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'[EE]: Cheap ruggedization'
2002\03\13@013754 by Nick Veys

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What would be some good, yet inexpensive ways to ruggedize PCBs?  We
want to be able to tolerate water, vibration and moderate impacts.
Without breaking into MILSPEC components of course!  The project I'm
involved in is 100% donation funded, and as a result our budget for
things like this is quite limited, and we like tricky methods that get
the job done. :)

One requirement would be to still have components easily accessible for
replacement or testing.

The areas will be fairly warm, but well within tolerances of "normal"
electronic components.

Ideas?  Get creative I want to hear everything.  Thanks! :)

spam_OUTnickTakeThisOuTspamveys.com | http://www.veys.com/nick

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2002\03\13@034602 by Jinx

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Are you talking about a bare PCB or boxed ?

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2002\03\13@072500 by Claudio Tagliola

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Get an IP66 or higher graded box with corresponding connectors.
Vibration is harder this way, does it have moving parts? Good vibration
protection is casting into some solid resin (used a web translator to
translate 'hars' to english, don't know if resin is the good word :).

It helps to specify what measure of protection you want. Submergable,
water drops, 1G shocks, 10G shocks, or even more? Want to drop it from
an airplane, drive over it with a tank. You quickly get to milspec if
you want that. If not, check farnell or some specialized boxing company,
they almost all have some high IP graded boxes. Costs are < $250 dollars
for a big box with a handfull of connectors. Cheaper is harder, try to
save on connectors needed, smaller boxes. Do some good heating tests for
your hardware before going live.

Other idea's: plastic spray coating directly on the PCB's. But same
here: depends on how reachable the stuff has to be.

Regards,

Claudio

{Original Message removed}

2002\03\13@083318 by Nick Veys

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Boxed.  This is an automotive application, and each board (maybe 2 in 1
box) will have it's own carbon fiber box which should keep the majority
of rain water out.

.....nickKILLspamspam@spam@veys.com | http://www.veys.com/nick

> {Original Message removed}

2002\03\13@083733 by Nick Veys

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> Get an IP66 or higher graded box with corresponding
> connectors. Vibration is harder this way, does it have moving
> parts? Good vibration protection is casting into some solid
> resin (used a web translator to translate 'hars' to english,
> don't know if resin is the good word :).
>
> It helps to specify what measure of protection you want.
> Submergable, water drops, 1G shocks, 10G shocks, or even
> more? Want to drop it from an airplane, drive over it with a
> tank.

It's an automotive application, it doesn't need to survive a crash,
simply tolerate non-stop driving for about a week.  So that involves
vibration and water pretty much.

> You quickly get to milspec if you want that. If not,
> check farnell or some specialized boxing company, they almost
> all have some high IP graded boxes. Costs are < $250 dollars
> for a big box with a handfull of connectors. Cheaper is
> harder, try to save on connectors needed, smaller boxes. Do
> some good heating tests for your hardware before going live.
>
> Other idea's: plastic spray coating directly on the PCB's. But same
> here: depends on how reachable the stuff has to be.

Thought about that but I wonder how easy it would be to remove socketed
ICs and things of that nature.  Not to mention de-soldering something if
need be.

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2002\03\13@084535 by Claudio Tagliola

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Don't. A week's worth of driving is nothing. It's automotive, so I guess
the car has reasonable shocks built in :)

We had a regular 4 layered PCB going over the Atlantic Ocean in a
sailboat. Just an IP67 box and connector's was all the ruggedizing we
did. We could've put the box on deck if we wanted, it was as wet inside
as it was on the outside. It went from the tropical equator heat and
humidity to the freezing North Sea without any problems.

For socketed IC's, our central PIC processor was a 44 pins PLCC housing.
We made an aluminum bottom with solderen on screwholders. The plate was
glued with two-component glue on the bottom of the box. This way, we
could screw out the complete PCB (was a rather large PCB, about 15 x 25
cm).

{Original Message removed}

2002\03\13@085813 by 859-1?Q?Alexandre_Guimar=E3es?=

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Hi,

> Thought about that but I wonder how easy it would be to remove socketed
> ICs and things of that nature.  Not to mention de-soldering something if
> need be.

   I would avoid using sockets as much as possible for an automotive
application. You can use the best sockets ever made and will probably still
have problems. If it really needs to be done and you have no other options
glue the chip to the socket with water soluble silicone rubber. Most
conformal coatings on the market allow reworking quite easilly but you have
to remember that the board has to be free of any flux residues, specially
the no-clean fluxes. Any acids that are trapped inside the coating will
react with the components and traces. Coatings are great but have to be used
with much care. An IP-66 or 67 box is a much easier option.

Best regards,
Alexandre Guimaraes

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2002\03\13@093426 by kent

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I remember there is a company called DEUTCH that makes
automotive boxes with built in plugs for <$10.
Kent

{Quote hidden}

> {Original Message removed}

2002\03\13@100507 by Reginald Neale

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>What would be some good, yet inexpensive ways to ruggedize PCBs?  We
>want to be able to tolerate water, vibration and moderate impacts.
>Without breaking into MILSPEC components of course!  The project I'm
>involved in is 100% donation funded, and as a result our budget for
>things like this is quite limited, and we like tricky methods that get
>the job done. :)
>
>One requirement would be to still have components easily accessible for
>replacement or testing.
>
>The areas will be fairly warm, but well within tolerances of "normal"
>electronic components.


  I have had good experience with Dow-Corning Silicone
  conformal coating applied by dipping. Pay close attention
  to the mfr recommendations for dilution. It does make
  component removal more difficult. But we did thousands of
  boards this way and they weren't as difficult to rework
  as we expected. If you have lots of connectors or other
  areas to be masked off it can be a hassle. Also, as
  someone else mentioned, your boards have to be really
  clean or you're sealing in contaminants.

  In any case this doesn't require a big investment in time
  or money to try.

  Reg

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2002\03\13@111831 by Alan B. Pearce

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>    I would avoid using sockets as much as possible for an automotive
>application. You can use the best sockets ever made and will probably still
>have problems. If it really needs to be done and you have no other options
>glue the chip to the socket with water soluble silicone rubber. Most


The best answer to this is to tie the components down once fitted in the
sockets. Use the old type linen lacing cord as it is very strong. The only
thing to watch is that the cord is secured where it comes through the holes
in the PCB as the fibreglass is very abrasive under vibration. A daub of
silicone rubber or contact cement in the hole to glue down the lacing cord
should do fine.

This is the way it is done on stuff for satellites where large components
have to be tied down to meet vibration testing requirements. You should also
determine the vibration requirements to see what size mass you have to
secure. Small capacitors such as CKR06 size ceramic ones on leads do well to
have a little epoxy to stake them to prevent them shaking under vibration -
this area is an example of a reason to go to SMD components, if for no other
reason.

Other than that if the unit is fitted into a suitably hermetically sealed
box such as the IP66 types should be fine. If the unit is mounted under the
bonnet (hood) of the vehicle then temperature will be your biggest
environmental enemy (as distinct from electrical noise).

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2002\03\13@114737 by Claudio Tagliola

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Use transparent nail polish to secure any non-screwed (heck, even the
screwed ones too) connectors.

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2002\03\13@134334 by Dwayne Reid

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At 12:35 AM 3/13/02 -0600, Nick Veys wrote:
>What would be some good, yet inexpensive ways to ruggedize PCBs?  We
>want to be able to tolerate water, vibration and moderate impacts.
>Without breaking into MILSPEC components of course!  The project I'm
>involved in is 100% donation funded, and as a result our budget for
>things like this is quite limited, and we like tricky methods that get
>the job done. :)

We do this regularly for many of our projects.

1) avoid IC sockets.  Solder the chips directly to the board.  There are
two reasons: the conformal coat gets into the pins and causes bad and/or
intermittent contacts *and* the chips can work their way out of the
sockets.  The pin contamination problem is by far the worst thing you have
to deal with.  Use a flash PIC and include an ICSP connector so that you
can upgrade the code without having to remove the chip.

2) glue or otherwise fasten large components to the board.  All
electrolytic caps should be glued (Plyobond (sp?) or contact cement applied
around the perimeter with a syringe works well and is quick.  The glue you
choose should shrink somewhat upon drying and remain flexible.  Silicone
sealant is NOT a good choice here.  Large power resistors are mechanically
strapped with wire loops.

3) Use a GOOD liquid conformal coating.  The spray stuff just doesn't cut
it for extended periods.  We use two different types from GE and Dow
Corning.  The Dow stuff is by far the better of the two.
Apply the coating by either brushing or dipping.  If you dip, you can also
use a vacuum pump and bell jar to get rid of air pockets (I normally don't
bother).

dwayne


Dwayne Reid   <dwaynerspamKILLspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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2002\03\13@135347 by Pic Dude

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Why specifically transparent?  I use bright red or pink nail-polish
to secure screws behind the dash of my car, non-structural screws,
etc.  This way, its easy to see which ones have nail polish on them.

However, walking into a drug store and purchasing pink nail polish
is another story in itself ...


{Original Message removed}

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