A21: Generally speaking, EMI/EMC design should be considered from both radiated and conducted aspects. The former belongs to the portion whose frequency is higher (more than 30MHz) while the latter to the portion whose frequency is lower (less than 30MHz). Therefore, both high-frequency portion and low-frequency portion should be noticed. A good EMI/EMC design should start from components’ placement, PCB stack up, routing, component selection etc. Once those aspects leave unconsidered, cost will possibly rise. For example, clock generator should not be close to exterior connector as much as possible. Additionally, connecting points should be properly selected between PCB and chassis.
A10: It all depends on the case whether regulations on test points are compatible with the requirement laid by test machines. In addition, if routing is run too densely and regulations on test points are very strict, there may be no ways to put test points on each segment of line. Of course, manual methods can be used to complement test points.
Q31: When it comes to a 4-layer PCB design, what side should receive copper coating on both sides?
A6: Differential pair traces should be properly close and parallel. The distance between differential pair traces is determined by differential impedance that is a key reference parameter in terms of differential pair design.
A9: Yes. During the procedure of characteristic impedance calculation, both power plane and ground plane can be regarded as a reference plane.
PCB Design Interview Questions
The PCB material must be chosen entirely on the basis of a balance of design requirement, volume production, and cost. Electrical elements that need be taken into account during high-speed PCB design are called design demand. In addition, the frequency should be taken into account when determining the dielectric constant and dielectric loss.
2: How can high-frequency interference be avoided?
The most important approach for overcoming high-frequency interference is to minimise crosstalk, which can be accomplished by increasing the distance between high-speed signals and analogue signals or by using ground guard or shunt traces alongside analogue channels. Furthermore, the noise interference induced by digital ground on analogue ground must be taken into account.
When designing traces carrying differential signals, two points should be kept in mind. On the one hand, two lines should be the same length; on the other, the spacing between two lines should remain parallel.
In order for traces carrying differential signals to work, both the signal sources and the receiving end must be differential signals. As a result, differential routing cannot be used with clock signals with only one output end.
5 .Is it possible to apply matching resistance between differential pairs at the receiving end?
At the receiving end, matched resistance is frequently applied between differential pairs. matching resistance is usually used.
Differential pair traces should be close and parallel to one other. Differential impedance, a critical reference parameter in differential pair design, determines the distance between differential pair traces.
Most automatic routers may now specify constraint constraints to regulate wire running manner and number of through holes. In terms of wire running methodologies and constraint condition setup, all EDA vendors differ significantly. The ability to run wires is closely connected to the difficulty of autonomous routing. As a result, this issue can be rectified by purchasing a router with a high throughput.
In most blank areas, copper covering is largely attached to the ground. Because coated copper reduces characteristic impedance a little, the distance between copper coating and signal lines should be carefully calculated. Other layers characteristic impedance should not be altered in the meantime.
Of course. Both the power plane and the ground plane can be used as reference planes in the calculation of characteristic impedance.
It depends on the situation whether test point regulations are consistent with test machine requirements. Furthermore, if routing is done too intensively and test point restrictions are too rigorous, there may be no way to put test points on each line segment. Manual procedures can, of course, be employed to supplement test points.
It all relies on the situation, such as the test point adding method and the signal running speed. Adding test points is accomplished by attaching them to lines or removing a segment.
According to Kirchoffs current law, when power or signals are delivered from Board A to Board B, an equal amount of current is returned from the ground plane to Board A, and the current on the ground plane flows back at the path with the lowest impedance. As a result, the number of pins contributing to the ground plane at each interface of power or signal connectivity should never be too small, in order to limit ground impedance and noise. In addition, the entire current loop should be examined, particularly the area where current is the greatest and the ground plane connection.
13: Can ground lines be added to differential signal lines in the middle?
Ground lines cannot be added to differential signal lines because the benefit of mutual coupling between differential signal lines, such as flux cancellation and noise immunity, is the most important aspect of the differential signal line principle. If ground lines are put between them, the coupling effect will be lost.
The idea is to use chassis ground to provide a low-impedance conduit for returning current and to control the path of that returning current. Screws, for example, are commonly used to connect the ground plane to a high-frequency component or clock generator. to limit the total current loop area as much as feasible, i.e. to reduce electromagnetic interference.
When it comes to digital circuits, the following steps should be followed in order. To begin, all power levels should be double-checked to ensure that the design requirement is met on average. Second, make sure that all of the clock signal frequencies are working properly and that there are no non-monotonic issues on the edge. Third, in order to meet the standard requirement, reset signals must be confirmed. If all of the above is true, the chip should send signals in the first cycle. Then, using the system operating protocol and the bus protocol, debugging will be carried out.
Crosstalk interference should be given special attention during the design of high-speed and high-density PCBs since it has a significant impact on timing and signal integrity. There are a few design options presented. First, the routing characteristic impedance should be regulated for continuity and matching. Second, observe the spacing, which is usually twice the line width. Third, the appropriate termination mechanisms should be chosen. Fourth, routing should be done in diverse directions in adjacent levels. Fifth, to expand route space, blind/buried vias might be used. Furthermore, differential and common-mode termination should be preserved to minimise the impact on timing and signal integrity.
17 .At analogue power, the LC circuit is commonly used to filter the wave. Why is it that LC sometimes outperforms RC?
When comparing LC with RC, its important to consider if the frequency band and inductance are properly chosen. Because inductance reactance is connected with inductance and frequency, LC performs worse than RC if the noise frequency of power is too low and inductance isnt high enough. However, one of the disadvantages of RC is that the resistor consumes a lot of energy and is inefficient.
The cost of a PCB board increases due to EMC, mainly because the layer count is increased to increase shielding stress and some components, such as ferrite beads or chokes, are prepared to halt high-frequency harmonic wave components. Other shielding structures on other systems should also be employed to meet EMC requirements. To begin, as many components with a low slew rate as possible should be used to reduce high-frequency sections created by signals. Second, high-frequency components should never be installed too close to connectors on the outside. Third, high-speed signals impedance matching, routing layer, and return current channel should be carefully planned to minimise high-frequency reflection and radiation.
The reason for separating digital and analogue modules is that noise is generated at power and ground when high and low potentials are switched, and the amount of noise is proportional to signal speed and current. Even though analogue and digital signals do not come across, analogue signals will be influenced by noise if analogue and digital modules are not split and the noise generated by the digital module is bigger and the circuit at the analogue region is similar.
20. How should impedance matching be implemented when designing high-speed PCBs?
When it comes to high-speed PCB design, impedance matching is crucial. one of the most important considerations The absolute relationship between impedance and routing can be found in impedance. Characteristic impedance, for example, is determined by a number of factors such as the distance between the microstrip or stripline/double stripline layer and the reference layer, routing width, PCB material, and so on. To put it another way, characteristic impedance cannot be determined until the circuit is routed. The most important answer to this problem is to prevent impedance discontinuity as much as feasible.
21. Which EMC/EMI mitigation measures should be taken throughout the high-speed PCB design process?
In general, both radiated and conducted components of EMI/EMC design should be considered. The former belongs to the segment with a higher frequency (greater than 30MHz), while the latter belongs to the portion with a lower frequency (less than 30MHz) (less than 30MHz). As a result, both the high-frequency and low-frequency portions of the signal should be noted. Component placement, PCB stack up, routing, component selection, and other aspects of a good EMI/EMC design should all be considered. Costs are likely to rise if such factors are ignored. The clock generator, for example, should be kept as far away from the external connector as practicable. Additionally, connecting points between the PCB and the chassis should be carefully chosen.
22. What is the topology of a routing network?
In a network with numerous terminators, routing topology, also known as routing order, refers to the order of routing.
23. What changes should be made to the routing topology to improve signal integrity?
Because this form of network signal is so complicated, the topology varies depending on the direction, level, and type of signal. As a result, determining which types of signals are favourable to signal quality is tough.
24 What is the significance of copper coating?
Copper plating is frequently done for a couple of reasons. To begin with, a huge ground or power copper covering will have a shielding effect, and some special grounds, such as PGND, can serve as a protective ground. Second, to assure superior electroplating or stop lamination performance. Copper should be coated on PCB boards with less routing to prevent deformation. Third, signal integrity necessitates the use of copper covering. High-frequency digital signals should have a complete return path, and DC network routing should be minimised. Thermal dissipation should also be taken into account.
25. What is the definition of return current?
High-speed digital signals move from drivers to carriers along a PCB transmission line, then back to the driver terminal via the quickest path along ground or power. Return current refers to the signals that return to ground or power.
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Are you an electronic technician and a professional designer of Printed Circuit Boards? If yes, then you are ready o take up a job with an electronic component manufacturer. To search for relevant jobs based on your skills and qualification, you can browse the www.wisdomjobs.com. Here you will get a detailed information of all the Printed Circuit Board Design jobs around the world. As a Printed Circuit Board Designer you will be able to use computer programs to work on electronic components which are used in cell phones, computers and other electronic devices. Go through the wisdomjobs page and apply in any of the reputed organizations, where your skills can be best put to use. Also read the Printed Circuit Board Design job interview questions and answers to be prepared for the interview process.
What to Expect in the PCB Designer Interview Process
I haven’t gone through a multi-decade career as a PCB designer just yet, but I’ve been on both sides of the table with regards to job interviews. I’ve had to hire engineers for my own company, I’ve succeeded and failed at PCB designer job interviews in the past, and I’ve gone through multiple vendor interviews with companies, some of whom I just happened to land as clients. What I want to share below reflects my own experience and opinions, so keep this in mind when reading what follows.
What are the PCB design interview questions?
- What is need for a PCB?
- What software or EDA tools are you familiar with?
- What if schematic symbols and footprints are not available in component library?
- How do you verify schematic symbols or footprints?
- What are basic checks while laying out MCU based design.
What is considered high speed PCB design?
What are the 3 types of PCB?
- Single Layer PCB. Single layer printed circuit boards are among some of the simplest to design and manufacture. …
- Double Layer PCB. …
- Multi-Layer PCB. …
- High Density Interconnect (HDI) PCB. …
- High Frequency PCB.