Method of making circuitized substrate with selected conductors having solder thereon
View Patent ↗A method of making a circuitized substrate in which conductors are formed in such a manner that selected ones of the conductors include solder while others do not and are thus adapted for receiving a different form of connection (e.g., wire-bond) than the solder covered conductors. In one embodiment, the solder may be applied in molten form by immersing the substrate within a bath of the solder while in another the solder may be deposited using a screening procedure.
1. A method of making a circuitized substrate, said method comprising:
providing a substrate including at least one dielectric layer having an external surface and a first plurality of conductors and a second plurality of conductors on said external surface;
applying a photo-resist covering over said first plurality of conductors but not over said second plurality of conductors on said external surface of said substrate;
applying a layer of sacrificial solder-resist material over said photo-resist covering;
exposing said first plurality of conductors having said photo-resist covering and said layer of solder-resist material thereon and said second plurality of conductors not having said photo-resist covering thereon to a quantity of molten solder so as to deposit said solder onto only said second plurality of conductors; and
thereafter removing said layer of solder-resist material on said photo-resist covering and said photo-resist covering over said first plurality of conductors.
2. The method of claim 1 wherein said applying of said photo-resist covering over said first plurality of conductors but not over said second plurality of conductors on said external surface of said substrate is accomplished using a lamination process.
3. The method of claim 2 wherein said lamination process is accomplished at a temperature within the range of from about 75 degrees Celsius to about 95 degrees Celsius for a time period of from about sixty to about eighty seconds.
4. The method of claim 1 wherein said applying said layer of sacrificial solder-resist material over said photo-resist covering is accomplished by selective screen printing and curing at a temperature within the range of from about 120 degrees Celsius to about 150 degrees Celsius for a time period of about ten to twenty minutes.
5. The method of claim 1 wherein said exposing said first plurality of conductors having said photo-resist covering and said layer of solder-resist material thereon and said second plurality of conductors not having said photo-resist covering thereon to said quantity of molten solder is accomplished by immersing said substrate within a bath of said solder.
6. The method of claim 1 wherein said removing said layer of solder-resist material on said photo-resist covering photo-resist and said removing of said photo-resist covering is accomplished using a chemical process.
7. The method of claim 6 wherein said removing said layer of solder-resist material on said photo-resist covering photo-resist is accomplished using a manual peeling operation.
8. The method of claim 6 wherein said removing of said photo-resist covering is accomplished using a chemical stripping operation.
9. The method of claim 1 , wherein said substrate comprises thru-holes therein, said thru-holes being filled with conductive paste.
10. The method of claim 9 wherein selected ones of said first plurality of conductors are formed on said substrate over respective ones of said thru-holes.
11. The method of claim 1 further including using hot air leveling to substantially level said solder deposited onto only said second plurality of conductors before said removing said layer of solder-resist material on said photo-resist covering and said photo-resist covering over said first plurality of conductors.