Hi,
Sounds like you have cracked joints on your bga.s.
This can happen if you reflow the bga side then wave solder the bottom side.
Try a board with thermocouples under the bga when it goes over the wave, you
will probably frighten yourself. The formally good bga joints can reach 180
to 200 Celsius which is enough to disturb the joints as the board flexes
with heat, but not enough to reflow them back into a consolidated joint.
If this is the case, go double sided reflow.
If it isn't, check your reflow conditions.
You cannot see these cracks with a standard transmission X ray equipment
because they are very narrow, which is why slight finger pressure will cause
the component to start working again.
It had me going when I first saw it, I thought it was an aerial effect.
Hope this helps
Regards
Eric Dawson
> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: Thursday, January 24, 2002 12:26 PM
> To: [log in to unmask]
> Subject: [TN] VERY INTERESTING, TO ME, BGA/CSP STUFF
>
> Folks,
>
> First a finding of interest to be sharred (one or two r's, never get this
> right - and I'm writing a book!) with all BGA/CSP officianados (haven't a
> clue how to spell that). Witnessed the strangest electronic packaging
> thing
> ever in my young and tender life the other day.
>
> A small, but very much on the rise non-manufacturing oriented telecom
> company (how about that for irony in these times), with whom I'm currently
> consulting, demonstrated a new way to assure circuit continuity. Boards
> are
> suspect and assemblies don't seem much better (why I'm here). Finger
> pressure on BGA device top and electrons flow and circuit "works." Finger
> gets hot and tired. Engineer uses woodworking "C" clamp to do the finger's
> work. Electrons flow. Just thought few of you could top this story.
>
> I do love this work so.
>
> This brings to mind another request. I have associations with several good
> fab shops. Hope Glynn Shaw is looking in and would like to build some
> quick
> turn 12 layer boards. Don't know a single good PCBA capability wanting to
> do protos and medium volume production assemblies with .8 csp's and a
> couple of FPGA's as one a perimeter and another a full array metal top
> variety (you all know the ones. If anyone knows of this type assembler, in
> the northern Ohio area, please let me know. I am a born again "HARD"
> supplier qualifier, however.
>
> Earl Moon ---- and don't leave home without your c clamps and a little
> wood
> for top and bottom insulators. I think balsa is best. Maybe IPC has this
> covered.
>
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