Hot answers tagged

8

You can get rough calculations of the breakdown voltage from calculators. This paper has some measurements from an etched 0.55mm tooth gap: Wan, F., Pilla, V., Li, J., Pommerenke, D., Shumiya, H., & Araki, K. (2014). Time Lag of Secondary ESD in Millimeter-Size Spark Gaps. IEEE Transactions on Electromagnetic Compatibility, 56(1), 28–34. doi:10.1109/...


7

For most circuits, it's a matter of aesthetics. For microwave circuits, it can make a very small difference to line impedance and losses. For very high voltage circuits, corona on sharp points might be an issue.


5

In effect it's an over voltage spark gap. If a line surge occurs, it will cause breakdown across the shark's teeth and (hopefully) offer some over-voltage protection to other parts of the circuit.


5

Decoupling caps should be physically close to the chips they decouple. Like, right next to them. KiCad doesn't have the smartest autorouter. Consider laying out the power traces by hand before letting the autorouter have its fun. KiCad will let you establish net classes; this, in turn, will let you define the traces on 5V to be thicker. Something about the ...


4

Ff you use a dental X-ray machine to look at PCB, it will not provide you with all the details you need in a PCB. See for yourself in this picture made using a dental X-ray machine to look at a PCB:


4

I know this is a very old question, but whomever is interested, I actually think there is one important thing wrong in the previous answer. It was assumed that the speed of light within the PCB track is the same as in vacuum, which is not the case. If we take FR4 (7628), its relative permittivity is ~4.5, thus refractive index will be 2.12 (how many times ...


4

Check your Gerber output configuration and make sure that none of the shown boxes are checked: If you check any of those boxes that particular mechanical layer will be merged with each of the other layers, something you seldom want.


4

I believe they're using "+/-" to mean "approximately" here. I've seen some people use it in that manner before, though it's always struck me as a bit odd since "~" is less ambiguous. The way a PCB is manufactured starts with a copper foil of some thickness on an FR-4 substrate, and then the thickness is increased by plating ...


4

You should be OK with the large copper area under the pad. However, you should use solder resist to define the pad area (the purple lines on pads 3 and 5) if soldering with solder paste, to stop the solder running away from the joint. This is less important if you are hand soldering, as you can just add more solder during soldering.


3

You need a large footprint part. If you need 5 mm clearance, you can't just use an 0805 capacitor or resistor and expect to have your clearances satisfied; you would want to use a properly rated high-voltage part, which should have appropriate clearance and creepage due to its design. That may mean wide lead spacing on a through-hole diode, or the use of an ...


3

Use a thin thermally isolated short connection to the pad for best soldering flow practices.


3

Properly constructed cables designed for specific types of interface are indeed impedance controlled; if they were not then energy would reflect back from them. Any such cable would specifically state both the cable impedance and loss per unit distance or the specific interface it is designed for such as USB, USB superspeed which will have the symbol on the ...


3

But what happens to these impedances beyond the connectors which the controlled-impedance traces are routed to? Are the impedances maintained? Many times, if not most, yes! If not, then is it really necessary to design/route the traces with the specific impedances? Hm, it's usually useful to at least make your PCB traces not work as antennas for the ...


3

1 - Noise pickup on the leads is not what you need to worry about. If nothing else, you can put your detector in a shielded enclosure, with filtered power in and a hole just large enough for the IR to illuminate the array. 2 - What you do need to worry about is (as Kevin White commented) the effects of those long traces on the input capacitance of the op amp....


3

Unreliable traces are usually a problem with the PCB itself, not caused by soldering. So, review your PCB production data (Gerber files) and make sure the copper of that traces continues under the ring of the via. Look at the ring of a board that's not soldered with a strong magnification (microscope?) to see whether there's anything suspicious. Also, look ...


2

It depends on many factors, like what chip are you connecting to, and how long is the distance from connector to chip, and whether you want it to work reliably, or have to pass the compliance testing. The resitors depend completely on the chip if it requires resistors or not. Some do, some don't. The USB interface is a differential signal, so it requires a ...


2

It'll almost certainly be fine Based on the comments, the analog signal is running from one opamp to the next. This means it has a low impedance source, so it will be quite robust. It also seems the power supply comes from a linear regulator, which will tend to produce a low-noise power supply. As long as the loads are well decoupled, they won't introduce ...


2

Yes, it can be used for that purpose, and it works well. You need to remember that the pictures are small, so several will need to be taken, with some overlap. Ideally you'd want the X-rays taken with a digital sensor, so there'll be no wait to develop the prints, and it should cost much less.


2

I know that for signal integrity, the PCB traces are always considered to be part of the electrical circuit. Not always. Slow edge digital signals, non-precision low current analogue circuits, will usually get away with anything. How should traces be considered in different situations, like high current, RF, high edge rates etc.? For high current, the ...


2

Yes, the impedances extend from chips to PCB, from PCB to connector, and from connector to cables. Cables are specifically manufactured with the required impedance, and these apply to all kinds of interfaces, including USB, HDMI, DVI, DisplayPort, SATA, Ethernet, CAN, RS485, even analog video interfaces such as VGA, component and RGB, composite, and S-video.


2

I don't think it's as much of the soldermasks fault as the thermal coefficient of expansion between copper an aluminum, and the large PCB and features. For aluminum its 21 - 24.0 (10-6 m/(m °C)) For copper its 16 - 16.7 (10-6 m/(m °C)) a aluminum feature that is 5cm will expand about 1.2um/C a copper feature that is 5cm will expand about 8.35e-6m/C Which ...


2

Have i done something wrong? Yes, you put the capacitors in the wrong place. They're decoupling capacitors, you're supposed to put them up against the thing you're decoupling. Move them there. The software makes sure you implemented the circuit as you drew it, not that you put things in places that make sense, so you can pass the DRC but have a very ...


1

The airwires only show the shortest possible connections for each net. If you look at U1, there is an airwire between pins 1 and 5 -- that is the shortest connection from OutA to +InB. You can insert a dummy component (like a resistor) on the schematic in the path somewhere to split the nets, then place the dummy component next to C1 on the PCB, route the ...


1

In precision voltage reference applications (analog), capacitance is the primary consideration, usually precluding a ground plane. In fact, up until the 1990s, zener-based references were hand-made.


1

Power supply wiring carries voltage (nearly unchanging) and current (which might have surges/spikes at relatively high frequency). So, capacitive coupling from signal to DC power wiring is usually not troublesome; after all, the power wiring voltage is nearly unchanging and only dV/dt terms show up in the signal from a capacitive sneak path. The current, ...


1

I cannot figure it out how the current calculated They're probably not calculated because they include strong safety margins for maintaining intrinsic safety thus, the current won't produce an excessive over-temperature (for a given track width) that might ignite a contacting gas. It's highly likely (that along with spark ignition testing on various gases), ...


1

The higher the impedance seen from outside, the more susceptible the pin to noise. If the unused pin is configured as input (analog or digital) or open-drain output, the pin will be more susceptible to noise. The best practice would be configuring them as push-pull digital outputs as the impedance seen from outside would be much lower.


1

Probably not by a lot. Proper grounding of the PCB and filtering of the input signal, the analog reference and PCB layout are more of an issue. That's built on a cheap 2-layer board so the layout cannot be all that great. If you flip that board over, you'll probably find large areas of copper pour that are at AC ground potential (either tied to GND or to a ...


1

It’s okay to leave I/O pins unconnected if you ensure that they’re programmed to have a pull-up or pull-down, or are programmed as outputs. What you don’t want is a floating input. That can lead to unstable operation and excess power draw. That said, if proximity to a noise source is a problem, you can bypass the (pull-up/down) pins with small capacitors.


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