Abstract A ternary barrier structure and method for forming the structure to be used on a conductive electrode. In electronic structures, dielectric substrates are used which have a plurality of connecting conductive areas which are wettable by solder. The region surrounding these connecting conductive areas are not wettable by solder. Barrier structures are used to prevent the flow of the solder while the solder is liquid during the manufacture of these electronic products. The present barrier structure covers at least a portion of one of these connecting conductive electrodes wherein the electrode is composed predominately of silver and a lesser quantity of one or more of the platinum metals. The barrier structure includes a gold bearing, non-wettable by solder, glaseous layer over a portion of the electrode. The portion of the conductive electrode under and adjacent to the barrier glaseous layer contains a gold-silver alloy which is produced during the formation of the barrier structure by diffusion of the gold from the glaseous layer into the conductive electrode. A particularly corrosion resistant barrier structure and conductive electrode combination is thereby produced at this rather critical point in the microminiature circuit structure.
The method of forming a barrier structure on a conductive electrode comprising: providing on a substrate a conductive electrode composed of predominently silver and a lesser quantity of one or more of a platinum group metal; depositing over a portion of said electrode a homogeneous mixture comprising a gold powder and a finely divided material which upon heating to an elevated temperature will coalesce and upon cooling form a continuous layer; heating and composite to said elevated temperature to cause said coalescence and for a time to cause a diffusion of a portion of said gold into said portion of the electrode wherein a gold-silver-platinum group metal alloy is formed therein; and cooling said composite.
Claim 2
Independent Claim
115 words
The method of forming a barrier structure on a conductive electrode comprising: providing on a substrate a conductive electrode composed of predominently silver and a lesser quantity of one or more of a platinum group metal; depositing over a portion of said electrode a homogeneous mixture comprising a gold powder and a finely divided material which upon heating to an elevated temperature will coalesce and upon cooling form a continuous layer; heating and composite to said elevated temperature to cause said coalescence and for a time to cause a diffusion of a portion of said gold into said portion of the electrode wherein a gold-silver-platinum group metal alloy is formed therein; and cooling said composite.
Claim 3
Dependent Claim
12 words
The method of claim 1 wherein the platinum group metal is palladium.
Claim 4
Dependent Claim
18 words
The method of claim 1 wherein the said elevated temperature is between about 750° C and 1050° C.
Claim 5
Dependent Claim
27 words
The method of claim 1 wherein the said diffusion is continued until there is greater than about 20% by weight gold in said portion of the electrode.
Claim 6
Dependent Claim
13 words
The method of claim 4 wherein the said platinum group metal is palladium.
Claim 7
Dependent Claim
18 words
The method of claim 5 wherein the amount of silver in said electrode is greater than about 75%.
Claim 8
Dependent Claim
26 words
The method of claim 1 wherein the composite is then subjected to a lead bearing solder which coats the entire said electrode except said continuous layer.
Claim 9
Dependent Claim
16 words
The method of claim 7 wherein said solder contains greater than about 80% by weight lead.
Claim 10
Dependent Claim
16 words
The method of claim 7 wherein said layer forms a barrier at a chip joining site.
Claim 11
Dependent Claim
15 words
The method of claim 7 wherein said layer forms a barrier at a cross-over site.