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24 PCB007 MAGAZINE I OCTOBER 2022 μm line/space resolution evaluation on larger 510 mm x 515 mm panels. A CCL/ABF substrate with a 10 μm- thick dry film resist was selected for this demonstration, resulting in lines with just over a 1:3 aspect ratio. Best dose and best focus were determined using a focus exposure matrix (FEM). Best dose was used for the resolu- tion demonstration. e figure indi- cates that CDs showed less than 10% deviation from -10 μm to -70 μm, at a DOF of 60 μm. e data from the FEM were used to generate a Bossung plot (Figure 5a) in which the X-axis is focus (μm) and the Y-axis is CD (μm). e plot shows the 60 μm DOF. Figure 5b also includes a lower magnification image of 3 μm, ing mechanical and laser drills. e "hole-less registration" is achieved through the "print- out image" characteristic of the photoresist, a color change of the resist during exposure that makes the latent polymerized features vis- ible. For both types of registration, the panel is placed on the machine's table for topside expo- sure. As vacuum is applied, the markers placed inside the table start to image the targets or holes on the bottom side of the panel. CCD cameras then align the panel to the table as the panel moves in, and the topside is imaged dur- ing the reverse movement. Aer flipping the panel, CCD cameras locate the target or hole marks on the bottom side; registration and imaging follow. Another method is shown in Figure 4. First, the recording heads of the DLP Towers are cal- ibrated (step a) and detect any position correc- tions using the alignment cameras and the reg- istration type (step b), then on fast computers compensation for scaling, rotation, position- ing, and enlargement to conduct highly reli- able and accurate imaging. Auto-focus follows the board and compensates for warping and board thickness. Summary In the application of DI for next generation ultra-HDI, Figure 5 shows the results of the 3 Figure 3: Many different registration techniques can be accommodated. Here are four different ways: 3 Figure 4: Setting up registration target to boards can differ quite a lot. Here is one scheme. (Source: Dainippon Screen Mfg. Co. Ltd.)