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'PIC project with lots of vibration - Best Sockets?'
1999\09\27@200613 by Mark Willis

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Have a shaking application, where the PIC chip will be mounted on a
piece of machinery that's vibrating.  A lot.  And am talking to someone
making a rocket telemetry unit in future using a PIC chip.

I'd sort of LIKE to socket this PIC chip, past experience (sumo robots
etc.) has been that IC's tend to do spurious resets from short Vcc
dropouts, etc. as the socket connectors bounce away from the IC pins,
when these robots collide.  I suggested soldering the MOT cpu in for
this particular app., seems my advice was good =)

Anyone here know what type of sockets are best for vibration-type
environments?  In future I'll be doing TOO much shaking applications,
some rocketry telemetry (I hope!) included.  I'd think an Augat would be
pretty good (multi-prong machined pin socket.)  I've thought of using a
ZIF socket, even though expensive they're pretty solidly contacted.  Or
is solder just THE best here?  (With /JW parts, versus flash parts,
things have changed to where soldering is not as bad of a pain as it
once was, with ICSP being available!)  Nice to avoid soldering if I can,
though.

One cheat for when you know there'll be socket drop-outs or power
faults:  Hard solder a cap or two across the uController, and perhaps do
the same for your pull-up resistor for !MClr - that tends to reduce
problems.  (But: it's a pain!)

 Mark

1999\09\27@224447 by Wagner Lipnharski

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Mark Willis wrote:
{Quote hidden}

Mark, I had some experience with electronics in Racing Car environment.
Just to you have an idea about vibration, some drivers need to replace
their dental fillings quite often (specially when they hit the wall...
hehe).

There are two ways to protect electronics: a) create a cushion system
for each sensible component, or b) tied as firmly as possible that
component to the pcb.  It sounds crazy, but sometimes cushion means
broken leads, some components just got ripped of from the board. It is
not difficult to find out some DIP 14 chips with two or more broken
legs, not even talking about circuit board thin tracks just cracked or
floating in the air. Missing smt resistors and capacitors is not rare.

The best thing to do is find out the vibration frequency and look for
the best cushion system for that particular frequency.  A complete
different cushion is required for a V-8 or V-12 cylinders engine racing
car.

A tick resin covering all components (epoxy or araldite) is what you can
find in some surplus boards, clearly sold somehow from military crafts.
Forget about maintenance.

Circuit board and tracks should be as tick as possible, sometimes with a
metallic frame to keep it straight.

If you really need sockets, the machined golden ones with an extra chip
holding clip would be a must. I would go for Flash devices that can be
on board programmable, avoiding sockets at any cost.

Use several small power capacitors around the board instead single big
one.

Silicon glue all crystals parallel to the board, with "S" leads shape to
avoid problems.

Just to have an idea what it is, just drop 10 ice cubes into the blender
and turn it on at max speed, imagine your circuit right there, close to
the blades, and think about which part will break first.

It is a complete new world.

1999\09\27@225333 by William K. Borsum

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At 01:20 PM 9/27/99 -0700, you wrote:
>Have a shaking application, where the PIC chip will be mounted on a
>piece of machinery that's vibrating.  A lot.  And am talking to someone
>making a rocket telemetry unit in future using a PIC chip.
biiig snip

Got three Pics plus sRAM and ADC and signal conditioning with four
accelerometers, three strain gages, and a rate sensor in two cubic inches,
three pcb's in cord wood packaging, surviving 500 G impacts.  NOT socketed!
All SMT and firmly soldered in place.

Trick is to dip first into GE-RTV silicone rubber (real watery, clear, self
releasing two part stuff) to provide an easily removable conformal coating.
Let it cure, then pot with a urethane or epoxy filled with micro-balloons
(syntactic foam filler) for strength and light weight.

Whole package is pretty much indestructible--and can still be taken apart
for repair or failure analysis.

kelly


William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<spam_OUTborsumTakeThisOuTspamdascor.com> & <http://www.dascor.com>San Diego, California, USA

1999\09\28@032209 by Anne Ogborn

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Best in a vibrating environment is solder, no connectors at all.
SMT components actually survive better, according to my SMT book.

1999\09\28@032622 by Anne Ogborn

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>Got three Pics plus sRAM and ADC and signal conditioning with four
>accelerometers, three strain gages, and a rate sensor in two cubic inches,
>three pcb's in cord wood packaging, surviving 500 G impacts.  NOT socketed!
> All SMT and firmly soldered in place.
>
What's cord wood packaging???

>

1999\09\28@035353 by Michael Rigby-Jones

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I used to work for a company that made train mounted equipment.  It involved
two fully duplicated systems, with several micros, dsp's and a whole load of
firmware.  Firmware updates were fairly frequent during the development
phase so socketed eproms were needed.  We soldered the eproms into turned
pin DIL headers (the type with the solder buckets) and these were plugged
into turned pin DIL sockets (all gold plated type).  There was enough room
under the socket to fit a small nylon tie wrap which held the whole
assembley pretty secure.  We had no problems, but the resulting arrangement
could hardly be called "low profile"

Regards

Mike Rigby-Jones



> {Original Message removed}

1999\09\28@102548 by Matt Bennett

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At 02:20 AM 9/28/99 , Anne Ogborn wrote:
>Best in a vibrating environment is solder, no connectors at all.
>SMT components actually survive better, according to my SMT book.

SMT components are better because they tend to be smaller than
the same part in a DIP, and therefore less mass.  F=MA, if you can't
reduce the acceleration, reduce the mass.  Through holes also reduce
the integrity of the PC board.

SMT is pretty much the only way to go for *high* G designs.  I've had
an off the shelf 16C71 (SMT) survive a 15,000 G acceleration easily.
(It was shot out of a 155mm howitzer with a max zone charge.)

Matt Bennett

1999\09\28@132329 by William K. Borsum

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At 08:52 AM 9/28/99 +0100, you wrote:
>I used to work for a company that made train mounted equipment.  It involved
>two fully duplicated systems, with several micros, dsp's and a whole load of
>firmware.  Firmware updates were fairly frequent during the development
>phase so socketed eproms were needed.  We soldered the eproms into turned
>pin DIL headers (the type with the solder buckets) and these were plugged
>into turned pin DIL sockets (all gold plated type).  There was enough room
>under the socket to fit a small nylon tie wrap which held the whole
>assembley pretty secure.  We had no problems, but the resulting arrangement
>could hardly be called "low profile"

Had another thought on this subject....
It used to be possible to buy just the machined fingers from standard
sockets. The holes in the PCB were held to fairly tight tolerances and the
fingers were press-fit directly into the holes.  Thus, the PCB itself
became the socket. Once all the debug and burn-in was complete--with the
socketed parts easily replaceable--the board was wave soldered.

Kelly


William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<.....borsumKILLspamspam@spam@dascor.com> & <http://www.dascor.com>San Diego, California, USA

1999\09\28@135124 by Wagner Lipnharski

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> Had another thought on this subject....
> It used to be possible to buy just the machined fingers from standard
> sockets. The holes in the PCB were held to fairly tight tolerances and the
> fingers were press-fit directly into the holes.  Thus, the PCB itself
> became the socket. Once all the debug and burn-in was complete--with the
> socketed parts easily replaceable--the board was wave soldered.
>
> Kelly

Do you know that exist that kind of sockets to be attached directly to
the pcb holes?
Yes, even that it allows a low profile pcb, they are expensive. For sure
you can destroy some machined sockets and use just the "fingers" to do
it, but the main gain here is the low profile. The problem with the
socket connection for high vibration is between the "finger" and the
component lead (mechanical stress), not between the "finger" and the
soldered PCB hole.

Wagner

1999\09\28@135932 by Andy Kunz

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>Had another thought on this subject....
>It used to be possible to buy just the machined fingers from standard
>sockets. The holes in the PCB were held to fairly tight tolerances and the

Yes, this is still possible.  You can get them from MilMax.  My contact for
them is Mike Rosen mrosenspamKILLspamhome.com

Andy

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1999\09\28@212312 by William K. Borsum

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I recall that the trade name we used years ago was "holetite" but wouldn't
swear to it.  Any of the major manufacturer should be able to supply them
eg AMP, Samtec, etc.  I know I saw them in a catalog that crossed my desk
in just the last couple of months.  Darned if I can recall whose it was
though--not one of the majors--but someone like MilMax or Samtec.

Fingers are indeed the problem when vibration exists.  There were a few
tricks to the holtites I can pass on if it becomes of serious interest.
kelly




At 01:34 PM 9/28/99 -0400, you wrote:
{Quote hidden}

William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<borsumspamspam_OUTdascor.com> & <http://www.dascor.com>San Diego, California, USA

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