In a message dated 3/7/02 12:46:50 PM Eastern Standard Time, [log in to unmask] writes: << At what stage the electroless nickel and immersion gold process is applied, is it after the solder mask application or before? I believe normally it is after the solder mask application but I want to verify it. I have heard that chemistry involved is very nasty if left on the board. If I plug or mask via holes from one side, I want to make sure that there is no residue left of that nasty chemistry. Can it be cleaned if mask from one end? Any comments? >> Ken, Yes, ENIG is normally applied after solder mask. Some shops have made boards doing the ENIG before mask - a process with pros and cons. Pro - it avoids attack on the solder mask. Cons - Solder mask can have adhesion issues to gold compared to copper, and obviously, you use more gold to plate all the circuitry rather than just the pads in the ENIG last process. The Electrolesss Nickel solution is quite hot in some processes - 160 to 190 degrees F. This tends to soften the mask and allow chemistry to "soak in". All the plating chemistry for ENIG is aqueous based - so long rinses in water - especially DI should clean up the board. Of course, chemistry that has "soaked in" will take a while to leach out again. If you mask from one end, this just makes the solution trasfer from hole wall to rinse water take longer. You are not getting fresh water into the hole barrel to dilute (rinse away) the contaminants. Would not suggest single sided mask down the ENIG line. Remember, all the solutions are aqueous, and the gold bath will try to "clean" the Electroless nickel solution out the holes too. Result - contaminated gold bath that plates too thin or shuts down. Denny Fritz MacDermid, Inc. --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------