Methyl chloroform-free desmear process in additive circuitization

In a method of additive circuitization of a glass and polymer printed circuit board comprising the steps of:

• a. drilling the printed circuit board, thereby forming glass and polymer smeared holes;
• b. vapor blasting the drilled printed circuit board to remove particulate residue therefrom;
• c. soaking the printed circuit board in a solvent to swell the drill smear and loosen and remove fibers, the solvent being chosen from the group consisting of:
• N-methyl-2-pyrolidone, ##STR6## ##STR7## d. removing solvent from the printed circuit board;
• e. passing a stream of an aqueous, acidic H.sub.2 SO.sub.4 --CrO.sub.3 oxidizing solution through the printed circuit board holes to remove fibers and smear in the thru holes and produce etchback of conductors;
• f. passing an aqueous sodium bisulfite reducing solution through the printed circuit board to reduce and remove the aqueous acidic solution and reduce the chromium from Cr.sup.+6 to Cr.sup.+3 ;
• g. rinsing the printed circuit board to remove the aqueous sodium bisulfite reducing solution;
• h. depositing a Pd seed layer on the printed circuit board;
• i. photolithographically defining circuitization on the printed circuit board;
• and
• j. additively plating through holes and surface features of the printed circuit board;
• the improvement comprising first passing a stream of heated air through the printed circuit board to remove the solvent from the printed circuit board by gas entrainment in the heated air before passing the aqueous, acidic oxidizing solution therethrough, and thereafter scrubbing the air to recover solvent therefrom.

In a method of additive circuitization of a glass and polymer printed circuit board comprising the steps of:

• a. drilling the printed circuit board, thereby forming glass and polymer smeared holes;
• b. vapor blasting the drilled printed circuit board to remove particulate residue therefrom;
• c. soaking the printed circuit board in a swelling solvent for the drilling smear to swell the drilling smear and to loosen and remove fibers from the printed circuit board, the solvent being N-methyl-2-pyrolidone, ##STR8## d. removing solvent from the printed circuit board;
• e. passing a stream of an aqueous, oxidizing, acidic H.sub.2 SO.sub.4 --CrO.sub.3 solution through the printed circuit board holes to remove fibers and smear in the thru holes and produce etchback of conductors;
• f. passing an aqueous, reducing sodium bisulfite solution through the printed circuit board to reduce and remove the aqueous, oxidizing, acidic solution and reduce the chromium from Cr.sup.+6 to Cr.sup.+3 ;
• g. rinsing the printed circuit board to remove the aqueous, reducing sodium bisulfite solution;
• h. depositing a Pd seed layer on the printed circuit board;
• i. photolithographically defining circuitization on the printed circuit board;
• and
• j. additively plating through holes and surface features of the printed circuit board;
• the improvement comprising passing a stream of heated air through the printed circuit board to remove the solvent from the printed circuit board by gas entrainment in the heated air before passing the aqueous, acidic oxidizing solution therethrough, and thereafter scrubbing the air to recover solvent therefrom.