A.S.
Engineers are a different breed than bankers, sales, operations managers, etc. Had my DH worn a suit and tie to the job interview he had for an IT engineering position making 100K+ they would not have given him the job. They said this after he was hired...he wore a button down shirt and pressed slacks. This was just last month. A suit would have indicated he was not a good fit with their laid back environment. It's the same with the IT companies I worked for (two really big silicon valley companies)
You have to get a read from the company via their website and people who work there. If they are laid back, a suit won't work. If they're more traditional, a suit is a better idea. GL! Hope he got the job!!