JP5073395B2 - Manufacturing method of multilayer printed wiring board - Google Patents

Description

  The present invention relates to a method for manufacturing a build-up type multilayer printed wiring board, and more particularly to a method for manufacturing a multilayer flexible printed wiring board including a step via structure in an interlayer connection portion.

  In recent years, electronic devices have been increasingly reduced in size and functionality. As part of this, multilayer flexible printed wiring boards have been widely spread, mainly in small electronic devices such as mobile phones (Patent Document 1 (P3, FIG. 1)). It has a flexible cable unit that integrates a separate flexible printed circuit board and flexible flat cable that connect via multilayer connectors and rigid printed circuit boards that mount various electronic components. Is.

  In particular, mobile phones are strikingly downsized and highly functional, and as a result, components mounted on multilayer flexible printed wiring boards are also replaced with CSP (chip size packages), packaging with high functionality and high density, and increasing board size. There is a trend to add high functionality without doing so.

  It has also been proposed to combine stepped via holes that enable high-density interlayer connection without increasing the number of steps, so-called step via holes (see Patent Document 2 (P3, FIG. 1)).

  This is a technique that enables batch connection of multilayered layers, and as the inner layer is reached, the diameter of the metal mask for laser processing, the so-called conformal mask, is reduced in consideration of misalignment and the like. Then, a hole for conduction is formed by laser processing, and interlayer connection is obtained by plating or the like.

  However, there are some problems in forming this step via hole. As described above, it is necessary to form a large conformal mask on the outer layer side in consideration of positional misalignment, and depending on the positional accuracy of lamination or the like, high-density interlayer connection may not always be achieved.

FIG. 2 is a cross-sectional view of a multilayer printed wiring board having a cable portion including a step via structure in a conventional interlayer connection portion. As shown in FIG. 2, laser processing is performed by using a conformal mask 201 formed in advance for laser processing and a conformal mask 202 formed on the double-sided core substrate 110 of the inner layer, so that a core substrate 110 and a build-up substrate 120 are formed. Then, conductive holes 201A and 202A that will be plated later are formed on the laminated circuit substrate constituted by the adhesive 130 to be via holes.
Japanese Patent No. 3427011 Japanese Patent No. 2562373 JP 2001-177248 A

  In this case, as shown in FIG. 2, misalignment occurs at the time of stacking, so the centers of the conformal mask 201 and the conformal mask 202 are not aligned. Since a positional deviation of about 100 μm at the maximum occurs, it is difficult to perform stable laser processing of the hole 202A formed below the conduction hole 202.

Furthermore, various proposals including the technique shown in Patent Document 3 have been made, and a method for manufacturing a multilayer printed wiring board having a cable portion capable of high-density mounting at a lower cost and more stably is desired.

  The present invention has been made in consideration of the above-mentioned points, and when manufacturing a multilayer printed wiring board including a step via structure in an interlayer connection portion, the centers of the upper hole and the lower hole of the step via are located at substantially equal positions. It is an object of the present invention to provide a method for stably and inexpensively manufacturing an arranged multilayer printed wiring board.

To achieve the above object, the present invention provides:
An inner layer core substrate having at least one conductive layer is formed on an insulating base material made of a resin film, and an outer layer buildup layer composed of a laminate having a conductive layer on at least one surface is bonded to the inner layer core substrate. To form a laminated circuit substrate, to form an interlayer connector including a step via hole having a larger diameter toward the outer layer side on the laminated circuit substrate, and to form three or more layers of the outer layer buildup layer and the inner layer core substrate In the method of manufacturing a multilayer printed wiring board for forming a step via hole connecting the layers of the wiring layer,
Prepare the outer buildup layer having a conductive layer thickness of 5 to 10 μm,
At the formation position of the step via hole in the inner layer core substrate, a land having a thickness that is thicker than the conductive layer of the outer buildup layer and that is 14 μm or more and can sufficiently withstand the energy of the laser necessary for penetration ,
Open an opening having a diameter substantially equal to the pilot hole diameter of the step via hole in the land,
The step via hole is formed by piercing the laminated circuit substrate by irradiating a laser beam having a diameter equal to the upper hole diameter of the step via hole with the opening as a center and capable of removing the conductive layer. Manufacturing method of multilayer printed wiring board,
Is to provide.

  According to the present invention, the copper thickness of the receiving land of the step via hole that connects the three wiring layers is thicker than the copper thickness of the receiving land of the blind via hole that makes the interlayer connection between the outermost layer and the wiring layer just below it. Thus, when the step via hole is formed, a conformal mask can be formed only in the outermost layer, and a pilot hole for the step via hole can be suitably formed at the center by direct laser processing. Therefore, it is possible to reduce the plating thickness necessary for improving the yield and ensuring the reliability.

  As a result, according to the present invention, in the multilayer printed wiring board including the step via structure in the interlayer connection portion, which is difficult with the conventional manufacturing method, the center of each of the upper hole and the lower hole of the step via is substantially equal. Can be stably arranged. Thereby, since the upper hole of a step via can be made small, the multilayer printed wiring board which can form a higher density step via can be manufactured cheaply and stably.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1A to 1C.

  1A to 1C are cross-sectional process diagrams illustrating an embodiment of the present invention. In this step, first, as shown in FIG. 1A (1), copper foils 2 and 3 having a thickness of 7 μm are provided on both sides of a flexible insulating base material 1 such as polyimide (here, polyimide having a thickness of 25 μm). A so-called double-sided copper-clad laminate 4 is prepared. And the hole 5 for conduction | electrical_connection is formed in this double-sided copper clad laminated board 4 with NC drill etc. The copper foils 2 and 3 at this time are preferably a rolled copper foil or a special electrolytic copper foil having excellent flexibility.

  Thereafter, a conductive treatment is performed, and a partial plating resist layer 6 is formed on a wiring pattern such as a cable in order to selectively perform electrolytic plating on a portion located on the inner wall without plating.

  At this time, including the through-hole lands having dimensions taking into account exposure misalignment, substrate dimension variation, NC drill machining position misalignment, etc., the inner wall of the conduction hole 5 and the reception of the interlayer connection hole with the buildup layer Electrolytic plating is selectively performed on the portion located on the land. However, since the land to be penetrated by the laser after build-up is not subjected to electrolytic plating, the resist layer 6 for partial plating is also formed at a portion corresponding to this.

  Next, as shown in FIG. 1A (2), electrolytic plating of about 10 μm is performed on the conduction hole 5 and the portion 8 located in the receiving land to form interlayer conduction. Through holes 7 are formed through the steps so far. The plating is also thickened on the portion 8 located on the receiving land.

  Next, as shown in FIG. 1A (3), a resist layer for forming circuit patterns on both sides by a photofabrication technique is formed. After the circuit pattern 9 and the lands 10a and 10b are formed by the photofabrication method using the resist layer, the resist layer is peeled off.

  The center hole of the land 10a functions as a conformal mask for subsequent laser processing. Here, the conformal mask diameter was 100 μm. The double-sided core substrate 11 that becomes the core substrate of the multilayer printed wiring board is obtained through the steps so far. In the first embodiment, the present invention is applied to a through-hole type double-sided core substrate, but it can also be applied to a via-hole type double-sided core substrate.

  Furthermore, after this, the copper surface of the double-sided core substrate 11 is subjected to a roughening process to improve adhesion at the time of subsequent coverlay formation, and stably improve the absorption of laser light during laser processing after buildup. Let Here, roughening treatment was performed using Multi Bond 150 manufactured by Nippon McDermitt Co., Ltd.

  As a result, adhesion was ensured and absorption of carbon dioxide laser light (wavelength: about 9.8 μm) on the copper surface could be improved. It was confirmed that the absorption of the carbon dioxide laser beam (wavelength: about 9.8 μm) was improved from about 20% to about 30% before and after the treatment.

  Thereafter, as shown in FIG. 1A (4), for example, a so-called coverlay 14 having an adhesive 13 such as acrylic / epoxy having a thickness of 20 μm is prepared on a polyimide film 12 having a thickness of 12 μm. The coverlay 14 is affixed to both sides by a vacuum press, a laminator or the like. Through the steps so far, the double-sided core substrate 15 with a coverlay is obtained.

  Next, as shown in FIG. 1B (5), a so-called single-sided copper-clad having a 7 μm-thick copper foil 17 on one side of a flexible insulating base material 16 such as polyimide (here, a polyimide having a thickness of 25 μm). A laminated board 18 is prepared. And this single-sided copper clad laminated board 18 is die-cut, and this is made into the buildup layer 18b of a multilayer printed wiring board.

  The adhesive 19 for building up the buildup layer 18b on the double-sided core substrate 15 with the coverlay is previously punched and aligned. The adhesive 19 is preferably a low-flow type prepreg, a bonding sheet, or the like with little flow-out.

  Since there is no need to fill the conductor layer here, the thickness of the adhesive 19 can be selected to be about 15 μm or thinner. The build-up layer 18b and the double-sided core substrate 15 with a coverlay are laminated with an adhesive 19 through a vacuum press or the like. The multilayer circuit substrate 20 is obtained through the steps so far.

  Furthermore, after this, a roughening process is performed on the copper foil surface of the build-up layer 18b of the multilayer circuit substrate 20, and the absorption of laser light when performing laser processing after the build-up is stably improved. Here, multi bond 150 of Nippon McDermitt Co., Ltd. was used in the same manner as described above.

  As a result, adhesion was ensured and absorption of carbon dioxide laser light (wavelength: about 9.8 μm) on the copper surface could be improved. It was confirmed that the absorption of the carbon dioxide laser beam (wavelength: about 9.8 μm) was improved from about 20% to about 30% before and after the treatment. In addition, the roughening treatment reduces the thickness of the copper foil by about 1 μm.

  In addition, as a process sequence which performs a roughening process on this copper foil surface, after (1) roughening a single-sided copper clad laminated board first and laminating | stacking on a double-sided core board, (2) After laminating | stacking on a double-sided core board | substrate There are two process orders for performing the roughening treatment, and in this embodiment 1, the process order is (2). The reason for this is that when the roughening treatment is performed before lamination as in (1) above, the surface state related to laser light absorption such as the shape and color tone of the roughened surface changes due to the history of lamination heat and pressure. It is because it ends up.

  Next, as shown in FIG. 1B (6), direct laser processing is performed on the copper foil 17 to form a conduction hole 21a for a step via hole. As for the laser processing method, since the copper foil penetration processing is essential, processing by an excimer laser, a UV-YAG laser, a YAG laser, a carbon dioxide gas laser, or the like that can remove copper by laser irradiation is necessary. In Example 1, a carbon dioxide laser having a high processing speed and excellent productivity was used.

  First, in order to form the conduction hole 21a for the step via hole, a laser beam having a beam diameter substantially equal to the upper hole diameter of the step via hole, in this case, a laser beam having a diameter of 200 μm, is irradiated to a predetermined position of the copper foil 17. The position where the laser beam is irradiated is aligned by X-rays or the like so as to aim at the center of the inner land 10a that is not shielded by the laser, that is, the center of the so-called conformal mask.

  Thereby, as shown in FIG. 1B (6), first, the copper foil 17 is penetrated to a diameter of 200 μm, and the resin up to the land 10a under the copper foil 17 is also removed. Thereafter, the land 10a is thickened by plating in advance. By the formal processing, the upper hole 21a for the conduction hole for the step via hole is formed. The via hole 21b for the via hole is also formed by direct laser processing that irradiates a laser beam having a beam diameter of 200 μm.

  Also in this case, since the land 10b is thickened by plating in advance, the via hole 21b for the via hole is formed without penetrating.

  Another method of aligning the laser beam with the hole in the center of the land 10a of the inner layer that is not shielded by laser can also be employed. That is, two or more marks that serve as alignment targets for the inner layer are arranged near the processing site. By reading this mark position, information such as the expansion and contraction of the substrate near the processing site is obtained, and calculation processing is performed. Then, the position of the processing site is corrected and the laser beam is irradiated.

  As in Example 1, a multilayer structure composed of various materials often does not exhibit uniform stretching behavior. In order to cope with this, it is desirable that the above-mentioned marks are preferably arranged at three or more points in order to detect a positional shift in the X direction and the Y direction.

  Next, as shown in FIG. 1C (7), the center of the pilot hole of the conduction hole 21a for the step via hole, that is, the center of the conformal mask of the inner land 10a is aimed by a technique such as image processing using X-rays, etc. The aperture is reduced to 200 μm and processed. Thereby, the copper foil 17 penetrates to a size approximately equal to the laser beam diameter, and further irradiation is performed to form a pilot hole for a step via hole.

  When the shape of the formed conduction hole 21a is arranged, the diameter of the upper hole of the conduction hole 21a is 200 μm, the lower hole of the conduction hole 21a is a hole diameter of 100 μm, and the upper diameter of the conduction hole 21a. It was stably formed at the approximate center.

  As shown in FIG. 1B, in the case where the conduction hole 21a and the conduction hole 21b are arranged at corresponding positions, the conduction hole 21a including penetration processing is taken into consideration that the land 10b is not penetrated. Is preferably formed first, and then the conduction hole 21b is formed.

  For this reason, in FIG. 1C, the upper conduction hole 21a in the drawing is processed first, and the lower conduction hole 21a and the conduction hole 21b are processed. Therefore, when the conduction holes 21a and the conduction holes 21b are in corresponding positions, if the conduction holes 21a are all located on the upper side, laser processing is first performed from all the upper conduction holes, and then In addition, it can be performed for all the conduction holes on the lower side, which is efficient.

As a condition example of a series of laser processing from FIG. 1B (6) to FIG. 1C (7), it was performed as follows. Using ML605GTXIII-5100U2 (manufactured by Mitsubishi Electric Corporation) as a carbon dioxide laser processing machine, alignment is performed by a technique such as image processing using X-rays, etc., and a beam diameter of 200 μm, a pulse width of 15 μsec, 15 mJ, 5 m, 5 A predetermined position of the copper foil 17 which is processed by shots and has a surface state in which the copper thickness is thin and the carbon dioxide laser beam is absorbed well is opened to a diameter of 200 μm.

  As a result, the resin up to the land 10a thickened by the plating below is also removed. The land 10a thickened by plating functions as a conformal mask without penetrating even if it is in a surface state with good absorption of carbon dioxide laser light, so that a conduction hole 21a for a step via hole is formed.

  In order to penetrate a predetermined portion of the copper foil 17a and the copper foil of the land 10a with a stable diameter, a laser optical system having a beam profile such as a Gaussian distribution having a high energy density at the center of the laser light is required.

  It has also been confirmed that if the copper thickness of the copper foil 17 is 10 μm or less, it penetrates with good reproducibility even at an energy amount of about plus or minus 30% of the laser processing conditions described above. If the thickness is 5 μm or less, the copper in the land to be left in the above-described roughening step, etching in the subsequent pre-plating process, or the like may be partially lost. Therefore, the copper thickness is preferably 5 to 10 μm.

  Regarding the copper thickness of the land 10a and the land 10b, a margin for penetrating the land 10b can be obtained by increasing the copper thickness of the land 10b located on the opposite side of the laser irradiation surface of the hole below the step via hole. Can do.

  Specifically, if it is 14 μm or more, it has been confirmed that the laser energy required for penetration is three times or more, which is a sufficient margin. For this reason, it is preferable that the copper thickness is 14 μm or more. Furthermore, a desmear process and a conductive process for performing interlayer connection by electrolytic plating are performed.

  Next, as shown in FIG. 1C (8), electrolytic plating of about 10 to 15 μm is performed on the multilayer circuit substrate 22 having the conduction hole 21a and the conduction hole 21b, and the step via hole 23a obtained from the conduction hole 21a. The via hole 23b obtained from the conduction hole 21b is formed to form interlayer conduction.

  Since the center of the upper hole and the lower hole of the step via hole 23a is not displaced, the upper hole of the step via can be made smaller. For this reason, step vias can be formed with higher density.

  In addition, the surroundings with plating on the hole below the conduction hole are stable, it is difficult for defects such as plating voids to occur, and the step via hole obtained by plating is structurally symmetric, Since the thermal stress generated in the step via hole 23a in the temperature cycle test or the like is uniformly dispersed, an effect of improving the interlayer connection reliability can be expected. Thereby, as described above, the electrolytic plating thickness is about 10 to 15 μm, and good interlayer connection reliability can be secured.

  Through the steps so far, the multilayer circuit base material 24 having completed interlayer conduction is obtained. In addition, when a through hole for mounting such as an insertion part is required, a through hole is formed with an NC drill or the like when forming a hole for conduction, and a through hole is formed simultaneously with the above via hole plating. Is also possible.

  Although step via holes are described in Patent Document 3 (P3, FIG. 1), etc., a method of forming step vias using the direct laser processing according to the present invention without misalignment of each wiring layer is mentioned. It is not done.

  Next, as shown in FIG. 1C (8), an outer layer pattern 25 is formed by a normal photofabrication technique. At this time, if there is a plating layer deposited on the cover film 12 of the core substrate 15, this is also removed. Thereafter, the surface of the substrate is subjected to surface treatment such as solder plating, nickel plating, gold plating, etc., if necessary, and a photo solder resist layer is formed and externally processed so that the multilayer printed wiring board 26 having a cable portion on the inner layer is obtained. Get.

  As a pattern forming capability required for a high-density mounting substrate, for example, if the size of a land on which a 0.5 mm pitch CSP is mounted is 300 μm, in order to pass one pattern between the lands, line / space = 50 μm / It is necessary to set the pitch to 50 μm and the pitch 100 μm.

  However, as described above, when electroplating of about 10 to 15 μm is performed on a 7 μm thick copper foil, the total conductor thickness of the outer layer is 17 to 22 μm, and it is sufficiently possible to form fine patterns with a pitch of 100 μm with good yield. Therefore, the requirements for high-density mounting can be satisfied.

  In addition, since the cable is arranged on the second layer, via holes connecting the first layer and the second layer can be arranged at a narrow pitch in order to connect the component mounting portions at the shortest distance. The two-layer wiring needs to be fine. Regarding the arrangement of the via holes, the via holes 23a and 23b can be formed with a via hole diameter of 200 μm, so that the pitch can be 0.4 mm or less.

  The interlayer connection structure of the multilayer printed wiring board having the cable portion according to the present invention employs the via hole 23a having a via hole diameter of 200 μm, so that it becomes a structure advantageous for high density and satisfies the demand for high density mounting. it can. A multilayer printed wiring board including a step via structure in an interlayer connection portion, wherein the center of each of the upper hole and the lower hole of the step via is arranged at a substantially equal position is manufactured inexpensively and stably. be able to.

Process sectional drawing which shows one Example of the manufacturing method of the multilayer printed wiring board which concerns on this invention. Process sectional drawing which shows one Example of the manufacturing method of the multilayer printed wiring board which concerns on this invention. Process sectional drawing which shows one Example of the manufacturing method of the multilayer printed wiring board which concerns on this invention. The conceptual cross-section block diagram of the manufacturing method of the multilayer printed wiring board which has a cable part by a conventional construction method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flexible insulating base material 2 Copper foil 3 Copper foil 4 Double-sided copper clad laminated board 5 Conductive hole 6 Partial plating resist layer 7 Through hole 8 The part located in a receiving land 9 Circuit pattern 10a Land 10b Land 11 Double-sided core board DESCRIPTION OF SYMBOLS 12 Polyimide film 13 Adhesive material 14 Coverlay 15 Double-sided core board 16 Flexible insulating base material 17 Copper foil 18a Single-sided copper clad laminated board 18b Build-up layer 19 Adhesive material 20 Multilayer circuit base material 21a Conductive hole 21b Conductive hole 22 Multilayer circuit substrate 23a Step via hole 23b Via hole 24 Multilayer circuit substrate 25 in which interlayer conduction is completed Outer layer circuit pattern 26 Multilayer printed wiring board 157 having a cable portion according to the present invention Through hole 158 Through hole land 159a Circuit pattern 159b Conformal mask 160 Double-sided core substrate 161 Polyimide film 162 Adhesive 163 Coverlay 164 Double-sided core substrate 165 with coverlay Flexible insulating base material 166a Copper foil 166b Conformal mask 167a Single-sided copper-clad laminate 167b Build-up layer 168 Adhesive 169a Multilayer circuit substrate 169b For conduction Multilayer circuit substrate 170a with holes Conduction hole 170b Conduction hole 171a Step via hole 171b Via hole 172 Multilayer circuit substrate 173 with completed interlayer conduction External layer circuit pattern 174 Cable portion 175 Multilayer printed wiring board having cable portion by conventional method

Claims (1)

An inner layer core substrate having at least one conductive layer is formed on an insulating base material made of a resin film, and an outer layer buildup layer composed of a laminate having a conductive layer on at least one surface is bonded to the inner layer core substrate. To form a laminated circuit substrate, to form an interlayer connector including a step via hole having a larger diameter toward the outer layer side on the laminated circuit substrate, and to form three or more layers of the outer layer buildup layer and the inner layer core substrate In the method of manufacturing a multilayer printed wiring board for forming a step via hole connecting the layers of the wiring layer,
Prepare the outer buildup layer having a conductive layer thickness of 5 to 10 μm,
At the formation position of the step via hole in the inner layer core substrate, a land having a thickness that is thicker than the conductive layer of the outer buildup layer and that is 14 μm or more and can sufficiently withstand the energy of the laser necessary for penetration ,
Open an opening having a diameter substantially equal to the pilot hole diameter of the step via hole in the land,
The step via hole is formed by piercing the laminated circuit substrate by irradiating a laser beam having a diameter equal to the upper hole diameter of the step via hole with the opening as a center and capable of removing the conductive layer. A method for producing a multilayer printed wiring board.

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