JP2020129593A - Method of manufacturing multilayer wiring board - Google Patents

Abstract

To further improve reliability of a multilayer wiring board formed by laminating a first substrate including a bus bar and a second substrate including a conductor in contact with the bus bar.SOLUTION: A manufacturing method of a multilayer wiring board of hot pressing a first board including a board body having an opening and a bus bar fitted in the opening and a second substrate including a conductor in contact with the bus bar in a state of being laminated via a resin sheet, includes the steps of: roughening a surface of the busbar after subjecting at least one edge part of the bus bar to an R chamfering process; and fitting the bus bar into the opening of the board body before hot pressing the first and second boards.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a method for manufacturing a multilayer wiring board in which a first substrate including a bus bar and a second substrate including a conductor in contact with the bus bar are laminated.

Conventionally, as a wiring board capable of passing a large current, a thick circuit conductor and an insulating material such as a glass epoxy material are formed to have almost the same thickness as the thick circuit conductor, and an inner side made of copper foil on both sides or one side. There is known one including an inner layer material (insulating base material) on which circuits are laminated, and an outer circuit made of copper foil laminated on the inner layer material via an insulating resin (prepreg material) (for example, Patent Document 1). 1). The inner layer material of this wiring board is provided with a hollow hole having substantially the same thickness and substantially the same shape as the thick circuit conductor, and the thick circuit conductor is fitted into the hollow hole. Further, in order to prevent discharge breakdown of the edge portion of the thick-walled circuit conductor when a high voltage is applied and improve the pressure resistance, the edge portion is rounded. Then, a prepreg material and a copper foil to be an outer circuit are laminated on the surfaces of the plate-shaped inner layer material and the thick circuit conductor, and fixed by hot pressing. The insulating resin of the prepreg material is melted during hot pressing and flows into a slight gap between the thick circuit conductor and the inner layer material, whereby the gap is filled with the insulating resin.

JP-A-8-148841

However, in the above-mentioned conventional wiring board, even if the edge portion of the thick-walled circuit conductor is rounded, it occurs due to the difference in the linear expansion coefficient between the thick-walled circuit conductor and the inner layer material after hot pressing The stress concentrates near the edge portion of the thick circuit conductor, which may cause the insulating resin to peel off from the thick circuit conductor. Therefore, the above-mentioned conventional wiring board may lead to poor conduction and deterioration of insulation, and there is still room for improvement in terms of reliability.

Therefore, the present disclosure mainly aims to further improve the reliability of a multilayer wiring board in which a first substrate including a bus bar and a second substrate including a conductor in contact with the bus bar are stacked.

A method for manufacturing a multilayer wiring board according to an embodiment of the present disclosure uses a resin sheet that includes a first substrate including a substrate body having an opening and a bus bar fitted in the opening, and a second substrate including a conductor in contact with the bus bar. A method for manufacturing a multilayer wiring board in which heat is pressed in a state of being laminated via, wherein after at least one edge portion of the bus bar is subjected to R chamfering, the surface of the bus bar is roughened, (2) Before the hot pressing of the board, the bus bar is fitted into the opening of the board body.

As described above, by roughening the surface of the bus bar with the R chamfering process applied to at least one edge portion before the hot pressing, the resin of the resin sheet melted by the hot pressing and the bus bar are closely attached. As a result, it is possible to sufficiently secure the property, and it is possible to favorably prevent the cured resin from peeling off from the bus bar. As a result, it is possible to further improve the reliability of the multilayer wiring board in which the first substrate including the bus bar and the second substrate including the conductor in contact with the bus bar are stacked.

FIG. 3 is a cross-sectional view showing a multilayer wiring board manufactured by the method of the present disclosure. 2 is an exploded view showing the structure of the multilayer wiring board of FIG. 1. FIG. It is explanatory drawing which shows the bus bar contained in the multilayer wiring board of FIG.

Next, modes for carrying out the invention of the present disclosure will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing a multilayer wiring board 1 manufactured by the method of the present disclosure, and FIG. 2 is an exploded view showing the structure of the multilayer wiring board 1. The multilayer wiring board 1 shown in these drawings constitutes a power device such as a voltage converter together with electronic components such as semiconductor elements mounted thereon. The multilayer wiring board 1 includes an intermediate substrate 10 as a first substrate, an upper substrate 20 and a lower substrate 30 as a second substrate, between the intermediate substrate 10 and the upper substrate 20, and between the intermediate substrate 10 and the lower substrate 30. And a resin sheet 40 as an insulating adhesive layer that is disposed between and. The multilayer wiring board 1 is formed by stacking and integrating the upper substrate 20 and the lower substrate 30 on the front surface (upper surface) and the back surface (lower surface) of the intermediate substrate 10 with the resin sheet 40 interposed therebetween.

The intermediate substrate 10 has a substrate body 11 obtained by impregnating a cloth (woven fabric) made of inorganic fibers such as glass fibers with a thermosetting resin such as an epoxy resin and completely curing the same, and has substantially the same thickness as the substrate body 11. For example, the plurality of bus bars 15 which are plate-shaped conductors made of copper are included. As shown in FIG. 2, the substrate body 11 is formed with a plurality of openings 12 into which the corresponding bus bars 15 are fitted, through holes 13 having lands, and the like. In the present embodiment, each opening 12 is formed at a predetermined position by punching or the like, and has a quadrangular cross-sectional shape with predetermined dimensions.

The bus bar 15 is formed by punching a conductive plate material by, for example, press working. In the present embodiment, the plurality of bus bars 15 are each formed in a rectangular parallelepiped shape having a predetermined dimension, and all the edge portions E (corners extending along the sides) of each bus bar 15 have the shape shown in FIG. As shown in, the R chamfering process is performed. The substrate body 11 and the bus bar 15 may have a thickness of, for example, 0.1 mm or more, and in the present embodiment, have a thickness of about 1 to 2 mm. As a result, it becomes possible to pass a large current through the circuit configured in the device including the multilayer wiring board 1. In addition, the bus bar 15 may be formed to have an L-shaped or T-shaped planar shape, for example.

The upper substrate 20 includes a substrate body 21 in which a cloth (woven fabric) made of inorganic fibers such as glass fibers is impregnated with a thermosetting resin such as an epoxy resin and completely cured. A wiring pattern 22 made of, for example, a copper foil or the like is formed (deposited) on the front surface and the back surface of the substrate body 21. Further, the substrate body 21 is formed so as to be in contact with the via hole 23 for conducting the wiring patterns 22 on the front and back surfaces and the corresponding bus bar 15 of the intermediate substrate 10, for example, a short cylinder or a short prism (a rectangular parallelepiped shape or a cubic shape). ), a plurality of posts (conductors) 25 are included. The plurality of posts 25 are formed on the wiring pattern 22 formed on the surface of the substrate main body 21 on the side of the intermediate substrate 10 (the lower surface in FIG. 2 ), for example, a refractory metal such as copper and a low melting point alloy such as tin-bismuth alloy. It is formed by printing an electrically conductive paste containing, and melting the low melting point metal by heat treatment and solidifying so as to surround the high melting point metal.

The lower substrate 30 also includes a substrate body 31 obtained by impregnating a cloth (woven fabric) made of inorganic fibers such as glass fibers with a thermosetting resin such as an epoxy resin and completely curing the cloth. A wiring pattern 32 made of, for example, a copper foil or the like is formed (formed) on the front surface and the back surface of the substrate body 31. Further, the substrate main body 31 includes via holes 33 for electrically connecting the wiring patterns 32 on the front and back surfaces, and a plurality of posts (conductors) 35 formed so as to be in contact with the corresponding bus bars 15 of the intermediate substrate 10. The plurality of posts 35 are also formed in the same manner as the posts 25 described above.

The resin sheet 40 is a prepreg that is semi-cured by impregnating a cloth (woven fabric) made of inorganic fibers such as glass fibers with a thermosetting resin such as an epoxy resin. That is, when the resin sheet 40 is heated, the thermosetting resin impregnated in the cloth is melted, and when the resin sheet 40 is cooled thereafter, the thermosetting resin is completely cured. As illustrated, the resin sheet 40 has a plurality of through holes (circular holes) 41 into which the corresponding posts 25 or 35 of the upper substrate 20 or the lower substrate 30 are inserted.

Next, a method for manufacturing the above-mentioned multilayer wiring board 1 will be described.

When manufacturing the multilayer wiring board 1, the intermediate substrate 10, the upper substrate 20, the lower substrate 30 and the two resin sheets 40 described above are individually manufactured. When manufacturing the intermediate substrate 10, a substrate body 11 having a plurality of openings 12 and the like is cut out from a base material in which a cloth made of an inorganic fiber is impregnated with a thermosetting resin, and through holes 13 and the like are formed in the substrate body 11. To do. A wiring pattern may be formed on the surface of the substrate body 11 if necessary. Further, the bus bar 15 is cut out from the plate body, and each edge portion E of the cut out bus bar 15 is subjected to the R chamfering process.

Further, in the present embodiment, the surface roughening treatment is performed on the entire surface of the bus bar 15 having the R chamfering processing on each edge portion E. In the surface roughening treatment, the entire surface of the bus bar 15 is provided with minute irregularities of, for example, several μm order. In the present embodiment, the surface of the bus bar 15 is roughened by, for example, micro etching. However, the surface roughening treatment may be a blackening treatment or a roughening treatment using a laser. Then, after the surface roughening treatment is completed, the plurality of bus bars 15 are fitted into the openings 12 of the substrate body 11 to obtain the intermediate substrate 10.

When manufacturing the upper substrate 20, a substrate body 21 having a plurality of holes and the like is cut out from a base material obtained by impregnating a cloth made of an inorganic fiber with a thermosetting resin, and a wiring pattern 22 and a via hole 23 are formed on the substrate body 21. And so on. Further, a conductive paste is printed on the wiring pattern 22 using a metal mask (not shown) and semi-sintered to form a plurality of posts 25. When manufacturing the lower substrate 30, similarly, a substrate body 31 having a plurality of holes and the like is cut out from a base material obtained by impregnating a cloth made of an inorganic fiber with a thermosetting resin, and the wiring pattern 32 is formed on the substrate body 31. The via hole 33 and the like are formed. Further, a conductive paste is printed on the wiring pattern 32 using a metal mask (not shown) and semi-sintered to form a plurality of posts 35. Further, the resin sheet 40 is cut out from the prepreg material to form a plurality of through holes 41.

After the intermediate substrate 10, the upper substrate 20, the lower substrate 30 and the two resin sheets 40 are prepared, the resin sheet 40 is superposed on the front surface and the back surface of the intermediate substrate 10, and further, the front surface (upper surface) side of the intermediate substrate 10 side. The upper substrate 20 is superposed on the resin sheet 40, and the lower substrate 30 is superposed on the resin sheet 40 on the back surface (lower surface) side of the intermediate substrate 10. The posts 25 and 35 of the upper substrate 20 and the lower substrate 30, which are superposed on the resin sheet 40, are inserted into the corresponding through holes 41 of the resin sheet 40, and the surface of the corresponding bus bar 15 fitted to the intermediate substrate 10. Abut.

Subsequently, the laminated intermediate substrate 10, upper substrate 20, lower substrate 30, and two resin sheets 40 are subjected to hot pressing. In the hot pressing, the upper substrate 20 and the lower substrate 30 are heated while heating the laminated intermediate substrate 10, upper substrate 20, lower substrate 30 and two resin sheets 40 to a predetermined temperature (for example, 160 to 200° C.). Is pressurized at a predetermined pressure so as to approach the intermediate substrate 10, and is preferably performed in a vacuum atmosphere. By such hot pressing, the height of each post 25, 35 from the corresponding wiring pattern 22, 32 and the thickness of each resin sheet 40 are adjusted, and the tips of the posts 25, 35 correspond to the intermediate substrate 10. Sintering is performed in a state of closely contacting the surface of the bus bar 15.

Further, when the hot pressing is performed, the semi-cured thermosetting resin contained in the resin sheet 40 is heated and melted, and the substrate body 11 (wall surface defining the opening 12) of the intermediate substrate 10 is formed. It flows into a slight gap between each bus bar 15. As a result, the thermosetting resin is filled in the gap between the substrate body 11 and each bus bar 15. At this time, since the surface of each bus bar 15 having the R chamfering process applied to each edge E is roughened, the thermosetting resin melted during the hot pressing should be closely adhered to the entire surface of the bus bar 15. It is possible to prevent the cured thermosetting resin from peeling off from the bus bar 15. When the thermosetting resin is completely cured according to the temperature decrease after the completion of the hot pressing, the manufacturing of the multilayer wiring board 1 is completed.

As described above, the manufacturing method of the multilayer wiring board 1 of the present disclosure includes the intermediate substrate (first substrate) 10 including the substrate body 11 having the opening 12 and the bus bar 15 fitted in the opening 12. The upper substrate 20 and the lower substrate 30 as the second substrate including the posts 25 and 35 which are conductors in contact with the bus bar 15 are heat-pressed in a state of being laminated via the resin sheet 40. After subjecting the edge portion E to the R chamfering process, the surface of the bus bar 15 is roughened, and the bus bar 15 is formed on the substrate before the intermediate substrate 10, the upper substrate 20, the lower substrate 30 and the two resin sheets 40 are hot pressed. It fits into the opening 12 of the main body 11.

As described above, by roughening the surface of the bus bar 15 having the R chamfering process on the edge portion E before the hot pressing, the thermosetting resin of the resin sheet 40 melted by the hot pressing is formed. Adhesion with the bus bar 15 can be sufficiently ensured, and peeling of the cured thermosetting resin from the bus bar 15 can be effectively suppressed. As a result, a multilayer in which the intermediate substrate (first substrate) 10 including the bus bar 15 and the upper substrate 20 and the lower substrate 30 as the second substrate including the posts 25 and 35 which are conductors in contact with the bus bar 15 are laminated. The reliability of wiring board 1 can be further improved.

It should be noted that one of upper substrate 20 and lower substrate 30 may be omitted from multilayer wiring board 1. Moreover, the intermediate substrate 10 does not necessarily need to include the plurality of bus bars 15, but may include at least one bus bar 15. Further, it is not necessary to perform the R chamfering processing on all the edge portions E of the bus bar 15, and the R chamfering processing on a part of the edge portions E may be omitted. The upper substrate 20 and the lower substrate 30 as the second substrate include posts 25 and 35 as conductors that contact the bus bar 15, but conductors other than the posts 25 and 35 that contact the bus bar 15 are included. Alternatively, for example, the wiring patterns 22 and 32 formed on the upper substrate 20, the lower substrate 30, or the like may be used.

Further, it goes without saying that the invention of the present disclosure is not limited to the above-described embodiments, and various modifications can be made within the scope of the extension of the present disclosure. Furthermore, the above embodiment is merely one specific form of the invention described in the summary of the invention, and does not limit the elements of the invention described in the summary of the invention.

INDUSTRIAL APPLICABILITY The invention of the present disclosure can be used in the manufacturing industry of multilayer wiring boards.

DESCRIPTION OF SYMBOLS 1 multilayer wiring board, 10 intermediate board, 11 board body, 12 opening, 13 through hole, 15 bus bar, 20 upper board, 21,31 board body, 22,32 wiring pattern, 23,33 via hole, 25,35 post, 30 lower substrate, 40 resin sheet, 41 through hole, E edge part.

Claims (1)

A multilayer structure in which a first substrate including a substrate body having an opening and a bus bar fitted in the opening and a second substrate including a conductor in contact with the bus bar are heat-pressed in a state of being laminated via a resin sheet. A method of manufacturing a wiring board, comprising:
After subjecting at least one edge portion of the bus bar to an R chamfering process, the surface of the bus bar is roughened, and the bus bar is attached to the opening of the substrate body before hot pressing the first and second substrates. A method of manufacturing a multilayer wiring board to be fitted.

Images