Method for forming vias on printed circuit boards
View Patent ↗A method for filling a via on a printed circuit board formulates a paste as a dispersion of copper particulate that includes nanocopper particles in a solvent and a binder and depositing the paste into a via cavity formed in the printed circuit board. Heating the paste-filled cavity removes most of the solvent. The method sinters the deposited paste in the via cavity, planarizes the sintered via, and overplates the filled via with copper.
1. A method for forming a via on a printed circuit board, the method comprising:
formulating a paste as a dispersion of copper particulate that includes, in a solvent and a binder, 50 to 90 percent by weight of combined nanocopper and micron-sized copper particles, wherein the nanocopper particles are from 5% to 99% of the metal in the dispersion;
depositing the paste into a via cavity formed in the printed circuit board;
removing most of the solvent by heating the paste-filled cavity;
sintering the deposited paste in the via cavity;
planarizing the sintered via; and
overplating the filled via with copper.
2. The method of claim 1 wherein sintering the paste comprises directing laser energy onto the deposited paste.
3. The method of claim 1 wherein sintering the paste is performed using an oven in a non-oxidative environment.
4. The method of claim 1 wherein formulating the paste further comprises using nanocopper particles encapsulated with a polymer.
5. The method of claim 1 wherein formulating the paste comprises using an organic solvent.
6. The method of claim 1 wherein formulating the paste comprises using a polymer binder.
7. The method of claim 1 wherein overplating comprises depositing a nanoparticle ink having a lower viscosity than the paste onto the planarized via and sintering the nanoparticle ink.