5 is longer than the length of the first connection wiring 4 between the plating wiring 6 and each of the plurality of electrode patterns 2. In the case of being short, a material having a higher electric resistance value than the material of the first connection wiring 4 is used for the second connection wiring 5. As such a material having a high electric resistance value, for example, a material obtained by adding more glass or ceramic powder than the first connection wiring 4 to the same metal material as the first connection wiring 4 can be cited. For example, if the first connection wiring 4 and the second connection wiring 5 are made of a metal material containing tungsten and copper, the second connection wiring 5 contains tungsten more than the first connection wiring 4. By increasing the ratio, the electric resistance value of the second connection wiring 5 can be increased more than that of the first connection wiring 4.

  As described above, since the first connection wiring 4 and the second connection wiring 5 have the same electrical resistance value, the electrical resistance value between the plating wiring 6 and each of the plurality of electrode patterns 2, and plating The difference between the electrical wiring 6 and the dummy pattern 3 can be reduced. Therefore, the difference in thickness between the plated metal layer deposited on the plurality of electrode patterns 2 and the plated metal layer deposited on the dummy pattern 3 can be reduced using the electrolytic plating method. In addition, the electrical resistance value of the 1st connection wiring 4 and the 2nd connection wiring 5 should just be set in the range from which the difference of the thickness of the said plating metal layer is less than 5 micrometers.

  A wiring pattern 7 is provided on the mother board 1 so as to be exposed on the upper surface of the mother board 1. The wiring pattern 7 is for bonding electronic components such as semiconductor elements. The wiring pattern 7 is electrically connected to the first connection wiring 4.

  When the material of the mother board 1 is resin, the materials of the electrode pattern 2, the dummy pattern 3, the first connection wiring 4, the second connection wiring 5, and the plating wiring 6 are copper, gold, aluminum Metal materials such as nickel, chromium, molybdenum, titanium, and alloys thereof can be used. As the material of the second connection wiring 5, a metal material having an electric resistance higher than that of the first connection wiring 4 is used. The electrode pattern 2, the dummy pattern 3, the first connection wiring 4, and the plating wiring 6, for example, transfer a copper foil processed into a predetermined shape onto a resin sheet made of glass epoxy resin, and the copper foil is transferred. It is formed by laminating the laminated resin sheets and bonding them with an adhesive. In such a case, the second connection wiring 5 is formed by transferring a gold foil onto the resin sheet. Of the first connection wiring 4 and the second connection wiring 5, the through conductor that penetrates the resin sheet in the thickness direction is attached to the inner surface of the through hole formed in the resin sheet by printing or plating the conductor paste. It may be formed or filled with a through hole. Such a through conductor is formed, for example, by integrating a metal foil or a metal column by resin molding, or by depositing the metal substrate 1 on the mother substrate 1 using a sputtering method, a vapor deposition method or the like.

  The wiring mother board as described above is divided into a plurality of wiring boards by being divided along the outer edge of the wiring board region 11.

The wiring mother board can be divided by cutting along the boundary between the wiring board regions 11 or the boundary between the wiring board region 11 and the surrounding region 12 by a slicing method or the like. Also, the wiring mother board is the mother board 1
Divided grooves may be provided at the boundary between the wiring substrate regions 11 or at the boundary between the wiring substrate region 11 and the surrounding region 12. When the wiring mother board has a dividing groove, it can be bent and divided along the dividing groove. The dividing groove can be formed by pressing the cutter blade against the generated shape for the mother substrate 1, cutting it with a slicing device smaller than the thickness of the generated shape, or cutting it after the baking with a slicing device smaller than the thickness of the mother substrate 1.

  Electronic components are mounted on the wiring board obtained by dividing the wiring mother board as necessary. The mounted electronic component is, for example, a semiconductor element such as an IC chip or an LSI chip, a piezoelectric element such as a crystal vibrator or a piezoelectric vibrator, and various sensors.

The wiring mother board in this embodiment is arranged in the mother board 1 having the wiring board area 11 and the surrounding area 12 surrounding the wiring board area 11, the electrode pattern 2 arranged in the wiring board area 11, and the surrounding area 12. A dummy pattern 3 and an electrode pattern 2 provided on the mother board 1 and a plating wiring 6 electrically connected to the dummy pattern 3 are provided. The electrode pattern 2 and the dummy pattern 3 are provided on the lower surface of the mother board 1. The plating wiring 6 is disposed in the peripheral region 12, and is electrically connected to the electrode pattern 2 by the first connection wiring 4 and electrically connected to the dummy pattern 3 by the second connection wiring 5. ing. Since the second connection wiring 5 has the same electrical resistance value as that of the first connection wiring 4, the difference in electrical resistance value in the current path from the plating wiring 6 to each of the electrode pattern 2 and the dummy pattern 3 can be reduced. . Therefore, the difference in the thickness of the plated metal layer deposited on the electrode pattern 2 and the dummy pattern 3 by the electrolytic plating method can be reduced, so that the difference in height between the electrode pattern 2 and the dummy pattern 3 can be reduced and the wiring mother can be reduced. Cracks generated in the substrate can be reduced.

  In addition, since the second connection wiring 5 is made of a material having a higher electric resistance value than the material of the first connection wiring 4, the area of the region where the second connection wiring 5 is provided can be reduced. The area where the connection wiring 4 is arranged can be increased. Since the area where the first connection wiring 4 is arranged can be increased, the degree of freedom in routing the first connection wiring 4 can be increased, and the wiring width of the first connection wiring 4 can be increased. The difference in electrical resistance with the connecting conductor 5 can be reduced.

(Second Embodiment)
Next, a wiring mother board according to a second embodiment of the present invention will be described with reference to FIGS.

  The wiring mother board in the second embodiment differs from the wiring mother board in the first embodiment described above in that the second connection wiring 5 is the first as in the example shown in FIGS. This is a point longer than the connection wiring 4. For example, in the example shown in FIGS. 3 to 5, the second connection wiring 5 is provided so as to meander around the peripheral region 12. In the examples shown in FIGS. The region 12 is provided so as to surround the wiring board region 11.

  The material of the second connection wiring 5 can be manufactured using the same material as that of the first connection wiring 4. From this, when manufacturing the wiring motherboard in the present embodiment, the conductor paste for the second connection wiring 5 can be printed simultaneously with the conductor paste for the first connection wiring 4. Therefore, compared with the wiring mother board in the first embodiment, the wiring mother board of this embodiment can reduce the number of steps in manufacturing, which is effective in efficiently manufacturing the wiring mother board.

  Since the electrical resistance value of the second connection wiring 5 can be adjusted by changing the length of the second connection wiring 5, the difference in electrical resistance value between the second connection wiring 5 and the first connection wiring 4 can be adjusted. It is effective for further reduction.

  Further, when the same material is used for the first connection wiring 4 and the second connection wiring 5, compared to the case where different materials are used for the first connection wiring 4 and the second connection wiring 5. The difference in expansion or contraction between the wiring board region 11 and the surrounding region 12 when the wiring mother board is heated or cooled is small. Therefore, partial deformation occurring in the mother board 1 between the wiring board region 11 and the surrounding region 12 due to a difference in expansion or contraction between the wiring board region 11 and the surrounding region 12 can be reduced.

  When each of the second connection wiring 5 and the plating wiring 6 is arranged so as to overlap with the dummy pattern 3 when seen through, as in the examples shown in FIGS. Since the dummy pattern 3 on the center side of the substrate 2 overlaps with the second connection wiring 5 and the plating wiring 6 and is densely arranged in parallel, the dummy pattern 3 on the lower surface 1b of the mother board 1 is arranged. The step on the surface can be reduced.

When the second connection wiring 5 and the plating wiring 6 are arranged so as not to overlap each other when seen in a plan view, a thick portion is formed on the lower surface 1a of the wiring mother board, so that ceramic green sheets are laminated. It is possible to reduce the occurrence of poor stacking in the thin portion when the pressure is applied, and disconnection of the second connection wiring 5 in the thick portion when the ceramic green sheets are stacked and pressed.

  If the second connection wiring 5 is provided over the entire circumference so as to surround the wiring board region 11 as in the examples shown in FIGS. 6 to 8, the peripheral region 12 is reinforced by metal, The strength of the peripheral region 12 of the mother board 1 can be increased over the entire circumference. Further, when the mother substrate 1 is ceramic, it is possible to reduce local deformation of the surrounding region 12 when the mother substrate 1 is fired.

  3 to 8, the electrode pattern 2 may be extended to a groove provided along the outer edge of the wiring board region 11, and when divided into individual wiring boards. A rectangular wiring board having a so-called castellation conductor can be obtained. In this case, as in the example shown in FIGS. 6 to 8, the first connection wiring 4 may be connected to the electrode pattern 2 serving as a castellation conductor.

  Moreover, the dummy pattern 3 may have the slit 3a like the example shown by FIGS. For example, when such a slit 3 a is provided on an extension line of the outer edge of the wiring board region 11, it can be used as a reference when dividing the wiring board region 11.

  In addition, this invention is not limited to the example of said embodiment, A various change is possible if it is the range which does not deviate from the summary of this invention. For example, when the material of the mother board 1 is ceramics, the electrode pattern 2 and the dummy pattern 3 are printed on the surface of the fired mother board 1 after a conductor paste is printed in a predetermined shape by a screen printing method or the like. By doing so, it may be provided at a predetermined position of the mother board 1.

  A second dummy pattern may be formed on the upper surface 1 a of the peripheral region 12 of the mother substrate 1. In the case where the mother substrate 1 is ceramic, warpage during firing of the mother substrate 1 can be reduced by providing the dummy pattern 6 and the second dummy pattern on the lower surface and the upper surface of the peripheral region 12 of the mother substrate 1. .

  One wiring board region 11 may be arranged at the center of the mother board 1.

DESCRIPTION OF SYMBOLS 1 ... Mother board 1a ... 1st main surface 1b ... 2nd main surface
11 ... Wiring board area
12 ... Surrounding area 2 ... Electrode pattern 3 ... Dummy pattern 4 ... First connection wiring 5 ... Second connection wiring 6 ... Plating wiring 7 ... Wiring patterns

Claims (4)

A mother board having a wiring board area and a surrounding area surrounding the wiring board area;
An electrode pattern provided on the lower surface of the mother board and disposed in the wiring board region;
A dummy pattern provided on the lower surface of the mother substrate and disposed in the peripheral region, and provided on the mother substrate and disposed in the peripheral region, and the electrode pattern is formed by a first connection wiring. And a wiring for plating electrically connected to the dummy pattern by a second connection wiring, and
The wiring mother board, wherein the second connection wiring is provided so as to have an electric resistance value similar to that of the first connection wiring. The second connection wiring is
2. The wiring motherboard according to claim 1, wherein the wiring mother board is made of a material having an electric resistance higher than that of the material of the first connection wiring. The second connection wiring is
The wiring motherboard according to claim 1, wherein the wiring mother board is longer than the first connection wiring.   2. The wiring motherboard according to claim 1, wherein the plating metal layer provided on the surface of the electrode pattern and the plating metal layer provided on the surface of the dummy pattern have the same thickness.

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