Does anyone know how many g's (acceleration) a typical circuit board
(surface mount if it matters) can withstand?
Recently, a rep from the U.S. Military purchased a few of my MAVRIC boards
and mentioned that they will be used for the IMU (inertial measurement
unit) on a CKEM (compact kinetic energy missile). Apparently these
missiles go from 0 to Mach 6 in just a few thousand meters.
I suspect they will be using my boards to prototype their software while
they are in the process of developing their own custom boards to actually
reside on the missiles themselves. But they did ask how many g's my
boards could withstand. I don't have a clue - any ideas?
There are a lot of factors to consider. You'd have to have a lab test it for
find out for sure.
Basically, the heavier an item is the more susceptable it is to G's.
It depends on what they put on your boards, crystals, connectors, large
parts like voltage regulators, capacitors would likely fail before
the surface mount parts. At really high G forces,even the SMT parts would
pull loose from the board, usually pulling traces off the substrate as they
I think it could do 50-100 g's face up, maybe more. But the crystals,
connectors or wires going to the board would likely fail first.
You can get 100's of G's of shock dropping the assembled board flat down
onto a hard surface from 3-5 feet up. Components face down would not be able
to handle as many G's as face up.
Put the board in something streamlined and drop it off a 500 foot tall
building onto the concrete below, that's good for maybe a 1000 g's or so.
Choose a part and somehow attach something to it, clamp the board down, with
a scale attached to the part, steadily pull it away until it lets go. Note
how much pressure/weight/pull was used to pull the part off. You can now
weight the part, compare it to how much it took to pull it off, and
calculate how many G's that would be.
To add to that. Don't forget that "g's" can also be a part of vibration.
If you have vertically mounted components, like TO-220 voltage regulators,
they can be susceptible to really nasty cyclical acceleration forces due to
vibration (going back and forth). This can make solder joints or the legs
On a component-by-component basis you could estimate forces with the simple
F = m x a formula. You need an idea of the mass of each product. The, of
course, there's the mounting of the board itself. The board could flex due
to inertial forces and traces/components crack.
If needed you could build an exo-support mechanism (plates that go on top
and bottom of the board to keep components from flying off or getting
over-stressed. Also, using epoxy lines under components and conformal
coating will add robustness to the overall assembly. Small SMT ceramic
components can be suceptible to cracking if the board underneath flexes
Want a cheap (but brutal) test? Zip-tie one of your boards to the
suspension (not the body) in your car. The sway bar or one of the A-arms
might be good. If you don't have an idea of how to do this safely (for both
you, the car and anyone else on the road) don't attempt it, you can get
killed or seriously hurt someone else. But, if you know how to do it, go
for a ride and see if your board works afterwards. I've done this in the
past, it's amazing what vibration can do to a board. Do this at your own
risk. I accept no liability for anything that may happen. It is very
Lot's to think about.
Sort of an extension of that question about using hobby servos in UAV's in
that a lot of the same criteria is applicable.
Well, I just did some quick calculations, and unless I made a mistake, I'm
guestimating the acceleration to be around 150 g's. This is assuming that
the missile starts off at zero velocity and undergoes constant accleration
for 5000 meters, at which time it's velocity is Mach 6, or 3846 m/s. I
came up with 2.6 seconds to travel the 5000 meters, which makes the
formula for acceleration:
v = a * t
a = 3846 / 2.6 = 1479 m/s^2 ~= 150 g's (1 g being 9.8 m/s^2)
That's probably OK for a ballpark working figure. Of course, I have no
details on the actual performance of these things - what little I can find
on the web is pretty vague. But I suppose if I really knew, I most likely
wouldn't be allowed to talk about it anyway :-)
I suppose a board could be encased in an epoxy to keep all the parts in
place, assuming the epoxy can withstand the stresses. But aside from
physical and structural integrity at high g, what about the actual
performance of the electronic components themselves? G-force is not
something I'm used to seeing in the spec sheets for electronics
components' "absolute maxiumum ratings" sections. Seems like capacitors
could distort which could change their behaviour. Crystals may run slower
(or faster) under high g. What else?
Maybe it's time for a little destructive testing :-)
Pot the boards in epoxy or silicone.
General electric makes silicones for this sort of thing, although I suspect
that epoxy would be more suitable. < I suppose this would make your nifty
screw terminals sort of problematic ;^) >
Hang on a mo'
before you start potting anything, if it is only 150 g's then the board is
probably fine. A 40 pin dip weighs around 5 gms, so at 150 g's 750 gms,
it'll take more than that to rip it off.
smt is lighter even if not quite so firmly attached.
I think I agree that the crystal is probably the weakest link, so why not
just dump the problem on your crystal supplier? Crystal suppliers usually
want you to consider g forces when mounting their parts, just in case some
one drops it. They should know.
Maybe you could specify the board is mounted at right angles to the major
accelerations or whatever looks most comfortable for it. Try resting 150
times the boards weight on the middle of it, stuff like that.
Robin G Hewitt
You could possibly get hold of a high speed motor from somewhere, attach a
balanced arm to it, and use it as a crude centrifuge to test a board to
destruction - the calculations for centripetal acceleration shouldn't be too
Just a thought.
I'm an electrical engineer in our (large electronics company)
government systems group. Our PLC equipment is very similar to your
MAVRIC board. We build control systems in electrical panels that have
to pass MIL-S-901D (shock) and MIL-STD-167-1 (vibration). Your board
will probably have to pass the same test as part of electrical control
Our boards are rated at 30 g operating. Looking at the MAVRIC board,
it will probably withstand 30 g. The only concern I would have is the
heat sink to the right of the "MAVRIC" label.
There are 2 ways that the military mounts control systems - hard mount
and using shock isolators. Either way, they will have to fashion a
clamp for the header pin connector. That's the weak point of the whole
system. Given the header pin connector, your board will easily pass
"shock & vib" using shock isolators and will probably also pass
I you want to test your board, I suggest contacting Wyle Laboratories.
That's who we use for shock & vib testing.
While conformal coating like epoxy can help increase the maximum
g-load on your electronics board, it is expensive and can also produce
heat problems. Conformal coating is a last resort unless corosion
resistance is required.
Actually, it's a new world now - COTS (Commercial Off The Shelf). The
military strives to use COTS components from commercial companies to
save money. No security clearances are required for COTS work
(although U.S. citizenship is usually a requirement).
You are certainly correct about bonding and insurance, though. It's
all about contract terms & conditions.
This isn't the whole picture. You cannot ignore vibration, harmonics,
resonance, etc. Particularly in something like a missile. Making a board
that can endure high, constant, single-axis acceleration is almost a trivial
excercise in engineering. The challenge is making something that can deal
with real world realities which include acceleration, shock, harmonics,
resonance and even metal fatigue.
Interestingly enough these are some of the same issues in making
earthquake-safe buildings. Ground acceleration isn't necessarily what
destroys a building. Shock and vibration along x,y,z (both translational
and rotational) can have devastating effects on a structure that would
otherwise endure substantial single-axis acceleration.
An interesting little experiment is to take a flexible metal ruler and clamp
it to a desk:
Now, strike various points on the desk with your fist and observe what
happens at the far end of the ruler. The tip will begin to oscillate. If
the strikes were periodic and at the right frequency you could cause
resonance, leading to potential fatigue and severe acceleration loads. You
can change the setup and clamp the ruler to the edge of the desk
(vertically) and see what that does.
Electronic components and boards are suceptible to this sort of a mechanism,
which is a lot more complex than single-axis acceleration. Certainly a
missile taking off is not a nice-clean single-axis acceleration environment.
Well, like I mentioned, I'm thinking they are actually using my boards as
rapid prototype boards so that they can develop the software for reading
and processing their sensor data, etc. I do believe that they will make
their own custom boards to their stringent MIL specs.
Actually, a number of my customers have used by boards in this way -
they'll pick up a couple of my boards for early development, which saves
time in the software development phase since they have a platform to work
from while testing out code, etc, and in the meantime they may be
developing their own custom boards for higher production quantities, or
to fit their own unique enclosure, etc.
Nope, just a few ... for now :-)
I was speaking mainly about Brian becoming a defense contractor
providing MIL spec versions of his board. They'd require strict MIL
specs for anything on-board a missle, because of the hypercritical
nature of the components. And because it's avionics, secrecy is usually
the order of the day -- if an enemy knows the system (because it's
commercially available), it's easier to figure out ways to jam it.
I sell to the gobment, including the military. I happen to have a
security clearance, but not for robotics (contract document automation
programming, for the IRS actually). Somehow I don't think the little
robot kits they've purchased from me have been for use in Tomahawks!
Robots for Less at Budget Robotics:
Lots of great info - thanks! You mention the "heat sink" to the right of
the MAVRIC label - that's actually a button-cell battery holder for the
battery backed real time clock which backs up the Dallas DS1307 I2C RTC.
I suspect it could actually just be removed for this application.
Thanks for the info! Lots to think about.
Does anyone else here get that depressing feeling of wasted effort when they
think about the obscene amounts of expensive components and precision
engineering that go into making things that are ultimately designed to
destroy themselves, and other expensive things and people in the process?
Yes. When you challenge the designers and manufacturers
of such equipment that it results in children having their arms
blown off and/or left to die horribly having been given first
degree burns over most of their body you meet a callous
reaction that makes Saddam Hussein seem to be an
If there could have been any good come of the attack
on the World Trade centre, it would have been the shock
and horror that results from realising the effects of weaponry upon
our fellow humans; the reaction of Yankland, however, was to
some extent to justify the attack that was made on them.
Ever since Gog realized that throwing a heavy stone meant he didn't need
to get within reach of Magog to plonk him, destruction at a distance has
been part of the human toolkit. There's no way to opt out.
Improved precision at least more closely couples intent with result. Not
having access to precise targeting/aiming technology just means that
more ordnance is dispersed over a wider area in order to achieve the
If they immerse it in a non conductive oil type liquid, it will withstand
pretty much anything, assuming you do not use components with large voids..
PS: Sorry about the top post, but I am responding to the SUBJECT LINE.
That's a good point - nothing seems to advance technology faster than the
military (though I think the computer game industry gave them some tough
competition for a while!). Watched a big documentary series about a year
ago, and it mentioned the fact that, without the technology for boring gun
barrels developed centuries earlier, they would never have been able to
build the cylinders for the steam engines that powered the Industrial