Writing technical job requirements can be daunting, especially if you're not personally familiar with the technologies the engineers in your organization use. I encourage you to get input early on from the engineers who will be working with a new hire to get a sense of what the requirements should be.
Keep the list of absolute must-have requirements to three or four bullet points. Talk to your engineering team members to understand what skills are necessary on day one to do the job, and leave everything else as nice-to-have. Each extra must-have decreases the number of qualified applicants you'll get and increases the amount of time it will take to find a good hire.
Phrase technical requirements in terms of results rather than specific tools where possible. Requirements like "Experience developing rich interactive web applications" or "Proficiency with CAD software to design complex mechanical components" leaves room for candidates who may not know the specific tools your engineers use, but can demonstrate that they have achieved the level of results your organization needs.
Ask candidates to prove their skills rather than just match the keywords in your job description. Require candidates to show an online portfolio, code samples, or other meaningful work deliverables that demonstrate past accomplishments. This is an excellent must-have requirement because it gives candidates the opportunity to show off their skills, but doesn't constrain them to one technology.