Hi Genny
I'm going with an opinion contrary to Inge, always a dangerous tack to
take but hopefully my course can avoid the rocks of despair.
We might leave it alone, hard to say without seeing it. You are simply
talking exposed fibers? If it is a tiny amount (e.g. less than
IPC-A-610D section 10.2.3) why would it be a problem? If you decide you
have to repair it, why not a room temp cure material - dab and leave
alone while the assembly proceeds.
Inge - you mention board edges and bad depaneling. How is it possible
to depanel a board and NOT expose fibers? You are always going to have
exposed fibers on the edge, and this is not problematic. Mouse bite
tabs - even worse, but again no reliability product in generic
products.
Venturing well off TechNet topics...
As for Inge's friend's boat, it is usually not water soaking into the
laminant that is a problem. The problem arises when the gelcoat and
laminant is damaged to the point where there is a path for water to get
through into a wooden core (structural reinforcement) or into foam
filled areas. Let's look at your friend's boat. 200 kg of water is .2
m3 volume. Assuming a 6m long boat, 1.5m width, that means the bottom
of the boat is about 9 square meters. If you distributed the 200 kg of
water evenly on the 9 sq. meters, you would have to have 2.2cm of water
soaked into a fiberglass laminant that is probably only about 1cm thick
- clearly violates the laws of physics, so we have to look elsewhere!
I'm willing to bet that if you drilled holes through into the flotation
sections of the hull you would get a LOT of water out of there. They
are filled with closed cell foam, but it's not truly waterproof and will
soak up considerable amounts of water over long time spans (years) if
exposed.
Sorry to get hung up on that. I have a boat, so this is a topic that
worries me a hull of a yacht.
regards,
Graham Collins
Process Engineer,
L-3 Communications Electronic Systems Inc.
Halifax
(902) 873-2000 ext 6215
>>> [log in to unmask] 06/19/07 07:15PM >>>
All right. This "prickly" issue is getting under my skin.
More questions:
If fibers are inadvertently exposed or disrupted by a board mod (a
knife or rotary tool slips a fraction of a mm too deep while cutting a
track...), but at a stage in the process where it will not go through
further reflow/wave-type heat stress, and it is not going into a harsh
environment; No boat is in danger of sinking here...
Would you repair it - dab some epoxy on and bake?
Or would you leave it?
Classic power struggle - margins are slim, and techs want to just push
a board through rather than invest more process time, but quality
inspectors and repair specialists want to fix it.
Techs want to know what could *possibly* go wrong from such a small
defect. Start describing how they used to do things and *those*
products didn't have problems. (not mentioning that in those days, the
thinnest trace or PCB layer was 20th, and the smallest component was an
0805)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
Sent: June 19, 2007 1:03 PM
To: [log in to unmask]
Subject: [TN] SV: [TN] fibers
Genny,
When you shrub your back against a board with exposed fibers, you may
get disrupted fibers into your skin.
What do the netters say? Will she be angry and disrupt the exposed
fiber on the PC and unplug?
Allright, we have to think then. Very odd question. The FR4 fibers are
from the beginning a woven mat with bundles of glass fibers. All is
surrounded and completely 'molded' in epoxy and cured. The only few
occasions when I've seen exposed fibers have been after(incorrect) board
repair or modifications of boards (machining with various tools). Also,
board edges have sometimes exposed some fibers from bad depaneling. What
I know, noone has been anxious about that, because normal humidity won't
penetrate far into the structure. However, compare with the gelcote on a
sailing boat's hull. If the gelcote is damaged, water can indeed
penetrate along the fibers in a long time scale. A friend of mine did
not care about his boat for many years, the gelcote was scratched after
endless pulling boat from water, across stone and sand to avoid
tidewater. It was a small boat for fishing. After some years he left the
boat in the water for one season, and...when I helped him to get it on
land for repair, it weighted tons. He did not understand. I did. The
glassfiber construction had sucked such a lot of water, that the weight
was about 200 kg extra!
One can't compare a plastic boat to a PWB, but logically, some water
may find its way into a FR4 structure likewise. Water molecules have a
infamous capability to diffuse into various materials, as we all know.
My two ounces
Inge
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Genny Gibbard
Skickat: den 19 juni 2007 17:26
Till: [log in to unmask]
Ämne: [TN] fibers
Trying again - would appreciate your knowledgeable responses or direct
me to some info or sources of reading on this:
What are the dangers associated with each of exposed fibers and
disrupted fibers in FR4 laminate?
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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
847-615-7100
ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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
847-615-7100 ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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 847-615-7100
ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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 847-615-7100 ext.2815
-----------------------------------------------------
|
