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Don't all boundary-scan tools detect shorts and opens? Isn't that the purpose of boundary-scan?
Yes, many tools (not all) can detect shorts and opens on simple nets, high end tools like Eclipse can detect them on both single ended nets, complex nets with termination and series resistors and on differential nets with and without termination. However, only Eclipse enables you to pinpoint the exact location of an open on what is called "point-to-point" nets.
Figure 2. Point-to-point net and open details
Consider a net with just two device pins on it, a driver and a receiver. Today's high-speed technology is virtually all point-to-point, one driver, one receiver, not bussed with many pins. Standard boundary-scan techniques would only identify that an open between the two devices existed. BGA devices prevent the visual inspection of these types of opens to determine which side is open. Eclipse and VFA will direct the technician where to probe so it can be determined whether the driver pin is open or the receiver pin is open. Without VFA, only a guess can be made as to which BGA device to remove and rework. If the guess is wrong (there is a 50-50 chance which is open, driver or receiver) then a second rework must be performed adding to the cost. The potential for damaging the device (the device will have to be re-balled too) is high and the potential for damaging the PCB is also high. VFA is included free with the standard Eclipse product, as an option on the low end, "http://www.intellitech.com/products/eclipse Limited" products, it is less than $1500.00. Test Departments can quickly receive a ROI (Return on Investment) greater than 1 (one) if just one PCB is saved from being damaged or two to three BGAs can be prevented from being unnecessarily reworked and re-balled.
Eclipse also pinpoints the locations of stuck nets (stuck-at-one, stuck-at-zero) and bridging faults. VIAs on the nets are identified so hard to diagnose pin-to-via and via-to-via shorts can be quickly identified. Without VFA, a failing board is either scrapped or brought into the repair lab for extensive analysis by the engineering group. If these boards could be repaired, then manufacturing yield could be increased, however the manual process adds significant costs in repair. With VFA, scrapped boards can now be diagnosed and repaired. This increases production yields and reduces both manufacturing and engineering costs.
VFA is an integral part of the Eclipse Test Development Environment. VFA correlates information from the Eclipse Boundary Scan Intelligent Diagnostics (BSID) diagnostics engine with CAD data to produce a graphical, interactive map of fault locations for a failing PCB. The Eclipse BSID engine runs in conjunction with Board Interconnect ATPG to analyze each fault and generate a list of pins and nets affected by each fault.
For example, when diagnosing a failure caused by shorted signals, VFA highlights each pin and via on a failing net so that you can view all possible points at which a net could be shorted. This helps the test technician determine the most probable location of the fault. For signals that a shorted to a power or ground trace, VFA will highlight the failing net and the adjacent power and ground nets, so that you can check the closest proximity power and ground nets for shorts.
Wouldn't a free GenCAM viewer or Allegro Viewer do the same thing?
PCB layout viewers are designed to analyze PCBs for problems associated with defects in the manufacturing of the bare PCB. Research has shown that a considerable amount of expertise and time is needed to properly setup the layers, silkscreen, via holes, copper pours, on both top and bottom of the PCB so proper solder fault type analysis can begin. Technicians and manufacturing personell are more comfortable when they can see a PCB view that looks like the PCB in front of them, rather than a more abstract view of the PCB design in various colors. With a PCB viwer, many of the operations are manual, especially for operations requiring identifying solder areas on either side of a PCB. While the PCB viewer does allow you to determine the distance from one VIA to another VIA, it is cumbersome and it must manually be done for every VIA. The process of debugging is further slowed since there is no interaction with the test tool, or mapping of faults to the possible locations. All of this must be done manually with the PCB layout viewer.
VFA helps you navigate areas of interest on a PCB in numerous ways:
VFA shows faults based on fault type and fault location:
Pin and Net Navigation Tools
VFA Fault Windows Display Diagnostic Information
VFA is a standard feature of the Eclipse Test Development Environment
VFA is integrated with Eclipse and Scan ExecutiveTM so engineers and technicians can perform fault diagnosis directly from either tool using the same project structure and script files. Design Engineers can cross probe between VFA and Schematic Logic ProbeTM (SLPTM) to debug and bring-up new designs in the lab.