Method for completely filling small diameter through-holes with large length to diameter ratio

Abstract

Abstract A METHOD AND APPARATUS FOR PLATING THROUGH LARGE LENGTH TO DIAMETER RATIO HOLES IN A SUBSTRATE IS DISCLOSED. THE METHOD CONSISTS OF FORMING HOLES IN A SUBSTRATE WHICH ARE TAPERED EITHER BY ELECTRON BEAM, OR LASER DRILLING, OR BY FORCING AN APPROPRIATE ETCHANT THROUGH A PREVIOUSLY DRILLED HOLE. THE SUBSTRATE MAY BE OF ANY MATERIAL AND CAN BE EITHER INSULATING OR CONDUCTIVE. IN THE INSTANCE OF THE FORMER, THE SUBSTRATE SHOULD BE OF SUCH A CHARACTER THAT IT IS AMENDABLE TO ELECTROLESS PLATING OR OTHER SURFACE METALLIZING TECHNIQUES. AFTER METALLIZING THE TAPERED HOLE WHERE THE SUBSTRATE IS CONDUCTIVE. THE INTERIORS OF THE TAPERED HOLES ARE ELECTROPLATED WHILE SIMULTANEOUSLY SUBJECTING THE TAPERED PORTION TO AGITATION BY FORCED CONVECTION. USING A PRIOR ART PLATING SOLUTION OF HIGH THROWING POWER, AND FORCING IT THROUGH THE TAPERED HOLES FROM THE LARGE END TOWARD THE SMALL END, CAUSING RELATIVELY HIGH DEPOSITION RATES AT THE WIDEST PORTION OF THE TAPER WHICH GRADUALLY DECREASE ALONG THE LENGTH OF THE TAPER UNTIL THE NARROW PORTION IS REACHED WHERE THE MINIMUM DEPOSITION RATE OCCURS. UNDER SUCH CIRCUMSTANCES, PLATING OCCURS NON-UNIFORMLY ALONG THE LENGTH OF THE TAPER SUCH THAT THE TAPERED HOLES ARE SUBSTANTIALLY CLOSED WITHOUT LEAVING LARGE, UNWANTED VOIDS WHICH CONTRIBUTE TO POOR CONDUCTIVITY, CHARACTERISTICS. THE LENGTH OF HOLES WHICH MAY BE FILLED CAN BE DOUBLED BY PROVIDING A TAPER WHICH DECREASES TOWARD THE MIDPOINT OF A SUBSTRATE AND FROM THERE INCREASES IN SIZE UNTIL THE OPPOSITE SIDE OF THE SUBSTRATE IS REACHED. USING THE SAME ELECTROPLATING SOLUTION OF HIGH THROWING POWER, PLATING THRUGH HOLES OF THIS CHARACTER CAN BE ACCOMPLISHED WHILE PERIODICALLY REVERSING THE DIRECTION OF FLOW TRUGH THE "DOUBLE TAPER" HOLES. APPARATUS FOR CARRYING OUT THE ABOVE DESCRIBED METHOD CONSISTS OF AN ENCLOSED CHAMBER HAVING INLET AND OUTLET PORTS THRUGH WHICH PLATING SOLUTION UNDER PRESSURE CAN BE FORCED. ANODES CONSISTING OF WIRE MESH ARE DISPOSED ADJACENT TO BOTH THE INLET AND OUTLET PORTS WHILE AN ELEMENT CONTAINING HOLES WHICH ARE TO BE PLATED-THROUGH FORMS THE CATHODE AND IS DISPOSED INTERMEDIATE THE ANODES. WHERE A SINGLE TAPER US USED, ELECTROPLATING SOLUTION IS FORCED IN ONE DIRECTION BUT, WHERE A "DOUBLE TAPER" IS UTILIZED, THE FLOW OF ELECTROPLATING SOLUTION IS PERIODICALLY REVERSED. THE METHOD AND APPARATUS OF THE PRESENT INVENTION PROVIDES COMPLETELY PLATED THRUGH-HOLES WHICH HAVE A LENGTH TO DIAMETER IN EXCESS OF 25 AND, IN ADDITION, HAVE EXTREMELY GOOD CONDUCTIVITY CHARACTERISTICS.

Inventors

• 👤 J Olsen
• 👤 L Romankiw

Bibliographic Details