Most of the interview was spent on subjects like reflow soldering, DOE, quality tools used in manufacturing. Usually, atleast one of the interviewers will brief about the final product and different steps involved in them. The interview questions more likely is to be targeted at the processes involved. The interviewer may also be interested in your previous work. The personnel interviewing for engineering role are mostly highly knowledgeable, so its best to your interest not to BS. You can always say "I did not have enough exposure on the subject, but will surely take interest to learn about it"