MACHINE VISION FOR SMARTPHONES Essential machine vision camera requirements to fulfill the needs of our society
INTRODUCTION With changes in our society, there is an increased demand in stateof-the art smartphones and tablets. This is driving other industries as well, including machine vision. The increase in the number of smartphones and tablets requires production with high-speed inspection with high yield. The advances in functionality require smaller and more complex components, resulting in a need for more accurate manufacturing and measurement. This is all happening on an aggressive time scale as consumers expect new improvements quickly, resulting in a fast innovation cycle. Not surprisingly, this is driving innovation in supporting industries, including machine vision. High-resolution cameras combined with high speeds that make full use of select image sensors provide the images required for inspection and metrology of the latest generation devices that go inside your latest smart phones and tablets. This includes supporting the move from 2D to 3D measurements. The growth in smartphones and corresponding cameras has allowed for dramatic improvements in CMOS sensors. This has also affected the available sensor technology for machine vision allowing machine vision cameras to then support the production of more smartphones. -2-
SMARTPHONE PRODUCTION HAS INCREASED WITH CHANGES IN SOCIETY A major trend in society is the needs to be mobile yet constantly stay connected 1 This has influenced our purchasing behavior to support how we want to live. For instance, there has been a dramatic increase in the adoption of smartphones: The pattern shows a likely 1 million new Smartphone users per week being added consistently by the fourth quarter of this year. The ripple effect is dramatic and has resulted in changes and advances in many markets, including machine vision. Infographic courtesy AYTM (Ask Your Target Market) and PaidViewpoint High-resolution cameras combined with high speeds that make full use of select image sensors provide the images required for inspection and metrology of the latest generation devices that go inside your latest smart phones and tablets. This includes supporting the move from 2D to 3D measurements. The growth in smartphones and corresponding cameras has allowed for dramatic improvements in CMOS sensors. This has also affected the available sensor technology for machine vision allowing machine vision cameras to then support the production of more smartphones. Source: www.asymco.com 2 While companies like Samsung and Apple are responding to and feeding the consumers demands, the semiconductor market has grown by focusing on supporting them 3. -3-
INCREASED SMARTPHONE GROWTH REQUIRES HIGH-SPEED INSPECTION WITH HIGH YIELD To increase the capabilities of smart phones, more powerful processors are required. This means higher density chips, smaller components and, among others, changes in packaging. These changes present new challenges for manufactures of inspection and metrology equipment. With semiconductor front-end manufacturing 4, smaller features must be detected without compromises in throughput. With semiconductor back-end manufacturing 5, there are changes in packaging such as flip chip 6 technology, which offers significant size savings. The trend towards continuous miniaturization results in smaller bump sizes and a greater number of bumps. This combined with the goal of 100% analysis at a high precision while maintaining high throughput; challenges bump inspection and component inspection equipment manufacturers. for gain in throughput. Supporting camera technology/ functionality such as burst mode, CoaXPress and region of interest (ROI) can further increase speeds. Throughput can also be increased with fewer movements. Utilizing high-resolution high-speed image sensors drives throughput in step-shoot-move inspection systems by both reducing scan time as well as the number of scan positions per object. Uniformity challenges increase as a larger optical field-of- view requires more complex optics and the increase of defects pixels in the sensor. Camera manufacturers can provide higher uniformity by grading the incoming sensor, including dedicated processing and eliminating blemishes in the manufacturing process and camera operation. Increase throughput For all of the inspection and metrology techniques such as bare wafer metrology or micro defect inspection, precision and accuracy must be increased while maintaining or increasing throughput. Image sensors with a higher frame rate are just a starting point. The challenge for camera manufacturers is to preserve image quality at the fastest frame speeds, but it is possible. The image sensor design must be able to handle these high data rates within a critical timing tolerance to reliably produce quality images. The resulting camera must ensure that the frame rates are actually captured in a consistent and dependable way. Higher frame rates allow -4-
Improve yield with reliable & stable performance The goals with better metrology are to detect problems and defects in order to correct for them to prevent yield problems or make process improvements to increase yield. Even a 0.1% improvement in yield can mean an increase in profitability of millions of dollars. Bare wafer metrology is a great example of this. Before any transistor is laid down, the incoming silicon wafer must be analyzed for flatness and defects. From this inspection, wafers can be classified to allow the best wafers to be used for the smallest technology node. Typically measurement techniques such as interferometry are used for this. Extremely stable cameras with low noise are needed for accurate measurements. Cameras with consistent performance reduce the metrology variability and serves to better determine any process variations. This reduces process deviations, allowing root cause analysis to take corrective action. As with all measurements, high quality means that the variations in the camera and the images are smaller than the variations of what you are trying to measure in the production line so you are not measuring within the noise of the camera. -5-
SMALLER AND COMPLEX The push into the 22 and 20 nm technology node 6 results in many changes. There has been an on-going evolution in front-end semiconductor manufacturing to move from in-line inspection rather than off-line, destructive analysis whenever possible. This requires a variety of inspection and metrology equipment with high quality and stable visible, Infra Red (IR), or Ultra Violet (UV) sensitive cameras to support the need for increased accuracy. The trend towards miniaturization and higher density is of course carried into PCB manufacturing as well, presenting new challenges for inspection equipment manufactures to maintain or improve accuracy. To increase performance while reducing size results in smaller chips, different packages, higher density printed circuit board, and multi-layered, more complex boards. There is also large variety of sizes of the components. Increased Accuracy As the objects to inspect/measure with both semiconductor front-end and back-end become smaller, higher resolution cameras with better spatial resolution can improve accuracy and precision. This does require a high quality camera design. As mentioned before, high quality means that the variations in the camera and the images are smaller than the variations of what you are trying to measure so you are not measuring within the noise of the camera. Also, particular care has to be given to the optical design and precision of the image sensor placement in the camera. The alignment of the image sensor in the camera is key to have an optimal optical path. This provides the accuracy for the overall system. Inspection (SPI) 8. Larger resolution cameras, such as 25 Megapixel, can be of benefit when dealing with a huge variety in components with a very flexible field of view. The move from 2D to 3D inspection and measurement is another way accuracy is improved. With solder paste inspection, 3D inspection and measurement is becoming more important with changes in the amount of solder paste used. As the solder bumps and balls become smaller, the volume of the solder paste is the important measurement rather than just the width. As the solder provides the connection between the printed circuit boards, it is critical to measure the solder volume to verify solder joint reliability. This is done both pre reflow and post reflow of the solder. Machine Vision Camera Requirements for 3D With just a 2D view from the top, one can only see defects such as shifts, rotations, and cracks, but not whether components are flat on the board or the volume of solder paste. With this only 1 image was required to get all of the measurements. While some 3D measurement systems may use 4-5 images per inspected ROI, more advanced systems use 20 images or even more to increase measurement accuracy and to add color vision. The migration from 1 image for measurement, to multiple images results in more demands on the camera-based imaging system. There can be at least two approaches to satisfy these requirements. With printed circuit board (PCB) Manufacturing, several verification steps are required, including automated optical inspection of the PCBs and components and Solder Paste -6-
Option 1 higher resolution cameras Higher resolution cameras allow for a larger area to be inspected at once and provide more data, which can improve accuracy. BUT since many images are required to perform quantitative measurements and the overall system throughput must be maintained, the camera frame rate must also be high. (for example 4 Megapixel at 180 fps or even 25 Megapixel at 32 fps and higher) Since multiple images are combined, the stability and reproducibility in the camera is more critical than in the past. Only intentional changes can occur between the images. This means black level, gain, among others must be exactly the same for all of the images. The camera manufacturer controls all these parameters through careful design and implementation. Option 2 multiple cameras Another option to reach these goals is through multiple cameras to capture all of the images. This could mean fewer illuminators and less stringent requirement on the speeds of the camera. This is attractive as it allows for scalability using more cameras for higher end systems, and can seem more cost effective since lower-end cameras can be used. This should be done with caution though as the cameras can have lower frame speed, but need to be extremely consistent, and well-matched for this technique to be accurate. -7-
INNOVATION DEMANDS DRIVE FAST INNOVATION Why is it that cameras for consumer electronic products, e.g. smartphones have more than 5 megapixel tiny cameras that cost next to nothing, are not used for machine vision? The larger pixel image sensors (greater than 5.5 um) can allow for the best accuracy (i.e. Full Well and Read Noise), but they also result in the highest costs due to large sensor sizes (silicon real estate consumed) and additionally expensive optics. Larger pixels are still used in the industrial and scientific market, but the trend in other markets has been towards much smaller pixel sizes. This is especially so with CMOS image sensors. These new image sensors are enabling better cameras for our smartphones and web cameras, with pixel sizes down to 1.4 um and extremely low cost. For machine vision, CMOS sensors with smaller pixels (even 2 to 3 um) may not be acceptable, especially with high-end inspection applications, such as semiconductor inspection, Flat Panel Display inspection, or electronic metrology applications. Smaller pixel image sensors should reduce the cost of the camera because of the camera size, or more pixels inside the same camera and optics, leading to higher resolution. These benefits are all appealing for machine vision too so what is given up? Our conclusion, based on a thorough analysis is that with pixels less than 4.5 um, is that too much functionality and performance is sacrificed for a lot of machine vision applications 9. The growth in smartphones and corresponding cameras has allowed for dramatic improvements in CMOS sensors. This has also affected the available sensor technology for machine vision allowing machine vision cameras to then support the production of more smartphones. CONCLUSION Our increasing need to stay mobile and connected translates to a worldwide adoption of smartphones and tablets. This trend has a major impact on the speed and growth of innovation. In the end, every OEM that uses machine vision benefits from this, including food inspection equipment or even intelligent traffic systems. While better CMOS sensors are allowing us to take better photos with our smartphones, better CMOS sensors are also used in the industrial cameras that guarantee the quality of the parts within the phones. High performance machine vision suppliers have been relied on to enable the advancements required. This includes the move from 2D to 3D. That being said, the constant drive for innovation with smartphone cameras has led to dramatic improvements in CMOS image sensors that are well-suited for machine vision cameras in a short time frame. These latest global shutter CMOS sensors allow for the machine vision cameras with highresolution combined with high-speed that are required to meet the accuracy and throughput needs of the latest inspection and metrology equipment as mentioned above. -8-
REFERENCES 1. http://www.peoriamagazines.com/ibi/2012/jan/year-of-mobility 2. http://www.asymco.com/2012/03/07/the-unrelenting-trends-in-the-us-smartphone-market/ 3. http://www.electroiq.com/semiconductors/2012/04/19/tablet-and-smartphone-sales-drivingglobal-semiconductor-market.html 4. http://www.adimec.com/en/service_menu/markets/machine_vision_cameras_for_semiconductor_ wafer_metrology 5. http://www.adimec.com/en/service_menu/markets/cameras_for_back_end_semiconductor_ packaging_inspection 6. http://en.wikipedia.org/wiki/flip_chip 7. http://en.wikipedia.org/wiki/22_nanometer 8. http://en.wikipedia.org/wiki/automated_optical_inspection 9. http://info.adimec.com/blogposts/bid/68684/can-small-pixel-cmos-image-sensors-be-useful-in- Machine-Vision -9-
ADIMEC Adimec specializes in the development and manufacturing of high-performance cameras that meet the application-specific requirements of key market segments, including machine vision, medical imaging, and outdoor imaging. Founded in 1992, the company partners with major OEMs around the world to facilitate the creation of industry-leading cameras. The unique Adimec True Accurate Imaging technology provides new levels of precision and accuracy to vision systems. Its diverse line of camera products meet a wide range of performance, size, cost, interface and application requirements. Adimec has offices around the world focused on creating customer value and satisfaction through local, personalized support. Need more inspiration? Contact us www.adimec.com -10-