"Exposured Weave" must be considered when assessing "minimum electrical spacing" (as opposed to physical spacing) as it is likely that normal processing contaminates (even airborne contaminates) can become lodged in the exposed weave.  That entrapment becomes a reservoir for metallic and ionic growths, and especially contaminates that can wick down the weave bundles.  This effectively and technically reduces the dielectric standoff, and increases leakage.

Another phenomenon associated with high voltage is a term called "partial discharge", which is generally associated with microscopic (closed cell) bubbles, voids and spaces, especially along glass filament bundles whose entrapped "gases" are charged by high energy levels.  The charged gases actually can conduct into, and be dissipated by the glass / resin system of the PCB itself without causing a arc that leaves a carbon trail.  This condition is exacerbated by "sharp conductors such as under-etched copper traces that harbor high energy corona.  Therefore, it only stands to reason that any area of a laminate system that enhances contaminate entrapment just adds fuel to the insufficient electrical spacing failure mechanism.

Best regards,
Ron McIlnay
Sr. Electrical Procurement Engineer
Medtronic Physio-Control
Phone: 425 867 4500
e-mail: [log in to unmask]




-----Original Message-----
From: John Perry [mailto:[log in to unmask]]
Sent: Thursday, June 27, 2002 10:12 AM
To: [log in to unmask]
Subject: [IPC-600-6012] Weave Exposure Criteria in IPC-6012 and IPC-6013


Afternoon Colleagues,

First off, thanks for eveyone's input relative to dielectric withstanding voltages earlier this month.  Your feedback is appreciated.

A question posed by a user of IPC-6013 applies for IPC-6012 as well.  The question refers to weave exposure.  This is covered in IPC-6013 under section 3.3.2.4 and under section 3.3.2.2 in IPC-6012A.

The paragraph's state that weave exposure is "acceptable for all classes, provided the imperfection does not reduce conductor spacing below the minimum."  The question is, does this apply to not only adjacent conductors on the same layer, but also conductors on adjacent layers?  I would think that if we were dealing with  exposed fibers on a layer-to-layer basis, they would then be classified as delamination or blistering and hence have similar criteria for maintaining minimum conductor spacing.  Am I not interpreting this correctly?

Thanks in advance for your feedback.

Best Regards,





John Perry
Technical Project Manager
IPC
2215 Sanders Road
Northbrook, Il 60062
1-847-790-5318 (P)
1-847-509-9798 (F)
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