On Thu, 14 Aug 2008 06:09:05 -0700 (PDT), wrote:

On Aug 14, 9:30 pm, Jim Wilkins wrote:

I believe that is an unintended consequence of Surface Mount
Technology, specifically thermal stress cracking

Agreed - its a known problem, if designed PROPERLY it can be avoided -
as you say, heart pacemakers dont fail after 3 years (with monotonous
regularity)

. I've worked on the
R&D side of electronic development and seen the shift from thru-hole
to SMT up close (literally & figuratively).

I havent - as a working tech, I don't see them till they fail -
strangely enough, at about the 3 year mark - a 3 year warranty is a
good marketing tool as the probability is there will be minimal claims
because thats how long it will last anyway.
And they keep on making the same old design "errors" after, what, 50
years of solid sate - cheap flexi bendable PCB's, low grade
electrolytics (with known failure curves) heat generating components
with inadequate heatsinking, even to the point of making the pads they
connect to too small...this ain't Rocket Science, its a way to make a
cheap product with a guaranteed short lifespan....(I think its called
Stress Engineering...)

In the lab a good tech can
replace almost any part with an iron or hot-air machine. But
prototypes don't suffer from environmental stresses like production
units, and temperature cycling a single hand-made example doesn't
predict the failure rate of 10,000 repaired units.

They don't need to - they know, from engineering knowledge, how long
it will last. Automated production machinery wil take care of the
tolerances involved and make a "perfect" product...

I didn't hear the
dictum that consumer-grade SMT boards were to be considered
unrepairable until they had been out for several years. Higher-value
assemblies such as the medical battery packs I worked on recently are
still repaired.

Old stuff has the problem of parts availability.

True - but there has been an after market, second or even third
supplier sourcing of spares for yonks - this is getting worse, I will
concede, due the decreasing model life of new consumer products,
which, strangely enough, are different inside from the previous
model....

Often they only stock an later model's equivalent part which isn't
quite an exact
replacement.

Funny that - oh, and BTW - when they can charge you more than the
cost of the appliance for a spare part, they can say they have
honoured there spares supply obligation......like, say, the $10
fusible resistor....and as for custom VLSI ic's - pick a number, any
number, bang a few zeros in there, and add exorbitant shipping and
handling to it...

I am slowly becoming the parts maker for the old washing
machine and lawn mower.

Good On Ya - thats what RCM should be, and is, all about - to develop
the skills to do this stuff ourselves...its "not economical" but we do
it for the sheer joy of beating the system.

Maybe its an age thing, but it rankles with me that perfectly good
gear has to be thrown out because a 10c part is No Longer available -
thats why I got into metalworking, so I could make the 10c part....
(its turned into another bloody obsession, which I dont need, but what
the hell...)

Regards,

Andrew VK3BFA.


Jim Wilkins
That's why the Myford's in the corner of the garage. Don't need to
make many "unavailable" parts to make a $1500 lathe a bargain.
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