| This Issue's Feature Article
The
importance of the correct choice in Bare Board ATEs
Gianotti
Nicoletta, Seica SpA, ITALY
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| The importance of the correct choice in Bare Board ATEs |
The continuous technological evolution of electronic components dictates ever-higher performance together with ever-smaller geography. This has significantly changed test strategies of populated electronic boards as well as printed circuit boards. Up to a few years ago the latter (PCBs) constituted only a minimum part of the technological "know-how" of the completed board, acting simply as a base support and interconnect medium for the electronic components, characterized by a relatively low cost and simplicity, which was easy to test for continuity and isolation on a bed of nails type fixture connected to a tester.
Today's scenario is completely different: it is very common to find multilayer printed circuit boards (PCBs) with thousands of pads, some maybe a few tenths of a millimeter wide, on both sides, along with embedded components. In this case it becomes extremely difficult, if not impossible, to build a fixture, especially in terms of cost and time required to build it. If you also consider the accelerated life cycle of today's electronic products (and therefore also their relative PCB) and the rapidity with which they are modified to satisfy evolving market trends, it is evident that it is becoming more and more difficult to justify the costs of a traditional "bed of nails" type test, especially in lower volume production runs.
This is why "flying probe" test systems have become an important part of most PCB manufacturing strategies. There are several things to keep in mind when evaluating the purchase of a flying probe
tester. For example, it should be able to probe both sides of the PCB simultaneously with at least four probes (two per side) and there should be a camera on each side for centering on fiducials of the bottom and top layers independently.
The test probes should have some degree of angle with respect to the board surface to facilitate contact on drilled pads, and it should be possible to program the pressure applied by each test probe on each test point, in order to adapt the test to different situations; for example to guarantee a stable contact when testing "no clean process" PCBs or to minimize impact on the pads of the printed circuit. The system should also be able to utilize controlled loop feedback on the Z axes to "learn" various points on the PCB in order to then compensate for warping, bowing, etc.
Another important factor in the "cost of ownership" of a flying probe tester is the setup time required for each new part number; program generation should be completely automatic, so it is essential that the software be able to import the CAD data (Gerber files) of the PCB using the most common standards, including the widely used
IPC356 standard (version A or B). The tester software should be intuitive and easy to use, and should include the capability to execute parametric tests of components such as resistors, capacitors, p-n junctions, which are embedded in a growing number of PCBs.
Loading the PCB into the system should be fast and easy for the operator; on the basis of the volumes of PCBs to test, it may make sense to choose a system which can be connected to a
magazine or automatic loader for faster (and autonomous) load and unload. The availability of a vacuum-type board support is a plus when testing flex circuits, inner layers or very thin PCBs.
After test, a software repair station is a useful tool that helps the operator to locate the position of the failing net on the board on the basis of the test results by displaying, for example, the most probable points for a fault to occur on the net. The repair station can be used as stand-alone software or in network configuration to exchange statistics data on the test.
Software tools, which enable a “distributed” test strategy, are also important in the context of the growing complexity of PCBs. These tools enable the user to “split” the test with respect to the system used to verify the various parts of the circuits; for example the flying probe tester could be used to test fine pitch or BGA areas, while the rest of the PCB could tested on a universal tester to maximize test coverage as well as throughput.
Gianotti Nicoletta, Seica
SpA, ITALY
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| Product/Service Focus |
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This issue's focus is Automatic Test Equipment/Bare Board Testers.
You can view or add to our existing list of these Products.
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| Next Issue's Product/Service Focus |
In our next issue of Product/Service Focus we will cover Calibration Equipment.
You can add or upgrade an inspection equipment before the next issue comes out.
If you would like to include an exclusive article on how to best select Calibration Equipment, please contact LouisUngar@ieee.org.
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