Reverse Pulse Plating at TraX
Earlier this year TraX started experimenting with reverse pulse plating , to meet the demands of customers requiring high layer count pcb's . One of the biggest challenges with high layer count pcb's is that the vias connecting all the layers require a high aspect ratio.
With traditional DC plating we have been able to achieve an aspect ratio of 6,4 : 1 but with reverse pulse plating aspect ratios as high as 14 : 1 are theoretically possible and our testing thus far confirms this.
Reverse pulse plating makes use of special high speed polarity switching rectifiers that plate forward for 20 milliseconds and then reverse polarity and plate backwards for 1 milliseconds at four times the forward plating current. This type of plating results in very even plating across the surface of the panel and through the via holes , whereas with traditional DC plating the edges of the board always tended to plate thicker than the middle of the board and the copper plating in the vias was always thinner in the middle of high aspect ratio holes. Even plating also has the additional benefit of preventing mushrooming of the plating over the top of the dry film which in turn benefits the etching.
One of the biggest challenges we soon discovered was controlling the brightners in the plating solution , in Europe one could typically outsource this analysis but at the tip of Africa this is not easily done. This ananysis of the plating solution requires very costly CVS equipment typically only found in well funded universities. Left with no choice if we wanted to do this properly, we ordered the CVS equipment from Switzerland in July and we are excited to announce that our first reverse pulse plating tank is up and running and the results have been beyond expectation and very exciting. Additional pulse rectifiers have been ordered and another two plating tanks will be commisioned before the end of the year. We will continue refining the techniques in the coming months and we look forward to sharing our improved capabilities in the near future.