JP4137279B2 - Printed wiring board and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a printed wiring board, a manufacturing method thereof, and a metal-clad laminate used at the time of manufacturing the printed wiring board.
[0002]
[Prior art]
The printed wiring board manufacturing method is roughly classified into a subtractive process and an additive process. The subtractive method is also called an etching method and is characterized by chemically corroding the surface copper foil of the copper clad laminate. Here, a method of manufacturing the printed wiring board (double-sided board) 41 by the subtractive method will be briefly described with reference to FIGS.
[0003]
First, a copper clad laminate 44 is prepared by sticking a copper foil 43 with a thickness of several tens of μm on both surfaces of the insulating base material 42. A through hole forming hole 45 is formed at a predetermined position of the copper clad laminate 44 by drilling or the like. When the drilling process is performed, smear is generated in the through-hole forming hole 45, so that the copper clad laminate 44 is treated with a desmear solution to dissolve and remove it. After the desmear process, a thin plating layer 47 is formed on the entire base layer 46 derived from the copper foil 43 and the inner wall surface of the through-hole forming hole 45 by electroless copper plating. After such a plating process, a mask 48 is formed on the thin plating layer 47. Then, a thick plating layer 50 is formed by electrolytic copper plating at a portion exposed from the opening 49 of the mask 48 (see FIG. 10). After such a plating step, the mask 48 is peeled off (see FIG. 11), and etching is performed with an etching resist formed on the thick plating layer 50 by solder plating or the like. By this etching, the thin plating layer 47 and the base layer 46 are removed, and the conductor patterns 52 are separated from each other. Then, when the etching resist is finally removed, a desired printed wiring board 41 is completed (see FIG. 12).
[0004]
[Problems to be solved by the invention]
However, such a method cannot accurately form a fine pattern having a good shape, and the bottom tends to be longer than the top in terms of etching characteristics, so that a so-called skirt-spreading conductor pattern 52 tends to be formed. Therefore, it is difficult to form a pattern of a portion (for example, a bonding pad portion) that requires finer and higher precision.
[0005]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing a printed wiring board and the like capable of forming a fine conductor pattern having a good shape.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, in the invention according to claim 1, in the method for manufacturing a printed wiring board including a plated through hole and a conductor pattern formed by a subtractive method, the thickness of both sides of the insulating substrate is 0. .A hole forming step for forming a hole for forming a through hole in a predetermined portion of a metal-clad laminate obtained by attaching a conductive metal foil of .5 μm to 7.0 μm, and dissolving a smear in the hole for forming a through hole. A desmear process of removing a desmear solution under conditions where the thickness of the conductive metal foil is reduced to 1/10 to 1/2 of the initial thickness, and a base layer derived from the conductive metal foil and the through A first plating step for forming a thin plating layer on the inner wall surface of the hole forming hole, and a mask is formed on the thin plating layer, and the portion exposed from the opening of the mask is thick. A second plating step for forming a plating layer, and etching after peeling the mask, thereby removing the thin plating layer and the underlying layer that were under the mask and separating the conductor patterns from each other The gist of the method for producing a printed wiring board is characterized by this.
[0007]
According to a second aspect of the present invention, in the first aspect, an electroless plating bath is used in the first plating step, and an electrolytic plating bath is used in the second plating step.
[0008]
In invention of Claim 3, in Claim 1, a sodium permanganate solution was used as said desmear liquid, and it was supposed that it processed for 5 to 20 minutes at 30 to 70 degreeC .
[0009]
According to a fourth aspect of the present invention, in any one of the first to third aspects, the conductor pattern dividing step by etching does not provide an etching resist on the thick plating layer formed by the second step. It was done in the state.
[0010]
According to a fifth aspect of the present invention, in the printed wiring board manufactured by the printed wiring board manufacturing method according to the first aspect , the conductor pattern has a thickness of 0.2 μm to 3. A metal underlayer of 0 μm, a thin plating layer of 0.5 μm to 2.5 μm formed on the metal base layer, and a thickness of 15 μm to 50 μm formed on the thin plating layer The gist of the present invention is a printed wiring board including a plating layer .
[0012]
Below, a description will be given of "action" in the present invention.
[0013]
According to invention of Claims 1-4, while the smear which generate | occur | produced at the time of a drilling process is melt | dissolved and removed by passing through a desmear process, electroconductive metal foil is also melted and removed at this time, and it becomes still thinner. Then, the thin plating layer is formed by the first plating step, and the thick plating layer is further formed by the second plating step, so that only the portion to be the conductor pattern later is selectively thickened. Thereafter, etching is performed to remove the thin plating layer and the underlying layer that were under the mask, thereby separating the conductor patterns. In the case of the present invention, since both the thin plating layer and the underlayer are thin, the thickness to be removed by etching in the conductor pattern cutting step is considerably small. Therefore, the conductor pattern formed by being divided is less likely to have a flared shape, and a fine pattern having a good shape can be accurately formed.
[0014]
According to the second aspect of the present invention, an electroless plating bath is used only when a plating layer is formed on the inner wall surface of the through-hole forming hole, and thereafter an inexpensive electroplating bath having a high plating deposition rate is used. Yes. For this reason, cost efficiency and productivity can be improved.
[0016]
According to the fourth aspect of the present invention, in the conductor pattern dividing step, the step of forming and removing the etching resist is not required. As a result, the man-hour is reduced and the productivity is improved. In addition, the thickness of the thick plating layer removed by the etching at this time is extremely small, and the pattern formation accuracy and the like are not particularly adversely affected.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a printed wiring board 1 according to an embodiment of the present invention and a method for manufacturing the same will be described in detail with reference to FIGS.
[0018]
As shown in FIG. 7, the printed wiring board 1 according to the present embodiment is a so-called double-sided board in which the conductor pattern 2 and the plated through hole 3 formed by the subtractive method are provided on the front and back of the insulating base 4. That is, this printed wiring board 1 has two conductor layers. As the insulating base material 4, for example, a glass cloth base material impregnated with an epoxy resin, a polyimide resin, a BT (bismaleimide triazine) resin or the like is used. In this embodiment, a base material (so-called glass epoxy base material) impregnated with a relatively inexpensive epoxy resin is selected. The insulating base 4 is derived from a copper-clad laminate 5 as a metal-clad laminate.
[0019]
The conductor pattern 2 formed on the front and back of the insulating base 4 includes a copper base layer 6 as a base layer having a thickness of 0.2 μm to 3.0 μm, and a thin copper plating layer 7 formed on the copper base layer 6. And a thick copper plating layer 8 formed on the thin copper plating layer 7. That is, the conductor pattern 2 has a three-layer structure. The copper underlayer 6 is derived from an ultrathin copper foil 9 that is an ultrathin conductive metal foil. Here, the space between the adjacent conductor patterns 2 is set to about 35 μm, and the line width (the width of the top portion) of the conductor pattern 2 is set to about 70 μm.
[0020]
The conductor patterns 2 formed on the front and back surfaces of the insulating base material 4 are electrically connected through a plated through hole 3 formed so as to penetrate the insulating base material 4. The conductor layer in the plated through hole 3 includes a thin copper plating layer 7 formed on the inner wall surface of the through hole forming hole 10 and a thick copper plating layer 8 formed on the thin copper plating layer 7. Become. That is, the conductor layer in the plated through hole 3 has a two-layer structure. The land 3a of the plated through hole 3 has the same structure as the conductor pattern 2, that is, a three-layer structure.
[0021]
Next, a procedure for manufacturing the printed wiring board 1 of the present embodiment will be described.
First, a copper clad laminate 5 as a metal clad laminate is prepared. As shown in FIG. 1, ultrathin copper foils 9 are attached to both surfaces of the insulating base 4 of the copper clad laminate 5. Specifically, the thickness of the copper foil 9 is preferably 0.5 μm to 7.0 μm, and particularly preferably 1.0 μm to 3.0 μm. If the copper foil 9 is made too thin, the handleability of the foil itself becomes poor and the bonding work becomes difficult. On the contrary, if the copper foil 9 becomes too thick, the thickness to be removed by etching in the conductor pattern cutting step described later cannot be sufficiently reduced. Therefore, here, a copper foil 9 having a thickness of 3.0 μm (an electrolytic copper foil having a purity of 99.8% or more) is used.
[0022]
As the metal foil other than the copper foil 9, for example, aluminum foil, tin foil, gold foil, silver foil, platinum foil, nickel foil or the like can be used. However, considering that it is inexpensive and has excellent etching properties, it is preferable to select the copper foil 9 as in this embodiment.
[0023]
In the subsequent drilling step, a through-hole forming hole 10 having a diameter of 0.1 mm to 0.2 μm is formed by drilling in a predetermined portion of the prepared copper-clad laminate 5 (see FIG. 2). When it is desired to form the through-hole forming hole 10 having a smaller diameter, laser processing may be performed instead of drilling.
[0024]
When such a drilling process is performed, smear is generated in the through-hole forming hole 10 due to heat generation. Therefore, the copper clad laminate 5 is treated with a desmear solution to dissolve and remove the generated smear. Note that desmear treatment can also be performed by a plasma method.
[0025]
In the desmear process, the desmear liquid is applied under conditions such that the ultrathin copper foil 9 does not disappear, specifically, under conditions such that the thickness of the copper foil 9 is reduced to 1/10 to 1/2 of the original thickness. It is good to process. In this case, a solution of sulfuric acid, chromic acid, alkaline permanganate or the like is used as the desmear liquid. In the present embodiment, a sodium permanganate solution having a low oxidizing power was treated at 30 ° C. to 70 ° C. for 5 minutes to 20 minutes. By such desmear treatment, smear was almost completely removed, and the thickness of the copper foil 9 was reduced to about 1/3 of the original thickness. As a result, as shown in FIG. 2, an underlayer 6 having a thickness of about 1.0 μm derived from the ultrathin copper foil 9 was formed. The thickness of the underlayer 6 is preferably in the range of 0.2 μm to 3.0 μm.
[0026]
After the desmear process, a catalyst nucleus is applied for depositing plating on the inner wall surface of the through-hole forming hole 10, and the catalyst nucleus is further activated. For imparting the catalyst nucleus, noble metal ions, noble metal colloids and the like are used, and generally palladium chloride, palladium colloids and the like are used.
[0027]
After applying the catalyst nucleus and its activation treatment, a thin copper plating layer 7 is then formed by electroless copper plating on the entire surface of the underlayer 6 and the inner wall surface of the through hole forming hole 10 (see FIG. 3). ).
[0028]
In the first plating step, an electroless copper plating bath which is a kind of electroless plating bath is used, and a thin copper plating layer 7 having a thickness of 0.5 μm to 2.5 μm is formed using the same. In the present embodiment, the thickness of the layer 7 is set to about 1.0 μm. If the layer 7 is too thin, there is a possibility that the electrolytic plating cannot be reliably deposited on the entire inner wall surface of the through-hole forming hole 10 in the subsequent plating step. Accordingly, there is a possibility that conduction failure of the plated through hole 3 may be caused and the reliability cannot be sufficiently improved. On the other hand, if the layer 7 is formed too thick, the productivity may be reduced and the cost may be increased, and the thickness to be removed by etching in the conductor pattern cutting step may not be sufficiently reduced. .
[0029]
After the first plating step, a predetermined mask 11 serving as a plating resist is then formed on the thin copper plating layer 7. In this case, the mask 11 is preferably formed using a commercially available dry film photoresist. This is because the use of a photosensitive material contributes to the improvement of pattern formation accuracy. Then, after laminating such a dry film photoresist, exposure and development are performed according to a conventional method. As a result, as shown in FIG. 4, a mask 11 having a thickness of 35 μm having an opening 12 at a predetermined location is formed.
[0030]
After the mask formation step, a thick copper plating layer 8 is formed in a portion exposed from the opening 12 using an electrolytic copper plating bath which is a kind of electrolytic plating (see FIG. 5). When such a thick copper plating layer 8 is formed, only the portion that will later become the conductor pattern 2 is selectively thickened. In this embodiment, a copper sulfate plating bath is used as the electrolytic copper plating bath. As a result of the second plating, a thick copper plating layer 8 having a thickness of about 15 μm to 50 μm is formed on the thin copper plating layer 7 located at the exposed portion. If the same layer 8 is made too thin, the thickness of the finally obtained conductor pattern 2 cannot be secured sufficiently. On the other hand, if the same layer 8 is made too thick, there is a risk that productivity will be reduced and costs will be increased. In the present embodiment, the thickness of the thick copper plating layer 8 is set to about 20 μm.
[0031]
After the second plating step, the mask 11 that is no longer needed is peeled off, and the thin copper plating layer 7 located thereunder is exposed (see FIG. 6). Then, an etching process is performed using an etchant that can dissolve copper, and the thin copper plating layer 7 and the copper underlayer 6 are completely removed. Here, since the processing is carried out without particularly providing an etching resist on the thick copper plating layer 8, the surface layer of the thick copper plating layer 8 is also etched by about 2 μm. And through the above process, the conductor patterns 2 were parted and the printed wiring board 1 of FIG. 7 was completed.
[0032]
Therefore, according to the present embodiment, the following effects can be obtained.
(1) In the manufacturing method of the present embodiment, the thin copper plating layer 7 and the copper underlayer 6 are both formed extremely thin. For this reason, the thickness to be removed by etching in the conductor pattern cutting step is about 2 μm, which is considerably smaller than the conventional one. Therefore, the conductor pattern 2 formed by being divided in the same process is less likely to have a flared shape, and a fine pattern having a good shape can be accurately formed.
[0033]
(2) In this embodiment, the printed wiring board 1 is manufactured by using an electroless copper plating bath in the first plating step and using an electrolytic copper plating bath in the second plating step. In other words, an electroless copper plating bath is used only when plating is deposited on the inner wall surface of the through-hole forming hole 10, and thereafter, an electrolytic copper plating bath that is extremely inexpensive and has a high plating deposition rate is used. For this reason, cost efficiency and productivity can be improved further.
[0034]
Moreover, since the very thin thin copper plating layer 7 is formed, the thickness to be removed by etching in the conductor pattern cutting step is also extremely reduced. Therefore, the selection of these plating baths surely contributes to the formation of a fine pattern having a good shape more accurately.
[0035]
(3) The conductor pattern dividing step in the present embodiment is performed by etching without providing an etching resist on the thick copper plating layer 8. Therefore, the step of forming and removing the etching resist in this step is basically unnecessary. As a result, the total man-hour is reduced and the productivity can be further improved. Further, the thickness of the thick copper plating layer 8 that is removed along with the etching at this time is as very small as about 2 μm. Therefore, even if the etching is performed, the pattern formation accuracy and cost are not particularly adversely affected.
[0036]
(4) A printed wiring board 1 obtained through the above manufacturing method includes a copper underlayer 6 having a thickness of about 1.0 μm derived from the copper foil 9, a thin copper plating layer 7 having a thickness of about 1.0 μm, A conductor pattern 2 composed of a thick copper plating layer 8 having a thickness of 20 μm is provided. Moreover, the metal which forms these three layers is the same kind (namely, copper). Such a conductor pattern 2 has an advantage that a sufficient thickness, shape, conductivity and the like as a conductive portion are ensured and high connection reliability is also ensured.
[0037]
(5) In the present embodiment, the printed wiring board 1 is manufactured using the copper-clad laminate 5 in which the copper foil 9 having a thickness of 0.5 μm to 7.0 μm is adhered to both surfaces of the insulating substrate 4. Is going. When such a copper-clad laminate 5 is used, smear can be removed almost completely by a soft desmear process, and a copper underlayer 6 having a suitable thickness can be easily and reliably formed. . Therefore, it can be said that this copper-clad laminate 5 is a very suitable material for obtaining an excellent printed wiring board 1 by the above manufacturing method.
[0038]
In addition, you may change embodiment of this invention as follows.
The present invention is not limited to the double-sided board as in the embodiment. For example, the multilayer printed wiring board 21 as another example shown in FIG. 8 may be produced using the printed wiring board 1 of the embodiment as a core substrate. Moreover, you may produce the buildup multilayer printed wiring board 31 like another example shown by FIG. 9 using the printed wiring board 1 as a base substrate.
[0039]
-The printed wiring board 1 is manufactured using various metal-clad laminates to which aluminum foil, tin foil, gold foil, silver foil, platinum foil, nickel foil or the like is attached other than the copper-clad laminate 5. Is also possible.
[0040]
-It may replace with the wet method as described in embodiment, and may perform the desmear process by the dry process represented by the plasma method etc., for example.
-In the first plating step, by using an electroless plating bath other than the electroless copper plating bath, for example, an electroless solder plating layer, an electroless gold plating layer, an electroless palladium plating layer, etc. may be formed thinly Good.
[0041]
In the second plating step, by using an electrolytic plating bath other than the electrolytic copper plating bath, for example, an electroless nickel plating layer, an electroless chromium plating layer, an electroless gold plating layer, or the like may be formed thickly.
[0042]
The thin electroless plating layer, the thick electroplating layer, and the underlayer do not necessarily have to be made of the same kind of metal as in the embodiment, and may be made of a combination of different kinds of metals.
[0043]
Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiments are listed below together with the effects as necessary. (1) In a printed wiring board provided with a conductor pattern (formed by, for example, a subtractive method), the conductor pattern is derived from a copper foil having a thickness of 0.5 μm to 7.0 μm attached to an insulating substrate. A copper base layer having a thickness of 0.2 μm to 2.5 μm, a thin electroless copper plating layer having a thickness of 0.2 μm to 2.5 μm formed on the copper base layer, and the thin electroless copper A printed wiring board comprising: a thick electrolytic copper plating layer having a thickness of 8.0 μm or more formed on a plating layer. Therefore, according to the invention described in the technical idea 1, it is possible to provide a printed wiring board that is extremely excellent in reliability, cost, and pattern formation accuracy and is wired with high density.
[0044]
(2) A multilayer printed wiring board using the printed wiring board according to any one of claims 5 and 1 as a core substrate. Therefore, according to the invention described in this technical idea 2, it is possible to provide a printed wiring board having excellent reliability, cost, pattern formation accuracy, and high functionality and high density.
[0045]
(3) A build-up multilayer printed wiring board using the printed wiring board according to claim 5 as a base substrate. Therefore, according to the invention described in the technical idea 3, it is possible to provide a printed wiring board having high reliability and cost, excellent pattern formation accuracy, and high functionality and high density.
[0046]
(4) A copper-clad laminate obtained by sticking a copper foil having a thickness of 0.5 μm to 7.0 μm on both surfaces of an insulating substrate. Therefore, according to the invention described in the technical idea 4, a material suitable for obtaining an excellent printed wiring board by performing the above manufacturing method can be provided.
[0047]
(5) A copper-clad laminate obtained by adhering a 1.0 to 3.0 μm thick copper foil to both surfaces of a glass cloth substrate impregnated with an epoxy resin, a polyimide resin or a BT resin. Therefore, according to the invention described in this technical idea 5, a material suitable for obtaining an excellent printed wiring board by carrying out the above manufacturing method can be provided.
[0050]
(8) In a printed wiring board including a conductor pattern formed by a subtractive method, the conductor pattern has a thickness of 0.2 μm to 2.m derived from an extremely thin conductive metal foil attached to an insulating base material. A printed wiring board comprising a 0 μm foundation layer and a plating layer formed on the foundation layer.
[0051]
(9) In a printed wiring board including a conductor pattern formed by a subtractive method, the conductor pattern has a thickness derived from a conductive metal foil having a thickness of 0.5 μm to 5.0 μm attached to an insulating substrate. A thickness of 0.2 μm to 2.0 μm, a thin plating layer formed on the base layer, and a thick plating layer formed on the thin plating layer. Printed wiring board characterized by
[0052]
【The invention's effect】
As described in detail above, according to the inventions described in claims 1 to 4, it is possible to provide a method for manufacturing a printed wiring board capable of forming a fine conductor pattern having a good shape.
[0053]
According to the second aspect of the present invention, cost and productivity can be improved .
[0054]
According to the invention described in claim 4, the productivity can be further improved by reducing the man-hours.
According to the invention described in claim 5, it is possible to provide a printed wiring board excellent in reliability, cost, and pattern formation accuracy.
[Brief description of the drawings]
FIG. 1 is a partial schematic cross-sectional view of a copper-clad laminate used for manufacturing a printed wiring board according to an embodiment of the present invention.
FIG. 2 is a partial schematic cross-sectional view for explaining a manufacturing procedure of the printed wiring board according to the embodiment.
FIG. 3 is a partial schematic cross-sectional view for explaining a manufacturing procedure of the printed wiring board.
FIG. 4 is a partial schematic cross-sectional view for explaining a manufacturing procedure of the printed wiring board.
FIG. 5 is a partial schematic cross-sectional view for explaining a manufacturing procedure of the printed wiring board.
FIG. 6 is a partial schematic cross-sectional view for explaining a manufacturing procedure of the printed wiring board.
FIG. 7 is a partial schematic cross-sectional view of the printed wiring board.
FIG. 8 is a partial schematic cross-sectional view of another example of a multilayer printed wiring board.
FIG. 9 is a partial schematic cross-sectional view of another example of a build-up multilayer printed wiring board.
FIG. 10 is a partial schematic cross-sectional view for explaining a conventional printed wiring board manufacturing procedure.
FIG. 11 is a partial schematic cross-sectional view for explaining a conventional printed wiring board manufacturing procedure.
FIG. 12 is a partial schematic cross-sectional view of a conventional printed wiring board.
[Explanation of symbols]
Reference numerals 1, 21, 31 ... printed wiring board, 2 ... conductor pattern, 3 ... plated through hole, 4 ... insulating substrate, 5 ... copper-clad laminate as metal-clad laminate, 6 ... copper underlayer as underlayer, DESCRIPTION OF SYMBOLS 7 ... Thin copper plating layer as a thin plating layer, 8 ... Thick copper plating layer as a thick plating layer, 9 ... Copper foil as conductive metal foil, 10 ... Through-hole formation hole, 11 ... Mask , 12 ... opening.

Claims (5)

In a manufacturing method of a printed wiring board provided with a plated through hole and a conductor pattern formed by a subtractive method,
A step of forming a through-hole forming hole in a predetermined portion of a metal-clad laminate obtained by sticking a conductive metal foil having a thickness of 0.5 μm to 7.0 μm on both surfaces of an insulating substrate;
A desmear process for dissolving and removing smear in the through-hole forming hole and treating the desmear liquid under a condition in which the thickness of the conductive metal foil is reduced to 1/10 to 1/2 of the original ,
A first plating step of forming a thin plating layer on the base layer derived from the conductive metal foil and the inner wall surface of the through-hole forming hole;
A second plating step of forming a mask on the thin plating layer and forming a thick plating layer in a portion exposed from the opening of the mask;
A method of manufacturing a printed wiring board, wherein the conductive pattern is separated by removing the thin plating layer and the underlying layer under the mask by etching after peeling the mask.   The method for manufacturing a printed wiring board according to claim 1, wherein an electroless plating bath is used in the first plating step, and an electrolytic plating bath is used in the second plating step. The method for producing a printed wiring board according to claim 1, wherein a sodium permanganate solution is used as the desmear liquid, and the desmear liquid is treated at 30 ° C. to 70 ° C. for 5 minutes to 20 minutes .   4. The method according to claim 1, wherein the conductor pattern dividing step by the etching is performed in a state where no etching resist is provided on the thick plating layer formed by the second plating step. 5. The manufacturing method of the printed wiring board of description. The printed wiring board manufactured with the manufacturing method of the printed wiring board of Claim 1 WHEREIN: The said conductor pattern is a metal base layer with a thickness of 0.2 micrometer-3.0 micrometers provided in the insulating base material, and the said metal A thin plating layer having a thickness of 0.5 μm to 2.5 μm formed on the base layer and a thick plating layer having a thickness of 15 μm to 50 μm formed on the thin plating layer. A printed wiring board characterized by comprising:

Images