Author Topic: Why am not able to get a grasp of PCB designing?  (Read 15780 times)

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Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #25 on: November 13, 2019, 06:51:30 am »
Maybe try some simpler PCBs first to get the hang of it? Lay out some stuff like 555 and transistor multivibrator LED blinkers, op-amp circuits, just easy stuff with a handful of components. Once you get the hang of the process it gets easier.
Ok, I will do that if I don't make any progress today.

Quote
Some people are also just better at visualizing spacial relationships, PCB layout came quite naturally to me but I've seen a lot of people struggle with it.
I'm honestly bad at those.

Btw, I placed a No connection flag on a capacitor but it has still populated on the PCB new.  :-//
 

Offline tautech

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Re: Why am not able to get a grasp of PCB designing?
« Reply #26 on: November 13, 2019, 07:22:01 am »
I have disabled ratsnet right now and started grouping components as per the schematic. Will post it once i am done for review
Don't, you need it to help visualize future routing.
While it seems like a curse and only confuses you it's a very valuable part of getting a PCB layout right.
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Offline tautech

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Re: Why am not able to get a grasp of PCB designing?
« Reply #27 on: November 13, 2019, 07:32:25 am »
Watch Dave:
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Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #28 on: November 13, 2019, 09:57:27 am »
FYI, the usual way I layout is to estimate total PCB size and shape (based on component size, PCB process and design target), place all parts outside PCB area, group parts by affinity and function, drag parts of vicinity to PCB area, arrange those parts, and repeat for other function blocks.

Once I have all parts roughly placed, I'll optimize the placement to effectively use boarder spaces between blocks and to make room for routing. This is the longest part. I always believe one should spend more time on placement than routing.

If you did a good job on placement, you should be able to visually see the routing even if they do not exist, so the remaining job is to just place tracks following what you can see.

There are always routing intensive parts that you can't see the way they are connected before the connection is done, and those are what you have to spend more time on layout than placement, but unless you mess with DDR memory or other massively parallel high speed buses, you will almost never encounter such cases.
I tried placing the parts as they were in the schematic, based on affinity and functionality, I wasn't able to route all traces. Should I connect the traces and place them inside the pcb?

Don't, you need it to help visualize future routing.
While it seems like a curse and only confuses you it's a very valuable part of getting a PCB layout right.
I felt it was easier to arrange the components that way. But the routing became a problem.
 

Offline tautech

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Re: Why am not able to get a grasp of PCB designing?
« Reply #29 on: November 13, 2019, 10:14:19 am »
Don't, you need it to help visualize future routing.
While it seems like a curse and only confuses you it's a very valuable part of getting a PCB layout right.
I felt it was easier to arrange the components that way. But the routing became a problem.
:)
It always is !
More layers if there is no other way but there are tricks like using bigger passives so to be able to route traces under them. Jumper wires and zero ohm links are other tricks.

Show us your efforts.
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Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #30 on: November 13, 2019, 10:31:57 am »
:)
It always is !
More layers if there is no other way but there are tricks like using bigger passives so to be able to route traces under them. Jumper wires and zero ohm links are other tricks.

Show us your efforts.

Thanks... Will see if I can use any of these.
 

Offline NivagSwerdna

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Re: Why am not able to get a grasp of PCB designing?
« Reply #31 on: November 13, 2019, 12:21:25 pm »
I am assuming to you are using both sides of the board for traces?  Show us what you have got so far. From the datasheet it looks quite do-able with 2 layers.
 

Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #32 on: November 13, 2019, 02:45:50 pm »
I am assuming to you are using both sides of the board for traces?  Show us what you have got so far. From the datasheet it looks quite do-able with 2 layers.

Guess I made some progress. I have completely ignored the layout rules on the datasheet but it's now better than before. 

871450-0

Here are the rules from the datasheet:
Quote
The power and current of the chip work are relatively large, and the position of the capacitor on the VSYS network will affect the stability of the DCDC operation. Capacitors on the VSYS network need to be as close as possible to the IC's VSYS pin and EPAD, and copper is spread over a large area, adding more vias to reduce the current loop area between the capacitor and the IC, reducing parasitic parameters. The VSYS pins are distributed on both sides of the chip, requiring capacitors to be placed on the adjacent pins on both sides, and the VSYS pins on both sides are connected together by a wider (not less than 100 mil) copper on the PCB.

10mOhm sampling resistor:
The chip samples the current flowing through the 10mOhm resistor through the VSN and VSP pins to control the input charging current, output overcurrent protection, and output light-load shutdown. Therefore, when drawing the PCB, the wiring requirements for the VSN and VSP pins are relatively high. It is necessary to avoid the signals with large interference, and separately route to the inside of the two pads of the 10mOhm sampling resistor, which cannot be combined with VSYS and other currents. The path that flows through has any coincident traces. Although VSP and VSYS are the same network on the PCB, the traces of the pins must be separated separately. A 100nF filter capacitor is required on the VSN and VSP pins, respectively, as close as possible to the IC pin to enhance the immunity of the sampled signal.

Trace from 10mOhm sampling resistor to input and output MOS tube Application example:
VOUT1 is equipped with a mobile phone that does not support fast charging. The VOUT2 port is equipped with a mobile phone that supports fast charging. Since multiple ports are simultaneously output, the system can only output 5V and charge two mobile phones at the same time. When the mobile phone on VOUT1 is pulled out, or the power consumption is less than the set value, the system will close the VOUT1 output port and then only keep the VOUT2 port output. In this case, the system can automatically restore the VOUT2 port fast charge function to the mobile phone on the VOUT2 port. Perform fast charging. To achieve the above automatic recovery fast charge function, it is necessary to accurately detect the output current on the VOUT1 port. The output current on the VOUT1 port is implemented by detecting the voltage difference between the VSN and VOUT1 pins. The threshold condition for turning off the VOUT1 port is a voltage difference of less than 1.8mV. Therefore, when there is no current on VOUT1, no other current can flow through any trace from VSN to VOUT1. Otherwise, if a current flows, a voltage difference will be formed, which will be misjudged as the current flowing out of VOUT1. The same principle is used for other outputs. In summary, the PCB traces from 10mOhm to VOUT1, from 10mOhm to VOUT2, from 10mOhm to VIN. There are separate traces at 10mOhm, and any two currents that flow in the same direction cannot overlap. Otherwise, the auto-recovery fast charge function described on the “Application Example” will be invalid, and may sometimes be absent.

If the wrong layout causes the output current of VOUT1 and VOUT2 to have a 1 milliohm coincident trace, when there is a 2A current output on VOUT2, a 2mV differential will be generated on the coincident 1 milliohm trace. In this case, even if it is pulled out When the device on VOUT1 is removed, it is impossible to judge that the device on VOUT1 is unplugged, and the fast charge function of the VOUT2 output port cannot be restored. The current required to be connected to the VOUT2 output is less than 1.8A, and the voltage difference generated on the coincident 1mohm trace is less than 1.8mV for 16ms to automatically restore the fast charge function of the VOUT2 output.

What should be the trace length? For VSYS, VBAT, VOUT  and GND it should be more than 100 mils. What about the other traces? What should be the gap between them?
« Last Edit: November 13, 2019, 02:48:22 pm by redgear »
 

Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #33 on: November 13, 2019, 03:08:54 pm »
(Attachment Link)

I feel routing this layout would be very difficult. What capacitors need to be really close to the IC? What capacitors can I afford to move to the other layer of the PCB(it's mostly unused). How do I create a pad to solder the battery connections?

The components with a NC flag is also populated on the board, I don't really want to use them should I remove them from the schematic or just leave the component unsoldered?
 

Offline NivagSwerdna

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Re: Why am not able to get a grasp of PCB designing?
« Reply #34 on: November 13, 2019, 03:33:06 pm »
I'm not sure you are listening to the advice being given to you... for example if you rotated the chip 90 clockwise the lines would be better organised radially.

Start drawing some traces and see what happens.
 

Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #35 on: November 13, 2019, 03:37:03 pm »
I'm not sure you are listening to the advice being given to you... for example if you rotated the chip 90 clockwise the lines would be better organised radially.
Sorry, i might have missed. But I am trying to follow and improve. I have rotated it now and here is a image.
871468-0
Quote
Start drawing some traces and see what happens.
What should be the width of the trace?
« Last Edit: November 13, 2019, 03:38:39 pm by redgear »
 

Offline grbk

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Re: Why am not able to get a grasp of PCB designing?
« Reply #36 on: November 13, 2019, 03:58:29 pm »
I don't think you're giving yourself nearly enough room for routing traces in that board. Is there a reason you can't make the board bigger and spread things out? That will make it a lot easier, especially for your first board. You can always make things more closely packed later on if you want to.

Trace size will be dependent on where you're manufacturing the board. Many fabs these days have 6 mil minimum trace width and 6 mil spacing but check the design rules for the pcb house you're using. That's a minimum; I would use bigger traces unless you absolutely need tiny traces. I tend to use 8mil traces as default. Use bigger traces if you need lower resistance. Use a pcb calculator to calculate trace resistance for a given width/length. Combined with the expected current, the trace resistance will give you voltage drop and temperature rise. Kicad has a basic multifunction pcb calculator built in but there are others out there, some with more features.

The NC flag in Kicad just means that you are not intending to connect anything to that pin. Normally the electrical rules checker will complain if any pins aren't connected to a net; the NC flag tells ERC that it isn't a mistake and that pin is intentionally disconnected. It does not tell kicad that you want that part excluded from the layout. If you don't want a part on your board, either remove the part from the schematic entirely, or edit its reference designator to start with a # (for example, if you didn't want R101 to be included in layout, call it #R101 instead). In this case I would recommend just deleting the part -- if you don't want it on the board, why is it in your schematic? You could also leave it in your schematic & layout, but not solder the part. In this case I would add a "DNP" (do not populate) note in the properties for the schematic symbol for the part to remind yourself or anyone else that the part should not be actually assembled onto the board.
 
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Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #37 on: November 13, 2019, 04:21:12 pm »
I don't think you're giving yourself nearly enough room for routing traces in that board. Is there a reason you can't make the board bigger and spread things out? That will make it a lot easier, especially for your first board. You can always make things more closely packed later on if you want to.
Yep, I am targeting that as my final board dimension. The back side of the board is largely unused, if I could move some components there, I guess I can make enough space to accommodate everything with in this board dimension. But I am not sure about the components that I can move to the other side without affecting the performance. Decoupling caps need to be as close as possible to the IC, I am not sure if they can be placed on the other side of the board.
Quote
Trace size will be dependent on where you're manufacturing the board. Many fabs these days have 6 mil minimum trace width and 6 mil spacing but check the design rules for the pcb house you're using. That's a minimum; I would use bigger traces unless you absolutely need tiny traces. I tend to use 8mil traces as default. Use bigger traces if you need lower resistance. Use a pcb calculator to calculate trace resistance for a given width/length. Combined with the expected current, the trace resistance will give you voltage drop and temperature rise. Kicad has a basic multifunction pcb calculator built in but there are others out there, some with more features.
Cool, thanks. I will try using the calculators.
Quote
The NC flag in Kicad just means that you are not intending to connect anything to that pin. Normally the electrical rules checker will complain if any pins aren't connected to a net; the NC flag tells ERC that it isn't a mistake and that pin is intentionally disconnected. It does not tell kicad that you want that part excluded from the layout. If you don't want a part on your board, either remove the part from the schematic entirely, or edit its reference designator to start with a # (for example, if you didn't want R101 to be included in layout, call it #R101 instead). In this case I would recommend just deleting the part -- if you don't want it on the board, why is it in your schematic? You could also leave it in your schematic & layout, but not solder the part. In this case I would add a "DNP" (do not populate) note in the properties for the schematic symbol for the part to remind yourself or anyone else that the part should not be actually assembled onto the board.
Oh, got it. Will make it a practice hereafter.
 

Offline tooki

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Re: Why am not able to get a grasp of PCB designing?
« Reply #38 on: November 13, 2019, 04:23:37 pm »
You absolutely can put decoupling caps on the other side, it’s actually a really common technique that often lets you get the cap even closer to the pin than you would on the same side.
 
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Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #39 on: November 13, 2019, 04:29:07 pm »
You absolutely can put decoupling caps on the other side, it’s actually a really common technique that often lets you get the cap even closer to the pin than you would on the same side.
Ok. Thank you. I will try modifying the layout.
 

Offline tautech

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Re: Why am not able to get a grasp of PCB designing?
« Reply #40 on: November 13, 2019, 06:08:36 pm »
Does Kicad have a single layer view/working mode ?
Put all the big components on the back side plus any LED's and the IC and most passives on the other side.
That alone should make this quite doable.
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Offline grbk

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Re: Why am not able to get a grasp of PCB designing?
« Reply #41 on: November 13, 2019, 07:29:51 pm »
Does Kicad have a single layer view/working mode ?
Put all the big components on the back side plus any LED's and the IC and most passives on the other side.
That alone should make this quite doable.

Yes, that's a good point. In Kicad you can turn off unnecessary layers by unchecking them in the layer pane on the right. This gives you complete control over which layers are displayed. There's also a "high contrast" display mode that I like a lot; when you turn it on the active layer is displayed as normal, but other layers are displayed in a unobtrusive gray color that helps them fade into the background. Like tautech says this can be very helpful for focusing on what's currently important, and I recommend you try it.
 
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Offline tautech

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Re: Why am not able to get a grasp of PCB designing?
« Reply #42 on: November 13, 2019, 07:38:13 pm »
Does Kicad have a single layer view/working mode ?
Put all the big components on the back side plus any LED's and the IC and most passives on the other side.
That alone should make this quite doable.

Yes, that's a good point. In Kicad you can turn off unnecessary layers by unchecking them in the layer pane on the right. This gives you complete control over which layers are displayed. There's also a "high contrast" display mode that I like a lot; when you turn it on the active layer is displayed as normal, but other layers are displayed in a unobtrusive gray color that helps them fade into the background. Like tautech says this can be very helpful for focusing on what's currently important, and I recommend you try it.
Yep.  :)
Still redgear has to get his head around working with multiple layers and assigning any components properties to the correct layer which when done lets you better see on which layer they actually are.

Not the easiest project for first up but a little guidance will get him there.
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Offline james_s

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Re: Why am not able to get a grasp of PCB designing?
« Reply #43 on: November 14, 2019, 02:53:02 am »
I really try to keep all components on one side of the board unless I really need some on the back, the only time I ever have is decoupling capacitors on some relatively dense boards. It's just a pain to assemble boards that have parts on both sides, especially when doing reflow soldering.
 

Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #44 on: November 14, 2019, 04:58:06 am »
Does Kicad have a single layer view/working mode ?
Put all the big components on the back side plus any LED's and the IC and most passives on the other side.
That alone should make this quite doable.

Yes, that's a good point. In Kicad you can turn off unnecessary layers by unchecking them in the layer pane on the right. This gives you complete control over which layers are displayed. There's also a "high contrast" display mode that I like a lot; when you turn it on the active layer is displayed as normal, but other layers are displayed in a unobtrusive gray color that helps them fade into the background. Like tautech says this can be very helpful for focusing on what's currently important, and I recommend you try it.

This feature has made working with the board easier. Thanks.

Yep.  :)
Still redgear has to get his head around working with multiple layers and assigning any components properties to the correct layer which when done lets you better see on which layer they actually are.

Not the easiest project for first up but a little guidance will get him there.

I'm currently working on rearranging the components on different layer, will post a pic once I'm done.
Thank you everyone for the amazing support.
 

Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #45 on: November 14, 2019, 05:07:06 am »
Many resistors are beefier in this design. I haven't calculated the power rating required and used slightly bigger ones. Proper calculation of power rating of resistors can help me bring down the size of the footprints, providing more space for traces.
 
P=V2/R, but what should be the value of the voltage? The voltage fed to the boost circuit? The maximum output voltage of the boost circuit?
 

Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #46 on: November 14, 2019, 08:15:26 am »
Yes, that's a good point. In Kicad you can turn off unnecessary layers by unchecking them in the layer pane on the right. This gives you complete control over which layers are displayed. There's also a "high contrast" display mode that I like a lot; when you turn it on the active layer is displayed as normal, but other layers are displayed in a unobtrusive gray color that helps them fade into the background. Like tautech says this can be very helpful for focusing on what's currently important, and I recommend you try it.
Yep.  :)
Still redgear has to get his head around working with multiple layers and assigning any components properties to the correct layer which when done lets you better see on which layer they actually are.

Not the easiest project for first up but a little guidance will get him there.

I have now utilized both layers of the PCB. Is my design any better than it was? Can it be properly routed?
871648-0
 

Offline tautech

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Re: Why am not able to get a grasp of PCB designing?
« Reply #47 on: November 14, 2019, 09:03:32 am »


I have now utilized both layers of the PCB. Is my design any better than it was? Can it be properly routed improved ?
(Attachment Link)
Yes.  :)

First thing I spotted, top 2 resistors by the switch....rotate them vertical for better connectivity/easier routing.
While the purists like every device group orientated the same sometimes it's easier to flip and swap to make for easier routing.
Apply similar thinking throughout the PCB and you'll be staggered how much easier things become.

Shift some component designators off the device so it's easier for us to pick a # that should be moved/flipped etc.
Stack
them
alongside
somehow
like this. :)
« Last Edit: November 14, 2019, 09:06:42 am by tautech »
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Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #48 on: November 14, 2019, 09:14:43 am »
Yes.  :)

First thing I spotted, top 2 resistors by the switch....rotate them vertical for better connectivity/easier routing.
While the purists like every device group orientated the same sometimes it's easier to flip and swap to make for easier routing.
Apply similar thinking throughout the PCB and you'll be staggered how much easier things become.

Shift some component designators off the device so it's easier for us to pick a # that should be moved/flipped etc.
Stack
them
alongside
somehow
like this. :)

Thanks a lot! I am working on making the changes.
 

Offline james_s

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Re: Why am not able to get a grasp of PCB designing?
« Reply #49 on: November 14, 2019, 05:16:36 pm »
Many resistors are beefier in this design. I haven't calculated the power rating required and used slightly bigger ones. Proper calculation of power rating of resistors can help me bring down the size of the footprints, providing more space for traces.
 
P=V2/R, but what should be the value of the voltage? The voltage fed to the boost circuit? The maximum output voltage of the boost circuit?

The maximum voltage across the resistor. This of course depends heavily on where it is used, in most cases the power will be very low except for resistors used for current sensing and such.
 
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