Thick-film conductor circuit and production method therefor

Details Thick-film conductor circuit and production method therefor Thick-film conductor circuit and production method therefor

1998-12-24

2001-08-07

Mai, Anh (Department: 2832)

Active solid-state devices (e.g., transistors, solid-state diode

Combined with electrical contact or lead

Of specified material other than unalloyed aluminum

C257S762000, C257S775000

Reexamination Certificate

active

06271589

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a thick-film conductor circuit for use in an industrial field of electronic elements or circuit elements, the sizes of which have furthermore been reduced and functions of which have been increased to manufacture a coil for a very small, high-performance, compact and flat motor, a precise coil for an optical pickup for reading high-speed data from a compact disk, an MD or a DVD, a circuit substrate including a precise wiring portion for an LSI or a circuit element for connecting a display device which has furthermore precisely been formed into a device, and to a manufacturing method therefor. More particularly, the present invention relates to a reliable thick-film conductor circuit including a portion, in which a shortest wiring pitch is shorter than 100 &mgr;m and which enables resistance can densely and freely be set, and a manufacturing method therefor.
BACKGROUND ART
The dense, low-resistance and reliable thick-film conductor circuit must have a short wiring pitch and incorporate a conductor having a large cross sectional area, that is, having a large height and satisfactory chemical stability, for example, acid resistance and corrosion resistance.
For example, the number of pins in each of IC and LSI (Large Scale Integrated Circuit), the performance of each of which has been improved in recent years, has been enlarged to meet a requirement for realizing improved performance. Moreover, the pitch of the pins has gradually been shortened. Liquid crystal display units have been required to have precise structures. Under the foregoing circumstances, the number of display scanning lines has significantly be enlarged. Moreover, intervals of electric wires have been excessively shortened to easily mount ICs for controlling display. Under the above-mentioned technological circumstances, there arises a requirement for a dense and low-resistance element for connecting different-pitch wiring elements to each other such that elements having considerably different wiring pitches, for example, an IC or an LSI having pins configured at small pitches and a mother board (having electric wires configured at long pitches owning to a manufacturing requirement) are connected to each other. Note that an element of the foregoing type is defined as an “interposer” in a document (Nikkei Electronics, 1995. 1. 16 (No. 626) pp. 79 to 86). In this specification, the foregoing element is defined as a “different=pitch-element connecting member”. As for performance which must be satisfied by the different-pitch-element connecting member, a report has been published in 6-th Microelectronic Symposium, pp. 43 to 46 about a fact that signal pulses are attenuated in inverse proportion to the resistance of the wiring when the CPU is operated at clock speed for a high speed operation. If the resistance of the wiring for connecting a control IC for a precise liquid crystal display device and a liquid crystal substrate is raised, the S/N ratio is lowered and thus the image becomes instable. As a result, the different-pitch-element connecting member must have a low-resistance circuit, short wiring pitches and satisfactory reliability.
As a means for improving the chemical stability of a conductor, plating of zinc, which has a base standard potential as compared with that of copper, on the surface of copper has been performed to prevent corrosion of the copper. However, the zinc plating method encounters a fact that the physical properties of a formed film are adversely affected by the plating conditions, that is, the composition of plating solution, the density of contained impurities, temperatures during a plating process and the density of electric currents. Therefore, the plating solution and process must delicately be controlled. A zinc film must have a large thickness to obtain the corrosion resistance. If the thickness and ratio of zinc having inferior electric conductivity to that of copper are enlarged, there arises a problem in that the electric conductivity deteriorates. Since a process using high frequencies encounters a problem in that the resistance of the surface of the conductor is raised, the surfaces of the conductor is sometimes plated with a noble metal, such as gold. However, a means cannot be obtained which is capable of reducing the thickness of a zinc film, maintaining the electric conductivity and preventing corrosion and oxidation of a copper pattern, which is an object of the present invention and which is applicable to a dense conductor circuit having a large surface area with respect to the cross sectional area of the conductor.
As a method of manufacturing a dense and thick-film conductor circuit, a method is known in which a copper-applied substrate, photolithography and etching are combined with one another. However, a thick-film conductor circuit obtainable from the above-mentioned method encounters difficulty to prevent a side etching phenomenon which takes place when copper foil is etched. If the density is raised, the reliability of the conductor deteriorates. In proportion to the height of the conductor, the above-mentioned phenomenon becomes critical. Therefore, the thickness of copper foil of usual copper-applied substrates is about 18 &mgr;m to 35 &mgr;m. Also the wiring density is lower than 20 lines/mm.
Another method of manufacturing a thick-film conductor circuit, methods have been disclosed in Japanese Patent Laid-Open No. 52-137666 and Japanese Patent Laid-Open No. 57-162489, in which a resin pattern is filled with a thick-film paste material. Another method is disclosed in Japanese Patent Laid-Open No. 55-41729, in which thick-film paste and a positive-type resist are mixed with each other, after which exposure and development are performed. However, the above-mentioned methods cause a thick-film conductor circuit to be obtained in which voids are formed in the conductor, a defect takes place owning to short circuit between conductors and the characteristics of the circuit deteriorate because of rise in the resistance of the conductor.
In Japanese Patent Laid-Open No. 59-198792, a method of manufacturing a thick-film conductor circuit has been disclosed which has the steps of: repeating lamination and exposure of photosensitive resin such that a conductive substrate is employed as a base, and performing development and electric plating. Although expectation can be made that the above-mentioned method will enable a resist pattern having a relatively high aspect ratio to be obtained and a low-resistance conductor circuit to be manufactured, a complicated process must be performed. What is worse, the deviation which occurs when the lamination and exposure are performed causes a defect to be introduced and short circuit to occur because of a defective resin change. Thus, there arises a multiplicity of problems in that the reliability of the circuit is unsatisfactory.
In Japanese Patent Laid-Open No. 56-94690 and Japanese Patent Laid-Open No. 60-161605, methods each of is capable of forming a fine pattern circuit have been disclosed, in each of which a conductive substrate and photolithography are combined with each other after which anisotropic electrolytic plating is performed. The foregoing method controls the design of the conductor by the plating start width. What is worse, the conductor has a spherical shape. Therefore, the above-mentioned method is unsatisfactory as a method of manufacturing a dense and low-resistance pattern conductor.
Moreover, the applicant of the present invention has disclosed, in Japanese Patent Laid-Open No. 6-260740, a method of processing a substrate for the purpose of obtaining a resist pattern having a high aspect ratio by improving the adhesiveness between photosensitive resin and conductive substrate. However, a thick-film conductor circuit obtainable from the above-mentioned method cannot include a predetermined layer containing zinc atoms in a surface layer of the conductor. Thus, there arises a somewhat problem in that satisfactory oxidation resistance cannot be obtained.
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