Subject: | |
From: | |
Reply To: | |
Date: | Fri, 2 Oct 1998 09:41:24 -0400 |
Content-Type: | text/plain |
Parts/Attachments: |
|
|
Water absorption is thought of in two ways. Total absorption and rate.
The total absorption is in wt% and measures the change in weight after
immersion in DI water for 24 hours. The sample is conditioned at
105-110C for multiples 1 hour until the "dry" weight stabilizes prior to
immersion.
% absorption = (dry weight - weight after immersion) / dry weight X
100%
The absorption rate is a measure of the change in % absorbed over time.
While this could be measured by a series of timed weightings (as above)
it's more typically measured as permeability through a thin layer of
material.
Permeability = grams / square meter / mil thickness /day
Be mindful of the subtle distinction. Absorption rate follows an
exponential decay as the total absorption limit for a material is
approached while the permeability is a measure of the materials inherent
flow through rate at steady state.
The permeability of polyimide film (Kapton) is 54 g/sq m/mil/day and the
total absorption is 2.8 wt%. The absorption rate changes rapidly over
time with a large percentage occurring in the first 5 min. and nearly
reaching completion in 30 min to an hour depending on the film type and
thickness. Another polyimide film (Upilex) has only 1.7 g/sq m/mil/day
permeability and 1.2 wt% absorption so you must know what specific
materials you're considering.
Andy Magee
Flex Guru
[log in to unmask]
Yuan Li wrote,
What is the meaning of Water absorption rate (wt%)? If it is 2.4%, how
do I
interpret it? Thanks,
Yuan Li
################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe: SUBSCRIBE TechNet <your full name>
To unsubscribe: SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################
|
|
|