Printed Circuit Design & Fab - April 2008 - (Page 34) FIGURE 5. Lot information – print times and scaling factors per image. FIGURE 6. X-Y scales chart per layer or per lot. photo-tool for each individual panel, the next best solution is to use the minimal number of photo-tools for the solder mask process, and still keep the design specification on the annular ring. There is special optimization software that allows you to compute the minimum number of groups that can be used to divide panels, allowing you to keep the desired annular ring accuracy. Shown in FIGURE 1, the process is outlined below. 1. The outer layer is exposed using LDI with global scaling. The scaling factor used for the imaging of each panel is recorded in the log of the LDI system. 2. After the outer layer process is finished and the next (solder mask or conformal mask) process begins, the system log, which includes the X- and Y-scaling factors for each panel, is fed into the optimization application. In addition, the desired annular ring, or hole-to-pad misalignment, is input into the application. 3. The optimization software tool then calculates: ■ The number of films that should be prepared for plotting, for the next (solder mask or conformal mask) stage ■ The scale factors for each individual film ■ The sorting of panels to their specific group (or phototool). The user can then sort the panels into the number of groups (or photo-tools) given by the optimization application, and continue with the solder mask (or other post-process) stage with the desired accuracy using the minimum number of photo-tools. If the PCB fabricator uses serial number stamps, they will be able to sort panel groups according to the stamp. 4. Since the scaling factors are already known, there is no need to measure the panels again in order to get the correct scaling factor for the plotter. This saves additional time, and reduces process complexity. 5. The LDI system can also be used to image the scaled data on a UV film, thus saving several process steps. This is not a primary LDI use, but in a few cases it could help get the best photo-tool in the first shot. The same software can be used for conformal mask before the mechanical drilling step. All of the previously listed benefits holds true for the conformal mask step as well. 34 If the customer employs conformal mask printing using the LDI, then the optimization application will generate the optimal number of scaling factors to be used in the mechanical drilling step. Not only is LDI compatible with your existing process, it can also be used to improve the process. There is a vast amount of imaging data stored on the LDI system that can be used to make improvements in other manufacturing processes. User Interface Using customer feedback has allowed for the improvement of the user interface to the point where ease-of-use alone has become a valid reason for using LDI in the PCB fabrication process. There is an intuitive graphical user interface, simple to operate and learn. An example is shown in FIGURE 2. The short learning curve for the equipment is seen as a necessary attribute. There is a strong focus on simple operational use. You can have full control of multiple LDI systems on a single display. This also allows fast and easy recall of previous fabrication work. The user interface has been designed for a quick and easy setup of new work. It is only a matter of minutes to go from the CAM data to the start of imaging. Since job preparation is done in parallel to production, it allows for high system utilization. Only minimal inputs are required from the operator (e.g. panel thickness and energy in mJ/cm2) but it is also very easy to change working parameters directly on the screen. The user interface also allows flexibility on how panel sides are imaged, either side A followed by side B for each panel (ABAB), or all the “side As” first, followed by “side Bs” (AABB). All these functions can also be controlled from an offline application, outside of the yellow room environment. Image Registration For image registration, the LDI system relies on acquiring target images on the panel. This real time image acquisition and analysis process is crucial for registration. Some LDI systems are compatible with a large number of different target types, and have the capability to define and add as many targets as you like. The types of targets that LDI must APRIL 2008 PRINTED CIRCUIT DESIGN & FAB
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.