Ramon, For some reason I see that the minus signs did not come through on my previous posting. Those temperatures should read 56 degrees C plus or minus 5 degrees C and -10 degrees C plus or minus 5 degrees C. David A Douthit Manager LoCan LLC Dehoyos, Ramon wrote: > Hi Graham: > The operating temp ranges for the Humiseal urethanes and acrylics are -65 to 125. The tg for acrylic IB31 is 14 deg C, what is the transition temperature for the urethanes? > Regards, > Ramon > > > >>-----Original Message----- >>From: Graham Naisbitt [SMTP:[log in to unmask]] >>Sent: Thursday, March 25, 2004 1:43 PM >>To: [log in to unmask] >>Subject: Re: [TN] acyrlic coating deformed BGA balls >> >>Hi everyone, >> >>I have been in France for the past couple of days, so did not respond to >>everyone earlier.....but here goes the duel! (You can't get rid of me that >>easily!) >> >>The subject in question is David's oft repeated reference to low Tg....and >>for the record the Tg of 1B31 is 14DegC not 15. >> >>So what? >> >>As Dewey said, and is no doubt backed-up in the Collins report submitted by >>Dave Hillman, this is not necessarily a bad thing. >> >>Circuits exposed to wide temperature variations, coupled with high levels of >>humidity are quite commonly conformally coated. The coating MUST therefore >>be capable of surviving temperatures commonly down to -65DegC and up as high >>as +125DegC or more. >> >>I have the distinct impression - and David please correct me if I am wrong - >>that David thinks that an acrylic coating such as 1B31, permits external >>"stuff" to descend through the coating and hence onto the circuit surface. >>Whilst this might be the case, there are most certainly many other forces at >>work or conditions that must be considered and it is inappropriate to >>zone-in on one issue in isolation. >> >>Definition of Tg: The temperature at which an amorphous polymer changes from >>a hard and relatively brittle condition to a viscous or rubbery condition. >> >>A simplistic view of a material's glass transition temperature (Tg) is the >>temperature below which molecules have very little mobility. On a larger >>scale, polymers are rigid and brittle below their glass transition >>temperature and elastic above it. >> >>The Space Shuttle Challenger disaster was caused by a rubber O-ring that was >>below its glass transition temperature and thus could not flex adequately to >>form a proper seal around one of the two solid rocket boosters. >> >>So how about a coating that has a high Tg, Would this be better David? In a >>purely high temperature environment the answer would be a definite maybe! >>However, below its Tg it is brittle, therefore the lower the temperature the >>more brittle it becomes and hey presto - the coating shatters allowing all >>that nasty stuff to get in through the cracks! >> >>So, as stated by Dewey: The key is to understand the end use environment and >>choose the coating that has the widest processing window, tolerates rework >>and functionally does the job. >> >>You will now have to excuse me for saying so, but this is the very reason >>why we have so many different coatings in our range - "horses for courses" >>or, as Dewey so poetically referred to it: We have a huge selection of >>quality Dust Bags whatever your needs - we even do latex but I don't want to >>go there right now.... >> >>TTFN everyone >> >>Graham Naisbitt - with a little (lot!) of help from Phil Kinner. >> >> >> >>>To all, >>>I thought for a moment we were going to have an old fashioned duel between >>>David and Graham.It would have been a shame to loose all that intellect and >>>humor in one fell swoop.We would have missed Graham, also( just kidding >>>Graham). >>> >>> >>> >>> >>--------------------------------------------------- >>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 847-509-9700 ext.5315 >>----------------------------------------------------- >> >> > >--------------------------------------------------- >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 847-509-9700 ext.5315 >----------------------------------------------------- > > > > --------------------------------------------------- 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 847-509-9700 ext.5315 -----------------------------------------------------