"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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