Critique my Nixie Clock PCB Layout - Page 1
Forum section: electronics / projects

author: Mighty Burger
author_rank: Regular Contributor
timestamp: December 09, 2021, 06:04:13 am
content: I still consider myself a beginner but perhaps it's time to start posting my project questions on this subforum instead!Check out my PCB layouts and let me know if you have any criticisms! Here's some more info:I've been working on a Nixie Tube clock design for a while. I'm hoping to eventually sell a few units as a side hobby. I'm a college student so time is a limited resource, but I've been finding a little time here and there to chip away at this.Hoping to place an order for boards and have them arrive not too long after Christmas, so I can try out my new hot air station!I've done quite a bit of testing, to the point where I feel comfortable enough that my circuit design should work. The question is whether my board layouts are poor enough to mess it up. I've already bought the parts - normally I'd wait but when I checked a couple weeks ago half the parts I designed for were just out of stock! Annoyingly I had to make a lot of substitutions and piece together parts from Digikey and Mouser. My biggest concern is whether the SI2337DS is a suitable replacement for the SI2307CDS MOSFETs. If not, I guess I'm placing another order!I attached the images below of my design. To avoid confusion, here is how I have it set up. There are two boards that I'm calling the "Base Board" and the "Top Board". The base board has the 170V power supply and the microcontroller, and the top board has the nixie tubes and driving circuitry. I also threw in some LEDs in case I want to use them, though I'd need to make new plastic bases for the nixie tubes. Let me know if you'd like more elaboration on the schematics.The Base Board is a two-layer board.The Top Board is four layers. I looked at it and thought it might be kinda tough to route everything on two layers without it being an absolute headache and probably an EMI nightmare. This is my first four-layer PCB design. I went with a regular stackup (signal, PWR, GND, signal). It was actually a lot more fun to route than a 2-layer board I thought.I'm guessing the board-to-board connector will cause some confusion. I'm using a "bottom-entry" connector, like this:https://www.digikey.com/en/products/detail/harwin-inc/M20-7810845/6564949It'll mate with a standard pin header on the other board:https://www.digikey.com/en/products/detail/samtec-inc/TSW-108-14-F-D/6679087This is just so I can get a smaller gap in between the two boards. Planning on 1/4" or 6.35mm. It'll leave more room for me to fit in the buttons in the enclosure.I'd like a quick sanity check on clearances. I ran ERC on both boards with the 170V clearance set to 35mil. Everything checked out. (There were a couple exceptions on the power board but I checked them manually and they're good.) It does not check out at 50 mils and many of those spots are just really hard to work around. Now a couple clearance calculators out there say I should have at least 50 mils clearance at 170V, unless it's a "coated" external layer which I guess means conformal coating. But would I really need conformal coating? Those same calculators say only 24 mils are needed at only 150V and below. Are they overly conservative?One other concern I have. I really had to squeeze in those traces coming out of the microcontroller on the base board. Is crosstalk a significant concern here?Thanks!

author: Mighty Burger
author_rank: Regular Contributor
timestamp: December 09, 2021, 06:05:56 am
content: There's a forum restriction on a maximum of 10 attachments per post. Kinda hard to fit all my design files in that so here's the rest. Let me know if this is against the rules and I won't do it again

author: strawberry
author_rank: Super Contributor
timestamp: December 09, 2021, 01:20:03 pm
content: if PCB is bent SMD components may crackcheck SMD part orientation

author: Mighty Burger
author_rank: Regular Contributor
timestamp: December 09, 2021, 05:12:48 pm
content: Quote from: strawberry on December 09, 2021, 01:20:03 pmThanks for double-checking. Yes, the way I have the SMD components oriented is a little unusual. When the clock is fully assembled, they will face down. The nixie tubes and LEDs are the only components that will face up.I'll be sure not to apply too much pressure to one area of the PCB to avoid bending it.That reminds me. I need to get an adhesive to glue down those electrolytic caps so they don't vibrate and break off in shipping. Anyone have suggestions for an adhesive?

author: strawberry
author_rank: Super Contributor
timestamp: December 09, 2021, 05:58:45 pm
content: horizontal oriented capacitors : double sided tape or solder down to PCB with solid copper wire loop(two vias on PCB) or some manufacturers use silicone or some other chemicals, glue