Hi Roger,

It is not quite clear to me what exactly happened.   However, I think it can
be answered as follow:

1.      I do not think the air expansion alone was so big to break barrel.
If the force is that big, it should have been popped out during its cure
cycle in the oven.   The cycling temperature of 125C tells me that the
expansion force of the air should have been much lower  than that when it
was in the cure.  Therefore,  it can not be a major source for the breakage.

2.      Most likey, I think it is due to the thermal cycling nature.  As the
cycling continued, the copper fatigued and failed to respond to the
expansion and contraction of the board in the z-direction, i.e., thickness
direction.  If this was the cause, the solution can be
either use of higher  Tg board or increase the glass content in the board.

Hope it can be of help.
Myung C. Chu 
CSS Asia Co., Ltd.
Tel: 82 2 523 8810   Fax: 82 2 523 1483
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