Patent EP0716429A2 successfully refreshed from Google Patents.
EP0716429A2
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EP
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Zinc phosphate coating for varistor and method
Assignee: Littelfuse Inc
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Filing: 1995-12-08
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Granted: —
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Expires: 2015-12-08
Abstract
Abstract A method of providing a semiconductor device (20) with an inorganic electrically insulative layer (34) the device having exposed semiconductor surfaces (34) and electrically conductive metal end terminations (30) in which the device is reacted with phosphoric acid to form a phosphate on the exposed surfaces (34) of the semiconductor but not on the metal end terminations (30), and in which the device is thereafter barrel plated in a conventional electrical barrel plating process and the plating is provided only on the end terminations (30) because the phosphate is not electrically conductive.
Inventors
- 👤 Palaniappan Ravindranathan
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 13:04
CPC Classifications
H; H01; H01C; H01C7/00; H01C7/18; H01C1/00; H01C1/02; H01C1/034; H01C7/10; H01C7/102
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
119 words
A method of making a nonlinear resistive device comprising the steps of: (a) providing a body for the nonlinear resistive device, the exterior of the body being a zinc oxide semiconductor except at a terminal region where an end termination is provided; (b) reacting a phosphoric acid with the body to form an electrically insulative zinc phosphate coating on the exposed zinc oxide semiconductor, the end termination not being coated with the zinc phosphate; and (c) barrel plating the body to plate the end termination with an electrically conductive metal, wherein the electrically conductive metal does not form on the zinc phosphate coated portions of the body during the barrel plating because the zinc phosphate is not electrically conductive.
Claim 2
Dependent Claim
27 words
A method as claimed in claim 1 wherein the end termination comprises a layer of a metal selected from the group consisting of silver, silver-platinum, and silver-palladium.
Claim 3
Dependent Claim
55 words
A method as claimed in claim 1 or 2 wherein the body comprises in mole percent, 94-98% zinc oxide and 2-6% of one or more of the additives selected from the group of additives consisting of bismuth oxide, cobalt oxide, manganese oxide, nickel oxide, antimony oxide, boric oxide, chromium oxide, silicon oxide, and aluminum nitrate.
Claim 4
Independent Claim
58 words
A method as claimed in any one of claims 1 to 3 wherein the step of reacting phosphoric acid comprises the step of submerging the body in the phosphoric acid, with the step of submerging the body comprising the step of submerging the body in a orthophosphoric acid solution for 25 to 35 minutes at 70° to 80°C.
Claim 5
Independent Claim
31 words
A method as claimed in any one of claims 1 to 4 wherein the electrically conductive metal comprises at least one of nickel and tin-lead, and the body is a varistor.
Claim 6
Independent Claim
118 words
A method of providing a semiconductor device as claimed in any claims 1 to 5 including an inorganic electrically insulative layer, the semiconductor device having an exposed semiconductor surface and electrically conductive metal end terminations, the method comprising the steps of: (a) exposing the semiconductor device to a phosphoric acid solution to form a phosphate coating on the exposed semiconductor surfaces, and not on the end terminations; and (b) barrel plating the semiconductor device with an electrically conductive metal plating in a process in which the device is electrically charged and submerged in a plating solution, the plating being formed on the end terminations and not on the phosphate coating because the phosphate coating is not electrically conductive.
Claim 7
Dependent Claim
20 words
A method as claimed in claim 6 wherein the exposed semiconductor surfaces comprise one of zinc oxide and iron oxide.
Claim 8
Independent Claim
20 words
A method as claimed in claims 6 or 7 wherein the phosphoric acid solution comprises orthophosphoric acid and deionized water.
Claim 9
Dependent Claim
16 words
A nonlinear resistive element made by the process of any one of claims 6 to 8.
Claim 10
Independent Claim
148 words
A method of providing an electrically insulative coating for a varistor, the method comprising the steps of: (a) providing an uncoated varistor having plural zinc oxide layers with electrodes therebetween, the electrodes contacting at least one of two exterior electrically conductive metal end terminations that are separated by an exposed surface of the zinc oxide layers; (b) submerging the uncoated varistor in a phosphoric acid solution for 25 to 35 minutes at 70°C to 80°C to form an electrically insulative zinc phosphate coating on the exposed surface of the zinc oxide layers, the end terminations not being coated with the zinc phosphate coating; and (c) subjecting the coated varistor to a barrel plating process in which the varistor is electrically charged and an electrically conductive plating material adheres to the charged portions of the varistor, the end terminations being plated and the zinc phosphate coating not being plated.
Claim 11
Dependent Claim
135 words
A nonlinear resistive element comprising: a body constituted by a varistor having stacked zinc oxide semiconductor layers; a planar electrode between each pair of said layers, each said electrode having a contactable portion that is exposed for electrical connection; plural spaced electrically conductive metal end terminations, each of said end terminations being on an end portion of said body for contacting at least one said contactable portion; an electrically insulative zinc phosphate coating covering said body between said end terminations; a metal plating covering said end terminations, and in which the body comprises in mole percent, 94-98% zinc oxide and 2-6% of one or more of the additives selected from the group of additives consisting of bismuth oxide, cobalt oxide, manganese oxide, nickel oxide, antimony oxide, boric oxide, chromium oxide, silicon oxide, and aluminum nitrate.
References Cited (Backward Citations)
US4316171A
Cited
US5115221A
Cited
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