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Hardware Engineer Intern interview questions shared by candidates

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Hardware Engineer Intern was asked...December 22, 2011

If you increase the width of a PCB trace, does it decrease or increase the trace impedance?

As you increase trace width, impedance is lowered.

The question is a little tricky (not really tho). The impedance of a straight line is described by Z=R+jX, where R is the resistance and X is the reactance. As the width of the trace is increased, R decreases. If we assume that there is no inductance, then the impedance will go down, as X=1/(jwC), and C=W*L*C0. However, in a very inductive space (like trace is curly and goes around itself a lot), then X = jwL, thus increasing the complex part of the impedance. I would go with the decreasing impedance, as on the PCBs resistance is the dominant term. Less

If you increase the width of the pcb trace then it will help decreasing the resistance of the PCB trace. I give you a simple analogy if for example we consider the inductance as the negligible amount then, ( R=c (L/A)) where c is resistivity . And we are increasing the Area of cross section that is A. Then that is inversely proportional to the resistance and hence it decreases the impedance. Less

What happens to a signal integrity as you increase length and when there is return current?

It is better to keep the return path as short as possible, since it will form a loop antenna and will give EMI/EMC problems based on the loop length matching with operating frequency. Less

Stairways in signals.

A time you had a bug and how you fixed it.

I talked about a program I wrote and how the recursion wasn't correctly operating and how I de bugged it. Less

It's essential to demonstrate that you can really go deep... there are plenty of followup questions and (sometimes tangential) angles to explore. There's a lot of Hardware Engineer I Intern experts who've worked at National Instruments, who provide this sort of practice through mock interviews. There's a whole list of them curated on Prepfully. prepfully.com/practice-interviews Less

What factors control the impedance of a trace?

width and thickness of the copper signal trace, thickness of the core or prepreg material on either side of the copper trace and dielectric constant of the core and prepreg material Less

Trace width, copper thickness, and dielectric width

There was nothing unexpected. Although manager really wants to see your thinking process. He was very good at explaining the questions

Very nice company to work for

Questions are not difficult. The interviewer asked me to talk about the experience that what is the most difficult problem I have met and how I solve it

Through questions like this, interviewers are mostly trying to test your skillset (and its relevance to the role) as robustly as possible, so be prepared for multiple offshoots and followups. It could be a useful exercise to do mocks with friends or colleagues in National Instruments to get a real sense of what the interview is actually like. Alternatively Prepfully has a ton of National Instruments Hardware Engineer I Intern experts who provide mock interviews for a pretty reasonable amount. prepfully.com/practice-interviews Less

Expanded from behavioral question to a technical one when talking about a project. (e.g. Tell me about a time you could not complete an objective in a project and then: Tell me what did you do technically to solve the challenge.)

Explain why a high frequency square wave distorts in an oscilloscope

What do you expect to see at the output when you connect 8 more inverters to an inverter?

not + (8* gate delay)+(8*track propogation delays)