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
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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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