Hideaki Sasazawa

Automated solder joint inspection system using optical 3-D image detection

An automated system has been developed for visually inspecting the solder joints of SMDs (Surface Mounted Devices). The system is capable of inspecting fine pitch components down to 0.3 mm pitch QFPs (Quad Flat Packages). A unique image detection method was also developed to obtain precise 3-D images of solder joints. The principle of a confocal microscope is employed but plural sensors are used to detect reflected light at different focusing positions simultaneously. The system is unaffected by secondary reflection and dead angles. The warp in a PC (Printed Circuit) board surface is calculated in real time using the detected 3-D images, and board height to be detected in successive areas is predicted based on this calculation. Real-time automatic focusing control is then performed using newly developed defect detection algorithms, the system can recognize leads, pads and solder fillets from the detected images. Because 3-D shape features are extracted and used for defect judgment, user-defined parameters have been made easy to understand and/or to modify. Operational evaluation of the system confirms a 100% defect detection rate and a very low false alarm rate (0.16%).

Highly Sensitive Focus Monitoring on Production Wafer by Scatterometry Measurements for 90/65-nm Node Devices

RENESAS factories are starting to use scatterometry for inline focus measurement. This paper presents the development of the method used for nondestructive, high accuracy, and high-speed focus measurement on production wafers. Focus change results in a subtle variation of the photoresist shape, and this phenomenon is parameterized by using a new eight-layer model. Partial least squares regression methods are used to calculate focus from scatterometry measurement results. The measurement error for a focus variation of 0.1 mum is within 30 nm. This method enables the focus offset to be corrected more frequently without increasing the aligner machine downtime and reduces the depth of focus required because of aligner fluctuation. With it, we will be able to get sufficient focus margins for mass production of devices beyond the 65-nm-node devices.