Designing a piece of electronic hardware is a very complex process. Interviewers want to ensure that you can accomplish this and that your techniques and processes are effective and efficient. Asking about pre-layout signal integrity helps the interviewer understand that you take steps to test your designs before fully implementing them. Since this is a technical question, your answer should be brief and to the point. You should also anticipate that the interviewer will ask follow-up questions since this topic seems to be important to them.