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Faster Flying Probe ROI
December 31, 1969 |Estimated reading time: 5 minutes
BY Mark Harding, Digitaltest Inc.
Flying probe test systems have captured a significant and growing section of the global production test market. The largest growth areas have been in those geographies that have seen a reduction in volume manufacturing work, and have consequently refocused their businesses on new product introductions (NPIs), lower volume, and higher technology. Many of these new flying probe test users can be found in Europe and North America, but a growing number of Asian manufacturers now provide the type of rapid prototyping and product launch services that require the flexibility a flying probe test system can offer.
The advantages of a flying probe tester are that no test fixtures are required; they can make NPI up to four weeks faster than bed of nail testers; non-recurring expenditure (NRE) is lower; design for test (DfT) constraints are lower; and it is design-change tolerant. Low operator intervention, push-button test processing, low false call rates, and higher diagnostic accuracy also are beneficial factors.
However, flying probe test systems also historically carry a host of limitations that make justifying capital investment for a system more difficult than for higher-volume test platforms such as manufacturing defect analyzer (MDA) and in-circuit test (ICT). These limitations are related to conventional test methodologies.
Limitations
Speed. The first, and most significant, limitation is directly related to the need to probe many hundreds, or more likely thousands, of test points by moving test probes. While great improvements in the speed and accuracy of probe movement are in the works, the test times for flying probe test systems are normally measured in minutes - not seconds. This is far slower than other structural test processes.
Coverage. Test coverage is restricted to the capability of the limited number of probes used. Analog test coverage remains high, but digital test coverage is normally near zero for flying probe systems. The dilemma for engineers and production managers justifying capital investment in flying probe test has been balancing its advantages against the limitations of conventional flying probe test options. Users want to extend test coverage and reduce time for combined test processes. This enables an accelerated return on their capital investment, while retaining all expected benefits of flying probe test.
Combined Test Approach
Integrating flying probe, ICT, automated optical inspection (AOI), functional test, memory programming, and boundary scan capabilities onto a flying probe test platform* allows test developers to select the best possible combination of tests for the task at hand. This approach recognizes that the task at hand, and thus required test schema, changes during a product’s life, as do manufacturing demands, letting users add or delete tests as time allows or requirements change during development and manufacture.
Figure 1. Next-generation flying probers must integrate a range of tests.
Increased Test Point Access. The capabilities of a multi-point test platform mean it can be used to reduce test time, with oft-accessed test points contacted through dedicated positions. This reduces the number of flying probe tests and probe movements, thus shortening test times.
Automation. Eliminating operator load and unload sequences, when combined with board magazines, allows productive test time to extend beyond the end of a normal work shift.
Automated Optical Test. An integrated camera unit can perform optical inspection through the flying probe test platform. This step, normally done at the start of a test sequence, detects gross defects, such as missing devices, before the assembly moves on through the other test techniques.
ICT. Having the capability to use multiple test points simultaneously and to apply power to the board under test means power-on digital tests can be conducted. This extends test coverage for boards populated with digital devices. Positioning spring probe test points below the unit under test - with magnetic probes or a probe adaptor plate for higher numbers of fixed probes - supports higher-probe-count test methodologies.
Boundary Scan. Boundary scan can be used at all stages of the product life cycle. This methodology ensures a higher degree of fault coverage for digital devices early in the product’s life cycle, when historically it is difficult to provide coverage. Boundary scan tests require integration of a controller, power at the correct voltage levels, and access ports onto the flying probe platform.
Functional Test. Routing test signals to integrated instruments controlled by the flying probe test system ensures a range of functional test processes can be accomplished. These include VXI and other standards.
Opens Check. Opens check is a vectorless test for open IC pins. It adds flexibility and increased test coverage. This test requires additional probes mounted in the flying probe test system’s test heads.
Enhanced ROI
Providing capabilities to both reduce test time and extend test coverage, next-generation flying probe test systems shift the decision point of flying probe test system investment into medium-volume test requirements, along with common use in low-volume, NPI, and high-mix production test.
Adding more capability on a single platform can remove the necessity to purchase multiple test-and-inspection platforms, leading to a reduced total cost of test. Faster test makes new flying probe test systems capable of much higher production test throughput, reducing the cost of test per board.
This also affects the decision point, normally taken when volumes ramp to medium or high capacity, to move to a higher-volume test platform. At this point, a traditional flying probe test system needs to be frozen and a dedicated test fixture commissioned - normally costing in excess of several thousand dollars. Practical experience shows that design changes often emerge soon after the test fixtures have been commissioned, resulting in further delays and spend on test fixtures.
Flying probe test systems need to offer high fault coverage and must ramp to increased volumes, circumventing the move to alternative, expensive test platforms. These capabilities ensure that ROI for flying probe systems is significantly accelerated, simplifying the decision to purchase a flying probe test platform.
* MTS500 Condor
Mark Harding, director of sales North America, Digitaltest Inc., may be contacted at 5046 Commercial Circle, Suite C, Concord, Calif., 94520; (925) 603-8650; mharding@digitaltest.net.