Questions for "Advanced PCB Layout Course" course
gyuunyuu1989 , 10-24-2023, 04:14 PM
I have created this thread for all questions related to the Advanced PCB Layout Course from Fedevel Academy.
I am on the first lesson and I can see that the lessons is quite dense. I think that it would be great if QA exists on course itself such that anyone that has signed up for the course can ask questions. I wish that Robert can fill in on this thread.
Starting at lesson 1 "Placement" at 37:00 to 39:00 minutes in the video, Robert is talking about decoupling capacitors. He places some that connect to VDDARM_IN_#[1..8]. There are seven decoupling capacitors. After placing a few capacitors Robert says this "At this stage, we would only like to see how much space we need. And what is more important, we would like to see, where is the free space. So, when we will be doing the fanout, we will actually move out everything away, from this area under the processor. You need to remember where was the free space. And then when you will start putting, putting the vias there, and we start putting the components back, you will know which direction (Robert moving hands now) you need to go. Yeah? You know where is the free space which you can use for the components. Just do rest of the components errr, by yourself. "
It is not completely clear what Robert is talking about here. First he places some capacitors then he says that we can't place them there because the BGA vias will go there. This raises the following questions:
1. Why did Robet put capacitors under the BGA when they can't actually go there due to BGA vias that shall be put there later?
2. What does Robert mean by "free space" here, since the BGA area shall be covered by vias, that is how we do BGA fanout right? What does he mean by "free space"?
3. What does Robert even mean when he is moving hands and saying "you will know which direction you need to go"? Where and what needs to go??
I shall be grateful if Robert could clarify these 2 minutes of the video. I am very much puzzled.
I am on the first lesson and I can see that the lessons is quite dense. I think that it would be great if QA exists on course itself such that anyone that has signed up for the course can ask questions. I wish that Robert can fill in on this thread.
Starting at lesson 1 "Placement" at 37:00 to 39:00 minutes in the video, Robert is talking about decoupling capacitors. He places some that connect to VDDARM_IN_#[1..8]. There are seven decoupling capacitors. After placing a few capacitors Robert says this "At this stage, we would only like to see how much space we need. And what is more important, we would like to see, where is the free space. So, when we will be doing the fanout, we will actually move out everything away, from this area under the processor. You need to remember where was the free space. And then when you will start putting, putting the vias there, and we start putting the components back, you will know which direction (Robert moving hands now) you need to go. Yeah? You know where is the free space which you can use for the components. Just do rest of the components errr, by yourself. "
It is not completely clear what Robert is talking about here. First he places some capacitors then he says that we can't place them there because the BGA vias will go there. This raises the following questions:
1. Why did Robet put capacitors under the BGA when they can't actually go there due to BGA vias that shall be put there later?
2. What does Robert mean by "free space" here, since the BGA area shall be covered by vias, that is how we do BGA fanout right? What does he mean by "free space"?
3. What does Robert even mean when he is moving hands and saying "you will know which direction you need to go"? Where and what needs to go??
I shall be grateful if Robert could clarify these 2 minutes of the video. I am very much puzzled.
gyuunyuu1989 , 10-27-2023, 04:18 PM
Also, Robert has mentioned microvias in this course several times but did not go into details of how a microvia differs from a through hole via or blind or buried via. This is quite seriously important but I don't think Robert has done it.
Is it possible to design high speed boards without microvias?
Is it possible to design high speed boards without microvias?
qdrives , 10-28-2023, 09:44 AM
Is it possible to design high speed boards without microvias?
First question is "what is high speed?"
For (very) high-speed the 'unused' part of a via will cause some negative effects as the signal bounces from the end of the via.
There are 3 solutions to that:
1) Back drilling
2) Mechanically drilled blind and buried via's
3) Laser drilled (micro) via's
All these techniques are more expensive than standard through hole via's as additional steps are required.
You can also check the Happy Holden videos from Azitech https://www.youtube.com/watch?v=aL0cVfYleWM
gyuunyuu1989 , 10-29-2023, 05:33 PM
Is it possible for a PCB design engineer in nowadays to never have to deal with a design that contains high speed interfaces like PCIe, DDR3, USB 3.0 e.t.c?
qdrives , 10-30-2023, 02:37 PM
Certainly. I have never made a design with those you mention.
The highest speeds I did was for USB2 (full speed), 100BaseT and 96MHz MCU.
The highest speeds I did was for USB2 (full speed), 100BaseT and 96MHz MCU.
gyuunyuu1989 , 11-02-2023, 03:40 PM
The RS232 driver IC is connected as follows:
Robert says that the ferrite bead are present to filter noise. But why do we also need the capacitors in C164 and C165?
Also, if we have capacitors that slow down the IC output and ferrite bead that also slow down the IC output, won't that reduce the edge rate of the output on the connector (the output that travels down the RS232 harness) to such an extent that the communication is not possible and high data rates anymore.
Very strange to put ferrite bead and also capacitors on a signal that is going out of the board. I mean, if a long harness being connected to the RS232 connector is already going to appear as a large capacitive load, it does not make sense to add so much burden on the signal paths to slow the rise and fall of the IC outputs.
Robert says that the ferrite bead are present to filter noise. But why do we also need the capacitors in C164 and C165?
Also, if we have capacitors that slow down the IC output and ferrite bead that also slow down the IC output, won't that reduce the edge rate of the output on the connector (the output that travels down the RS232 harness) to such an extent that the communication is not possible and high data rates anymore.
Very strange to put ferrite bead and also capacitors on a signal that is going out of the board. I mean, if a long harness being connected to the RS232 connector is already going to appear as a large capacitive load, it does not make sense to add so much burden on the signal paths to slow the rise and fall of the IC outputs.
qdrives , 11-02-2023, 03:51 PM
The ferrite beads and capacitors form a low pass LC filter. However, this filter is for outside noise. It does not work as good for noise from inside to outside.
I have never placed any filtering on the RS232 lines of products I have designed. Thousands in the field, no issues. Both in domestic and industrial environments.
In my opinion you can leave the ferrites and capacitors out of the design. As long as you make sure it is capable of 15kV ESD (as this one mentions).
I have never placed any filtering on the RS232 lines of products I have designed. Thousands in the field, no issues. Both in domestic and industrial environments.
In my opinion you can leave the ferrites and capacitors out of the design. As long as you make sure it is capable of 15kV ESD (as this one mentions).
gyuunyuu1989 , 11-02-2023, 08:46 PM
So you mean that the noise from outside won't get in but noise from inside can get out? Robert said that ferrite is there so that noise from inside does not go outside. He did not discuss the capacitor arrays at all.
gyuunyuu1989 , 11-02-2023, 08:55 PM
Now one more thing, so Robert discussed ESD protection in one part of the lesson 1.
USB port uses ESD protection (BGX50AE6327) with choke(ACM2012-900-2P-T002).
SIM card slot uses ESD protection (BZA956A,115)
The first confusion and it is massive confusion, why does the USB port use a part that is "bridge rectifier" while the SIM card slot uses a part that is "TVS diodes". Shoudn't both of them be TVS diodes, with the USB port using TVS diodes that have low capacative loading so the USB port can run at high speed?
Also, the part used with the USB port is called choke. But the part used with the RS232 that I mentioned earlier is called ferrite bead? Whaaat is the difference?
Schematic for the USB port is attached, it is a double connector with two USB ports one stacked on top of the other.
USB port uses ESD protection (BGX50AE6327) with choke(ACM2012-900-2P-T002).
SIM card slot uses ESD protection (BZA956A,115)
The first confusion and it is massive confusion, why does the USB port use a part that is "bridge rectifier" while the SIM card slot uses a part that is "TVS diodes". Shoudn't both of them be TVS diodes, with the USB port using TVS diodes that have low capacative loading so the USB port can run at high speed?
Also, the part used with the USB port is called choke. But the part used with the RS232 that I mentioned earlier is called ferrite bead? Whaaat is the difference?
Schematic for the USB port is attached, it is a double connector with two USB ports one stacked on top of the other.
qdrives , 11-03-2023, 06:35 PM
To answer your question on the ferrite beads:
qdrives , 11-03-2023, 06:57 PM
For your ESD protection it is best to start a new thread next time. Otherwise you might have the problem that I am the only one answering...
Anyhow - what is ESD? The bridge rectifier converts the 'AC' to DC, right?
The USD D+ and D- have a diode from Gnd to the signal and from the signal to Vbus. On Vbus is a big capacitance of 330uF and 100nF.
The bridge device just has 4 diodes so both D+ and D- are connected to the 'AC' terminals. The capacitance of this bridge is very low at 1.5pF!
An ESD discharge is like a capacitor of 100pF and 8kV (HBM - Human Body Model).
If that 8kV goes through the diodes to the capacitors we get a capacitive divider. The 100nF will have a much lower inductance so most of it wil go there (first).
8kV and 100pF will be like 8V on the 100nF. Just make sure that the inductance of the signal, through the diode to the capacitor (100nF) is very low. I state inductance here as resistance is your friend in this case (damping/losses)
The BZA956A has a much higher capacitance (>30pF) and therefor not suitable for USB.
The simple way I see it is that a choke is an inductor intended to filter (choke noise). However, this is not how others always see it.
A ferrite bead is an inductor too. See the video mentioned in the previous comment.
Ferrite beads are to filter differential noise whereas the common mode choke use in this design is to filter common mode noise.
Differential filters on differential signals is problematic as each signal can be filtered differently and that makes a difference (kind of tong twister sentence).
The common mode choke leaves the differential signal as is, but only filters out common mode (ESD and other noise has a large common mode part to it).
Anyhow - what is ESD? The bridge rectifier converts the 'AC' to DC, right?
The USD D+ and D- have a diode from Gnd to the signal and from the signal to Vbus. On Vbus is a big capacitance of 330uF and 100nF.
The bridge device just has 4 diodes so both D+ and D- are connected to the 'AC' terminals. The capacitance of this bridge is very low at 1.5pF!
An ESD discharge is like a capacitor of 100pF and 8kV (HBM - Human Body Model).
If that 8kV goes through the diodes to the capacitors we get a capacitive divider. The 100nF will have a much lower inductance so most of it wil go there (first).
8kV and 100pF will be like 8V on the 100nF. Just make sure that the inductance of the signal, through the diode to the capacitor (100nF) is very low. I state inductance here as resistance is your friend in this case (damping/losses)
The BZA956A has a much higher capacitance (>30pF) and therefor not suitable for USB.
The simple way I see it is that a choke is an inductor intended to filter (choke noise). However, this is not how others always see it.
A ferrite bead is an inductor too. See the video mentioned in the previous comment.
Ferrite beads are to filter differential noise whereas the common mode choke use in this design is to filter common mode noise.
Differential filters on differential signals is problematic as each signal can be filtered differently and that makes a difference (kind of tong twister sentence).
The common mode choke leaves the differential signal as is, but only filters out common mode (ESD and other noise has a large common mode part to it).
gyuunyuu1989 , 11-05-2023, 07:09 AM
Robert has spent a lot of time on circuit protection from ESD. However, he has said nothing about circuit protection from overvoltage or reverse polarity at the input. Is overvoltage and reverse polarity at the input port not considered important topic for circuit designs usually?
qdrives , 11-05-2023, 12:53 PM
ESD happens mostly unintended and is relatively easy to solve.
Overvoltage protection You have an input for 5V and someone supplies it with 24V. Now what? You 'fix' the input to withstand 24V, but now they connect 230Vac to it. To which voltage are you protecting?
Reverse polarity Some connectors have a key which does not allow wrong connection. For others... well the customer made a mistake, so it is no warranty.
But for those that want all in one power connection including soft-start:
As you can see, a huge amount of components are needed and a lot more complicated.
Overvoltage protection You have an input for 5V and someone supplies it with 24V. Now what? You 'fix' the input to withstand 24V, but now they connect 230Vac to it. To which voltage are you protecting?
Reverse polarity Some connectors have a key which does not allow wrong connection. For others... well the customer made a mistake, so it is no warranty.
But for those that want all in one power connection including soft-start:
As you can see, a huge amount of components are needed and a lot more complicated.
gyuunyuu1989 , 11-06-2023, 12:32 PM
I was hoping that Robert would also show how to combine battery power with external power but that is not part of this course. Anyway, so Robert mentioned something called standoff connectors. These are connectors in which we are going to place a card e.g PCIe mini card. And the card is going to be a few mm above the PCB surface. This means that we can fit some small components between the PCB surface and the external card that is put into the connector.
The problem is that when I do google search using the term "pcb standoff connector", I get unexpected results that show stuff that goes into the mounting holes to keep the PCB off the chasis floor or off the bench surface.
Is the correct term for the connectors specified by Robert actually standoff connectors?
The problem is that when I do google search using the term "pcb standoff connector", I get unexpected results that show stuff that goes into the mounting holes to keep the PCB off the chasis floor or off the bench surface.
Is the correct term for the connectors specified by Robert actually standoff connectors?
qdrives , 11-06-2023, 01:53 PM
I would say they are "card edge connectors".
Digikey then has it as "Edgeboard Connectors".
Just pick 1 from the over 600k types....
Digikey then has it as "Edgeboard Connectors".
Just pick 1 from the over 600k types....
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