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Method of Enhancing Infrared Absorption of Copper Dressing Blocks

IP.com Disclosure Number: IPCOM000046208D
Original Publication Date: 1983-Jun-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Klein, DL: AUTHOR

Abstract

In order to remove excess solder from packaging substrates after integrated circuit chip removal, a technique has been used employing porous copper blocks. The blocks while held against the substrate site to be dressed free of solder are heated by infrared (IR) radiation. The molten solder on the substrate is withdrawn into the porous copper block. Since IR radiation is inefficiently absorbed by bright copper surfaces, it is necessary to alter the surfaces of the blocks.

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Method of Enhancing Infrared Absorption of Copper Dressing Blocks

In order to remove excess solder from packaging substrates after integrated circuit chip removal, a technique has been used employing porous copper blocks. The blocks while held against the substrate site to be dressed free of solder are heated by infrared (IR) radiation. The molten solder on the substrate is withdrawn into the porous copper block. Since IR radiation is inefficiently absorbed by bright copper surfaces, it is necessary to alter the surfaces of the blocks.

A method to enhance IR absorption has been developed that is both rapid and simple to achieve. One of the surfaces of the copper blocks is normally tinned with Sn/Pb (63/37%) solder to enhance solder removal from the substrate. If this block (approximately 1/16" x 3/16" x 3/16") is exposed to fumes above, or directly submerged in, a solution of ammonium sulfide (diluted to approximately 8% (NH4)2S) the five bare surfaces react to form black copper sulfide (CuS). The tinned surface remains unaffected, while dense black coatings are achieved on the copper surfaces in about five minutes. After blackening, the blocks are washed free of ammonium sulfide by rinsing in rapidly flowing water. The sulfide- blackened surfaces have been found to be stable in the presence of flux at 400OEC. When functionally tested, using a tungsten lamp as the infrared source, the following was observed:

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The improved IR absorption of the sulfi...