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OCTOBER 2024 I DESIGN007 MAGAZINE 63 cially enabled acceptable testing throughput. Using the offal instead of removing it offers great advantages, including more robust test- ing during roll-to-roll processing, early test- ing for audits as might be needed, and lower cost electrical test fixtures. Audits of singu- lated circuits can still be used to verify pro- duction lots. Knowing the customer's specification for net resistance and having a good test method, the process optimization narrowed to two pro- cesses: mSAP copper plating and mSAP etching. e mSAP process enables preserving circuit trace dimensions much more precisely than print and etch, necessary for not only resolv- ing the fine features well but more especially for meeting the customer's resistance specifi- cation with excellent precision. mSAP Copper Plating e mSAP plating process can affect the geometry of features by directly affecting the thickness of copper deposited, which is inversely proportional to net resistance. While this seems like a simple correlation to control, there are several additional factors to consider, such as shielding, contact quality and spac- ing, feature-size variation, feature spacing and proximity, circuit layout for R/R production, anode design, and current density. e initial trials of the nested multi-"UP" layout with roll- to-roll processing had a large amount of scrap due to plating thickness variation, which nor- mally meets other specifications. Adjustments and adaptations to the factors named above provided great improvement for meeting the resistance specification. e adjustments resulted in reduction of variability equal to nearly a third of the original standard deviation. A two-sample T-Test of resistance measurements taken before and aer the pro- cess optimization also showed a reduction in variability to better control the mSAP process. ere was also a mean thickness target to meet which could easily be changed by adjusting one simple parameter (i.e., process speed), easily opening the door for the customer to change the target mean thickness quickly whenever needed. However, more optimization work beyond plating was needed. mSAP Etching is process optimization included the study of factors beyond just those within the etching module setup, including material orientation and mSAP seed layer characteristics. However, none of these additional factors contributed significantly to eventual resistance results. e dwell time in the etching module is controlled by adjusting the "breakpoint," where the mSAP seed layer etches cleanly through to the base film. e primary focus of the DOE was to determine the effect of mSAP etching vari- ables on circuit resistance. On an elementary level, more dwell in the etching module would Figure 3. Figure 4.