As electronic equipment becomes smaller and more sophisticated, integrated circuit (IC) and large-scale integration (LSI) packages on printed-circuit boards (PCBs) need to be downsized. To meet the needs of this trend, a technique called flip-chip bonding where an IC chip is directly mounted facedown on a printed-circuit board has become important. In addition, three-dimensional packaging using stacked chips is also important for creating smaller electronic devices. These techniques rely on creating small solder bumps on the microchips to serve as connection terminals. The bumps have a height of about 20 μm, although this can vary depending on the chip size. If the bumps are too small, the bond between the microchips may not be complete. To prevent defects during the PCB bonding process and short circuits after the process, it is essential to accurately measure the height of the bumps.
Olympus' STM7 measuring microscope is one of the best tools for quickly and accurately measuring these bumps. The microscope’s highly rigid guide, resistant to deterioration with age, is equipped with a high-precision scale, enabling accurate height measurement with a resolution of 0.1 μm. The most notable characteristic of the STM7 microscope is the auto focus function, that can obtain accurate data for the top and bottom positions of a bump (Figures 1 and 2). The tracking mode makes it easy to measure the height of the bumps in just a few seconds simply by moving the XY stage. The autofocus’ light source uses a laser, enabling you to narrow down the focus point to a micron-sized area, making it possible to securely focus on an area as small as the top of a wafer bump.