One thing no one has asked:
What PPM are you at right now!!!
Is it stable or is it changing (you can tell this on a control chart)
Is the product / componenet related to PPM causing you other troubles (problem reports from the customer, for example) or high rework costs?
How does it compare to similar ppm's in your company, any benchmarks.
Make a decision:
Am I okay where I am at, as long as I don't get worse?
I am not okay where I am at, I must get better.
The result of this decision becomes your goal - maintain the current PPM, or achieve an improvement in the PPM. And a control chart of the PPM would tell who if you achieve your goal in future results.