Capability · 03 · Electrical

Test benches for power electronics

A converter rarely fails at a steady-state point; it fails after many load cycles. We test the thermal path from the liquid-cooled module into the coolant — for each load point and over the service life, with a deionised water circuit whose conductivity is monitored.

Power electronics test bench as a continuous front: on the left the power section cabinets with power supply drawers and control cabinet, in the middle the test fixtures with pneumatic cylinders above B6 bridges on cold plates, on the right and in the base the conditioning fluid system with distribution headers, pumps and valve branches — Power section, test fixtures and conditioning — one plant

The task

Measuring the thermal path — over the service life

A converter rarely fails at a steady-state point; it fails after many load cycles. What matters is the path of the heat from the module into the coolant and how it changes over time.

Thermal resistance R_th — from the junction into the coolant, for each load point.
Load cycling / power cycling — up to the failure criterion, for service life assessment.
Influence of the contact pressure — module on heat sink, measured instead of assumed.
Regenerative DC and AC load — real current loading instead of a heating resistor.
Deionised water circuit — with monitored conductivity, because ions have no business inside a converter.
Fast acquisition — galvanically isolated, up into the kHz range.

How the thermal resistance shifts with the load point.

Characteristic values

Electrical and thermal

The test bench applies real current to the test item and measures the thermal path while doing so.

Quantity	Value (design)	Note
Load	DC and AC, regenerative	instead of a heating resistor
Test current	up to 1,000 A	depending on the module
Voltage	up to 1,500 V DC	depending on the application
Measured quantity	R_th per load point	junction to coolant
Acquisition	up to 50 kHz	galvanically isolated
Coolant	Deionised water, water-glycol	conductivity < 2 µS/cm monitored
Flow temperature	+15 to +65 °C	warm-water cooling included
Flow rate	1 to 60 l/min	per test item

Design values, not a project commitment. The ranges are the limits of our modular system; what is possible in your plant is stated in the functional specification — to be confirmed by engineering before go-live.

Process diagram of the test bench · symbols to ISO 10628, designations to EN 62424 · deionised water circuit, test branch and regenerative electrical side

Power cycling

Load cycles up to the failure criterion

The power cycler applies current to the module cyclically, measures the junction temperature without a sensor — via V_CE at a small measuring current as the temperature-sensitive parameter — and runs until a failure criterion is met. Based on the ECPE guideline AQG 324.

QL-01 · PC_sec

Second-range cycles

Short current loading, steep temperature swings: fatigues bond wires and chip solder. Tests the packaging and interconnection close to the chip.

QL-02 · PC_min

Minute-range cycles

Slow heating through of the whole module: fatigues the solder layer to the base plate. Tests the large-area thermal path.

Z_th measurement

Cooling curve

Thermal impedance from the step response — resolved layer by layer, from the chip into the coolant. The change over the cycles shows which layer is ageing.

Double pulse

Switching behaviour

Switching energies and overvoltages for each operating point — the electrical side of the same test item, on the same cooling circuit.

Standards

Tests and the standards behind them

The qualification of power modules is standardised. We build the test benches so that the procedures set out in them run cleanly — and so that the evidence is in the test record.

Test	Basis	What it stresses, what is measured
Power cycling, second-range cycles (PC_sec)	ECPE AQG 324 QL-01 · IEC 60749-34	Short current loading with a steep temperature swing; fatigues bond wires and chip solder. Failure criterion typically +5 % V_CE or +20 % R_th
Power cycling, minute-range cycles (PC_min)	ECPE AQG 324 QL-02 · IEC 60749-34	Slow heating through of the whole module; fatigues the solder layer to the base plate. The same criteria, a different damage mechanism
Thermal resistance R_th(j-c)	JEDEC JESD51-14	Transient dual interface: two cooling curves, with and without thermal interface material; the separation point of the structure function gives the junction → case transition
Thermal impedance Z_th	JEDEC JESD51-1 · IEC 60747-9	Step response over time, resolved layer by layer; its change over the cycles shows which layer is ageing
Switching behaviour, double pulse	IEC 60747-9	E_on, E_off and switching times for each operating point, with the thresholds laid down there (10 % / 90 % / 2 %) as the integration limits
Temperature cycling (TST)	IEC 60068-2-14 · AQG 324	Passive cycles without current loading; separates thermomechanical fatigue from the effect of the module's own losses
Continuous junction stress (HTRB / HTGB)	IEC 60749-23 · AQG 324	Blocking or gate voltage at maximum temperature over a long period; the leakage current trend is the criterion
Humidity under voltage (H3TRB)	IEC 60749-5 · AQG 324	85 °C and 85 % relative humidity under blocking voltage; tests the passivation and the encapsulant
Safety of the set-up	IEC 62477-1	Clearances and creepage distances, protective separation, protection against contact — a requirement on the test set-up, not only on the test item

We build the test benches, we do not certify. The plants are designed so that the procedures named can be run on them; responsibility for the test itself and its evaluation lies with whoever carries it out. Which edition of a standard applies in the project is laid down in the functional specification.

Test items

What we test

From the single module to the finished power stage.

Power modules

IGBT and SiC modules, thermal resistance and power cycling.

Converters and inverters

Efficiency, temperature rise, load cycling under real current loading.

Charging and DC/DC electronics

Thermal behaviour and endurance running on liquid cooling.

Liquid-cooled heat sinks

Pressure drop, contact pressure, temperature distribution.

Design

This is the window we work in

Quantity	Value (design)	Note
Test items	Modules · converters · charging electronics	Component to power stage
Load	DC/AC regenerative, up to 1,000 A	up to 1,500 V DC
Measured quantity	R_th, efficiency, temperature	per load point
Cooling circuit	Deionised water / water-glycol	Conductivity monitored
Traceability	Test record per test item	Time stamp, test equipment no.

From the project

A look inside

A photograph of the plant and the test station, together with the renderings of the power cycling test bench.

Power electronics test bench with deionised water circuit — Test bench and deionised water circuit

Power module on a liquid-cooled heat sink — Module on a liquid-cooled heat sink

Rendering of the power cycling test bench: 19-inch cabinet with power supplies, next to it the test station with IGBT modules, busbars and the deionised water circuit in a wireframe shell — Power cycling test bench — rendering

Rendering of the test station: IGBT modules on copper busbars with gate driver and cooling connections, half photorealistic, half engineering drawing — Module test station with busbars — rendering

Rendering: test fixture on the trolley — pneumatic cylinders press the contact bridge with its pogo pin adapter onto the B6 bridge, below it in the cabinet the conditioning fluid system — Test fixture on the trolley — rendering

Something to test?

Tell us the test item, the medium and the ranges — we will design the test bench for it.

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