Process for single mask C4 solder bump fabrication

A method of removing Ball Limiting Metallurgy layers from a surface of a substrate in the presence of a Pb/Sn bump, said method comprising the steps of:

• a) exposing said surface of said substrate and said Pb/Sn bump to a first etchant wherein a first metal layer is removed from said surface of said substrate and wherein a PbO layer is formed over said Pb/Sn bump;
• b) exposing said surface of said substrate and said Pb/Sn bump to a second etchant wherein a second metal layer is removed from said surface of said substrate and wherein at least a portion of said PbO layer remains on said Pb/Sn bump after being exposed to said second etchant;
• c) exposing said Pb/Sn bump to a third etchant wherein said PbO layer is removed from said Pb/Sn bump.

A method of removing Ball Limiting Metallurgy layers from a surface of a substrate in the presence of a Pb/Sn bump, said method comprising the steps of:

• a) exposing said substrate and said Pb/Sn bump to a H.sub.2 SO.sub.4 +H.sub.2 O.sub.2 +H.sub.2 O etchant wherein a copper layer is removed from said surface of said substrate and wherein a PbO layer is formed over said Pb/Sn bump;
• b) exposing said substrate and said Pb/Sn bump to a CH.sub.3 COOH+NH.sub.4 F+H.sub.2 O etchant wherein a titanium layer is removed from said surface of said substrate and wherein said at least a portion of said PbO layer remains on said Pb/Sn bump after being exposed to said CH.sub.3 COOH+NH.sub.4 F+H.sub.2 O etchant;
• c) exposing said Pb/Sn bump to a HCl+NH.sub.2 CSNH.sub.2 +NH.sub.4 Cl+H.sub.2 O solution wherein said PbO layer is removed from said Pb/Sn bump.

A method of removing Ball Limiting Metallurgy layers from a surface of a substrate in the presence of a Pb/Sn bump, said method comprising the steps of:

• a) exposing said substrate and said Pb/Sn bump to a H.sub.2 SO.sub.4 +H.sub.2 O.sub.2 +H.sub.2 O etchant wherein a nickel layer is removed from said surface of said substrate and wherein a PbO layer is formed over said Pb/Sn bump;
• b) exposing said substrate and said Pb/Sn bump to a HF+H.sub.2 O etchant wherein a titanium layer is removed from said surface of said substrate and wherein said at least a portion of said PbO layer remains on said Pb/Sn bump after being exposed to said HF+H.sub.2 O etchant;
• c) exposing said Pb/Sn bump to a 2HCH.sub.3 SO.sub.3 +H.sub.2 O solution wherein said PbO layer is removed from said Pb/Sn bump.

A method of removing Ball Limiting Metallurgy layers from a surface of a substrate in the presence of a Pb/Sn bump, said method comprising the steps of:

• a) exposing said surface of said substrate and said Pb/Sn bump to a first etchant wherein a first metal layer is removed from said surface of said substrate and wherein a protective layer is formed over said Pb/Sn bump;
• b) exposing said surface of said substrate and said Pb/Sn bump to a second etchant wherein a second metal layer is removed from said surface of said substrate and wherein said protective layer is removed from said Pb/Sn bumps such that no substantial etching of said Pb/Sn bump occurs.