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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