Dear CL Chong: You have some of the answers already about electroless nickel gold, and you have some misinformation: Immersion gold plating occurs when a small amount of the electroless nickel is dissolved into the gold solution, and gold is deposited in place of the nickel (oxidation - reduction reaction). 4-10 microinches are normal deposit thicknesses, but not much more can be deposited since nickel stops dissolving through the gold layer. Yes, electroless nickel is required as a barrier for the gold (as in any copper/nickel/gold construction since copper and gold migrate rapidly into each other). Also, electroless nickel is a convenient souce of nickel ions to reduce the gold in solution. Electroless plating coats all the copper traces - top and sides, without continuous conductor attachement as in electroplate. Gold is most commonly electroplated when the original copper foil gives conductive continuity, or when the circuits are "bussed" together as in connector tabs. I am very surprised that 20 microinches of gold gave you embrittlement as gold is thought to be compatible in solder to 3 or 4%. That means that you were putting down less than 600 or 800 microinches of solder paste - true? Anyway, the thinner immersion gold plate will give you less gold in your solder joints. Ohter points: Most LPI type solder masks are now compatible with electroless nickel/immersion gold processing. That is feature most mask suppliers have been working on. Yes, phosphorus is co-deposited with the electroless nickel. But, running the process by the seller's instructions makes the phosphorus deposit consistant with bath age, bath loading, etc. Most currnent thought about solderability of electroless nickel/immersion gold does not focus on the phosphorus content of the deposit, but on the corrosion rate of caused by the immersion gold bath. Run properly by the manufacturers instructions, there should be a uniform corrosion of the nickel/phosphorus, and a uniform deposit of the immersion gold. 4 microinches of immersion gold will have some porosity and lower shelf life. Deposits nearer the 10 microinch thickness should store and solder well for months. Please contact me off line if you want more specific information - Dennis Fritz MacDermid. Inc ############################################################## 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 ##############################################################