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How Flying Probers Optimize Test Strategy
Takaya APT-9411 CE flying prober.
By John Oaf, Applications Manager, TEXMAC, Inc., Takaya Group
Manufacturers are constantly looking for ways to maximize the use of the equipment on their manufacturing floor. Resources are limited, time is precious and traditional testing is being challenged by new technologies that continue the push to design with smaller components.
Over the past few years there has been a shift in test philosophy for manufacturing. More and more products that have traditionally been tested on Bed-of-Nails ICT testers have been migrating to flying probe test. The reason for this is the cost of fixturing and engineering resources to support ICT.
By nature, Flying Probe Test (FPT) requires longer test times than ICT. But by maximizing the FPT resources, the overall effectiveness of FPT can be greatly enhanced while reaping the benefits of reduced overall test time.
Flying probe testers have evolved over the past 20 years to a test platform that can rival that of ICT. Test strategies such as Power-up, Functional, AOI, BSCAN and ISP are now commonplace on flying probe testers. By utilizing these features to their fullest, a flying probe test strategy can be developed that will ensure best overall test coverage.
Functional test of simple logic devices.
By taking into account the strengths of each one of these test/inspection tools, a FPT solution can be created to maximize test coverage. In addition by ensuring that no redundant testing is performed by any one of these processes, the overall test time can be significantly reduced to optimize the test throughout.
Bed-of-Nails (BON) In-Circuit testers typically have electrical access to all nets of the Unit-Under-Test (UUT) with memory backed driver sensor pin electronics that allow driving ones and zeros (logic levels) and sensing the logic levels at the device outputs to detect stuck at 1 and stuck at 0 faults.
The Takaya FPT system does not utilize a BON fixture or memory backed driver sensor pin electronics so how would it be possible to implement some of these functional tests? What hardware would be needed?
The company offers several different options depending on the functional testing that is needed. There are several popular options.
Power Relay Board.
This option allows for connecting external GPIB Power Supplies to the UUT through underside probes or a PCB connector to provide DC voltages to the UUT.
Coaxial Scanner Board.
This option allows connecting external GPIB Source and Measurement equipment to the UUT through high frequency coaxial cables directly to the UUT.
Programmable DC Power Source.
This option allows application of a Programmable DC voltage on the UUT through the "flying probes" or two (2) underside probes. This option can also measure the consumption current while applying the DC voltage.
Boundary Scan and ISP Hardware and Software.
This option allows performing BSCAN and ISP programming on the FPT.
The first thing you must do is review the PCB schematics to determine the UUT power requirements that will be needed and what type of functional testing can be implemented. Do you have voltage regulators? Are there relays that you may want to activate? What about Op-Amps and simple logic devices like buffers, line drivers, etc.?
Comparing test/inspection strategies.
Let's look at some examples of functionally testing a few devices at a high level without getting into the actual test statements.
Functional Test of Voltage Regulators.
Voltage regulators can be tested using either the GPIB power supplies or the programmable DC power source (PDC). First determine what voltage and current will be required. Is it a single board or a panel board configuration? If it is a one-up (single) board, then depending on the input voltage and current requirements, you can use either the GPIB Power Supplies to provide the DC voltage to the UUT through underside probes, or the Programmable DC power supply to provide the DC input voltage directly through two of the flying probes. Once the voltage regulator section is powered up, the correct regulation of the output voltage can be tested using the voltmeter through a second set of flying probes.
If the UUT is in a panel configuration, the number of GPIB power supplies needed may exceed the FPT system resources, so the easiest way to test the voltage regulators is to use one set of flying probes to apply the input voltage and a second set of flying probes to verify the correct output voltage.
Functional Test of Op-Amps.
Use the GPIB power supplies to power up the board, or at least the section of the circuit that provides the power to the Op-Amps being functionally tested. Using two of the flying probes, apply a small differential voltage across the Op-Amp inputs (if single ended input, then apply voltage from single input to ground) then test for correct expected output response by measuring the Op-Amp output voltage using the remaining two flying probes and the FP voltmeter. Repeat this procedure while reversing the applied input voltage to the Op-Amp. This type of functional test can perform a rail-to-rail or gain test depending on the configuration of the Op-Amp.
Functional Test of Relays.
Relays are statically tested during the non-powered, analog In-Circuit test. The inductance or resistance of the coil is checked, and then the normally open (NO) to common (C) and the normally closed (NC) to common (C) terminals are checked for correct default states. To functionally test the relays, use the programmable DC voltage source and two of the flying probes to apply the correct relay voltage directly to the nets or pins connected to the relay coil. This will energize the relay and then the second set of flying probes can be used to verify proper operation of the relay.
Functional Test of Simple Digital Devices.
Many simple logic devices can be functionally tested using the FP test system, devices like buffers, inverters, differential line drivers, differential line receivers, etc.
The ability to functionally test these types of devices really depends on the circuit design. For example an octal buffer could be functionally tested so long as the output control pins (OE & /OE) are connected to pull-up/pull-down resistors or tied directly to VCC/GND. Once the board is powered-up, the flying probe test system can apply the logic levels ("1"s and "0"s) to each of the input pins using two of the flying probes while the second set of flying probes and the voltmeter are used to check for the correct output logic levels of each device in the package.
When implementing these functional tests, you would usually be on the Tester which prevents the Tester from being utilized to test products. This is where the Real Map option can be a very big help. Real Map is a new software option available on the Takaya APT-94XX systems that allows placing the PCB in the system and then capturing the board image using the standard system camera. Once the PCB image has been captured, the system will use it to display failing test with the probe point locations overlaid and highlighted on the PCB image. Real Map allows for switching back and forth between the small field of view (FOV) of the system camera and the Real Map virtual PCB image so you can zoom in/out to quickly move to any area on the PCB board.
Real Map allows use of the captured PCB image off-line on a test programming development PC at your desk. Real Map will allow you to implement the various functional tests as well as review, add or change test point probe locations, review or change probe permissions, add graphical "High Fly" zones for tall components and other test enhancements without the need to have a PCB board or tie-up the flying probe test system resources.
Takaya fixtureless testers offer unmatched reliability, accuracy, ease of use and programming for complete detection of manufacturing faults on loaded PCB boards as well as power up capability, Boundary Scan and AOI (parts present, absent and orientation).
As described above, the Takaya Flying Probe Test Systems can do a lot more than just non-powered in-circuit fixture-less testing. With the right hardware options and functional testing strategy, the Takaya flying probe systems can provide complete manufacturing process verification for your Prototype, New Product Introduction (NPI), and other manufacturing test needs.
Contact: TEXMAC Inc., Takaya Group, 3370 Montgomery Dr., Santa Clara, CA 95054
408-970-9171 fax: 408-970-9178 E-mail: email@example.com Web:
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