Vlad is correct, but let me elaborate. You can pop them off with a screwdriver or other instrument of death, but it can be messy and if you are interested in voids that don't come up to the underfill/part interface, you may not see them that way. Planar sectioning is best. But as Dr Brian Toleno points out in his underfill course (a little free advertising there, New Dad), a normal vertical cross-section will show you if you have any filler settling. This of course assumes you are using an underfill with a filler in it. :)
Bev
RIM
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Tue Sep 22 07:39:24 2009
Subject: Re: [TN] Acoustic Microscopy for Under fill Coverage
Amol,
Probably the only other choice you have is to grind off the package gradually and inspect the underfill coverage.
Regards,
Vladimir
SENTEC
SENTEC
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
-----Original Message-----
From: "Kane, Amol (349)" <[log in to unmask]>
Date: Tue, 22 Sep 2009 07:30:22
To: <[log in to unmask]>
Subject: Re: [TN] Acoustic Microscopy for Under fill Coverage
Guys, thank you for all the interest in the subject. Lots of good information indeed. Yes, I did talk to Sonoscan and they pretty much corroborated what most people here are saying in that there are too many interfering layers to effectively look at underfill coverage and any voids or dewetting to the board/component surface.
So let me ask this...HOW CAN I look at a underfilled BGA and determine how good/bad my process for underfilling them is? (I am setting up a new process for manually underfilling BGAs). I want to determine if the underfilling technique used is consistently producing good results across BGAs and if the board cleanliness level is sufficient to ensure complete wetting and spread underneath the BGA. I am working with test vehicle now, but the actual boards will be used in a shock application. Any established standards (formal or informal) out there? The bottom line is that I need to be able to show the customer that the process produces underfilled BGAs with minimal voiding and dewetting.
Werner, are the critical areas (i.e. the corners) the same for shock/vibe as for more gradual stresses on a BGA?
Thanks,
Amol
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Monday, September 21, 2009 11:12 PM
To: [log in to unmask]
Subject: Re: [TN] Acoustic Microscopy for Under fill Coverage
Hi Werner -- there have been a number of examples in which a component
construction interaction of a "partial underfill" has resulted in
increased degradation of the solder joint integrity in comparison to a
"complete underfill" case.
Dave
Werner Engelmaier /* <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
09/21/2009 06:17 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
[log in to unmask]
To
[log in to unmask]
cc
Subject
Re: [TN] Acoustic Microscopy for Under fill Coverage
Hi Guys,
The premise of the original question was by inference that completeness of
the underfill coverage is necessary.
Would not be an underfill 'ring' covering the first 5 or so 'SJ squares'
accomplish what is desired?better reliability? That would make this
discussion academic.
Werner
-----Original Message-----
From: Vladimir Igoshev <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, Sep 21, 2009 6:47 pm
Subject: Re: [TN] Acoustic Microscopy for Under fill Coverage
C-SAM does do a beautiful work on flip-chip packages and of cause not in
the
transmission mode.
Regards,
Vladimir
SENTEC
SENTEC
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
-----Original Message-----
From: "David D. Hillman" <[log in to unmask]>
Date: Mon, 21 Sep 2009 17:30:36
To: <[log in to unmask]>
Subject: Re: [TN] Acoustic Microscopy for Under fill Coverage
Hi Bev - I have attempted to use Acoustic Microscopy for underfill
coverage on BGAs and as other folks have detailed, the number of
interfaces and structures cause significant signal reflection problems
making analysis very difficult. Some specific focused interface
examination efforts can be conducted but are still very difficult to
analyze.
Dave Hillman
Rockwell Collins
[log in to unmask]
Bev Christian <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
09/21/2009 05:16 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond=2
0to
Bev Christian <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] Acoustic Microscopy for Under fill Coverage
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 scenar
io 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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