Aluminium bonding wire is drawn aluminium or aluminium-silicon wire, from about 18 µm to 500 µm in diameter, that is ultrasonically wedge-bonded at room temperature to connect chips to lead frames, substrates and terminals. Fine AlSi1 wire serves sensors, hybrids and chip-on-board work; heavy high-purity wire carries the current in power modules. This guide covers grades, sizes, process, testing and how to specify wire from Metline.
Wire bonding is still the most common way to make electrical connections inside a semiconductor package. Gold and copper wire dominate ball bonding in integrated circuits; aluminium wire dominates wedge bonding, and above all the heavy-wire connections in power electronics.
Aluminium wire is bonded by ultrasonic energy without heating the package. A wedge tool presses the wire onto the pad and vibrates it, scrubbing away oxide and forming a solid-state weld. Because no flame-off ball is formed and no heated stage is required, aluminium wedge bonding suits temperature-sensitive assemblies, hermetic ceramic packages, and large power modules that would be difficult to heat uniformly.
Aluminium bonding to an aluminium chip pad is also a single-metal joint. That avoids the intermetallic growth that can weaken gold-to-aluminium bonds at high temperature, which is one reason aluminium wire has a long track record in military, automotive and industrial electronics.
Aluminium bonding wire is really two product families, with different alloys, tempers and uses. The usual dividing line is about 100 µm (4 mil).
| Property | Fine aluminium wire | Heavy aluminium wire |
|---|---|---|
| Typical diameter | approx. 18 – 75 µm (0.7 – 3 mil) | approx. 100 – 500 µm (4 – 20 mil) |
| Typical material | AlSi1 (Al + 1 % Si); AlMg1 as an alternative | 99.99 % or 99.999 % Al; micro-alloyed grades |
| Condition | Hard-drawn or stress-relieved; low elongation (a few %) | Fully annealed, soft; high elongation (often 10 – 30 %) |
| Main job | Signal and low-current links on small pads | High-current links in power devices, often in parallel |
| Typical packages | Chip-on-board, hybrids, sensors, MEMS, hermetic ceramic and metal cans, RF modules | IGBT, MOSFET and SiC modules, power discretes (TO packages), battery connections |
| Bonder | Fine-wire wedge bonder | Heavy-wire wedge bonder |
The silicon in fine wire is not an accident: pure aluminium is too soft to draw reliably down to 25 µm and still hold the breaking load needed for looping, so about 1 % silicon (or magnesium) is added to harden it. In heavy wire the priority reverses: softness protects the chip during bonding, so very high purity is used.
The default fine wedge wire. Silicon raises strength for drawing and looping. Used widely for chip-on-board, hybrid circuits and sensors. A historic reference is ASTM F487, now withdrawn but still cited in some purchase specifications.
Magnesium-strengthened alternative to AlSi1. Magnesium stays in solid solution, avoiding silicon precipitates, and some users report steadier properties after high-temperature storage.
The workhorse for power modules and power discretes. Soft, conductive and easy to bond on aluminium metallisation and nickel-plated substrates.
Highest purity for the softest wire and the most consistent deformation, preferred for thin or sensitive chips.
Small, controlled additions (nickel or other elements in the ppm range) improve resistance to humidity and slow grain coarsening. Very pure aluminium can corrode faster in hot, humid conditions, so these grades suit unsealed or gel-filled modules.
Grades with dispersed particles or alloying that resist recrystallisation at high junction temperature, aimed at extending power-cycling life in automotive and SiC modules.
Proprietary alloy names differ between wire makers. Specify the required composition limits, breaking load and elongation rather than a brand name, so equivalent material can be qualified.
Bonding wire diameters are quoted in micrometres or mil. The table gives the cross-sectional area, the calculated DC resistance per metre for high-purity aluminium at 20 °C (resistivity about 2.65 µΩ·cm) and the mass per metre (density 2.70 g/cm³). These are geometric calculations; AlSi1 has a slightly higher resistivity than pure aluminium. Breaking load and elongation are set by the purchase specification and reported per spool.
| Diameter (µm) | Diameter (mil) | Area (mm²) | DC resistance (Ω/m) | Mass (g/m) | Family |
|---|---|---|---|---|---|
| 18 | 0.7 | 0.00025 | 104.1 | 0.0007 | Fine |
| 25 | 1.0 | 0.00049 | 54.0 | 0.0013 | Fine |
| 32 | 1.3 | 0.00080 | 33.0 | 0.0022 | Fine |
| 38 | 1.5 | 0.00113 | 23.4 | 0.0031 | Fine |
| 50 | 2.0 | 0.00196 | 13.5 | 0.0053 | Fine |
| 75 | 3.0 | 0.00442 | 6.0 | 0.012 | Fine |
| 100 | 3.9 | 0.00785 | 3.4 | 0.021 | Heavy |
| 125 | 4.9 | 0.0123 | 2.2 | 0.033 | Heavy |
| 150 | 5.9 | 0.0177 | 1.5 | 0.048 | Heavy |
| 200 | 7.9 | 0.0314 | 0.844 | 0.085 | Heavy |
| 250 | 9.8 | 0.0491 | 0.540 | 0.133 | Heavy |
| 300 | 11.8 | 0.0707 | 0.375 | 0.191 | Heavy |
| 380 | 15.0 | 0.1134 | 0.234 | 0.306 | Heavy |
| 500 | 19.7 | 0.1963 | 0.135 | 0.530 | Heavy |
The first bond is made on the chip, the wire is looped to the second pad, the second bond is made, and the wire is torn or cut. Because a wedge bond has a direction, the bonder rotates the part or head so that the wire leaves along the bond axis. Key settings are bond force, ultrasonic power, bond time and the loop profile.
Common faults include under-bonded interfaces (weak, lift off in pull testing), over-deformed bonds that thin the heel, heel cracks from poor loop geometry, and chip cratering when force or energy is too high. Clean pads matter as much as wire quality: organic contamination and thick oxides on the pad are frequent root causes of non-stick.
| Failure mode | Typical cause | What to change |
|---|---|---|
| Non-stick on pad | Contamination, thick oxide, low energy | Plasma clean pads; raise power or time |
| Heel break in pull test | Over-deformation, sharp tool, low loop | Reduce deformation; adjust loop; check tool wear |
| Bond lift-off after cycling | Thermal-expansion mismatch fatigue | Softer or alloyed wire; process optimisation; consider ribbon or copper |
| Chip cratering | Excessive force or ultrasonic energy | Lower parameters; softer wire |
| Wire sway / sagging | Wire too soft or loops too long | Adjust breaking load or loop geometry |
Incoming wire is checked for diameter, breaking load, elongation, surface cleanliness and winding quality. Finished bonds are checked by the assembler.
Heavy wire in IGBT, MOSFET and SiC modules for traction inverters, drives, solar and wind converters.
TO-220, TO-247 and similar packages where one or more heavy wires connect the source to the lead.
Fine AlSi1 wire bonded directly to circuit boards and thick-film substrates.
Pressure, inertial and automotive sensors where room-temperature bonding protects the device.
Ceramic and metal packages for aerospace and defence electronics with aluminium-to-aluminium bonds.
Heavy aluminium wire bonded between cylindrical cells and busbars, acting as a conductor and a cell-level fuse in some designs.
It makes internal connections in semiconductor devices: fine wire links chip pads to boards, hybrids and sensor packages, and heavy wire carries current from power chips to substrates and terminals in power modules and discretes.
Pure aluminium is too soft to draw to 25 µm and keep a usable breaking load. Adding about 1 % silicon (or magnesium in AlMg1 wire) strengthens it enough for drawing, spooling and stable loops.
Fine wire (roughly 18 – 75 µm) is hard AlSi1 or AlMg1 for signal connections. Heavy wire (roughly 100 – 500 µm) is soft, high-purity aluminium for power connections. They use different bonders and tools.
No. Aluminium is normally wedge-bonded ultrasonically at room temperature, which is one of its advantages for heat-sensitive assemblies and large modules.
When the number of parallel heavy wires becomes impractical, or when power-cycling life is not enough. Aluminium ribbon gives more current per bond with a lower loop; copper wire gives longer life but needs a protected chip metallisation and a narrower process window.
Yes. Send diameter, grade, breaking load and elongation ranges, spool type and quantities. Metline proposes matching material with lot certificates for your qualification.
Send the diameter, grade, mechanical properties, spool type and quantity. We reply with supply options, documents and delivery terms.
