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Special Mask for Circuit Repair Via Laser Exchange Plating

IP.com Disclosure Number: IPCOM000037051D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

von Gutfeld, RJ: AUTHOR

Abstract

The use of the positive shift in the rest potential for plating at a copper/copper 2+ interface has been described in several earlier references, e.g. [*]. The shift to a more positive potential occurs when a portion of the interface is heated, causing it to become cathodic. The cooler or unheated region gives up ions, and thereby charge conservation is maintained. Thus, plating and etching occur simultaneously but along different portions of the sample, depending on its temperature; hence, a thermally driven exchange plating occurs. One of the difficulties with using this method for plating to bring about a repair is that there can be a shortage of sacrificial ions from the circuit needed to maintain the charge neutrality. Thus, the colder portion of the circuit can become very thin or even dissolve completely.

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Special Mask for Circuit Repair Via Laser Exchange Plating

The use of the positive shift in the rest potential for plating at a copper/copper 2+ interface has been described in several earlier references, e.g.
[*]. The shift to a more positive potential occurs when a portion of the interface is heated, causing it to become cathodic. The cooler or unheated region gives up ions, and thereby charge conservation is maintained. Thus, plating and etching occur simultaneously but along different portions of the sample, depending on its temperature; hence, a thermally driven exchange plating occurs. One of the difficulties with using this method for plating to bring about a repair is that there can be a shortage of sacrificial ions from the circuit needed to maintain the charge neutrality. Thus, the colder portion of the circuit can become very thin or even dissolve completely. Also, overheating of the circuit board can take place if the laser is not perfectly lined up with the region undergoing repair if the substrate is very thin or made of low melting material.

In this article a special copper mask containing small openings of various dimensions approximating typical sizes found for open circuits requiring repair is proposed. The mask thickness should be on the order of several mils, much thicker than the lines undergoing repair. A variety of different size openings can be made on a single mask. The thermal mass of the mask will be sufficiently thick to prevent the ma...