Transistor package with built-in galvanic isolation on thermal pad - Page 1
Forum section: electronics / projects

author: rs20
author_rank: Super Contributor
timestamp: October 15, 2016, 11:19:24 pm
content: TLDR: What is the package name/transistor series that has galvanic isolation built right-in to the package?I hope this wasn't just a wonderful dream, but I recall coming across a transistor datasheet (something like a TO-264 type device) mentioning that the thermal pad on the package wasgalvanically isolated, meaning you could mount it directly to a heatsink with no regard to the voltages on the die (within reason of course). But now I'm searching to try to find this again, and I can't find it! Any leads would be greatly appreciated.I appreciate that many other options exist (Sil-pads, isolated heatsinks, etc), but there seems to be so much scope for the manufacturers to do a far better job (e.g., apply a 50 micron layer of BeO to die backside to give 0.01 K/W thermal resistance at 500V breakdown on 5x5mm die) than any Sil-Pad could ever do (not to mention the attendant extra fabrications steps and messiness).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 16, 2016, 12:13:32 am
content: Dunno that ceramic enamels are getting any use.I'd suspect, everything that has good film-forming properties has poor thermal properties. (Most things have adjustable expansion rates, by adjusting composition, so that's not usually a problem, unless the material has to be very pure to achieve its conductivity, which is the case with BeO.) You also wouldn't be able to make a proper "reinforced" layer, I think. A crack in the underlying coating would be a stress raiser in the top layer...The usual approach is DBC (direct bonded copper), an engineered ceramic base (AlNO I think?), coated with metal on both sides. You get a heavy metal tab or back plate (TO-220, 218, 247, 264, SOT-277, etc.), and the die is soldered (or bonded however) to the plate. Thermal resistance is only a little worse than conventional construction, but you don't need mica or Sil-Pads or anything. Worth the cost, where you can find it.IXYS I think owns the patent on DBC? They have the most offerings with it, IIRC. Also seen diodes, thyristors, etc., from various manufacturers. Of course, it becomes much more common in the more expensive packages; I don't think I've seen a SOT-227 (or larger) without isolation.Tim

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 16, 2016, 03:28:35 am
content: Isolated triacs are very common as they're used in light dimmers.

author: edavid
author_rank: Super Contributor
timestamp: October 16, 2016, 03:31:48 am
content: Isolated transistor packages are commonly called "Fullpak", and add an F to the package name, e.g. TO220F.They don't usually have an exposed heat spreader pad, just an epoxy mounting surface.

author: TiN
author_rank: Super Contributor
timestamp: October 16, 2016, 04:06:17 am
content: ISOTOP package. Or SOT-227 other name. I used these for DC load project, they also have very nice thermal conductivity.The drawback usually gate capacitance and cost, but for me it was worthy to install few of those than to replace TO-220 MOSFETs after every overload event

author: Dago
author_rank: Frequent Contributor
timestamp: October 16, 2016, 05:10:48 am
content: I've also seen quite many TO-247 packages with isolated tabs. But most of them do not have isolated tabs.

author: edavid
author_rank: Super Contributor
timestamp: October 16, 2016, 06:16:50 pm
content: Quote from: Dago on October 16, 2016, 05:10:48 amThe isolated version is called TO247F or SOT199.