The dress shirt beneath a black tie jacket is always white; there is no room for negotiation here. Collars should ideally be turndown, with the collar points hidden behind the bowtie, but modern black tie (particularly in America) has come to accept the sharply-pointed wing collar as well. Traditionalists consider the wing collar too ostentatious for proper black tie, but it is still widely available; men are here, as with peaked lapels, encouraged to consider carefully how much they want to draw attention specifically to their outfits.
Well-made dress shirts should always have a doubled-over "bib" of fabric up the front of the garment, usually decorated with narrow, closely-spaced pleats. The shirt fastens with studs, not buttons, which should always match the cufflinks and are generally restricted to black, gold, or mother-of-pearl, with black being the most common.
The most formal option in men's business wear is a plain white shirt with a well-pressed, non-button-down collar. It's always a safe option for an interview, though hardly the only appropriate one -- use it as your baseline rather than your absolute standard. Bright colors or bold patterns would be inappropriate for an interview, but some subtle elements in either area help make a conservative outfit more unique without appearing frivolous.
If you opt for a white shirt, consider a subtle texturing to make it more eye-catching. A herringbone weave in plain white is much more interesting to the eye than untextured monochrome. Modest patterning is also appropriate, especially on a primarily white base; small, regularly-sized checks in light blue -- with their visual nod to graph and drafting paper -- are particularly worthwhile for engineers.
In an interesting reversal of the usual business preferences, engineers may find employers more willing to accept button-down collars and less inclined to look favorably on French cuffs. The former have both a practicality and a traditional association with manual labor that go over well in most engineering firms, while the latter are a purely fashionable gesture that can get in the way of work with the hands.