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May 2016 • The PCB Magazine 67 although avoiding excessive adhe- sion could also be the objection. Take the example of surface prepa- ration before dry photoresist lami- nation (Figure 1): • Failure to achieve good adhe- sion in a print-and-etch process will cause etchant attack under the re- sist and ultimately an open defect. • Failure to achieve good ad- hesion in a plating process will cause tin/lead underplating, ulti- mately leading to shorting defects ("shorts"). • Failure to achieve good re- lease of unexposed resist during development can cause etch retar- dation in a print-and-etch process, ultimately leading to shorts. • Failure to achieve good re- lease of unexposed resist during development in a plating process can cause poor adhesion of the plated copper to the copper base ("copper-copper peelers"). • Failure to achieve good release of exposed resist in a print-and-etch process on innerlayers can inhibit the formation of multilayer bonder on such a copper surface. • Failure to achieve good release of exposed resist in a plating process can cause etch retar- dation. Resist Lamination Variables There are several factors that one can control during the resist lamination process. First and foremost achieving intimate contact between the resist and the copper surface is required in order to meet adhesion standards. Failure to ob- tain optimum contact can lead to the creation of open circuits (Figure 2). One should also be aware of the laminate weave texture and overall topography of the copper surface. Heavy glass weaves make it dif- ficult for the resist to conform to the surface. However, do not attempt to increase lamina- tion temerature above the resist manufacur- ers' recommendation to compensate for heavy weave texture. primary imaGinG for pattern platinG, part 1 Secondly the line operator can control the contact time between the resist, the board and the hot roll laminator. Additional contact time will improve the adhesion of the resist to the surface. While it is critical to ensure the proper hot roll lamination temperature (as suggested by the resist suppplier), do not attempt to in- crease the temperatue above that recommend- ed. The excessive temperature will damage the photoresist. PCB References 1. IPC Process Effects Handbook 5001 (IPC, Bannockburn, Illinois). Michael Carano is VP of technol- ogy and business development for RBP Chemical Technology. To reach Carano, or read past columns, click here. Figure 2: Resist does not completely conform to surface, caus- ing potential for nicks or opens in the circuitry. (Source: IPC Pic- ture archive-Bannockburn, Illinois)