Issue link: https://iconnect007.uberflip.com/i/1508761
50 SMT007 MAGAZINE I OCTOBER 2023 nents are missing cov- erage or have low cov- erage that results in test escapes. A l o n g - s t a n d i n g question that layout engineers have asked of test engineers is whether accessibil- ity can be improved and where the lay- out engineer should concentrate on add- ing the test access. Are there s o m e a c c e s s e s t h a t will be more beneficial than others? Yes, of course, but we need to understand where the most likely test escapes are. Predictive coverage simulation will show where the most benefit will be to add missing access, if possible. One of the concepts being applied with the simulation of structural test strategies is the idea of "pushing test le." If good results can be achieved with the structural test strategies, then perhaps functional test can be reduced. Functional test has two significant issues that lead to difficulties: e cost of implemen- tation of functional test can be high for com- plex boards, and the diagnostic resolution from functional test can be difficult, which requires advanced training for technicians and can lead to bone piles of boards that can't be diagnosed or fixed. If most of the coverage can be pushed "le" to the structural test where diagnostic resolution is better, then func- tional test can concentrate on only the areas where coverage just can't be achieved with structural test. is will result in quicker func- tional test times, and fewer functional testers to be deployed. Also, the predictive coverage simulation will show which components are not able to be tested in structural testing, giv- ing the technicians the knowledge of where to look for defects on the functionally failing boards. From these ideas, you can see that if pre- dictive models of the test strategies are per- formed, and continually tuned with available data, you can gain a thorough understanding of the coverage on the board prior to implemen- tation and development of the test programs. Instead of driving for as much coverage as possible at each test strategy, a more intelligent method can be used which places the right cov- erage at the right strategy, substantially reduc- ing wasted duplication and therefore providing cost savings. We can then apply this idea to the CAD conversion process for producing the test programs, performing real coverage measure- ment to evaluate the results, and check that the results match the simulation. is all means a nice feedback loop in the pro- cess that allows tuning of the simulation mod- els and the actual test process, so improvement is always being made. What better way to use the concept of the digital twin than to achieve real benefit in the test and inspection world where the results will be quickly evident? SMT007 Will Webb is technical director at ASTER Technologies.