4N aluminium (99.99 %)
The standard grade for general power-module ribbon. Good conductivity, low hardness and a well-understood process window on aluminium-metallised chips and nickel- or copper-plated substrates.
Power semiconductor interconnects
Aluminium Bonding Ribbon for IGBT, SiC & Power Modules
Aluminium bonding ribbon is a thin, flat strip of high-purity aluminium that is ultrasonically wedge-bonded to connect power chips, substrates and terminals inside a power module. One ribbon can carry the current of two or more heavy round wires, with a lower loop profile and a larger bonded area. This guide explains sizes, grades, selection and reliability testing, and how to specify ribbon when you buy it from Metline.
- Material
- 99.99 – 99.999 % Al, Al alloys
- Width
- approx. 0.5 – 2.0 mm
- Thickness
- approx. 0.08 – 0.30 mm
- Process
- Ultrasonic wedge bonding
What is aluminium bonding ribbon?
Bonding ribbon is the flat cousin of heavy bonding wire. Instead of a round cross-section, it has a rectangular one, typically 0.5 – 2 mm wide and 0.1 – 0.3 mm thick. It is fed from a spool through a ribbon wedge bonder, which presses it onto a pad and applies ultrasonic vibration to form a solid-state weld without melting.
Inside an IGBT, SiC MOSFET or diode module, the semiconductor chips sit on a ceramic substrate (DBC or AMB) with copper tracks. The top side of each chip still has to be connected to the circuit, and for most of the last four decades that link has been made with several parallel aluminium wires of 300 – 500 µm diameter. Ribbon does the same job with fewer, wider bonds.
Because the flat ribbon lies close to the chip surface, it spreads current over a larger contact footprint, produces a lower loop, and sees less bending stress at the heel of each bond during temperature cycling. These are the reasons ribbon has moved from niche to mainstream in automotive traction inverters, solar and wind inverters and high-power industrial drives.
Bonding ribbon vs heavy aluminium wire
Ribbon is not automatically better than wire. Each geometry has a place, and many modules use both: ribbon on the main power path and wire for gate and sense connections.
| Factor | Heavy round wire (100 – 500 µm) | Flat ribbon |
|---|---|---|
| Current per bond | Limited by diameter; several wires run in parallel | One ribbon often replaces 2 – 4 heavy wires |
| Bond footprint | Narrow, elongated wedge | Wide, flat contact spreading current across the pad |
| Loop height | Higher loops needed to avoid heel stress | Lower loop; better for thin packages |
| Inductance at high frequency | Higher for an equal cross-section | Lower, owing to the flat geometry |
| Routing flexibility | High; easy to change direction and pitch | Lower; ribbon must be bonded in a straight line between pads |
| Pad size needed | Can bond small pads | Requires pads wide enough for the ribbon |
| Equipment | Standard heavy-wire wedge bonder | Ribbon-capable bonder head, tool and guide |
| Thermal-cycling life | Proven baseline | Studies report longer life at the heel for comparable cross-sections |
If you are still comparing round wire and ribbon, read our aluminium bonding wire guide alongside this page, and the wire bonding vs ribbon bonding article for a process-level comparison.
Purity grades and alloy options
Ribbon for power devices is almost always made from very pure aluminium, because purity keeps the metal soft. A soft ribbon deforms readily under the bonding tool, so less ultrasonic energy and force are needed, and the risk of cratering the silicon or SiC chip underneath is reduced.
5N aluminium (99.999 %)
Tighter impurity control for the softest ribbon and the most consistent bond formation. Chosen where chips are thin or fragile and where qualification data must be reproducible lot to lot.
Micro-alloyed aluminium
Small additions (for example a few tens of ppm of nickel, or magnesium) raise recrystallisation resistance and slow grain coarsening at high junction temperatures, which can extend power-cycling life. Composition is agreed per specification.
Aluminium-clad copper ribbon
A copper core with an aluminium outer layer. Copper carries more current and has a lower expansion coefficient, while the aluminium skin keeps the bond compatible with aluminium chip metallisation. Used where pure aluminium reaches its limit.
Temper (soft vs half-hard)
Ribbon is supplied annealed to a target breaking load and elongation. Softer ribbon bonds more gently; slightly harder ribbon holds its loop shape better over long spans.
Surface condition
Clean, oxide-controlled, free of lubricant residue and burrs. Edge quality matters: a burr can snag in the guide or tear during looping.
Common ribbon sizes and what they carry
Ribbon is specified by width and thickness, quoted in millimetres or in mil (thousandths of an inch). The table lists representative sizes with their cross-sectional area, the calculated DC resistance per metre for high-purity aluminium at 20 °C, and how many round heavy wires of 500 µm or 380 µm the same area equals. Resistance is calculated from geometry and the resistivity of pure aluminium (about 2.65 µΩ·cm); it is a guide, not a guaranteed value.
| Width × thickness (mm) | Approx. (mil) | Area (mm²) | DC resistance (mΩ/m) | = 500 µm wires | = 380 µm wires |
|---|---|---|---|---|---|
| 0.50 × 0.10 | 20 × 4 | 0.050 | 530 | 0.3 | 0.4 |
| 0.75 × 0.10 | 30 × 4 | 0.075 | 353 | 0.4 | 0.7 |
| 1.00 × 0.10 | 39 × 4 | 0.100 | 265 | 0.5 | 0.9 |
| 1.00 × 0.15 | 39 × 6 | 0.150 | 177 | 0.8 | 1.3 |
| 1.50 × 0.10 | 59 × 4 | 0.150 | 177 | 0.8 | 1.3 |
| 1.50 × 0.15 | 59 × 6 | 0.225 | 118 | 1.1 | 2.0 |
| 2.00 × 0.15 | 79 × 6 | 0.300 | 88 | 1.5 | 2.6 |
| 2.00 × 0.20 | 79 × 8 | 0.400 | 66 | 2.0 | 3.5 |
| 2.00 × 0.25 | 79 × 10 | 0.500 | 53 | 2.5 | 4.4 |
| 2.00 × 0.30 | 79 × 12 | 0.600 | 44 | 3.1 | 5.3 |
Breaking load and elongation depend on size, purity and temper. They are set by the purchase specification and reported for each spool, so no fixed values are given here.
Typical supply range
- Width
- approx. 0.5 – 2.0 mm (20 – 80 mil); other widths by agreement
- Thickness
- approx. 0.08 – 0.30 mm (3 – 12 mil)
- Material
- 4N and 5N aluminium, micro-alloyed aluminium, aluminium-clad copper
- Spool
- Standard ribbon spools to suit common bonders; length per spool depends on cross-section
- Documentation
- Certificate of conformance with dimensions, breaking load and elongation per lot
Selecting ribbon width and thickness, step by step
- Size by currentStart from the RMS and peak current through the connection and the allowed temperature rise. Ribbon heats along its free span, so long spans need more cross-section than short ones. Calculate I²R loss and check it against the module thermal model.
- Fit the padsThe ribbon must land fully on the chip pad and the substrate track with margin on both sides. Pad width usually limits ribbon width on the chip side.
- Check the chipThicker ribbon needs more bonding energy. Thin chips, SiC dies and chips with soft top metallisation may need thinner or softer ribbon, or a buffer layer, to avoid cracks.
- Define mechanicalsAgree breaking load, elongation and temper with your process engineers; these control loop shape and bond formation.
- Confirm the equipmentVerify that your bonder head, wedge tool, guide and cutter handle the chosen width and thickness, and that the spool type fits.
- QualifyRun pull and shear tests, cross-sections and power cycling on samples before releasing the specification for volume orders.
How ultrasonic ribbon wedge bonding works
Ribbon bonding is a room-temperature, solid-state process. The bonder clamps the ribbon under a grooved wedge tool, applies a controlled normal force, and vibrates the tool at ultrasonic frequency parallel to the bond surface. The vibration breaks up the oxide films on the ribbon and pad, and the clean metal surfaces form a metallurgical bond. The head then forms a loop to the second pad, makes the second bond, and cuts the ribbon.
The key process variables are bond force, ultrasonic power, bond time and touchdown parameters. Too little energy gives weak or partly bonded interfaces that fail in pull testing; too much over-deforms the ribbon, thins the heel and can damage the chip. The usual metallisations are aluminium alloy on the chip and nickel, nickel-gold or bare copper on the substrate side.
Heel cracking
The thin section where the ribbon leaves the bond is the most stressed point during thermal cycling. Loop geometry and ribbon softness both influence heel life.
Bond lift-off
Cracks that start at the edge of the bond and grow along the interface. This is the classic wear-out mechanism of aluminium interconnects under power cycling, driven by the expansion mismatch between aluminium and silicon or SiC.
Chip damage
Excess force or energy can crack the die or damage the metallisation stack. Process windows are set on test chips before production.
Inspection, testing and qualification
Ribbon quality is controlled at two levels: the incoming material and the finished bond. On the material, buyers usually specify width, thickness, breaking load, elongation, surface cleanliness, edge quality and winding. On the bond, the module maker runs its own tests.
| Test | What it shows | Common reference |
|---|---|---|
| Pull test | Bond and loop strength; failure location (heel, bond, ribbon) | MIL-STD-883 Method 2011; DVS 2811 |
| Shear test | Strength of the bonded interface | DVS 2811; JEDEC JESD22-B116 (concepts for wire bonds) |
| Cross-section | Bond deformation, interface quality, any chip cracks | Internal procedure |
| Power cycling | Wear-out life of the interconnect under real heating | AQG 324 (automotive power modules) |
| Thermal shock / cycling | Robustness against package-level temperature swings | AQG 324; JEDEC JESD22-A104 |
A useful practice is to release a ribbon specification only after a complete qualification on the target module, and then to lock the material grade, temper and dimensions so that any later source change is treated as a formal requalification.
Where aluminium bonding ribbon is used
- Automotive traction inverters: IGBT and SiC modules for battery-electric and hybrid vehicles, where power cycling life is a qualification gate
- On-board chargers and DC-DC converters: compact modules where low loop height helps packaging
- Solar and storage inverters: long-life modules that see daily thermal cycles for decades
- Wind converters and rail traction: high-current, high-voltage modules with large chips
- Industrial motor drives and welding power supplies: heavy-duty switching modules
- Battery packs: cell-to-busbar connections in some pack designs use ultrasonic aluminium ribbon bonding
How to specify and order bonding ribbon
- Describe the applicationDevice or module type, chip and substrate metallisation, and the current per connection.
- State the ribbonWidth, thickness and tolerance; material grade (4N, 5N, micro-alloyed or clad); breaking load and elongation ranges.
- Spool and lengthSpool type for your bonder, winding direction and length per spool.
- Quantity and documentsSample and volume quantities, certificate of conformance, and any customer-specific test data.
- DeliveryRibbon ships in clean, sealed packaging to protect the surface, by air or courier on EXW, FCA or DAP terms worldwide.
References and standards
- MIL-STD-883, Method 2011 – Bond strength (destructive bond pull test)
- DVS 2811 – Testing of wire bonds (pull and shear testing of heavy wire and ribbon bonds)
- ECPE AQG 324 – Qualification of power modules for use in power electronics converter units in motor vehicles
- JEDEC JESD22-A104 – Temperature cycling
- IMAPS – A comprehensive evaluation of Al heavy wire bonding and ribbon bonding in high-power WBG power modules
Aluminium (aluminum) bonding ribbon: frequently asked questions
What is aluminium bonding ribbon used for?
It connects the top side of power semiconductor chips (IGBTs, SiC MOSFETs, diodes) to substrate tracks and terminals inside power modules. It is chosen where currents are high and a single flat ribbon can replace several heavy round wires.
How many wires does one ribbon replace?
It depends on cross-section. A 2.0 × 0.2 mm ribbon has an area of 0.40 mm², about twice that of a 500 µm wire and about 3.5 times that of a 380 µm wire. Thermal behaviour along the span must still be checked, so treat area matching as a starting point.
Can aluminium ribbon be bonded on a standard wire bonder?
Only if the machine has a ribbon-capable bond head, with the correct wedge tool, ribbon guide and cutter for the chosen width. Many heavy-wire platforms offer ribbon heads as an option.
Why is high-purity aluminium used instead of an alloy?
Purity keeps the ribbon soft, so it bonds with less force and ultrasonic energy and is less likely to damage the chip. Micro-alloyed grades are used where better resistance to grain growth at high temperature is worth a slightly narrower process window.
What is the main reliability risk with aluminium ribbon?
Wear-out under power cycling, seen as heel cracks or cracks that run along the bond interface. Loop design, ribbon softness and the bonding process all affect it, which is why modules are qualified by power cycling before production.
Do you supply ribbon to an existing specification?
Yes. Send your current width, thickness, material, breaking load, elongation and spool details, and Metline will propose matching material with lot certificates for your qualification.
Need aluminium bonding ribbon?
Send your size, grade, mechanical properties, spool type and quantity. We reply with supply options, documents and delivery terms.
