In an earlier post, I had suggested several factors influencing surface:hole plating and surface to surface distribution. One other explanation with respect to surface distribution is looking at the limitations of mass transport. We have a great deal of documentation showing that non uniform solution movement across a panel (like dead spots where there is little or no air due to a variety of reasons) leads to surface distribution issues. If mass transport limitations do exist, it is possible that one could cause uneven copper ion distribution across the diffusion layer. This non uniformity in solution movement leads to over plating in some areas on the panel. This is why it is suggested to have uniform mass transport. This does not the agitation of the solution has to "blow the chemisty" out of the tank. The agitation system needs to provide a uniform field of flow at the work surface. In other words, we want to cut down the thickness of the cathode diffusion layer uniformly. With respect to rack design, a rack should be designed with first knowing how many amps the rack will be required to carry. If you have a very complicated design, you may want to consider a picture frame type rack with many contact points for the work piece. Cross sectional area of the rack is critical as well. Good luck, Mike Carano ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################