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).
> >
> >
>
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