I have several examples of depletion mode parts now, and
they do have their charms. The self-bias is convenient for
some designs, not so convenient for others.
😎
they do have their charms. The self-bias is convenient for
some designs, not so convenient for others.
😎
FYI, the 175C limit is possibly just the 180C plastic transition point of the package. Similar parts have been used at 800C!
800C. I just realized that in the near future our transistors
may be giving off that red glow that makes tubes special.
😎
may be giving off that red glow that makes tubes special.
😎
No john, I think he's right. Most metal types of things start glowing about 1200 or so...
Hey, since you're the "push 'em over the edge" expert here.
How would you go about soldering a device that gets so hot?
I did some playing around with pushing devices real hard, back then, the only solution I found, was to crimp instead of solder.
Magura 🙂
EDIT: And you might as well spill the beans. How do we get that plastic casing off, without damaging the fet?
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Higher temp solder 🙂
You need some movement allowence for expansion and contraction. Maybe a spring or clip like N.P. uses...
Fumming Nitric Acid I think 😀
Dealing in extremes is always interesting, my friend John who now works at Linear Tech used to design inferred image sensors for Ratheon. They lost the cooling unit that FedEx delivered and the bean counters came looking. Apparently to cool his chip to zero kelvin and be light enough to be packaged into a satellite, the unit the size of a coffee can cost 1 million dollars. I keep trying to get him interested in audio and he will not come around. I may work the other end and get his wife interested, maybe she can influence him in ways I can not.
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As far as decapsulating ICs and transistors/fets, various sorts of nastiness are required. For the usual black epoxy used in potting modules and such, glacial acetic acid was used - not nice stuff at all, but it gets worse. We used to use a particularly refractory and recalcitrant epoxy to encapsulate our power devices. Red fuming nitric acid was the only stuff to dissolve it. RFNA is so obnoxious that you grind down the epoxy to the last few mils and use a jet of the nasty stuff to get the rest of the way to limit your involvement. Fortunately, I'm in applications, so it's the process and Q/A guys that get to work with the real methyl-ethyl bad stuff.
isn't little skill with sanding appropriate for de-nude back of part ?
in case that is even of any benefit for our purposes .....
in case that is even of any benefit for our purposes .....
Why de-cap the thing? Do the nucleate boiling thing to control temp. Immerse the part in an inert fluid (flourinert)with a boiling point at about the temp you want to limit at (175C happens to be a popular temp amongst the Burn-In crowd). Of coarse the fluid must be cooled also. The bubles boiling off the hot device are at the boiling point and flowing away constantly taking the heat with them. Lower temp fluid immediately rushes in to take the bubbles place. There are limits to this process also but I have had a 1cm sq die running at 20+ watts without pushing the limit at all. I suppose there will just be 1 giant bubble of 175 degree gas surrounding your device when you reach the limit 😀
I did suffer some "noise" while measureing these boiling devices. It seemed to me that it was actually the temp fluctuation due to the boiling rate. Never quite sorted that out but that could be a show stopper to us low noise fanatics🙁
I did suffer some "noise" while measureing these boiling devices. It seemed to me that it was actually the temp fluctuation due to the boiling rate. Never quite sorted that out but that could be a show stopper to us low noise fanatics🙁
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