Actually if you have an open via field behind that QFP and open via holes
you could under fill it from the back of the board "as is" with a little
ingenuity - minimal tooling, say a 3/8 inch aluminum "nozzle" on a liquid
dispenser with a circular recess machined into the end face for a 1/4 inch
ID O ring machined to half O ring thickness as the depth - contact the back
of the board in the via field behind the QFP, apply light pressure
referenced to the top of the QFP and apply pressure to the liquid
dispenser...8-)


John Burke
(408) 515 4992


-----Original Message-----
From: John Burke [mailto:[log in to unmask]] 
Sent: Friday, March 12, 2010 1:23 PM
To: 'Inge'; [log in to unmask]
Subject: RE: [TN] Vibration issue

Inge, the mass of the package is probably not helping here. Have you tried
an approach such as using a low height standoff on the part and then
effectively under filling the assembly?


John Burke
(408) 515 4992


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Friday, March 12, 2010 10:48 AM
To: [log in to unmask]
Subject: [TN] Vibration issue

Hi all,
we are making a  very vital part for a aircraft builder. Problem with TQFPs,
some 200 legs. There are resonance peaks that kill the package legs. 
Redesign is not to think of from the customer, so we must do something on
inside of the box.  One solution (not popular) is to use a string of a glue
along the leg rows in order to lock them.  Another is to place a vibration
dampening mat on one side of the board. That one is more tricky , but  there
is a US  company with lots of stuff for that purpose.  Anyone with
experience from this area? I should add that not all legs are broken, just
one or two after 100 hs of random vibration, but that is of course not
acceptable.  BGAs would solve the problem, but there is no time for
redesign.
I'm sorry for coming with a  serious message at this holy time of the week.
Thanks
/Inge 


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