High Current Density Plating Area

Explanation of High Current Density Plating Areas 

Copper plating is achieved by submersing the production panel into copper sulfate solution and applying electricity to the bath, measured in amps.  The amps are calculated by multiplying a factor of 11 amps per square foot to the square feet of exposed area on the production panel. 

For example, if the production panel has 10 customer pieces on it and each piece has 0.1 SF of copper area, then the panel has 1 SF of copper area and we will apply 11 amps to that side of the panel.  A similar calculation would have to be made for the other side of the panel. 

Often, there are designs that have sparse populations of circuits and/or copper features with heavier copper features on other areas of the board.  While the total square feet and resulting amps are calculated based on the sum of these features, the amperage does not always get equally distributed to each feature based on its area. 

Spare areas such as isolated circuits turn into what is called a High Current Density plating area, meaning it will attract more than it’s fair share of amperage, which results in much heavier surface copper plating.  Due to both its sparcity and now taller profile, this makes those circuits more prone to mechanical disruption in the course of handling and also in the event of mishandling.  

Our suggestion to resolve this is to add dummy copper thieving to all fiberglass areas of the board nearby to these isolated copper features.  Not only will this help to balance the amperage and lower the profile of these circuits, but the surrounding copper will also help to protect these isolated features.  

Below are before and after examples of what we are suggesting to do.  We have kept all dummy copper 25 mils from active copper features to prevent “noise”.