JPS6058599B2 - Photo-etching method of glass-ceramic layer of multilayer circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a glass-ceramic multilayer circuit board, and more particularly to a method for photoetching a glass-ceramic layer of a multilayer circuit board.

The trend toward higher performance and higher integration of LSIs has been accelerating in recent years, and with this trend, the multilayer structure and fine wiring of ceramic multilayer substrates on which LSIs are mounted are being used to increase density. .

One such high-density multilayer ceramic circuit board is a glass ceramic multilayer circuit board, which is manufactured by the following method. A conductor paste is applied to the entire surface of the sintered ceramic substrate using a screen printing method, a conductor circuit is formed by photo-etching after firing, and a glass-ceramic paste is applied to this circuit and the entire surface of the ceramic substrate using a screen printing method. , forming a via hole by photo-etching after firing is repeated to form a multilayer structure. In this method, photo-etching is utilized to improve the fineness and accuracy of conductor circuits and via holes in the glass ceramic layer, thereby achieving high density. However, in order to perform deep etching of 20 to 40 μm using a hydrofluoric acid-based etching solution for the glass-ceramic layer, the adhesion of the photoresist to the etching-resistant glass-ceramic layer and side etching (undercut) are required. becomes a problem. That is, a negative photoresist (for example, a photoresist used for etching SiO2 in semiconductor device manufacturing) can withstand hydrofluoric acid-based etching solutions, but when this photoresist is simply applied to a glass-ceramic layer, may peel off from the glass ceramic during etching or during washing with water after etching because of insufficient adhesion to the glass ceramic. If it peels off during washing after etching, the following problems will occur. Even if the etching rate is clear and the thickness of the insulating layer is clear, there will be variations in the thickness, so there is a risk that some parts will not be etched. If it has peeled off, re-etching cannot be performed. Also,
It is advantageous to fill the via holes with conductive paste while the resist is still attached. Furthermore, regarding the relationship between the etching solution and side etching, the etching rate is slow and the side etching becomes large with the hydrofluoric acid-ammonium fluoride based etching solution that is generally used for etching SiO2. It is not suitable for etching glass-ceramic layers as thick as ~40 μm.

Large side etch is contrary to refinement. An object of the present invention is to provide a method for photoetching a glass-ceramic layer without increasing the adhesion of a photoresist to a glass-ceramic and without increasing side etching.

The aforementioned objects can be achieved by the following method of photoetching fired glass ceramic layers of a multilayer circuit board.

That is, the baked glass-ceramic layer is lightly etched, the glass-ceramic layer is brought into contact with stearic acid, and then a photoresist is applied to improve the adhesion between the photoresist and the glass-ceramic. By etching the glass ceramic layer with a hydrofluoric acid monosulfuric acid based etching solution using a photoresist as a mask, a desired etching can be performed with suppressed side etching. The glass-ceramic can be a hydrofluoric acid-etchable crystallized glass or a glass-ceramic mixture of glass and ceramic, which are commonly used in the manufacture of multilayer circuit boards.

Lightly etching the glass-ceramic layer before applying the photoresist means etching the surface of the fired glass-ceramic layer with about 1 to 2 μml of an appropriate etching solution, so that the surface roughness of the glass-ceramic layer remains unchanged after firing. (Rnlax 3 to 3.5 μTrL) is slightly larger than the state (Rmax 3 μm or less).

The adhesion between the photoresist and the glass-ceramic layer is improved by bringing stearic acid into contact with the glass-ceramic layer, regardless of the contact method (immersion method, spinner method). .5%
If it is above, it is effective. When stearic acid is dissolved in xylene, its preferred concentration is 1.5-2.0
%. Each of the above-mentioned light etching and contact with stearic acid improves the adhesion of the photoresist, but the improvement of adhesion is insufficient if each is used alone without being combined, so it is necessary to combine them. As a result of research on etching solutions, an etching solution made by mixing 46% sulfur (hydrogen fluoride) and concentrated H2SO, (sulfuric acid) at a ratio of 1°1 (volume ratio) and adding H2O (water) to this was found to be effective in side etching. It turned out to be small and suitable for etching glass ceramics.

The purpose of adding water is to control the etching rate; if there is too little water, the etching rate will be too fast, and if there is too much water, it will be too slow. The mixing ratio by volume is preferably 3:2 to 7:3. Hereinafter, the present invention will be explained based on examples.

Example 1 Polysilicate powder and alumina powder were mixed at a ratio of 1:1 (weight ratio), and a binder, dispersant, solvent, etc. were added and kneaded to form a glass-ceramic paste.

This paste was screen printed on the entire surface of the alumina substrate to a thickness of about 50 μm, and one powder was fired at 900° C. to form a glass ceramic layer. After the surface of the fired glass ceramic layer was subjected to the treatments shown in Table 1, a photoresist (0MR-83SS) was applied to a thickness of approximately 5 μm.
It was exposed to light using a pattern having a via hole of 0 μmφ, and after the phenomenon was completed, it was post-baked at 170°C. Further etching and cleaning operations as follows: Etching (46% HF
:CONCH2SO4:H2O=1.5:1.5:2,
(Immersion method, 5 minutes) ↓ Water washing (under running water, 1 minute) ↓ Ultrasonic cleaning (underwater, 2 minutes) The presence or absence of peeling of the photoresist was examined.

The results are also shown in Table 1. Note: "Post-etching stearic acid application" in the process refers to the following process.

Etching (46% HF:COnCH2SO4:H2O
= 1.5:1.5:2, 10 seconds) → Washing (under running water, 1
minutes) → Drying (120℃, 2 powders) → Stearic acid coating (
Xylene solution containing 2% stearic acid, 1000 rpm
Spinner) → Heat treatment (120℃, 3 minutes) → Photoresist coating. Example 2 A glass ceramic layer was formed in the same manner as in Example 1, lightly etched and coated with stearic acid as described in the notes to Table 1, and then photoresist treated as in Example 1. .

The resulting glass-ceramic layer with the photoresist placed thereon was etched by a dipping method using an etching solution having the composition shown in Table 2.
Etching was performed for minutes, and the etching rate and etching factor were measured. The results are shown in Table 2. Note that the etch factor is the value obtained by dividing the etch depth in the vertical direction of the glass ceramic layer by the length of the side etch (undercut) in the lateral direction of the layer, and the larger this value is, the smaller the side etch is. . As is clear from Table 2, the etching rate of the hydrofluoric acid monosulfuric acid based etching solution is faster than the other two examples, and the side etch is small.

Claims (1)

Claims: 1. A method of photoetching a fired glass-ceramic layer of a multilayer circuit board, comprising: lightly etching the glass-ceramic layer before forming a photoresist on the glass-ceramic layer; A method for photoetching a glass-ceramic layer of a multilayer circuit board, characterized by contacting the ceramic layer with stearic acid. 2. A method of photoetching a fired glass-ceramic layer of a multilayer circuit board, in which the glass-ceramic layer is lightly etched, the glass-ceramic layer is brought into contact with stearic acid, and then a photoresist is applied, and the photoresist is A method for etching a glass ceramic layer of a multilayer circuit board, characterized in that the glass ceramic layer is etched using a hydrofluoric acid-sulfuric acid based etching solution as a mask.