JP2017112191A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly insulation printed wiring board in which occurrence of electrochemical migration is prevented in a multilayer substrate.SOLUTION: A second insulating layer is formed on a first insulating layer while covering a microstrip line formed by etching a conductor layer laminated on the first insulating layer serving as a substrate, and a rear electrode of the microstrip line is formed on the second insulating layer. A printed wiring board structure where the microstrip line is provided in the middle layer of a multilayer substrate is obtained by providing the rear electrode on the surface of the second insulating layer, opposite to the surface in contact with the microstrip line.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a printed wiring board having high insulation properties that prevents the occurrence of electrochemical migration in a multilayer board.

  Recently, with the integration of electrical and electronic circuits, multilayered printed wiring boards have been promoted. In addition to the miniaturization of printed wiring boards, there is an increasing demand for the development of insulation technologies that can be used in high electric fields and high temperature and high humidity environments. In particular, there is a strong demand to avoid the problem of insulating deterioration caused by electrochemical migration or the like in a printed wiring board.

  Incidentally, electrochemical migration (hereinafter referred to as “migration”) means that the ionization of the halogen-based material used in the manufacturing process of the printed wiring board proceeds from the DC electric field applied to the printed wiring board, and the conductive electrode material This is a phenomenon in which a conductive member is deposited in the insulating layer of the printed wiring board by an electrochemical reaction. The conductive member formed by such migration gradually forms a conductive path toward the electrode in the printed wiring board, which causes a dielectric breakdown of the printed wiring board due to a short circuit. In addition, such migration is likely to occur in electrode portions provided on the surface layer of the printed wiring board mainly under a high DC voltage applied between the electrodes of the printed wiring board.

  The halogen-based material is blended with, for example, an etching material such as iron chloride used in the manufacturing process of a printed wiring board, or a flame retardant containing a glass epoxy material used as a core material as an insulator.

  There are also many places where alternating current is applied between the electrodes of the printed wiring board. Therefore, for example, in order to ensure EMC (electromagnetic environment compatibility) of a high-frequency line composed of a conductor wiring pattern, it is also important to suppress migration that occurs due to dielectric barrier discharge described later. Incidentally, the migration caused by the dielectric barrier discharge becomes a factor causing a change in wiring impedance in the printed wiring board.

  For such a problem, for example, Patent Document 1 proposes to form sensitive high-speed wiring such as operation wiring and control wiring on a printed wiring board as a microstrip line. A structure of a printed wiring board on which a microstrip line having a rear electrode (back electrode) is formed and a technique for reducing the conductor loss of the microstrip line are disclosed in, for example, Patent Document 2.

  Here, the structure of a printed wiring board provided with a microstrip line will be briefly described. FIG. 5 is a diagram showing a schematic configuration of a conventional general printed wiring board 1, and 2 is a first insulating layer which forms the base of the wiring board. Reference numeral 3 denotes a back electrode laminated on the first insulating layer 2, and reference numeral 4 denotes a second insulating layer laminated on the back electrode 3. Reference numeral 5 denotes a microstrip line formed on the second insulating layer 4. Reference numeral 6 denotes a resist layer that covers the microstrip line 5 and is provided on the surface of the printed wiring board 1.

  Incidentally, the printed wiring board 1 having the above structure is manufactured by firstly as shown in FIG. 6A, the first insulating layer 2, the first conductor layer 3a forming the back electrode 3, and the second insulating layer 4. Then, a laminated substrate material 1a in which the second conductor layers 5a for forming the microstrip line 5 are sequentially laminated is prepared. Then, as shown in FIG. 6B, the microstrip line 5 having a predetermined wiring pattern is formed by etching the second conductor layer 5a positioned on the surface layer of the laminated substrate material 1a. Is done. FIG. 7 is an external perspective view showing an example of the printed wiring board 1 manufactured by providing the microstrip line 5 in this manner. In FIG. 7, reference numerals 7 and 8 denote electronic components mounted on the printed wiring board 1.

  When the DC high electric field is applied between the microstrip line 5 and the back electrode 3 in the printed wiring board 1 having such a structure, the above-described migration is likely to occur. Further, when an alternating high electric field is applied between the microstrip line 5 and the back electrode 3, the dielectric barrier discharge A described above may occur. For example, as shown in FIG. 8, the dielectric barrier discharge A is generated from both sides of the wiring line of the microstrip line 5 on the surface layer of the printed wiring board 1 toward the air. Incidentally, the part where the dielectric barrier discharge A is generated is a triple junction part B indicated by a black circle in FIG. Here, the triple junction portion B refers to a portion where the second insulating layer 4, the second conductor layer 5 a forming the microstrip line 5, and the resist layer 6 are in contact with each other.

  Then, migration occurs along the creeping surface of the second insulating layer 4 in the printed wiring board 1 due to the dielectric barrier discharge A. FIG. 9 is a view schematically showing a state of migration M generated in the printed wiring board 1 due to the dielectric barrier discharge A. FIG. Such migration M can be confirmed by observing the cut surface of the printed wiring board 1 that crosses the microstrip line 5 as an SEM image.

  Incidentally, the migration described above is likely to occur in a high humidity environment. Therefore, conventionally, as a technique for solving the migration problem, for example, it has been proposed that the surface of the printed wiring board 1 is water-repellent coated with an ontadecanethiol solution or the like to suppress moisture absorption on the surface layer of the printed wiring board 1. . In addition, a metal material having a higher ionization tendency than that of the back electrode 3 is dispersed and mixed in the sealing material of the printed wiring board 1, thereby generating along the creeping surface of the second insulating layer 4 from the back electrode 3. It has also been proposed to suppress migration.

JP 2007-20142 A JP 2006-66563 A

  By the way, the migration in the printed circuit board 1 does not occur in the manufacturing process of the printed circuit board 1, but in addition to the electric field that is applied for a long time between the electrodes when the printed circuit board 1 is used, It progresses gradually due to external stress environment such as humidity and humidity. However, the usage environment of the printed circuit board 1 is various, and it is difficult to sufficiently secure the insulation reliability of the printed circuit board 1 only by the conventional migration countermeasure described above.

  The present invention has been made in consideration of such circumstances, and its purpose is to have high insulation reliability capable of reliably preventing the occurrence of electrochemical migration in a multilayer substrate even under a long-term use environment. It is to provide a printed wiring board.

  The present invention relates to a printed wiring board having a multilayer structure in which a plurality of conductor layers are laminated via an insulating layer, and in particular, the above-described dielectric barrier discharge when a DC electric field is applied or the above-described dielectric barrier discharge is printed. It is made paying attention that it is easy to generate | occur | produce in the surface layer of a wiring board.

  Therefore, in order to achieve the above-described object, the printed wiring board according to the present invention forms a microstrip line by etching a conductor layer laminated on the first insulating layer serving as a base, and covers the microstrip line. A second insulating layer is formed on the first insulating layer, and a multilayer structure is formed by laminating the back electrode of the microstrip line on the second insulating layer.

  Incidentally, the surface of the second insulating layer on which the back electrode is formed is the surface opposite to the surface in contact with the microstrip line of the second insulating layer. Specifically, the surface in contact with the microstrip line of the second insulating layer is an etching surface of the microstrip line formed by etching the conductor layer. Therefore, the microstrip line is formed as a middle layer of a printed wiring board having a multilayer structure.

  The back electrode may form a surface layer of the wiring board, or may be a middle layer in a printed wiring board having a multilayer structure.

  In addition, the printed wiring board, for example, dicing a large printed wiring board in which a plurality of circuit wiring patterns including the microstrip line are formed in parallel, thereby a plurality of circuit wiring patterns individually provided with the plurality of circuit wiring patterns. When realized as a circuit component, it is also preferable to individually seal each bulk end face (substrate end face) divided and exposed by dicing with a resin sealant.

  According to the present invention, the microstrip line formed on the first insulating layer is positioned in the middle layer of the printed wiring board having a multilayer structure in which the etching surface is covered with the second insulating layer. A back electrode of the microstrip line is formed on the second insulating layer. In other words, the microstrip line is enclosed by the first and second insulating layers and sealed as a middle layer of the printed wiring board. As a result, even when a DC voltage is applied between the electrodes, electrochemical migration is less likely to occur at the interface where the microstrip line is etched.

  Further, since it is provided as a middle layer of the printed wiring board of the microstrip line, it is possible to suppress the occurrence of the dielectric barrier discharge described above by weakening the alternating electric field applied to the triple junction portion on the etching surface of the microstrip line. As a result, even when an AC voltage is applied between the electrodes, the occurrence of electrochemical migration due to the dielectric barrier discharge can be suppressed.

  Furthermore, by sealing the diced substrate end face with resin, moisture permeation into the middle layer of the printed wiring board can be suppressed, and even when the printed wiring board is used in a high temperature and high humidity environment, Moisture absorption of the wiring board can be prevented. As a result, it is possible to achieve a great practical effect such as ensuring sufficient insulation reliability of a printed wiring board used in various environments.

The figure which shows typically the layer structure of the printed wiring board which concerns on one Embodiment of this invention. The figure which shows typically the manufacturing process of the printed wiring board shown in FIG. The figure which shows typically the layer structure of the printed wiring board which concerns on another embodiment of this invention. The external appearance perspective view which shows the example of the printed wiring board which concerns on another embodiment of this invention. The figure which shows schematic structure of the conventional general printed wiring board The figure which shows typically the manufacture process of a printed wiring board. The external appearance perspective view which shows the example of a printed wiring board. The figure which shows typically the mode of the dielectric barrier discharge which arises on the surface layer of a printed wiring board when an alternating voltage is applied. The figure which shows typically the mode of the electrochemical migration which generate | occur | produced in the printed wiring board resulting from dielectric material barrier discharge.

  Hereinafter, a printed wiring board according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram schematically showing a layer structure of a printed wiring board 10 according to an embodiment of the present invention. The printed wiring board 10 includes a microstrip line 12 formed on a first insulating layer 11 serving as a base, and a first insulating layer 11 formed on the first insulating layer 11 so as to cover the microstrip line 12. Two insulating layers 13 are provided. Further, the printed wiring board 10 has a multilayer structure including a back electrode 14 of the microstrip line 12 formed on the second insulating layer 13. A resist layer 15 is provided on the surface of the printed wiring board 10 so as to cover the back electrode 14.

  That is, the printed wiring board 10 is provided in the middle layer of the multilayer structure in which the microstrip line 12 is sandwiched between the first insulating layer 11 and the second insulating layer 13, and the back side of the microstrip line 12 This is realized as a member having a layer structure in which the electrode 14 is provided on the surface layer side.

  For example, as shown in FIG. 2A, the printed wiring board 10 having such a layer structure is manufactured by firstly forming the first insulating layer 11 and the first microstrip line 12. A laminated substrate material 11a on which the conductor layer 12a is laminated is prepared. Next, as shown in FIG. 2B, the microstrip line 12 having a predetermined wiring pattern is formed by etching the first conductor layer 12a in the laminated substrate material 11a.

  Thereafter, as shown in FIG. 2C, the second insulating layer 13 is formed on the first insulating layer 11 so as to cover the microstrip line 12, and the microstrip line 12 is connected to the first and first microstrip lines 12. It is embedded between two insulating layers 11 and 13. Thereafter, a second conductor layer as the back electrode 14 is formed on the second insulating layer 13 as shown in FIG. By forming the resist layer 15 so as to cover the back electrode 14 thus formed, the multilayer printed circuit board 10 in which the back electrode 14 is positioned on the surface layer is realized.

  As shown in FIG. 3, it is also possible to provide a multilayer printed circuit board 20 in which a third insulating layer 16 is further provided on the back electrode 14 and the back electrode 14 is positioned in the middle layer.

  Thus, according to the printed wiring boards 10 and 20 having the multilayer structure in which the microstrip line 12 is provided in the middle layer, the etching surface of the microstrip line 12 is covered with the second insulating layer 13. The back electrode 14 is provided on the surface of the second insulating layer 13 opposite to the surface in contact with the etching surface of the microstrip line 12.

  Therefore, compared with the creeping surface of the microstrip line 5 on the surface layer where the electrochemical migration is likely to occur in the conventional printed wiring board 1 having a general layer structure, the creeping property of the microstrip line 12 provided in the middle layer is increased. Electric field concentration can be avoided. As a result, the extension of electrochemical migration along the creeping surface of the microstrip line 12 can be effectively suppressed.

  That is, in the conventional printed wiring board 1, since the etching surface of the microstrip line 5 is formed along the surface layer surface of the multilayer substrate, the electric field concentration that causes electrochemical migration is exclusively, It tends to occur on the surface layer of a multilayer substrate. In this respect, according to the printed wiring boards 10 and 20 having the layer structure described above, the back electrode 14 is provided on the surface opposite to the etching surface of the microstrip line 12 with the second insulating layer 13 interposed therebetween. , Positioned in the middle layer of the multilayer substrate. Therefore, even if a DC high electric field is applied between the electrodes, the second insulating layer 13 prevents electric field concentration on the etching surface of the microstrip line 12. As a result, electrochemical migration along the creeping surface of the microstrip line 12 is less likely to occur.

  Further, since the microstrip line 12 is positioned in the middle layer of the multilayer substrate, moisture hardly penetrates into the microstrip line 12 even when the printed wiring boards 10 and 20 are used in a high humidity environment. . Therefore, since the microstrip line 12 can be kept in a dry condition, the electric field concentration can be suppressed also in this respect, and the occurrence of electrochemical migration can be effectively prevented.

  Further, even when an AC electric field is applied to the printed wiring boards 10 and 20, as described above, the microstrip line 12 is positioned in the middle layer of the multilayer board. Dielectric barrier discharge does not occur. Therefore, the occurrence of migration due to dielectric barrier discharge can be effectively prevented. As a result, the insulation reliability of the printed wiring boards 10 and 20 used in various environments can be sufficiently secured, and the practical advantages are great.

  By the way, the above-described electrochemical migration accelerates in a high temperature and high humidity environment with an electric field applied to the printed wiring boards 10 and 20. Further, the printed wiring boards 10 and 20 absorb more moisture from the exposed bulk exposed surface than the surface layer. That is, a large printed wiring board (not shown) in which a plurality of circuit wiring patterns including the microstrip line 12 are formed in parallel is diced, whereby a plurality of prints including the microstrip line 12 are individually provided. When the wiring boards 10 and 20 are cut out, it cannot be denied that the bulk end surfaces exposed by dicing of these printed wiring boards 10 and 20 are exposed.

  Such a bulk end surface has higher hygroscopicity than the surface layers of the printed wiring boards 10 and 20. Therefore, in order to suppress the above-described electrochemical migration, it is preferable that the bulk end surface exposed by dicing of the printed wiring boards 10 and 20 is water-tightly sealed with the resin sealant 17 as shown in FIG. The resin sealant 17 is sufficient if it has a property of blocking moisture, such as silicone, a silicone-based adhesive, and further an epoxy-based adhesive. However, silicone gel and other gel-based materials have many gaps microscopically because they have gel properties, and many have high moisture permeability from the gaps. Therefore, it is inappropriate to use this kind of gel material as the resin sealant 17.

  If the bulk end surfaces of the printed wiring boards 10 and 20 are sealed with the resin sealant 17 in this way, moisture (humidity) to the middle layer of the printed wiring boards 10 and 20 can be obtained even in a high temperature and high humidity environment. The entry can be suppressed. Therefore, the occurrence of migration can be prevented more reliably.

  The present invention is not limited to the embodiment described above. Here, the four-layer printed wiring boards 10 and 20 shown in FIG. 1 and the five-layer printed wiring boards 10 and 20 shown in FIG. 3 have been described, but the present invention can be similarly applied to a multilayer printed wiring board. In addition to the structure described above, the surface layer surface of the printed wiring boards 10 and 20 on which the resist layer 15 is formed is further coated with silicone putty, silicone resin, or epoxy resin to increase the water repellency of the surface layer surface. It is also effective to suppress the hygroscopicity of the printed wiring board. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 1 Printed wiring board 2 1st insulating layer 3 Back electrode 3a 1st conductor layer 4 2nd insulating layer 5 Microstrip line 5a 2nd conductor layer 6 Resist layer 10,20 Printed wiring board 11 1st insulating layer 12 Microstrip line 13 Second insulating layer 14 Back electrode 15 Resist layer 16 Third insulating layer 17 Resin sealant

Claims (5)

A multilayer printed wiring board in which a plurality of conductive layers are laminated via an insulating layer,
A microstrip line formed by etching a conductor layer laminated on a first insulating layer serving as a base;
A second insulating layer laminated on the first insulating layer covering the microstrip line;
A printed wiring board comprising: a back electrode of the microstrip line formed by being laminated on the second insulating layer.   2. The printed wiring board according to claim 1, wherein a surface of the second insulating layer on which the back electrode is formed is a surface opposite to a surface in contact with the microstrip line of the second insulating layer.   The printed wiring board according to claim 2, wherein a surface of the second insulating layer that contacts the microstrip line is an etched surface of the microstrip line formed by etching the conductor layer.   The printed wiring board according to claim 1, wherein the back electrode is provided in a middle layer of a multilayer printed wiring board.   The printed wiring board according to any one of claims 1 to 4, wherein the bulk end face exposed by dicing is water-tightly sealed with a resin sealant.

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