Electrolyte and tin-silver electroplating process

An electrolyte for depositing a tin-rich tin-silver alloy upon a substrate, comprising a basis solution containing:

• a solution soluble tin compound and a solution soluble silver compound, wherein the tin compound is present in an amount which is greater than that of the silver compound to provide a deposit that contains about 85 to 99% by weight tin and about 0.5 to 15% by weight silver;
• a tin chelating agent of a polyhydroxy compound in an amount sufficient to complex tin ions provided by the tin compound;
• and
• a silver chelating agent of a heterocyclic compound in an amount sufficient to complex silver ions provided from the silver compound;
• wherein the silver chelating agent is a compound having the formula:
• wherein each R is the same or different and is —H, —NH, —NH2,(CH2)y—CO, —(CH2)y—C(O)OZ, or —(CH2)y—CH3, y is 0 to 5 and Z is —H, —NH4 or an alkali or alkaline earth metal and R′ is —H, —(CH2)y—CO, —(CH2)y—C(O)OZ, or —(CH2)y—CH3, y is 0 to 5 and Z is —H, —NH4 or an alkali or alkaline earth metal.