41
votes
Accepted
Why is there a difference between pad-to-trace and trace-to-trace clearance?
But it makes me wonder why the PCB manufacturer sees the 2 as
different things.
It's likely that this is due to the solder mask tolerance.
With two side-by-side tracks, the solder resist ...
- 466k
33
votes
Accepted
Pattern on a PCB
The pattern is a pair of spark gaps, a kind of low-cost voltage limiter. The closely-spaced pointy conductors favor the formation of a spark, and the soldermask is removed (the tan rectangular area) ...
- 176k
27
votes
Is my PCB design good or really bad?
There are some oddities on the schematic:
The power input would most likely benefit from an electrolytic capacitor near the connector. I don't know the ratings here, but I would guess something 100 ...
- 43.3k
27
votes
How can I find where a short has occurred inside of a PCB?
You could connect an audio signal generator and run as much audio current as possible through the short, at something like 400 Hz or 1 kHz. Then make a pickup coil (often the iron core and coil from ...
- 931
25
votes
Accepted
PCB Edge connector: nipples on each finger?
Those traces are used to short all the terminals together before the card is cut out of the panel. While immersion gold doesn't require it, hard gold that's capable of surviving dozens to hundreds of ...
- 36.2k
24
votes
Accepted
What is an ideal layout for a normally-open solder jumper?
Take this layout:
|¯¯\ \¯¯|
|__/ /__|
Just make the arrows better than I did here :D
Slide with solder left to right to close, right to left to open. Reduce the ...
- 571
19
votes
Can solder on wireless device PCB be vaporized during electrical storm?
What you see is a rather common no-clean flux residue left over from selective soldering of through hole components.
If you look closely you will see the outline of the selective solder mask that was ...
19
votes
Accepted
Second opinion on PCB design for relay made in Altium
In addition to what has already been said:
One neat trick (...from the 1980s) is to place through-hole resistors vertically so that they don't take up as much board space. You shouldn't have ...
- 21.6k
19
votes
Accepted
Why is the MOSFET in this fan control circuit overheating?
It looks like you have an N-channel MOSFET operating as a "source-follower", otherwise known as "common-drain". That means the source is always a few volts lower than the gate (by ...
- 42.1k
18
votes
PCB Edge connector: nipples on each finger?
The connections are required to short together the fingers so they can be electroplated with thick hard gold (typically after a nickel barrier layer). The shorted fingers become the cathode in the ...
18
votes
Accepted
Does making a ground plane and a power plane on a PCB make the board behave like a large capacitor?
It would act as a small capacitor regarding capacitance, only large in area.
The capacitance of the planes will help, but distributing that small capacitance over a large area means it will only be ...
- 164k
16
votes
How can I find where a short has occurred inside of a PCB?
If you apply a significant current (several amperes or more) then you can follow the path to the short by measuring voltage gradients with a multimeter on a low range (10uV or 100uV resolution, more ...
16
votes
Does making a ground plane and a power plane on a PCB make the board behave like a large capacitor?
The amount of capacitance that can be achieved between two layers of a PCB tend to be low. For example 4mil separation with FR4 dielectric gives about 250pF/sq inch. (Calculate interplane capacitance)
...
- 33.8k
16
votes
Accepted
What are these cylinders with holes for in a universal PCB enclosure?
Those lower bosses are for mounting your circuit board inside the enclosure. You may have to supply your own screws for that. The raised ones are for mounting the lid. Those screws usually come ...
- 5,048
16
votes
Accepted
How important is a "no reflection" strategy for 1 Hz systems?
Reflections depend on edge rate and required signal quality; and any extenuating circumstances, like if slow edges cause excessive power dissipation or chattering/oscillation of logic gate inputs, or ...
- 43.3k
15
votes
What is an ideal layout for a normally-open solder jumper?
The correct answer is probably: there exists no ideal layout.
Or at least none which the PCB CAD and/or manufacturer will approve. Usually the default clearance area around a pad/trace is too wide to ...
- 21.6k
15
votes
Do all crystals need capacitors?
Do all crystals need capacitors?
and
I tried to look on datasheets, but I didn't understand
You really must read the data sheet more carefully: -
- 466k
14
votes
Connecting GPIOs on two boards with independent power supplies
In situations like this, I like to use an optical coupler (example) in between the two systems. The systems will remain electrically isolated, so no current will flow between them in either direction. ...
- 1,128
14
votes
Accepted
Decoupling capacitors where VDD/VSS pins are spaced apart
The inductance to the caps is what is important, not the physical distance.
With 4 layers, you will have a ground plane, and probably a power plane also.
Planes have very low inductance, so you want ...
- 16.6k
14
votes
How to design a 12V to <100mV 15A DC-DC converter?
Your requirements are quite close to the CPU VRM found on a PC motherboard, which outputs around 1V at huge current (50-100A). So you should be able to find the same parts, which are available and ...
- 80.3k
14
votes
Is my PCB design good or really bad?
The main comment I have is regarding the schematic: don't go for this "blocky" layout of a schematic. Many "professionals" who have not seen a good schematic in their career seem ...
14
votes
Why did my DC/DC Buck Circuit fail?
If you are absolutely sure you soldered it the right way around, cause of death should be overvoltage as per Andy's post.
You can add a TVS and/or an aluminium electrolytic of a few hundred µF at the ...
- 80.3k
14
votes
How to connect to "upstands" on the PCB without soldering?
The PCBs are identical.
They both have a connectors for a detachable screw terminal.
The other PCB just has the detachable PCB terminal block attached and the other one has it detached.
- 164k
13
votes
Why is there white stuff on these inductors?
The windings on the inductors can move just a tiny bit, especially if there's a lot of current flowing through the coil. The magnetic field generated by the current flowing in the coil makes the ...
- 73k
13
votes
Accepted
Why did my DC/DC Buck Circuit fail?
Any appreciable wire inductance from the 24 volt source is going to cause a ringing spike of anything up to twice 24 volts at the input to the chip and, that chip has an absolute maximum rating of 30 ...
- 466k
13
votes
Pattern on a PCB
That looks like an area with two pairs of pointy “teeth” with a small air gap between them, and no solder mask over that area. Most likely this is part of the board’s EMC protection, providing a place ...
- 14.9k
13
votes
Pattern on a PCB
According to this NXP document, PCB spark gaps have an approximate breakdown voltage of V = 3000pd + 1350 where p is the pressure in atmospheres and d is the gap in mm. So a 0.5mm spark gap would have ...
13
votes
How important is a "no reflection" strategy for 1 Hz systems?
The big takeway is that you are using "fast" chips so you have a "fast" design. The fact that the signals through the fast system are 1 Hz signals is irrelevant, because fast chips ...
- 164k
13
votes
Accepted
Power line crossing data lines via the ground plane
it's less about the fact that these are power traces, it's problematic because now the return current for these data lines can't travel directly below them, but needs to take a shared detour around ...
- 98.2k
12
votes
Which type of female connector is this?
These are generally known as board to board connectors, in this case more specifically as "Bottom Entry" board to board connectors. The picture below shows examples of both top entry and ...
- 10.5k
Only top scored, non community-wiki answers of a minimum length are eligible