Combining the Advantages of ICT and FCT in a Single Test Adapter: A Case Study
Apr 13, 2020
In-Circuit Testing (ICT) is an established method for analyzing an electronic product in production. Typically, a bed-of-nails approach is used to test a non-powered circuit board, and techniques such as Direct Digital Synthesis (DDS) and Discrete Fourier Transform (DFT) are applied to generate stimulus signals and perform analog measurement analysis.
This allows the In-Circuit Analyser (ICA) to measure real-world attributes such as inductance, capacitance, impedance, and resistance to verify that all Device Under Test (DUT) test node results are within tolerance and to detect any components that are open, shorted, incorrect, or misoriented, all without powering up the DUT.
The interconnection between the nail contacts and the relevant analog channel or digital Driver/Sensor (D/S) on the pin board is achieved using a relay multiplexer (Figure 1).
Fig. 1: Typical bed-of-nails 2x16 relay multiplexer (only one channel shown in the diagram)
Firstly, ICT bed-of-nails probes are not rated to carry the supply voltage or load current required for a full functional test on powered devices. A dedicated FCT test fixture uses heavy-duty contacts designed to handle higher currents or voltages without overheating, arcing, or excessive wear. The disadvantage is that these contacts occupy more space, so FCT test adapters typically evaluate only one DUT at a time.
Secondly, the ICA internal programmable power supplies, relays, and electronic loads are not designed for high-current testing. Simply swapping in more powerful units can introduce interference with sensitive ICT analog measurements, including measurement inaccuracies caused by ground-bounce, voltage drops along wiring, and transients from switching inductive loads. Measurements in a dedicated FCT adapter are usually lower resolution with heavier filtering, making them less sensitive to interference. Additionally, the power supplies and relay contacts are more robust and capable of switching more than one amp.
Thirdly, relay interface hardware and software control typically use a Parallel Input/Output (PIO) controller and relay driver (Figure 2). In ICT applications, relay switching speed is generally not critical since relays are mainly reconfigured at the end of each DUT test to multiplex connections from one pin assembly to the next. In an FCT test adapter, however, relays adjust the functional test setup for each test on each DUT, so control data throughput to the relays is higher. In a dedicated FCT setup, this is not an issue because only one DUT is tested at a time, but in a combined ICT/FCT adapter, relay control speed becomes a significant bottleneck.
The interconnection between the nail contacts and the relevant analog channel or digital Driver/Sensor (D/S) on the pin board is achieved using a relay multiplexer (Figure 1).
Fig. 1: Typical bed-of-nails 2x16 relay multiplexer (only one channel shown in the diagram)
The Traditional Separation of ICT and FCT
In some advanced systems, the ICA module can also perform limited functional testing (FCT) by applying power to the device and measuring input and output characteristics under load. More often, this test is conducted separately with a second test adapter. There are several practical reasons for this:Firstly, ICT bed-of-nails probes are not rated to carry the supply voltage or load current required for a full functional test on powered devices. A dedicated FCT test fixture uses heavy-duty contacts designed to handle higher currents or voltages without overheating, arcing, or excessive wear. The disadvantage is that these contacts occupy more space, so FCT test adapters typically evaluate only one DUT at a time.
Secondly, the ICA internal programmable power supplies, relays, and electronic loads are not designed for high-current testing. Simply swapping in more powerful units can introduce interference with sensitive ICT analog measurements, including measurement inaccuracies caused by ground-bounce, voltage drops along wiring, and transients from switching inductive loads. Measurements in a dedicated FCT adapter are usually lower resolution with heavier filtering, making them less sensitive to interference. Additionally, the power supplies and relay contacts are more robust and capable of switching more than one amp.
Thirdly, relay interface hardware and software control typically use a Parallel Input/Output (PIO) controller and relay driver (Figure 2). In ICT applications, relay switching speed is generally not critical since relays are mainly reconfigured at the end of each DUT test to multiplex connections from one pin assembly to the next. In an FCT test adapter, however, relays adjust the functional test setup for each test on each DUT, so control data throughput to the relays is higher. In a dedicated FCT setup, this is not an issue because only one DUT is tested at a time, but in a combined ICT/FCT adapter, relay control speed becomes a significant bottleneck.
Finally, while ICT measurements can be performed in milliseconds, FCT procedures are typically slower, as measurements on a powered device require outputs to settle before reliable data can be taken. FCT usually takes five to ten times longer than ICT for the same product. Combining both processes in one ICT/FCT platform can create a production bottleneck. Separating the two processes allows one ICT machine to feed several FCT test fixtures in parallel, increasing test throughput and reducing delays.
From the outset, Zdenek Martinek, application engineer at Elmatest, recognized this as a complex project. Key challenges included combining ICT/FCT in a multi-panel design, managing high relay control throughput, accelerating the FCT process, and handling high power levels without damaging sensitive probes. In close collaboration with Markus Stöger from RECOM’s R&D department, solutions were found for all issues.
The solution was a test module on each multi-panel, providing access to all ICT nodes needed to verify proper assembly. Once the conventional ICT procedure was completed on the test module, the remaining modules required only FCT.
Fig. 3: Top and bottom images of the multi-panel PCB showing the ICT test module in the corner.
Standard relay drivers in the GenRad Teststation are controlled via the PIO controller, which receives commands from the PC over an MXIbus (Figure 2). This setup was too slow for processing different FCT measurements within a single test vector using the high-speed system controller. To accelerate relay switching, a novel relay driver topology called ‘active burst’ was implemented in the RECOM test adapter.
In active burst, some relays are driven directly from the D/S outputs instead of the PIO controller. Each D/S output can be configured with nine functions, including Drive, Sense, Hold, and Collect CRC. In this case, the Drive function powered the relays directly. D/S Drive outputs are normally TTL-limited, insufficient for relay operation, but Darlington transistor current amplifier coils allowed direct control. This made relay switching virtually instantaneous and simplified coding.
Case Study: High-Current DC/DC Testing for RECOM Power
For a newly developed DC/DC product series by the Austrian company RECOM Power, the cost and time of two separate test adapters were unacceptable. A solution was needed to combine the high-speed advantage of ICT with the comprehensive quality assurance of 100% functional testing in a single test adapter. The challenge was significant: devices had up to 6A output current and input voltages up to 60V, and each PCB panel contained forty partly-finished modules requiring parallel testing with heavy-duty power supplies. High data throughput and precise timing were critical. RECOM contracted Elmatest in the Czech Republic to build a combined ICT/FCT test adapter for the Teledyne Teststation LH used by the EMS provider.From the outset, Zdenek Martinek, application engineer at Elmatest, recognized this as a complex project. Key challenges included combining ICT/FCT in a multi-panel design, managing high relay control throughput, accelerating the FCT process, and handling high power levels without damaging sensitive probes. In close collaboration with Markus Stöger from RECOM’s R&D department, solutions were found for all issues.
Challenge 1: Integration and EMC Shielding
The first challenge was integrating ICT/FCT into the multi-panel design. Each PCB contained 40 independent circuits, fully assembled and enclosed, with some internal nodes inaccessible to the ICT pin panel. This was deliberate, as the DC/DC converters switch at high frequencies, and the metal case with its multi-layer PCB forms a six-sided Faraday cage to prevent EMI. External connections to internal high-frequency nodes could compromise EMC shielding and cause measurement errors.The solution was a test module on each multi-panel, providing access to all ICT nodes needed to verify proper assembly. Once the conventional ICT procedure was completed on the test module, the remaining modules required only FCT.
Fig. 3: Top and bottom images of the multi-panel PCB showing the ICT test module in the corner.
Challenge 2: Overcoming Relay Control Bottlenecks
The instructions for executing a test and measurement process are called a test vector. The input, output, and analog channel configurations are transmitted as a data burst, loaded into local on-board memory, and simultaneously activated by a timing strobe signal. This configuration remains latched until the test is completed and measurement data are returned to the CPU. Meanwhile, the next data burst can be preloaded to await the following strobe. This test methodology allows ICT to achieve fast throughput of around 4µs per vector.Standard relay drivers in the GenRad Teststation are controlled via the PIO controller, which receives commands from the PC over an MXIbus (Figure 2). This setup was too slow for processing different FCT measurements within a single test vector using the high-speed system controller. To accelerate relay switching, a novel relay driver topology called ‘active burst’ was implemented in the RECOM test adapter.
In active burst, some relays are driven directly from the D/S outputs instead of the PIO controller. Each D/S output can be configured with nine functions, including Drive, Sense, Hold, and Collect CRC. In this case, the Drive function powered the relays directly. D/S Drive outputs are normally TTL-limited, insufficient for relay operation, but Darlington transistor current amplifier coils allowed direct control. This made relay switching virtually instantaneous and simplified coding.
Challenge 3: Accelerating FCT and Protecting Probes
Another challenge was accelerating the FCT measurements, as waiting for analog levels to settle would have been too slow. Processing power in the ICA system, using DDS and DFT techniques, enabled rapid measurement. Instead of applying a fixed load and waiting for stabilization, output loads were pulsed for milliseconds, with processed results used to derive final characteristics, reducing measurement time by up to 80%.
A key development issue was integrating dynamic load and supply switching with the GenRad test station software, written in Pascal, Assembler, and Basic. Despite GenRad ceasing operations in 2003, the hardware remains robust enough to support modern operating systems.
Pulsed loading also protected sensitive probes. Short pulses prevented local heating even with 6A peak current through a probe rated for 2A. On/off ratios were programmed to allow probe cooling between sequential measurements, avoiding burning or scorching and preventing power supply overload.
ICT also measures internal voltage divider resistances used to preset output voltage, enabling the system to calculate output voltage, output current, and input voltage range. These values feed into the FCT program, ensuring functional testing is accurate and preventing operator errors that could damage the product or expensive test equipment.
Fig. 5: The finished test adapter in action
Pulsed loading also protected sensitive probes. Short pulses prevented local heating even with 6A peak current through a probe rated for 2A. On/off ratios were programmed to allow probe cooling between sequential measurements, avoiding burning or scorching and preventing power supply overload.
ICT also measures internal voltage divider resistances used to preset output voltage, enabling the system to calculate output voltage, output current, and input voltage range. These values feed into the FCT program, ensuring functional testing is accurate and preventing operator errors that could damage the product or expensive test equipment.
The Bottom Line: Faster Combined ICT/FCT Throughput
The result is a combined ICT/FCT test time of 1.8–1.9 seconds per DC/DC module, allowing full PCB multi-panel testing in under 80 seconds, including PCB removal and placement. For a production run of 5000 units, this time-saving was critical to the product series’ success. The RPM module design has since expanded from a single series with eight variants to three series totaling twenty-two variants, all sharing the same footprint and test adapter.
Fig. 5: The finished test adapter in action