Hi, Peter

Just to clarify - the solder balls remain attached to the board and don't
come away with the component body? I think this is pretty normal if it's
the case. Bear in mind that the (usually Nickel) pads on the component have
been trhough two major thermal excursions, whereas the board will only have
gone through one. If dewetting is going to happen, it will most likely
happen at the component side, through oxidation, intermetallic layer growth
or whatever. Removal profile should not have much of an effect on this,
adnin any case, removal profile should be the same one as the replacement
profile. Replacement is more important than removal.

Just make sure that the BGA site is properly cleaned of solder and flux
residues before putting the new component down. I have had a lot of flux
left inside via holes in the past, that could not be seen once the new
component was in place. It can take some time and patience to clean the
area thoroughly, so make sure your operators are coscientious about it.

Boards should be pre-baked prior to BGA removal to avoid risk of popcorning
components. This is especially of concern if the rework station bottom
heater heats the entire board and not just the BGA area.

Can I ask, what is destructive X-Ray testing?

Peter



Peter Lee <[log in to unmask]>  18/09/2002 08:23 AM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to Peter Lee

              To:  [log in to unmask]
              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
              Subject: [TN] BGA failure and Rework








Technet,

If I may continue my question on BGA rework process:

Recently we have seen intermitted failures from a few BGA assemblies.
After removing the suspicious BGA on the rework station we noticed
dewetting on a majority number of pads of the removed BGA. The solder
ball residues were mostly attaching to the board.

Has anyone seen this before? How likely can this be caused by a
non-optimum rework removal profile Is baking of the board normal prior
to rework (removal/re-placement)?

We are tackling this issue from the part supplier side and looking at
performing destructive X-ray analysis. Can someone give me an idea of
what the ball attachment process is on the BGA?

Rgds,
Peter

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