JP2002252449A - Method for filling through hole of printed board with resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for filling a through hole of a printed board with resin whereby bubbles caught up in the through hole can be sufficiently emitted, without providing any special equipment and process at a low cost, and to improve the reliability of the through hole. SOLUTION: Just after filling the through hole of the printed board with a heat/ultraviolet curing-type resin 3, only the lower part of the resin 3 is so cured by ultraviolet rays as to prevent the resin 3 remaining in the through hole from flowing out to the lower side of the through hole. Then, after emitting the bubbles 4 remaining in the resin 3 in the through hole by heating the resin with a temperature, at which the heat/ultraviolet curing-type resin 3 is most cured, for a fixed period of time, the upper part of the resin is ultraviolet-cured, and finally, the whole of resin 3 is heat-cured by heating the printed board with the temperature, at which the heat/ultraviolet curing-type resin 3 is cured, for fixed period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of filling a through hole with a resin when manufacturing a printed circuit board having a through hole.

[0002]

2. Description of the Related Art A printed circuit board is provided with circuit patterns formed on the front and back surfaces of the substrate, and through holes are formed in the printed circuit boards to establish electrical continuity between the circuit patterns. And a pattern is formed thereon. In particular, build-up wiring boards have been used as high-density mounting boards in order to respond to the recent advances in functions and miniaturization of devices. And for example
High reliability is required for printed circuit boards of electronic devices used for supercomputers, space rockets, space satellites, and the like. All of these printed circuit boards have a multi-layered printed circuit board with through-holes used as a base substrate, and it is necessary to fill the through-holes with resin for filling holes, and this filling is very important. At the same time, high reliability is required.

In order to fill through holes in a printed circuit board with a resin, a screen printing method is generally used. FIG. 2 is an explanatory view of a method of filling a through hole of a printed circuit board with a resin. In FIG. 2, reference numeral 1 denotes a substrate of a printed board, 2 denotes through-hole plating, 3 denotes a thermo-ultraviolet curing resin filled in the through-hole, and 4 denotes air bubbles caught in the resin in the through-hole.

[0004] The filling of the through holes of the printed circuit board with resin is specifically performed by the following method. (1) A thermo-ultraviolet curable resin 3 whose viscosity has been adjusted and defoamed is filled in a through hole of a printed circuit board by screen printing. (FIG. 2) (2) The upper surface and the lower surface of the heat / ultraviolet curable resin 3 are cured by irradiating ultraviolet rays to both sides of the printed circuit board. (FIG. 2) (3) Heat for curing the heat / ultraviolet curable resin 3 is applied to the printed circuit board for a certain period of time to cure the inside of the heat / ultraviolet curable resin 3. (Fig. 2)

[0005]

However, in the above-mentioned screen printing method, as shown in FIG. 2, when the thermo-ultraviolet curable resin 3 is applied to the through-holes, bubbles 4 may be entrained, and the through-holes may remain as they are. There is a case where the air bubbles 4 are brought into the inside as small bubbles 4 and finally the air bubbles 4 remain even after the resin is cured, and voids are generated in the resin layer.

[0006] The voids expand due to thermal stress applied to the printed circuit board in a later step and generate stress, which causes breakage of the through-hole plating 2 and cracks in the through-hole such as cracks in the base material 1. Sometimes. As a technique for discharging the bubbles, Japanese Patent Laid-Open No. 6-2914 is disclosed.
Japanese Patent Application Laid-Open No. 10-2, No. 62, No. 62, which discloses a technique for preventing air bubbles from being trapped by resin filling under vacuum.
As disclosed in Japanese Patent No. 9247, there is a technique of discharging air bubbles by immersing a printed circuit board filled with resin in water or a liquid having a high specific gravity. The above-mentioned defects due to voids may occur during the production of boards by printed circuit board manufacturers,
What is more problematic is that it is caused by thermal stress due to repeated temperature changes while the electronic component is mounted and the electronic device is operating.

According to the present invention, a method for filling a resin in a through-hole capable of sufficiently discharging the air bubbles 4 trapped in the through-hole without any special equipment or process is provided in order to prevent the above-mentioned problems from occurring. It aims to provide at low cost and increase the reliability of through holes.

[0008]

According to the present invention, there is provided a method of filling a through hole of a printed circuit board with a resin according to the present invention. The resin in the through-hole was prevented from flowing downward, and then the heat at a temperature at which the thermosetting and UV-curable resin softened the most was applied for a certain period of time to discharge bubbles remaining in the resin in the through-hole. Thereafter, the upper side is cured with ultraviolet rays, and finally, heat for curing the thermo-ultraviolet curable resin is applied to the printed circuit board for a certain period of time to thermally cure the entire resin. According to this resin filling method, after only the lower side of the filled resin is cured, the resin is once softened and the residual air bubbles are naturally discharged, so that the reliability of the through hole can be increased at low cost.

[0009]

Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view of a method of filling a through hole of a printed circuit board with a resin. In FIG. 1, the same or equivalent parts as those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the present invention, the filling of the through holes of the printed circuit board with resin is performed by the following method. (1) A thermo-ultraviolet curable resin 3 whose viscosity has been adjusted and defoamed is filled in a through hole of a printed circuit board by screen printing. (FIG. 1) (2) The lower surface of the heat / ultraviolet curable resin 3 is cured by irradiating ultraviolet rays to the lower side of the printed circuit board to prevent the heat / ultraviolet curable resin 3 from flowing out. (FIG. 1) (3) Heat is applied to the printed circuit board at a temperature at which the heat / ultraviolet curable resin 3 is softest for a certain period of time, and bubbles 4 inside the heat / ultraviolet curable resin 3 are discharged. (FIG. 1) (4) The upper surface of the heat / ultraviolet curable resin 3 is cured by irradiating the upper side of the printed circuit board with ultraviolet rays. (FIG. 1) (5) Heat for curing the thermo-ultraviolet curable resin 3 is applied to the printed circuit board for a certain period of time to cure the inside of the thermo-ultraviolet curable resin 3. (Fig. 1)

[0011]

(Embodiment) An embodiment of filling a through hole with a resin according to the method of the present invention will be described below. The heat / ultraviolet curing resin 3 is manufactured by Yamaei Chemical Co., Ltd. as PHP-900 DC-5.
-4 A heat-curable epoxy resin combined with light (ultraviolet light) was used. (1) A thermo-ultraviolet curable resin 3 whose viscosity has been adjusted and defoamed is filled in a through hole of a printed circuit board by screen printing. (2) The lower surface of the heat / ultraviolet curable resin 3 is cured by irradiating the lower side of the printed circuit board with ultraviolet rays having an integrated amount of 1000 mJ / cm ² . (3) Heat is applied to the printed circuit board at 80 ° C for 2 hours.
The bubbles 4 inside the ultraviolet curing resin 3 are discharged. (4) The upper surface of the heat / ultraviolet curable resin 3 is cured by irradiating the upper side of the printed circuit board with ultraviolet rays having an integrated amount of 1000 mJ / cm ² . (5) Heat is applied to the printed circuit board at 150 ° C. for 1 hour to cure the inside of the heat / ultraviolet curable resin 3.

(Comparative Example) Next, a comparative example of filling a through hole with a resin according to a conventional method will be described below. As the heat / ultraviolet curable resin 3, the same resin as in the above (Example) was used. (1) A thermo-ultraviolet curable resin 3 whose viscosity has been adjusted and defoamed is filled in a through hole of a printed circuit board by screen printing. (2) Both sides of the printed circuit board are irradiated with an ultraviolet ray having an integrated light amount of 1000 mJ / cm ² to cure the upper surface and the lower surface of the heat / ultraviolet curable resin 3. (3) Heat is applied to the printed circuit board at 150 ° C. for one hour to cure the inside of the heat / ultraviolet curable resin 3.

The conditions and results of the above (Example) and (Comparative Example) are shown in Table 1.

[Table 1]

As is apparent from Table 1, the bubble generation rate is 9
From 9.6% to 23.3%, the maximum cell size (diameter) was greatly reduced or reduced from 283.5 μm to 97.0 μm, and the average cell size (diameter) was reduced from 120.7 μm to 51.9 μm, respectively. Was. The reliability of the through-hole largely depends on the number and size of the bubbles 4 remaining in the thermo-ultraviolet curing resin 3. That is, the smaller and smaller the bubbles 4, the smaller the stress due to the thermal stress and the higher the reliability.

[0015]

According to the method of embedding a resin in a through hole of a printed circuit board according to the present invention, air bubbles trapped in the through hole can be sufficiently discharged without providing any special equipment or process, and low cost is achieved. Thus, the reliability of the through hole can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a method for filling a through hole of a printed circuit board with a resin according to the present invention.

FIG. 2 is an explanatory view of a conventional method of filling a through hole of a printed circuit board with a resin.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Through-hole plating 3 ... Heat and ultraviolet curable resin 4 ... Air bubbles

Claims (1)

[Claims] 1. Immediately after a thermo-ultraviolet curable resin is filled in a through hole of a printed circuit board, only the lower side is cured by ultraviolet rays to prevent the resin in the filled through hole from flowing out to the lower side.・ Apply heat for a certain period of time at the temperature at which the UV-curable resin softens most to discharge bubbles remaining in the resin in the through-hole, then UV-cur the upper part, and finally cure the heat-UV-curable resin A method of filling a through hole of a printed circuit board with resin by applying heat to the printed circuit board for a predetermined time to thermally cure the entire resin.