The present invention relates to an aluminum (Al) electrode for a chip resistor; more particularly, to a thick-film Al electrode paste for forming the Al electrode to fabricate the chip resistor, where the Al electrode is capable of being electroplated (with a pretreatment), highly conductive (with a high metal content), highly thermally dissipative (with a vanadium(V)-oxide series glass) and highly dense with few pores (with the V-oxide series glass); and the thick-film Al electrode paste for forming the Al electrode has specific composition to fabricate the chip resistor with an anti-plating pretreatment.
A thick film printed electronic device needs conductive electrodes for connection to work well. On consideration of high conductivity, modernly-used conductive electrodes are mainly fabricated through sintering a metal silver (Ag) in the air or a metal copper in a reducing atmosphere. However, when there is sulfur existed in the environment, the conductive electrode will be sulfurized so that the conductivity is significantly reduced and the function of the conductive electrode is lost. To solve the sulfurization problem of the conductive electrode, a conductive thick-film printed Al electrode having high conductivity was proposed. The proposed conductive Al electrode did not react with sulfur in a general sulfurization reliability test. Sulfurization was avoided and the original high conductivity of the electrode were still maintained.
However, the main disadvantages of the thick-film-printed Al electrode include the followings: (a) Its conductivity is much lower than that of the thick-film printed Ag electrode sintered in the air and that of the the thick-film printed copper electrode sintered in the reducing atmosphere. (b) After sintering, its porosity is too high yet its density is too small. (c) Metal is hard to be further plated owing to an oxide layer easily generated on the surface of the Al electrode. These problems for the conductive Al electrode would cause the following troubles on applying the fabrication of the chip resistor: (1) The resistance is unstable after laser trimming (as conductivity is too low). (2) The resistance will drift after the subsequent thermal treatment (as density is small with too many pores formed after sintering). (3) Its weldability is so poor that nickel and tin are not plated easily (on the surface of oxide layer or glass). (4) The resistances greatly vary for short-term overload voltage tests (as heat-dissipation is bad with too many pores formed after sintering).
As is described above, the modern chip resistor and its terminal electrodes are mainly made of conductive Ag material. However, metallic Ag easily reacts with sulfur in environment and generates silver sulfide thereby to further affect the features of the chip resistor. In particular environments having high temperatures, high humidity, and high sulfur concentrations, reactions in applications like automotive electronics are especially vigorous. At present, for producing an anti-sulfurization chip resistor for automobile, a high content of palladium (Pd) (more than 5 mole percent) is added to an Ag terminal electrode to form an Ag—Pd alloy for reducing the reaction activity of forming silver sulfide with sulfur. As a result, the material cost of the terminal electrode has a dramatic rise and, as the curing environment becomes more severe, there is a certain risk of forming silver sulfide. Hence, the prior arts do not fulfill all users' requests on actual use.
The main purpose of the present invention is to replace the original Ag terminal electrode with an Al terminal electrode for significantly reducing material cost.
Another purpose of the present invention is to replace the original Ag terminal electrode with the Al terminal electrode for completely overcoming the original sulfurization problem for chip resistors and solving the conventional problem of material migration of the Ag electrode under high voltage and high humidity, which greatly benefits the applications of the chip resistors in the field of automobile electronics.
To achieve the above purposes, the present invention is a composition of thick-film Al electrode paste, where the composition is of a conductive Al paste to form a terminal electrode of a chip resistor on an Al ceramic substrate; the composition comprises an RO-zinc(Zn)-boron(B)-based glass, a metal oxide (MO), Al granules, and an organic additive; in the total weight of the RO—Zn—B-based glass, the Al granules, and the organic additive, the RO—Zn—B-based glass has a content of 3˜30 weight percent (wt %), the MO has a content of 0.1˜15 wt %, the Al granules has a content of 50˜70 wt %, and the organic additive has a content of 10˜20 wt %; and the RO—Zn—B-based glass is a V—Zn—B-based glass (V2O5—ZnO—B2O3) or a barium(Ba)—Zn—B-based glass (BaO—ZnO—B2O3). Accordingly, a novel composition of thick-film Al electrode paste is obtained.
The present invention will be better understood from the following detailed description of the preferred embodiment according to the present invention, taken in conjunction with the accompanying drawings, in which
The following description of the preferred embodiment is provided to understand the features and the structures of the present invention.
Please refer to
On using the present invention, by using a thick-film screen printing technology, a thick-film Al electrode paste (e.g. V—Zn—B-based glass) is directly formed into an Al terminal electrode on an alumina ceramic substrate to replace the terminal electrode formed of the original conductive silver (Ag) paste for fabricating a chip resistor. As shown in
The conductivity, dissipation rate and density (porosity) of the thick-film-printed Al electrode mainly relate to the composition of the glass of thick-film Al paste coordinated with the formula of the Al metal powder. The present invention reveals the relationship between the characteristics of the thick-film-printed Al electrode applied to a chip resistor and the composition of the glass of thick-film conductive Al paste along with a pretreatment of the thick-film Al electrode before metal plating.
According to Table 1, the conductive Al paste of the RO—Zn—B-based glass is sintered at 600° C. and 850° C., where the MO is SiO2, MnO2, CuO, Cr2O3, ZrO2, Al2O3, B2O3, ZnO, and Li2O; and the conductive Al paste is compared with other conductive Al pastes of Zn—B-based glass:
Firstly, an absolute relationship is found between the conductivity of the thick-film-printed Al electrode and the metallic Al contents, the Al particle sizes, and the added glass amount contained in the metallic Al paste. Therein, the conductivity of the Al electrode increases as the Al solid content increases; the conductivity is better with bigger Al granules; a very low glass content with too much pores results in low connectivity; and, yet, the connectivity of Al is significantly reduced with a high insulation rate owing to the too high glass content.
Next, regarding the thermostability of the thick-film-printed Al electrode (thermally treated at 200° C.), only the RO—Zn—B-based glass is most helpful for improving the thermostability for the chip resistor. In
Furthermore, the short-term overload resistance test is related to the type and content of glass in the metallic Al paste. Only the RO—Zn—B-based glass is most helpful to improve the short-term overload resistance test for the Al electrode. In
Besides, the present invention uses the anti-plating treatment to solve the problem where metal plating followed is hard to be processed owing to an oxide layer generated on electrode surface even though the Al paste using the RO—Zn—B-based glass achieves high density after being sintered.
Finally, a high-temperature Al electrode 72a is obtained on an alumina ceramic substrate 71 through a high-temperature sintering (above the melting point of metallic Al (660° C.), about 850° C.); and, then, a cryogenic Al electrode 72b is formed through a low-temperature sintering (below the melting point of metallic Al, about 600° C.), whose structure of two-layer Al electrode plated with nickel and tin 73,74 is shown in
The present invention uses an Al terminal electrode 81 to replace the original Ag terminal electrode. The chip resistors plated with nickel and tin 82,83 are shown in
The present invention compares the Ag electrode and the Al electrode of the chip resistor under high voltage and high humidity as shown in
Hence, the thick-film-printed Al electrode proposed according to the present invention has the following features:
(1) The material cost is significantly reduced by replacing the original Ag terminal electrode with the Al terminal electrode.
(2) The original sulfurization problem for chip resistor is completely overcome by replacing the original Ag terminal electrode with the Al terminal electrode, which greatly benefits the applications of the chip resistors in the field of automobile electronics.
To sum up, the present invention is a thick-film Al electrode paste with a pretreatment before metal plating for fabricating a chip resistor, where the chip resistor having electrodes fabricated with the thick-film Al paste improves its ability on anti-sulfurization and solves the conventional problem of material migration of the Ag electrode under high voltage and high humidity; and the material cost of the terminal electrode of the chip resistor is also significantly reduced.
The preferred embodiment herein disclosed is not intended to unnecessarily limit the scope of the invention. Therefore, simple modifications or variations belonging to the equivalent of the scope of the claims and the instructions disclosed herein for a patent are all within the scope of the present invention.
Number | Date | Country | Kind |
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107121738 | Jun 2018 | TW | national |