Issue link: https://iconnect007.uberflip.com/i/359006
August 2014 • The PCB Magazine 59 PRESSURE IN HOT ROLL LAMINATION OF DRy FILM PHOTORESIST continues rolls and with crowned rolls. "Open" defects as detected by AOI were plotted as a function of the location on the board. High columns in- dicate a high occurrence of opens. The results of the "base" condition (i.e., low pressure and straight rolls) are shown in the upper left hand corner of Figure 4. One can see the high rate of defects in the center of the board, in machine direction, due to the bowing of the rolls. The higher pressure scenario, still with straight rolls, is shown on the lower left side of Figure 4. The higher pressure give a lower overall defect rate, but the pattern of higher defects in the center line due to bowing remains visible. The result shown on the upper right-hand side of Figure 4 shows the beneficial effect of crowned rolls: The defect rate is now more even across the board, with some random defects remaining. Adding high pressure to this condition as shown on the lower right hand side of Figure 4 then yields the overall best results. PCB figure 4: "open" defect plots for different pressure settings and different roll construction. Karl dietz is president of Karl dietz consulting llc. he offers consulting services and tutorials in the field of circuit board and substrate fabrication technol- ogy. to view past columns or to reach dietz, click here. dietz may also be reached by phone at (001) 919-870-6230.