In a message dated 7/27/04 9:37:01, [log in to unmask] writes:
> Ofer,
> As you have already seen from Brain, Jeff and others, there are varying
> thoughts on this subject.
> That said, here are mine.
> Unused pads on inner layer can play an important part in the construction
> and reliability of your PCBs.
> I recommend removal of unused pads on low layer count, low Z axis CTE
> materials to improve manufacturability at fab.
> There will be longer drill life, less inner layer misregistration
> possibilities, etc.
> I adamantly refuse to allow removal of unused pads on high layer counts
> and/or high Z axis CTE or mismatched CTE materials.
> The reasons for this is pretty simple, first if the laminate material
> stretches the copper barrel enough then the PTH barrel can actually end up longer
> than the PCB is thick (very strange looking phenomena), also stretching of the
> plated barrel can cause reliability issues due to cracking and subsequent
> opens (read this as field failures).
> Leaving at least a minimal annular ring on inner layer pads will aid in
> supporting the PTH and reduce the likelihood of damage cause by PCB Z axis
> expansion.
> I think you will find most fabricators would prefer to see unused pads
> removed as that will commonly improve manufacturability, where most reliability
> types would prefer to see all pads remaining to improve barrel
> anchoring/strength and integrity.
> Talk to your fabricator and your quality guys to help reach the best
> decision for your specific construction.
> Remember communicate your issues and most of them will have an acceptable
> solution.
> Hope it helps,
> FNK
>
Frank is right on the money.
Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com
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