Why does anything need machining? The thermal connection is flush with the top of the device, so all it requires is a flat heatsink with a thin conformal pad & the board held / clamped / sprung against it.
Screws through the board into the heatsink to put pressure on the thermal pad.if the device is PCB top mounted, then how do you do that? We need to do it simply, without much requirement for labout intensity.
Thanks, thats very true......and i am sure you would agree that if an SMD FET does not have a top-side metal heat tab, (ie, its top-side is plastic), then the thermal path to a top mounted heatsink is worse than going through a PCB from a SMD FET with a bottom side heat tab?Going via the PCB to a below-board heatsink will result in a much! higher thermal resistance from the device to the heatsink.
Obviously.i am sure you would agree that if an SMD FET does not have a top-side metal heat tab, (ie, its top-side is plastic), then the thermal path to a top mounted heatsink is worse than going through a PCB from a SMD FET with a bottom side heat tab?
Basically, the SMD FETs, with top side heat tab, are so rare (and going obselete), that they are not worth using....it says it all that you cant even search for them. If used, they are most likely to go nil-stocked.I don't see how that relates to the question re. using those top heatsink devices, though?
You do not "mount" the heatsink - you mount the PCB (to the heatsink).If they are used (top tabbers), then heatsinking is labour intensive if you try and mount heatsink to their top with screws etc...
...Thanks, yes, thats the way our customer does it in the SMPS they have sent us.....the "top-tab" SMD FETs are mounted to the bottom of the board, and you screw the board to the aluminium baseplate, and put a bit of gap -pad on the fet top, ,and thats it......but you need to gouge out a "pit" in the baseplate, so the fet can protrude into it.You do not "mount" the heatsink - you mount the PCB (to the heatsink).
Is that why there are "only" 4,440 hits for that exact package?the SMD FETs, with top side heat tab, are so rare (and going obselete)
No.. Just no. There is no "need" to have anything but a flat mounting surface, to use that device type.but you need to gouge out a "pit" in the baseplate, so the fet can protrude into it.
Yes i agree, but the PCB is screwed to that same surface....the SMD FET protrudes out from the PCB underside....so you have to gouge out a "pit" for the protrusion of the fet...but yes, the bottom of that "pit" is indeed flat, as you say. I wish i could share the enclosure picture, but unfortunately it would probably be deemed giving away secrets.No.. Just no. There is no "need" to have anything but a flat mounting surface, to use that device type.
Sorry, I did not realise you thought I was a mind readerbut the PCB is screwed to that same surface.
Thanks, though you have answered the question perfectly in one sense, with your depiction of the complicated assembly routine for these fets above....you depict how more complicated assembly is than a "back-tabber"...thankyou for that.....that was of definite massive interest.n other words, how on earth does that relate to the fundamental use or not of that specific type of device, with no other restrictions stated, as in the original question!
"Top-tabber" fets look incredibly difficult to heatsink in all circumstances though
with your depiction of the complicated assembly routine for these fets above....you depict how more complicated assembly is than a "back-tabber"
Thankyou , this is great info!...i will digest your comments.Having a PCB hard against metalwork for any normal electronics seems crazy to me
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