Hello Gary,

Imagine your ground planes before laminating..
Large expanse of copper foil with little, empty buckets around each
'padless' hole.
During lamination, the only thing that flows is resin. So, the resin will
tend to flow towards the 'padless' hole areas, making them resin rich as
Gary Ferrari has previously stated. Higher resin content means greater
z-axis expansion, giving the plated through holes a hard time.
Plating thickness in the hole may be an issue.
When hand soldering, is the solder flowing completely through the board,
forming a fillet on both sides. Partially soldered holes will have the
effect of concentrating the expansion stresses to the unsoldered part of the
hole.
I put a note on my fab drawings dis-allowing modification of the copper
artworks in an effort to stop this sort of thing from happening.
(once had a fab shop expand my internal plane clearances to the point that
some areas became open circuit.)

regards,

Phil.


From: Bremer, Gary [mailto:[log in to unmask]]
Sent: Tuesday, 25 June 2002 00:13
To: [log in to unmask]
Subject: [DC] High Performance Electronic Design



I am forwarding this question from one of the design engineers at work.  We
advertise we build class 3 products, but with all of our thick boards, we
get open traces whenever a hand soldering operation is required.  We just
found out that one of our board vendors has been removing all the unused
pads on the inner layers without out knowledge.  The board type we generally
use for our backplanes is type 3c per IPC-2222.

Does getting rid of unused pads on all inner layers have any profound affect
on the PHT barrel integrity especially with high layer count / thick circuit
boards?

Thanks for your help,

Gary Bremer
Manufacturing Engineer
Phone (626) 449-3090 ext. 219