Lead-free solder alloy powder paste use in PCB production
AssigneeMulticore Solders Limited
InventorHector Andrew Hamilton Steen
Life of this patent
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Abstract
Tombstoning susceptibility and reflow peak temperature reduction of solder alloys, in particularly lead-free solder alloys, has been found to be achieved effectively by mixing the solder alloy in the form of an alloy paste with a low melting alloy utilised in powder form, in particular a Bi-containing alloy.
Claims20
A method for reducing tombstoning tendency when using a lead-free alloy in a solder paste to attach a chip component to a printed circuit board in a reflow soldering process, which comprises formulating the solder paste used by adding to a paste of a first solder alloy powder, which paste is a lead-free solder paste, a SnBi alloy powder, which is lower melting than the first solder alloy powder, to produce a bismuth containing final alloy containing from 1-10% bismuth, the first solder alloy containing 0-5% Cu, 0-10% Ag and 0-5% Sb, the reminder being Sn and at least one of Cu, Ag and Sb being present in a minimum amount of 0.1%, wherein said first solder alloy and said SnBi alloy are preselected to provide a final alloy having a melting point range sufficient to inhibit tombstoning.
A method for reducing tombstoning tendency when using a lead-free alloy in a solder paste to attach a chip component to a printed circuit board in a reflow soldering process, which comprises:
- formulating the solder paste used by combining a first lead-free solder alloy powder and a second SnBi alloy powder, which has a lower melting point than the first solder alloy powder, and forming a final solder paste,
- wherein said final paste contains from 1-10% bismuth, and said first solder alloy powder contains 0-5% Cu, 0-10% Ag and 0-5% Sb, the reminder being Sn and at least one of Cu, Ag and Sb being present in a minimum amount of 0.1%, and
- wherein said first solder alloy powder and said SnBi alloy powder are preselected to provide a final paste having a melting point range sufficient to inhibit tombstoning.
Dependencies are inferred from the claim text.