JPH03196694A - Formation of through hole of thick film circuit board - Google Patents

Abstract

PURPOSE:To prevent development of cracks at an edge part of a through hole by providing an area deliberately which has no conductor part to the edge part of a conductor part of the through hole and by releasing a stress during thermal contraction. CONSTITUTION:Conductor paste which is printed while attracted to a ceramic substrate 11 forms a land 12 in print of a surface of the substrate 11 and forms a land 16 in print of a rear thereof. At the same time, conductor paste which creeps and attaches also to a hole wallside overlaps in the hole wallside to constitute a through hole 15 whose rear and surface are conducting. In the print process, an area 13 wherein conductor paste is not printed is provided to an edge part of the through hole 15 deliberately. The area 13 is on a metal mesh screen 23 to be used for print and a print resist 25 to prevent conductor paste from attaching is provided to a part 26 corresponding to an edge of the through hole 15. Thereby, it is possible to release a stress during thermal contraction and to prevent development of cracks at an edge of the through hole.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming null-holes in a thick film circuit board using a ceramic substrate and a thick film conductor paste.

BACKGROUND OF THE INVENTION In recent years, opportunities to use thick film circuit boards have increased, and the reliability of their through-hole structures has become an important issue.

Conventionally, when creating a thick film circuit board, Aq paste, A
Measures have been taken to form conductor patterns using q-Pd paste, Au paste, or Cu paste by a printing method using a metal mesh screen.

Thick film circuit boards that use only one side of a ceramic board are
Easily formed by printing alone. However, recently, thick film circuits are often formed using the front and back sides of the substrate.
Inevitably, through holes are increasingly being used. Null holes are formed in thick film circuit boards by printing a conductor circuit wiring pattern on a ceramic substrate having holes penetrating through the front and back surfaces while suctioning the conductor circuit wiring pattern using a conductor paste.

Hereinafter, an example of forming through holes in the above conventional thick film circuit board will be described with reference to FIGS. 3 and 4.

As shown in FIG. 3, a conductor base 6 is pressure-printed on the surface of the ceramic substrate 1 via a metal mesh Nu-Clean e.

At this time, lands 8 are formed in the holes 4 provided in the substrate 1, in which the conductive paste enters the holes 4 due to air flow through the holes provided during printing.

The above air flow is provided by suction means or the like from the back side of the substrate.

After printing on one side, after going through a drying process, conductive paste is printed on the opposite side of the board using the same method as described above, and on the wall of the through hole 4, a land 8 is formed in which the conductive paste is continuously adhered to the front and back sides of the board. be done. Thereafter, the thick film circuit board is completed by drying and baking. FIG. 4 shows a cross section of the through hole portion of the completed thick film circuit board.

Problems to be Solved by the Invention The conventional through-hole structure of a thick film circuit board constructed as described above has the disadvantage that cracks occur at the edge portions of the null holes during high-temperature firing.

Conventionally, Ag-pci has been the main conductor paste for thick film circuit boards. However, since Aq-Pd is a precious metal, it is expensive and lacks price stability. Furthermore, in terms of electrical characteristics, the impedance is 10~
It has a value of 30 mΩ/hole, and is 3 to 5 of copper foil printed circuit board.
It had the disadvantage of being higher than mQ1. From this point of view, Cu paste has attracted attention as a conductive paste and has been put into practical use.

However, Cu paste has a higher thermal shrinkage rate than Aq-Pd paste, and when through-holes are formed using the method described above, the conductor base printed under pressure on the board surface and the conductor best suctioned inside the hole are different. Since the thermal shrinkage rates are different, there is a problem in that cracks 3 occur at the edge portions of the substrate during the firing process due to thermal contraction.

The present invention solves the above problems, and when forming a thick film circuit board using a conductive paste on a ceramic substrate,
It is an object of the present invention to provide a method for forming a through-hole that does not cause cracks in forming a null-hole that penetrates the front and back sides and provides conduction.

Means for Solving the Problems In order to achieve the above object, the present invention prints conductive paste into holes penetrating the front and back sides of a ceramic substrate while sucking it from each side, thereby making the front and back conductive, and then drying and drying. This is a method of forming a through hole in a thick film circuit board by firing, and the through hole is formed by forming a part of the edge of the through hole to which conductive paste does not adhere.

The present invention uses the method described above to form a part of the edge of a null hole without intentionally printing the conductor paste to be applied, so that the heat shrinkage of the conductor base during firing is caused by this unprinted part. As a result, cracks do not occur at the edges of the through holes.

EXAMPLE An example of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 shows a cross-sectional perspective view of a through-hole structure of a thick film circuit board according to an embodiment of the present invention.

As shown in the figure, the conductor base printed on the ceramic substrate 11 in an arched manner forms a land 12 by printing on the front surface of the substrate 11, forms a land 16 by printing on the back surface, and also penetrates into the hole wall surface. The conductive paste adhered to the hole wall surface becomes electrically conductive, forming a null hole with conduction between the front and back sides.

In this printing process, a portion 13 where no conductor base is printed is intentionally provided at the edge of the null-hole. This portion 13 is realized by providing an emulsion (hereinafter referred to as printing resist) on the metal mesh screen 23 used for printing in a portion corresponding to the edge of the through hole to prevent conductive paste from adhering.

Second, an embodiment of the printing means using the metal mesh screen of the present invention will be described. Figure B shows a metal mesh screen 23 on a ceramic substrate 21 with through holes 22.
2 shows in cross section the means by which the conductor base is set and the conductor base is printed. A printing resist 24 corresponding to the conductor pattern to be printed and a printing resist 25 covering portions corresponding to the edge portions 2e of the holes 22 of the substrate and part of the lands are provided on the double clean 23. Figure A shows an example pattern. The edge 26 of this printing resist 25U hole 22
It is provided from the position extending in the inner radial direction.

When printing is performed using suction using the metal mesh screen 23 described above in the same manner as shown in FIG. Conductive paste adheres to the wall of the hole.

After printing on the front side, the conductive paste is dried at 120 degrees for 30 minutes, and the same printing and drying is carried out on the back side to obtain the through-hole structure shown in FIG.

Thereafter, the thick film circuit board is completed through a baking process at 900 degrees Celsius for 10 minutes in a nitrogen atmosphere.

To explain the operation in the above method, the portion 13 where the conductive paste is intentionally not printed on the edge portion of FIG. 1 contracts during firing as shown by the arrow 14 in the figure due to the absence of the conductive paste, and the shrinkage stress is released. function as a part.

Therefore, the other parts can be contracted without generating stress, so that the effect of preventing cracks from occurring can be obtained.

As described above, according to the through-hole forming method of the embodiment of the present invention, by intentionally providing a portion where no conductor paste is applied to the edge portion of the conductor portion of the through-hole, it is possible to form a through hole without adding a new process. , it is possible to obtain the effect that cracks do not occur at the edges.

This effect is effective in the case of Cu-paste, which has a large thermal shrinkage, but it goes without saying that the same effect can be obtained for other conductive bases. Furthermore, it is expected that a similar effect will be obtained when a portion where no conductive paste is intentionally printed is provided only at one end of the through hole, and this has actually been confirmed.

Effects of the Invention As is clear from the above embodiments, the present invention intentionally provides a portion without a conductor at the edge of the conductor of the through-hole to release stress during heat shrinkage, thereby improving the edge of the through-hole. This has the effect of preventing cracks from occurring in the parts.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional perspective view of a through hole portion of an embodiment of the present invention, FIGS. 2A and 8 are a plan view and a side view showing a printing means using a metal mesh screen of an embodiment of the present invention,
To Fig. 3, B, (:: is a cross-sectional view showing the procedure of the printing formation method of a null hole, and Fig. 4 is a cross-sectional view showing a conventional through-hole structure. 11...Ceramic substrate , 12... Land made of printed conductive paste, 13...
Intentionally unprinted portion, 14...Arrow indicating direction of heat shrinkage, 15...Through hole, 16...
... Land made of printed conductor paste, 21.
... Ceramic substrate, 22 ... Hole provided in ceramic substrate, 23 ... Metal mesh cleaner, 24 ... Printing resist, 26 ...
...Printing resist, 26...Edge of hole.

Claims (1)

[Claims] By printing the conductive paste while sucking it into the holes penetrating the front and back sides of the ceramic substrate from each side,
A method for forming a through hole in a thick film circuit board by making the front and back sides conductive, then drying and firing, the method forming a through hole in a thick film circuit board, the method forming a part on the edge of the through hole to which conductive paste does not adhere. A method for forming a through hole in a thick film circuit board, the method comprising printing a conductive paste while sucking it using a metal mesh screen having a printing resist that covers a part of the edge of the through hole.