JPH11145592A - Method for filling through-hole of circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent voids, cracks, or large recessed parts from being generated in a solder resist which is filled in a through-hole. SOLUTION: A metal mask 25 is set on the upper surface of a circuit board 21 and a solder resist 23 supplied on the metal mask 25 is moved by a squeegee 28 as to be expanded along the metal mask 25, thereby filling a quarter to a half of a through-hole 2 with the solder resist 23. After drying and curing the solder resist 23, a screen mask 29 is set on the circuit board 21, and the solder resist 23 supplied on the screen mask 29 is moved by a squeegee 30 so as to be expanded along the screen mask 29, thereby filling the remaining part of the through-hole 22 with the solder resist 23 and forming the pattern of the solder resist 23 on the upper surface of the circuit board 21 through screen printing, and then it is dried and cured.

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 in a circuit board with a solder resist.

[0002]

2. Description of the Related Art For example, a plastic BGA (Ball Grid Array) package, whose demand is rapidly increasing in response to recent demands for higher density, higher speed, and more pins in a semiconductor package, is a plastic BGA substrate. A semiconductor chip is die-bonded to the upper surface of the BGA substrate and sealed with a sealing resin, and a large number of solder balls are arranged as connection electrodes on the lower surface of the BGA substrate. This BGA board is
Through holes for electrically connecting the wiring on the upper and lower surfaces are formed, and a plating film serving as a conductor layer is formed on the inner peripheral surface of the through holes. Generally, a solder resist is filled in the through hole to protect the plating film on the inner peripheral surface of the through hole.

[0003]

In the conventional through-hole filling method, a solder resist is filled in the through-hole by one printing. However, recent BGA substrates tend to be multi-layered and have a large thickness, and the through-holes are becoming deeper. As described above, when the deep through-hole is filled with the solder resist by one printing, as shown in FIG. 2, when the solder resist 12 is filled into the through-hole 11, air is trapped in the solder resist 12 and When voids are generated or when the filled solder resist 12 is dried and hardened, the solder resist 12 contracts, so that a relatively large dent is generated on the surface of the solder resist 12 or a crack is generated inside the solder resist 12. There were drawbacks. These solder resists 12
Voids, cracks, and dents in the film cause a decrease in reliability with respect to the temperature / humidity cycle. There is also a method of filling the through-hole 11 with a solder resist dedicated to the through-hole. In this case, however, the solder resist is raised on both surfaces of the through-hole, and it is necessary to remove the raised portion. At that time, the circuit forming surface of the substrate may be damaged, which causes a reduction in yield.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and accordingly, it is an object of the present invention to prevent voids, cracks, and large dents from being generated in a solder resist filled in a through hole and to form a circuit. It is an object of the present invention to provide a method for filling a through hole in a circuit board, which can improve the reliability with respect to temperature and humidity cycles without lowering the yield due to surface damage.

[0005]

In order to achieve the above object, a method of filling a through hole in a circuit board according to the present invention is to fill a quarter of the through hole with a solder resist and cure it. After that, the remaining portion in the through hole is filled with a solder resist and cured. That is, 1
In the first filling, the filling amount of the solder resist is set to ４ to の in the through hole, and the filling amount is reduced to prevent air from being caught in the solder resist at the time of filling. In addition to preventing the occurrence of cracks, the amount of shrinkage of the solder resist during curing is reduced to prevent the occurrence of cracks. In the second filling, the remaining portion in the through hole is filled with the solder resist. In this case, too, since the filling amount is small, no air is trapped in the solder resist and no void is generated. In addition, since the center portion in the through hole is hardened by the first filling and hardening of the solder resist, cracks do not occur in the second solder resist, and the shrinkage of the solder resist is small, The surface dent is also small.

In this case, since a raised portion of the solder resist cannot be formed on both surfaces of the through hole portion, a step of shaving off the raised portion of the solder resist is not required, and the yield is not reduced due to damage on the circuit forming surface.

[0007] The first filling amount is set to 1 in the through hole.
If it is less than / 4, the second filling amount becomes too large, voids are generated, and the final dent becomes large. Further, if the first filling amount is 以上 or more of the inside of the through hole, the first filling amount becomes too large, and cracks occur at the center.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of filling a through hole according to an embodiment of the present invention will be described with reference to FIG. The circuit board 21 used in the present embodiment is, for example, a plastic BGA
A substrate having a thickness of, for example, 0.4 mm and a through hole 2
2 has a diameter of, for example, 0.2 mm. A plating film serving as a conductor layer is formed on the inner peripheral surface of the through hole 22. The filling of the through hole 22 with the solder resist 23 is performed by [1] filling printing (first filling), [2] 1
Second curing, [3] screen printing (second filling),
[4] Performed in each step of the second curing. Hereinafter, each of these steps will be described.

[1] Fill-in-the-blanket printing (first filling) The circuit board 21 is set on the lower fixing jig 24, and the metal mask 25 is set on the upper surface of the circuit board 21. The lower fixing jig 24 has a spot facing portion 2 directly below the through hole 22.
6 are formed, and the metal mask 25 has through holes 2
2, a circular opening 27 is formed. The diameter of the opening 27 is larger than the diameter of the through hole 22 (for example, 0.2 mm), and is set to, for example, 0.4 mm. In fill-in printing, the solder resist 23 supplied on the metal mask 25 is moved by a squeegee 28 so as to be spread along the metal mask 25, and from the opening 27 of the metal mask 25 to １ ／ to 1 of the through hole 22.
/ 2 is filled with the solder resist 23. On this occasion,
The filling amount of the solder resist 23 may be adjusted by appropriately adjusting any of the diameter of the opening 27, the viscosity of the solder resist 23, the inclination angle and the hardness of the squeegee 28, and the like.

[2] First Curing Dry curing of the solder resist 23 filled in the through hole 22 is performed, for example, at 150 ° C. for 30 minutes. still,
The solder resist 23 may be dried and cured by ultraviolet irradiation.

[3] Screen Printing (Second Filling) A screen mask 29 is set on the circuit board 21 on which the solder resist 23 has been dried and cured. The screen mask 29 has a circular opening just above the through hole 22, and the screen mask 29 has a printed pattern for forming a solder resist pattern on the upper surface of the circuit board 21. Have been. The solder resist 23 supplied on the screen mask 29 is moved by a squeegee 30 so as to be spread along the screen mask 29, and the remaining portion in the through hole 22 is filled with the solder resist 23, and the solder resist 23 is provided on the upper surface of the circuit board 21. Screen printing of the resist pattern. When a solder resist pattern is screen-printed on the lower surface of the circuit board 21, the solder resist pattern is screen-printed in the same manner as described above.

[4] Second curing The drying and curing of the screen printed solder resist 23
For example, the heat treatment is performed at 150 ° C. for 30 minutes. Incidentally, the solder resist 23 may be dried and hardened by ultraviolet irradiation.

According to the through hole filling method described above, in the first filling, the filling amount of the solder resist 23 is set to １ ／ to の in the through hole 22 and the filling amount is reduced. Air is not caught in the solder resist 23, and voids are not generated.
Moreover, by reducing the filling amount, the solder resist 2
Since the amount of shrinkage at the time of curing of No. 3 decreases, cracks do not occur.

In the second filling, the through hole 2
2 is filled with the solder resist 23, but also in this case, since the filling amount is small, no air is trapped inside the solder resist 23 and no void is generated. Also, 1
Since the central portion in the through hole 22 is hardened by the second filling and hardening of the solder resist 23, cracks do not occur in the second solder resist 23 and the shrinkage of the solder resist 23 is small. The surface dent is also small.

According to the experimental results of the present inventor, if the first filling amount is less than 1/4 of the inside of the through hole 22, the second filling amount becomes too large, and air is entrained to generate voids. , The final dent was also larger. Also,
When the first filling amount was set to １ ／ or more of the inside of the through hole 22, the first filling amount was too large, and the amount of shrinkage in the first curing treatment was large, and a crack was generated at the center. For this reason, it is appropriate that the first filling amount is １ ／ to の of the through hole.

According to the experimental results of the present inventor, if the first filling amount is １ ／ to の in the through hole 22,
No voids or cracks were generated inside the filled solder resist 23, and the depression was 5 μm or less (1/6 or less of the conventional size). On the other hand, in the conventional filling method, voids and cracks frequently occurred inside the solder resist, and the dent was as large as 30 μm.

[0017]

As is apparent from the above description, according to the method for filling a through hole of the present invention, one of the through holes can be filled.
After filling and hardening the solder resist in the portion of 部分 to 、, the remaining portion in the through hole is filled with the solder resist and hardened, so that the solder resist filled in the through hole has voids, The generation of cracks and large dents can be prevented, the reliability against temperature / humidity cycles can be improved, and the yield does not decrease due to scratches on the circuit formation surface.

[Brief description of the drawings]

FIG. 1 is a process diagram showing a through hole filling method according to an embodiment of the present invention.

FIG. 2 is an enlarged longitudinal sectional view showing a state of filling a conventional solder resist filled in a through hole.

[Explanation of symbols]

Reference numeral 21: circuit board, 22: through hole, 23: solder resist, 25: metal mask, 28: squeegee, 29 ...
Screen mask, 30 ... Squeegee.

Claims (1)

[Claims] 1. A method of filling a through hole formed in a circuit board with a solder resist, wherein a quarter of the through hole in the through hole is filled with a solder resist and cured to form a through hole. A method for filling a through hole in a circuit board, comprising: filling a remaining portion in the hole with a solder resist and curing the solder resist.