JPH09266364A - Printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the through-hole connection property with use of a conductive paste by cutting concentric circular grooves into lands of through-holes of a circuit board having circuit layers which are formed on both sides of the board and connected by the conductive paste. SOLUTION: At forming of a circuit pattern 1, concentric circular grooves 5 are cut into lands of through-holes 2 to bury a conductive paste on the lands into the grooves 5, resulting in undercuts to a horizontal force, thus making them durable against this force and greatly reducing the break of the hardened paste. The grooves 5 are formed by etching a Cu foil of a cu-lined laminated board, resulting in that a fine rough surface of the original Cu foil is transferred to the grooves 5, hence the adhesion of the Cu paste is more strong than that at the Cu foil surface of the lands to thereby contribute to the reliability improvement at parts mounting with solder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board having through holes formed by connecting circuit layers with a conductive paste.

[0002]

2. Description of the Related Art In recent years, a through hole is provided in a land portion of a printed circuit board such as a paper phenol board or a glass epoxy board, and a conductive silver paste (hereinafter referred to as silver paste) or a conductive copper paste (hereinafter referred to as copper) is provided therein. A method of manufacturing a printed wiring board by embedding a conductive paste (such as a paste) by screen printing and then heat curing it has become popular.

The reliability of these conductive pastes is greatly affected by the adhesion of the through hole to the circuit land portion. Therefore, in order to improve the adhesion with the copper foil, the circuit board is subjected to polishing, blasting, chemical surface treatment, etc., and the conductive paste is considered to be improved by various prescriptions. However, when a circuit board is manufactured, it is not always produced under the optimum curing conditions that allow the characteristics of the conductive paste to be maximized. Chips are more likely to occur.

Further, even if cured under optimum conditions,
It is often the case that several tens to several hundreds of circuit boards can be stacked in various processes including the production site. At that time, the substrates are often rubbed with each other or impacted, and the conductive paste on the land is often chipped, which is a problem.

[0005]

The printed wiring board of the present invention solves the above problems by devising the shape of the land, remarkably enhances the through-hole connection reliability by the conductive paste, and improves the production yield. It contributes to improvement and stability.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a printed circuit board having through holes formed by connecting respective circuit layers formed on both sides of the board with a conductive paste has concentric circles on lands of through holes. The present invention relates to a printed circuit board having a groove.

In the present invention, the above-described land shape allows the conductive paste on the land to be embedded in this groove and undercut against a horizontal force, so that it can withstand this force. The occurrence of chipping of the cured conductive paste can be greatly reduced. Furthermore,
Since this groove is created by etching the copper foil of the copper clad laminate, there is unevenness that is transferred from the fine unevenness of the original copper foil, so the adhesion of the copper paste is better than that of the land copper foil surface. Become stronger. (The copper-clad laminate uses an electrolytic copper foil with a micro unevenness on one side to firmly maintain the adhesion between the copper foil and the insulating base material. In addition, it also becomes stronger against the force generated by the difference in expansion and contraction amount of the copper paste and the board due to heat, for example, and contributes to the improvement of reliability when mounting components by soldering.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of the present invention will be described below with reference to the drawings. The printed circuit board used in the present invention is a paper-based phenol resin copper-clad laminate, a glass-based epoxy resin copper-clad laminate, or the like. The circuit patterns 11 are formed by etching the copper foils on both sides, and through holes 12 for connecting the layers on both sides with a conductive paste are formed at desired locations. Further, the land 13 of the wiring is provided in the through hole 12 in a circular shape (FIG. 1).

A conductive paste 14 is filled in the through hole 12 by, for example, a screen printing method, and is cured under predetermined conditions to electrically connect the circuit layers on both sides (FIG. 2). In FIG. 2, (a) is a state where the conductive paste is filled, and (b) is a state where the conductive paste is cured.

In the present invention, as shown in FIG. 3 and FIG.
When the circuit pattern 1 is formed, the land portion 3 is etched so that the grooves 5 are formed concentrically. By forming the land portion 3 in such a shape, as shown in FIG. 5, the conductive paste 4 embedded in the through hole 2 is formed in the groove 5 at a portion above the land.
Due to this, it becomes an undercut shape and can withstand the force in the horizontal direction, and the occurrence of chipping can be greatly reduced. Normally, one concentric groove may be provided, but two or more may be provided.

[0011]

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples. Example 1 A paper base phenol resin copper clad laminate having a plate thickness of 1.6 mm is processed to form a through hole having a diameter of 0.5 m.
m, the land diameter was 1.0 mm, and the groove was formed with a width of 0.1 mm in the center of the outer diameter of the land and the edge of the through hole (FIGS. 3 and 4). A copper paste for through holes was filled in the through holes by screen printing and cured under predetermined conditions (FIG. 5). The printed circuit board used in the present invention has a size of 300 mm × 300 mm, and the number of through holes is 3000 holes. 50, 100, and 500 printed circuit boards obtained in this way were stacked and placed on a trolley, and a step having a width of 5 cm and a height of 1 cm was reciprocated 20 times. Counted. The results are shown in Table 1.

(Example 2) A glass-based epoxy resin copper-clad laminate was processed in the same manner as in Example 1 to prepare a printed circuit board, and the same test was carried out.

(Example 3) A printed circuit board was prepared in exactly the same manner as in Example 1 except that a silver paste for through holes was filled in place of the copper paste and cured under predetermined conditions.
A similar test was performed.

Comparative Examples 1 to 3 In Examples 1 to 3,
A circuit board was processed and tested in exactly the same manner except that no groove was formed in the land.

[0015]

[Table 1]

[0016]

In the conventional printed circuit board having through holes formed by connecting the circuit layers on both sides of the board with the conductive paste, when the circuit boards are stacked from several tens to several hundreds, There was often a problem that the conductive paste on the land was chipped due to rubbing or impact, but in the present invention, the conductive paste and the land portion are closely attached by forming concentric grooves on the land of the through hole portion. It is possible to increase the power to solve the above problem, and therefore, the reliability of through-hole connection by the conductive paste is remarkably improved, and the production yield is improved and stabilized.

[Brief description of drawings]

FIG. 1 is a perspective sectional view of a printed circuit board having a land.

FIG. 2 is a cross-sectional view of a printed circuit board filled with a conductive paste.

FIG. 3 is a plan view of a printed circuit board having a land shape according to the present invention.

4 is a cross-sectional view of the printed circuit board of FIG.

5 is a cross-sectional view of the printed circuit board in FIG. 3 with a conductive paste filled and cured.

[Explanation of symbols]

 1,11 Circuit pattern 2,12 Through hole 3,13 Land 4,14 Conductive paste 5 Groove

Claims (1)

[Claims] 1. A printed circuit board having through holes formed by connecting conductive layers between the circuit layers formed on both sides of the board, wherein concentric grooves are provided on the lands of the through holes. And printed circuit board.