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BillWM
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Freelancer
Re: A Horripilation of Ball Grid Arrays
BillWM   9/26/2013 5:01:32 PM
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The PQFP and similar packages are better for this but still have limits to the thermal cycling issue -- This can be partly addressed with underfills for All the different types of packages -- When thinking of the ROHS aspects to the underfill -- remember that half as many boards will need to be built -- providing a much bigger impact in this Aspect of Underfill vs No Underfill -- also not using the corner three balls enhances life by at least a factor of two -- with underfill and no corner BGA ball use one can get 5-10x the life out of a BGA in an aerospace application.

Max The Magnificent
User Rank
Blogger
Re: A Horripilation of Ball Grid Arrays
Max The Magnificent   9/26/2013 4:47:43 PM
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@BillWM: ...(50-80G's)

Ah, much like driving with my mother (LOL)

BillWM
User Rank
Freelancer
Re: A Horripilation of Ball Grid Arrays
BillWM   9/26/2013 4:33:05 PM
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The boards have to pass the shock test in all axis -- the columns will shear in two of the axis without the supporting mount. (50-80G's)

Max The Magnificent
User Rank
Blogger
Re: A Horripilation of Ball Grid Arrays
Max The Magnificent   9/26/2013 4:22:41 PM
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@BillWM: The CGA's often require an IC mount that is around the peripheral of the board for high shock applications.  (Example hard landing with an aircraft)

Is this because the peripherly of the board is better supported, while the center tends to flex more?

(Can't we just ask the pilots to make softer landings? " :-)

BillWM
User Rank
Freelancer
Re: A Horripilation of Ball Grid Arrays
BillWM   9/26/2013 4:19:03 PM
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The CGA's often require an IC mount that is around the peripheral of the device for high shock applications.  (Example hard landing with an aircraft)

Max The Magnificent
User Rank
Blogger
Re: A Horripilation of Ball Grid Arrays
Max The Magnificent   9/26/2013 2:34:42 PM
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@betajet: Aren't there issues with maintaining column stiffness under stress?  :-)

They are formed from a stiffer mix in the middle and a softer (more meltable) mix at the ends. My understanding is that they are very rugged and reliable and are used in things like military applications.

betajet
User Rank
CEO
Re: A Horripilation of Ball Grid Arrays
betajet   9/26/2013 2:18:51 PM
NO RATINGS
I haven't had experience with column grid arrays.  I would think you'd still have the concern that solder doesn't flex as reliably as copper or aluminum.  Aren't there issues with maintaining column stiffness under stress?  :-)

Max The Magnificent
User Rank
Blogger
Re: A Horripilation of Ball Grid Arrays
Max The Magnificent   9/26/2013 10:03:16 AM
NO RATINGS
@betajet: My chief worry is stresses on the balls caused by thermal mis-match between a BGA package and its underlying PC board

Being a string man, I'm going to totally ignore the opertunity to make jokes about stresses on your balls due to thermal management and instead ask if you've had any experiance with column grid arrays (CGAs) in which the solder balls are replaces with solder columns that mitigate against thermal stress (much like wearing looser undergarments :-)

zeeglen
User Rank
Blogger
Re: A Hackery of Software Developers
zeeglen   9/25/2013 7:45:53 PM
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Poking proctological fun at non-engineers:

A promise of politicians

A scourge of salesmen

A loathe of lawyers

A bill of doctors

A menagerie (or zoo) of managers

A butt of bosses

betajet
User Rank
CEO
Re: A Horripilation of Ball Grid Arrays
betajet   9/19/2013 6:46:28 PM
NO RATINGS
FYI: Disadvantages of BGAs.  My chief worry is stresses on the balls caused by thermal mis-match between a BGA package and its underlying PC board.  Those tiny solder balls don't flex like proper metal leads -- they crack.  And who knows whether those mechanical stresses are causing tin whiskers, since that phenomenon is not well understood.  "Oh my ears and whiskers!"

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