Author Topic: First 4 Layer PCB: Traces on each layer a good idea?  (Read 8165 times)

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Offline asmi

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Re: First 4 Layer PCB: Traces on each layer a good idea?
« Reply #75 on: July 28, 2020, 03:52:22 am »
And saying "well, just don't use those companies that charge more for them" is entirely missing the point that such cost differences exist for practical reasons.
Assembly companies are infamous for doing whatever you want and secretly hiding the cost from you. They won't tell you you are secretly paying a premium for 0402 parts, or that piss-poor panel layout, or *insert any other production related thing here*.
As long as the quote's bottom line is in line with what I think it should be, and it's within my project's budget - I'm OK with that and don't really care to read them justifying each and every cent in the quote. I don't race to the bottom with my products, so I don't need to shave every cent off the production cost, the quality is more important that price (up to the point of course). Pretty much all of my boards are at least 4 layers, with 6 layers being the most popular, so PCB area savings provided by miniaturization are important, which is why I prefer parts in BGA packages (as long as ball pitch is reasonably large to not require HDI) over QFPs (because latter are much larger, sometimes over 2x size, for example in my latest project I chose to use STM32H7 in BGA240+25 package as opposed to QFN208, because latter is exactly 4 times the area -  28x28 vs 14x14). Same reason I don't even think about limiting myself to a single-sided loads. I also order my production boards at WellPCB as opposed to JLCPBC, because while being a bit more expensive, they provide much better PCB quality.
But perhaps I'm in a minority here, because most of my boards are rather expensive, with BOM costs of a single board being in the 100s of dollars, sometimes quite a few 100s actually, encroaching on 1000$. For example, if you take a look at the FPGA board project in my signature - that is a very simple project by my standards, and quite inefficient in terms of PCB area utilization - because I designed it for hand assembly by people who perhaps are not as experienced with hand assembly as I am, and I wanted to keep full cost under $100 for PCB production + 1 hand assembled board. BTW if you are looking for material for your next PCB review - I would love if you review that board, as I'm always looking forward for constructive criticism and ways to improve. It's an open source and open HW project, so everyone is free to use it however they see fit.

Offline EEVblog

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Re: First 4 Layer PCB: Traces on each layer a good idea?
« Reply #76 on: July 28, 2020, 04:23:32 am »
BTW if you are looking for material for your next PCB review - I would love if you review that board, as I'm always looking forward for constructive criticism and ways to improve. It's an open source and open HW project, so everyone is free to use it however they see fit.

What board are you referring to?
 

Offline asmi

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Re: First 4 Layer PCB: Traces on each layer a good idea?
« Reply #77 on: July 28, 2020, 04:49:12 am »
What board are you referring to?
https://www.eevblog.com/forum/fpga/custom-spartan-7-board-for-beginners/
Description, some photos and links to Github repos are in that post.
 
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Offline -gb-

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Re: First 4 Layer PCB: Traces on each layer a good idea?
« Reply #78 on: July 28, 2020, 09:30:23 am »
Quote
You will probably want to pull USB connector closer to the edge so that the line marked "PCB Edge" would actually be on the edge. Otherwise looks good to me on a first sight.

I don't want anything. But when i pull it to the marking, then a bit will look over the pcb edge. This is OK when the PCB goes inside a housing.

Quote
Why go to double sided load?
Sure, if you need the form factor or electrical requirements, fine. But you didn't seem to need it before, so why now?
Fine if it's a one-off or low volume run of course, not big deal. But you usually don't just go to double sided load for no reason.

Totally right. As said, i don't need anything, it is not my project i just had time to spare and tried an area optimised version. I am no professional and only do hobby projects which i handsolder with hot air. Double sided load saves me money with smaller PCB area. With handsoldering you can do many things you wouldn't do in production, unplugges Vias in pads e.g. for even higher component density.
 

Offline asmi

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Re: First 4 Layer PCB: Traces on each layer a good idea?
« Reply #79 on: July 28, 2020, 01:53:22 pm »
I don't want anything. But when i pull it to the marking, then a bit will look over the pcb edge. This is OK when the PCB goes inside a housing.
These USB connectors often have a "lip" that is supposed to hang on the the side of a board, helping to prevent user from ripping connector out when inserting the cable. Look at this one for example: https://www.snapeda.com/parts/10118193-0001LF/Amphenol%20FCI/view-part/?ref=digikey If you take a look at the 3D model you will see what I mean.

Offline poorchava

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Re: First 4 Layer PCB: Traces on each layer a good idea?
« Reply #80 on: August 06, 2020, 12:47:18 am »
Buck converter:
-layout is just bad. Large loops, long & thin traces between the chip and the inductor. Pleas do yourself a favor and follow the guidelines from the chip datasheet.

USB interface:
-use a smaller crystal. That crystal is probably 12MHz for USB. U can easily find that in a 2.5x3.2mm package.  Or just ditch the CH340 (that's what I assume it is) and use something like FT230X. It's available in a 16-pin QFN package and doesn't require a crystal at all. Also, the CH340 are worse than FTDI when it comes to high speed transmission. I could push FT230XQ up to about 2.5mbit, whereas CH340 craps out just about 1mbit.

general:
-use smaller passives. Those look like 0805. I mean come on, it's not 19th century. Go for 0402. You have small packages in there anyway, so that shouldn't be any problem
-fpga decoupling caps are routed in sub-optimal fashion. The power supply and ground lines should "fly through" a capacitor and then into the chip. If you have a ground plane, then just place a cap near the pins and a groundplane via on the opposite side of the cap, than the FPGA
I love the smell of FR4 in the morning!
 


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