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PICList Thread
'PIC project with lots of vibration -Cordwood'
1999\09\28@132325 by William K. Borsum

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At 12:23 AM 9/28/99 -0700, you wrote:
>>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???

Back in the Gud Olde Days when I was doing packaging for the LEM/Appolo,
surface mount was unknown--everything was through hole.  So the technique
for very dense packaging was to stack components between two PCB's.
Resistors, for example, would be bundled together with the lead from one
end going to one PCB, and the lead from the other end going to the other
PCB.  Hence the term stacked like "cordwood".

For those yungin's among you that have never chopped and stacked firewood,
cordwood also refers to a pile of wood stacked with all the pieces parallel
to form the densest possible mass.  As I recall, a stack 4 x 4 x 8 feet was
a cord.

With SMT, cordwood usually implies stacking board via hard soldered
pins--usually along the edges--but sometimes scattered.

Cordwood for through-hole parts was inherently non-repairable, so the
modules were kept small, and a set of leads was kept to plug into another
"carrier" PCB.  A typical module might be a three transistor
instrumentation amplifier with 6 resistors and some bypass capacitors.  I
guess you might think of it as the precursor to the "integrated circuit."

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@134502 by Wagner Lipnharski

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"William K. Borsum" wrote:
[snip]
> Back in the Gud Olde Days when I was doing packaging for the LEM/Appolo,
> surface mount was unknown--everything was through hole.  So the technique
> for very dense packaging was to stack components between two PCB's.
> Resistors, for example, would be bundled together with the lead from one
> end going to one PCB, and the lead from the other end going to the other
> PCB.  Hence the term stacked like "cordwood".
[snip]
> Cordwood for through-hole parts was inherently non-repairable, so the
> modules were kept small, and a set of leads was kept to plug into another
> "carrier" PCB.  A typical module might be a three transistor
> instrumentation amplifier with 6 resistors and some bypass capacitors.  I
> guess you might think of it as the precursor to the "integrated circuit."

I fixed some oldies IBM machines that used tubes (yes, oldies), so it
was this package with the tube, socket, all required resistors and
capacitors below the tube, the way you described (two small round
boards, components in between), everything packed with a metal shield at
the top and a handler, a connector at the bottom that goes to somekind
of "mother board". You should exchange the package at once when
repairing.  You are right, it was very solid construction, even with the
glass tube in between.

SMT components for high vibration requires as a tick PCB, if not, they
just pop out easily. Just grab a regular pcb with SMT components and
bend the board several times back and forth, and prepare yourself to
catch few small components at the floor.  :)

Wagner

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