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'[EE]: smt vs thru hole - vibration prone enviromen'
2007\09\24@170031 by alan smith

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Have a board where I need to spin it, client indicated he wants to stick to thru hole technology because its mounted on a device that is prone to vibration.  Anyone have experience of SMT in a similar application?  Its not like a shake table, maybe more of automotive.  Im thinking that if its conformal coated, that should take care of keeping smt parts where they belong?

     
---------------------------------
Don't let your dream ride pass you by.    Make it a reality with Yahoo! Autos.

2007\09\24@172531 by Mike Hord

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I've been party to several boards passing through pretty
extreme shake testing- HALT tests including +/-50g
vibration for many minutes with pretty extreme (200C)
temperature shifts.

I've only seen two types of components become a
problem: tall surface mount electrolytic can caps and
tall surface mount wire-wound ferrite core inductors.

In both cases we began putting epoxy under the part
before soldering and the part stayed firmly in place
thereafter.  For smaller chip components and ICs, no
problems.

Mike H.

On 9/24/07, alan smith <spam_OUTmicro_eng2TakeThisOuTspamyahoo.com> wrote:
> Have a board where I need to spin it, client indicated he wants to stick to thru hole technology because its mounted on a device that is prone to vibration.  Anyone have experience of SMT in a similar application?  Its not like a shake table, maybe more of automotive.  Im thinking that if its conformal coated, that should take care of keeping smt parts where they belong?
>
>
> ---------------------------------
> Don't let your dream ride pass you by.    Make it a reality with Yahoo! Autos.
> -

2007\09\24@175222 by Matt Pobursky

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face
On Mon, 24 Sep 2007 14:00:28 -0700 (PDT), alan smith wrote:
> Have a board where I need to spin it, client indicated he wants to stick
> to thru hole technology because its mounted on a device that is prone to
> vibration.  Anyone have experience of SMT in a similar application?  Its
> not like a shake table, maybe more of automotive.  Im thinking that if
> its conformal coated, that should take care of keeping smt parts where
> they belong?

One of my larger customers makes ABS Braking Systems for over-the-road
trucks. Virtually all their ABS ECU computers are SMD with the exception of
connectors and they have very few vibration related failures. Most of their
units are potted but some of the other accessories are just conformal
coated. Most of the devices I work on get mounted on truck trailer chassis
and take a good amount of abuse.

We're designing a monitoring device right now that will be retrofitted to
(plugs in series with) existing ABS systems and debating whether it needs
to be potted or can simply be conformal coated. Potting is expensive (as
you probably know) but it does make the electronics package into a brick.
;-)

Through hole is bad mojo unless you pot the unit. Conformal coating doesn't
help much with vibration control/resistance either. Thankfully, I've left
almost all through hole design in my rear view mirror several years ago. I
much prefer SMD for pretty much anything it can be used for.

Matt Pobursky
Maximum Performance Systems

2007\09\24@175609 by alan smith

picon face
Sorta what I thought.  Seems tall cans are prone to just being bumped as well, and pop'ed off.

Mike Hord <.....mike.hordKILLspamspam@spam@gmail.com> wrote: I've been party to several boards passing through pretty
extreme shake testing- HALT tests including +/-50g
vibration for many minutes with pretty extreme (200C)
temperature shifts.

I've only seen two types of components become a
problem: tall surface mount electrolytic can caps and
tall surface mount wire-wound ferrite core inductors.

In both cases we began putting epoxy under the part
before soldering and the part stayed firmly in place
thereafter.  For smaller chip components and ICs, no
problems.

Mike H.

On 9/24/07, alan smith  wrote:
> Have a board where I need to spin it, client indicated he wants to stick to thru hole technology because its mounted on a device that is prone to vibration.  Anyone have experience of SMT in a similar application?  Its not like a shake table, maybe more of automotive.  Im thinking that if its conformal coated, that should take care of keeping smt parts where they belong?
>
>
> ---------------------------------
> Don't let your dream ride pass you by.    Make it a reality with Yahoo! Autos.
> -

2007\09\24@183640 by Bob Axtell

face picon face
alan smith wrote:
> Have a board where I need to spin it, client indicated he wants to stick to thru hole technology because its mounted on a device that is prone to vibration.  Anyone have experience of SMT in a similar application?  Its not like a shake table, maybe more of automotive.  Im thinking that if its conformal coated, that should take care of keeping smt parts where they belong?
>  
Personally, I hate generalities, but GENERALLY SPEAKING (see? I already
screwed up) SMT devices are better for vibration-prone environments, no
question about it. The exception are connectors. Connectors need to be
thru-hole, because a 60mil by 60mil pad will NOT support a vibrated
connector. Even those tiny cute 2mm connectors hold up better if thruhole.

The primary reason devices work better as SMT is that the mass is MUCH
smaller.

--Bob A

2007\09\25@032739 by Ruben Jönsson

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> Personally, I hate generalities, but GENERALLY SPEAKING (see? I already
> screwed up) SMT devices are better for vibration-prone environments, no
> question about it. The exception are connectors. Connectors need to be
> thru-hole, because a 60mil by 60mil pad will NOT support a vibrated
> connector. Even those tiny cute 2mm connectors hold up better if thruhole.
>
> The primary reason devices work better as SMT is that the mass is MUCH
> smaller.
>

I agree - Generally speaking :-)

However, I have heard that a customer has had severe problems with a certain
type (don't know exactly which) of multilayerd ceramic capacitors, standard
0805 size. The cap was mechanically damaged so one or more of the plates became
disconnected from the ends, causing the capacitance to be reduced a lot (even
to 0 in some cases). This may have been due to the board was flexed under
vibration because of other, heavier compontents on it.

The lesson here is to make sure that the board is secured in a way that it
can't bend from the vibrations. Note that there can be resonance frequencies
that makes the board swing more. This is just like with EMC - some frequencies
are worse than others. Make sure that those frequencies are not a problem, move
them or make sure that the effects at the critical frequency is reduced to a
minimum (also just like EMC).

/Ruben==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
rubenspamKILLspampp.sbbs.se
==============================

2007\09\25@054517 by Morgan Olsson

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Den 2007-09-25 09:27:33 skrev Ruben Jönsson <.....rubenKILLspamspam.....pp.sbbs.se>:

> I have heard that a customer has had severe problems with a certain
> type (don't know exactly which) of multilayerd ceramic capacitors, standard
> 0805 size. The cap was mechanically damaged so one or more of the plates became
> disconnected from the ends, causing the capacitance to be reduced a lot (even
> to 0 in some cases). This may have been due to the board was flexed under
> vibration because of other, heavier compontents on it.

I have seen somewhere (farnell?) a ceramic SMT capacitor range being marketed as having flexible termination or some similar wording.


--
Morgan Olsson

2007\09\25@061046 by Tamas Rudnai

face picon face
Hi,

Does anybody have an experience with a box filled up with epoxy or if there
are some more useful material for the same purpose, so that the circuit
become more resistant to vibration and also makes it water proof?

Thanks
Tamas



On 9/25/07, Morgan Olsson <EraseMEost011spam_OUTspamTakeThisOuTosterlen.tv> wrote:
{Quote hidden}

>

2007\09\25@064050 by wouter van ooijen

face picon face
> Does anybody have an experience with a box filled up with
> epoxy or if there are some more useful material for the same
> purpose, so that the circuit become more resistant to
> vibration and also makes it water proof?

Non experience, but I would have my doubts. In my university days two
fellow students who did mechanics had opposite ideas of making something
robust: one would make things heavy and rigid, the other favoured light
and flexible. Your idea seems to much heavy and rigid to me.

Imagine what would happen if (part of) the expoxy would not stick well
to the PCB (and maybe to the components) and starts vibrating a little
bit different from the PCB. Your components would be much better of
without that expoxy rubbing them off the PCB!

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu



2007\09\25@064211 by Alan B. Pearce

face picon face
>> I have heard that a customer has had severe problems with a certain
>> type (don't know exactly which) of multilayerd ceramic capacitors,
>> standard 0805 size. The cap was mechanically damaged so one or more
>> of the plates became disconnected from the ends, causing the
>> capacitance to be reduced a lot (even to 0 in some cases). This may
>> have been due to the board was flexed under vibration because of other,
>> heavier compontents on it.

I would class that as bad mechanical design of the PCB mounting, causing
amplification of the vibration magnitude by the Q of the PCB flexure.

> I have seen somewhere (farnell?) a ceramic SMT capacitor range being
> marketed as having flexible termination or some similar wording.

This is probably more to do with stress due to temperature cycling of
assembly. Some PCB materials (such as 'normal' FR4 fibreglass) have quite
high co-efficients of expansion with temperature changes. This really kills
you when using large BGA packages as well as some of the TQFP type packages
which have constrained leads.

We get involved in this problem quite a bit on earth orbit satellites where
in an hour you go from heating due to sun radiation to cooling on the dark
side of the earth. his can give thermal stresses on PCBs that have to be
taken into account.

This is on top of the vibration test that the instrument has to go through
before delivery. Typically this will consist of a minute at around 9G broad
band 10 Hz to 2kHz (actual spec depends on launch vehicle, and other
satellite construction details) with swept sine passes before and after to
find resonances in the instrument, and see if they change due to the actual
vibe test.

SMD components are specified now despite these strict thermal and vibration
constraints. However a fair amount of work goes into CAD modelling of the
mechanicals to ascertain vibration resonances, and place ribs and mounting
points in a manner that minimises these problems.

2007\09\25@074011 by Tamas Rudnai

face picon face
That's why I'm asking, as I know elastic fixing is good for the mirror on my
car as it will not brake if I hit the gate :-) but it might not as good for
the huge electrolytic cap as Mike mentioned. Maybe if the component is too
huge it worth to fix somewhere else and use some cabling?

Tamas



On 9/25/07, wouter van ooijen <@spam@wouterKILLspamspamvoti.nl> wrote:
{Quote hidden}

> -

2007\09\25@082938 by Alan B. Pearce

face picon face
> I have seen somewhere (farnell?) a ceramic SMT capacitor range being
> marketed as having flexible termination or some similar wording.

Hmm, this weeks copy of Electronics Weekly arrived today, and happens to
have an item about these. The manufacturer is given as Holystone and it is
the Superterm series, 'offering a flexible polymer layer in the termination
structure which can absorb mechanical stress ...'

http://www.holystonecaps.com/


2007\09\25@101110 by Xiaofan Chen

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On 9/25/07, Tamas Rudnai <KILLspamtamas.rudnaiKILLspamspamgmail.com> wrote:
> Does anybody have an experience with a box filled up with epoxy or if there
> are some more useful material for the same purpose, so that the circuit
> become more resistant to vibration and also makes it water proof?
>

Yes in many cases filling will help to achieve a more robust design.
In my previous job, many inductive proximity switch sensors are
filled with various type of resin, including Epoxy. I also designed a
Fieldbus Terminator for Profibus PA and Foundation Fieldbus and
it is also filled with Epoxy.

For waterproof, filling is also a method. Ultrasonic welding is another
method (not easy to fill an photoelectric sensor). But sometimes
temperature cycling will cause the sensor to be swollen if plastic
housing is used.

It is a pain to troubleshoot filled sensors though. Last time my
colleague tried to troubleshoot EMI problem with a filled
vibration fork based level sensor -- painful exercises...

Sometimes filled design is more heavy and may fail shock test.
For example, some PLC I/O modules are sit on a terminal base
and the I/O modules can fly off the terminal base when under
shock test...

Xiaofan

2007\09\25@113543 by Bob Axtell

face picon face
Tamas Rudnai wrote:
> Hi,
>
> Does anybody have an experience with a box filled up with epoxy or if there
> are some more useful material for the same purpose, so that the circuit
> become more resistant to vibration and also makes it water proof?
>
> Thanks
> Tamas
>
>
>  
In the USA a dipped coating is sold for the purpose of coating metal
pliers to make them easier to handle and to
keep them from carrying electricity. I use it to coat tiny PCB's being
used in commercial applications. Works VERY
well, and is very rugged.

--Bob

2007\09\25@115023 by Walter Banks

picon face
I agree with Bob that dip coating is easy works well and is inexpensive.
Only drawback is it is a thermal insulator. Take care for over heated
components.

w..


Bob Axtell wrote:

{Quote hidden}

> -

2007\09\25@131740 by Brooke Clarke

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Hi:

I have what's literally a "Black Box" beacon transmitter probably designed to
be run over by a tank.  Can only speculate on what it was made for.  The PCB is
all surface mount, no coating.  PCB is NOT attached to the machined metal case
but is sandwiched between foam.  See:
http://www.prc68.com/I/BlkBox.shtml

It's my understanding that electronics that gets shot from 155 mm howitzers is
made with SMT since the forces trying to shear the part depend on it's mass and
the the acceleration from the gun.  Smaller mass means less shearing force.

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam

2007\09\25@152903 by Sean Breheny

face picon face
I would like to mention that I've seen problems with thru hole tall
caps, not just SMT tall caps. I've had thru hole ones vibrate until
the leads failed, even when soldered right up against the PCB.
Anything like that would need to be supported at both ends .

Sean


On 9/25/07, Walter Banks <RemoveMEwalterTakeThisOuTspambytecraft.com> wrote:
{Quote hidden}

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