Passing the Test

With so many different part numbers running through a production facility, it can be difficult to know how well a process is running. One way that the IC manufacturers solve this issue is to measure specific coupons (test structures) on a parametric die that is placed on each wafer in addition to special parametric wafers. Probe stations can be set up at specific process steps to test these parametric coupons and dies to provide feedback as to whether the process is running in bounds.

Having a specific coupon that is sensitive to a specific process can signal a process problem before it hurts production. The accumulation of these process effects on design can be measured at final test and should correlate with a specific first-pass yield (FPY) model.

The coupon methodology can also be applied to PCB manufacturing. There are many parametric analysis and characterization coupons available for PCBs, forming an important part of a quality assessment process. These process coupons cover reliability, end-product, work-in-process, and process parameter evaluations.