JP2009253080A - Printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed wiring board having excellent connection reliability by using conductive paste. <P>SOLUTION: A printed wiring board 1 is provided with a first conductive layer 3, an insulating layer 2 provided on the surface of the first conductive layer 3, and a second conductive layer 4 provided on the surface of the insulating layer 2 and electrically connected with the first conductive layer 3. Moreover, the printed wiring board 1 is provided with: a via hole 5 that is formed in the insulating layer 2 and the second conductive layer 4 and has the first conductive layer 3 as a bottom surface and the insulating layer 2 and the second conductive layer 4 as wall surfaces; and conductive paste 6 that is filled in the via hole 5 to electrically connect the first conductive layer 3 and the second conductive layer 4. The opening diameter R1 of the via hole 5 in the insulating layer 2 is set larger than the opening diameter R2 of the via hole 5 in the second conductive layer 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a printed wiring board for electrically connecting conductive layers using a conductive paste.

  In recent years, in the field of electronic devices, printed wiring boards have been widely used for various applications as electronic devices become denser and smaller. For example, a printed wiring board is used as a substrate for a magnetic head suspension for mounting a magnetic head in a hard disk drive that requires high-speed data transfer.

  As such a printed wiring board, for example, an insulating layer and a conductive layer having a predetermined wiring pattern are formed on both surfaces of the insulating layer, and via holes are filled in the conductive layers formed on both surfaces of the insulating layer. A printed wiring board electrically connected by a conductive paste is disclosed.

More specifically, as shown in FIG. 15, the insulating layer 51, first and second conductive layers 52 and 53 provided on both surfaces of the insulating layer 51, the insulating layer 51 and the second conductive layer. Proposed printed wiring board 50 including via hole 54 formed in 53 and conductive paste 55 filled in via hole 54 to electrically connect first conductive layer 52 and second conductive layer 53 Has been. When the conductive paste 55 is filled into the via hole 54, a mask film (not shown) having a predetermined opening formed on the surface of the second conductive layer 53 is provided, and the conductive film 55 is conductive through the mask film. A method of filling the via hole 54 by printing the paste 55 is employed (see, for example, Patent Document 1).
JP 2007-281336 A

  However, in the conventional printed wiring board 50, as shown in FIG. 16, when the filling position of the conductive paste 55 is shifted when the conductive paste 55 is filled in the via hole 54, the wall surface of the via hole 54 is formed. The second conductive layer 53 may not come into contact with the conductive paste 55. In addition, as shown in FIG. 17, when the conductive paste 55 is filled in the via hole 54, if the amount of the conductive paste 55 is small, the second conductive layer 53 constituting the wall surface of the via hole 54 becomes conductive paste. 55 may not contact. Therefore, it becomes difficult to electrically connect the first conductive layer 52 and the second conductive layer 53 via the conductive paste 55, and the first conductive layer 52 and the second conductive layer 53 are not connected. There was a problem that connection reliability was lowered.

  Then, this invention is made | formed in view of the above-mentioned problem, and it aims at providing the printed wiring board which has the outstanding connection reliability by using an electrically conductive paste.

  In order to achieve the above object, the invention according to claim 1 is provided with a first conductive layer, an insulating layer provided on a surface of the first conductive layer, a surface provided on the surface of the insulating layer, A second conductive layer electrically connected to the first conductive layer, an insulating layer and a second conductive layer, the first conductive layer being a bottom surface, the insulating layer, and the second conductive layer; And a via paste filled in the via hole and electrically connecting the first conductive layer and the second conductive layer, and the opening diameter of the via hole in the insulating layer is the second A printed wiring board having a larger opening diameter than a via hole in a conductive layer.

  According to this configuration, when filling the via hole with the conductive paste, even if the filling position of the conductive paste is shifted or the filling amount of the conductive paste is small, The two conductive layers can be reliably brought into contact with the conductive paste. In addition, since the cross-sectional shape of the filled conductive paste becomes a shape capable of exhibiting an anchor effect, adhesion between the conductive paste and the wall surface of the via hole is improved. Accordingly, the first conductive layer and the second conductive layer can be reliably electrically connected via the conductive paste, and the connection reliability between the first conductive layer and the second conductive layer can be improved. Can be improved.

  In addition, when filling the via hole with the conductive paste, a mask film for filling the conductive paste becomes unnecessary, and therefore the filling process of the conductive paste can be simplified.

  The invention according to claim 2 is the printed wiring board according to claim 1, wherein the insulating layer portion of the via hole has an opening diameter of the via hole in the insulating layer from the second conductive layer side to the first conductive layer. It has a tapered shape that gradually decreases toward the side.

  According to this configuration, it is possible to reduce the amount of conductive paste required for contact with the second conductive layer. Therefore, when filling the via hole with the conductive paste, even if the filling position of the conductive paste is shifted or the filling amount of the conductive paste is small, the second conductive layer constituting the wall surface of the via hole And the conductive paste can be more reliably brought into contact with each other. As a result, the first conductive layer and the second conductive layer can be more reliably electrically connected via the conductive paste, and the connection reliability between the first conductive layer and the second conductive layer can be ensured. Property can be further improved.

  The invention according to claim 3 is the printed wiring board according to claim 1 or 2, wherein the surface of the second conductive layer is covered with a plating layer.

  According to this configuration, it is possible to reduce the amount of conductive paste necessary for contact with the plating layer. Therefore, when filling the via hole with the conductive paste, even if the filling position of the conductive paste is shifted or the filling amount of the conductive paste is small, the second conductive layer constituting the wall surface of the via hole The plating layer provided on the surface and the conductive paste can be reliably brought into contact with each other. As a result, the first conductive layer and the second conductive layer can be more reliably electrically connected via the conductive paste, and the connection reliability between the first conductive layer and the second conductive layer can be ensured. Property can be further improved.

  The invention described in claim 4 is the printed wiring board according to claim 3, wherein the plating layer is a nickel-gold plating layer.

  According to this configuration, the connection reliability between the second conductive layer and the conductive paste can be improved.

  Moreover, the printed wiring board according to claims 1 to 4 of the present invention can reliably connect the first conductive layer and the second conductive layer through the conductive paste, Since it has the outstanding characteristic that the connection reliability between a 1st conductive layer and a 2nd conductive layer can be improved, it is for suspensions used for a hard-disk drive like the invention of Claim 5. It can be suitably used as a printed wiring board used as a substrate.

  According to the present invention, in a printed wiring board including a plurality of conductive layers, it is possible to reliably connect electrically conductive layers via a conductive paste, and to improve connection reliability between conductive layers. Can do.

(First embodiment)
Hereinafter, a preferred embodiment of the present invention will be described. FIG. 1 is a cross-sectional view showing a schematic configuration of a printed wiring board according to the first embodiment of the present invention. This printed wiring board 1 is a double-sided printed wiring board, as shown in FIG. 1, provided on each of the insulating layer 2 formed of a flexible resin film and both surfaces of the insulating layer 2, First and second conductive layers 3 and 4 having a wiring pattern are provided.

  As the insulating layer 2, a resin material having excellent flexibility is used. As such a resin, for example, a resin having versatility for a printed wiring board, such as polyester, can be used. In addition, it is particularly preferable to have high heat resistance in addition to flexibility, and as such a resin film, for example, a polyamide-based resin or a polyimide-based resin such as polyimide or polyamideimide is preferably used. Is done. Moreover, in this embodiment, the thickness of the insulating layer 2 can use 5 micrometers-200 micrometers suitably.

  Moreover, copper foil is used suitably as metal foil which comprises the 1st and 2nd conductive layers 3 and 4 which have a predetermined wiring pattern. Moreover, the first and second conductive layers 3 and 4 having a predetermined wiring pattern are formed by etching and processing this metal foil by a conventional method. In the present embodiment, the first and second conductive layers 3 and 4 having a thickness of 2 μm to 50 μm can be suitably used.

  In the present embodiment, as shown in FIG. 1, a via hole 5 for connecting the first conductive layer 3 and the second conductive layer 4 is formed in the printed wiring board 1. As shown in FIG. 1, the via hole 5 has the first conductive layer 3 as a bottom surface and the insulating layer 2 and the second conductive layer 4 as wall surfaces.

  The via hole 5 is filled with a conductive paste 6, and the first conductive layer 3 and the second conductive layer 4 are electrically connected via the conductive paste 6. . As this electroconductive paste 6, what contains electroconductive fillers, such as a metal particle, and disperse | distributed the said electroconductive filler in binder resin can be used. Here, as the metal particles, for example, silver, platinum, gold, copper, nickel, palladium and the like can be used, but among these, when silver powder or silver-coated copper powder is used, excellent conductivity is preferable. . Moreover, as a binder resin, an epoxy resin, a phenol resin, a polyester resin, a polyurethane resin, an acrylic resin, a melamine resin, a polyimide resin, a polyamideimide resin, etc. can be used, for example. Of these, from the viewpoint of improving the heat resistance of the conductive paste 6, it is preferable to use a thermosetting resin, and in the present embodiment, it is preferable to use an epoxy resin.

  The epoxy resin to be used is not particularly limited. For example, bisphenol A type, F type, S type, AD type, or a copolymer type epoxy resin of bisphenol A type and bisphenol F type, or naphthalene type epoxy is used. Resin, novolac type epoxy resin, biphenyl type epoxy resin, dicyclopentadiene type epoxy resin and the like can be used. A phenoxy resin that is a high molecular weight epoxy resin can also be used.

  The binder resin can be used by dissolving in a solvent. As the solvent to be used, for example, organic solvents such as ester, ether, ketone, ether ester, alcohol, hydrocarbon, and amine can be used. Here, since the conductive paste 6 is filled in the via hole 5 by screen printing or the like, it is preferable to use a high boiling point solvent excellent in printability, and more specifically, carbitol acetate or butyl carbitol. Preference is given to using acetate. A plurality of these solvents can be used in combination. These materials are mixed and dispersed by a three roll, rotary stirring defoaming machine or the like to obtain a uniform state, and the conductive paste 6 is produced.

  Here, in the present embodiment, as shown in FIG. 1, the opening diameter R1 of the via hole 5 in the insulating layer 2 is larger than the opening diameter R2 of the via hole 5 in the second conductive layer 4 (that is, R1> R2). ) There is a feature. With such a configuration, when the conductive paste 6 is filled into the via hole 5, even if the filling position of the conductive paste 6 is shifted or the filling amount of the conductive paste 6 is small, the conductive paste 6 The first conductive layer 3 and the second conductive layer 4 can be reliably electrically connected via the paste 6.

  More specifically, as shown in FIG. 2, when the conductive paste 6 is filled into the via hole 5, even when the filling position of the conductive paste 6 is shifted, The portion 4 a on the insulating layer 2 side of the second conductive layer 4 is in reliable contact with the conductive paste 6. Further, as shown in FIG. 3, when the conductive paste 6 is filled in the via hole 5, the second conductive layer 4 constituting the wall surface of the via hole 5 even when the amount of the conductive paste 6 is small. The portion 4 a on the insulating layer 2 side is surely in contact with the conductive paste 6. Therefore, the first conductive layer 3 and the second conductive layer 4 can be reliably electrically connected via the conductive paste 6.

  In addition, since the cross-sectional shape of the filled conductive paste 6 becomes a shape that can exert the anchor effect, the adhesion between the conductive paste 6 and the wall surface of the via hole 5 is improved. Further, when the conductive paste 6 is filled in the via hole 5, the mask film for filling the conductive paste described in the above prior art becomes unnecessary.

  The opening diameter R1 of the via hole 5 in the insulating layer 2 is preferably 30 to 300 μm. This is because, when the opening diameter R1 is smaller than 30 μm, the connection area of the via hole 5 becomes small, so that the connection resistance increases when the first conductive layer 3 and the second conductive layer 4 are electrically connected. If the opening diameter R1 is larger than 300 μm, the conductive paste 6 necessary for filling the via hole 5 increases, so that the first conductive layer 3 and the second conductive layer 4 are formed. This is because the conductive paste 6 necessary for electrical connection increases.

  Further, the opening diameter R2 of the via hole 5 in the second conductive layer 4 is preferably 20 to 300 μm. This is because if the opening diameter R2 is smaller than 20 μm, the contact area between the second conductive layer 4 and the conductive paste 6 may be small or it may be difficult to fill the via hole 5 with the conductive paste 6. When the opening diameter R2 is larger than 300 μm, the conductive paste 6 necessary for filling the via hole 5 increases, so that the first conductive layer 3 and the second conductive layer 4 are electrically connected. This is because there is an inconvenience that the conductive paste 6 necessary to do so increases.

  The ratio of the opening diameter R1 and the opening diameter R2 (opening diameter R1 / opening diameter R2) is preferably 1.01 to 1.30. This is because if the ratio is smaller than 1.01, the first conductive material is passed through the conductive paste 6 when the filling position of the conductive paste 6 is shifted or the filling amount of the conductive paste 6 is small. This is because the effect of reliably electrically connecting the layer 3 and the second conductive layer 4 may not be sufficiently exhibited, and when the ratio is greater than 1.30, the conductive paste 6 is filled. This is because a void may easily remain in the portion of the via hole 5.

  In addition to the circular shape, the shape of the via hole 5 can be an arbitrary shape such as an elliptical shape or a polygonal cross section, and in the case of a shape other than the circular shape, the maximum length of the opening in the insulating layer 2 Let the thickness be the opening diameter R1, and let the maximum length of the opening in the second conductive layer 4 be the opening diameter R2.

  Next, an example of a method for manufacturing the printed wiring board shown in FIG. 1 will be described with reference to the drawings. 4A to 4H are cross-sectional views for explaining a method for manufacturing a printed wiring board according to the first embodiment of the present invention.

  First, as shown to Fig.4 (a), what provided the 1st and 2nd conductive layers 3 and 4 comprised by metal foils, such as copper foil, on each of both surfaces of the insulating layer 2 is prepared. . Next, as shown in FIG. 4B, a resist 15 having a predetermined opening pattern is formed on the surface of the second conductive layer 4. The resist 15 can be formed by a known method such as using a dry film resist. Then, as shown in FIG. 4C, using the resist 15 as a mask, the second conductive layer 4 is etched by a known etching method such as chemical etching (wet etching), for example. By selectively removing the conductive layer 4, the second conductive layer 4 is made into a predetermined shape. Next, as shown in FIG. 4D, the above-described resist 15 is removed using, for example, a known resist stripping solution. Thereafter, as shown in FIG. 4E, a resist 16 having a predetermined opening pattern is formed on the surface of the second conductive layer 4. The resist 16 can be formed by a known method such as using a dry film resist as in the case of the resist 15 described above.

  Next, as shown in FIG. 4F, a resist 16 (this resist 16 may be made of another type of resist by removing the etching resist 15) is used as a mask. The insulating layer 2 is etched by a known etching method such as chemical etching (wet etching), and the insulating layer 2 is selectively removed, whereby the first conductive layer 3 and the second conductive layer 4 are removed. A via hole 5 for connection is formed. At this time, the insulating layer 2 is adjusted such that the opening diameter R1 of the via hole 5 in the insulating layer 2 is larger than the opening diameter R2 of the via hole 5 in the second conductive layer 4 by adjusting the etching time. Etching is performed. Next, as shown in FIG. 4G, the above-described resist 16 is removed using, for example, a resist stripping solution or the like.

  Next, as shown in FIG. 4 (h), by filling the via hole 5 with the conductive paste 6, the first conductive layer 3 and the second conductive layer 4 are electrically connected via the conductive paste 6. Connect. As a method for filling the via hole 5 with the conductive paste 6, for example, by a method such as screen printing, the surface of the first conductive layer 3 that is the bottom surface of the via hole 5 and the second conductivity that is the wall surface of the via hole 5 are used. A method of filling the via hole 5 with the conductive paste 6 by applying the conductive paste 6 so that the surface of the layer 4 is continuous can be employed. If necessary, after the conductive paste 6 is filled, the conductive paste 6 may be heat-treated and cured.

According to the present embodiment described above, the following effects can be obtained.
(1) In this embodiment, the opening diameter R1 of the via hole 5 in the insulating layer 2 is set larger than the opening diameter R2 of the via hole 5 in the second conductive layer 4. Therefore, when filling the via hole 5 with the conductive paste 6, the wall surface of the via hole 5 is configured even when the filling position of the conductive paste 6 is shifted or the filling amount of the conductive paste 6 is small. The second conductive layer 4 and the conductive paste 6 can be reliably brought into contact with each other. Therefore, the first conductive layer 3 and the second conductive layer 4 can be reliably electrically connected via the conductive paste 6, and the first conductive layer 3 and the second conductive layer 4 can be connected. The connection reliability between them can be improved.

  (2) Moreover, since the cross-sectional shape of the filled conductive paste 6 becomes a shape capable of exhibiting the anchor effect, the adhesion between the conductive paste 6 and the wall surface of the via hole 5 is improved. Therefore, the first conductive layer 3 and the second conductive layer 4 can be reliably electrically connected via the conductive paste 6, and the first conductive layer 3 and the second conductive layer 4 can be connected. The connection reliability between them can be improved.

  (3) Further, when filling the conductive paste 6 into the via hole 5, a mask film for filling the conductive paste becomes unnecessary, so that the filling process of the conductive paste 6 can be simplified.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. FIG. 5 is a cross-sectional view showing a schematic configuration of a printed wiring board according to the second embodiment of the present invention. In addition, about the component similar to the said 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted. The method for manufacturing the printed wiring board is also the same as that in the first embodiment described above, and a detailed description thereof is omitted here.

  In the present embodiment, as shown in FIG. 5, the insulating layer 2 has an opening diameter R1 of the via hole 5 in the insulating layer 2 from the second conductive layer 4 side toward the first conductive layer 3 side (that is, It is characterized in that it is formed to have a tapered shape that gradually decreases (in the direction of the arrow X shown in FIG. 5). With such a configuration, when the conductive paste 6 is filled into the via hole 5, even if the filling position of the conductive paste 6 is shifted or the filling amount of the conductive paste 6 is small, the conductive paste 6 The first conductive layer 3 and the second conductive layer 4 can be more reliably electrically connected via the paste 6.

  More specifically, the insulating layer 2 portion of the via hole 5 has a tapered shape, so that the insulating layer 2 portion of the via hole 5 has a tapered shape as compared with the case where the insulating layer 2 portion of the via hole 5 does not have a tapered shape. Volume decreases. As a result, the amount of the conductive paste 6 filled in the insulating layer 2 of the via hole 5 can be reduced. Therefore, it is possible to reduce the amount of the conductive paste 6 necessary for contact with the second conductive layer 4. As a result, as shown in FIG. 6, when the conductive paste 6 is filled into the via hole 5, even if the filling position of the conductive paste 6 is shifted, the second conductivity constituting the wall surface of the via hole 5. The portion 4 a on the insulating layer 2 side of the layer 4 comes into more reliable contact with the conductive paste 6. In addition, as shown in FIG. 7, when the conductive paste 6 is filled into the via hole 5, the second conductive layer 4 constituting the wall surface of the via hole 5 even if the amount of the conductive paste 6 is small. Thus, the portion 4 a on the insulating layer 2 side comes into more reliable contact with the conductive paste 6. Therefore, the first conductive layer 3 and the second conductive layer 4 can be more reliably electrically connected via the conductive paste 6.

According to this embodiment described above, in addition to the effects (2) and (3) described above, the following effects can be obtained.
(4) In the present embodiment, the portion of the insulating layer 2 of the via hole 5 is formed to have a tapered shape in which the opening diameter R1 gradually decreases from the second conductive layer 4 side toward the first conductive layer 3 side. It is configured to do. Therefore, it is possible to reduce the amount of the conductive paste 6 necessary for contact with the second conductive layer 4. As a result, when the conductive paste 6 is filled in the via hole 5, the wall surface of the via hole 5 is configured even when the filling position of the conductive paste 6 is shifted or the filling amount of the conductive paste 6 is small. Thus, the second conductive layer 4 and the conductive paste 6 can be brought into contact with each other more reliably. As a result, the first conductive layer 3 and the second conductive layer 4 can be more reliably electrically connected via the conductive paste 6, and the first conductive layer 3 and the second conductive layer 4 can be electrically connected. The connection reliability between the conductive layers 4 can be further improved.

  In addition, this invention is not limited to the said embodiment, A various design change is possible based on the meaning of this invention, and they are not excluded from the scope of the present invention.

  For example, as shown in FIG. 8, in the printed wiring board 1 described in the first embodiment, the surface of the second conductive layer 4 may be covered with a plating layer 8. By providing such a plating layer 8, when the conductive paste 6 is filled in the via hole 5, the filling position of the conductive paste 6 is shifted or the filling amount of the conductive paste 6 is small. In addition, the first conductive layer 3 and the second conductive layer 4 can be more reliably electrically connected via the conductive paste 6.

  More specifically, when the surface of the second conductive layer 4 is covered with the plating layer 8 and the surface of the second conductive layer 4 is not covered with the plating layer 8 as in the first embodiment described above. As compared with the above, the thickness of the surface of the second conductive layer 4 in the via hole 5 is increased by the thickness of the plating layer 8, and the volume of the via hole 5 can be reduced. Therefore, since the amount of the conductive paste 6 filled in the via hole 5 can be reduced, the amount of the conductive paste 6 required for contact with the plating layer 8 can be reduced. Therefore, as shown in FIG. 9, when the conductive paste 6 is filled into the via hole 5, even if the filling position of the conductive paste 6 is shifted, the second conductive layer constituting the wall surface of the via hole 5. The plating layer 8 provided on the surface of 4 is in contact with the conductive paste 6 with certainty. Further, as shown in FIG. 10, when the conductive paste 6 is filled into the via hole 5, the second conductive layer 4 constituting the wall surface of the via hole 5 even if the filling amount of the conductive paste 6 is small. Thus, the plating layer 8 provided on the surface of the conductive layer 6 is surely brought into contact with the conductive paste 6. Therefore, the first conductive layer 3 and the second conductive layer 4 can be more reliably electrically connected via the conductive paste 6, and the first conductive layer 3 and the second conductive layer can be connected. The connection reliability between the four can be further improved.

  In consideration of the environment, it is preferable to use the plating layer 8 not containing lead. Further, from the viewpoint of improving the connection reliability between the second conductive layer 4 and the conductive paste 6, a nickel-gold plating layer can be used as the plating layer 8 not containing lead. The plating process on the surface of the second conductive layer 4 is performed by an electroless plating method or an electrolytic plating method, and when the nickel-gold plating layer is provided, the exposure shown in FIG. First, a nickel plating layer 9 as a diffusion preventing layer is formed on the surface of the second conductive layer 4, and then a gold plating layer 10 is formed on the surface of the nickel plating layer 9.

  Similarly, as shown in FIG. 11, in the printed wiring board 1 described in the second embodiment, the surface of the second conductive layer 4 is covered with the plating layer 8. Similar effects can be obtained. That is, by covering the surface of the second conductive layer 4 with the plating layer 8, the via hole 5 can be formed as compared with the case where the surface of the second conductive layer 4 is not covered with the plating layer 8 as in the second embodiment. The thickness of the surface of the second conductive layer 4 is increased by the thickness of the plating layer 8, and the volume of the via hole 5 can be reduced. Therefore, since the amount of the conductive paste 6 filled in the via hole 5 can be reduced, the amount of the conductive paste 6 required for contact with the plating layer 8 can be reduced. Therefore, as shown in FIG. 12, when filling the via hole 5 with the conductive paste 6, even if the filling position of the conductive paste 6 is shifted, the second conductive layer constituting the wall surface of the via hole 5 is used. The plating layer 8 provided on the surface of 4 is in contact with the conductive paste 6 with certainty. Further, as shown in FIG. 13, when the conductive paste 6 is filled into the via hole 5, the second conductive layer 4 constituting the wall surface of the via hole 5 even if the filling amount of the conductive paste 6 is small. Thus, the plating layer 8 provided on the surface of the conductive layer 6 is surely brought into contact with the conductive paste 6. As a result, the first conductive layer 3 and the second conductive layer 4 can be more reliably electrically connected via the conductive paste 6, and the first conductive layer 3 and the second conductive layer 4 can be connected to each other more reliably. The connection reliability between the conductive layers 4 can be further improved.

  The first conductive layer 3 may be configured to use a metal substrate instead of a metal foil such as a copper foil. As this metal substrate, for example, a metal foil made of stainless steel, aluminum, iron, copper, nickel, titanium, molybdenum, chromium, zinc or the like can be used. Moreover, it is preferable to use the metal foil which consists of stainless steel which is excellent in heat dissipation, spring property, and corrosion resistance among these metal foils. A metal substrate having a thickness of 1 μm to 100 μm can be suitably used. Also in this case, as in the case of the above-described embodiment, the first conductive layer 3 and the second conductive layer 4 can be reliably electrically connected via the conductive paste 6. Since it has an excellent characteristic that the connection reliability between the conductive layer 3 and the second conductive layer 4 can be improved, the printed wiring board is used as a suspension substrate used in a hard disk drive. It can be used suitably.

  In the above-described embodiment, the double-sided printed wiring board has been described as an example, but it goes without saying that the present invention can also be applied to a printed wiring board having a multilayer structure. As a printed wiring board having this multilayer structure, for example, as shown in FIG. 14, the printed wiring board 1 in the first embodiment described above is used as the printed wiring board for the inner layer, and on the surface of the insulating layer 31. The outer printed wiring board 30 provided with the third conductive layer 32 and the outer printed wiring board 35 provided with the fourth conductive layer 37 on the surface of the insulating layer 36 are bonded to the adhesive layer 40, The printed wiring board 45 which has the multilayer structure laminated | stacked on the printed wiring board 1 via 41 is mentioned. As shown in FIG. 14, the first conductive layer 3 and the third conductive layer 32 are electrically connected via the conductive paste 6 filled in the through hole 33 formed in the printed wiring board 30. Has been. Similarly, the second conductive layer 4 and the fourth conductive layer 37 are electrically connected via a conductive paste 6 filled in a through hole 38 formed in the printed wiring board 35.

  As an application example of the present invention, a printed wiring board that electrically connects conductive layers using a conductive paste can be cited.

It is sectional drawing which shows schematic structure of the printed wiring board which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows schematic structure of the printed wiring board which concerns on the 1st Embodiment of this invention, Comprising: The figure which shows the state which the filling position of the conductive paste shifted | deviated especially when filling a conductive paste in a via hole It is. It is sectional drawing which shows schematic structure of the printed wiring board which concerns on the 1st Embodiment of this invention, Comprising: It is a figure which shows the state with little filling amount of conductive paste especially when filling a conductive paste in a via hole. is there. (A)-(h) is sectional drawing for demonstrating the manufacturing method of the printed wiring board which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows schematic structure of the printed wiring board which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows schematic structure of the printed wiring board which concerns on the 2nd Embodiment of this invention, Comprising: The figure which shows the state which the filling position of the conductive paste shifted | deviated especially when filling a via hole with a conductive paste It is. It is sectional drawing which shows schematic structure of the printed wiring board which concerns on the 2nd Embodiment of this invention, Comprising: It is a figure which shows the state with little filling amount of an electrically conductive paste especially when filling an electrically conductive paste to a via hole. is there. In the printed wiring board demonstrated in 1st Embodiment, it is sectional drawing which shows the state which coat | covered the surface of the 2nd conductive layer with the plating layer. FIG. 3 is a cross-sectional view showing a state in which the surface of the second conductive layer is covered with a plating layer in the printed wiring board described in the first embodiment, and particularly when the conductive paste is filled in the via hole, It is a figure which shows the state which the filling position of the paste shifted | deviated. FIG. 3 is a cross-sectional view showing a state in which the surface of the second conductive layer is covered with a plating layer in the printed wiring board described in the first embodiment, and particularly when the conductive paste is filled in the via hole, It is a figure which shows the state with little filling amount of a paste. In the printed wiring board demonstrated in 2nd Embodiment, it is sectional drawing which shows the state which coat | covered the surface of the 2nd conductive layer with the plating layer. FIG. 9 is a cross-sectional view showing a state where the surface of the second conductive layer is covered with a plating layer in the printed wiring board described in the second embodiment, particularly when the conductive paste is filled in the via hole. It is a figure which shows the state which the filling position of the paste shifted | deviated. FIG. 9 is a cross-sectional view showing a state where the surface of the second conductive layer is covered with a plating layer in the printed wiring board described in the second embodiment, particularly when the conductive paste is filled in the via hole. It is a figure which shows the state with little filling amount of a paste. It is sectional drawing which shows the modification of the printed wiring board of this invention. It is sectional drawing which shows schematic structure of the conventional printed wiring board. It is sectional drawing which shows schematic structure of the conventional printed wiring board, Comprising: It is a figure which shows the state which the filling position of the conductive paste shifted | deviated especially when filling a via hole with a conductive paste. It is sectional drawing which shows schematic structure of the conventional printed wiring board, Comprising: When a conductive paste is filled with a via hole especially, it is a figure which shows the state with little filling amount of a conductive paste.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Printed wiring board, 2 ... Insulating layer, 3 ... 1st conductive layer, 4 ... 2nd conductive layer, 5 ... Via hole, 6 ... Conductive paste, 8 ... Plating layer, 9 ... Nickel plating layer, 10 ... Gold plating layer, R1... Opening diameter of via hole in insulating layer, R2... Opening diameter of via hole in second conductive layer

Claims (5)

A first conductive layer;
An insulating layer provided on a surface of the first conductive layer;
A second conductive layer provided on a surface of the insulating layer and electrically connected to the first conductive layer;
A via hole formed in the insulating layer and the second conductive layer, having the first conductive layer as a bottom surface, the insulating layer, and the second conductive layer as a wall surface;
A conductive paste that fills the via hole and electrically connects the first conductive layer and the second conductive layer;
The printed wiring board, wherein an opening diameter of the via hole in the insulating layer is larger than an opening diameter of the via hole in the second conductive layer.   The insulating layer portion of the via hole has a tapered shape in which the opening diameter of the via hole in the insulating layer gradually decreases from the second conductive layer side toward the first conductive layer side. Item 4. A printed wiring board according to item 1.   The printed wiring board according to claim 1, wherein a surface of the second conductive layer is covered with a plating layer.   The printed wiring board according to claim 3, wherein the plating layer is a nickel-gold plating layer.   The printed wiring board according to any one of claims 1 to 4, wherein the printed wiring board is used as a substrate for a suspension used in a hard disk drive.

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