Mail*Link(r) SMTP FWD>DES/FAB/ASSY: Ruggedized PWA's
Jeff,
When we "ruggedize" a product it means we do some things to improve the
product's survivability when subjected to a particular environment. Many
Class 2 products can be "ruggedized" to meet more severe
"industrial/commercial" environments without becoming Class 3 products or
having Class 3 product requirements. Remember, Class 3 products are for
critical applications where failure is not acceptable.
Depending on your customers "ruggedized" requirements, if you have to meet all
environments (shock/vibration, thermal/power cycling, wide ranging
environmental temperature, then you definately will approach a Class 3 like
product. However, many electrical/electronic products are "ruggedized"
without going to Class 3. Think of some of you portable electronic
instruments, industrial controllers and sensors, etc., I suspect many of these
are "ruggedized" Class 2 products.
1) If thermal shock/cycling or power cycling is a concern, then design and
manufacture to minimize the effect on component mountings (solder joints),
that is design compliance (stress relief) into the design.
2) If your product is to be subjected to shock/vibration, design for
shock/vibration, or retrofit shock/vibration reinforcement
stiffeners/dampeners into the product. Better yet, if the product hasn't been
designed (or can be revised) modify the design to "break-up" large spans of
unsupported printed boards.
3) If your product is subjected to a hot/cold environment then thermal
management needs to be evaluated.
As an example, consider "ruggedizing" the very popular personal computer
mother boards. In general they are would not be considered a "ruggedized"
product. But, if all the module plug-in connectors in the mother board were
securely mounted to a mounting frame, and a standoff spacers (screwed type,
not press or slide-in) were located on a grid of about 75-100 mm centers, then
the mother board would become more robust and low frequency resonances would
be eliminated. The plug-in boards are a problem, so you would need to design
a "card-cage" to secure the one-end that currently is not supported, and along
the length of the longer plug-in printed board assemblies. You also may need
to worry about thermal management. In a more severe environment, the
ventilation system would not hack-it. So you would need to design in a more
efficient method of heat transfer (removal).
(In the case of a "ruggedized PC" it would be cheaper to buy one from those
who currently manufacture them.)
IMO, Class 3 IPC products do not have to be "ruggedized", this is because the
products use-environment may not require it. A classic example is a heart
pace-maker: it doesn't need to survive say a 50g shock, 5 g vibration 20
minutes each axis 5-2000 Hz, or a 100 or so -50 to +125 degree thermal cycles
because the implanted pace-maker might survive, but the patient would most
probably croak and be long-gone.
The key for you is to work with your customer and identify the requirements
for "ruggedizing" the product.
Ralph Hersey,
e-mail [log in to unmask]
--------------------------------------
Date: 7/22/96 4:41 PM
From: Jeff Seeger
Hello, TechNet!
I have a situation where our customer is being asked for "ruggedized"
product. The product category is generally Type 3 and 4 PWB's, with
Class 2 expectations, fine pitch components both sides, (of course)
moderate high-speed rules. Product is built in ~100 piece lots.
Is there a general scheme of "ruggedizing" the PWA, or does this
simply imply an upgrade to Class 3 standards? I'm not sure density
will allow a full Class 3 implementation.
Is there anything non-subjective about "ruggedizing"? I've not seen
it mentioned anywhere.
Would selective upgrades to Class 3 qualify as "ruggedized"? Which
areas?
Of course, I have no specific performance requirements, just the
word "ruggedized". From the nature of the product, I would guess
there could be application for mobile equipment.
Can any "rugged" folks out help an old soft-in-the-head design guy?
Thanks alot, and best regards,
Jeff Seeger Applied CAD Knowledge Inc
Chief Technical Officer Tyngsboro, MA 01879
[log in to unmask] 508 649 9800
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Subject: DES/FAB/ASSY: Ruggedized PWA's
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