a) Change in Mechanical design and support will able change to the resonant freq. on the TQFP (as mentioned in your email). Best solution in reliability.
b) Stake/Pot the corners of the TQFP (3M 2216, 2 parts material).
Ensure that no coating underneath the TQFP if it is conformal coated.
Is the "open" always in around the same corner? Sometime different types of washer and holding/supporting points might help.
________________________________
From: TechNet on behalf of Inge
Sent: Sat 3/13/2010 6:15 AM
To: [log in to unmask]
Subject: Re: [TN] Vibration issue
Odd idea, ol' biker. Will sleep on your proposal. Don't know if that will
stop leads from resonating. The high speed camera may show.
Anyway, must find a very secure way, because you will fly with that box one
day...top engineering solution needed, no place for amateur trials.
/Inge
--------------------------------------------------
From: "John Burke" <[log in to unmask]>
Sent: den 12 March 2010 13:35
To: "'Inge'" <[log in to unmask]>; <[log in to unmask]>
Subject: RE: [TN] Vibration issue
> 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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