JPH1051094A - Printed wiring board, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a printed wiring board landless and enable the density elevation of wiring patterns and the flattening of component mounting surface, by directly connecting the obverse and reverse conductors of the printed wiring board with only the conductive paste filling a through hole. SOLUTION: The width of a conductor 4A fronting on the brim of the opening of a through hole 3 is made equivalent to or smaller than the diameter of the through hole 3, and conductive paste 7 connecting with the conductive paste 6 filling the through hole 3 is made in the form of a land including this conductor 4A. Hereby, the obverse and reverse conductors 4A of the printed wiring board are directly connected with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board and a method for manufacturing the same, and more particularly, to a printed wiring board having landless through holes for connecting conductors of wiring patterns formed on both front and back surfaces of a substrate. The present invention relates to the manufacturing method.

[0002]

2. Description of the Related Art In recent years, a low-cost double-sided printed wiring board having a structure in which a conductive paste such as a silver paste is filled in through holes by a screen printing method or the like to electrically connect front and back conductors has appeared. In addition, it is widely used in various electronic devices and has high reliability.

FIG. 3 is a partial cross-sectional view showing an example of this type of conventional double-sided printed wiring board, and FIG. 4 is a plan view of a through-hole portion. 3 and 4, a wiring pattern 12 is formed on both front and back surfaces of the insulating substrate 11, and a through hole 13 is formed in the insulating substrate 11 corresponding to the land portion 12a of the wiring pattern 12. By filling the through holes 13 with the conductive paste 14 by a screen printing method or the like, the front and back wiring patterns are connected to each other, and the conductive paste 14a is formed on the surface of the land portion 12a in a raised state. further,
A solder resist layer 15 is formed on the surface of the insulating substrate 11 except for the land portions 12a and the parts to be soldered. In FIG. 4, A is the opening diameter of the solder resist 15 with respect to the through hole 13, and B is the land 12a.
, C is the diameter of the conductive paste 14a, and D is the diameter of the through hole 13.

[0004]

By the way, in mounting components on a through-hole type double-sided printed wiring board,
In many cases, a surface mounting method is adopted, and in this case, it is desirable that the surface of a portion where the surface mounting component is mounted be flat. However, in the double-sided printed wiring board as described above, the conductive paste 14
In order to ensure electrical conduction between the front and back conductors, the conductive paste 14a is also printed on the surface of the land portion 12a to a smaller diameter than the land portion 12a and formed in a raised state, so that the surface portion of the through hole is formed. The total thickness including the land portion 12a in the above reaches 50 to 100 μm,
It protrudes more than other areas. So, for example,
If the above-described through-holes exist in the mounting area of the surface mount component such as a semiconductor package such as a QFP, this portion hinders the mounting and soldering of the surface mount component, and the electrical connection of the surface mount component becomes poor. The problem of uncertainty arises.

Further, a conductive paste 14 filled in a through hole 13 between conductors on the front and back surfaces of a printed wiring board.
In this case, a land is formed of copper foil around the opening of the through-hole 13 and a conductive paste is also printed on the land.
In order to maintain the relationship between the diameter of the land and the diameter B of the land and the diameter C of the conductive paste on the land as shown in FIG. 4, it is difficult to reduce the diameter of the land. Etc., and the wiring density and the mounting density decrease.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned points, and has a landless structure by directly connecting the front and back conductors of a printed wiring board with only a conductive paste filled in through holes. It is an object of the present invention to provide a printed wiring board and a method for manufacturing the same, which enable high density and flattening of a component mounting surface.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, according to the present invention, there is provided a wiring pattern formed on the front and back surfaces of a substrate, wherein a part of the conductors is formed on the substrate at the position of the conductor. A printed wiring board connected by filling a conductive paste into a through hole, wherein a width of a conductor viewed from an opening edge of the through hole is formed to a width equal to or smaller than a through hole diameter, and a through hole including the conductor is formed. A conductive paste connected to the conductive paste in the through hole is formed in a land shape on the periphery of the opening. Therefore, in the printed wiring board of the present invention, since the front and back conductors of the printed wiring board are directly connected only with the conductive paste filled in the through-hole, it is possible to make a landless, and at the periphery of the opening of the through-hole. The diameter of the entire conductive portion for connecting the front and back conductors to be formed is reduced, and the height thereof is reduced, so that the wiring pattern can be made denser and the component mounting surface can be flattened.

The present invention also relates to a method of manufacturing a printed wiring board for connecting conductors on both front and back surfaces by filling a conductive paste in a through hole, wherein a first method for forming a through hole in a double-sided metal foil-clad board is provided. A step of forming a wiring pattern with an etching resist on the metal foil and forming a conductor of the wiring pattern looking into the through hole in a landless manner, and after removing the metal foil other than the wiring pattern, A third step of removing an etching resist on the wiring pattern, a fourth step of forming a solder resist layer on a surface of the substrate other than an opening peripheral portion of the through hole and a portion soldered to the wiring pattern, The conductive paste is filled in the holes, and the conductive paste is landed on the periphery of the opening of the through hole. It is made and a fifth step of electrically connecting the conductor facing the opening edge of the through hole is formed on. Therefore, in the method of the present invention, since the front and back conductors of the printed wiring board are directly connected only with the conductive paste filled in the through-holes, it is possible to make landless, and at the periphery of the opening of the through-hole. In addition to reducing the diameter of the entire conductive portion for connecting the front and back conductors and reducing the height thereof, it is possible to increase the density of the wiring pattern and flatten the component mounting surface.

Further, according to the present invention, the thickness of the conductive paste formed on the periphery of the opening of the through hole is adjusted by the thickness of the solder resist layer formed on the surface of the substrate other than the periphery of the opening of the through hole and the portion soldered to the wiring pattern. The peripheral wall of the solder resist layer surrounding the conductive paste at the peripheral edge of the through-hole opening,
It also serves as a dam effect of preventing abnormal approach between adjacent conductors due to the migration phenomenon of the conductive paste and preventing bleeding.

[0010]

1 and 2, an embodiment of a printed wiring board according to the present invention and a method for manufacturing the same will be described. FIG. 1 is an explanatory diagram showing a procedure of a manufacturing process of a printed wiring board according to an embodiment of the present invention.

First, as shown in FIG. 1A, a through-hole 3 is formed in a double-sided copper-clad board 1 having copper foils 2 adhered to the front and back surfaces at locations where the front and back conductors are to be electrically connected. Next, a wiring pattern is formed on the copper foil 2 with an etching resist by a screen printing method, a photographic method, or the like. In this case, the wiring pattern looking into the through hole 3 is formed in a landless manner. Thereafter, the copper foil 2 other than the wiring pattern formed by the etching resist by the etching process is removed, and the etching resist on the wiring pattern is further removed, so that the wiring pattern 4 shown in FIG.
To form In this case, the width of the conductor 4A looking into the through hole 3 of the wiring pattern 4 is formed to have a width equal to or smaller than the diameter of the through hole, and the conductor 4A is directly seen at the opening edge of the through hole 3 by landless. ing.

Next, as shown in FIG. 1C, a solder resist layer 5 is formed on the surface of the substrate 1 except for the peripheral edge of the opening of the through hole 3 and the soldering portion 4B for the wiring pattern 4. In this case, as shown in FIG. 2, the opening diameter E of the solder resist layer 5 surrounding the opening peripheral portion of the through hole 3 is formed to have a size corresponding to the land diameter B shown in FIG. Next, as shown in FIG. 1 (D), a conductive paste 6 such as a silver paste is filled in the through-hole 3 by a dispenser method or the like, and a conductive paste 7 is landed on the peripheral edge of the opening of the through-hole 3. To electrically connect between the conductors 4A of the wiring pattern 4 looking at the opening edges of the through holes 3. At this time, the diameter C of the conductive paste 7
Is formed in the same diameter as that shown in FIG. 4, as shown in FIG. The thickness of the conductive paste 7 formed on the periphery of the opening of the through-hole 3 is approximately equal to the thickness of the solder resist layer 5.

Although not shown, after the conductive pastes 6 and 7 are hardened, a protective overcoat layer is applied to the surface of the conductive paste 7 and the other surface except for the soldered portion 4B. It has become.

According to the printed wiring board according to the present embodiment, the conductor 4 looking at the opening edge of the through hole 3
A is formed to have a width equal to or smaller than the diameter of the through-hole 3, and a conductive paste 7 connected to the conductive paste 6 filled in the through-hole 3 is formed around the opening of the through-hole 3 including the conductor 4 </ b> A. By forming in a land shape, the front and back conductors 4A of the printed wiring board are directly connected to each other.
The entire conductive portion for connecting the front and back conductors formed on the peripheral edge of the opening of the through hole can be reduced in diameter and its height can be reduced. Thereby, the distance between the wiring pattern, the chip land and the like adjacent to the through hole can be set narrower, and the density of the wiring pattern can be increased, and the height of the conductive paste 7 can be reduced. In addition, the component mounting surface can be flattened.

The thickness of the conductive paste 7 formed on the peripheral edge of the opening of the through hole 3 is adjusted by the solder resist layer 5 formed on the surface of the substrate other than the peripheral edge of the opening of the through hole 3 and the portion to be soldered to the wiring pattern 4. The thickness of the solder resist layer 5 surrounding the conductive paste 7 at the periphery of the opening of the through-hole is reduced to the same level as the thickness of the solder resist layer 5.
The opening peripheral wall 5A prevents bleeding due to the dam effect, and causes a migration phenomenon of the conductive paste 7 (a phenomenon in which silver or the like in the conductive paste is ionized by current, humidity and temperature and grows in a branch shape) between adjacent conductors. Abnormal approach can be avoided.

[0016]

As is apparent from the above description, according to the present invention, the width of the conductor viewed from the opening edge of the through hole is formed to be equal to or smaller than the diameter of the through hole, and the width of the through hole including this conductor is reduced. By forming a conductive paste that is connected to the conductive paste filled in the through-hole in the periphery of the opening in a land shape, the front and back conductors of the printed wiring board are directly connected, enabling landlessness. In addition, the entire conductive portion for connecting the front and back conductors formed on the periphery of the opening of the through hole can be reduced in diameter and height can be reduced, and accordingly, the wiring pattern adjacent to the through hole, The distance between chip lands can be set narrower, making it possible to increase the density of wiring patterns. By pressing the height low,
The component mounting surface can be flattened.

Further, according to the present invention, the thickness of the conductive paste formed on the periphery of the opening of the through hole is reduced to approximately the same as the thickness of the solder resist layer. The peripheral wall of the opening of the solder resist layer 5 surrounding the conductive paste 7 prevents bleeding due to the dam effect, and can avoid abnormal approach between adjacent conductors due to the migration phenomenon of the conductive paste 7.

[Brief description of the drawings]

FIGS. 1A to 1D are explanatory views showing a process for manufacturing a printed wiring board according to an embodiment of the present invention.

FIG. 2 is a plan view of a through hole portion according to the embodiment of the present invention.

FIG. 3 is a partial cross-sectional view showing a conventional printed wiring board.

FIG. 4 is a plan view of a conventional through-hole portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Double-sided copper-clad board 2 Copper foil 3 Through hole 4 Wiring pattern 4A Conductor 4B Solder part 5 Solder resist layer 6, 7 Conductive paste

Claims (2)

[Claims] 1. Printed wiring for connecting between conductors of a part of a wiring pattern formed on both front and back surfaces of a substrate by filling a through-hole formed in the substrate with a conductive paste at a position of the conductor. A plate, wherein the width of the conductor viewed from the opening edge of the through hole is formed to a width equal to or smaller than the diameter of the through hole, and the conductive paste in the through hole is formed on the periphery of the opening of the through hole including the conductor. A printed wiring board, wherein a conductive paste to be connected is formed in a land shape. 2. A method of manufacturing a printed wiring board for connecting conductors on both front and back sides by filling a conductive paste in through holes, a first step of forming through holes in a double-sided metal foil-clad board, A second step of forming a wiring pattern with an etching resist on the metal foil and forming a conductor of the wiring pattern looking into the through hole in a landless manner;
A third step of removing the etching resist on the wiring pattern after removing the metal foil other than the wiring pattern, and a solder resist on the surface of the substrate other than the peripheral edge of the opening of the through hole and a portion soldered to the wiring pattern. A fourth step of forming a layer; and filling the conductive paste in the through-hole and forming the conductive paste in a land shape around the opening of the through-hole, and the conductor looking into the opening edge of the through-hole. And a fifth step of electrically connecting between them.