does seem a bit odd...According to the NASA documents (if I'm reading them
correctly) they are
only using one type of flip-chip BGA in multiple locations. I would think
they would want to use a variety of BGA's.
Ken
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Friday, November 19, 2010 4:59 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Falling off PCA
That statement, when was that? We tested a large number of boards, intention
was to test until failure. We stopped at 100,000 temp cycles with no
falures. Largest BGAs were Xilinx 560s .Correctly designed and processed,
BGAs are excellent. Especially when vapour phase soldered. Drop tests are
obligatory, 1 meter fall on wooden plate. And we use the bad reputated ENIG
!
If I can find it, I will send a photo where we lift 1,000 kilograms mounted
to a superBGA.
Inge
----- Original Message -----
From: "John Parsons" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, November 19, 2010 10:35 PM
Subject: Re: [TN] BGA Falling off PCA
> The nominal pad diameter on the device is 0.030" and this is the pad
> diameter on the board. Solder mask definition reduces this diameter to
> 0.026". Thanks for the information on drop testing. After the initial
> accidental drop I think that they "tested" 4 more assemblies from what
> they
> way was 1 foot and the BGA popped off of all of them. One of the three
> assemblies that we received looks questionable in that there is burnt flux
> residue on and around the BGA area. I believe that they are screen
> printing
> paste on the entire assembly. The assembly sees two stages, single sided
> SMT (paste and reflow) and then wave soldering of some through hole
> capacitors and a number headers and jacks.
>
>
>
> John
>
> _____
>
> From: Dennis Fritz [mailto:[log in to unmask]]
> Sent: Friday, November 19, 2010 1:16 PM
> To: [log in to unmask]; [log in to unmask]
> Subject: Re: [TN] BGA Falling off PCA
>
>
>
> John,
>
>
>
> I wish I could say I am surprised at your results, but only a little.
> BGAs
> perform very poorly in drop shock testing. Both the original JCAA-JGPP
> study at
>
>
>
>
http://www.acqp2.nasa.gov/LeadFreeSolderTestingForHighReliability_Proj1.html
>
>
>
> And now the results from NASA/DoD phase two - papers by Polina Snugnovsky
> and Tom Woodrow at SMTAI last month show that BGAs fail first of all the
> compents on the test boards!! JGPP data shows that over 60% of the
> failure
> cause on JGPP boards is (drum roll, please) - the kind of component!!!
> BGAs
> fail first in most all kinds of stress - thermal cycle, drop shock,
> vibration, combined environments, but by far the first in drop shock.
>
>
>
> In the SMTAI report data from Polina Snugnovsky at Celestica - all but one
> BGA failed to pass 20 successive drops from JEDEC test procedure
> JESD22-B110A. On the same board, all 90 chip scale components passed the
> same test.
>
>
>
> My theory about the BGA failures is that the weight of the balls, and the
> distance the chip is from the board creates tremendous shear on the ball
> solder joints when dropped. BGAs do significantly better in thermal cycle
> than the early failure demonstrated in drop testing.
>
>
>
> That said, a one foot drop, one time sounds pretty mild and I would still
> examine the board closely. Notoriously, ENIG finishes have suffered from
> "black pad". You will need some EDAX elemental analysis of the board
> surface to get a feel for how much phosphorus shows up.
>
>
>
> I don't think the mask defined pad can be the only issue, but typically,
> the
> mask defined pads are on the package, and solder is allowed to completly
> wet
> the pad on the board. I trust the pad sizes are about the same on the
> package and on the board? Finally, you may have access to a dye syringe,
> so
> that dye-and-pry testing can be done on the assemblies to see if there is
> already cracking of the BGA joints from thermal problems in assembly, or
> if
> there is a "head-on-pillow" issue of poor wetting of balls to the paste
> applied to the board for assembly. (presumes the assembler is using paste
> stencilling, and not just tacky flux direct to the ENIG pads on your
> board.
>
>
>
> Denny Fritz
>
> SAIC, Inc.
>
>
>
>
>
>
>
> -----Original Message-----
> From: John Parsons <[log in to unmask]>
> To: TechNet <[log in to unmask]>
> Sent: Fri, Nov 19, 2010 3:30 pm
> Subject: [TN] BGA Falling off PCA
>
> I am not seeing a lot of the usual Friday quiz traffic so I know you
> guys-n-gals are just itching for some real work :o).
>
>
>
> We are a PCB fabricator and one of our customers has returned some
> assemblies to us for feedback. What they noticed when someone
> accidentally
> dropped an assembly is that the BGA (352 pin Cirrus Logic EP9312-CBZ)
> popped
> off the board. They then proceeded to drop a few more from a height of
> about a foot with the same results. All the other components on this
> Pb-free assembly stay fast.
>
>
>
> We have received three PCA's and 5 BGA's. On one of the BGA's a single
> ball
> has remained on the PCB. The rest of them all the balls have broken
> cleanly
> from the PCB leaving a very flat (under x10 magnification) dull gray
> surface. I sure wish that I could take photo's but lighting is critical
> and
> I don't think that I have the resources to get photo's that would do
> justice
> to what the naked eye is seeing.
>
>
>
> Also of note is that the BGA lands are mask defined with a 31mil circuit
> pad
> and 26mil solder mask relief.
>
>
>
> Does anyone have any ideas as to how we can determine the root cause of
> this
> failure. This part has been built for some time but previously the
> surface
> finish on the PCB was a solder finish. This is the first run of the
> boards
> that has an ENIG finish. This doesn't look to me like a raw board issue
> but
> that is where everyone looks first isn't it ;o).
>
>
>
> Regards
>
>
>
> John Parsons
>
>
>
>
>
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