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).
>>>
>>>
>>>
>>>
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