Hello,It depends on the company that you are applying to.For few companies in few colleges like TCS for Generic Coder Post 1 or 2 current backlog will be allowed.But for most of the core comapanies there will be condition of no history of backlogs .So apply accordingly and prepare according to the company.

Dear student, if you have a backlog in your last semester, you won't be allowed to sit for the campus interview until you clear your backlog and your results come out. And till the results of last semester backlogs come out, the companies would have already recruited students from your campus. It would be difficult to get a campus placement then.