The best way to do it would be to funnel all communication with the engineers through the manager. This includes questions, ideas for new features, feedback from customers, and so on.

What you want to avoid is random people (and that includes higher ups) pinging the engineers directly. That can be incredibly distracting and can result in large decreases in productivity, not to mention higher likelihood of bugs and other problems as the engineer is kicked out of their "zone" and loses their concentration.

http://heeris.id.au/2013/this-is-why-you-shouldnt-interrupt-...