Complex waveform for electrolytic plating

A method of plating a metal on an electronic substrate, wherein the electronic substrate comprises one or more features, wherein the one or more features comprise one or more through-holes in the electronic substrate, the method comprising the steps of:

• a) preparing the electronic substrate to receive metal plating thereon;
• b) bringing the electronic substrate and at least one counter electrode into contact with an electroplating solution comprising a source of metal ions of the metal to be plated;
• c) electrically polarizing first and second sides of the electronic substrate to initiate metal plating thereon, wherein the electroplating solution plates the one or more through-holes using a plating cycle until metallization is complete;
• wherein the plating cycle comprising the steps of, in order:
• 1) pulse plating for a first time period on a first side and a second side of the electronic substrate to cause metal to preferentially plate in the center of the one or more through-holes, wherein the metal merges together in the center of the one or more through-holes to form two opposing blind vias;
• and
• 2) direct plating for a second time period to fill the two opposing blind vias formed by pulse plating;
• wherein the pulse plating step comprises applying an electrical current to electrodeposit metal from the electroplating solution to the first side and second side of the electronic substrate, wherein the electrical current is applied as a pulse plating cycle comprising a repeatable sequence,
• wherein the repeatable sequence comprises a set of pulse plating periods,
• wherein each set of pulse plating periods consists of, in any order:
• a) a first forward pulse of a first forward duration and first forward intensity;
• b) a second forward pulse of a second forward duration and second forward intensity;
• c) a third forward pulse, the third forward pulse having at least substantially the same duration and/or intensity as the first forward pulse;
• d) a first reverse pulse of a first reverse duration and first reverse intensity;
• e) a fourth forward pulse, the fourth forward pulse having at least substantially the same duration and/or intensity as the first forward pulse;
• f) a fifth forward pulse, the fifth forward pulse having a different forward duration and/or a different forward intensity from at least one of the first forward pulse and the second forward pulse;
• and
• g) a sixth forward pulse, the sixth forward pulse having at least substantially the same duration and/or intensity as the first forward pulse;
• and
• wherein a pulse break is interposed after one or more of steps a) to g).