3 ms·

Author here: I'm sure there are people on HN who have experience with modern chip layout, and I'd be thrilled if you can explain more about the transistor struc

by kens 6y ago

Author here: I'm sure there are people on HN who have experience with modern chip layout, and I'd be thrilled if you can explain more about the transistor structures and so forth. I mostly look at chips from the 1970s and 80s, and a lot has changed since then :-)

cushychicken 6y ago
That tiny little heatsink is very cool. (Pun not intended.) Do you happen to have a post about the setup you use to photograph these die, Ken? I'd love to get my hands on something similar.
- kens 6y ago
  I have a post about my setup [1]. The main secret is a metallurgical microscope: unlike most microscopes, this shines light from above, through the lens, so you get good illumination of the die. (A ring light is easier, but it doesn't help at high magnification. Also, light from the side doesn't work as well.) I use a low-end metallurgical microscope that I found on eBay. You can see interesting stuff with a regular microscope, so take a look at chips if you have one, but a metallurgical microscope makes a huge difference. For the die photos, I stitch together multiple photos using the "Hugin" software package. I might use a dozen to 50 individual photos to produce a high-resolution image. Hugin has a learning curve, though. The final thing is how to decap the chip. Usually, I stick to ceramic or metal packages that I can open with a chisel or hacksaw. For epoxy packages, I don't want to mess around with boiling acids, but I have friends who can do this. [1] http://www.righto.com/2015/12/creating-high-resolution-integrated.html http://www.righto.com/2015/12/creating-high-resolution-integ...
  - cushychicken 6y ago
    Awesome! I'll check that out. Can't blame you for not wanting to handle boiling acid. Ain't nobody got time for that. (Except for your friends, and ZeptoBars.)
ramshorns 6y ago
Cool stuff. Did you test the isolation? Say, by powering it from 5VDC that's riding on 120VAC or something.
- kens 6y ago
  I didn't test the isolation. I wanted to avoid accidentally destroying the chip, since that would mess up the analysis. I was tempted to hook the chip up to the 40 kV spark generator we had sitting around, but that would probably be a bad idea.
  - ableal 6y ago
    Probably the package would need to be over 1cm tall to withstand that. (I think that the electric power guys get "30kV/cm" etched into their brains - the field strength at which sparks start to fly between conductors separated by air.)
subhobroto 6y ago
This was an awesome read. Would you mind digging into those cheap Chinese isolated DC-DC converters in little black rectangular boxes potted in epoxy of similar wattage? "b0505" or similar Probably Recom knockoffs
- segfaultbuserr 6y ago
  +1. Those are hybrid circuits with real components and magnetic cores inside, not a single-chip solution, but I wonder what types of chips are used inside.
kayson 6y ago
EE here. I agree with most of your guesses as far as layout goes. There are definitely some diodes in there - the devices with a more square aspect ratio and large square contacts in the middle. The large power transistors are laid out in multiple "fingers" so current is distributed among them. This both reduces the effective diffusion resistance and alleviates concerns related to electromigration. There are a lot more guard rings than I'm used to seeing, and they're very wide. This is probably to avoid latchup due to the potentially high switching currents, and possibly also for moisture protection ("seal rings" would be on every metal layer in addition to the front end layers). There's one very odd layout structure that has me puzzled. In your "collection of transistors", the top left image has a non-rectangular structure in the middle. I wonder if there was a metal structure there that required a diffusion opening. Or maybe its a BiCMOS BJT?

by kens 6y ago

cushychicken 6y ago

That tiny little heatsink is very cool. (Pun not intended.) Do you happen to have a post about the setup you use to photograph these die, Ken? I'd love to get my hands on something similar.

kens 6y ago
I have a post about my setup [1]. The main secret is a metallurgical microscope: unlike most microscopes, this shines light from above, through the lens, so you get good illumination of the die. (A ring light is easier, but it doesn't help at high magnification. Also, light from the side doesn't work as well.) I use a low-end metallurgical microscope that I found on eBay. You can see interesting stuff with a regular microscope, so take a look at chips if you have one, but a metallurgical microscope makes a huge difference. For the die photos, I stitch together multiple photos using the "Hugin" software package. I might use a dozen to 50 individual photos to produce a high-resolution image. Hugin has a learning curve, though. The final thing is how to decap the chip. Usually, I stick to ceramic or metal packages that I can open with a chisel or hacksaw. For epoxy packages, I don't want to mess around with boiling acids, but I have friends who can do this. [1] http://www.righto.com/2015/12/creating-high-resolution-integrated.html http://www.righto.com/2015/12/creating-high-resolution-integ...
- cushychicken 6y ago
  Awesome! I'll check that out. Can't blame you for not wanting to handle boiling acid. Ain't nobody got time for that. (Except for your friends, and ZeptoBars.)

ramshorns 6y ago

Cool stuff. Did you test the isolation? Say, by powering it from 5VDC that's riding on 120VAC or something.

kens 6y ago
I didn't test the isolation. I wanted to avoid accidentally destroying the chip, since that would mess up the analysis. I was tempted to hook the chip up to the 40 kV spark generator we had sitting around, but that would probably be a bad idea.
- ableal 6y ago
  Probably the package would need to be over 1cm tall to withstand that. (I think that the electric power guys get "30kV/cm" etched into their brains - the field strength at which sparks start to fly between conductors separated by air.)

subhobroto 6y ago

This was an awesome read. Would you mind digging into those cheap Chinese isolated DC-DC converters in little black rectangular boxes potted in epoxy of similar wattage? "b0505" or similar Probably Recom knockoffs

segfaultbuserr 6y ago
+1. Those are hybrid circuits with real components and magnetic cores inside, not a single-chip solution, but I wonder what types of chips are used inside.

kayson 6y ago

EE here. I agree with most of your guesses as far as layout goes. There are definitely some diodes in there - the devices with a more square aspect ratio and large square contacts in the middle. The large power transistors are laid out in multiple "fingers" so current is distributed among them. This both reduces the effective diffusion resistance and alleviates concerns related to electromigration. There are a lot more guard rings than I'm used to seeing, and they're very wide. This is probably to avoid latchup due to the potentially high switching currents, and possibly also for moisture protection ("seal rings" would be on every metal layer in addition to the front end layers). There's one very odd layout structure that has me puzzled. In your "collection of transistors", the top left image has a non-rectangular structure in the middle. I wonder if there was a metal structure there that required a diffusion opening. Or maybe its a BiCMOS BJT?