Ryan - An additional note - Charles S. (Stu) Leech can be reached at [log in to unmask] - they have done a considerable amount of additional work since the publication that Dave refers to. Regards - Kelly -----Original Message----- From: David Hillman <[log in to unmask]> To: [log in to unmask] <[log in to unmask]> Date: Friday, June 02, 2000 8:58 AM Subject: Re: [TN] Baking of boards >Hi Ryan! Get a copy of the following article: "Removing Moisture from >Electronic Components and Assemblies", authored by Charles S. Leech, JR. , >Circuits Assembly May 1994, it covers some of the basic physics of water >loss in detail - especially the issue of vacuum moisture removal. In the >article the vaporization of water via vacuum is discussed as not being the >most effective moisture removal method in all instances - the change of >physical states (liquid to vapor) can result in the formation of ice (the >article describes a neat demonstration of this reaction) which impedes the >removal of water from a board. I participated in a DOE in which we showed >that a standard baking procedure in a convection oven was more effective >than a vacuum bake process. However, you don't get anything for free - the >convection bake process degraded the board solderability much more the >vacuum bake process . Good Luck. > >Dave Hillman >Rockwell Collins >[log in to unmask] > > >O.K. Doug and Ron, I'm going to put you an the spot. > > Two weeks ago, I set up an experiment to see how long I would have >to vacuum to get some PBGA's dry. The vacuum drying was run in parallel >with 125?C bake and just air drying (20% RH here in the high desert). The >vacuum drying didn't do much better than air drying. > > The part were supersaturated with water, and the experiment only >ran >for 24 hours. But projecting the desorption of the moisture, it would have >taken a week to dry them, compared to 24 hours with the bake. > > The vacuum was done with our plasma etcher at 0.5 torr (no plasma), >so I fear that I may have frozen the moisture in the component. Any ideas >as to why the moisture didn't come out? In theory, vacuum should work! > >Thanks > >Ryan Grant >Advanced Technology Engineer >MCMS >(208) 898-1145 >[log in to unmask] > > > >> >> I agree with that, Doug. For many years we have vacuum baked all of our >> boards. It helps even more if you back-fill with dry Nitrogen as we do. >> Ron Dieselberg >> BAE SYSTEMS >> Cincinnati Electronics Corp. >> > >> >> >> If you are really concerned about the effects of heat on the polymer >> qualities or the oxidation of the surfaces, consider using a vacuum or >> vacuum-make operation. Gets the water out with less heat. >> >> Doug Pauls > >############################################################## >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 >############################################################## ############################################################## 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 ##############################################################