Semi back-end packaging inspection uses multiple high resolution cameras to detect bumps, packages and other properties of packaged wafers. An ever-increasing detail is obtained by high resolution cameras that have to deliver their precise pixel measurements at continually increasing speeds. CoaXPress matches all the requirements posed by this challenging machine vision application.

Semiconductor back-end overview

After the wafers have been packaged into a chip, the package is inspected for various imperfections to guarantee flawless operation. Some of the properties looked at are the inspection of missing bumps, bridges, nodules, bump shapes and missing material. The inspection of BGA substrates, lead frames, surfaces, marks, post dicing and the packages themselves are also part of the Semi back-end inspection process. Several cameras are used to simultaneously examine the ROIs (Regions of Interest), where one of the cameras is used as an overview and others focus on a specific inspection task. The acquired high-quality pixels from the individual cameras are passed on to the frame grabber, which offers them to a PC system for further analysis. The main criteria are resolution and pixel depth. Typically, a resolution of 25 megapixels and a pixel depth of 12 bits is standard in today’s semiconductor factories. This however does not mean that speed isn’t a concern. Frame rates of 80 fps for 100 percent real time inspection still pose quite a challenge for getting all the right pixels in the right place at the right time. CoaXPress has no problem whatsoever meeting these challenges.

CoaxPress for Semi Back-end

Semi Back-end: Smaller and Faster

Several challenges face the production of chips, which are fortunately part of the solution as well. The consumer electronics market, especially that of mobile phones and smart cameras, has given rise to powerful CMOS chips and continues to raise the bar. These CMOS chips now oversee the chip manufacturing process that, besides the trend towards smaller and more precise packages, is not immune to precious time requirements. And as is the case throughout the manufacturing industry, chip manufacturers also feel the need to produce smaller production which runs more flexibly, decrease their design cycles, time-to-market and reduce costs. Modular design, higher throughputs and smaller footprints provide the answers, but will also have to be addressed by vision systems and their individual components. What does this mean for the communication standards of pixels? Mainly a need for more bandwidth, with a high level of data integrity. A high bandwidth is required as transporting more information faster simply means a bigger ‘pixel highway’, and a high level of data integrity as OEMs only want raw pixels that have not been degraded by external effects, such as electromagnetic effects. Interpreting this data belongs to their core business. The better the pixel quality they can obtain, the better decisions they will be able to make, setting themselves apart from the competition.

Semi Back-end: a Perfect Match

CoaXPress not only addresses the need for higher data rates – 6.25 Gb/s for the current version, with a promise of 12.5 Gb/s for version CoaxPress 2.0 in 2017 – but also offers unrivalled protection against EMI. Why? Because, being a serial point to point standard, it provides all the advantages of a coax cable: robust shielding, even at greater cable lengths up to 100 meters. With the same cable, it also provides power for connected cameras and carries signals for triggering and synchronization. And as for scalability, CoaXPress might be the only viable high speed-option for a modular design. The high data rates allow for fewer frame grabber connections, which also means that cameras can more easily be added at a later stage. This is especially the case, since CoaXPress cables don’t have to be assembled at the factory, but the connector can easily be attached after installing the cable.