Three wire-bond regimes are in common use, and they differ in exactly one thing: what supplies the energy that welds the wire to the pad. Thermosonic — heat plus ultrasonic scrub — is the one most gold work uses. The other two are defined by what they leave out. Aluminum wedge bonding runs on ultrasonic energy with no heat. Thermocompression runs on force and heat with no ultrasonics. Both are solid-state welds, and both exist because there are jobs thermosonic cannot do.
Aluminum wedge bonding: the cold bond
Aluminum wedge bonding presses the wire against the pad with a wedge tool and welds it using ultrasonic scrub alone, at room temperature. It can skip the heat for a specific metallurgical reason: aluminum carries a hard, brittle native oxide, and the ultrasonic energy shatters that oxide and sweeps it aside so clean aluminum can meet clean pad. No heat is needed to make the metal flow the way a gold ball needs.
That cold process is exactly why wedge bonding wins two kinds of work:
- Power loops — heavy aluminum wire carries high current, and wedge bonding lays it in thick, low-loop-inductance spans that gold cannot economically match.
- Temperature-sensitive assemblies — a die or an already-attached component that cannot take a heated stage stays at room temperature through the bond.
Wedge bonding also makes the wire direction matter: the wedge feeds wire along one axis, so the loop layout is more constrained than a ball bonder's, which is a design consideration for a dense pattern rather than a limitation.
Thermocompression: the bond that faded for wire
Thermocompression is the oldest of the three — force and heat, no ultrasonic assist, at a stage temperature of 300 °C and above. It still exists as a concept and has returned in other forms elsewhere in packaging, but as a wire process it is largely obsolete, for three compounding reasons:
- A stage at 300 °C or more damages plastic packaging and stresses temperature-limited die.
- With nothing scrubbing the interface, the process is far more sensitive to surface contamination, because it relies entirely on force and heat to achieve intimate contact.
- Its long dwell cannot feed a modern autobonder, whose bonds complete in milliseconds.
Thermosonic bonding is what replaced it for gold wire: adding ultrasonic scrub buys back the cleaning and the speed and lets the stage temperature drop by roughly half. Seeing why is the clearest way to understand what the ultrasonic energy is actually for — thermosonic wire bonding covers that comparison and the who-does-it-as-a-service question.
How the bonds are verified
Aluminum wedge bonds are verified by destructive wire pull to MIL-STD-883 Method 2011 and by wedge shear, with non-destructive pull to Method 2023 where a programme screens every wire. Acceptance is set as a multiple of the Method 2011 minimum for the wire size, and per-lot pull and shear monitoring keeps a qualified bonding window honest in production.
Where to start
Two facts point to the right regime:
- How much current the connection carries — a high-current power loop points at heavy aluminum wedge bonding.
- What temperature the assembly can tolerate — a temperature-limited die or an already-attached component points at room-temperature ultrasonic wedge over a heated process.
We run ultrasonic aluminum wedge bonding — including heavy aluminum wire for power loops and ribbon on request — alongside thermosonic gold ball bonding in Halethorpe, Maryland, on US soil. More on our wire bonding services page.
Answered.
What is aluminum wedge bonding?
A wire-bond process that presses aluminum wire against the pad with a wedge tool and welds it using ultrasonic energy alone, at room temperature. Aluminum's brittle native oxide is shattered and swept aside by the ultrasonic scrub, so clean metal meets clean pad with no heat needed. It is the standard process for power loops and temperature-sensitive assemblies.
Why does aluminum wedge bonding not need heat?
Because the ultrasonic scrub does the work heat would otherwise do. Aluminum carries a hard native oxide that the ultrasonic energy fractures and clears, exposing clean metal without warming the stage. Gold, by contrast, has no oxide but a gold ball needs heat to flow — which is why gold ball bonding is thermosonic and aluminum wedge bonding is not.
What is thermocompression bonding?
The oldest wire-bond regime: force and heat with no ultrasonic assist, at a stage temperature of 300 °C and above. As a wire process it is largely obsolete because the high temperature harms plastic packaging, the lack of an ultrasonic scrub makes it very sensitive to contamination, and its long dwell cannot match modern autobonder speeds.
Why did thermocompression bonding fade for wire?
Thermosonic bonding replaced it. Adding ultrasonic energy to the heat cleans the interface and forms the weld in milliseconds, which lets the stage temperature drop by roughly half and feeds a high-speed autobonder. Thermocompression's 300 °C-plus stage and long dwell could do neither.
Do you offer aluminum wedge bonding in the US?
Yes — ultrasonic aluminum wedge bonding, including heavy aluminum wire for high-current power loops and ribbon on request, alongside thermosonic gold ball bonding, in Halethorpe, Maryland, on US soil. Bonds are verified by pull to MIL-STD-883 Method 2011 and by shear.