Was the test performed on the flex itself and not the whole assembly? If the 
answer is ' yes',  I do understand better, because then the test was a test 
on the PI's resistance to humidity. With other words, a water vapour 
penetration test.
Inge


----- Original Message ----- 
From: "Eric CHRISTISON" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, June 25, 2008 9:50 AM
Subject: Re: [TN] Bias voltage test in damp heat


> 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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