The throwing power (TP) is defined as  the % ratio of copper thickness in the 
middle of the hole relative to the  entrance of the hole, or the surface. 
Always reported in conjunction with aspect  ratio. Example: The bath gives 60 % 
throw in a 10 :1 aspect ratio hole. This  same bath may give 90% throw in a 5:1 
aspect ratio  hole. 
There are 2 main factors that affect the  throwing power of the acid copper 
bath in a PWB  application. 
Bath  Chemistry 
The organic additive package 
The proper choice of organic additives  is critical.  
The key ingredients in the organic  additives that affect TP are the Carrier 
(suppressor) and the Leveling agent.  The carrier increases polarization 
resistance and improves copper thickness  distribution, by reducing the overall 
variability in current density throughout  the part. The leveler is more of a 
localized suppressor that reacts with the  higher current density areas on the 
plated part. 
The brightener component is the primary  grain refiner and has a direct 
impact oin the physical properties of the plated  copper (tensile strength, % 
elongation  and also appearance).  
The inorganic components 
Higher conductivity baths ( low copper  and high acid) enhance TP. 
Mass Transfer 
During plating the copper ion  concentration is depleted in the immediate 
vicinity of the cathode. This is  normally overcome by chemical diffusion. If the 
plating rate is much higher than  the rate of diffusion additional solution 
or part agitation would be  needed. 
A high aspect ratio hole would require  enhanced solution transfer in 
conjunction with diffusion. Slower (low current  density) plating reduces the rate of 
deposition and allows diffusion more time  to be a critical factor in mass 
transfer. 
Solution agitation must be properly  designed. This impacts mass transfer 
thru the hole as well as the conveying of  the leveling agent to the localized 
higher current density parts (the entrance  and the knee of the hole). 
E-ductors, air sparging and part agitation are  critical areas that must be optimized. 




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