On this particular IC,the metal substrate is on the TOP side of the IC.Just
right for adding a heat sink! The PCB does not dissipate any heat from the
IC except for what comes thru the leads.I suspect the studs were intended
for a HS that someone else thought unnecessary,or an extra expense.
I would not overtighten those nuts, it might cause IC failure
itself;mechanical strain.
I thought I understood until I read this. According to the pictures and
the previous description, the tab looks like it sits on the board.
There's room to add a nut who's top sits at the level of the IC top???
If there's any room between the tab and the board, the mounting stresses
on the package would be enormous. This assumes the studs go thru the
board. Just occurred to me that the studs could be pressed into the tab
and not go thru the board at all???
If the chip sits on the tab, the optimum setup might be to put a
threaded spacer on the left end that fits inside the notch, without
binding the plastic, to get a solid conductive path to the heatsink
on that end. Contact with the top of the chip should be irrelevant
if all the heat is coming out the tab. Also might want to grind the
anodize off the heat sink (keeping it FLAT) for better thermal contact
with the stud material.
I'd still like to see the temperature numbers. The question would be,
"What mode should the system be in for max heat?"
High sweep rate would put the most stress during sweep, but holdoff
would reduce the duty factor. So, tests at different sweep speeds
while activelly triggered might be in order. Just letting it free-run
at high sweep won't maximize the duty factor. Which brings up another
issue.
Back when I was designing pulse generators, I read an article that
suggested that the primary failure mode of output transistors was
thermal cycling. Given the thermal time constants in the package,
the worst case for thermal cycling was in the 10-100Hz. rep rate range.
So, if you leave the scope sitting untriggered in auto-trigger mode,
you're running the sweep circuits near maximum thermal cycling stress.
From now on, I'm gonna turn off auto-triggering on my scopes when I'm
not using 'em.
So, DaveC, can you give us some temperature readings in various modes?
Thanks, mike
--
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