Issue link: https://iconnect007.uberflip.com/i/1221561
MARCH 2020 I PCB007 MAGAZINE 29 require a very exacting copper etch budget in the fabrication process. Specifically, etching of the target pads must be precisely controlled for both traditional electroless copper and direct metallization processes (Figure 2). The equipment team and product specialist group at MacDermid Alpha have now taken the development of the carbon black process to the latest stage of its evolution. The new- est line configurations for Blackhole Advanced Direct Metallization are capable of mSAP on panels starting with foils as thin as 3 µm, and the entire process has now been optimized for thin foil HDI metallization. Advancements in Equipment Configurations To optimize the direct metalliza- tion to work with mSAP process- ing, several equipment designs were tested and evaluated in pilot- scale lines before ramping up to full production. The result of this is that the process can offer unifor- mity of the carbon black coating under a wide range of conditions. Several equipment modifica- tions were selected for the Black- hole Advanced Direct Metalliza- tion system, in particular. A new roller configuration in the carbon application module uses a patented roller with saturation control to ensure the uniformity of the carbon black seed layer. The result of this change is that the carbon dispersion is deposited as a thinner coating and with most of the excess carbon removed from the surface before leav- ing the module. This is to prevent excessively thick deposits in blind vias or under the knee of the through-hole. The etch module was also extensively rede- signed. Fabricators are quite con- cerned about the potential of leav- ing a target pad that has only been partially cleaned, which leaves carbon residue after processing. In this case, the panel would pass electrical testing but have a re- duced cross-sectional area, result- ing in the via not being as robust under assembly reflow conditions. With microvia diameters being re- duced from a traditional 100–150 microns diameter down to 60–80 microns, the importance of the up- graded etching step is critical to product reliability. Studies conducted on how to elim- inate the chances of leaving carbon Figure 1: Direct metallization processes offer substantial environmental and financial benefits to fabricators. Figure 2: Shrinking line/space requirements for PCBs have created a need for stringent control of etch depth.