Patent ID: 6854636

Claim:
A method for creating a lead free solder melting hierarchy for first level assembly comprising the steps of; providing an electronic circuit chip having ball limiting metallurgy pads on a bottom surface of said chip; placing off-eutectic lead free solder on said ball limiting metallurgy pads; heating said off-eutectic lead free solder to reflow said off-eutectic lead free solder and form off-eutectic lead free solder bumps on said ball limiting metallurgy pads; providing a chip carrier having electrical contact pads on a top surface of said chip carrier; placing a lead free solder alloy in contact with said contact pads; placing said off-eutectic lead free solder bumps in contact with said lead free solder alloy; and heating said off-eutectic lead free solder bumps to reflow said off-eutectic lead free solder bumps to form off-eutectic lead free solder fillets which adhere said chip to said chip carrier.