Wireless handsets, PCs, game consoles, and hand-held devices that are used to communicate and access the Internet demand reliability, high performance, small size, and low cost. Where portability is of paramount importance, designers must consider the importance of device packaging standards before developing their products.
"Fine-pitch quad- flat-pack devices are large and fragile, having both high I/O count and close lead spacing," says Vern Solberg of Tessera (San Jose, CA). "And, while plastic and ceramic ball-grid-array (BGA) devices have a wider contact pitch, the package outline for BGAs is greater than the die within the package," he says. To meet the growing demand for more area-efficient IC packages, component manufacturers and device assembly service specialists have developed chip-scale packaging that feature the same size or are only slightly larger than the die itself.
As the size of semiconductor packages becomes smaller, the demands placed on semiconductor-inspection equipment also increases. To detect cracks and other defects in chip-scale packages, companies such as RVSI Electronics (Hauppauge, NY) are incorporating off-the-shelf PC-based 2-D vision systems into their products in addition to performing 3-D coplanarity inspection. The RVSI LS-7700 3-D laser scanner, for example, also incorporates the Visionscape 2400 2-D vision system from sister company RVSI Acuity CiMatrix (Canton, MA) to perform 2-D mark and visual package inspection.
The Visionscape 2400 vision board features an on-board RISC CPU coupled to an ASIC developed specifically to accelerate low-level image processing and analysis operations (see Vision Systems Design, Oct. 1998, p. 7). Deterministic control of all vision-related functionality including image capture, processing, display, and I/O is accomplished using the VxWorks real-time operating system from Wind River Systems (Alameda, CA).
RVSI Electronics chose a Visionscape 2000 PCI-based vision processing board coupled to a CAMI/O 400 digital camera interface daughtercard. This piggyback interface board allows the 2000 processor to act as both a frame grabber and a complete vision system in a single PCI board. To attain the high resolution required to image CSPs, the CAMI/O 400 daughtercard is coupled to an A113P megapixel digital camera from Basler (Exton, PA).
"With a resolution of 1300 x 1030, this particular model camera is capable of capturing images at 12 frames/s and transferring them via a single 8-bit RS-644 interface to the Visionscape 2400 board," says John Agapakis, general manager of machine-vision business for RVSI Acuity CiMatrix. "However, in the setup used in the LS-7700 system, the camera and strobed lighting system are driven by a robotic drive system over a tray of CSP devices and high resolution images captured and processed approximately once every 250 ms."
Highly specular surfaces containing surface defects and laser marks are typical characteristics of CSPs. To detect cracks and defects in such packages, the LS-7700 vision subsystem uses a combination square continuous diffuse illuminator (SCDI) and LED strobed ring light from RVSI NER (Weare, NH). Designed for applications involving highly specular surfaces, the SCDI is coupled to a ringlight that provides low-angle illumination to the region of interest. "This combination of illumination," says Agapakis, "enhances contrast and is particularly suited for CSP applications."
