GaN With the Wind

snipped-for-privacy@yahoo.com wrote in news: snipped-for-privacy@googlegroups.com:

Looks like you've GaN fishin' for performance.

You're a real GaNer. We'll never get you back.

I assume you have a good microscope/ viewer. Is the problem needing tiny tools/ manipulators?

George H.

I love the EPC parts, but I can't solder or replace them myself. I have experts that can do that.

We use solder-mask-defined pads, which some board houses can do right

and some not so right.

These are for the tiniest 4-ball parts, same size as the 2036. The tiny BGA parts are mechanically fragile, so I glop them with drops of Bondic first thing.

Here's a 50 volt pulse, 25v into a 50 ohm load:

with < $2 worth of GaN fets. The circuit can do 100v.

That pulse is lowpass filtered for beauty. It's natively faster but kind of ratty looking.

I don't have a microscope & haven't needed one. I just did it caveman-style. (Are we still allowed to say 'caveman'?)

The difficulties were many, ranging from seeing any markings on the mirror-shiny silver die's back surface, to applying tiny bits of solder to refresh the super-close balls, not blowing the part off with the hot air, getting all the balls to solder, not shorting, not having the die shift off the lands, etc.

Just about every problem you could have, I had.

But eventually, it worked.

Cheers, James Arthur

The vendors say GaN FETs don't avalanche, and yes, the gate drive affecting reverse conduction will take a bit of planning when inductances ring.

I saw EPC and GaN Systems literature today to the effect that GaN should operate to 300C. EPC's website says GaN theoretically has three orders of magnitude of improvement left in it, whatever that means.

Glopping 'em seems smart. The 1x1mm CSP I re-worked was amazingly fragile--the pads are so tiny, a little sideways accidental tap rips them right off.

I like the back-door thermal access. That might make up for the poor pads-to-board path.

That's pretty.

Cheers, James

Oh! James on someones advice here, I bought a ~$70 dollar chinese 'viewer' single fairly long range microscope and lcd view screen above. I tried some fine (for me) soldering with blue wire wrap wire (30 mil?) Anyway it's totally worth it. At maximum focus there's about a 1" working distance. (max focus is reported to be x1k... I measured around that (with big error bars.. too lazy to get calipers from shop.) I'll have to look back to find the brand name if you have interest. I only says 'microscope' on the outside and when I turn it on. (I can give you the version number :^)

George H.

If I search SED for tardigrade, I can probably find it.

Am 22.06.20 um 01:32 schrieb snipped-for-privacy@yahoo.com:

I was more lucky. My first 2 tries worked immediately with just a little bit of hot air. Very little, or they fly away. That was a test structure from a corner of a larger board made by PCBWAY. HAL, I removed the excess tin with some unsolder braid and used paste then. PCBWAY spotted the mask on the pad as designed by EPC's Altium example. Worked after declaring it OK.

cheers, Gerhard

I wasn't happy with my PCBWAY board. Resolution and registration were bad, and they didn't read my stackup specs. Their default 4-layer stack has *four mils* of dielectric between layers 1 and 2, and between 3 and 4. That is really nasty. That stack is common in cheap chinese proto houses.

That would be OK for slow, not very demanding stuff.

We always buy gold flash, ENIG boards, whicg are nice and planar and solder very well.

That's nasty indeed. Who'd use a stackup like that?

Jeroen Belleman

people that want 100R differential for e.g. LVDS with a track width that works with BGA

Someone who wants narrow microstrips on the top level?

In fact, I'm just asking a local board maker for sth. similar, with the middle of the stack made from thick FR4 for stability and on the outside thin Rogers 4003 or whatever for thin micro- strips and low radiation loss at 10 GHz.

It looks like the eval board of the ADF5356 has a similar stack, just from visually inspecting the milled sides.

Up to now I had no single problem with PCBWAY other than that they use DHL express which leads to some fee f*cking here in .de and constant trouble with the customs in Leipzig. I did not let them make multilayers up to now.

I made a test run with JLCPCB, they have now a proxy man here in .de. That adds theoretically 2 days or so, but the proxy handles the customs which may result in an speedup over all. The proxy gets a pack with the daily production for the EU and relays it per local mail with a new tracking number.

It is now technically an inland buy, they collect the local VAT in advance. Works nicely.

Gerhard

I know microscopes are helpful and good, but this isn't something have ever done, do, or ever will do on a regular basis. I've done it exactly once.

So I used an electric fryer pan for the pre-heat and a $35 eBay hot air station (it's very good, actually), tinned the pads with good 'ol leaded wire solder, then dabbed some liquid flux-specks on top. How does one mount one's microscope on an electric frying pan?

Sure, I could've ordered all the orthodox supplies, waited, then used them, once. But it was faster just to blast ahead with what I had on hand.

Cheers, James Arthur

I might! Just two days ago I was calculating how much capacitance I could squeeze out of a PCB pour. Consulting my calculator, 0,1mm spacing and 5 x 5cm gets me 97nF with just 100 layers' stackup :)

Cheers, James Arthur

That's a nice picture.

Paste would've helped my misadventure quite a lot.

One of the most annoying problems was that I was hand-applying solder to the board's pads, then adding liquid flux, before stacking the die on top. But it's quite impossible to tin precisely equally-tall bumps onto those tiny pads at these scales, so when you'd go to place the die on top, the uneven bumps would hold the die at a slanted angle, ready to fall off, slide sideways, or blow away in the hot air.

Any number of times instead of being drawn into self-alignment by the reflow surface tension, the part was pulled off-alignment to a position shorting the pads, instead.

(On the plus side, the uneven bumps made it easy to see when the solder had successfully melted.)

If I'm going to be prototyping with these nifty GaN FETs I may have to cave and get the "real" supplies. But it's super wasteful, since doing this once a year, they'd go bad each time before I'd use them again.

Cheers, James Arthur

or be lucky to find something in surplus , modify it and add an LED ring lamp.

Surgeons might use head-mounted arrangement with probe+cam+viewer or a heads up display.

With 10x view it becomes 10x easier but you need even more light due to lens loss.

So you did well on your own.

My Mantis is one of my favorite things. Makes me feel like an eagle flying all over, looking for mice or whatever.

The Mantis can do things like that. I use it to peep at tiny parts on a board, still in a rackmount box. It's great for avoiding probe slips too.

Figure a tempco ballpark +900 PPM. And a lot of nasty DA.

We made our own eval boards to test the parts. It's amazing that EPC doesn't.

I need amps at kV in