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Boundary Scan JTAG
opens and shorts
opens and shorts
» VFA Brochure

» Eclipse Family Overview » Test Development
» Manufacturing Test
» Diagnostics and Repair

Standard Features:


» Introduction
» Finding Pins/Nets
» Viewing Nets
» Debugging Opens
» Debugging Shorts
» Debugging Stuck-Ats
» Cross Probing


Opens and Shorts for PCBs using Boundary-Scan

jtag shorts opens boundary scan

                           Figure 1. Boundary Scan Shorts on LVDS

Visual Fault Analyzer displays the actual locations of manufacturing defects on a graphical image of the PCB,  to identify opens on point-to-point nets and accelerate the fault isolation and resolution process for bridging faults and stuck nets.  The VIAs associated with the nets, especially those vias underneath component bodies are identified and their proximity to each other are evaluated.  VIAs related to 'opens' are also pinpointed so a technician can easily identify which BGA device needs to be removed and re-soldered.  Without sophisticated tools like VFA, PCB fault resolution forces a test technician to just "guess" as to where a short or open may be located.   

Use the links on the left to get short step-by-step tutorials


     "The engineers here at IMS have years of experience in developing leading edge Automatic Test Equipment. That same expertise was used when we chose our 1149.1 based ATE provider. We found Intellitech's products had the features we needed for fast prototype debug and comprehensive test of our densely populated PCB's. The products offered an excellent value. I would not hesitate to recommend them."     
John Liebengood
Project Leader
IMS - a Credence Company
    

 

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.

                              shorts opens jtag boundary scan

                                   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.  Test departments can quickly receive a positive ROI (Return on Investment) if just one PCB is saved from being damaged or two to three BGAs can be prevented from being unnecessarily reworked and re-balled.

Boundary Scan Shorts and Stuck-At faults

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 Overview

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:

  • Viewer Window -The main window that displays the entire image of the PCB
  • Zooming - Zoom into selected regions of the PCB, or zoom out to view the entire board.
  • Fit in Window - Redisplay the entire PCB at any time after zooming operations.
  • Thumbnail Window - The thumbnail view of the PCB displays where the viewer is in relation to the entire PCB. The thumbnail view is useful when zooming in to debug small areas of the PCB.
  • Toggle Button - VFA can switch quickly between top and bottom views of the PCB.

VFA shows faults based on fault type and fault location:

  • Show Pin Faults - Displays all pin faults
  • Show VIA Faults - Displays all via faults
  • Show All Pin and VIA shorts - Displays all pins and vias that are shorted
  • Show All Power and Ground Nets - Displays all pins and vias that are connected to power and ground. The power pins are designated with a '+' sign and the ground pins are marked with a '-'. Knowing the location of power and ground nets is invaluable when diagnosing stuck-at faults.

Pin and Net Navigation Tools

  • Find Pins - VFA's pin-finding search engine allows you to enter the name of a pin (or wildcard) and see the location of the pin highlighted on the image of the UUT.
  • Find Nets - VFA's net-finding search engine allows you to enter the name of a net (or a wildcard) and see the location of all pins and vias on the image of the UUT. When diagnosing failing nets, this feature shows all potential failure points.
  • Show All Pins and Vias on Net - Click on any pin or via and see the net name and all other pins and vias on the net.

VFA Fault Windows Display Diagnostic Information

  • Fault Types - VFA filters the display of faults by fault type: Stuck at 1, Stuck at 0, Short, Open.
  • Failing Nets - VFA display faults by net that allows you to select a specific failing net or set of failing nets to view. When a fault type is also specified, all failing nets of that fault type are displayed.

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.

VFA Benefits

  • VFA is a standard feature of Eclipse Test Development Environment
  • VFA Enhances text-based diagnostics so technicians and operators can quickly resolve faults
  • VFA finds non-visible faults under BGA devices so boards can be more efficiently reworked
  • VFA can be used with SLP to Cross Probe and Debug New Designs
  • VFA can quickly pinpoint the location of Stuck-at-one and Stuck-at-0 shorts