EPC GaN fets : caution

Den mandag den 5. marts 2018 kl. 18.01.18 UTC+1 skrev John Larkin:

how about those squishy thermal pads? I'm thinking it would also contact the sides of the part and the pcb

They're fun to blow up too. I got to blow up some GaN FETs (on purpose) on one of Uber's laser boards last summer. The idea was to show that the plaintiff's (i.e. Waymo's) expert's account of how they worked was completely wrong, which it was. The lasers sure got brighter while they and the FETs survived. ;)

Cheers

Phil Hobbs

Too much power dissipation, or too much voltage? They do seem to avalanche and foldback at a bit over 2x their rated drain voltage, but that's not destructive if the current is limited.

There are some impressive thermal putties too, numbers like 5 to 10 w/m-K. Putty would fill in all the nooks and crannies without stress.

(Whatever nooks and crannies are.)

Isn't it fun to trash the opposition's expert witness... some of my most fun days have been spent giving depositions >:-}

Even more fun is trashing attorneys who have no clue of electronics. ...Jim Thompson

The exact details are covered by a protective order, so I can't be too specific.

It's no secret that pulsed-lidar lasers are driven by discharging a small capacitor through the laser. The cap is usually a few nanofarads, and charged to 40-50V to improve the rise time. The opposing expert said the Uber circuit was "equivalent" to a patented circuit, so I modded the circuit to test that equivalence. The mod substantially increased the discharge current, which blew up the FET after a few seconds. When they saw my report and deposition, Waymo dropped their patent case entirely. (Which was good, because no infringement was in fact taking place.)

The inductance of a laser diode, an 0402 cap, and one of those flipchip GaN FETs can be less than 400 pH total.

Cheers

Phil Hobbs

Lots of guys are pretty straight shooters, mentioning the helpful stuff without mentioning the not-helpful stuff but not making stuff up. I've rebutted those sorts of folks with no ill feeling.

But then sometimes when the case is weak, lawyers hire the less-straight shooters, of whom there are also a fair number. _Those_ ones are really fun to blow up because they deserve it it so much. You can't put too much English on the rebuttal, though, because judges get tired of that stuff really fast. A little humour can help, but it can also be dangerous.

Well, they don't trash me for not knowing much about practicing law. They're good at what they're good at, I'm good at what I'm good at.

I did have a good time in my one cross-examination--the attorney got mad and said some stupid stuff, enough to get him reprimanded by the judge. ;)

Cheers

Phil Hobbs

You have to worry about cycling though, at least with paste--there's a tendency for the fines to wash out as the fluid moves, leaving stacks of flat platelets that wedge the surfaces apart. Turns out that it's the fines that make the stacks good heat conductors. We had issues with the otherwise very good Shin Etsu paste at IBM a decade ago.

Cheers

Phil Hobbs

(Who finds that he's been out on his own for 9 years now.)

They're those things they put in English muffins to fill up the space inside. I was going to suggest some goop, and maybe a metal can over the top.

George H.

I just finished an English muffin for lunch. I filled it with chicken and ham.

What do they call an English Muffin in England?

You find it fun to trash people? Yes, we all knew that.

A selection of muffins on England:

We also eat crumpets; the classic is to toast them on a fork in front of an open fire. Then add lashings of butter, let it soak into the crevices, and try to eat it without getting your fingers greasy.

Our English Muffins look about like

but we don't use ancient grains.

They are good for sandwiches, or just toasted with breakfast.

We get good crumpets here. But we toast them in a toaster.

Licking fingers solves that last problem.

A defendant once used me as expert witness in a wrongful death lawsuit. The defendant's attorney advised me to keep my answers short and answer with a simple yes or no whenever possible. The attorney advised me that reticence was the best policy. The plaintiff's attorney tore into me and tried to get me to lose my cool, but that didn't happen. My testimony was kept succinct and terse. Attacks on my expertise followed by long periods of silence didn't phase me in the least. Matter of fact, those awkward lulls provided ample opportunity for me to collect my thoughts. It's a game, you see. The best way to help your side is to forget about your own ego and instead focus on the game. Especially when the stakes are high, as they are in a wrongful death lawsuit. That's how you win in the end.

Thank you,

As you can see, "muffin" means just about whatever the manufacturer wants it to mean.

Yup. Same here.

The old way of roasting chestnuts was to skewer them and rest them on the metal grate of an open fire. One was left unskewered; when it exploded the others were cooked, and if it landed in someone's lap they were the next to get married.

Much to the delight of my daughter and her friends, I still use that "is cooked" alarm clock when I roast chestnuts in the oven.

If they're trying to take advantage, to grab large piles of what is not theirs, then I like to demolish their bs too.

NT

a muffin here is an overgrown cupcake, typically undecorated and with a rough finish.

NT