JPH02209798A - Forming of through hole in thick film circuit substrate - Google Patents

Abstract

PURPOSE:To prevent crack in and imperfect conduction of conductors at substrate corners having edge parts by doubly applying conductor paste on a sharp edge of each hole to round said edges and at the same time printing said paste thick. CONSTITUTION:A ceramic substrate 20 (1) is mounted on the printing table 21 of a printer. During suction with a suction blower 22 from the lower part, a plate is made, and printing is performed with copper paste 23. The state of paste 24 inserted into holes 7 is observed while a suction pressure is changed. the suction pressure is determined according to the state of a first print conductor 2, that is, so that the copper paste may be applied also to the rear of the ceramic substrate 20. After drying with a constant-temperature drier, the ceramic substrate 20 is reversed and mounted on the printing table 21 and a second print conductor 3 is formed on the inner walls of the holes 7 to the depth of about the half of the thickness of the substrate 1 during suction with the suction blower 22 from the lower part. After drying with the constant-temperature drier, the substrate is baked in a neutral-atmospheric belt furnace in which nitrogen is passed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to the manufacture of electronic circuit boards, and more particularly to a method for forming through holes in thick film circuit boards.

Conventional Technique In the conventional technique of forming through-holes in a thick film circuit board with conductors formed on both sides using conductor bases,
The conductive paste was printed from both sides of a ceramic substrate with holes previously formed, and at the same time, the printing was performed while suctioning the paste so that it overlapped with the center of the hole. The holes in the ceramic substrate used at that time include laser processing using a carbon dioxide laser or the like on a ceramic substrate that has been sintered in advance; (2) punching holes in a ceramic green sheet using a mold; , and then sintering to obtain a ceramic substrate with holes. (1) Ceramic substrate processed by laser processing is suitable for small-scale production at the laboratory level, and ceramic substrate processed by molding (2) is suitable for mass production.

On the other hand, as shown in FIGS. 3(al) and 3(b), it has been widely known that the laser-processed hole 71 and the mold-processed hole 72 have different shapes due to differences in their manufacturing. is a cross-sectional view of a hole 7I of a laser-processed ceramic substrate 1, in which laser irradiation 8 is performed from the upper side of the ceramic substrate 1 with a carbon dioxide laser to form a hole 71.
is formed. At this time, the laser-processed hole 71 has the characteristic that the entrance side where the laser is irradiated is always wide, and the corner part 9 on the laser-processed side is always rounded due to the melting of the substrate by the laser.

On the other hand, FIG. 3 (1)) is a cross-sectional view of hole processing using a mold for green sheet molding, and shows the green sheet 14.
is placed on the lower punching die 12, and the hole 72 is punched out by the upper punching die punch IO. At this time, the punching upper die bunch 10 has a punching corner portion 11 for processing and reinforcement purposes. Because of this punching corner portion 11, a punching side corner portion 15 is formed in the green sea H4 in a rounded shape after punching, and this corner portion remains even after sintering. Therefore, it is also possible to determine whether the board is front or back by looking at a part of this corner.

FIG. 2 is a cross-sectional view of a ceramic circuit board formed using conventional printing methods. A hole 7 is formed in the ceramic substrate 1 by laser processing or punching with a die. First, a first printed conductor 2 is formed using a screen printing method, and at the same time, a conductive paste is inserted halfway into the inner wall of the hole by sucking it up from the side opposite to the surface on which the first printed conductor is formed, and then dried in a dryer. A method of firing after this is also used. Next, invert the ceramic substrate 1 and
At the same time as printing and forming the second printed conductor 3, the conductor paste is inserted partway into the inner wall of the hole by suctioning from the side opposite to the second printed conductor forming surface, and the conductor paste is inserted halfway into the hole inner wall to connect the first printed conductor forming surface and the conductor shape portion 4. form and conduct the conductor circuits on both sides. After this, drying and firing are performed to form conductive circuits on both sides and conduct the through holes. This is used to form through holes in thick film circuit boards.

Problems to be Solved by the Invention Conventionally, Ag-Pd paste has been mainly used as a conductor material for thick film circuit boards. However, recently, Cu paste has come into use because of its low cost and advantageous electrical properties. In AgPd paste,
Although there were no problems with the through-hole type bottom formed by the conventional method as shown in FIG. 2, the following new problems have arisen by using Cu paste.

When printing a conductive paste, especially when using a ceramic board with holes punched by a mold when printing a green sheet as shown in Figure 3 (bl), the second side of the board opposite to the punching has the hole-machined edge. As shown in the figure, the conductive paste becomes extremely thin at the corner 6 of the board opposite to the punching, and in severe cases, cranking often occurs, resulting in poor conduction.

In view of the above-mentioned problems, the present invention solves the problem of occurrence of cracks in a conductor at a part of a board corner having an edge part.
The method for forming through-holes in film circuit boards is to form holes using a mold.7! - When forming a through hole using a board, first, a part of the corner of the board on the punching side is used as the first printed conductor forming surface, and at the same time, the first printed conductor is formed using a screen printing method; After the first printing, conductor paste is inserted from the side opposite to the first printed conductor forming surface so as to cover the entire inner wall of the hole by suctioning from the side opposite to the S body forming surface, and then dried in a dryer. do. Next, the board is reversed to form a second printed conductor, and at the same time, the conductive paste is inserted partway into the inner wall of the hole by suction from the side opposite to the second printed conductor forming surface, and the conductive paste is inserted halfway into the hole inner wall, and This forms a conductor shaped portion and connects the conductor circuits on both sides.

Thereafter, by drying and baking, a thick film circuit board with conductor circuits and through holes formed on both sides is completed.

Function As explained above, if the through-hole forming technique according to the present invention is used, conductor paste is also applied to the edge of the hole on the opposite side when forming the first printed conductor, thereby making the edge of the hole rounded. I can do it.

Next, when forming the second printed conductor, the printed conductor at the edges is double-coated because it is further printed from above the rounded corner that was formed when the first printed conductor was formed and includes the printed conductor. This allows for less printing compared to conventional through-hole formation, which prevents the occurrence of cranks after firing.

As a result, it is possible to completely form through holes in a double-sided thick film circuit board, and a thick film circuit board without conduction defects can be obtained.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1, 4, and 5. Vertical 90 fins: 1001 horizontal fins, with holes punched out of a green sheet using a die.
m: A ceramic substrate 1 having a thickness of 0.81 mm was prepared. The large number at that time was 500, and the hole diameter was O; 4 am. Next, commercially available DuPont Co., Ltd. 9153 copper paste was used as the conductor paste. The printing machine used was a 15GTN manufactured by New Long, which is capable of suctioning the same substrate. The plate making for printing is 1. having the same center point for a hole diameter of 0.41. A plate made of 250 mesh stainless steel with an emulsion thickness of 10 μm and having a circular pattern was prepared.

Figure 5 shows a schematic diagram of the printing method.

First, the above-mentioned ceramic substrate 20 + 11 is placed on the printing table 21 of the printing machine, and while being sucked from below by the suction blower 22, using the above-mentioned plate making and copper paste 23,
Printed. Observing the state of the paste 24 inserted into the hole 7 while changing the suction pressure, the first printed conductor 2 in FIG.
The suction pressure was determined so that the copper paste was also applied to the back surface of the ceramic substrate 20.

Next, it was dried in a constant temperature dryer at 120°C for 10 minutes.

Thereafter, the ceramic substrate 20 is similarly inverted and placed on the printing table 21, and while suction is applied from below by the suction blower 22, the second printed conductor 3 shown in FIG. Form it and heat it in a constant temperature dryer at 120℃.
After drying for 10 minutes, it was fired in a neutral atmosphere belt furnace in which nitrogen was flowed at a peak temperature of 900°C, a holding time of 10 minutes, and a total process of 60 minutes. Figure 1 shows a cross section of the completed thick film circuit board. Here, 5 is a part of the substrate corner on the punching side, and 6 is a corner part of the substrate on the opposite side to the punching.

On the other hand, by adjusting the same suction pressure, a through-hole substrate using the conventional method as shown in FIG. 2 was also printed and fired at the same time. The number of printed circuit boards is 10 each, and the number of through holes is 500.
0 locations were formed. Thereafter, each through hole was visually observed using a stereomicroscope, and continuity was checked using a continuity checker.

Figure 4 shows the results. As shown in the figure, in the conventional through hole forming method, for 5000 holes, 3151
In contrast, in the through-hole forming method according to the present invention, four cracks occurred, resulting in a non-defective rate of 99.9% or more. In addition, if the continuity checker is used to detect poor continuity, the conventional through-hole formation method 3.
In contrast, the through-hole forming method according to the present invention had 0 through holes, resulting in a non-defective rate of 100%.

Effects of the Invention As is clear from the above, the through-hole printing method according to the present invention is particularly effective for forming sharp holes on one side edge portion, such as a ceramic substrate having holes punched using a green sheet mold. By double-coating the body paste to give it a rounded shape and at the same time printing it thickly, it is possible to eliminate cracks and provide a highly reliable double-sided thick-film circuit board.

In the embodiments of the present invention, DuPont's 9153 was used as the conductive paste, but this paste is not limited to this in any way, and can be widely used other than copper paste.
It is clear that it is also effective for g1pd and Au paste.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the hole/through-hole portion of a double-sided thick film circuit board formed by the through-hole printing method of the present invention, and Fig. 2 is a double-sided thick film circuit board formed by the conventional through-hole printing method. Figure 3 is a cross-sectional view of the hole/through-hole portion of the ceramic substrate (al is a cross-sectional view of the ceramic substrate processed by laser processing, Figure 3 fbl is a schematic diagram of hole processing using a ceramic green sheet mold, and Figure 4 is a cross-sectional view of the ceramic substrate according to the present invention). A graph showing the investigation and test results after through-hole printing by the conventional method, and FIG. 5 are schematic diagrams of the through-hole printing and forming method of the present invention. 1... Ceramic substrate, 2... ...1st printed conductor, 3...2nd printed conductor, 4...
...Conductor assembly part, 5...Part of the corner of the board on the punching side, 6...Part of the corner of the board on the opposite side of the punching. Name of agent: Patent attorney Shigetaka Kurino Only one name! Regret? -... Laser processing surplus clasif occurred Vaginal examination passed product loading trial game 20 - - 22 - Otsu - - Zumi Tsukui Tsuku i'I! 1 EnJlJ stand au g + Laroi it stop paste (inbetsu break) m body paste (hole! Nita printing 2 hota)

Claims (3)

[Claims] (1) Print a circuit pattern using conductive paste on both sides of a ceramic substrate with holes pre-drilled in it, and at the same time print the conductive paste on the inner wall of the hole while suctioning it from the side opposite to the side to be printed, to make the circuit pattern on both sides conductive. When forming through-holes in thick-film circuit boards, first print from the direction in which the holes are made in the ceramic board, then insert the conductive paste into the holes up to the opposite side of the board, and then print from the opposite side of the ceramic board. A method for forming a through hole in a thick film circuit board, which comprises inserting a conductive paste into the hole about half the thickness of the board during printing and overlapping it with the conductive paste that was first printed. (2) The method for forming through holes in a thick film circuit board according to claim 1, characterized in that the hole-processed ceramic substrate is a ceramic substrate punched using a mold at the time of green sheeting. . (3) A method for forming through holes in a thick film circuit board according to claim 2, characterized in that a ceramic substrate having holes formed using a mold during green sheeting is used, and the conductive paste is a copper paste. .