JPS60143688A - Method of printing thick film circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Page 2 Field of Industrial Application The present invention relates to a method of printing thick film paste into through holes in the production of thick film circuits that can be used in electrical equipment such as televisions.

Conventional structure and problems thereof FIG. 1 shows an example of a thick film circuit. The thick film paste printed on the alumina substrate 1 is dried and fired to form a thick film conductor layer 2. A thick film resistor 3 is formed. Thick film paste for conductors is generally composed of silver-palladium alloy powder, glass frit, resin binder, organic solvent, etc. Furthermore, the thick film paste for the resistor uses ruthenium oxide instead of silver-palladium, and is otherwise composed of approximately the same material as the paste for the conductor. A chip capacitor 4 is connected to the thick film conductor layer 2 by solder 5 on the alumina substrate 1 .

With the recent demand for smaller electronic devices, there is an increasing need for circuit boards used there to be smaller and more highly integrated. Therefore, from the conventional general substrate using only one side as shown in FIG. 1 to the one shown in FIG. Double-sided thick film circuits that effectively utilize both sides have come into use.

In the conventional manufacturing process for double-sided thick film circuits, as shown in Fig. 3, a conductive paste 2 containing silver-palladium metal powder is preliminarily applied to an alumina substrate 1 with a thickness of 0.5 mm to 0.6 mm using an ink returner 7. Spread the circuit part 13 on the board 1 on the damp screen 8 and draw a vacuum from the suction port 11 with the squeegee 9.
A method of applying conductive paste 2 into the through holes 6 is generally practiced.

However, in this method, the paste is spread over the entire surface of the screen 8, and when the squeegee 9 starts sucking while descending, the entire surface of the screen is attracted to the substrate 1, and the paste 2 is sucked from the patterned part of the screen 8 and becomes the emulsion 12. The paste may adhere and cause bleeding. In particular, since the suction time for the pattern portion on the printing end side of the squeegee 9 is longer than the printing start position, the amount of paste 2 that comes out is large and causes smudging. Furthermore, although the smearing of Paste 2 and the smearing of the pattern area are decreasing, there is a problem in that the paste is not sufficiently coated within the through-holes. This is thought to be because, as shown in FIG. 4, in conventional screen printing, the suction force is maximum at the beginning and end of printing, and decreases as it approaches the latter.

In other words, because the suction force is not constant during printing,
The problem mentioned above was occurring.

Furthermore, when a material containing silver is used as a conductor material, it is necessary to completely cover the conductor on the through-hole wall with an insulating film to prevent circuit shorts caused by migration due to potential difference, and it is necessary to completely cover the conductor on the wall of the through hole with an insulating film, etc. However, as they used screen printing in the same way as conductor printing,
I had a similar problem.

In addition, when mounting components on the conductor part by soldering in a later process, resist printing is generally performed with a pattern that partially exposes the conductor electrode part, but as mentioned above, due to the bleeding phenomenon, the exposed area of the conductor is Since the surface area of the fine pattern electrodes is small, the back side of the screen must be wiped clean with a considerable degree of dispersion.

Purpose of the Invention The present invention solves the above-mentioned drawbacks, and simultaneously prints the conductor on the substrate (printing the turn part and coating the conductor inside the through hole,
The purpose is to prevent the conductor pattern from bleeding and to improve the reliability of the through holes.

Structure of the Invention The present invention provides a thick film circuit printing method in which thick film paste is printed on a substrate having newly supplied through holes in each of the outward and return passes of the squeegee operation. be.

Preferably, printing is performed using an outgoing squeegee on the outgoing trip, and printing is performed using a returning squeegee on the returning trip.

More preferably, when printing the thick film paste on one side of the substrate by operating the squeegee, vacuum suction may be applied from the other side of the substrate.

Furthermore, by applying the thick film paste printing method to both sides of the substrate, the inner surface of the through-hole pagel can be extremely well covered with the thick film paste.

In the present invention, any thick film paste may be used; for example, there is a conductive paste composed of metal powder made of silver and palladium, glass frit, a resin binder, and an organic solvent, and there is also a thermosetting or ultraviolet curable resin paste. This is especially effective when printing through-holes and printing flat areas of double-sided conductor thick film circuits using conductive paste at the same time. Furthermore, if the thick film paste printing method described above is similarly applied to a fired thick film circuit board in which conductors on both sides of the board are connected through through holes, the surfaces of the conductors in the through holes can be covered extremely well. .

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. Board size 10
0mm x 90mm x 0.8 tmm, diameter is 0.6ψ
A suction jig 1 removes an alumina substrate 1 having through holes 6 between the
o, and use a vacuum pump to suction at a vacuum level of 31MHg or more from the suction port 11, and then move the outgoing squeegee 9a from the front to the first position.
As shown in Examples 1 to 6 in the table, the viscosity of the 7'' silver-palladium paste 2 was changed and 25
Using a stainless steel screen 8 with a mesh size of 0 to 350, screen printing was performed on the conductor circuit portion on the substrate and the inside 6 of the through hole, where the conductor width was 0.2 mm or more and the conductor interval was 0.2 mm or more.

Note that the paste viscosity was measured under the following conditions.

Margin below Tokukai Sho GO-143fli8B (3) 91 1 Measuring instrument: E-type viscometer (Tokyo Keiki type).

V I S CON I C-EHD )2 Measurement method:
Cone and plate (cone angle 3 degrees, cone radius 1
．． 4crn) 3 Plate rotation speed: 1 r, pom.

4 Measurement temperature: 26°C Next, the printed substrate was discharged, and as shown in Fig. 6, a new alumina substrate 1 was set in the suction jig 1o in the same manner as in the outward printing, and the silver used in the outward printing was removed. - Screen printing was performed while vacuum suctioning the palladium paste 2 using the return squeegee 9b under the same conditions as the outward printing.

As a result, as shown in Fig. 4, in screen printing according to the present invention, since the paste is spread on the screen in advance, the suction pressure is constant, the printing condition is exactly the same on the outward and return passes, and the paste viscosity is low. The higher the throughhole formation yield, the better the throughhole formation yield. However, if the viscosity of the paste is too low, smearing occurs in the conductive circuit portion on the substrate, resulting in poor printability. In other words, when the paste viscosity of the first embodiment is 90 pas or less, bleeding occurs on the conductor circuit section on the vane of the substrate 1o, and
From 0 to 300 pas, the throughhole formation yield is 10
At 0%, good printability was obtained. Also, at 310 pas or more in the sixth example, the printability of the conductor circuit portion on the substrate was good, but the through hole formation yield was less than 90% due to the high viscosity. It gets worse.

Table 2 shows the vacuum suction force, through hole formation yield, and printability.

Margin below: 11'\- According to this, the higher the vacuum suction force, the better the through hole formation yield, and when the vacuum suction force was 3 cm Hg or more, the through hole formation yield was 10%, and good printability was obtained.

In particular, when looking at the state of paste adhesion inside the through holes, 5 c
m Hg is best.

Further, although a flat squeegee was used in this embodiment, similar results can be obtained with a square squeegee, and the present invention is not limited to a flat squeegee.

Due to the above conditions, resin paste was used instead of conductor paste, but as shown in Fig. 7, the insulating resin film 14 was uniformly coated on the entire inner wall of the through hole, completely preventing the conductor in the through hole from being exposed. was completed. Further, there was no bleeding phenomenon of the resin paste.

Effects of the Invention As described above, according to the present invention, unlike conventional screen printing, the paste is not spread on the screen in advance by returning the ink, so the suction pressure is constant from the beginning to the end of printing, and therefore there is no through-flow. In forming holes, fine patterns, etc., a substrate with extremely high printing precision can be obtained. In addition, because the conductor circuits on the board and the inside of the through-holes are printed simultaneously using two squeegees alternately, the conventional method of printing was once when the squeegee went back and forth, but now it is printed twice on the outward and return passes. It is possible to improve productivity. Furthermore, the risk of circuit short circuits caused by migration of through-hole conductors can be completely eliminated, so there is no need for resin sealing after component mounting.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an example of a thick film circuit, Fig. 2 is a sectional view showing a thick film circuit using both sides of a substrate, Fig. 3 is a sectional view of conventional screen printing, and Fig. 4 is a sectional view of a conventional screen printing method. A diagram showing the relationship between squeegee position and vacuum suction force in screen printing and the screen printing of the present invention, FIG. 6 is a sectional view of an apparatus implementing an embodiment of the present invention during forward printing, and FIG. 6 is also a diagram showing the return printing. FIG. 7 is a cross-sectional view of a through-hole portion in another embodiment of the present invention. 1...Alumina substrate, 2...Silver-palladium paste, 6...Through hole, 8...
...Screen, 14''-2 9... Squeegee, 9a... Squeegee for outward trip, 9b... Squeegee for return trip, 1o...
...Suction jig, 12... Emulsion, 13...
- Conductor circuit section, 14...Insulating resin film. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3 Figure 4 Squeegee specifications -

Claims (1)

[Claims] 0) A thick film circuit characterized in that a thick film paste is printed on a substrate having newly supplied through holes in each of the forward and return passes of the squeegee operation. printing method. (2) The method for printing a thick film circuit according to claim 1, wherein printing is performed using a squeegee for the outward path and a squeegee for the return path is used for the return path. (3) A method for printing a thick film circuit according to claim 1, wherein when printing the thick film paste on one side of the substrate by operating a squeegee, vacuum suction is applied from the other side of the substrate. @) The method for printing a thick film circuit according to claim 1, wherein the thick film paste is a conductive paste. (5) The method for printing a thick film circuit according to claim 1, wherein the thick film paste is a resin paste.