JP6303364B2 - Method for forming through hole in core substrate - Google Patents

Description

  The present invention relates to a method of forming a through hole for performing interlayer connection on a core substrate of a multilayer wiring board used for a printed wiring board or the like.

  In a multilayer wiring board in which conductor layers and insulating resin layers are alternately laminated, interlayer connection structures between multilayer conductor layers are arranged everywhere in order to realize a fine circuit. The interlayer connection structure is generally formed by forming a through hole with a drill or the like and filling the inside of the through hole with plating. The through hole is a hole formed in the insulating resin layer in order to connect the conductor layers.

  With the miniaturization of the wiring pattern of the printed wiring board, the hole diameter of the through hole becomes smaller, but when using a drill for forming the through hole, the drill diameter is about 0.15 to 0.20 mm, The via land diameter formed around the interlayer connection structure cannot be reduced. Therefore, it is difficult to form a high-density pattern by forming a through hole using a drill.

  For this reason, in order to form a fine interlayer connection structure, a through hole is formed by a laser and a via is filled by filled plating. In Patent Document 1, an interlayer connection structure having a relatively large thickness of an insulating layer is formed by irradiating a laser from both sides of a double-sided copper-coated resin plate to form a hole having a shape in which tapered tops are attached to each other. A laminated wiring board that facilitates filling of vias when forming the substrate and realizes high-density pattern formation is realized.

Japanese Patent Laid-Open No. 2003-46248

  However, in the through-hole forming method of Patent Document 1, since laser processing is performed from both sides of the insulating layer when forming the through-hole, due to variations in position accuracy of laser irradiation performed on each surface of the insulating layer, The position and hole diameter of the constricted part formed in the middle part of the hole change. When the variation in laser irradiation position accuracy is large, there is a possibility that a through hole may not be formed, and the reliability of interlayer connection is impaired.

  The problem to be solved by the present invention is to provide a method of forming a through hole that can form a through hole in a core substrate with high accuracy.

The present invention relates to a method for forming a through hole for forming a through hole in a substrate provided with a first metal layer and a second metal layer on both surfaces of an insulating layer. The insulating layer is bonded to the first metal layer and the second metal layer via an adhesive, and the arithmetic average roughness Ra of the first metal layer and the second metal layer is 0.1 μm or less. And forming the first opening by selectively removing a part of the first metal layer at the position where the through hole is formed, by etching, A step of forming a via reaching the second metal layer by irradiating the insulating layer exposed from the opening of 1 with a laser, and removing a part of the second metal layer at the bottom of the via by etching; Forming a through hole, and removing a part of the inner wall portion of the through hole on the second metal layer side by desmear to form a constricted portion at substantially the center in the thickness direction of the substrate. .

Alternatively, the insulating layer, the first metal layer, and the second metal layer are bonded via an adhesive, and the arithmetic average roughness Ra of the first metal layer and the second metal layer is 0.1 μm. The method for forming a through-hole according to the present invention is to selectively remove a part of the first metal layer and a part of the second metal layer at the through-hole formation position by etching, A step of forming the first opening and the second opening so that the position of the substrate in the planar direction corresponds to the first metal layer and the second metal layer, and the first opening is exposed from the first opening. By irradiating the insulating layer with laser, a step of forming a through hole and a part of the inner wall portion of the through hole on the second metal layer side are removed by desmear so as to be approximately at the center in the thickness direction of the substrate. And a step of forming a constricted portion.

  According to the present invention, the through hole can be formed in the core substrate with high accuracy.

Schematic sectional view showing an example of a double-sided copper-clad laminate used in the through hole forming method according to the first embodiment Schematic sectional drawing which shows the process of the through-hole formation method which concerns on 1st Embodiment The figure explaining the positional relationship of the opening of a through-hole and a constriction part Schematic sectional drawing which shows the process of the through-hole formation method which concerns on 2nd Embodiment

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing an example of a double-sided copper-clad laminate used in the through hole forming method according to the first embodiment, and FIG. 2 shows the steps of the through hole forming method according to the first embodiment. It is a schematic sectional drawing shown.

  First, as shown in FIG. 1, a double-sided copper-clad laminate 10 in which ultrathin copper foils 12a and 12b are thermocompression bonded to both sides of an insulating resin layer 11 is prepared. The insulating resin layer 11 is made of prepreg or the like. The thickness of the insulating resin layer 11 is, for example, 100 μm or more and 200 μm or less. The thickness of the ultrathin copper foils 12a and 12b is, for example, 5 μm to 18 μm.

  In addition, the adhesiveness between the ultrathin copper foils 12a and 12b and the insulating resin layer 11 generally defines the arithmetic average roughness (Ra) of the ultrathin copper foil 12 to about 0.1 to 0.5 μm. Can be secured by the anchor effect obtained by the above. However, as Ra becomes smaller, the amount of etching in the copper foil removing process can be reduced, and there is an advantage that unnecessary etching such as side etching is reduced. Therefore, by using the ultra-thin copper foils 12a and 12b, which are smooth ultra-thin copper foils 12a and 12b with Ra of 0.1 μm or less, and an adhesive layer is formed on the adhesive surface with the insulating resin layer 11, It becomes possible to sufficiently adhere to the insulating resin layer 11 and suppress variations in etching.

  Next, as shown in FIG. 2A, resists 15 a and 15 b are formed on both surfaces of the double-sided copper-clad laminate 10. At this time, the resist 15a is formed by photolithography so that the opening 14 is provided on the ultrathin copper foil 12a at the position where the through hole is formed.

  Next, as shown in FIG. 2B, a part of the ultrathin copper foil 12a exposed from the opening 14 is removed by wet etching. As a result, the opening 16 is provided in the ultrathin copper foil 12 at the position where the through hole is formed on one side of the double-sided copper-clad laminate 10, and the insulating resin layer 11 is exposed from the opening 16.

  As described above, before the through hole is formed in the insulating resin layer 11 by laser processing, the opening 16 is formed in advance in the ultrathin copper foil 12a at the position where the through hole is formed by a method other than laser processing (wet etching or the like). Keep it.

  Next, as shown in FIG. 2C, the resists 15a and 15b are removed.

Next, a part of the insulating resin layer 11 is removed by irradiating a part of the insulating resin layer 11 with a laser through the opening 16 using the ultrathin copper foil 12a as a mask. As the laser, a CO ₂ laser, a UV-YAG laser, or the like can be used. As a result, as shown in FIG. 2D, the bottomed via 20 that reaches the ultrathin copper foil 12 b is formed in the insulating resin layer 11. At this time, the resin of the insulating resin layer 11 sublimated by laser processing is reattached to the bottom surface of the bottomed via 20 and becomes a resin residue 17. In addition, a part of the ultrathin copper foil 12 b sublimated by laser irradiation may adhere to the bottom surface of the bottomed via 20 as the copper residue 18.

  In this embodiment, before processing the insulating resin layer 11 with a laser, an opening 16 is formed in advance in the ultrathin copper foil 12a by wet etching or the like, and then a laser is transmitted from the opening 16 to the insulating resin layer 11. Irradiated to form a bottomed via 20. Thereby, it is not necessary to laser process the ultrathin copper foil 12a, and it is possible to suppress the occurrence of copper burrs in the peripheral portion at the top of the through hole. Further, since the opening of the copper foil formed by etching becomes the via diameter, there is an advantage that the processing speed of the bottomed via 20 can be increased without reducing the diameter of the laser.

  Next, as shown in FIG. 2E, a part of the ultrathin copper foil 12b and the copper residue 18 which are the bottom of the bottomed via 20 are removed by wet etching or the like, and the through hole 21 is formed. Form. At this time, the copper foil portion other than the bottom portion of the bottomed via 20 is also etched, but the bottom portion of the bottomed via 20 is etched from the front and back, so that the removal proceeds quickly. Therefore, as shown in FIG. 2E, the through hole 21 can be formed while leaving the ultrathin copper foils 12 a and 12 b on the insulating resin layer 11.

  Next, as shown in FIG. 2F, the resin inside the through hole 21 is removed by desmear. At this time, the desmear treatment is performed more strongly than the case of removing the normal resin residue 17. As a result, the side surface of the through-hole 21 is removed by desmear, but the resin in the through-hole 21 is selected leaving a substantially central portion in the thickness direction due to the liquid flow of desmear and the glass at the center of the prepreg. Removed. As a result, the through-hole 21 becomes a constricted through-hole 30 having a constricted portion 22 (that is, a portion narrowed in a taper shape with respect to the opening on the substrate surface) at a substantially central portion in the thickness direction of the insulating resin layer 11. . Through the above steps, the core substrate 40 having the constricted through hole 30 is obtained.

  In the present embodiment, when connecting the ultrathin copper foils 12a and 12b, the connection is not performed in the state of the bottomed via 20, but the connection is made in the state of the through hole 30 with a constriction. Connection failure due to the tearing of ultrathin copper foil does not occur. In addition, since the constricted through hole 30 is formed by laser irradiation and desmearing from one side, the diameter of the through hole is reduced due to variations in laser position accuracy as in the method of forming a through hole in which laser irradiation is performed from both sides. Therefore, connection failure does not occur.

  FIG. 3 is a diagram for explaining the positional relationship between the opening of the through hole and the constricted portion. In FIG. 3, the position of the opening formed on one surface and the other surface of the core substrate 40 and the position of the constricted portion 22 are specified by double arrows.

  In the method of performing laser irradiation twice from both surfaces of the insulating resin layer 11, the position shift of the constricted portion with respect to the opening of the through hole becomes a problem due to the positioning error at the time of laser irradiation. On the other hand, in this embodiment, after forming the through-hole 21 by performing laser irradiation once with respect to the insulating resin layer 11 from the one surface side of the double-sided copper-clad laminate 10, the constricted portion is formed by desmear treatment. Therefore, the positional deviation between the opening of the through hole 30 with the constriction and the constricted portion 22 in the planar direction of the core substrate 40 can be suppressed. Specifically, as shown in FIG. 3, the center C1 of the opening formed on the ultrathin copper foil 12a of the core substrate 40, the center C2 of the opening formed on the ultrathin copper foil 12b of the core substrate 40, The center C3 of the constricted portion 22 can be accommodated in a circle having a radius of 5 μm when viewed from any one side of the core substrate 40. It can be said that projections of the centers C1, C2, and C3 onto a plane parallel to one surface of the core substrate 40 are included in a circle having a radius of 5 μm. Therefore, according to the through hole forming method according to the present embodiment, it is possible to improve the positional accuracy between the two openings of the constricted through hole 30 formed on both surfaces of the core substrate 40 and the constricted portion 22.

(Second Embodiment)
FIG. 4 is a schematic cross-sectional view showing the steps of the through hole forming method according to the second embodiment.

  In the first embodiment, the example in which the opening 14 is formed in one ultrathin copper foil 12a provided on the double-sided copper-clad laminate 10 by etching and then laser processing is performed has been described. As in the embodiment, laser processing may be performed after an opening is formed in the ultrathin copper foil 12b on the back side at the time of laser irradiation by etching.

  First, as shown in FIG. 4A, resists 15 a and 15 b are formed on both surfaces of the double-sided copper-clad laminate 10. At this time, the resists 15a and 15b are formed by photolithography so that the openings 14a and 14b are provided on the ultrathin copper foils 12a and 12b at the formation positions of the through holes. At this time, the openings 14a and 14b are formed so that the positions in the plane direction of the double-sided copper-clad laminate 10 correspond (that is, substantially overlap).

  Next, as shown in FIG. 4B, a part of the ultrathin copper foil 12a and a part of the ultrathin copper foil 12b exposed from the openings 14a and 14b are removed by wet etching, and the openings 16a and 16b are removed. Form.

  Next, as shown in FIG. 4C, the resists 15a and 15b are removed.

  Next, as shown in FIG. 4D, using the ultrathin copper foil 12a as a mask, a part of the insulating resin layer 11 exposed from the opening 16a is irradiated with a laser to remove a part of the insulating resin layer 11. To do. Thereby, as shown in FIG.4 (d), the through-hole 21 is formed. Resin residue 17 remains in the through hole 21.

  Next, as shown in FIG. 4E, the resin inside the through hole 21 is removed by desmear. At this time, the desmear treatment is performed more strongly than the case of removing the normal resin residue 17. For the same reason as in the first embodiment, the resin on the inner wall portion of the through hole 21 is selectively removed leaving a substantially central portion in the thickness direction. As a result, the through hole 21 becomes a constricted through hole 30 having a constricted portion 22 at a substantially central portion in the thickness direction of the insulating resin layer 11. Through the above steps, the core substrate 40 having the constricted through hole 30 is obtained.

  In the present embodiment, since a part of the ultrathin copper foil 12b that becomes the back side at the time of laser irradiation is previously removed, the through hole 21 can be formed without forming a bottomed via. In this method, since it is not necessary to remove the ultrathin copper foil at the bottom by etching after forming the bottomed via, the thickness of the ultrathin copper foils 12a and 12b can be kept substantially constant throughout the manufacturing process. .

  In addition, a multilayer wiring board can be manufactured using the core board | substrate 40 with the through-hole 30 with a constriction obtained with the manufacturing method which concerns on each said embodiment. For example, after an interlayer connection structure is formed on the core substrate 40 by via filling, one or more wiring layers are formed on both surfaces of the core substrate 40 after the interlayer connection structure is formed by using a build-up method. A wiring board can be manufactured.

  In addition, a method suitable for the size of the wiring to be formed can be selected as appropriate. For example, a multilayer wiring board may be manufactured by using a build-up method for forming a fine wiring layer and using a conventional method of laminating a prepreg and a copper foil for a wiring layer whose wiring size is not fine. Is possible.

  Moreover, although each said embodiment demonstrated the example which forms a through-hole in the double-sided copper clad laminated board 10 which provided the ultrathin copper foil 12a and 12b on both surfaces of the insulating resin layer 11, both surfaces of the insulating resin layer 11 were demonstrated. The metal layer provided on may be a metal layer other than copper, such as gold or silver.

  Examples in which the present invention is specifically implemented will be described below. This example corresponds to the manufacturing method (FIGS. 1 and 2) according to the first embodiment.

  First, a copper foil PF-E (thickness 12 μm) made by Nihon Electrolytic Co., Ltd. was bonded to both surfaces of a high Tg glass epoxy multilayer material 679FG (thickness 100 μm) manufactured by Hitachi Chemical Co., Ltd. Wet etching was performed with HE500 manufactured by JCU to obtain a double-sided copper-clad laminate with a copper foil thickness of 7 μm (see FIG. 1).

  Next, after laminating a dry film resist SL-9025 (thickness 25 μm) manufactured by Hitachi Chemical Co., Ltd. on both sides of the obtained double-sided copper-clad laminate, an opening was formed in the resist on one side by photolithography. (See FIG. 2 (a)). Next, the copper foil exposed from the opening was removed with an aqueous sulfuric acid solution (HE-500) by etching (see FIG. 2B). The diameter of the opening formed in the copper foil was 80 μm.

Next, a bottomed via having a diameter of 80 μm was formed by irradiating a CO ₂ laser through the opening of the formed copper foil (see FIG. 2C).

  Next, after removing the resist (see FIG. 2D), the bottom surface of the bottomed via is removed by removing the surface of the copper foil by a thickness of 4 μm by wet etching using a sulfuric acid-peroxide solution (HE500). The formed copper foil was removed to form a through hole 21 (see FIG. 2 (e)).

  Subsequently, the double-sided copper-clad laminate having through-holes 21 is immersed in a mixed solution of potassium permanganate 60 g / L and potassium manganate 15 g / L at a liquid temperature of 70 ° C. for 30 minutes, and the resin residue inside the through-holes And a part of the inner wall of the through hole that became the back side during laser irradiation was removed to obtain a core substrate having a constricted through hole having a maximum inner diameter of 100 μm and an inner diameter of the constricted portion of 50 μm (FIG. 2 ( f)).

  The through hole forming method according to the present invention can be used for manufacturing a multilayer wiring board provided with an interlayer connection structure through a through hole.

10 Double-sided copper-clad laminate 11 Insulating resin layer 12a Ultra-thin copper foil (first metal layer)
12b Ultra-thin copper foil (second metal layer)
14 opening 14a opening (first opening)
14b Opening (second opening)
15a, 15b Resist 16, 16a, 16b Opening 17 Resin residue 18 Copper residue 20 Bottomed via 21 Through hole 22 Constricted part 30 Constricted through hole 40 Core substrate

Claims (3)

A through hole forming method for forming a through hole in a substrate provided with a first metal layer and a second metal layer on both sides of an insulating layer,
The insulating layer, the first metal layer, and the second metal layer are bonded via an adhesive, and the arithmetic average roughness Ra of the first metal layer and the second metal layer is 0.1 μm or less,
Forming a first opening by selectively removing a part of the first metal layer at the formation position of the through hole by etching;
Irradiating the insulating layer exposed from the first opening with a laser to form a via reaching the second metal layer;
Removing a portion of the second metal layer at the bottom of the via by etching to form a through hole;
A step of removing a part of the inner wall portion of the through hole on the second metal layer side by desmear to form a constricted portion at a substantial center in the thickness direction of the substrate. . A through hole forming method for forming a through hole in a substrate provided with a first metal layer and a second metal layer on both sides of an insulating layer,
The insulating layer, the first metal layer, and the second metal layer are bonded via an adhesive, and the arithmetic average roughness Ra of the first metal layer and the second metal layer is 0.1 μm or less,
By selectively removing a part of the first metal layer and a part of the second metal layer at positions where the through holes are formed by etching, the first metal layer and the second metal are removed. Forming each of the first opening and the second opening so that the position of the substrate in the planar direction corresponds to the layer;
Irradiating the insulating layer exposed from the first opening with a laser to form a through hole;
A step of removing a part of the inner wall portion of the through hole on the second metal layer side by desmear to form a constricted portion at a substantial center in the thickness direction of the substrate. . The center of the opening of the through hole on one surface of the substrate, the center of the opening of the through hole on the other surface of the substrate, and the center of the constricted portion of the through hole are one surface of the substrate. The method of forming a through hole according to claim 1 or 2 , wherein the through hole is contained within a circle having a radius of 5 µm when viewed from above.