Richard,

UL uses simple recirculating ovens to conduct the aging so %RH is uncontrolled.

Your question is very perceptive of the underlying physics. One of several
mechanisms that can degrade (or enhance) the bond strength during this test is
corrosion buildup on the copper, and that will vary with humidity. Which failure
mechanism is going to control the thermal aging performance depends on the test
conditions (time, temp, RH), sample configuration (SL, ML, line width), and
material types (dielectric, copper, adhesive).

Andy Magee
Flex Guru
[log in to unmask]

Richard Haynes wrote:

> Andy,
> Is there a %RH that goes along with the UL accelerated test? It is
> probability "well known" but they are so many that leave out the important
> variabiles.
> Thanks
> Richard
>
> -----Original Message-----
> From: Andy Magee <[log in to unmask]>
> To: [log in to unmask] <[log in to unmask]>
> Date: Tuesday, September 29, 1998 4:58 PM
> Subject: Re: [TN] Autoclaving Flex PWBs
>
> >Eric,
> >
> >Underwriters Laboratories has a thermal index  (10 and 56 day
> >accelerated tests) that provides a maximum continuous operating
> >temperature rating for flex materials. The majority of rated materials
> >on the market are limited to 105C.  There are a few choices rated in the
> >150-160C range, so you do have the option of specifying something like
> >125C performance.
>

<snip>

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