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INDUSTRY VIEW
December 31, 1969 |Estimated reading time: 4 minutes
Flying Probe - From Prototype to Production
First introduced in 1986 by Takaya, fixtureless flying-probe testers have become a mainstay in most electronics manufacturing facilities. Many unique features have made them welcome additions to the test-and-inspection arsenal. The ability to do in-circuit test (ICT) without building a bed-of-nails test fixture and the ability to access very fine-pitch SMT devices are two main reasons for the flying-probe tester’s popularity.
Now that flying-probe test has joined the mainstream as an essential, proven, and reliable test technology, it’s time for OEMs and EMS providers to think more broadly about how the technology fits into their overall test-and-inspection strategy. Given the unique characteristics of flying-probe testers, electronics manufacturers should ask themselves if they are using this technology to achieve optimal test coverage, throughput, cost reduction, and time-to-market.
Having spent more than 25 years in test - from semiconductor through ICT and functional board test - I thought I knew what drove the need for flying-probe test. When working for an ICT vendor, ICT was the PCB test workhorse that made mass production of PCBs possible. Flying-probe systems were developed to provide cost-effective ICT to manufacturers who didn’t have the volume to justify the purchase of a bed-of-nails fixture for every board type, and could live with the slower test speeds dictated by the need to physically move probes around the board. At least that’s what I thought when we added flying-probe systems to our product portfolio. And, strictly for diagnostics at the end of the line or for field returns, this view may be correct.
When Takaya developed the flying-probe tester, the company was in the contract manufacturing (CM) business, and found that ICT wasn’t fast enough. The actual test time was fine, but the time to develop a program and fixture was unacceptable given the demands being put on CMs for prototypes and new products first being introduced into manufacturing. They developed the system with an emphasis on probing accuracy, measurement repeatability, long-term reliability, and fast program development. Flying-probe systems were designed for prototype and NPI applications and, as test times have come down, have been increasingly used in low- to mid-volume production, providing diagnostics for boards that fail functional test or are returned from the field for repair. These systems have found their way into areas of PCB manufacturing where an offline system can be used, but do they have a role in higher-volume in-line applications?
ICT traditionally has been the test tool that has made volume production of PCBs both possible and practical. However, as competition within the EMS/ODM industry has grown, the drive to lower test costs, while dealing with loss of access issues, has led to greater use of both automated optical inspection (AOI) and automated X-ray inspection (AXI) systems, along with the hope of eliminating ICT. While the demise of ICT has been predicted for a long time, inspection has not eliminated the need for electrical test; therefore, ICT has continued to fill this important role.
New flying-probe systems have been developed that may be more attractive for use in line in high-volume applications. These systems are smaller, faster, and cost less. They provide the accuracy, reliability, and fast program generation of their higher performance siblings, but they don’t need to do the entire job themselves, since they are most appropriately used as electrical process-verification tools, complementing inspection tools that are already being used in most lines.
Even though these new systems are faster, they still cannot do a full electrical test of the board and keep up with the line beat rate. However, they can effectively be used for sampling either a designated number of boards per lot or focusing in on specific areas of the board that have the highest probability of problems or the highest cost to diagnose.
There are real-world examples of manufacturers moving in those directions. One user wants to concentrate on testing for shorts on costly, very fine-pitch, high-pin-count digital devices, verifying that shorts are eliminated before the boards go to functional test. Another wants to use multiple systems in line, each testing a separate section of the board, to verify that the boards have been manufactured correctly. The benefit here is the ability to eliminate the delay time associated with electrical-test development when a new design or design changes are introduced to volume production.
Conclusion
The same characteristics that made flying-probe systems a solution for high-quality manufacturing defect detection in prototype and NPI applications can make them the most suitable partner to AOI and AXI systems in volume manufacturing to identify process problems that can only be found with electrical test. Manufacturers need to take another look at ways to use flying-probe test as part of their overall test strategy in high-volume applications. When getting a new product to market faster, or ensuring that products ramp quickly to high-volume production, the solution may not be the system that can deliver the fastest test time. The solution may be one that produces an accurate, repeatable test the fastest; offers the flexibility to modify and add tests on-the-fly as needed; and performs those tests consistently and reliably in a manufacturing environment.
Roy McKenzie, West Region manager, Texmac, Inc., may be contacted at (408) 970-9171; rmckenzie@texmacusa.com.