Hmmm! I can't see anything in your points 1 to 3 that would directly cause
you any trouble, and the conductive residues I had in mind ranged from
ionic contaminants on the surfaces to any solder balls that might have
become lodged underneath.
You didn't answer if you've tried testing at elevated temperature prior to
underfilling, and one thing I didn't ask (because I 99.99...% know the
answer) is are your devices hermetically sealed? I'ld try doing a
cross-section of some of the BGA's that failed after underfilling and see
if any of the epoxy has got inside and damaged anything.
More things spring to mind - like did you bake out the assemblies prior to
underfilling? The Dexter Hysol (sorry, Loctite) underfill that I use
recommends pre-baking of assemblies prior to underfilling. If the BGA's
have been out of their bag longer than a couple of days before
underfilling, they have probably absorbed a lot of moisture. I can't say
for sure what effect heating moisture-laden components to 120 or even 150
deg for 20 minutes or so would have, but your 3% may have suffered some
delam at some point. Or it may be warping and breaking/losing contact and
underfill is getting between the contact surfaces and isolating them.
Cross-sectioning and analysis should show this up too.
About tapped out of ideas again for now. Good luck with your search for a
cause - I'ld be interested in hearing what you find.
Peter Duncan
"Joseph H.
Smith" To: [log in to unmask]
<Tony_Zhang@H cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
ZMOT.COM> Aero/ST Group)
Sent by: Subject: Re: [TN] No power on after underfill
TechNet
<[log in to unmask]
ORG>
11/20/01
08:58 AM
Please
respond to
"TechNet
E-Mail
Forum."
1.The PCB we use is Ni/Au but there is Tin plated on the BGA side and the
solder paster type is Alpha RMA 9147
2. we have done the experiement for letting the epoxy only underfill 50%
BGA size , the result is still bad
3. we reduce the curing temperature from 150 C to 120C , also no effective
4. what is conductive residues when we applying no-clean soldering process
?
By the way, if you need MDS of 3513, I can send to you .
Thanks for your great help.
Tony
-----Original Message-----
From: <Peter George Duncan> [SMTP:[log in to unmask]]
Sent: Monday, November 19, 2001 10:27 AM
To: [log in to unmask]
Subject: Re: [TN] No power on after underfill
Hi, Joseph,
I cannot find the 3513 material data sheet, but that probably doesn't
matter. The main thing I can think of that would cause your problem is
the
thermal excursions needed to apply and cure the underfill. Am I
correct to
say that the boards passed test at room temperature before the
underfill is
applied?
You may have a manufacturing problem where the balls make contact
enough to
pass test, but fail at elevated temperature. I would try testing the
boards
at 100 or 115 degrees C prior to underfilling them and see if they
still
pass. If they do, but fail again after underfilling, then the problem
is
probably related to your underfilling process. It is quite easy to
apply
too much if you're not using an automated process or have not
correctly
calculated the amount of material to apply. It does flow more prior to
curing at curing temperature, and if it's getting into nearby
interface
contacts as a result, you will need to look at damming the area around
the
BGA with a peelable masking to contain the underfill until it's cured,
or
reducing the amount of material applied.
One other thing might be contamination under the BGA. If you have any
conductive residues left on the board, especially if you use no-clean
soldering processes, they may be picked up by the underfill and
there's a
chance you're suffering from short circuits through the increased
conductivity of the epoxy. It's very important to the performance of
the
underfill that the underneath of the BGA's are very clean.
Hope this gives you some clues and you find a solution.
Peter Duncan
"Joseph H.
Smith" To: [log in to unmask]
<Tony_Zhang@H cc: (bcc: DUNCAN
Peter/Asst Prin Engr/ST
ZMOT.COM> Aero/ST Group)
Sent by: Subject: [TN] No power on
after underfill
TechNet
<[log in to unmask]
ORG>
11/19/01
03:48 PM
Please
respond to
"TechNet
E-Mail
Forum."
Pls help me to solve this issue
We use undefilll for two BGA in one product ,the epoxy is Loctite LPD
3513
and the curing condition is 115C , 15 minutes , the BGA' s package is
below
.
U3 information : Body size, 9*9mm ; height 1.7 ; bump diameter
0.3 ;
pitch, 0.8*0.8 ;bump array 10*10
U1 information : Body size, 12*12 ; heigh t1.7 ; bump diameter
0.3 ;
pitch, 0.8*0.8 ; bump array 14*14
Before the underfilll we check the electric function .All are good
ones .
But after curing , some phone failed because "can not power on ", and
some
failed for "check SIM card ", the defect sample is closed to 3%. I
think
"check card "issue" may caused by the underfill material emission
which
cover the SIM card lead .
But I can not get any idea for further.
Thanks
Tony
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