Bury the Dog Bone

There has been a push in the plating industry to electroplate a given metal at a faster pace to ramp up production rates.  Unless you are willing to construct enormous plating lines, the only way to speed up plating production is to plate faster. Plating faster means plating at higher amps per square foot (asf). Seems to be a simple a simple task, but there are obstacles that need to be considered. One issue, and probably the most significant is the “dog bone effect”.  When plating occurs at higher ASF and plating times are compressed, larger amounts of metal are deposited in the high current density areas.   For example, look at a long threaded rod, the high current density areas are out the ends and the low current density areas are in the middle.  The rod, rack plated at 40 plus ASF will average 10 times the thickness of deposited metal in the high current density areas of that deposited in the middle of the rod (LCD).  Imagine, if you will, what that looks like under x-ray. The resemblance would be that of a dog bone.  This occurrence is less than desireable because  of the excess metal build in the high current density areas.  Thusly producing parts that are rejected because they do not meet dimensional tolerances.  It can also be an expensive endeavor for the plater because it is unlikely that you will be compensated for the extra metal deposited on the part.

In recent years, to correct issues such as the “dog bone effect”, processes using pulse plating and periodic reverse have shown great results in achieving even distribution of metal deposition at higher ASF and shorter plate times.  In these methods,  the DC current is changed through rectification and shows even distribution with many high efficiency processes. (bright NI, Sn, Acid Cu, and Zn).  Even though these methods are extremely effective, the change in rectifiers can result in a large capital investment.  Recently, modifications and changes in chemistry have allowed even distribution of metal deposition at higher ASF with compressed plating times, without having to change types of rectifiers.

In the past, requirements of 22 minutes plate time and 15 ASF to achieve .0004 of plating thickness. Now, with the modifications in chemistry, plating time can be compressed to less than 6 minutes at 65 ASF to achieve that same thickness with relatively even distribution.  Proper bath chemistry and additives buffer the high current density areas to allow more plating in the low current density areas to effectively BURY the “dog bone”.