Automatic optical inspection of SMD tapes

When was the last time you had to wind your watch? The key to time-keeping in world famous Swiss watches is most likely the tiny piece of quartz found on the watch interior. When it comes to the production of watch components, a high-quality vision system is required to inspect the large numbers of precision components. At Micro Crystal in Switzerland, the Cognex In-Sight 5401 inspects the packaging of ceramic surface-mounted devices (or SMDs for short) which is home to the all important oscillating quartz. These high-frequency mini tuning forks (32,768 vibrations a minute) ensure constant frequencies and time information in products all over the world.

No room for defects

Micro Crystal, a Swatch Group company, has had just one objective since its foundation in 1978: maximum precision. The world's leading manufacturer of quartz crystals for clocks and mobile telephones, among other things, cannot afford quality defects. In addition to quality assurance in the production process for oscillating quartzes and SMDs, optimized packaging is also of great importance for customer satisfaction. SMDs which have been incorrectly positioned or labelled have to be detected and removedIn in strips packaged in numbers of between 7,000 and 16,000. The same applies to the packaging areas of the SMD tapes which have gaps.

Only the best make the final cut

Since mid-2007, the company has been using an Optical Tape End-Controller with an In-Sight 5401 to perfect packaging quality. Similar to a film-cutting table, the roll of uninspected SMD tape is guided over a worktable on which the In-Sight 5401 subjects the individual miniature packages measuring only millimetres and containing the vital quartz to an automatic optical inspection.

The following criteria are examined and the results transferred to the monitor of a connected PC:

• Is there an SMD in the package?
• Is the position of the SMD correct?
• Is the batch number lasered onto the ceramic housing of the SMD and if so, can it be perfectly read?

Vision tools that meet the challenge

The qualities that have made the SMD so attractive for years, namely its tiny housing free of connecting wires and the small space required by components as a result, is also what makes quality inspection a challenge. To meet the challenge, the In-Sight 5401 is supported by Cognex PatMax, the revolutionary object location tool that uses pattern-matching technology. PatMax locates objects reliably even if they are of different sizes, differently aligned, if their appearance is poor or even if they are partly covered. With the LED lighting, the full benefits of the Cognex vision system are realized. Using PatMax, the detection of the laser marked batch numbers, which are not sharply contoured 100 % of the time is completely reliable.

Reliable component location

PatMax uses geometric measurement instead of a pixel matrix to identify the most important individual features in the image of the object. It then sets the spatial relationships between the central features of the taught image in relation to the real-time image. By analysing the geometrical information, PatMax is able to determine the position of the object clearly.

Future vision applications – error proofing the packaging process

Identifying the batch number is not a simple job. According to the packaging specifications of Micro Crystal, the gold contact surfaces of the ceramic housing must always be on the side facing away from the camera, and so they should be invisible to the vision system. If the Cognex system detects fluctuations in brightness triggered by the gold areas on the grey ceramic surface, the Optical Tape End-Controller sounds the alarm. The faulty section is then moved to a pre-determined processing point and removed by hand. Highly satisfied with the results of the SMD inspection system with optical inspection, Micro Crystal is already thinking ahead. From 2008, In-Sight and PatMax are to be used a step earlier, for packaging the SMD itself. In this way, they hope to detect and eliminate faults as early as the packaging process.

About Cognex
COGNEX designs, develops, produces and sells machine-based vision systems and computers which allow machines to see "intelligently". Cognex is the world's leading supplier of machine-based vision systems, with over 350,000 systems already supplied, corresponding to a cumulative turnover of over 2 billion USD since the company was founded in 1981. The Modular Vision Systems Division of Cognex is based in Natick, Massachusetts, and specializes in machine-based vision systems used in the automated production and quality assurance of individual parts. The Surface Inspection Systems Division headquartered in Alamenda, California, concentrates on the high-speed surface inspection of sheet product made of metal, paper and plastic. In addition to the headquarters in Natick, Massachusetts, there are other subsidiaries in North America, Japan, Europe and South-East Asia. The head office of Cognex Europe is in Rueil-Malmaison, near Paris. For more information, see our website at http://www.cognex.net.