I think that since "bingo, you change the part it works", is the key. The
part is bad.
But, here is what I would do:
Take bad assembly; Heat = pass; Freeze = pass; Ambient = fail.
Remove PBGA and replace. Ambient = pass ? Heat = pass ? Freeze = pass ?
Remove PBGA; put original one back on. Same as first step? Heat = pass;
Freeze = pass; Ambient = Fail ?
component is bad; board and joints are good.
I would have a Failure Analysis done on the PCBA. Take lots of pictures.
Also, I would have
the tray of parts checked for planarity of the balls and/or warp of the
package.
I don't know enough about BGA joint confirmation, but I am positive that
others on this list do.
Can someone else suggest a way to look at those ball/joints before Ioan
pulls off the PCBA ?
Valerie
"Brinkman, Mark" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
09/23/2005 03:58 PM
Please respond to TechNet E-Mail Forum; Please respond to "Brinkman, Mark"
To: [log in to unmask]
cc:
Subject: Re: [TN] Soldering or design problem?
At this point I think I would try to isolate the problem by debugging
the failing board. The designer should be able to find what is not
working. He should know the sequence of events that should take place
once power is applied to get the design up and running. He's going to
have get dirty. Find the event that is not working. What would cause
this event not to happen? Find it and see if it's the same on the other
failed boards.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Friday, September 23, 2005 2:40 PM
To: [log in to unmask]
Subject: [TN] Soldering or design problem?
Hi Technos,
we are faced here with a very delicate problem: the customer suspects a
workmanship issue on our side, we are suspecting a design or component
problem.
Here it goes: 50% of the cards do not function due to the same problem,
something wrong with the same PBGA. We tweaked the thermal recipe, we
are at about 220C peak; no improvement. We played with lower
temperatures for fear not to thermally stress the part; no improvement.
Now I get into the weird zone:
* if the BGA is heated, it instantly starts working, but also
starts working if the BGA is frozen
* it also works if we freeze the opposite side of the PCB
* We use the flying probe to test for open joints, everything
seems to be OK, but the card does not work
* we did all kinds of re-reflow of the BGA on the bad boards, in
the oven, but also on the rework station, even at extreme temperatures
that send the top of the part at 280C. Same pattern, heat/freeze, it
works, ambient temperature - fail. So we didn't even manage to kill the
part for good.
* we change the component, bingo, it works in 90% of the cases
I am sure the soldering is OK and the joints are properly formed, but
don't have a solid proof, for some people BGA soldering is still the
cause of all problems.
My question is: if it's not the soldering, what else can it be? Can an
electronic design be borderline so that it does not work with the first
time reflowed BGA, but works right after replacing the part with parts
from the same tray? Can something be in the design of the PCB, in the
manufacturing of the PCB?
And a last one, what is the test that can confirm the absence of open
joints under a BGA? Can the balls be cross-sectioned parallell with the
PCB, like half-ball, so an eventual open be redily spotted?
Thanks,
Ioan
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