JPH09199829A - Method of manufacturing printed-wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the pitch of a plurality of through holes by a method wherein, before finishing the setting step of a thermo-setting resin but after stopping pressurization, heating in the etching capable stage, the through holes are formed so as to apply a conductive paint having the thermosetting temperature exceeding the setting temperature of the thermo-setting resin. SOLUTION: The pressurizing and heating step is stopped in the state of setting phenol resin before finishing the setting step (C stage close to the status of B stage) but to the extent capable of performing copper foil etching later step. Next, the copper foil is etched away to form circuit pattern. Successively, in the punching step, a specific position on a circuit pattern is punched by a punching pin made of a punch to form a plurality of through holes. Finally, the through holes are filled up with silver paint made of silver particle added thermosetting resin binder comprising epoxy resin at the thermosetting temperature exceeding that of phenol resin to be thermoset at a prescribed temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a printed wiring board, and more particularly to a method for manufacturing a printed wiring board having a through hole conductive portion.

[0002]

2. Description of the Related Art As a method for manufacturing a printed wiring board, a through hole is formed by punching in a substrate formed by curing a prepreg impregnated with a thermosetting resin, and a conductive portion is formed in the through hole to perform printing. There is a method of manufacturing a wiring board. Specifically, it is manufactured by the following method. First, a copper foil is laminated on a prepreg impregnated with a thermosetting resin. Next, these are heated while being pressed so as to be sandwiched by stainless plates in the stacking direction to cure the thermosetting resin. Then, after the thermal curing is completed, the copper foil is etched to form a circuit pattern, and punched at a predetermined position of the circuit pattern with a punching pin such as a punch to form a through hole. Next, a conductive coating material obtained by adding a conductive powder to a thermosetting paste is filled in the through holes, and then the conductive coating material is heated and cured to form a through hole conductive portion to manufacture a printed wiring board.

[0003]

However, since the prepreg after the thermosetting resin is thermoset is hard, when a plurality of through holes are formed by punching, as shown in FIG. A crack C occurs between the hole 2 and the hole 2. Therefore, in the conventional method, there is a limit in reducing the interval between a plurality of adjacent through holes. For example, pore size 0.7
With a 0.8 mm through hole, the pitch (distance between the center points of adjacent through holes) P could not be made smaller than 2.5 mm. Therefore, there has been a limit in increasing the density of the circuit pattern formed on the printed wiring board.

It is possible to reduce the hole diameter of the through holes to shorten the distance between adjacent through holes in order to increase the density. However, when the hole diameter of the through holes is reduced, the through hole conductive portion is formed. When doing so, there arises a problem that it becomes difficult to fill the conductive paint into the through holes.

Therefore, the inventor has considered punching the prepreg at the stage where the thermosetting of the thermosetting resin is not completely completed to prevent the occurrence of cracks. However,
In this case, the mechanical strength of the printed wiring board is reduced because the prepreg is not completely cured as it is. Therefore, a heating step for completely curing the resin is separately performed after punching.

An object of the present invention is to provide a method of manufacturing a printed wiring board which can shorten the pitch of a plurality of through holes.

Another object of the present invention is to provide a method of manufacturing a printed wiring board which can delay the occurrence of short circuit due to the development of migration when silver paint is used as the conductive paint for forming the through hole conductive portion. To do.

[0008]

In order to solve the above problems, the present invention uses a thermosetting resin capable of stopping the progress of curing at the B stage as the thermosetting resin impregnated in the prepreg. The pressurization and the heating are stopped before the hardening of the thermosetting resin is completed and at the stage when the hardening of the thermosetting resin is advanced to the extent that etching is possible. afterwards,
Punching is performed to form through holes. And
As the conductive coating material for forming the through-hole conductive portion, one having a heat curing temperature higher than that of the thermosetting resin is used. Before the curing of the B stage is completed (the B stage state near the C stage), the prepreg still has flexibility, so that cracking is unlikely to occur even if punching is performed at this stage. Therefore, the interval (pitch) between adjacent through holes can be made shorter than before without reducing the inner diameter of the through hole.
Therefore, it is possible to manufacture a printed wiring board that can easily fill the through-holes with the conductive paint for forming the through-hole conductive portions, and can increase the density of the circuit pattern. Further, in the present invention, as the conductive coating material for forming the through-hole conductive portion, the one having a heat curing temperature higher than the heat curing temperature of the thermosetting resin is used. Therefore, in order to cure the conductive coating material when forming the through hole conductive portion. At the same time, the thermosetting resin can be completely cured by heating. Therefore, there is an advantage that a separate heat step of completely curing the thermosetting resin is not required.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a copper foil is laminated on a prepreg impregnated with a thermosetting resin, and these are heated while being pressed in the laminating direction to cure the thermosetting resin. To form a circuit pattern by punching, form a through hole by punching, fill the through hole with a conductive paint with conductive powder added to a thermosetting paste, and then heat cure the conductive paint to form a through hole conductive part. A method for manufacturing a printed wiring board by forming a substrate. In the present invention, a thermosetting resin that can stop the progress of curing at the B stage is used as the thermosetting resin. And
Before the hardening of the thermosetting resin is completed, and when the hardening of the thermosetting resin has progressed to the extent that etching is possible, pressurization and heating are stopped. Then, punching is performed to form through holes. Then, as the conductive coating material forming the through-hole conductive portion, one having a heat curing temperature higher than the heat curing temperature of the thermosetting resin is used.

As the thermosetting resin with which the prepreg is impregnated, any resin can be used as long as it can stop the progress of curing at the B stage, and a phenol resin, an epoxy resin, a polyester resin or the like can be used. . As the conductive paint forming the through-hole conductive portion, silver paint, copper paint or the like can be used. As the thermosetting resin for the binder of the conductive paint, those having a heat curing temperature higher than the heat curing temperature of the thermosetting resin may be used. When a phenol resin is used as the thermosetting resin with which the prepreg is impregnated, a modified phenol resin, an epoxy resin or the like can be used.

Further, when the conductive portion is formed by using silver paint, migration is likely to occur. However, according to the present invention, since it is possible to suppress the occurrence of cracks when forming through holes, there is an advantage that it is possible to delay the occurrence of short circuits between circuits caused by the development of migration along the cracks. is there. When a silver paint is used as the conductive paint, it is preferable to form the reinforcing substrate with paper and use a phenol resin as the thermosetting resin.

Further, it is preferable to control the curing of the thermosetting resin by keeping the heating temperature constant and adjusting the heating time. This is because it is difficult to reproduce the same condition by adjusting the heating temperature and controlling the hardness. Also, if the heating temperature is changed, thermal strain remains in the substrate.

When the center portion in the thickness direction of the inner wall portion of the through hole after punching bulges inward in the radial direction, the punching pin having a diameter slightly larger than the diameter dimension of the through hole is first used for the semi-working through hole. Then, the inner wall surface of the semi-processed through hole may be cut using a punching pin having a desired diameter dimension of the through hole to form the through hole.

[0014]

EXAMPLES In the examples of the present invention, printed wiring boards were manufactured as follows. FIG. 1 (A) shows a manufacturing process of the printed wiring board of this embodiment, and FIG. 1 (B) corresponds to the manufacturing process by setting the curing degree of the thermosetting resin (phenolic resin) with which the prepreg is impregnated. Is shown. First, in the impregnation step shown in this figure, a paper sheet was impregnated with A-stage phenolic resin to prepare a prepreg having a thickness of 0.20 mm. Next, the phenol resin is heated to 80 to 1 by a heating process.
After heat-curing to the B stage at a constant temperature of 00 ° C., a copper foil having a thickness of 0.035 mm was laminated on both surfaces of the prepreg to form an uncured laminate in the laminating step.
Next, in the pressurizing and heating step, the uncured laminate is sandwiched between two stainless steel plates in the stacking direction by 100 to 12
Curing of the phenol resin was started by heating at a constant temperature of 170 ° C. while applying a pressure of 0 Kg / cm ² . Then, before the progress of curing of the phenol resin is completed (B near the C stage).
Pressing and heating were stopped at the stage (stage state) and at the stage (1.0 to 1.5 hours after the start of pressing and heating) of the phenol resin being cured to the extent that the copper foil in the subsequent step could be etched. Then, in the etching step, the copper foil was etched to form a circuit pattern. Next, in a punching step, a predetermined position on the circuit pattern was punched with a punching pin made of a punch to form a plurality of through holes. In this embodiment, in order to remove the bulging portion formed by bulging the inner wall portion of the through hole inward in the radial direction, punching with a punching pin having a diameter slightly larger than the diameter dimension of the through hole to be first obtained. Was performed to form a semi-processed through hole, and thereafter, the inner wall surface of the semi-processed through hole was cut using a punching pin having a desired through hole diameter dimension to form a desired through hole. In this example, the pore size is 0.60
Two 0.70 mm through holes were formed adjacent to each other at a pitch of 1.50 mm, but no crack was observed. Further, the dimensional accuracy such as the hole diameter was the same as the conventional one. At this stage, a DuPont falling ball impact test was also conducted, and the same results as the conventional one were obtained. FIG. 2 is a diagram showing the relationship between the change in curing of the phenol resin and the heating time when the B-stage phenol resin of the prepreg is heated to the C stage at a constant temperature. The punching is performed by stopping the pressurization and heating of the laminated plate before the completion of the curing of the phenol resin (B stage state near C stage).
In addition, it may be performed at the stage where the phenol resin is cured to the extent that the copper foil can be etched, and may be performed within the range T shown in FIG.

Next, after performing a short open test by electrical measurement, a through hole conductive portion forming step is performed.
The through hole was filled with a silver coating material in which a silver powder was added to a thermosetting resin binder made of an epoxy resin. As the thermosetting resin binder, one having a heat curing temperature equal to or higher than the heat curing temperature of the phenol resin may be used. In this example, the silver paint was heat-cured at a constant temperature of 160 to 170 ° C. for 1.5 hours to cure the silver paint and completely cure the phenol resin of the prepreg to complete the printed wiring board.

Next, a migration test was conducted using the printed wiring boards manufactured in this example and the conventional method. The printed wiring manufactured by the conventional method is B
Instead of punching in the stage, the phenol resin was heated and cured up to the C stage, punching was performed in the C stage to form a semi-processed through hole, and the others were manufactured by the same method as this example. This test was conducted as follows. First, each printed wiring board is left in a thermo-hygrostat having a temperature of 40 ± 2 ° C. and a humidity of 90 to 95%, and a DC voltage of 20 V is applied between adjacent through-hole conductive parts formed of silver paint. The change in the insulation resistance value between the through-hole conductive portions with time was measured. Note that the insulation resistance is measured by leaving each printed wiring board at room temperature for 24 hours and then applying DC 1 between the adjacent through-hole conductive parts.
The measurement was performed by applying a voltage of 0V. FIG. 3 shows the measurement results. From this figure, the printed wiring board manufactured by the method of this example is less likely to cause cracks than the printed wiring board manufactured by the conventional method. It turns out that insulation can be prevented.

Although the through hole is formed by punching twice in the above embodiment, it is needless to say that the through hole may be formed by punching only once.

Further, in the above-mentioned embodiment, the present invention is applied to a method for manufacturing a double-sided copper foil printed wiring board, but a copper foil circuit pattern is formed on one surface and a conductive paint is used on the other surface. The present invention can also be applied to the case where a circuit pattern is formed by using.

Further, in the above embodiment, punching is performed after etching, but punching may be performed before etching.

The constitutions of some of the inventions described in the specification will be described below.

(1) A copper foil is laminated on a prepreg impregnated with a thermosetting resin, these are heated while being pressed in the laminating direction to cure the thermosetting resin, and the copper foil is etched. Circuit pattern is formed by punching, a plurality of adjacent through holes are formed by punching, and the conductive paint obtained by adding conductive powder to thermosetting paste is filled in the plurality of through holes, and then the conductive paint is heated. A method for manufacturing a printed wiring board by curing to form a plurality of through-hole conductive portions, wherein a thermosetting resin capable of stopping the progress of curing at a B stage is used as the thermosetting resin, The pressurization and heating are stopped before the curing of the curable resin is completed and when the curing of the thermosetting resin has progressed to the extent that the etching can be performed, and then the pan is removed. A method for manufacturing a printed wiring board, wherein a through-hole is formed by etching to form a through hole, and a heat-curing temperature that is higher than the heat-curing temperature of the thermosetting resin is used as the conductive paint.

(2) For the through hole, a semi-machined through hole is first formed by a punching pin having a diameter larger than that of the through hole, and then a punching pin having a desired diameter of the through hole is used. The method for producing a printed wiring board according to (1) above, wherein the inner wall surface of the semi-processed through hole is cut and formed.

[0023]

According to the present invention, it is possible to manufacture a printed wiring board in which the pitch of a plurality of through holes can be shortened to increase the density of circuit patterns. Further, according to the present invention, there is an advantage that the conductive paint can be easily filled in the through hole, and a special heat treatment step for completely curing the resin of the prepreg is not required.

[Brief description of drawings]

FIG. 1A shows a manufacturing process of a printed wiring board of this embodiment, and FIG. 1B shows a curing degree of a thermosetting resin (phenolic resin) used for manufacturing the printed wiring board in the manufacturing process. Is shown.

FIG. 2 is a diagram showing a relationship between a change in curing of the phenol resin of the prepreg and a heating time when the phenol resin of the prepreg is heated at a constant temperature from the B stage to the C stage.

FIG. 3 is a diagram showing a result of a migration test of a printed wiring board used in the test.

FIG. 4 is a diagram schematically showing a state of cracks generated between two adjacent through holes of a printed wiring board manufactured by a conventional method.

[Explanation of symbols] 1, 2 through holes C crack P pitch

Claims (3)

[Claims] 1. A copper foil is laminated on a prepreg impregnated with a thermosetting resin, these are heated while being pressed in the laminating direction to cure the thermosetting resin, and the copper foil is etched. A through hole is formed by forming a circuit pattern, forming a through hole by punching, filling the inside of the through hole with a conductive paint made by adding conductive powder to a thermosetting paste, and then curing the conductive paint by heating. Forming a printed wiring board, wherein a thermosetting resin capable of stopping the progress of curing at the B stage is used as the thermosetting resin, and the progress of curing of the thermosetting resin is completed. Before and at the stage where the thermosetting resin has hardened to the extent that the etching is possible, the pressing and heating are stopped, and then the punching is performed to form the through hole. The method for producing a printed wiring board is characterized in that a heat-curing temperature of the conductive coating material is equal to or higher than the heat-curing temperature of the thermosetting resin. 2. A copper foil is laminated on a prepreg impregnated with a phenol resin, and these are heated while being pressed in the laminating direction to cure the phenol resin, and the copper foil is etched to form a circuit pattern. Then, a through hole is formed by punching, and a silver coating made by adding silver powder to a thermosetting paste is filled in the through hole, and then the silver coating is heat-cured to form a through hole conductive portion. A method for manufacturing a printed wiring board, wherein the pressurization and heating are stopped before the completion of the curing of the phenolic resin and at the stage where the curing of the phenolic resin has progressed to the extent that the etching is possible, Then, the punching is performed to form through holes, and the silver coating material having a heat curing temperature equal to or higher than the heat curing temperature of the thermosetting resin is used. A method for manufacturing a printed wiring board, comprising: 3. The method for manufacturing a printed wiring board according to claim 1, wherein the control of the curing of the thermosetting resin is controlled by keeping the heating temperature constant and adjusting the heating time.