IPC can only provide guidelines to achieve an acceptable yield. If a company can demonstrate that it has control over the solderability of its components and pwbs such that it can achieve 6 sigma DPMO without nitrogen, why would they be "required" to use nitrogen? If IPC were to "require" nitrogen, how much of a ppm of oxygen is acceptable? While the use of a nitrogen blanket is a good practice in most cases, many companies find the decrease in DPMO is so small that it is not cost effective to run nitrogen. There are many other variables that need to be controlled, nitrogen is just one of the factors and it is not anywhere close to being the most important, unless, of course there are little or no controls put in place to preserve the solderability of the parts and pwbs. Some ovens use nitrogen so excessively that they are useless, so why bother to turn it on? Other ovens with a properly designed reflow chamber use the nitrogen efficiently such that you can achieve an O2 level of less than 75 ppm inside the reflow chamber, without having to go through 10 billion liters of nitrogen per hour to achieve that reading. This is why there is no "requirement" for nitrogen. Most of the newer solder pastes are actually formulated to do away with the nitrogen requirement. If you are not using one, I would suggest you get a sample and start performing a qualification. As to tombstoning, it has been my experience that the addition of nitrogen increases tombstoning (does not make it better), for the very reason it improves the surface tension which leads to improved wetting. In the industry, many companies turn off the nitrogen for assemblies heavily populated with 0402's or smaller. This is a common practice. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Russ Nowland Sent: Monday, December 18, 2006 12:07 PM To: [log in to unmask] Subject: [TN] Nitrogen usage Hello Technetter's, Sometimes in life you find yourself in a pickle and wonder how the heck you got there. It always brings me to that famous quote "It is hard to soar with the eagles when you work with a bunch of turkeys". I have a question: I am working with and "MAJOR" EMS that does not use nitrogen with either Sn/Pb or Pb-free reflow. In this day and age I have never heard of this. They have it available but will only use it if I require it. At a price, of course. They don't seem to take into account it will improve their yields as well. Is there an IPC, NEMI, or any other standard that requires/recommends N2 usage for either Sn/Pb or Pb-free reflow process? --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------