I am a chemical engineer and have been writing copy designed to sell products and services to engineers for 10 years.
Engineers have a low opinion of advertising - and of people whose job it is to create advertising.
Make your advertising and direct mail informational and professional, not gimmicky or promotional. Engineers want to believe they are not influenced by ad copy - and that they make their decisions based on technical facts that are beyond a copywriter's understanding. Let them believe it - as long as they respond to our ads and buy our products. There is a raging debate about whether engineers respond better to a straight technical approach, clever consumer-style ads or something in between. He will respond to creativity and cleverness just like everyone else.