Questions tagged [pcb-design]

About designing the boards which carry the components of an electronic circuit. For questions about getting them built instead use PCB-fabrication. If your question is specific to a certain CAD tool, say which tool and version you are using.

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125
votes
5answers
19k views

Why does Samsung include useless capacitors? [closed]

I do component-level repair of tablet mainboards, and I have seen this puzzling situation on two different models of Samsung tablet mainboards so far (SM-T210, SM-T818A). There are ceramic chip ...
111
votes
8answers
36k views

Best One-Off DIY PCB Creation Technique

I have finally built up a lab to design electronics in. I have quite a few designs I would like to test. I have tried the printer toner/iron technique a few times but have found that I cannot create ...
84
votes
6answers
6k views

Looking for circuit board material that can be dissolved

We are working on a product where the entire device needs to be dissolved in liquid after the device has operated and the device is no longer usable or desired. This is a down-hole application. The ...
58
votes
6answers
31k views

What is Copper Thieving and why use it?

On many boards I've seen, there are little copper dots used for the purpose of "Copper Thieving". They're small round copper dots connected to nothing and arranged in an array. Supposedly they're for ...
56
votes
4answers
153k views

What do the PCB markings mean?

On a printed circuit board, I see lots of tiny letters and numbers. Is there some kind of standard that dictates what letter indicates what type of component?
49
votes
3answers
13k views

How to go from a development board to a production board?

Ok, I am a software guy and new to electronics. My product needs a small computer and currently I have developed everything on development boards like raspberry pi and such. As the development board ...
44
votes
7answers
53k views

What is the usage of Zero Ohm & MiliOhm Resistor?

I am new to PCB design and I noticed that some schematics use 0Ω or 100mΩ resistors. What is their purpose and why do we need to use them in our PCB design? Normally if we wish to probe how much ...
44
votes
4answers
6k views

What are the advantages of this gold finger shape?

Some PCBs, like the PCI card specification have gold fingers which start very narrow near the bottom edge, and gain their usual width much higher, where the actual contact is expected to be made. ...
43
votes
8answers
15k views

Can we build capacitors on a PCB board?

For the magnitude of nF or µF capacitors, I hope I can build them on a PCB board. The capacitor is like a two metal layer and something between them. Is this possible? Not buying the capacitor, ...
43
votes
3answers
27k views

Why are vias placed this way on a PCB?

I used to check complex commercial PCBs specially those of graphics cards to see how professional PCB designers do their layout and learn from their techniques. When I checked the card shown below I ...
43
votes
7answers
7k views

How do you document your hardware design decisions?

How do you document your hardware decisions in the design phase? How do you avoid having to ask yourself the following questions while reviewing an hardware design that you made in the past: Why did ...
40
votes
4answers
26k views

The best stack-up possible with a four-layer PCB?

I'm designing a 4 layer PCB and I know that the standard stack-up is Signals GND VCC Singals (GND and VCC can be switched depending on the layer with more signals) The problem is, I don't really ...
39
votes
1answer
12k views

Sharp corners in PCB traces

Why does a typical PCB always has rounded tracks? What harm can a sharp edged PCB track can cause? Please explain!
38
votes
2answers
25k views

What are the advantages of having two ground pours?

I've seen many 2-layer PCBs that have a ground pour on both the top and bottom layers, I was wondering why do that ? and wouldn't it be better to use the top layer for power and signals and the bottom ...
38
votes
2answers
6k views

Why wiggle nearby tracks on a PCB?

I've been reading an article (TheMagPi eMagazine) relating to the Raspberry Pi; "An ARM GNU/Linux box for $25." In the article, page 17 at the bottom it shows an area on the Pi where a track zigzags ...
38
votes
2answers
33k views

Competing PCB Crystal layout recommendations

This is related to this question: How's my crystal oscillator layout? I'm trying to layout a 12MHz crystal for a micro controller. I've been reading through several recommendations specifically for ...
36
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5answers
6k views

Why does a commercial PCB need this much rework?

I found a PCB that has had some rework done. When I saw it, I thought that someone had actually repaired it after purchase:- It's got additional wiring (white & brown) and under the hot glue are ...
36
votes
8answers
6k views

How to prototype?

How is prototyping done in a professional EE environment? Do you do your prototypes on breadboards, on copper clad boards, Manhattan style, or do you just draw schematics, order PCBs made and ...
34
votes
12answers
17k views

Why do we need so many transistors?

Transistors serve multiple purposes in an electrical circuit, i.e switches, to amplify electronic signals, allowing you to control current etc... However, I recently read about Moore's law, among ...
33
votes
4answers
12k views

Reason of multiple GND and VCC on an IC

What is the reason that most of ICs (e.g. MCU) has multiple (A/D)GND and (A)VCC pins? If it is to increase performance of an IC, how does it help to performance? or is it easier for the IC designer ...
33
votes
10answers
24k views

Looking for a good freeware/open source PCB design software equivalent to Altium [closed]

I am familiar with Altium PCB design software in my workplace. But thats an expensive suite to maintain. Is there any decent enough free software which I can use at home for my pet projects? I have ...
31
votes
2answers
12k views

Purpose of “wave shaped” PCB traces

On some PCB designs, specific traces are routed in curious ways. This probably has to do with high frequency design considerations and general signal behavior that I am not familiar with. Let's take ...
30
votes
2answers
9k views

What is Manhattan routing?

In an answer by The Photon he mentions 'Manhattan routing' in regards to PCB design. I haven't found a lot of relevant information about this term on the internet; therefore the question: What is ...
29
votes
5answers
7k views

What reasons are there to avoid vertical through-hole resistors?

I'm working on a layout for a PCB and I need to include a handful of pull-up resistors. The board I'm working on will be a proof of concept, and it is likely I will only need one (and order two). That ...
29
votes
5answers
8k views

Should I really divide the ground plane into analog and digital parts?

I am about to design my first PCB as part of my graduation project. Of course, as the first step, I try to learn as much as possible. A part of the research I found this 3 part article, that suggests ...
29
votes
3answers
9k views

Should I worry about the risk of tombstoning?

A colleague has (apparently unsuccessfully :-)) tried to convince me of the risk of tombstoning in the following situation: He claims pad 1 for R55 and R59 will lose heat faster during ...
29
votes
2answers
16k views

Why route air gaps for voltage isolation on PCBs?

Learning about PCB design for power supplies, I frequently see boards with routed gaps to separate low and high voltage sections of the layout. Why go to the trouble of routing an air gap when ...
28
votes
6answers
4k views

Is it better to route a pad to a trace, or a trace through a pad?

When routing a PCB, is it better to route a trace through a pad as in 1 below, or to route a pad to a trace as shown in ...
27
votes
5answers
4k views

Why are GND pads often only connected by four traces? [duplicate]

I have seen this everywhere but cannot figure out why it would make sense to essentially compromise the quality of the ground connection. Is this done for visual reasons? Here is an example:
27
votes
7answers
29k views

vias directly on SMD pads?

I was looking at an example board schematic provided by TI and I noticed something rather curious: vias were placed directly on SMD pads. Is this a normal/acceptable practice to follow? Or is it ...
27
votes
5answers
66k views

What pad hole (drill) size is appropriate for a given through-hole lead diameter?

I am making some new through-hole parts in Eagle for components that are not already in the various libraries. I've realized that the drill size needs to be a little larger than the lead diameter, but ...
27
votes
4answers
6k views

At what frequencies does PCB design get tricky?

I have designed many mixed-signal PCB's where the highest-frequency component is the microcontroller's crystal oscillator itself. I understand the standard best practices: short traces, ground planes,...
26
votes
6answers
32k views

Finding air wires in Eagle

I am almost done routing a board. However, is telling me that there is still one more wire. I have looked but I just can't seem to find it. Is there a to make Eagle tell me where it is?
26
votes
5answers
5k views

Board Design for High Impact Environments

I'm looking to design a PCB that can reliably survive constant impact. The board will be rigidly mounted to an enclosure that will protect the board from actually hitting anything. The nature of the ...
26
votes
2answers
3k views

'bridges' on a PCB copper layer

I've come across a design where each pad was connected using 4 'bridges' to the GND copper layar. What stands behind these 'bridges'? Why not make a full copper layer with only solder-mask defining ...
26
votes
5answers
11k views

Standard PCB Layout Book

Are there any good references on advanced PCB design/layout/routing? There seems to be a large wealth of circuit design books, books about RF PCB design, and books dealing with high-speed digital ...
25
votes
6answers
9k views

Have I placed too much on this PCB layout?

I am doing my first PCB layout (using Altium) and have finally gotten past the auto-router stage. The result is a mess and there are some missing nets and design rule violations. Have I packed too ...
25
votes
6answers
5k views

Is it OK to route a trace through a pad?

Will I have any trouble routing the traces in this way? (VCC and GND) Is it OK considering that the entire circuit current is under 50mA?
25
votes
5answers
7k views

How to create measurement points on a PCB for diagnostics?

What is the best way to implement a point on a PCB, where a voltage (e. g. output of a regulator) could be measured with multimeter for the purpose of verification of the assembly or diagnostics in ...
25
votes
2answers
3k views

What's the meaning of Electrical Inches?

I was reading a PCB design notes and guidelines from Xilinx for their 7 series FPGAs and came across this sentence: The capacitors should be placed as close as possible to the FPGA. Any placement ...
23
votes
6answers
14k views

New to PCB design - why doesn't auto placing components exist?

The circuit design software I have seen has the ability to automatically route traces etc. on a PCB. But why doesn't this software have the ability to automatically place components on a PCB say to ...
23
votes
3answers
8k views

Odd PCB Layout for Voltage Regulator

I am reverse-engineering a board which has a Xilinx Spartan 3E FPGA, with VCCAUX powered by a 2.5 volt regulator. Below is the PCB layout for the regulator part of the circuit, and something seems ...
23
votes
3answers
20k views

Should I isolate grounds of an isolated DC/DC converter?

If I use an isolated DC/DC converter, when designing the PCB, should I isolate the ground of the input and the ground of the output as shown below? I've never isolated grounds (except for AGND and ...
22
votes
4answers
6k views

Different PCB color (is it a different material?)

I have acquired this PCB. The right side of the PCB handles high voltage AC power (250 V maximum,) while the left side handles low DC voltages (24 V maximum.) They are separated, not ...
22
votes
4answers
19k views

When to use ground plane cutouts?

I've been reading more about proper grounding techniques and using ground planes. From what I've read, ground planes provide a large capacitance with adjacent layers, faster heat dissipation, and ...
21
votes
3answers
25k views

Mounting hole on a PCB

Here is a picture of 3 mounting holes on three different PCBs. The red one is what I prepared on Eagle CAD and used "hole" button on the left side menu , something like this: Do I need to use "...
20
votes
2answers
10k views

Termination resistors: are they needed?

For a project I'm designing, I'm using an IS42s32800 (TSOP) SDRAM with an LPC1788 (QFP) microcontroller. On the PCB I have 4 layers with a ground plane right below the top signal layer and a VDD plane ...
20
votes
3answers
5k views

Getting started with PCB Layout for BGA Packages

Are there any good resources for learning the intricacies of PCB layout when dealing with BGA packages? I'm very familiar with layout for almost every SMT part that has leads on the edge (QFP, TSSOP, ...
20
votes
2answers
15k views

Castellated/Edge-plated PCBs: Comments on Mechanical/Electrical contact reliability

(This is a follow-up to this related question). I'm interested in some feedback from people's design results/experiences with Castellated PCBs as a method of attaching one PCB to another. By ...
19
votes
4answers
3k views

Removal of unused pads?

I was reviewing a design earlier, and I noticed something interesting. The designer had removed unused pads on the chip. I have never seen this done before. Is this something that is good practice? ...