New SnAg solder-joining method
Publication Date: 2014-Oct-13
The IP.com Prior Art Database
Disclosed are new Tin-Silver (SnAg) solder-joining method and process that reduces Tin oxides at the surface of SnAg solders.
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New SnAg solder -joining method
Tin alloys are widely used as solder for microelectronic interconnections . Tin solder surfaces tend to have tin oxides, which need to be removed from the solder surfaces in an interconnection reflow process such as flip chip joining . A strong flux needs to be employed for reflow in order to remove tin oxides so that metallic tin is exposed at the surface in a molten state and then joined to another metal .
A strong flux leaves flux residue that cannot be cleaned in case of large chips and narrow chip-substrate gaps. The leftover flux residue often causes reliability problems in final semiconductor products. A solder joining process with mild flux or without flux can make high performance chip joining processes more effective with a reduced cost . If Tin-Silver (SnAg) solder surface oxides can be reduced with an atmospheric plasma , a mild flux or no flux can make solders joined and remove the need for flux cleaning .
Current documentation [1, 2] describes chemical reduction of Indium (In) or In-alloys by SET North America (SETNA) reducing-chemistry atmospheric plasma so that In or In-alloys can be joined without flux. The documents claim that the chemical reduction could be proved by Ellipsometry.
The novel contribution is a new SnAg solder-joining method and process. Tin oxides at the surface of SnAg solders can be chemically reduced in an atmospheric plasma just prior to chip joining. A mild flux that leaves benign residue can be employed for solder
joining reflow processes. Even no flux can make solders joined if oxidation of metallic tin can be prevented or minimized.
In an experiment, tin foils were treated with SETN...