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Reflow of Electrochemically Fabricated Eutectic C4 using a Glycrol-based Water Soluble Flux

IP.com Disclosure Number: IPCOM000117937D
Original Publication Date: 1996-Jul-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Cotte, J: AUTHOR [+3]

Abstract

Electrochemical fabrication of eutectic C4s involves through-mask plating, photoresist stripping, and selective etching of seed layers between C4s. During the etching step, C4s are protected by passive layers and hence are covered with reaction products. These reaction products were found to interfere with the eutectic C4 solder reflow process and to constantly leave debris on the reflowed C4 solder surface. These debris were found difficult to remove by both acid etching and intensive water rinse. Since these debris may either hinder the latter joining process or leave voids in solder joints, it is essential to remove these debris and to achieve reflowed C4s with clean, smooth, and round surface.

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Reflow of Electrochemically Fabricated Eutectic C4 using a Glycrol-based
Water Soluble Flux

      Electrochemical fabrication of eutectic C4s involves
through-mask plating, photoresist stripping, and selective etching of
seed layers between C4s.  During the etching step, C4s are protected
by passive layers and hence are covered with reaction products.
These reaction products were found to interfere with the eutectic C4
solder reflow process and to constantly leave debris on the reflowed
C4 solder surface.  These debris were found difficult to remove by
both acid etching and intensive water rinse.  Since these debris may
either hinder the latter joining process or leave voids in solder
joints, it is essential to remove these debris and to achieve
reflowed C4s with clean, smooth, and round surface.

      It was found that a novel water-soluble flux and the associated
reflow process can achieve this goal.  The flux contains glycerol and
isopropyl alcohol in a ratio of 4:1.  In fact, the ratio of glycerol
to isopropyl alcohol can be tailored to fit the required reflow
temperature for different solders.  However, the present composition
is suitable for the purpose of reflowing eutectic (63Sn-37Pb) or
close-to-eutectic Pb-Sn solders.  The reflow temperature can be in a
range of 190 to 250 degree C.  The glycerol was found to provide
sufficient retention capability so that the flux can cover and
prevent the solder from oxidation during heating and cooling of
reflo...