In a message dated 05/16/2000 11:42:49 AM Central Daylight Time,
[log in to unmask] writes:
<< Good day everyone,
Is the failure mechanism for moisture absorption immediate or latent?
Thanks,
Gary Camac >>
Hi Gary!
(munch,munch...'scuse me, eatin' a big Mac...)
There's a couple of good web sites I found during lunch (munch,munch..) that
address moisture sensitive devices. One is:
http://epims.gsfc.nasa.gov/ctre/act/techdocs/pems/pem.htm
It has a report called; "Fundamentals of Plastic Encapsulated Microcircuits
(PEMs) for Space Applications" and gets into all the details about moisture
sensitivity. Below is a paste from one of the pages that talks about the
failures caused by moisture absorption:
PEMs are susceptible to the same types of package/lead damage and the same
types of electrostatic discharge (ESD) damage as hermetic devices. As a
result, similar precautions for handling and storage are in order for both
types of packages. However, PEMs are unique in that they are also susceptible
to moisture and contamination which may be absorbed by the encapsulant
material. This susceptibility, as discussed earlier, can lead to a number of
serious failure mechanisms. Examples are corrosion of the aluminum die
metallization and, in certain instances, bondpad cratering and package
cracking during circuit board installation. Although these mechanisms may not
cause an immediate failure, over a period of time, they may degrade overall
device reliability."
So according to that statement, it's probably going to be latent, but may be
an immediate failure.
Below is another good web site on the subject. Go to:
http://www.aecouncil.com/Papers/aec8.pdf
This paper presents a detailed analysis of how moisture is distributed in
molded plastic packages and how the use of dry box storage and bake out
effect the floor life of plastic packaged moisture sensitive surface mounted
components. One point to note is that simply placing a part in a dry box
does not stop the floor life clock. The primary author of this paper, Dr. R.
L. Shook, is well know in the field of moisture sensitive surface mount
components. He is the primary source for the technical data used to develop
the IPC/JEDEC industry standards J-STD-020, and J-STD-033 on moisture
sensitivity.
Lunch is over now, B-U-U-R-R-P!!! (not bad manners, good food! hehehe)
-Steve Gregory-
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