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78 DESIGN007 MAGAZINE I JULY 2019 Results and Discussions Figure 4 shows the first screen print results: fiducials for the microvia drilling and reference pads. The reference pads are mainly used to facilitate inspection of the dimensions and po- sitions of the drilled microvias. Without these reference pads, the actual measurement has to be done to understand the actual tolerances of the drilled vias. With these reference pads, the quality of the drilled vias can be quickly obtained under the microscope by comparing to the reference pads. The automatic inspec- tion process can be quickly developed and em- ployed. Figure 5 shows the actual measurements of the reference pads. The target diameter of the Figure 3: Reflow profile of low-temperature soldering process. Figure 4: Screen-printed fiducials and reference pads. Figure 5: Measurements of the reference pads.