Oxidation, oxidation, oxidation! I don't mean to oversimplify but that is predominately what is occurring. I've seen samples where a strip of Kapton tape is placed on the board before reflow. The section under the tape doesn't darken while the rest does. > ---------- > From: Jana Carraway[SMTP:[log in to unmask]] > Reply To: TechNet E-Mail Forum.;Jana Carraway > Sent: Thursday, April 11, 2002 2:04 PM > To: [log in to unmask] > Subject: Re: [TN] Chemistry of discoloration? > > Rudy, you can even use "free radical initiation"! There must be some > formulations folks out there who can divulge a bit more about the > reactions > without giving away formulation secrets! Dr. Roos, you out there??? > > Thanks for the info Rudy, > Jana Carraway > MSEI > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]]On Behalf Of Rudy Sedlak > Sent: Thursday, April 11, 2002 12:11 PM > To: [log in to unmask] > Subject: Re: [TN] Chemistry of discoloration? > > > Jana: > > You have asked a BIG question. > > There really is no known absolute answer. > > Organics tend to discolor, if they have any sort of reactivity left in > them, > and often, under the right circumstances even if they do not have any > reactivity left in them. > > The general rule is they turn dark(er). The reactions are many, and > clearly > going to be dependent on the base material. Discoloration is driven by > heat, > and often exposure to sunlight. > > Not to get too technical, but polymers (laminate, and soldermask, for > example) only rarely really react fully, and there is almost always some > unreacted polymer (called monomer when it is totally unreacted, and > oligomer > when it is partially reacted) lurking in the matrix. When this contacts > air, > water, and heat and UV, all sorts of unexpected things happen. In fact, > these very polymers often have added "preservatives" to prevent these > post-polymerization reactions from occurring. > > The bottom line is (as if this really has ANY significanse in our > industry) > that this discoloration rarely affects the physical properties of the > polymer. I think a great English playwright described this situation > centuries ago..."Much ado about nothing"? > > Rudy Sedlak > RD Chemical Company > > -------------------------------------------------------------------------- > -- > ----- > 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 the archives of previous posts at: http://listserv.ipc.org/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 > -------------------------------------------------------------------------- > -- > ----- > > -------------------------------------------------------------------------- > ------- > 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 the archives of previous posts at: http://listserv.ipc.org/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 > -------------------------------------------------------------------------- > ------- > --------------------------------------------------------------------------------- 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 the archives of previous posts at: http://listserv.ipc.org/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 ---------------------------------------------------------------------------------