JPH0149655B2 - - Google Patents

Description

[Detailed description of the invention]

[Overview] Glass paste for overcoating using polymethyl methacrylate and a small amount of ethyl cellulose as a binder. [Industrial Application Field] The present invention relates to the structure of an overcoat paste that can be fired in an inert atmosphere. 2. Description of the Related Art As information processing devices that process large amounts of information at high speed have progressed, electronic components used therein have become increasingly smaller and more integrated, and various integrated circuits have been put into practical use. A typical example of this is the semiconductor integrated circuit (Monolithic IC), and as integration progresses, LSI,
VLSI has been put into practical use. On the other hand, using ceramic or glass-ceramic substrates, screen printing technology is used to print fine wiring patterns, resistor patterns, insulating layers, etc. using conductor paste, low antibody paste, dielectric paste, etc. as printing materials. However, thick film integrated circuits (thick film ICs), which are formed by firing to form integrated circuits, have also been put into practical use. In general, semiconductor ICs are often mounted on thick film ICs made of passive elements. Now, the conductor pastes that make up the conductor patterns of conventional thick film ICs include gold (Au) paste, silver (Ag) paste, palladium/gold (Pb/Au) paste, and Pd/Ag paste, which can be fired in the atmosphere. paste was used. However, as the integration of semiconductor ICs progresses and VLSIs are put into practical use, the ceramic substrates on which they are mounted become multi-layered, and wiring patterns become finer, materials with lower resistivity than before are needed. Copper (Cu) paste has started to attract attention. In other words, by using Cu paste, it is possible to create thick-film ICs with low electrical resistance, good solder wettability, and no phenomena such as migration. However, the Cu that makes up the Cu paste easily oxidizes to cuprous oxide (Cu ₂ O) or copper oxide (CuO) when fired in the _atmosphere . It is necessary to apply an overcoat to prevent oxidation even after firing. The present invention relates to improvements in overcoat pastes used for this purpose. [Prior Art] Conventionally existing overcoat pastes have been used for interlayer insulation or crossover purposes. In other words, a conductive paste is printed on a ceramic substrate using the screen printing method and fired to create a fine circuit pattern.Overcoat paste is printed on the entire surface except for the contact hole area and fired, and then on top of this is printed a fine circuit pattern. It is used for interlayer insulation to form conductor patterns. Furthermore, when there is a three-dimensional intersection in a wiring pattern formed on a ceramic substrate, an overcoat paste is screen printed and used for insulation only at the intersection. The overcoat paste used for such applications is similarly made for firing in the atmosphere, since the conductor paste is made for firing in the atmosphere. In other words, the overcoat paste is mainly composed of a low dielectric constant glass powder such as borosilicate glass powder, to which is added cellulose such as ethyl cellulose or a resin such as polybutyl methacrylate as a binder, and a small amount of a dispersant. It is made by adding a solvent such as turpentine or cellosolve to the mixture and making it into a paste. During firing after screen printing, these binders are oxidized to carbon dioxide (CO ₂ ) and water vapor (H ₂ O), and in the end, only the glass powder remains and melts, forming a conductor. Covering with patterns etc. is performed. However, as mentioned above, if the conductor pattern is formed using Cu paste, the printed overcoat pattern must be baked in an inert atmosphere (in most cases _N2 atmosphere) to prevent this oxidation. There is. However, in this case, the binder is not oxidized and remains carbonized, resulting in lower insulation and no longer functioning as an overcoat. Therefore, attempts have been made to reduce the amount of ethyl cellulose added as much as possible and bake for a long time, but the printability of the paste is poor due to the small amount of binder added, and the decomposition and scattering of ethyl cellulose It is not suitable for practical use because of its poor insulation resistance and low insulation resistance, and it is desired to create an overcoat paste that can be fired in an inert atmosphere. [Problems to be solved by the invention] As explained above, it is necessary to have an overcoat paste that exhibits a sufficiently high insulation resistance value when fired in an inert atmosphere. The problem is to select a binder that has good printability, dissolves in a solvent, exhibits appropriate viscosity, and completely disintegrates and scatters during the firing process. [Means for solving the problem] The above problem can be solved by using a binder for glass paste for overcoating, which is made by dispersing glass powder and a binder in a solvent and can be fired in an inert atmosphere. This problem can be solved by using an overcoat paste that is mainly composed of polymethyl methacrylate and contains a smaller amount of ethyl cellulose. [Function] The present invention was developed as a result of research into the necessary conditions for a binder that decomposes and scatters when heated in an inert atmosphere. In other words, a polymer compound is used as a binder in order to exhibit appropriate viscosity, but in order for this to decompose and scatter when heated, the straight chains of molecules must be broken by heating and decomposed into multiple low-molecular materials. ,
Materials that take the form of evaporation are suitable. The inventors focused on the fact that acrylic materials, particularly polymethyl methacrylate (abbreviated as PMMA), exhibit this type of thermal decomposition property, and selected this material as the binder. However, commercially available PMMA has various molecular weight distributions, and experimental results show that those with a relatively low molecular weight of 1.1×10 ⁵ to 2.2×10 ⁵ have good decomposition and scattering properties. Note that when only PMMA is used as a binder, it has poor wettability with glass powder and printability is poor. Therefore, it is necessary to add a small amount of a material that improves printability as a binder. The inventors selected ethyl cellulose, which has traditionally been used as a binder, as this material. However, although this ethyl cellulose has good wettability with glass powder, it is easily carbonized when heated in an inert atmosphere. Therefore, in the paste according to the present invention, a small amount is added to improve printability. Commercially available ethyl cellulose has a wide molecular weight distribution of 5,000 to ⁵ x 105, but those with a low molecular weight of 5,000 to 50,000 are suitable for use as binders due to their ease of decomposition. There is. In summary, the overcoat paste according to the present invention uses PMMA and a small amount of ethyl cellulose as a binder for conventionally used overcoat pastes, and has good printability and insulation resistance after firing. This realizes a high value overcoat. [Example] The table shows the composition of an overcoat paste in which the present invention was implemented.

【table】

〔Effect of the invention〕

As described above, by implementing the present invention, it is possible to put into practical use an overcoat paste that can be fired in an inert atmosphere and exhibits good insulation properties.

Claims (1)

[Claims] 1 The binder of the glass paste for overcoating, which is mainly composed of glass powder and a binder and dispersed with a solvent and can be fired in an inert atmosphere, is mainly composed of polymethyl methacrylate, with a smaller amount than this. An overcoat paste characterized in that it is composed of ethyl cellulose added thereto.