Both...
The individual glass fibers don't absorb much but the fiber bundle as a mechanical structure does...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Eric CHRISTISON
Sent: Tuesday, September 16, 2008 9:26 AM
To: [log in to unmask]
Subject: Re: [TN] Bias voltage test in damp heat
"Glass fibres absorb moisture"....? I'm surprised.
Is it the glass itself that absorbs the moisture or the coating on the
fibres that absorbs the moisture?
Regards,
arnaud grivon wrote:
> Steve,
>
> From the description you gave, the particles you detected may
> correspond to E-glass fibers (assuming Al instead of Cl in the
> elements ). You can refer to IPC-4412A to have a detailed description
> of a glass fiber composition.
> Dimensions you indicated fits also well with glass fibers and glass
> fibers do absorb moisture.
> Difficult to explain however how to include glass fibers into a
> polyimide film...
> Just a thought.
> Best regards,
>
> Arnaud Grivon
>
> Steve Kelly a écrit :
>> Good Day To All,
>>
>> I am back with this thread I started in April this year with some more
>> questions.
>>
>> After extensive analysis we have found evidence of what IPC 4203 and
>> 4204
>> calls inclusions in the raw material we use to make the flex
>> circuits. These
>> inclusions are usually in the 5-10 micron range and they usually come in
>> groups (few particles in a group). From the SEM/EDX scans they
>> consist of
>> Si, Mg, Ca and Cl. Carbon and oxygen are also present in the spectra.
>> What
>> the exact possible formulations are - I am open to suggestions or
>> theories.
>> Our theory is that whatever these are they absorb moisture and the
>> result
>> is they form ions and lower the dielectric breakdown between the
>> adjacent
>> tracks which are at 100 micron space. Under the bias voltage we get a
>> high
>> resistance short.
>>
>> Questions: a) does this theory make sense or any comments
>>
>> b)at the present time my customer believes
>> this test
>> helps define that the part will work for 25 years and getting them to
>> change
>> their mind is not likely to happen. On the next generation product
>> they have
>> moved the spacing to 200 microns - my concern is they may just be
>> postponing
>> the inevitable- may make it through 500 hours and fail at 750 for
>> example.
>> Comments on this would be appreciated. Thanks again to the TechNet on
>> this
>> issue- especially to Mr. Pauls and Mr. Ellis for previous help.
>>
>>
>>
>> Steve Kelly
>>
>> PFC Flexible Circuits Limited
>>
>> PH: (416) 750-8433
>>
>> Fax: (416) 750-0016
>>
>> Cell: (416) 577-8433
>>
>>
>>
>> From: [log in to unmask]
>> [mailto:[log in to unmask]] Sent: Wednesday, June 25, 2008
>> 12:37 PM
>> To: TechNet E-Mail Forum; Steve Kelly
>> Subject: Re: [TN] Bias voltage test in damp heat
>>
>>
>>
>>
>> Steve, I agree that this is madness, unless the telecom supplier has
>> an end use
>> environment of 85/85 where power-on in humid conditions is a reality.
>> Assuming that the equipment is not functioning in a steam
>> environment, here
>> is the "science" that you are looking for.
>> Designers, when they have knowledge of the material characteristics,
>> will
>> design spacings dependent on the dielectric strength or dielectric
>> withstanding voltage of the laminate. The values in the data sheets
>> for the
>> laminates specify these parameters, but only for lab ambient
>> conditions, not
>> after 85/85 conditioning. When you expose a hydrophilic material to
>> a long
>> exposure in hot/humid conditions, then you don't have that same
>> dielectric
>> strength (dramatically reduced) and you have violated the design
>> assumptions. Polyimide is such a hydrophilic material. I believe Brian
>> Ellis referred to it as blotter paper, in which I would concur. If you
>> allow the circuit to dry out, then you return to the expected dielectric
>> strength. You may already be at an unrealistic threshold with 2500
>> volts/mm gradient, as Brian also pointed out.
>> Unless the designer had a firm value for dielectric strength of the
>> substrate after 85/85 conditioning, which would change as the substrate
>> rapidly dried out, then the design would not and could not work.
>> Doug Pauls
>>
>>
>>
>>
>>
>> Steve Kelly <[log in to unmask]> Sent by: TechNet <[log in to unmask]>
>> 06/25/2008 10:09 AM
>>
>> Please respond to
>> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
>> Steve Kelly <[log in to unmask]>
>>
>>
>> To
>>
>> [log in to unmask]
>>
>> cc
>>
>>
>>
>> Subject
>>
>> [TN] Bias voltage test in damp heat
>>
>>
>>
>>
>>
>>
>>
>>
>> Good Day To All,
>>
>> Back in April I posted some queries on the tech-net about high voltage
>> testing after 85C/85RH testing and was basically told this test was
>> impossible and I agree with that assessment. But some things have a
>> life of
>> their own.
>>
>> To re-iterate: We are building a 4 layer flex circuit. All layers are 18
>> micron copper and all lines and spaces assuming perfect etch are 100
>> micron
>> lines and 100 micron spaces. My customer for some reason signed up to
>> pass a
>> 250 volt test after 1000 hours of 85C/85RH damp heat test. My premise is
>> being in this case a polyimide build if they dried the circuit after
>> this
>> test it should pass. They do not want to dry it and still have it pass.
>> The previous threads in summary said this test was "madness" - I
>> agree but
>> what is the scientific explanation of why this is madness.
>> Please note this requirement is being driven by very large telecom
>> companies
>> and the worlds largest provider of internet gear.
>> Thanks again for the help.
>>
>> Regards Steve Kelly
>>
>>
>>
>> Steve Kelly
>>
>> (416) 750-8433 (work)
>>
>> (416) 750-0016 (fax)
>>
>> (416) 577-8433 (cell)
>>
>>
>>
>>
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--
Eric Christison Msc
Mechanical Engineer
Consumer & Micro group
Imaging Division
STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom
Tel: +44 (0)131 336 6165
Fax: + 44 (0)131 336 6001
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