JP3727374B2 - Multilayer printed wiring board and manufacturing method thereof - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a multilayer printed wiring board and a method for manufacturing the same.
[0002]
[Prior art]
As a manufacturing technique of a multilayer printed wiring board in recent years, a full additive process for forming a conductor circuit only by electroless plating is known. Here, the flow of a general full additive process will be briefly described with reference to FIG.
[0003]
First, after producing the inner layer board | substrate 22 provided with the inner layer conductor circuit 21, the additive adhesive agent layer 23 is formed by application | coating and hardening of a resin varnish. Next, a recess for forming a photo via hole is formed in the additive adhesive layer 23 by photolithography. Next, after roughening the additive adhesive layer 23, a hole for forming a through hole is formed by using a drill or the like (drilling step). Next, after performing desmear treatment and application of catalyst nuclei, a plating resist 24 is formed on the additive adhesive layer 23. Next, by performing electroless copper plating, copper plating 25 is deposited on the inner wall surface of the recess for forming the photo via hole, the inner wall surface of the hole for forming the through hole, or the like. Thereafter, through an inspection process, a multilayer printed wiring board 28 having an outer layer conductor circuit 26, a plated through hole 27, and a photo via hole (not shown) is obtained.
[0004]
[Problems to be solved by the invention]
By the way, in the full additive process, in order to remove the copper plating 25 and the like abnormally deposited on the plating resist 24, a surface polishing process by a polishing machine may be performed after the electroless plating process.
[0005]
However, as shown in FIG. 9, when the drilling process as described above is performed, the cutting scraps of the drill coming out from the upper opening of the through-hole forming hole are scattered and welded around the hole, so that There was a problem that the swell part 30 was formed. This is because, in the case of a full additive substrate, unlike a subtractive substrate using a copper clad laminate as a starting material, heat generated during cutting is not easily dissipated from the surface. Therefore, when the surface polishing process is performed, the copper plating 25 on the upper surface of the raised portion 30 is scraped off, and disconnection often occurs in that portion. Therefore, conventionally, a cutting waste removal operation using a soft brush or the like has been required. However, this method cannot completely remove the cutting waste, and the operation itself is troublesome.
[0006]
Furthermore, as another failure mode resulting from the drilling process, as shown in FIG. 10, it has been known that a chip 31 or a crack 32 is generated in the opening of the through hole forming hole due to an impact of a drill or the like. . For this reason, not only the appearance of the plated through hole 27 is deteriorated, but also the reliability of the plated through hole 27 is easily lowered.
[0007]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a multilayer printed wiring board that can achieve prevention of disconnection and improved reliability in a plated through hole portion, and a method of manufacturing the same. There is.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, in the invention according to claim 1, the inner layer substrate on which the inner layer conductor circuit is formed , the additive adhesive layers on the front side and the rear side formed on the inner layer substrate, In a multilayer printed wiring board having a plated through hole penetrating an inner layer substrate, the surface of the additive adhesive layer on the surface side is provided with a photo via hole having a diameter larger than that of the plated through hole at a place where the plated through hole is to be formed . a front Symbol plated through hole opening surface side of the provided on the back side additive adhesive layer of the plated through hole and coaxially and back side of the opening in the plated through holes誘設the same diameter And a multilayer printed wiring board characterized by comprising:
[0009]
According to a second aspect of the present invention, in the first aspect, a part of the inner layer conductor circuit is routed to the bottom of the photo via hole, and the upper surface and the side surface 2 of the routed inner layer conductor circuit are provided. The surface is bonded to the plating in the photo via hole.
[0010]
In the invention according to claim 3, a step of forming an additive adhesive layer made of a photosensitive resin on the front surface side and the back surface side of the inner layer substrate on which the inner layer conductor circuit is formed, and plating of the additive adhesive layer on the front surface side forming a recess for the photo via hole formed by photolithography in the through hole formation planned portion, by drilling from the inner layer substrate and the back side surface side of the additive adhesive layer wherein the recesses are formed in the A multilayer printed wiring comprising a step of forming a through-hole forming hole that opens at the bottom of a recess, and a step of forming a plated through-hole by depositing plating in the through-hole forming hole The gist of the manufacturing method of the plate.
[0011]
[Action]
According to the third aspect of the present invention, since the tip of the drill does not come into direct contact with the additive adhesive layer on the surface side during the drilling step, the generation amount of cutting waste that causes swelling is extremely reduced. In addition, since the additive adhesive layer is less susceptible to impact, chipping and cracking are less likely to occur around the opening of the through hole forming hole.
[0012]
According to the first and second aspects of the invention, since the opening on the surface side of the plated through hole has a large diameter, filling of the paste into the plated through hole is facilitated. According to invention of Claim 2, the connection reliability in a plating through-hole improves by increasing the junction area of conductors.
[0013]
【Example】
[Example 1]
Hereinafter, an embodiment in which the present invention is embodied in a method for manufacturing a multilayer printed wiring board by an additive process will be described in detail with reference to FIGS.
[0014]
FIG. 7 shows a multilayer printed wiring board 1 in the present embodiment. The multilayer printed wiring board 1 is a so-called four-layer board having four conductor layers. Inner layer conductor circuits 3 and 4 are formed on both the front surface S1 and the rear surface S2 of the inner layer substrate 2 constituting the multilayer printed wiring board 1. Additive adhesive layers 5 and 6 having a thickness of several tens of μm are formed on both the front and back surfaces of the inner layer substrate 2 so as to cover the inner layer conductor circuits 3 and 4. A permanent resist 7 as a plating resist and outer layer conductor circuits 8 and 9 are formed on the upper surfaces of these additive adhesive layers 5 and 6. Further, in the additive adhesive layers 5 and 6 on the front surface S1 and the back surface S2, an interstitial via hole 10 as a photo via hole is formed. The interstitial via hole 10 is formed by depositing copper plating 12 on the inner wall surface of the recess 11 for forming the photo via hole. The interstitial via hole 10 on the surface S1 side electrically connects the inner layer conductor circuit 3 and the outer layer conductor circuit 8 existing outside thereof. Similarly, the interstitial via hole 10 on the back surface S2 side electrically connects the inner layer conductor circuit 4 and the outer layer conductor circuit 9 existing outside thereof.
[0015]
The multilayer printed wiring board 1 is provided with a plated through hole (in this embodiment, an inner diameter D2 = about 0.3 mm) 13. The plated through hole 13 is formed by depositing the copper plating 12 on the inner wall surface of the through hole forming hole 14. The plated through hole 13 electrically connects the outer layer conductor circuit 8 on the front surface S1 side and the outer layer conductor circuit 9 on the rear surface S2 side.
[0016]
Another interstitial via hole 15 having a role different from that of the interstitial via hole 10 is formed at a predetermined position in the additive adhesive layer 5 on the surface S1 side. The interstitial via hole 15 is formed by depositing copper plating 12 on the inner wall surface of the recess 16 for forming the photo via hole. The plated through hole 13 is provided coaxially so as to penetrate the bottom of the interstitial via hole 15. Therefore, the interstitial via hole 15 is a surface side opening 13 a in the plated through hole 13.
[0017]
The inner diameter D1 of the interstitial via hole 15 is set to be equal to or larger than the inner diameter D2 of the plated through hole 13, more preferably about 0.1 mm to about 0.2 mm larger than the inner diameter D2. The range in which the inner diameter D1 can be changed, of course, varies depending on the value of the inner diameter D2. If the value of the inner diameter D1 is too small, an impact is likely to be applied to the additive adhesive layer 5 at the time of drilling, and chipping and cracking may not be sufficiently prevented. On the other hand, if the value of the inner diameter D1 is too large, there will be no problem with chipping, cracking, etc., but there is a risk that it will hinder fineness. In consideration of such circumstances, in this embodiment in which the inner diameter D2 is set to about 0.3 mm, the inner diameter D1 is set to about 0.5 mm.
[0018]
On the other hand, in the case of the multilayer printed wiring board 1, the additive adhesive layer 6 on the back surface S2 side is not provided with the interstitial via hole 15 as described above. That is, in the multilayer printed wiring board 1 of the present embodiment, it can be grasped that only one end portion of the plated through hole 13 (that is, only the end portion on the surface S1 side) has a large diameter. Thereafter, the first interstitial via hole 10 is referred to as “first IVH 10” and the second interstitial via hole 15 is referred to as “second IVH 15” to distinguish between the two.
[0019]
Next, a procedure for manufacturing the multilayer printed wiring board 1 will be described with reference to FIGS.
First, a copper clad laminate (FR-4, thickness 0.6 mm in this embodiment) is used as a starting material, and copper foil is etched according to a normal subtractive process. As a result, the inner layer substrate 2 including the inner layer conductor circuits 3 and 4 is manufactured.
[0020]
Next, a resin varnish for forming an additive adhesive layer is applied to the front surface S1 and the back surface S2 of the inner substrate 2 by a coating device such as a roll coater. The resin varnish is obtained by dispersing a resin filler that is easily soluble in a roughening agent in a photosensitive resin matrix that is hardly soluble in a roughening agent such as chromic acid. Furthermore, the applied resin varnish is cured by heating and drying the inner layer substrate 2. As a result, as shown in FIG. 2, additive adhesive layers 5 and 6 having a thickness of 40 μm to 80 μm are formed on the inner layer substrate 2. In this embodiment, the additive adhesive layers 5 and 6 having a thickness of 50 μm are formed by applying and curing a resin varnish composed of a photosensitive epoxy acrylate and a thermosetting epoxy.
[0021]
Next, by performing exposure / development using a photomask, the first IVH 10 is applied to a predetermined portion of the additive adhesive layers 5 and 6, that is, a portion corresponding to the inner layer conductor circuits 3 and 4 that need to be electrically connected. A recess 11 for forming is formed (see FIG. 3). In this step, a circular recess 16 for forming the second IVH 15 is formed at a predetermined location of the additive adhesive layer 5 on the surface S1 side, that is, a plating through-hole formation scheduled location P1. In this embodiment, the inner diameter D1 (specifically, the inner diameter of the bottom) D1 of the recess 16 is 0.5 mm. Here, the recess 16 is formed by an optical technique called photolithography. Therefore, unlike the case of the mechanical method using the drill 17 or the like, there is no problem such as the scattering and welding of the cutting waste.
[0022]
Next, as shown in FIG. 4, the resin filler in the additive adhesive layers 5 and 6 is selectively dissolved by treating the inner layer substrate 2 with the recesses 16 formed with a roughening agent such as chromic acid. Let As a result of such roughening treatment, roughened surfaces 5a and 6a are formed on the surface layers of the additive adhesive layers 5 and 6.
[0023]
Next, by using a drilling tool such as a drill 17 or the like, the plated through hole formation scheduled point P1 of the inner layer substrate 2 that has undergone the roughening process is drilled only from the surface S1 side where the recess 16 is formed (FIG. 5). reference). In this case, the center axis of the drill 17 is aligned so as to penetrate substantially the center point of the recess 16. Then, as a result of the drilling step, as shown in FIG. 6, through-hole forming holes 14 penetrating the front surface S1 and the back surface S2 of the inner substrate 2 are provided. The upper end of the through-hole forming hole 14 is open at the bottom of the recess 16. In this embodiment, a drill 17 having a blade diameter of 0.3 mm is used. Further, when carrying out the drilling step, the inner substrate 2 is fixed to a jig (not shown) with the back surface S2 in close contact therewith.
[0024]
Next, after performing desmear treatment and applying catalyst nuclei according to a conventionally known procedure, as shown in FIG. 7, a permanent resist 7 is formed in a predetermined region on the additive adhesive layers 5 and 6 by photolithography.
[0025]
Next, by performing electroless copper plating using a conventionally known electroless copper plating bath, a copper plating 12 having a thickness of about 20 μm is deposited on portions other than the permanent resist 7. Further, the surface is polished by a wet belt sander (# 600) to remove the copper plating 12 that is abnormally deposited on the surface layer. Thereafter, through an inspection process, the multilayer printed wiring board 1 of FIG. 1 including the outer layer conductor circuits 8 and 9, the plated through holes 13, the first and second IVH holes 10 and 15 and the like is obtained.
[0026]
The manufacturing method of the multilayer printed wiring board 1 according to the present embodiment is characterized in that the concave portion 16 is formed in advance by photolithography at the plating through hole formation scheduled place P1 before the drilling step. Further, the recess 16 formed in this case is larger than the diameter of the drill 17. Therefore, the tip of the rotating drill 17 does not directly contact the additive adhesive layer 5 but contacts the inner layer substrate 2 under the additive adhesive layer 5. Therefore, the additive adhesive layer 5 is not scraped off by the drill 17, and the generation amount of cutting waste that causes the swell is extremely reduced. Therefore, it is possible to reliably prevent occurrence of disconnection when the surface polishing step is performed. In addition, since the troublesome work of removing cutting waste using a soft brush or the like is not required, simplification of the entire process is achieved.
[0027]
Furthermore, according to the manufacturing method of the present embodiment, the tip of the drill 17 does not come into direct contact with the additive adhesive layer 5, so that the impact applied to the additive adhesive layer 5 during the drilling process is extremely small. Therefore, chipping and cracks are less likely to occur around the opening of the through hole forming hole 14. Therefore, it is possible to improve the appearance and reliability of the plated through hole 13.
[0028]
In addition, the second IVH 15 essential in this embodiment can be formed simultaneously with the formation of the first IVH 10 which is a normal photo via hole. Therefore, special equipment and processes are not particularly required, and it is extremely advantageous for implementation.
[0029]
Further, according to the manufacturing method of this embodiment, the second IVH 15 constituting one opening of the plated through hole 13 is only one of the additive adhesive layers 5 and 6 on both sides (that is, the surface S1 side). In the additive adhesive layer 5 only). The plated through hole 13 having the second IVH 15 in the additive adhesive layer 5 on the front surface S1 side and the plated through hole 13 having the second IVH 15 in the additive adhesive layer 6 on the back surface S2 side are provided as one sheet. Of course, it is also possible to mix in a multilayer printed wiring board (not shown). However, when producing such a multilayer printed wiring board, since it is necessary to perforate the inner layer substrate 2 from two directions in the drilling step, it is necessary to turn the inner layer substrate 2 upside down. Considering the above, the configuration of the present embodiment requires less labor and time for the drilling process, and is more convenient for facilitating manufacturing.
[0030]
And in the case of the multilayer printed wiring board 1 of a present Example, by providing 2nd IVH15, the surface side opening part 13a of the plating through hole 13 is large diameter. Such a configuration is advantageous when, for example, the internal space of the plated through hole 13 is to be filled with a conductive paste or the like. That is, if the paste is filled from the second IVH 15 side having the large diameter, the paste can be introduced into the internal space relatively smoothly and reliably. Therefore, the paste filling operation is facilitated.
[0031]
Also, when soldering a surface-mounted component to the surface side opening 13a without filling the paste, the solder can be caught to some extent in the recessed second IVH 15 to improve the bonding strength. There are advantages.
[Example 2]
Next, the multilayer printed wiring board 19 of Example 2 and its manufacturing method are demonstrated based on FIG. Here, it demonstrates centering on difference with Example 1, and shall attach | subject the same member number only about a common part.
[0032]
As shown in FIG. 8, in this multilayer printed wiring board 19, a part of the inner layer conductor circuit 3 on the surface S1 side is routed to the bottom of the second IVH 15. The two surfaces of the routed inner layer conductor circuit 3, the upper surface 3 a and the side surface 3 b, are in a state of being joined to the copper plating 12 deposited in the second IVH 15 (ie, a two-point connection state). Therefore, in the case of this multilayer printed wiring board 19, an electrical connection between the inner layer conductor circuit 3 and the plated through hole 13 is achieved.
[0033]
When the multilayer printed wiring board 19 is manufactured, the inner layer substrate 2 needs to be manufactured according to the first embodiment. At that time, the inner-layer conductor circuit 3 is also routed to the through hole formation scheduled place P1. In the present embodiment, the inner layer conductor circuit 3 has a circular pattern and has a diameter larger than at least the inner diameter D2 of the through hole forming hole 13. The center of the circular inner layer conductor circuit 3 substantially coincides with the center of the recess 16 for forming the second IVH 15 to be formed later. Then, according to Example 1, the process from the formation process of the additive adhesive layers 5 and 6 to the roughening process is performed. Next, using a drill 17 or the like, the plating through hole formation planned location P1 of the inner layer substrate 2 that has undergone the roughening treatment is drilled only from the surface S1 side. After the drilling step, a through hole forming hole 14 penetrating the front surface S1 and the back surface S2 of the inner layer substrate 2 is formed. At this time, the routed inner layer conductor circuit 3 is punched out into a donut shape by a drill 17.
[0034]
Next, the steps of desmear treatment, application of catalyst nuclei, formation of permanent resist 7 and electroless copper plating are performed again in accordance with Example 1. As a result, copper plating 12 having a thickness of about 20 μm is deposited on the through hole forming hole 14 and the inner wall surface of the recess 16. At this time, the copper plating 12 is similarly deposited not only on the resin surface but also on the upper surface 3a and the side surface 3b of the inner conductor circuit 3 exposed in the recess 16. Thereafter, through the surface polishing step and the inspection step, the multilayer printed wiring board 19 of FIG. 8 including the outer layer conductor circuits 8 and 9, the plated through hole 13, the first and second IVH holes 10 and 15 and the like is obtained. .
[0035]
Needless to say, the manufacturing method of the multilayer printed wiring board 19 of the second embodiment as described above has the same effects as those of the first embodiment. In particular, in this multilayer printed wiring board 19, the copper plating 12 is deposited not only on the side surface 3b of the inner layer conductor circuit 3 routed around the recess 16, but also on the upper surface 3a. Therefore, the bonding area between the conductors is ensured by the area of the upper surface 3a of the inner layer conductor circuit 3, and as a result, the connection reliability inside the plated through hole 13 is also reliably improved. Therefore, the multilayer printed wiring board 19 which is more excellent electrically can be obtained.
[0036]
In addition, according to the configuration of the present embodiment, since a suitable connection between the conductors is ensured in the inner layer, unlike the conventional case, there is no need to make a three-point connection state by performing etch back. That is, the processing conditions can be relaxed as compared to the conventional case where the desmear processing needs to be performed under strong conditions. This surely contributes to shortening of manufacturing time and cost reduction.
[0037]
The present invention can be modified as follows, for example.
(1) The inner layer conductor circuit 3 routed in the second embodiment is not necessarily a circular pattern, and may be an arbitrary shape such as a linear pattern. However, the pattern having the shape as in Example 2 has an advantage that the bonding area is relatively large.
[0038]
(2) Since the shape of the second IVH 15 does not have to be circular, it may of course be an elliptical shape, a rectangular shape, a polygonal shape, or the like. However, it is desirable that the opening area of the second IVH 15 is at least larger than the opening area of the surface side opening 13 a of the plated through hole 13.
[0039]
(3) The electroless plating on the non-formed portion of the permanent resist 7 is not limited to the electroless copper plating as in the first and second embodiments, and may be, for example, electroless nickel plating. Moreover, you may use together electroless copper plating and other plating.
[0040]
(4) In place of the method of Examples 1 and 2 in which the additive adhesive layers 5 and 6 are formed by applying and curing the resin varnish, for example, a method of laminating an additive adhesive forming sheet can be employed. is there.
[0041]
(5) The present invention is not limited to the four-layer board as in Examples 1 and 2, but also a three-layer board or a multilayer board having five or more layers (in this case, the additive adhesive layers 5 and 6 on one side are plural layers). Of course, it is also possible to apply the above.
[0042]
Here, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiments and other examples are listed below together with the effects thereof.
(1) A photo via hole having a diameter larger than that of the plated through hole is provided at a predetermined position of the additive adhesive layer formed on the inner layer substrate having the inner layer conductor circuit, and the photo via hole is one of the plated through holes. It is an opening, and a part of the inner layer conductor circuit is routed to the bottom of the photo via hole, and the upper surface and the side surface of the routed inner layer conductor circuit are arranged in the photo via hole hole. Plating through-hole structure joined with plating. With this configuration, improvement in reliability can be achieved.
[0043]
(2) In Claim 3, an inner diameter of the recess is larger than a diameter of a drilling tool used when drilling the inner layer substrate (that is, larger than an inner diameter of a through hole forming hole to be formed). ) A method for producing a multilayer printed wiring board. With this method, swells, chips and cracks in the opening can be reliably prevented.
[0044]
(3) In Claims 1 to 3, the photo via hole constituting one opening of the plated through hole is formed only in one of the additive adhesive layers on both sides. In this way, manufacture is facilitated.
[0045]
The technical terms used in this specification are defined as follows.
“Plating through hole: This refers to a metal plating such as copper plating deposited on the inner wall surface of a hole formed in a base material.”
[0046]
【The invention's effect】
As described above in detail, according to the third aspect of the present invention, it is possible to provide a method for manufacturing a multilayer printed wiring board capable of preventing disconnection and improving reliability in the plated through hole portion. In addition, according to the first aspect of the present invention, it is possible to provide a multilayer printed wiring board that is not only excellent in reliability in the plated through hole portion but also relatively easy in paste filling operation and the like. Furthermore, according to the invention described in claim 2, it can be made more excellent in reliability.
[Brief description of the drawings]
1 is a partial schematic cross-sectional view showing a multilayer printed wiring board of Example 1. FIG.
FIG. 2 is a partial schematic cross-sectional view for explaining the manufacturing procedure.
FIG. 3 is a partial schematic cross-sectional view for explaining the manufacturing procedure.
FIG. 4 is a partial schematic cross-sectional view for explaining the manufacturing procedure.
FIG. 5 is a partial schematic cross-sectional view for explaining the manufacturing procedure.
FIG. 6 is a partial schematic cross-sectional view for explaining the manufacturing procedure.
FIG. 7 is a partial schematic cross-sectional view for explaining the manufacturing procedure.
8 is a partial schematic cross-sectional view showing a multilayer printed wiring board of Example 2. FIG.
9A is a partial plan view for explaining a problem of a conventional multilayer printed wiring board, and FIG. 9B is a cross-sectional view taken along the line AA.
FIG. 10 is a partial schematic cross-sectional view for explaining a conventional problem.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,19 ... Multilayer printed wiring board, 2 ... Inner layer board, 3, 4 ... Inner layer conductor circuit, 3a ... Upper surface of inner layer conductor circuit, 5, 6 ... Additive adhesive layer, 12 ... Copper plating, 13 ... Plating through hole, 13a ... (surface side) opening, 14 ... hole for forming a through hole, 15 ... second IVH as a photo via hole, 16 ... a recess for forming a photo via hole.

Claims (3)

In a multilayer printed wiring board having an inner layer board on which an inner layer conductor circuit is formed, an additive adhesive layer on the front side and the back side formed on the inner layer board, and a plated through hole penetrating the inner layer board,
Provided by the large-diameter photo via hole than the plated through hole in the plated through hole to be formed location of the additive adhesive layer of the surface side, and the opening surface side of the front Symbol plated through holes,
Provided in the additive adhesive layer on the back side, the opening on the back side in the plated through hole coaxially and the same diameter as the plated through hole, and
A multilayer printed wiring board characterized by comprising:   A part of the inner layer conductor circuit is routed to the bottom of the photo via hole, and the upper surface and the side surface of the routed inner layer conductor circuit are joined to the plating in the photo via hole hole. The multilayer printed wiring board according to claim 1. A step of forming an additive adhesive layer made of a photosensitive resin on the front surface side and the back surface side of the inner layer substrate on which the inner layer conductor circuit is formed;
Forming a concave portion for forming a photo via hole by photolithography at a planned through hole formation planned position of the additive adhesive layer on the surface side ;
By drilling from the inner layer substrate and the back side surface side of the additive adhesive layer wherein the recesses are formed, and forming a through-hole forming hole opened at the bottom of the recess,
Forming a plated through hole by depositing plating on the through-hole forming the hole,
A method for producing a multilayer printed wiring board, comprising:

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