Richard: Let us first identify the fact that you are in the UK, and what is "tinning" for you is not tinning to much of the rest of the world. The "tinning" you refer to is probably Tin/Lead solder? The key question is how is it applied, via hot air leveling (HAL, or HASL?) or is it fused/reflowed electroplated Tin/Lead? In either case the problem is almost certainly dirty Copper as the Tin/Lead is applied, but if it is fused/reflowed Tin/Lead, it is most likely oxidation, and I actually wrote a paper more than 10 years ago about the problem. Get back to us on how the "Tinning" is applied, and we can assist more. And incidently, do you do business with my friends at W. Canning, now MacDermid-Canning? Rudy Sedlak RD Chemical Company ############################################################## 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 Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################