In-Situ Measurement of Chip Temperature During Soft Solder Die Bonding Using Integrated Microsensors

We report a novel microsensor-based in-situ temperature monitoring method for industrial soft solder die attach processes. The method is demonstrated on an automatic die bonder. Nine aluminum-based thermistors were integrated at several locations on a test chip and read out during the attach process. The aluminum metallization of a commercial CMOS process was used as sensing material. A custom-made pick-and-place tool enabled the electrical connection of external measurement equipment to the microsensors without interference with the machine operation. This connection tool consisted of flexible copper fingers aligned with special over-sized bonding pads on the test chip. The soft solder alloys PbSn10 and SnSb8.5 were used. Solder quantity, bond height, impact dynamics, chip backside metallization, and leadframe coating were individually varied. The dependence of temperature profiles on the process parameters could be definitely and consistently assessed. Typical temperature rise derivatives of 6 K ms –1 and temperature differences up to 76 K on the test chip surface were measured during die bonding. In addition to the experiments we built a simplified transient thermal finite element (FE) model. It allowed to estimate the solder temperature during bonding, and showed that the temperature is lower for bonding with the modified pick-and-place tool, compared to bonding with a standard tool. This cooling effect does not exceed –10 K for our structure.