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May 2015 • The PCB Magazine 67 karl's tEch talk QUICK-TUrN CIrCUIT BOArD SHOPS continues Table 1: Comparison of direct metallization process sequence with electroless copper plating. on another layer). Figure 2 shows the elements of a typical laser imaging tool. Direct Metallization Processes Direct metallization processes allow cop- per plating in through-holes without having to go the lengthy electroless copper process. Direct metallization process uses either carbon, graphite, or palladium catalyst, or a conductive polymer to initiate copper electroplating on the dielectric hole wall. These processes avoid the use of problematic chemicals that are part of the electroless copper formulation; they use less water, typically have a smaller equipment footprint, and use fewer processing steps, which allow the quick-turn shop to reduce processing time. Table 1 compares a graphite-based direct metallization process with the sequence of steps that make up the electroless copper process. Multilayer Bonder A multilayer bonder treatment (oxide or oxide alternative) is typically applied after in- nerlayer print and etch. Some quick-turn shops have had success with a process flow whereby the multilayer bonder is applied to the innerlay- er copper surface before resist lamination, expo- sure and development. In this process, the resist adheres to the multilayer coating, not to the copper. Dry film compatibility with this process sequence needs to be checked in terms of resist adhesion to such a surface, which is normally very good, and clean resist stripping needs to be established. This processing sequence takes the bonder treatment out of the critical time path for the board manufacture since the multilayer treatment can be done off line, in advance of the board manufacture. The bonder can also be beneficial as an anti-halation layer that pre- vents unwanted reflection of UV light from the board surface into non-exposure areas. Legend Print Legend print is traditionally done by screen printing, which involves the time-consuming screen preparation. In recent years, legend print-