Die-to-package bonding materials are the fine wires and flat ribbons that carry signals and current from the pads on a chip to the leadframe, substrate or module terminals. The right choice depends on four things: the bonding process (ball or wedge), the current each connection carries, the pad metallisation and the reliability test the package must pass. This guide maps those decisions across gold, copper, silver and aluminium. Metline supplies the aluminium wire and ribbon; the other metals are explained for comparison.
Inside almost every packaged semiconductor, the chip is glued or soldered to a pad and then connected electrically by metal links welded to its bond pads. Wire bonding remains the most widely used way of making those links, even as flip-chip and copper-clip interconnects grow, because it is flexible, mature and cheap per connection. The material in the link has to be soft enough to weld without damaging the chip, strong enough to survive moulding and handling, and stable enough to last decades of temperature swings.
Two formats cover nearly all wire-bonded packages. Round bonding wire ranges from fine wire around 15 – 50 µm in diameter, used for signal connections in ICs, LEDs and discrete devices, up to heavy wire of 100 – 500 µm that carries tens of amps in power modules. Bonding ribbon is a flat strip, typically a few tenths of a millimetre thick and up to about 2 mm wide, which replaces several heavy wires in high-current or high-frequency connections.
Four metals are used for these links. Gold was the original standard and is still chosen where process stability and corrosion resistance matter most. Copper, usually palladium coated, has replaced gold in most high-volume IC packages on cost. Silver alloy wire serves LED and some memory packages. Aluminium, either as fine aluminium-silicon wire or as heavy high-purity wire and ribbon, dominates wedge bonding and power electronics.
| Point of comparison | Round bonding wire | Bonding ribbon |
|---|---|---|
| Cross-section | Round, 15 µm to about 500 µm diameter | Rectangular, roughly 0.1 – 0.3 mm thick and 0.5 – 2 mm wide (aluminium) |
| Bond footprint | Small; fits fine-pitch pads | Larger; needs wide pads but one ribbon can replace several wires |
| Current capacity | Fine wire for signals; heavy wire for power | High current per bond with low resistance |
| Inductance and high-frequency loss | Higher per connection | Lower, because of the larger surface for skin-effect currents |
| Loop profile | High, low or complex loops possible | Low, flat loops; little package height needed |
| Bonding process | Ball (thermosonic) or wedge (ultrasonic) | Wedge (ultrasonic, sometimes thermosonic) |
| Throughput | Very high for fine wire | Fewer bonds needed per high-current path |
| Typical packages | IC, LED, discrete, sensors, power modules (heavy wire) | IGBT and SiC modules, battery interconnects, RF and microwave hybrids |
In power modules the choice is often between several heavy aluminium wires in parallel and one or two aluminium ribbons. Ribbon reduces the number of bonds and the stack height and spreads current more evenly across the die metallisation; heavy wire is more forgiving of layout changes and works on standard heavy-wire bonders. Our wire bonding vs ribbon bonding article goes deeper into that trade-off.
| Property | Gold | Copper | Silver | Aluminium |
|---|---|---|---|---|
| Resistivity of pure metal, µΩ·cm (approx. 20 °C) | 2.44 | 1.68 | 1.59 | 2.65 |
| Thermal conductivity, W/m·K | 318 | 401 | 429 | 237 |
| Density, g/cm³ | 19.3 | 8.96 | 10.5 | 2.70 |
| Usual process | Ball bonding (thermosonic) | Ball bonding in forming gas | Ball bonding | Wedge bonding (ultrasonic, room temperature) |
| Usual product forms | Fine wire, ribbon | Fine wire (bare or Pd-coated), heavy wire, ribbon | Alloy fine wire, coated alloy wire | Al-1 % Si fine wire, heavy pure or alloyed wire, ribbon |
| Key strength | Stable process, no oxidation | Conductivity and low cost | Conductivity, optical reflectivity in LEDs | Same metal as most chip pads; ideal for power cycling and wedge bonds |
| Main limitations | Cost | Hardness can crack pads; oxidation; corrosion in humid tests | Migration and sulphur tarnish; usually alloyed | Lower conductivity; not used for ball bonding in volume |
| Relative material cost | Very high | Low | Medium | Low |
Bulk values for pure metals from standard reference data such as the CRC Handbook of Chemistry and Physics. Wire properties depend on purity, dopants, diameter and temper and are reported per lot.
A strong reason to use aluminium is metallurgical: most silicon and silicon-carbide chips have aluminium or aluminium-alloy pad metallisation. An aluminium wedge bond to an aluminium pad is a monometallic joint with no intermetallic growth, so it does not suffer the Kirkendall voiding that can affect gold-aluminium bonds at high temperature. Gold and copper ball bonds on aluminium pads rely on well-controlled intermetallic layers instead, which is why their reliability testing focuses on high-temperature storage and humidity.
| Package or device | Common materials | Why |
|---|---|---|
| Logic and memory ICs (QFN, QFP, BGA) | Pd-coated copper, gold, silver alloy | Fine pitch ball bonding at very high speed; copper on cost, gold where qualified processes require it |
| LED packages | Gold, silver alloy, gold-coated silver | Ball bonding; silver alloys reflect light well and cost less than gold |
| Discrete transistors and diodes | Gold, copper, aluminium | Depends on die size and current; heavier aluminium wire on larger dies |
| IGBT, MOSFET and SiC power modules | Heavy aluminium wire, aluminium ribbon, heavy copper wire | High current, power cycling and room-temperature wedge bonding on aluminium pads |
| Battery packs (cell-to-busbar) | Aluminium wire and ribbon | Ultrasonic bonds that also act as fusible links; low cost and low mass |
| MEMS and sensors | Al-1 % Si fine wire, gold | Low-temperature wedge bonding protects sensitive structures |
| RF, microwave and hybrid circuits | Gold wire and ribbon, aluminium wire | Low inductance and stable contacts; aluminium in chip-on-board and hermetic hybrids |
| Chip-on-board and hybrid microelectronics | Al-1 % Si fine wire, gold | Wedge bonding without heating the board |
Aluminium with about 1 % silicon, drawn to fine diameters (typically from about 18 µm to 75 µm) for ultrasonic wedge bonding in hybrids, sensors, COB and discrete devices. The silicon raises strength so the wire can be drawn fine and handled reliably.
4N to 5N aluminium in diameters of roughly 100 – 500 µm for power semiconductors. High purity keeps the wire soft, which protects the die during bonding, and gives low resistance.
Doped aluminium wires (for example with small additions of nickel or magnesium) offer higher strength, better power-cycling life or corrosion resistance for demanding automotive and traction modules.
Flat 4N/5N aluminium strip, typically 0.5 – 2.0 mm wide and 0.1 – 0.3 mm thick, with smooth, burr-free edges for ultrasonic ribbon bonding in power modules and battery packs.
Wire and ribbon wound on standard spools for automatic bonders, sealed and packed to limit contamination and oxidation in transit.
Each lot is supplied with a certificate reporting diameter or dimensions, breaking load and elongation; additional tests can be agreed for qualification.
For full specifications see our pages on aluminium bonding wire, aluminium bonding ribbon and heavy wire and ribbon for power semiconductors.
| Test | Common reference | What it shows |
|---|---|---|
| Destructive wire pull | MIL-STD-883, Method 2011 | Bond and wire strength, failure location (heel, neck, bond lift) |
| Non-destructive pull | MIL-STD-883, Method 2023 | Screens every bond in high-reliability hardware |
| Ball or wedge shear | JEDEC JESD22-B116 | Bond adhesion and intermetallic coverage |
| High-temperature storage | JEDEC JESD22-A103 | Intermetallic growth and voiding over time |
| Temperature cycling | JEDEC JESD22-A104 | Heel cracking and lift-off from thermal-expansion mismatch |
| Power cycling | AQG 324 (automotive power modules) | Wire lift-off and heel cracking in power modules |
| Copper wire qualification | AEC-Q006 | Additional automotive requirements for copper wire bonds |
When changing material or supplier, compare like for like: same diameter, breaking load and elongation window, the same pad metallisation, and the same bonder settings as a starting point. A small difference in elongation or hardness can change loop shape and the ultrasonic energy needed, so a short design-of-experiments on the bonder is normal before qualification.
They are the fine wires and ribbons, usually of gold, copper, silver or aluminium, that are welded to the bond pads of a chip and to the leadframe, substrate or terminals to make its electrical connections inside the package.
Use ribbon when one connection must carry high current with low resistance and inductance, or when package height is tight, as in IGBT and SiC power modules, battery interconnects and RF circuits. Round wire is better for fine-pitch pads and complex loop shapes.
Aluminium bonds ultrasonically at room temperature, forms a monometallic joint with the aluminium pads on most power chips, is soft enough to protect the die and costs far less than gold. Heavy aluminium wire and ribbon are the established solution for power cycling performance.
Gold, copper and silver alloy wires are used mainly in ball bonding, where a free air ball is formed at the wire tip. Aluminium and Al-1 % Si wire, and all ribbons, are used in wedge bonding.
Only if the process changes from ball to wedge bonding and the package layout allows it. Aluminium is widely used for wedge-bonded hybrids, sensors and power devices, but high-volume fine-pitch IC packages normally use gold or copper ball bonding.
No. Metline supplies aluminium bonding wire and ribbon only. Gold, copper and silver are covered on this page as comparisons to help you choose where aluminium fits your package.
Send your package type, current specification, dimensions and sample quantity. Our team will propose a matching aluminium wire or ribbon and arrange samples.
