The difficulty in convincing hard-boiled manufacturing managers is that it is very difficult to provide 100% proof that defective parts are actual ESD failures. We would suggest starting by demonstrating in some way that static is ever-present, and at quite high levels, and then show pictures of the defective product, to demonstrate that the problems are extremely small in scale, and need little static energy.
Add to this a brief outline of the cost of the failure, and the consequential damage to the company’s reputation.
Try and put some numbers to the problem – how many customer returns may be the cause of static damage during manufacture? What is the ball park cost of each of these? Having a measurement of the current situation, put in place a monitoring system which will relate field defects to specific manufacturing batch codes.
You need to be particularly convincing with the last point, which is to persuade her/him that the cost savings will take time to show themselves, so a realistic attempt to control ESD has to happen perhaps for a year or more before you can verify that the field problems were ESD-related.
Depending on your role within the company, and your expertise, you may also be able to measure the susceptibility of the design to ESD events.