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84 PCB007 MAGAZINE I AUGUST 2019 Figure 6 shows an example of a flexible cir- cuit made with the SAP utilizing LMI base cop- per and the new etchant. The trace width is 24 microns, the space between traces is 11 mi- crons and the conductor height is 15 microns. It is extremely challenging to achieve clean etching with this geometry with conventional methods and equipment. The newly developed organic solvent mixed etching chemical allows this process with conventional conveyor hori- zontal spray machine. This indicates the cop- per height is controlled to 7–8 microns, then 5 microns each of the trace and space design can be achievable. Fully Additive Process In addition to semi-additive processes, the LMI catalyst can be used with a fully additive process. The process is as follows. The first step is the catalyst coating over the substrate which is dried and cured. The next step is the patterning of an etching resist with a positive image of the circuit. Conventional thin dry film resist can be used. This is followed by etching. A common acidic etchant such as ferric chlo- ride system can be used. Next, the etching re- sist is removed with common processing. The last step is electroless plating. The substrate is dipped into the electroless copper bath and the copper is deposited over the catalyst but not in the areas where it was removed (Figure 7). Figure 8 is an example from a test vehicle. The conductive pattern is made with the ful- ly additive process described in Figure 7. The base material is polyimide film and the cop- per thickness is 1 micron. There is no issue forming a 5-micron trace. Trace copper does grow elliptically, so the copper height (thick- ness), will have a limit. This height issue is not only in this fully additive process, but also Figure 7: Full additive process with LMI catalyst. Figure 8: Test pattern formation with a full additive process.