Pete,

It stills looks like CAF to me. All the characteristics you mention 
point in that direction.

Regards,

Gary

[log in to unmask] wrote:
> All:
>
> A few weeks ago I sent out a question to the community - Why do I have
> low resistance isolation between isolated circuits.  The general answer
> that came back was  - I have CAF.  Fast forward a couple weeks and I
> have more information - I don't think I have a CAF issue - I may have
> invented something new.
>
> Quick description: 14 layer, polyimide material.  Single lamination
> cycle (no blind/buried vias), .093" thick.  We have identified the
> shorts to be created between layers 7/8.  I have gone as far as milling
> down through layers 1 - 7 and evaluated the entire board.  There are no
> anomalies until we get to the dielectric layer between 7/8.  There are
> cracks/delaminations between holes in the BGA socket area but nowhere
> else on the board.
>
> Pictures of what we are seeing are below.
>
> The first horizontal section shows cracks/delamination - the resistance
> measured 150 ohms (or so), That coupon was sent out for analysis.  We
> received back some SEM photos with an explanation that the copper plated
> from one hole to the other.  One hole acted as a cathode, the other an
> anode and the moisture in the board was the carrier. We in essence
> created a mini plating cell.  In these pictures you'll see copper
> plating actually plating around the fiberglass bundles.  The voltage on
> this device is 3.3 volts.  The shorts showed up in hours of operation
> (maybe up to 20- 40 hours).  The boards were not baked prior to
> assembly.  The boards do get temperature cycled (-53 - +54 C) but this
> short will appear with just 0 or 1 cycle.  (I have 4 boards with no
> thermal cycles other than assembly).
>
> Any suggestions on what I actually have?
>
> Thanks,
> Pete
>
>
>
>
> Horizontal Cross section
>  <<Picture (Device Independent Bitmap)>> 
>
> You can see three areas with delamination - all three areas have reduced
> resistance.
>
> We had this section evaluated with SEM/EDS which revealed:
>
>  <<Picture (Device Independent Bitmap)>> 
>
> Higher magnification of the same location:
>  <<Picture (Device Independent Bitmap)>> 
>
> The light areas are identified as copper.
>
>  <<Picture (Device Independent Bitmap)>> 
> New sample - horzonatal view of copper connecting holes.
>
> Pete Menuez 
> Supplier Quality Engineering Manager 
> L-3 Communications Cincinnati Electronics 
> 7500 Innovation Way 
> Mason, Ohio 45040 
> [log in to unmask] 
> 513-573-6401 Voice 
> 513-573-6767 Fax 
>
>
>
>