Hi Ofer,
I assume that you normally get "plugged" after HASL. This would lead to the
solderball problem you describe. Why not plug before LPI and HASL, sealing
off the hole from solder all together. You would still need to allow the air
to escape from the "back" side of the hole, but it should solve the
solderball problem.
Tom

-----Original Message-----
From: Ofer Cohen [mailto:[log in to unmask]]
Sent: Tuesday, May 27, 2003 10:19 AM
To: [log in to unmask]
Subject: [TN] Plugging under BGAs


Technetters,
Most of our boards carry BGA (pitch => 1 mm). The finish is HASL, which,
from various reasons, can't be changed. The general rule is to plug all the
through-hole vias from the print side, apart of BGA locations, where the
plugging is from the BGA side (mostly components side).

In a new design, there are pairs of identical BGA-packaged components from
both PCB sides, using the same TH vias. I have two options:
1.      To select one side to plug (danger of solder balls under the BGA of
the other side), or
2.      Plug from both sides (danger of over-stress on the hole plating
during the reflow, because of the air pressure inside the hole.

What is your opinion?

Regards
Ofer Cohen
Quality Assurance Manager
Seabridge Ltd.

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