Jeez, I was just getting warmed up with an answer until you referenced the
Engelmaster. Now, I've become technet shy.
Anyway, I yeild to a position of one so much knowledgeable about matters
laminataion/relamination. Love you Werner, but this might be about what the
poor "downcast" recluse is complaining. How can we lesser beings compete? It
ain't possible, yet you ask the question - Steve. Still, I can't help but
learn and respect.
Earl Moon
----- Original Message -----
From: Wanner Bernhard <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, August 27, 1999 11:35 AM
Subject: [TN] crushed prepreg integrity
> Hi all
>
> I have to analyze failures of a subassemblies of our subcontractor. As
cause
> of problem I suppose cracks/voids in the prepreg (of a16-layer pcb),
caused
> either by poor siloxane-treatment between glass and epoxide - or - because
> crushing of prepreg integrity by microlocal mechanical stress during the
pcb
> press operation. As cause of this stress I assume following: During the
> press operation the prepreg conforms to the bounds formed by the laminate
> and their conductors at both sides. Between the walls/shoulders ot two
> buried vias the prepreg will be pressed, the resin will flow away, but the
> glass will be squeezed. I think glass fibres squeezing together can
resulte
> to resin recession.
>
> But let me tell you some details: The failing subassemblies I've to
analyze,
> contains transformer windings which are implemented as a 16-layer pcb. The
> winding shows dielectric breakdown between different winding layers (and
> sometimes between different windings on the same layer). This breakdown
> happens after some hours run-in at 120°C and 500VDC (500VDC as test
voltage,
> failures also at lower tension at at AC) .Before them, all pcb has passed
> successful a hi-voltage test at ambient temperature.
> The diel. strength for the closest distance of 65mm prepreg should be
around
> 2.5kV, or a little bit less because IPC-2221, § 4.1.2, not 500V!
> I tend to see any loss of the electric strenght of a laminate/prepreg as
> function of the temperature, the hi-temp aging, and material defects.
> The occuring pcb temperature of 120°C seems in accordance with IPC-2222, §
> 4.3. So I'm looking for material defects, especially cracks: if cracks
span
> a part of
> the 65mm (prepreg), the electric strenght will decrease, because the
> electric strenght of a cracks (like air) amounts 1kV/mm (instead of
40kV/mm.
>
>
> Hope to get some engelnotes.
>
> Bernhard
>
> ##############################################################
> TechNet Mail List 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 web site (http://www.ipc.org/html/forum.htm) for
additional
> information.
> If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
> 847-509-9700 ext.5365
> ##############################################################
##############################################################
TechNet Mail List 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 web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################
|
