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|17th January 2013, 07:50 PM||#12|
Join Date: Dec 2012
Location: SF Bay Area
You kind of have to ask the question ... why metal cans?
Its not really like they do anything in a normal conservative design. In the "old days" they put (everything) in metal cans for 4 reasons:
 Because they hadn't worked out "engineering plastic" that could safely be squeezed onto chips during manufacture. [Resolved by the early 1960s]
 Because metal cans were hermetic, preventing moisture in particular, but for industry, other noxious gases from touching the semiconductor surfaces (which can gradually degrade and destroy them)
 To dissipate greater power through air convection (especially when transistors, even "low power" ones were near their limits in power dissipation
 Shielding and "input super-resistance" (i.e. ensuring that things like MOSFETs and JFETs had their gates attached directly to a pin that is insulated with glass, one of the best insulators when clean. When making "sample and hold" circuits, this is a large requirement.)
And I suppose
 Military requirements, spec-sheet conformance, to allay the fears (or ultimate-demands) of nervous designers and equipment builders.
Seriously though ... in the last 35 years, the dissipation thing has been answered (best!) by simply making more efficient op-amps and higher conduction plastics. The "insulation" thing has been resolved for decades. The plastics are great insulators (and moreover have been engineered to prevent tribo-electric effects AKA "static electricity from rubbing"). In terms of interference and shielding, the present-day op-amps are placed on circuit boards that are carefully laid out, and it isn't a problem. Op-amp chips ... unbeknownst to most people ... have been almost entirely re-engineered in the last 20 years, even if they carry "standard" designations. Much lower power, better onboard transistors, much higher accuracy of thin-film resistors. Higher Hfe and gm.
So... unless you have either
 Esthetics ... 'cuz cans look cool -- or --
 Opportunity... A bag of them sitting around
in mind, I recommend staying away from them, for circuit-to-circuit, you're far more likely to get an older "NOS - new old stock" item that has significantly more variable noise performance, dissipation and quiescent drift characteristics than a brand new, state of the art, recent-product-addition.
So sez me.
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