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September 2008

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From:
Steve Kelly <[log in to unmask]>
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Date:
Tue, 16 Sep 2008 17:15:14 +0000
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Hi Arnaud,

This is a flex circuit- basically kapton and polyimide glue- I

do not see where the glass would come from. Regards Steve Kelly

Sent from my BlackBerry device on the Rogers Wireless Network



-----Original Message-----

From:         arnaud grivon <[log in to unmask]>



Date:         Tue, 16 Sep 2008 18:15:20 

To: <[log in to unmask]>

Subject: Re: [TN] Bias voltage test in damp heat





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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