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80 PCB007 MAGAZINE I FEBRUARY 2021 CVS analysis is used to measure the organic addition agents' concentration present in the copper plating solution. is method is adapt- able to quantifying both suppressors and the grain refiner/brightener in the working so- lution. is allows the fabricator to make re- quired additions of critical components prop- erly without the risk of over-adding or allow- ing the key components in the plating solution to fall out of balance. Filtration e need for filtration cannot be overem- phasized, mainly when plating in through- holes and blind vias. Any void in the plating in the hole caused by small contaminants causes a reduction in the area available to carry the electric current. Rejects would also be caused when insoluble debris is co-deposited on the surface of the hole. Flow rates are the only means of carrying solids to a filter or bringing a new solution into contact with the particulate matter. e flow rate is referred to as the turnover—total gallons pumped per hour concerning the size of the tank (for example, 200 gal/h on a 100-gallon tank is two turnovers per hour). Dirt-holding capacity is essential and can be attained with throw-away paper cartridges of different po- rosities, or filter surfaces coated with filter aid. Porosities of 100 microns down to less than 1 micron are typical. In practice, the average plating solution is turned over once per hour. e recommended flow rates should provide at least two complete tank volume turnovers per hour. However, to achieve the ultimate clari- ty, turnovers of up to 10 times per hour may be necessary. Keep in mind that the initial flow rate is not the average flow rate. In other words, if one started at 1000 gal/h, and cleaned or re- placed the filter when the flow was reduced to 200 gal/h, the actual average flow would prob- ably be about 600 gal/h, depending upon the type of filter media used. Ineffective filtration leaves debris in the rinse and process tanks (Figure 6). ⁰F ⁰C ⁰K Rate Increase _______________________________ 72 22 295 — 90 32 305 2-3X (200-300%) 108 42 315 1 ½X (150%) 126 52 325 1X (100%) At some point, the reaction rate increase starts to level off. What's the point to this? Figure 6: Sediment remaining in a process tank that used no filtration. Temperature Control All too oen, while process engineers and technicians focus on wet analysis, the operat- ing temperature checks often go overlooked. Rinsing and developing are typical processes that are more effective with tempered rinses. All too oen, w hen r insing u ses i ncoming w a- ter (during the winter months in very cold cli- mates), the water temperature is quite cold un- less heaters are in place. An increase of 10°K at temperatures not far from room temperature will increase the reac- tion rate by a factor of 2 to 3 (see chart below).