This board is dense... - Page 1
Forum section: electronics / projects

author: technix
author_rank: Super Contributor
timestamp: September 21, 2016, 04:40:57 pm
content: So I challenged myself to design an Arduino-compatible board using STM32F103CB. Specs:* MCU: STM32F103CB or STM32L152CC (pin-to-pin compatible)* Break every single pin out one way or another.* Arduino Uno board footprint and pinout* Switch-mode supply for VIN->5V and 5V->3.3V (so the board will have low enough power conversion loss to justify a STM32L152CC version)* Break native USB out to a micro-B socket* Connect a USB to Serial adapter to USART1* HSE, LSE crystals and backup battery all present.* 2 buttons: Reset and Wake-Up* 2 LEDs: Power and System (connected to a GPIO pin)* Single-side loading* Double sided board, no inner layersAnd the resulting board is dense as hell to me.My next challenge would be designing a STM32F107VC Arduino-compatible board with RTL8201 Ethernet PHY and PoE.

author: Dubbie
author_rank: Unknown
timestamp: September 21, 2016, 09:27:48 pm
content: Have you printed and assembled it?

author: janoc
author_rank: Super Contributor
timestamp: September 21, 2016, 10:03:06 pm
content: You could have actually saved some space by using SWD instead of JTAG, that chip certainly does support it.Nice work, though! Stuffing everything from that list into that layout and with only 2 layers is an achievement.

author: rs20
author_rank: Super Contributor
timestamp: September 21, 2016, 10:20:38 pm
content: Regarding the three slot cuts at the bottom left (for the DC power jack), it looks to me like you've got a normal circular hole there and are relying on the PCB house noticing your comment and fixing it up for you. This seems like a bad idea to me, every PCB program I've ever used has native support for non-round holes -- in kicad, what you want is (rather incorrectly) called "oval" holes. Feel free to leave the comment there of course, but get the design files right as well.

author: bson
author_rank: Unknown
timestamp: September 21, 2016, 10:26:51 pm
content: Always nice to see a well done 2L PCB. Nice schematic, too.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 22, 2016, 04:48:19 am
content: Nah, that's not dense. There's still copper pouring between everything! (Stitch it, BTW!)Probably, the connectors could be 1mm pitch, assorted semiconductors can be SOT-323 or smaller, or DFNs and QFNs, that sort of thing... 4 or 6 layer PCB with two sided load... Plenty of space to save, I bet it could be 1/4 the area yet.Tim

author: mariush
author_rank: Super Contributor
timestamp: September 22, 2016, 05:43:16 am
content: You could have used a resistor network for the 10k and 4.7k resistors around the first chip and make your design look more nicer.For examplesomething like thiscould replace R1, R2 , R4 , R15 , R5 and R6 , or at least 5 of those because there's only 8 resistors in the network (for the last three just use two resistors in parallel to get 5k instead of 10k, which is close enough to 4.7k)If you have the ground on the bottom layer, it would be fairly easy to move the resistors to the top where R5 and R6 are and just use vias to connect them to ground.I see you used one for the JTAG and so you're not scared of them.ps. and you could have replaced your two resistors networks with one of the above linked, since they're independent of each other.And you could replace both IC2 and IC3 with just one chip with two outputs, likeTPS54294PWPfor example, or cheaperTPS542951RSAR

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 22, 2016, 06:59:22 am
content: STM32F103C8T6 in close to arduino nano form...http://www.ebay.com.my/itm/STM32F103C8T6-ARM-STM32-Minimum-System-Development-Board-Module-For-Arduino-/311156408508?hash=item48725e00bc:g:ngMAAOSwygJXhGtV

author: prasimix
author_rank: Unknown
timestamp: September 23, 2016, 05:39:52 am
content: Don't know what is practice with this MCU but X2 could be placed much closer to the MCU with some rearrangement.

author: CM800
author_rank: Frequent Contributor
timestamp: September 23, 2016, 07:32:24 am
content: Quote from: blueskull on September 22, 2016, 07:23:16 amCrikey,Have a look at this:http://www.elmomc.com/products/gold-twitter-servo-drive.htmHow's that for power density?

author: CM800
author_rank: Frequent Contributor
timestamp: September 23, 2016, 10:13:19 am
content: Quote from: blueskull on September 23, 2016, 08:32:00 amHow much?Sounds perfect for oversized DRSSTCs...Are you designing with dies for an actual semiconductor module company then?

author: technix
author_rank: Super Contributor
timestamp: September 23, 2016, 10:22:24 am
content: Quote from: Mechatrommer on September 22, 2016, 06:59:22 amThat board have quite a few features missing or not broken out. The RTC battery is missing and USB is probably missing too. My board have broken every single pin out.

author: technix
author_rank: Super Contributor
timestamp: September 23, 2016, 10:25:20 am
content: Quote from: T3sl4co1l on September 22, 2016, 04:48:19 amThe left 2/3 of the bottom pour is VDD so there is no stitching. 4-layer or 6-layer board will cost me at least 5x than a double-layer board, and I hand assemble it so DFN/QFNs, or parts smaller than 0603 can be very problematic.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 23, 2016, 10:36:20 am
content: The board looks like it's designed for easy hand-soldering and modifications, which might be the point, but I wouldn't call it dense at all, except maybe by 1980's standards. I would start calling it dense after squeezing it in about one third of the current area.Personally, I mostly design in this same density level unless I absolutely need to go denser, for the sake of prototyping; I tend to need to change some resistor values, cut traces, add fix wires etc. When I need to, I use 0402, since it's still easy to hand-solder; but being slightly harder than 0603, there is no point in using 0402 in the majority of the cases when it's not needed for any reason. But for example, on 0.5mm QFP CPUs with multiple GND and Vdd pins, using 0402 bypass caps instead of 0603 is a HUGE help. So my boards tend to have the passive case distribution of about 10% 0805, 80% of 0603, and 10% 0402. I even may have mixture of 100n (edit: 0.1u for those from the USA) ceramics in 0402 and 0603 sizes, which would be stupid for machine assembly, but for a human, it's nicer to have 0603's when there is space.I agree that you don't need 4 layer board for this kind of simple project, where cost is also important.

author: technix
author_rank: Super Contributor
timestamp: September 23, 2016, 11:30:33 am
content: Quote from: Siwastaja on September 23, 2016, 10:36:20 amHand soldering is my first design restraint as I have no reflowing equipment other than a crude hot air gun (not a rework station might I mention.) I default to 0603 everything as that size is easy to hand solder for me (I have no microscope and rely solely on my naked eyes, although having 20/20 vision helps) and stocking components of the same type is much cheaper.I actually squeezed a few more components in there after this revision.

author: ConKbot
author_rank: Super Contributor
timestamp: September 23, 2016, 01:25:27 pm
content: "Thats not dense, THIS is dense"https://d3nevzfk7ii3be.cloudfront.net/igi/gBpUcOrPcrDlZBJ1.hugeMoto360 smart watch PCB

author: technotronix
author_rank: Regular Contributor
timestamp: September 23, 2016, 01:38:35 pm
content: Great! Good Job.

author: CM800
author_rank: Frequent Contributor
timestamp: September 23, 2016, 03:09:45 pm
content: Quote from: blueskull on September 23, 2016, 03:03:57 pmNice... They should contact one of the big names in DRSSTC design (Eric Goodchild, Steve Ward etc.) and offer a few bricks / SiC chips for advertisement, Use them to break the worlds biggest DRSSTC record... Could make great advertising material for a startup. 100kHz... could even do for a QCWDRSSTC.World Record known:http://www.mastersoflightning.com/(there is a contact link at the bottom if you really think this could be of interest)

author: djQUAN
author_rank: Frequent Contributor
timestamp: September 23, 2016, 03:47:02 pm
content: Quote from: ConKbot on September 23, 2016, 01:25:27 pmDo I see two SMD dc-dc converter modules there?

author: technix
author_rank: Super Contributor
timestamp: September 23, 2016, 04:18:45 pm
content: Quote from: ConKbot on September 23, 2016, 01:25:27 pmHow many layers does this board have? And is almost every single pad sitting on a via of some sort?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 23, 2016, 05:18:49 pm
content: Quote from: technix on September 23, 2016, 04:18:45 pmI'd guess 8 layers. HDI, so yes: via-in-pad, through any layer pair, laser drilled and copper filled.Tim