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Measuring the Height of Wafer Bumps


1. Application

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.

2. Olympus' solution

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.

top position of bump
Figure 1. The top position of a bump.
bottom position of bump
Figure 2. The bottom position of a bump.

Products used for this application


STM7NEW

The STM7 microscopes offer excellent versatility and high performance three axis measurements of parts and electrical components, with sub-micron precision. Whether samples are small or large, simple or complex, or measurements are being taken by a novice or an expert, the Olympus STM7 range features measuring microscopes tailored to fit your needs.
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