PCB DESIGN INTERVIEW QUESTIONS

PCB design is a domain in which we should not have knowledge only for PCB design. We should have basic knowledge of PCB fabrication, PCB assembly, we should understand circuit flow in schematic.
Including above things, PCB design have 3 group:

Basic PCB design:

In this type of design, designer has to simply draw traces as per circuit flow.

High speed PCB design:

In this type of designs, designer has to follow all interfaces guideline.

HDI board:

HDI is the short form of “HIGH DENSITY INTERCONNECT”.
Now a days these type of PCB design are used in industries and demand only PCB designers who worked HDI boards.

In HDI board, Designers has to take care high speed interfaces guideline as well as DFM.
Here I have mentioned questions which will covers interview Questions which is related to technology, but there is no limit, because who is taking interview can ask questions as per there knowledge and work experience.

1. What are major problems have you faced in your design?
2. What is the meaning of Aspect ratio?
3. Classes of IPC standard?
4. Which standards we follow for PCB design?
5. What is the use of decoupling capacitor?
6. What is difference between decoupling and by pass capacitor?
7. What is the use of stitching capacitor?
8. Why we use Copper filling?
9. Why we Place Crystal close to IC?
10. What is relative permeability of FR4?
11. What is the significant of FR4 and why we used this material?
12. What is meaning of EMI/EMC? What precautions should take care for EMI/EMC?
13. What is the meaning of fan-out?
14. What is difference between analog and digital design?
15. What is meaning of mixed signal board, what precaution will take care in mixed signal design?
16. What is difference between local and global fiducial?
17. What id difference between blind and buried vias?
18. What is Ratsnest in PCB Layout terminology?
19. Does analog effect digital signals or digital signals effect analog signals?
20. What is star Grounding?
21. What is the difference between impedance and resistance?
22. How many type of impedance have you should in design & for which interfaces? What precautions should take care for 100 ohms impedance?
23. What is difference between balanced and unbalanced stack up?
24. How you will make sure that you have achieved target impedance without hyperlynx?
25. What precautions should take care for high speed design?
26. What is the meaning of DFM/DFT? Why we used?
27. What is difference between solder mask and solder paste?
28. Why we should avoid split plane?
29. What is difference between thermal pad and antipad?
30. If will increase trace width what effect will come on impedance?
31. What types of high speed interfaces you have used in design?
32. What will be trace width in below cases :
    1. If 1Amp Current-DC
    2. If 1Amp Current-AC
    3. If 1 Amp Current-AC/50Hz

33. What is the meaning of signal integrity?
34. How can say that a signal is high speed signal?
35. What is the definition of characteristic impedance?
36. Give any few tips to maintain integrity of a signal on a PCB?
37. Why differential signaling is preferred for high speed signals
38. What is IBIS model?
39. What is termination resistor? Where and why they in PCB?
40. What is cross talk in PCB?
41. Why does ringing occur on the signals?
42. Why length matching required in high speed board?
43. What is micro strip & strip line?
44. What is propagation delay
45. What is skin effect?
46. What is the meaning of GND bounce?
47. What are current/ground loops in a PCB layout?
48. What is back drilling and stacked vias?
49. What are finished material used in fab industry?
50. What is the meaning of tenting and feeling vias?
51. Why does signal reflection occur in a PCB?
52. What is active and passive Component?
53. What is difference between crystal and Oscillator?

At the time of interview preparation, study all the interfaces guidelines which you have used in your design. If you never worked on any interfaces which is available in market. Search and study related to data to that interface also, because some time interviewer check that you never worked it’s ok but you have knowledge so they consider your candidature.

Soon I will share all high speed interfaces guideline which will helpful for you, so keep in touch

Best of luck for your interview

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How to calculate ESR of capacitor

ESR is the short form of equivalent series resistor.

Theoretically Ideal capacitor would be lossless and have an ESR of zero. As being ideal capacitors and Inductor has a series resistor, this resistance is defined as the equivalent series resistance (ESR).

For calculating ESR of any capacitor we should know dissipation factor i.e. DF (Dissipation factor is known as the tangent of the loss angle and is commonly expressed in percent) and capacitive reactance Xc = (2* π*f*C)

Hence

ESR=DF*XcDF/(2* π*f*C)

For example if you want to calculate ESR of ceramic capacitor of value 0.1uF/50V

Dissipation factor DF is 5% at 120Hz

therefore,

5/2*3.14*120*0.1×10^-6x100

= 66.34Ohms

so the ESR of ceramic capacitor of 0.1uF/50V will be 6.6mOhms

For Power integrity and Signal integrity analysis,ESR is the important factor.

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