JP2007281336A - Method of manufacturing double sided printed wiring board and multilayer printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve both a problem of unintended mask film exfoliation due to desmear processing and a problem of binding agent and adhesive residues on a conductor after printing in the case of manufacturing a double-sided printed CCL wiring board. <P>SOLUTION: In the case of manufacturing the double sided printed wiring board 30 wherein conductive paste for inter-layer conduction are filled in via-holes, when the mask film 14 is directly adhered to one side of a conductor layer 12 of a double sided board 10 with conductor layers 12, 13 whose circuits on both sides are not formed yet, and the via-holes 17, 18 are formed by using the mask film 14 for a print mask, an opening 16 whose diameter is greater than the diameter of the via-hole is opened to the mask film 14 by laser emission, the conductive paste 31 is filled into the via-holes 17, 18, and thereafter the filled conductive paste 31 is cured by thermal press curing and then the circuit for the conductor layers 12, 13 is formed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a double-sided printed wiring board having a structure for obtaining interlayer conduction by filling a via hole with a conductive paste, and a multilayer printed wiring board including the double-sided printed wiring board manufactured by the manufacturing method.

  2. Description of the Related Art In recent years, finer, higher density, and multi-layered wiring of printed wiring boards has been progressing along with reductions in size and size of electronic devices, miniaturization of semiconductor chips and components, and narrowing of terminal pitch. The characteristics required for a multilayer printed wiring board are required to be thin and to have high reliability of electrical connection between layers.

  Technologies for achieving inter-layer conduction using plating include through-hole (TH) plating that drills through holes in a substrate with a drill or the like, and lasers that drill holes in a surface layer with a laser and plate in the corresponding areas A via hole (LVH) is known, but the process is complicated and the number of steps is large, which is disadvantageous in terms of cost. Further, since the conductor thickness is increased by plating, there are disadvantages such as an increase in the total thickness of the substrate and a circuit step. Furthermore, since it is impossible in principle to arrange a wiring circuit in the TH peripheral portion or LVH peripheral portion, it is disadvantageous for finer wiring.

In recent years, a multilayer substrate using a conductive paste has been proposed as an interlayer connection method instead of plating. For example, it is known as a trade name such as ALIVH (Any Layer Intermediary Via Hole) of Matsushita Electric Industrial Co., Ltd. and B ² it (Buried Bump Interconnection Technology) of Toshiba Corporation.
In ALIVH, as shown in FIG. 7, the insulating resin plate 101 is used as a starting material (see FIG. 7A), and the printing mask films 102 and 102 are pasted on both sides thereof (see FIG. 7B). The hole 103 is opened (see FIG. 7C), and the conductive paste 104 is filled into the through hole 103 by a printing method (see FIG. 7D). And after peeling off the mask films 102 and 102 for printing (refer FIG.7 (e)), the copper foils 105 and 105 are crimped | bonded to the front and back of the insulating resin board 101 (refer FIG.7 (f)), and a circuit pattern ( After the formation (not shown), a plurality of wiring boards are bonded together to obtain a multilayer wiring board.

  In Patent Document 1 (conductive paste-filled substrate and manufacturing method thereof), a blind via is formed by laser processing on a single-sided CCL having a heat-adhesive layer on the surface of an insulating layer, and the metal is filled with the conductive paste. A foil is laminated on the heat-adhesive layer by heating and pressing, and a circuit is formed to obtain a double-sided substrate filled with conductive paste (see paragraphs 0046 to 0048 of Patent Document 1). However, this method uses single-sided CCL as a starting material, and cannot be applied to double-sided CCL. In addition, since the substrate is thickened by the amount of the heat-adhesive layer for attaching the metal foil, it is disadvantageous for thinning, and there is a problem that the number of steps increases due to the attachment of the metal foil.

In patent document 2 (manufacturing method of a composite multilayer wiring board), in a manufacturing method of a multilayer board in which via holes are filled with a conductive paste for interlayer conduction, a mask for printing is formed on one side after forming a double-sided CCL circuit pattern. A technique of attaching a resin film with an adhesive is used. According to this method, in the desmear treatment step after via formation by laser, there is a problem that the mask film peels off when the adhesive force of the mask film is insufficient or the circuit filling property is insufficient. Furthermore, if the mask film is peeled off after printing, the adhesive 205 of the mask film (indicated by a two-dot chain line in FIG. 8 (a)) remains on the conductor surface, resulting in lack of adhesion. There is a problem that the contact between the protrusion of the conductive paste 204 and the land conductor 202 becomes incomplete (see FIG. 8C), and the reliability of electrical connection is lost.
In FIG. 8, reference numeral 201 is a polyimide layer, 202 and 203 are copper foils (conductors), 204 is a conductive paste, and 205 is the remaining adhesive.

  In Patent Document 3 (circuit board connecting material and multilayer circuit board manufacturing method using the same), a release film is provided on both sides of an organic porous base material, through holes are formed at desired positions, and a printing method is provided on this. After embedding a conductive paste, copper foil is bonded from both sides to obtain interlayer conduction. According to this construction method, there is a problem that the starting material is limited to a hard material such as a prepreg having high rigidity. Furthermore, since it has the process of bonding copper foil after printing, there are many man-hours and it is disadvantageous also in terms of cost.

  In Patent Document 4 (manufacturing method of multilayer printed wiring board), a through hole for connection is provided at a predetermined position of a single-sided board on which a circuit pattern is formed, and the hole is filled and embedded with a conductive composition, A multilayer substrate is manufactured by aligning and laminating insulator layers filled and embedded with a conductive composition. However, this method is limited in principle to application to a single-sided plate and cannot be applied to a double-sided plate.

  In addition, as a generally known technique, there is a method of filling a via hole with a conductive paste using a screen mask or a metal mask as a printing mask. However, since these printing masks generally have a thick substrate, the protrusions of the conductive paste formed after the mask is peeled off become thick, which hinders thinning and surface smoothness of the multilayer substrate. There is. In addition, a printing mask having a thin base material is expensive.

  Generally, polyimide used as a base material for FPC (Flexible Printed Circuit) is known for its high water absorption. That is, the material has a dimensional change of the substrate depending on the degree of water absorption or temperature change. When the substrate undergoes a dimensional change, it becomes difficult to align the position of the mask hole and the via hole, and the position accuracy during printing is lowered. That is, a method that can cope with a change in the dimensions of the substrate is preferable.

  As described above, in the technique of obtaining the interlayer conduction by filling the via hole or the through hole with the conductive paste, the conventional technology uses the RPC insulating resin base material or the FPC single-sided CCL as the starting material, and the FPC double-sided CCL as the starting material. There is hardly any mention of the material. When the double-sided CCL of the FPC is used as a starting material, the mask film is pasted on the circuit pattern surface according to the prior art, so the circuit fillability of the mask film (the adhesive fills the unevenness and steps of the circuit) If the degree) is insufficient, there arises a problem that the mask peels off in the plasma desmear process starting from this. Further, the conductor land is heated by the laser processing, and the adhesive of the mask film in contact with the conductor land is cured, resulting in a defect that it remains as a smear.

As described above, there is no method for solving both mask peeling by desmear treatment and residual adhesive smear in the method of obtaining interlayer conduction by filling a via hole with a conductive paste. Furthermore, after printing the conductive paste, there is no technique in the prior art that peels off the mask film adhesive and adhesive so as not to remain on the conductor.
JP-A-2005-116660 JP 2004-055577 A Japanese Patent Application Laid-Open No. 07-147464 Japanese Patent Laid-Open No. 06-252551

  The present invention has been made in view of the above circumstances, and is not intended by desmear processing when a double-sided printed wiring board in which a via hole is filled with a conductive paste for interlayer conduction is manufactured using double-sided CCL as a starting material. It is an object of the present invention to provide a method for solving both the peeling of the mask film and the residue of the adhesive and the sticky substance on the conductor after printing.

In order to solve the above problems, the present invention provides a method for manufacturing a double-sided printed wiring board in which via holes are filled with a conductive paste for interlayer conduction, and a double-sided board having a conductor layer in which circuits on both sides are not formed. When a mask film is directly attached to one side of the conductor layer and a via hole is formed using the mask film as a printing mask, an opening having an opening diameter larger than the via diameter is opened by laser irradiation on the mask film, and the via hole is electrically conductive. Provided is a method for producing a double-sided printed wiring board, wherein after filling with a conductive paste, the filled conductive paste is cured by hot press curing, and then the circuit of the conductor layer is formed.
Moreover, this invention provides the multilayer printed wiring board characterized by including the double-sided printed wiring board manufactured with the manufacturing method of the above-mentioned double-sided printed wiring board.

  In the present invention, since the double-sided substrate having the conductor layers on both sides is used as the starting material, there is no need for the step of attaching the second conductor layer to the insulating base material as in the case of using the single-sided substrate as the starting material, and fewer steps. A double-sided printed wiring board can be manufactured by a number. Moreover, the material of the insulating base material is not limited to a hard material such as a prepreg, and a flexible material can be applied, and the material can be selected from a wide range of options.

By directly attaching the mask film to one side of the conductor layer of the double-sided board having a conductor layer in which circuits on both sides are not formed, the surface of the work is uniform and there are no in-plane variations, irregularities, or steps. For this reason, the mask film adheres well to the surface of the double-sided substrate that is the starting material, and unintended mask peeling due to desmear treatment can be prevented.
In addition, since a conductor layer (metal layer such as copper foil) with high thermal conductivity is present in the entire surface of the workpiece, the periphery of the via is used during laser processing for mask film opening and via hole formation. Heat can be quickly diffused, and curing of the mask film adhesive due to local temperature rise can be avoided. For this reason, after the mask film is used up, it can be surely peeled without the adhesive remaining, and in principle no defect due to the adhesive remaining after printing occurs.
Also, when forming a via hole using the mask film as a printing mask, an opening having an opening diameter larger than the via diameter is opened in the mask film. The paste adheres to the portion of the conductor layer exposed at the opening. As a result, the conduction between the conductive layer on the printing surface side where the mask film is attached and the conductive paste can be made more reliable.
Furthermore, since the conductive paste filled in the via is cured by hot press cure and then the circuit formation of the conductor layer is performed, the shape of the protruding portion of the conductive paste does not collapse during circuit formation. When the substrates are laminated, the paste protrusions can be used to ensure electrical continuity with the circuit on the other substrate side.

The present invention will be described below with reference to the drawings based on the best mode.
1A to 1G are cross-sectional views illustrating an example of a method of forming a via hole in a double-sided substrate in the present invention in the order of steps. 2A to 2D are cross-sectional views illustrating an example of a method for printing and filling a conductive paste in a via hole in the present invention in the order of steps. 3A to 3F are cross-sectional views illustrating an example of a method for producing a single-sided substrate used for a multilayer printed wiring board in the order of steps. 4A to 4B are cross-sectional views for explaining an example of a method for producing a multilayer printed wiring board by laminating the double-sided board produced in FIG. 2 and the single-sided board produced in FIG.

<Manufacturing process of double-sided printed wiring board 30>
(1) Mask Laminate Prepare a double-sided CCL (CCL: Copper-Cladded Laminate) 10 having copper foils 12 and 13 on both sides of the insulating base 11 as shown in FIG. A mask film 14 is bonded to the printing surface (L2 surface) of the double-sided CCL 10 as shown in FIG. An example of a method for laminating the mask film 14 is a vacuum laminator.
In the present invention, by directly attaching the mask film 14 to the copper foil 12 on which the circuit of the double-sided substrate 10 is not formed, the mask film 14 is applied to a workpiece having a uniform in-plane and no in-plane variation, irregularities, or steps. Since it will be affixed, the mask film 14 is satisfactorily laminated to the workpiece, and unintended mask peeling of the mask film 14 can be prevented.

(2) Opening of Vias Vias 20 and exposure guide holes 15 of the L2 / L3 double-sided substrate 10 are opened as shown in FIGS. The method for opening these holes is not particularly limited, and examples thereof include laser processing such as CO ₂ laser and YAG laser, and machining such as NC drill.
Recently, with the development of laser technology, it is possible to perform direct laser processing that directly opens a via using a CO ₂ laser, a YAG laser, or the like. The via 20 may be opened using this technology. According to this technique, the number of man-hours can be reduced as compared with the method of opening the copper foil portion by etching.
In the case of the present invention, a conductor layer having a high thermal conductivity (copper foil 12 in this embodiment) is present throughout the surface of the workpiece, and therefore the opening 16 of the mask film 14 and the via holes 17 and 18 of the substrate 10. When the film is opened by laser irradiation, ambient heat can be quickly diffused, and curing of the adhesive of the mask film 14 due to local temperature rise can be avoided. For this reason, the mask film 14 after printing can be smoothly peeled without an adhesive remaining.

First, as shown in FIG. 1C, an exposure guide hole 15 is opened on the double-sided CCL 10 using laser processing, an NC drill, or the like. Next, as shown in FIG.1 (d), the opening part 16 is opened to the mask film 14 by laser irradiation. Next, as shown in FIGS. 1E and 1F, the via portion 17 of the copper foil 12 on the L2 surface and the via portion 18 of the insulating base material 11 are opened by laser processing or the like. Finally, in order to ensure the filling property of the conductive paste, as shown in FIG. 1G, a small hole 19 for venting air is formed in the copper foil 13 on the L3 surface.
Here, the opening diameter of the opening 16 of the mask film 14 is formed larger than the via diameter (the diameter of the via portions 17 and 18). As a result, the exposed portion 21 is formed in the copper foil 12 around the via portions 17 and 18, so that the conductive paste 31 is applied to the mask film when the conductive paste 31 is filled (see FIG. 3, details will be described later). 14, the conductive paste 31 adheres to the copper foil 12 of the exposed portion 21. As a result, the conduction between the conductive paste 31 and the copper foil 12 on the L2 surface can be made more reliable.

(3) Desmear After the via 20 is opened, the resin smear generated during via processing is removed (desmear). The desmear method is not particularly limited, and examples thereof include plasma desmear treatment.

(4) Conductive Paste Printing As shown in FIG. 2A, the conductive paste 31 is printed from the surface of the mask film 14 and filled into the via 20, and the vias 20 of the double-sided CCL 10 and the openings 16 of the mask film 14 are formed. Embed in. After the filling, as shown in FIG. 2B, the mask film 14 is peeled off from the surface of the copper foil 12 of the double-sided board. Thereby, the conductive paste protrusion 32 is formed so that the conductive paste 31 fills the via 20 and protrudes from the copper foil 12.
In the present invention, there is no circuit level difference on the surface of the copper foil 12 on which the mask film 14 is laminated by heat during laser processing, and the adhesive of the mask film 14 is not cured. The adhesive or sticky material of the mask film 14 does not remain on the 12th surface.

(5) Press cure As shown in FIG.2 (c), in order to harden the printed conductive paste 31, a hot press cure is performed. Since the filling with a paste is insufficient for curing by an oven, a hot press cure is preferable. By completely curing the conductive paste 31 before circuit formation, the filling property of the conductive paste 31 is improved. Further, the cured paste protrusion 32A can maintain the shape during circuit formation and does not peel off from the copper foil 12.

(6) Circuit formation As shown in FIG. 2 (d), the circuit formation of the copper foils 12 and 13 on both surfaces of the double-sided substrate 30 is performed to form the second layer circuit L2 and the third layer circuit L3. The circuits L2 and L3 on both sides are made conductive by a paste via 33 made of a conductive paste 31 filled in the via.

The double-sided board 30 manufactured by the above process has no adhesive or sticky residue on the surface of the copper foil 12, so that the resistance value of the interlayer connection by the paste via 33 is low, and the reliability of the characteristics is high. . The double-sided board 30 can be used as a double-sided printed wiring board by providing circuit protection means such as a cover lay or a cover coat as necessary.
It can also be used to produce a multilayer substrate by laminating two or more double-sided substrates 30 together.
It can also be used to produce a multilayer substrate by laminating one or more double-sided substrates 30 and a single-sided substrate 40. In this case, the single-sided substrate 40 can be manufactured by, for example, a process exemplified below.

<Manufacturing process of single-sided substrate 40>
(1) As shown to Fig.3 (a), the single-sided CCL which has the copper foil 42 is prepared for the single side | surface of the insulation base material 41, the copper foil 42 of this single-sided CCL is circuit-formed, FIG.3 (b) As shown in FIG. 3C, the first layer circuit L1 is formed (2). As shown in FIG. 3C, the interlayer adhesive 43 is laminated on the surface of the insulating substrate 41 of the single-sided CCL, and the laminated interlayer adhesive 43 is further laminated. A mask film 44 is laminated as a printing mask.

(3) As shown in FIG. 3 (d), a via (through hole) 45 is drilled on one side CCL with a YAG laser or the like. Here, the mask film 44, the interlayer adhesive 43, and the insulating base material 41 are opened using a YAG laser or the like from the mask film 44 surface side. A small hole 46 having a diameter smaller than that of the through hole 45 is formed in the copper foil 42 on the L1 surface so that air is removed when the paste is filled.
(5) The resin smear generated in the via opening process is removed by plasma desmear or the like.
(6) As shown in FIG. 3E, the conductive paste 47 is printed from the mask film 44 surface side and filled into the via 45.
(6) After printing, as shown in FIG. 3 (f), when the mask film 44 is peeled off, a paste protrusion 48 is formed so that the conductive paste 47 filled in the via 45 protrudes from the surface of the interlayer adhesive 43. The
Thus, the outer substrate 40 having the paste via 49 filled with the conductive paste 47 is produced.

<Lamination process>
The double-sided substrate 30 and the single-sided substrate 40 manufactured as described above are aligned with each other as shown in FIG. 4 (a), bonded together, and subjected to a hot press process, and as shown in FIG. A layer FPC multilayer substrate 50 is completed.

  In the above embodiment, a double-sided CCL is used as a starting material, and a mask film is pasted on a copper foil with no circuit formed thereon to form a via hole and fill the via hole with a conductive paste. The double-sided printed wiring board can be manufactured with a smaller number of steps, without the step of attaching the second copper foil to the insulating base as in In addition, since the surface of the work to which the mask is applied is uniform and there are no in-plane variations, irregularities, or steps, unintended mask peeling can be prevented.

  Because copper foil with high thermal conductivity exists throughout the surface of the workpiece, the heat around the via can be quickly diffused through the copper foil (conductor metal layer) during laser processing for via hole formation, Curing of the mask film adhesive due to local temperature rise can be avoided. For this reason, after the mask film is used up, it can be surely peeled without the adhesive remaining, and in principle no defect due to the adhesive remaining after printing occurs.

In the above example, a three-layer FPC multilayer substrate having a circuit of one layer (L1) on the outer layer substrate and two layers (L2, L3) on the inner layer substrate has been shown, but the present invention does not depart from the gist thereof. Various modifications can be made within the range, and the circuit, substrate material, number of layers, etc. are not limited.
In this embodiment, the insulating base material of the double-sided substrate is not limited to a hard material such as a prepreg, and a flexible material can be applied, and the material can be selected from a wide range of options. it can.

  Hereinafter, the present invention will be specifically described with reference to examples. In addition, this invention is not limited only to these Examples.

[Application example of multilayer printed wiring board as core double-sided board]
[Example 1]
A three-layer FPC multilayer substrate having a structure in which a double-sided substrate is manufactured by the process of the present invention and a single-sided substrate is bonded to one surface of the double-sided substrate by the following materials and manufacturing steps (see FIGS. 1 to 4). Was made.

<Materials used>
-CCL for L1: single-sided CCL, copper foil thickness 12 μm, polyimide thickness 25 μm
・ CCL for L2 / L3: Double-sided CCL, copper foil thickness 12μm, polyimide thickness 25μm
・ Mask film: Adhesive thickness 15μm, PET thickness 12μm
・ Interlayer adhesive: Adhesive thickness 25μm

<Inner layer (L2 / L3) manufacturing process>
(1) Mask Lamination As shown in FIG. 1B, a mask film 14 is bonded to the printing surface (L2 surface) of the double-sided CCL10. Here, a vacuum laminator was used, and the conditions were 90 ° C., evacuation 20 seconds, pressurization pressure 0.3 MPa, and pressurization time 5 seconds.

(2) Laser Processing As shown in FIGS. 1C to 1G, the vias 20 and the exposure guide holes 15 of the L2 / L3 double-sided substrate are opened with a YAG laser. Here, the via 20 is formed by direct laser processing. The direct laser processing is processing for removing the copper foil 12 and the polyimide 11 at the via portion directly by a CO ₂ laser, a YAG laser, or the like.
First, as shown in FIG. 1D, an opening 16 having a diameter of 130 μm is formed in the mask film 14 by laser irradiation. Next, as shown in FIGS. 1D and 1E, the via portion 17 of the copper foil 12 on the L2 surface and the via portion 18 of the polyimide 11 are removed by laser with a via diameter of φ100 μm. Finally, in order to ensure the filling property of the conductive paste, as shown in FIG. 1 (g), an air vent small hole 19 is opened at φ20 μm in the copper foil 13 on the L3 surface.

(3) Desmear Smear generated in the laser processing step is removed by plasma desmear treatment.
(4) Conductive Paste Printing As shown in FIGS. 2A and 2B, the conductive paste 31 is printed from the surface of the mask film 14, filled into the via 20, and after filling, the mask film 14 is peeled off. Then, the conductive paste 31 is embedded in the via 20 and the protrusion 32 is formed so as to protrude from the copper foil 12. When the surface of the substrate was observed after the mask film 14 was peeled off, no adhesive or sticky material of the mask film 14 remained.

(5) Press cure Hot press cure is performed to cure the printed conductive paste 31. Since the filling with a paste is insufficient for curing by an oven, a hot press cure is preferable.
(6) Circuit formation Circuit formation of the copper foils 12 and 13 on both surfaces of the double-sided substrate 30 is performed.

<Outer layer (L1) manufacturing process>
(1) Circuit formation As shown in FIG.3 (b), circuit formation is performed for the copper foil 42 of the single-sided CCL.
(2) Interlaminar adhesive laminating Interlaminar adhesive 43 is laminated on the PI41 side of one side CCL.
(3) Mask Film Lamination As shown in FIG. 3C, a PI film 44 is laminated as a printing mask on the laminated interlayer adhesive 43 surface.

(4) Laser processing As shown in FIG. 3 (d), the mask PI44, the interlayer adhesive 43, and the CCL base PI41 are opened with a YAG laser from the surface of the mask film 44 to form a via 45. Further, a small hole 46 for venting air is formed in the copper foil 42.
(5) Desmear Resin smear generated in the laser processing process is removed by plasma desmear treatment.
(6) Conductive Paste Printing As shown in FIG. 3 (e), the conductive paste 47 is printed from the mask PI 44 surface side and filled into the via 45. After filling, the conductive paste projection 48 is formed by peeling the mask film 44.

<Lamination process>
The inner layer substrate 30 and the outer layer substrate 40 manufactured as described above are aligned and bonded together as shown in FIG. 4, and a target three-layer FPC multilayer substrate is completed through a hot pressing process.

[Comparative Example 1-1]
A double-sided substrate was manufactured by a conventional conformal mask method (see FIG. 5), and a three-layer FPC multilayer substrate having a structure in which the single-sided substrate was bonded to one side of the double-sided substrate was manufactured. In Comparative Example 1-1, the copper foil in the via portion of the double-sided substrate was opened in the etching process during circuit formation, and a commercially available mask film (PET film with adhesive) was used as the printing mask.

<Materials used>
Same as the material used in Example 1.

<Inner layer (L2 / L3) manufacturing process>
(1) As shown in FIGS. 5A and 5B, an exposure guide hole 15 of the L2 / L3 double-sided substrate 10 is opened using an NC driller.
(2) Next, as shown in FIG. 5C, the circuit of the L2 / L3 double-sided substrate 10 is formed. Simultaneously with this circuit formation, the copper foil 12 of the L2 via on the printed surface is opened by etching, and a conformal mask 21 of φ100 μm is provided.
(3) Next, as shown in FIG. 5D, a mask film 14A is laminated on the L2 surface. Here, a vacuum laminator was used, and the conditions were 90 ° C., evacuation 20 seconds, pressurization pressure 0.3 MPa, and pressurization time 5 seconds.

(4) Next, as shown in FIG. 5E, the double-sided substrate 10 is opened with a YAG laser to form vias. Here, laser light is irradiated from the L2 surface side that is the printing surface, and the mask film 14, the base PI11 of the double-sided CCL, and the small holes 19 of the L3 copper foil 13 are opened in this order. The diameter of the vias 17 and 18 was set to φ100 μm.
(5) The resin smear generated in the laser process in the plasma desmear process is removed. If the adhesion between the mask film 14A and the substrate 10 and the circuit filling property are insufficient, the mask film is peeled off in this step.
(6) Next, as shown in FIG. 5F, the conductive paste 31 is printed on the mask film 14 and embedded in the via. After printing, the mask film 14A is peeled off as shown in FIG.

<Outer layer (L1) manufacturing process and lamination process>
Same as Example 1.

[Comparative Example 1-2]
A double-sided substrate was manufactured by a conventional conformal mask method (see FIG. 5), and a three-layer FPC multilayer substrate having a structure in which the single-sided substrate was bonded to one side of the double-sided substrate was manufactured. In Comparative Example 1-2, the mask film laminating condition of (3) of the inner layer (L2 / L3) manufacturing process was performed under the conditions of 90 ° C., evacuation 20 seconds, pressurizing pressure 0.3 MPa, and pressurizing time 60 seconds. Except for the above, the materials used and the production process were the same as in Comparative Example 1-1.

[Comparative Example 1-3]
A double-sided substrate was manufactured by a conventional conformal mask method (see FIG. 5), and a three-layer FPC multilayer substrate having a structure in which the single-sided substrate was bonded to one side of the double-sided substrate was manufactured. In Comparative Example 1-3, both the materials used and the manufacturing process were the same as Comparative Example 1-1 except that a high adhesion type PET film with an adhesive was used as the mask film used in the inner layer (L2 / L3) manufacturing process. The same was done.

[Results and discussion]
For each of Example 1 and Comparative Examples 1-1, 1-2, and 1-3, 10 samples of three-layer FPC multilayer substrate samples were produced. These samples were provided with a daisy chain pattern in which 100 vias were continuously conducted for resistance value testing. The daisy chain pattern here is a pattern in which the L2 and L3 surfaces are connected in a chain form by paste vias as shown in FIG.

  The results for the three-layer FPC multilayer substrate are shown in Table 1. In Table 1, “Mask 1” is a commercially available PET film with an adhesive, “Mask 2” is a PET film with an adhesive of a high adhesive strength type, “DL method” is a direct laser processing method, and “CM method”. Represents the conformal mask method.

<Peeling>
The numbers in Table 1 indicate the number of sheets (out of all 10 sheets) from which one or more mask films were peeled off in the plasma desmear process after the via opening by laser. It is obvious that the peeled material causes wrinkles and defective printing of the conductive paste in the process after the desmear process, particularly in the conductive paste printing process. According to the results shown in Table 1, peeling failure occurred only in Comparative Example 1-1 among the four cases carried out.

In Comparative Example 1-1, peeling occurred in 4 sheets out of all 10 sheets. This is thought to be because the mask film was peeled off due to insufficient circuit fillability of the mask film.
In Comparative Example 1-2, there was no peeling. It is considered that peeling after the desmear treatment did not occur because the pressurizing time at the time of lamination was increased to improve the adhesive force and the circuit filling property.
In Comparative Example 1-3, there was no peeling. It is considered that peeling after the desmear treatment did not occur because a high adhesion type mask film was used to solve the lack of adhesion.
In Example 1, there was no peeling. Since the mask film is laminated on the conductor surface before the circuit is formed, there is no circuit level difference as a starting point of peeling. Therefore, peeling after desmear treatment does not occur in principle.

<Remaining adhesive>
The numbers in Table 1 indicate the number of sheets (out of 10 sheets) in which one or more adhesives remained on the double-sided substrate when the mask film was peeled after printing the conductive paste. It is self-evident that the adhesive material remaining causes deterioration of the electrical characteristics and reliability of the via and causes a characteristic defect. In the results shown in Table 1, although defects occurred in Comparative Examples 1-1, 1-2, and 1-3, the defect was zero in Example 1.

In Comparative Example 1-2, 7 sheets out of all 10 sheets, and in Comparative Example 1-3, all 10 sheets generated adhesive residue. In Comparative Example 1-2, the mask lamination conditions were strong, and in Comparative Example 1-3, the adhesive strength of the mask film was too strong, so that the adhesive remained after peeling.
In Comparative Example 1-1, although the mask lamination conditions were weak, adhesive residue was generated in 2 sheets out of all 10 sheets. This is presumably because the land irradiated with the laser has a small diameter of φ300 μm and the heat is not easily diffused, so that the conductor land portion becomes locally hot and the adhesive is cured.
In Example 1, although the copper foil portion was removed with a high energy laser, no adhesive residue was generated. The reason why the adhesive did not remain was that it was possible to laminate the mask film weakly because there was no fear of peeling by desmear treatment, and because the heat generated by laser processing was likely to diffuse, It is considered that the agent did not cure.

<Resistance value>
The numbers of resistance values in Table 1 indicate the average value of N = 10 for a daisy chain pattern in which 100 vias are continuously conducted. Moreover, the standard deviation of the resistance value in Table 1 shows a standard deviation of N = 10 for the same measured value. The daisy chain pattern here is a pattern in which the L2 and L3 surfaces are connected in a chain form by paste vias as shown in FIG.
In Comparative Examples 1-1, 1-2, and 1-3, an adhesive residue is generated when the mask is peeled off. For this reason, when laminating | stacking an outer layer board | substrate, when an adhesive agent remains as shown in FIG. 8, the contact with an electrically conductive paste and copper foil is inhibited by an adhesive agent, and the tendency for resistance value to become high is seen. . Along with this, the variation (standard deviation) in resistance value is also large. In Example 1, since the adhesive residue is not derived, the resistance value is small and stable.

  From the results of Example 1 and Comparative Examples 1-1, 1-2, and 1-3 described above, the process for solving both the mask peeling during desmearing and the adhesive remaining after printing is only Example 1. As for electrical characteristics, Example 1 was found to be the most excellent.

[Example of application as a single-sided FPC]
[Example 2]
A double-sided FPC was manufactured by the process of the present invention using the following materials and manufacturing steps.

<Materials used>
CCL: Double-sided CCL, copper foil thickness 12 μm, polyimide thickness 25 μm
・ Mask film: Adhesive thickness 15μm, PET thickness 12μm
・ Coverlay film: Adhesive thickness 25μm, polyimide thickness 25μm

<Manufacturing process>
(1) to (6) of <Inner layer (L2 / L3) manufacturing process> of Example 1 are similarly performed. Thereafter, coverlay (CL) films are bonded to the front and back surfaces of the double-sided substrate on which the circuit pattern is formed, and hot press cure is performed.

[Comparative Example 2-1]
A double-sided FPC was manufactured by the TH plating method.
(1) NC drilling TH and exposure guide holes are drilled on the double-sided CCL with an NC drill. The TH diameter is 100 μm.
(2) DPP (Direct Placing Process)
In order to form a base layer for electrolytic copper plating, a conductive film such as a carbon film or palladium is adsorbed by a DPP process.
(3) TH plating TH plating is performed using commonly used copper sulfate plating. At this time, a 10 μm-thick plating layer is formed on the entire surface of the double-sided CCL copper foil together with the TH portion.
(4) Circuit formation (5) CL cure A coverlay (CL) film is bonded to the front and back of the double-sided substrate on which the circuit pattern is formed, and hot press cure is performed.

[Comparative Example 2-2]
A double-sided FPC was manufactured by land TH plating.
(1) Drilling NC Drill NC and exposure guide holes with an NC drill. The TH diameter is 100 μm.
(2) DPP (Direct Placing Process)
Similar to (2) of Comparative Example 2-1.
(3) Photoresist laminating A photosensitive photoresist for land TH plating is laminated.
(4) Exposure The photoresist is exposed using a photomask having only a land pattern having TH.
(5) Development In the development process, only the land portion having TH is removed from the photoresist.
(6) Land TH plating Land TH plating is performed using commonly used copper sulfate plating. Since only the land pattern having TH is opened in the photoresist formed in the previous step, only the land and the TH portion are plated.
(7) Resist stripping (8) Circuit formation (9) CL cure A coverlay (CL) film is bonded to the front and back of the double-sided substrate on which the circuit pattern is formed, and hot press curing is performed.

[Results and discussion]
Ten sheets of double-sided FPC samples were produced for each of Example 2 and Comparative Examples 2-1 and 2-2. In these samples, a daisy chain pattern in which 100 paste vias (Example 2) or plating THs (Comparative Examples 2-1 and 2-2) are continuously conducted for resistance value testing (FIG. 6). Reference).
The results for the double-sided FPC are shown in Table 2.

<Resistance value>
The numbers of resistance values in Table 2 are daisy chain patterns in which 100 paste vias (Example 2) or plating TH (Comparative Examples 2-1 and 2-2) are continuously conducted (see FIG. 6). ) For N = 10. Moreover, the standard deviation of the resistance value in Table 2 indicates a standard deviation of N = 10 for the same measured value.
In Comparative Example 2-1, the conductor thickness of the circuit pattern is increased by the plating due to TH plating, and the resistance value is slightly increased. Further, since there is a variation in plating thickness within the pattern, the standard deviation of the resistance value is also large.
Since Comparative Example 2-2 is plated only on the land TH, the resistance value is the lowest and the standard deviation of the resistance value is stable.
Since the conductor thickness of Example 2 is thinner than that of Comparative Example 2-1, the resistance value can be relatively small. However, since the volume resistance exists in the paste via itself, the characteristics as the land TH plating cannot be obtained.

<Minimum L / S>
For the minimum L / S, for the line width (L) and space width (S) of the conductor pattern, pattern preparation was attempted with various L / S widths, and the minimum width without pattern defects was measured.
In Comparative Example 2-1, the thickness of the conductor layer of the double-sided CCL is increased by 10 μm as a whole by TH plating. Therefore, it is disadvantageous to form a finer circuit, and the minimum L / S is 60/60 μm.
In Example 2 and Comparative Example 2-2, the thickness of the circuit pattern portion remained the thickness of the CCL copper foil, and the minimum L / S was 30/30 μm.

  As a result of evaluating the double-sided substrate alone from the results of Example 2 and Comparative Examples 2-1 and 2-2, the double-sided FPC by the method of the present invention (Example 2) is TH-plated (Comparative Example 2-1). It turns out that it has the characteristic more than double-sided FPC using. However, when comparing the method of the present invention (Example 2) and land TH plating (Comparative Example 2-2), the latter is superior in terms of electrical characteristics, but land TH plating requires the formation of a mask. Since a photoresist forming process (lamination, exposure, development, resist stripping) is required, the number of processes increases, which is disadvantageous in terms of cost. Therefore, it can be said that the process in which both the reliability and the cost are balanced in manufacturing the double-sided FPC is the method of the present invention (Example 2).

  The present invention can be used for manufacturing various multilayer printed wiring boards regardless of the type such as FPC and RPC.

(A)-(g) is sectional drawing explaining an example of the method of forming a via hole in a double-sided board in order of a process in the present invention. (A)-(d) is sectional drawing explaining an example of the method of printing and filling the conductive paste to a via hole in order of a process in this invention. (A)-(f) is sectional drawing explaining an example of the method of producing the single-sided board | substrate used for a multilayer printed wiring board in order of a process. (A)-(b) is sectional drawing explaining an example of the method of laminating | stacking the double-sided board produced by FIG. 2, and the single-sided board produced by FIG. 3, and producing a multilayer printed wiring board. (A)-(g) is sectional drawing explaining an example of the method of forming a paste via in a double-sided board by a conformal mask method in order of a process in a comparative example. It is sectional drawing explaining the pattern of a daisy chain. (A)-(f) is sectional drawing which shows the manufacturing procedure of ALIVH which is one of the prior arts in order of a process. (A) shows the state of the conductive paste before lamination, (b) shows the state of the normal conductive paste after lamination, and (c) shows that the conductive paste after lamination becomes incomplete due to the adhesive remaining. It is sectional drawing which shows the state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Double-sided CCL, 12, 13 ... Conductor layer (copper foil) 14 ... Mask film, 16 ... Opening part, 20 ... Via, 30 ... Double-sided printed wiring board (double-sided board), 31 ... Conductive paste, 33 ... Paste via 40 ... single-sided printed wiring board (single-sided board), 50 ... multilayer printed wiring board (multi-layered board).

Claims (2)

A method for manufacturing a double-sided printed wiring board in which via holes are filled with a conductive paste for interlayer conduction,
When a mask film is directly attached to one side of a conductor layer of a double-sided board having a conductor layer in which circuits on both sides are not formed, and the via hole is formed using the mask film as a printing mask, the opening diameter is larger than the via diameter. The double-sided structure is characterized in that a part is opened by laser irradiation on a mask film, and the via hole is filled with a conductive paste, and then the filled conductive paste is cured by hot press curing, and then the circuit of the conductor layer is formed. Manufacturing method of printed wiring board.   A multilayer printed wiring board comprising a double-sided printed wiring board manufactured by the method for manufacturing a double-sided printed wiring board according to claim 1.

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