BGA packages in high vibration environments

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Hi

Anyone have any experience of BGA's (especially fine pitch types) in high
vibration environments? Is there a more appropriate newsgroup for this
topic?

TIA

Geoff



Re: BGA packages in high vibration environments
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I'm not having experience.
The pcb must not flex due to vibrations.
Given the high number of balls in relation to the
tiny mass of the chip above, I'd worry about other
more massive components first.
How many g's at what frequencies were you thinking at ?

Rene
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Re: BGA packages in high vibration environments
163942.news.uni-berlin.de:

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A fellow that designs testing equipment to be attached on rotating machine
elements told me that he cannot use BGA. They tend to fall off, so he
prefers SQFP. He thinks that the long pins of LQFPs reduce the forces on the
solder by their flexibility.

cheers
Gunther

Re: BGA packages in high vibration environments
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Couple of choices- try to get CGA instead of BGA- the additional solder of
the column might save the day while not increasing the footprint, or get a
BGA-PGA (or appropriate form factor) adaptor and make sure tha the adaptor
card has exactly the same coeffiecient of expansion (or as close as is
reasonably possible) to your BGA to ad least minimize the thermal
stresses that accelerate stress fractures.


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Re: BGA packages in high vibration environments
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I wonder why a simple mechanical fixture wouldn't be enough to solve
that problem.  I.e. if you want to prevent a thing from falling off,
why not just nail/screw/press it into position?  If all else fails,
you can still flood the PCB casing with epoxy, turning it into a
virtually indestructable blcok.

As to that rotating gear, that should be even simpler to fix: make
sure the BGA chip is mounted on the *inner* side of the PCB, seen from
the rotation axis, so the centrifugal pseudo-forces press it into
place instead of trying to rip it off.
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Re: BGA packages in high vibration environments
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The BGA is flat, not curved to match the orbit it's following. So the
force is unevenly applied along the length of the chip, meaning that
it's constantly being flexed (to try and conform to its orbit,
basically) when the device is in motion. It relaxes as the device
slows down and tenses as the device speeds up. It seems easy to
understand why the joints are failing, especially when you consider
that the BGA is laid down on a substrate of relatively flexible
fiberglass PCB (to match thermal expansion coefficient of the PCB on
which it lives) and the solder balls are quite fragile.

The QFPs are by comparison rigid bodies that don't change size/shape
as much when the same uneven force is applied. And any change in shape
is more readily absorbed by the springy wires that tie it down to the
PCB. Think of the leverage exerted on the QFP's solder fillet by the
package changing shape; the force is concentrated in a tiny area of
flexible wire which fights a relatively large, solid bond area.
Compare to the force exerted on a solder ball being subjected to
shear. The wire can bend; the solder ball won't do so as readily.

As an experiment, take any PCB containing a QFP and a BGA, and clamp
it down firmly. Grasp the chip package and apply enough force to move
it 0.5mm along any vector parallel to the board. The QFP will survive,
albeit with bent leads. The BGA will take a lot more force to move,
but once you do move it, it will fail.

Potting would probably help, true.

Re: BGA packages in high vibration environments
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It strongly depends from your vibration requirements.

I currently use electronic boards installed into railway equipments which use
BGA components, and they are conforme to the European Union railway equipment
manifacturing specification

Regards

/Alessandro

Re: BGA packages in high vibration environments
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Hi Alessandro,
are there any specifications on the vibration ?
Frequency, amplitude, pattern ?
Perhaps a defined testing procedure ?


Rene
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& commercial newsgroups - http://www.talkto.net


Re: BGA packages in high vibration environments
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This thread might do well in comp.arch.fpga.  There are several FAEs
there who love digging into just this sort of issue.  

I have crossposted there.  

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Re: BGA packages in high vibration environments
Xpost 2 cae and caf, no Fup.

Hallo,

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Actually that's a very hot topic as BGA seems to get usual in the
world of FPGAs and ASICs. I know that our mechanical engineers
allready research on this topic, as we are very likely to have some
fine pitch BGA in a high vibration environment in future.
I would guess, that you should ask in some mechanical newsgroups as
well.
A big problem using FBGA is the test, wether you connected all balls
proberly [1], as you have no chance of easy visual inspection.

bye Thomas

[1] in a mechanical aspect. Of course you get a quick answer if one IO
has no electrical connection.

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Re: BGA packages in high vibration environments
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I recently saw a product that allows visual inspection of the solder
balls on a mounted BGA.  It is a fiber optic microscope and has tiny
fiber probes that can run between the balls.  I'll look for the info if
anyone is interested.  

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Re: BGA packages in high vibration environments
In newsgroup: comp.arch.fpga
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A lot of people seem to do X-ray inspection, which I guess could be
considered "visual" in some way.

    -hpa
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Re: BGA packages in high vibration environments
Rick,

I'd certainly be interested in more info on the fiber microscope you
mentioned.  Debugging designs with lots of big BGAs is tough enough without
wondering whether it's an assembly issue or not, and traditional xray
techniques are good for showing shorts, but no so good for opens ...

-----
Ron Huizen
BittWare

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high



Re: BGA packages in high vibration environments

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There's also JTAG tools that can read and write arbitrary values to
I/O pins.  Roughly $1K for benchtop systems, $10K for a production
tester.  If the BGA is hooked to other chips with JTAG, you can make
a rather complete test.

And of course there's traditional bed-of-nails, not used much due to
cost of implementing on proto hardware.

Dave Kinsell



Re: BGA packages in high vibration environments
Sorry I did not get back to you sooner.  The original contact was ASG at
www.asg-jergens.com.  They make the IS-1000 which gets under the BGA
from what I can see.  So you can see each and every ball.  But you
should get a demo since the sales pictures don't clearly indicate if
they are looking at the edge row of balls or an inner row.  

With a google search I found this - http://www.caltexsci.com /
They seem to make a similar product, but the web page is not too clear
if they are just looking at it from the outside.  


Ron Huizen wrote:
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Rick "rickman" Collins

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