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 N Kimmey CID+
Principle PCB Designer
Powerwave Technologies
EDH 916-941-3159
FAX 916-941-3195
CEL 916-804-2491
-----Original Message-----
From: Ofer Cohen [mailto:[log in to unmask]]
Sent: Tuesday, July 27, 2004 3:48 AM
To: [log in to unmask]
Subject: [TN] Removal of non functional pads
Technetters,
Are there any guidelines regarding removal of non functional pads in thick (>2.5 mm) PCBs? Are the guidelines documented somewhere?
Regards
Ofer Cohen
Manager
Quality Assurance, Reliability and Production Technologies
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