John and others,
But wouldn't it be even worse trying to use transmission mode because of the nature if the circuit board underneath the component (copper barrier(s), glass fiber bundles and epoxy?
Nobody from Sonotek or Sonoscan on TechNet?
Bev
----- Original Message -----
From: John Burke <[log in to unmask]>
To: 'TechNet E-Mail Forum' <[log in to unmask]>; Bev Christian
Sent: Mon Sep 21 18:00:16 2009
Subject: RE: [TN] Acoustic Microscopy for Under fill Coverage
Not a discontinuity as such just an interface, and you are right, the
signal reflections will be from every interface, so for a BGA (without a
lid) the interfaces will be as follows:
1 Liquid to top of package molding compound
2 Molding compound to silicon
3 Silicon to die attach
4 Die attach to substrate
5 4 or so interfaces in the substrate itself (copper to substrate
pre-preg)
6 Substrate to under fill (or NOT!)
Depending of the acoustic impedance between the Material travelling
from/Material travelling to, more or less ultrasound energy will be
reflected at each of the interfaces.
Of the layers above I believe that the strongest reflection will be from
level 6 above.
It is 30 years since I last played with non destruct testing using
ultrasonics, but I would bet from my experiences then that you would do far
better using through transmission for this scenario rather than reflected
signals due to Bev's comment, particularly due to the substrate interface
reflections masking the ones between the package and the under fill.
John Burke
(408) 515 4992
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Monday, September 21, 2009 2:07 PM
To: [log in to unmask]
Subject: Re: [TN] Acoustic Microscopy for Under fill Coverage
Since when can an acoustic signal punch through a BGA? I know you can do if
for flip chips, but aren't there too many density discontinuities for CSPs
abd BGAs?
Bev
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Mon Sep 21 14:40:48 2009
Subject: [TN] Acoustic Microscopy for Underfill Coverage
Anybody know a good lab in the North East that does acoustic microscopy? I
need to verify under fill coverage under BGAs.
Thanks,
Amol
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