# Tag Info

55

There is no problem routing traces through pads (like you have done). Be aware when routing power/GND of the current that will be travelling through these traces. This will dictate trace thickness. In addition, search for "power planes", "ground pours" for more information. I can see where your confusion may come from. I'm not a fan of ...

38

Let's look at the formula and equivalent circuit for a transmission line. (1) Impedance rather than reactance. Reactance refers to the opposition to the change in current (of an inductor) or voltage (for a capacitor) - single components. The transmission line has $R,L$ and $C$ components - impedance is the ratio of voltage phasor to current phasor. (...

30

A transmission line has distributed inductance and capacitance along its entire length. We can think of it as infinitely many little inductors and capacitors along the line: simulate this circuit – Schematic created using CircuitLab Each inductor serves to limit the rate at which the capacitor can charge. But, as we divide the line into increasingly ...

21

Adding to what Phil said: Now imagine everything starts out at 0 Volts and Amps in this long chain of inductors and capacitors, then you put a voltage step in one end. The way the inductors slow down how the capacitors are charged, a steady current will flow, which will be proportional to the voltage you put in. Since you have a voltage and a current ...

18

Yes. Fixing production errors by using jumper wire is a time honored tradition by those blessed with hindsight. For Power rails or low speed GPIO (Think Push Buttons inputs or LED outputs), a simple wire would work. As a precaution, you could cut the trace, and carry the full load on the jumper you are adding. If the jumper fails, the load would try to go ...

17

But for a mechanical strain relief for over stress on users with kids and USB plugs getting torn out, it is excellent. The main board has a good 3 point screw hole mount to eliminate torsional stress on brittle ceramic parts and the breakaway allows more board bending stress to occur at the gap without stress on the ceramic chips. Meaning OK for open board ...

16

There are two values you need to worry about: voltage drop, and power dissipation. Both are simple Ohm's Law and are functions of the trace resistance. The trace resistance is a product of its cross sectional area, and its length. Reduce the length and you reduce the resistance. Reduce the width and you increase the resistance. So you can have a shorter ...

15

Since they're labeled TF, it's safe to state they're thermal fuses. Therefor, since inductance is likely irrelevant, you could replace them with through-hole fuses of the correct value. The current value depends on copper layer thickness, but for 1 oz. Cu, 0.4 mm would be about 1.5 A and 0.6 mm ~2.5 A... but it would be better to find out what the actual ...

14

No, it is not a problem routing through a pad. You might wish to consider adding ground and power planes to the design.

13

That's actually two separate questions. It's the circuit voltages that determine the clearance requirements, while the current levels determine the width (and thickness) requirements. Trace Width Dealing with the latter first, it's the width and thickness of a copper trace on a PCB that determine its cross-sectional area, in the same way that the diameter ...

13

I know this isn't exactly an answer to your question but I thought it might help others. I still use perfboard a lot because it is more commonly available and I have a bunch of it laying around, but since I discovered stripboard, it is my preference. If you workout your layout, you can minimize the number of traces you have to create with soldier or wire. ...

13

I'm going to attempt to answer this question from my own research into this. Many of the online calculators for trace width vs current is derived from a document that was published apparently years ago. Some sources have said it was in the 1950s, but I haven't been able to find the first date it was published. (In fairness, I didn't look that hard either). ...

12

Jim had a very good answer. To expand on a few, however: 2) 50 Ohms is 50 Ohms (kind of). The dielectric constant of a material IS slightly frequency dependent. Therefore, the trace height and width you choose for 1 GHz will be a slightly different impedance at 10 GHz (if you need to worry about the difference, you probably already know about the difference!...

12

Can a ground plane be used as a current return path? The major benefit for using ground planes is that they are used for this very reason. For instance, any circuit using a "perfect" ground plane guarantees that the local return path of current is directly beneath the forward (non ground) current flow: - The bottom-line is that current takes the path of ...

12

The breakdown voltage of air varies significantly due to changes in humidity, pressure, and temperature. However, a rough guide is that it takes 1 kV per millimeter. Since that's about where arcs happen, you want to be nowhere near that in a real circuit. On a circuit board, you also have to consider conduction along the surface. This is why you often ...

11

When to consider a digital signal fast enough to treat the interconnect (PCB trace) as a transmission line depends on two things: Electrical length of the signal Rise/fall-time (which is another way to say frequency content) As a rule-of-thumb(*) whenever the electrical length of the trace is longer than some fraction of the rise/fall time, you will see ...

11

It is to reduce the thermal gradient across the device. A longer meandered track will carry less heat to and through the part than a short straight track. Note also that the PCB substrate has been milled away between the tracks; the PCB probably conducts most of the heat. We normally think of a PCB as performing mainly the electrical function of connecting ...

10

Yes, but these disadvantages may be negligible. Disadvantage 1: High frequency signals encounter a discontinuity. I would start worrying at a few hundred megahertz because the change in trace width changes the characteristic impedance (not just dc resistance) of that line. The discontinuity changes scattering parameters, creates harmonics, reflections, and ...

10

The number you need is called "MOT" (maximum operating temperature) for the laminate you have in mind. You also need to know what the internal temperature will be in your product (including the heat the relay connections add). For FR-4 to maintain electrical properties, that might be 130°C (a bit higher for mechanical properties). If the maximum temperature ...

10

When considering traces as transmission lines for digital signals, switching frequency does not matter. Forget about your MHz. Or kHz. Only slew rate matters. Detailed explanation: A driver is connected to a transmission line. It switches from 0 to 1 in a time T. The waveform propagates along the transmission line, reflects at both ends, and the ...

10

I have a PCB with tracks of no controlled impedance. The longest track is shorter than 1/5000 of a wavelength. Does the impedance of the track even matter? No it won't matter. It starts to matter (as a rule of thumb) when the track (or wire) length becomes about one tenth of the wavelength of the highest frequency signal of importance. If not, then ...

9

For one thing, many PCB layout programs will allow, or automatically incorporate, "necking" of traces due to unconnected pads or keep-out areas. This is a reduction of trace width for a portion of the trace. There are some concerns with such trace width reduction: If the reduced trace width is over an extended distance, then the increased resistance of ...

9

Sometimes called a "Solder-Short" pattern. To create it you could use two half-moon shaped pads placed very close together, be sure to keep solder mask off the junction area. Usually the idea here is if you need the two signals shorted you then put down a solder blob covering both pad ends. With this method you start out with an open. A way to create it and ...

9

There is no* way to measure trace impedance with a simple multimeter. Measuring trace impedance requires, at minimum, an oscilloscope and an impulse generator of some sort. Here's an article about how you can measure the impedance of a cable (or PCB) with a signal generator. Doing "Proper" impedance measurements requires a special tool, called a network ...

9

In general, adding an inductor in series with a chip's power feed and not adding decoupling capacitors to ground (at the pins) is really bad. Just don't do this whether you split it into three or just have a common track. Even if you add capacitance you have to ensure that any changes in the current taken by the chip do not suddenly produce resonance ...

9

This is an example of length matching (which can be necessary for both differential pairs and certain interface bus types). This is done so that a set of signals that are launched together arrive within a short time of each other (how much they can be off depends on the timing error budget available); note that no amount of length matching will guarantee ...

9

This should not be a problem if the pad is used, i.e. soldered before use. That will increase the current carrying capacity many times. Additionally, each side of the ring looks about as thick as the trace, so even without soldering, current capacity has been doubled. But what does current carrying capacity really mean anyway? The pad is tiny, there will ...

8

Temperature rise is something you have to consider, but usually the resistance and the resulting voltage drop at full current have been the limiting factors when I've gone through this. That said, 100°C is a large temperature rise. That's not enough to be a problem for a copper trace on a FR4 board by itself, but that's going to affect the apparent ...

8

That is one option if your design can handle the additional (capacitive/inductive) impedance created by the wire. Another option if the trace has no solder mask over it is to build up a large amount of solder along the trace in order to increase its ampacity.

8

One way which works well, is to use a different soldering technique. I use a small 'toaster oven' (cost about 20GBP) solder paste in a syringe, and a lighted magnifying glass. I also have a multi-meter with a temperature probe to monitor the process, but in reality a small torch, shone into the oven gives very good feedback. Look for all the solder paste to '...

Only top voted, non community-wiki answers of a minimum length are eligible