It looks like delamination at an area below a ground plane.  There may
be area's that look "white" in the clearances.  Dropping alcohol over
area may make it easier to see in the clearance area.  You can also try
a sonoscan of the board and look for declamation.

Rene 

-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of
Constantino J. Gonzalez
Sent: Friday, October 28, 2005 2:50 PM
To: [log in to unmask]
Subject: [IPC-600-6012] Dent

Hello does anybody has a clue what this can be if it is not a blister?
Please read below and see attachments



Attached is the best photo I can get.

Fr top it sinking down, fr bottom it's budging up.

We see this right after reflow on random location.

It is not blister, the cross section photo does not show that.

Only abnormalities is difference in Cu thickness ( slight thinner on
dent area).



Any clue??



Hello Constantino,
How are you ??
I need your advise on recent issue I'm facing in our line.  It pretty
new for me ..
I hv  this PCA which produce "dent mark" during rework.

This dent appeared after performing rework to remove the SRAM (the
location that you see dent) with hot air blower, the temp is set to 350
deg C, blow time is around 15 seconds (dent will be created - in shape
of circle about 10mils diameter ), effective temperature on the comp is
290 deg C.

Every single board which we rework produce this condition.
It's not d/c related as we see similar condition on other d/c as well.
More then one d/c and more one location.
We try to simulate the hot air rework on raw card and the dent appears
too.

Today line found 2 more boards with dent after going through IR reflow
only ( no rework involved ).

The PCB supplier perform cross section on the dent location,  there is
no abnormalities seen expect for a difference in the copper thickness
before and after the dent.

I hv attached the cross section photo.. I can not get a snap shot of
the dent due to glossy appearance and light reflection.

I can not figure out the root cause..
1) What actually caused this dent ?? Mechanical or thermal
2) Thermal should expand not contract !!
3) Why the dent appear only after reflow / rework ??

Even the PCB suppliers cracking their head.
This board is not failing   ICT/ FVT however it not as simple as
cosmetic
defect !!!

I really hope to hear fr you.