Alternatively you could suggest to the customer that they save time on
qualification by ditching the 1000 hours 85/85 and simply submerge the
equipment in a bucket of warm water for a day. The water uptake will be
much the same.
Good luck.
Douglas O. Pauls wrote:
> 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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