Wire bonding looks like one process with a few settings. It is really three processes that happen to share a machine, and the choice between them is usually made for you — by what metal is on the pad, how much current the loop has to carry, and how much heat the assembly can take. Get that mapping wrong and the symptoms show up as yield, not as a design review comment.
The three types, and what each is for
Thermosonic gold ball bonding
The tool melts the wire tip into a free-air ball, presses it onto the pad, and adds ultrasonic energy with the stage held at a moderate temperature. Because a ball is round, the second bond can go in any direction — so the tool does not have to be reoriented per wire, and dense, awkward layouts stay practical.
That directional freedom plus speed is why ball bonding dominates fine-pitch work. The cost is that it wants gold, and it wants some stage heat.
Ultrasonic aluminum wedge bonding
No ball. The wedge tool deforms aluminum wire directly against the pad using ultrasonic energy and force, at room temperature. Two consequences follow. First, it suits assemblies that cannot take added heat, and aluminum pads where a gold ball bond would need metallisation that is not present. Second, the bond is directional — the tool has to be oriented along the wire path, so every loop costs a rotation, and layout matters more.
Heavy aluminum wire belongs in this family too. When a loop has to carry real current, conductor cross-section is the whole argument, and fine gold wire cannot reach it.
Ribbon bonding
A flat ribbon rather than a round wire. For a given loop height it presents considerably more conductor area, which buys two things: current capacity, and lower inductance across a given span — the reason ribbon keeps appearing in RF and microwave assemblies where a round wire's inductance starts to matter to the circuit. We run ribbon with sizes matched to the span and the electrical requirement, quoted on request.
What actually decides it
1. The pad metal
This settles most cases before anything else is discussed. Aluminum pads point at aluminum wedge. Gold metallisation opens up thermosonic ball. Mixed metallurgy inside one package is normal, and so is running more than one bond type on the same assembly.
2. Current
Signal I/O is a fine-wire problem. A power loop is a cross-section problem, and that means heavy aluminum wire or ribbon. Teams often discover this late, having laid out a power path on the same wire diameter as the signals.
3. Thermal budget
Ultrasonic aluminum wedge bonding runs without an elevated stage. If there is a temperature-sensitive die in the package, or something already attached that a second heated cycle would disturb, that alone can decide the process.
4. Pitch and layout
Ball bonding's non-directional second bond is worth a great deal on dense parts. Minimum achievable pitch, though, is a property of the bonder and your pad geometry together — not a single number worth quoting. Ours runs on an ASM AERO Eagle; the useful conversation is about your actual pad layout, not a spec-sheet floor.
One thing we do not do
We do not run copper wire bonding. Copper is a legitimate and widely used process in high-volume commercial packaging, with real advantages in cost and electrical performance. It is simply not a process we run, and saying so is more useful to you than a capability list that quietly includes everything.
Gold and aluminum, fine wire from 15µm to 50µm, heavy aluminum for power, ribbon on request.
How the bond gets proven
A wire bond is only as good as the evidence behind it, and the evidence is destructive. Pull testing to MIL-STD-883 Method 2011 is the standard method, and it sets a minimum. Sitting just above a minimum is not a process under control — it is a process that happens to be passing.
Production bonds typically run 3-4x the Method 2011 minimum. We report that as a multiple rather than a raw force number on purpose: the multiple tells you how much margin the process holds, which is the thing you actually want to know. There is more detail on what Method 2011 does and does not verify in our write-up on wire bond pull testing.
Where to start
Three answers scope a wire bond build almost completely, and all three are usually known early:
- What metal is on the pads, on both the die and the substrate.
- What the worst-case current through any single loop is.
- Whether anything in the package is heat-sensitive, or already attached.
Full detail on all three bond types, wire ranges and verification is on our wire bonding services page. If the interconnect choice is still open, the comparison worth reading alongside this is wire bond versus flip chip.
Wire bonding, answered.
What are the main types of wire bonding?
Three, in practice. Thermosonic gold ball bonding, ultrasonic aluminum wedge bonding — including heavy aluminum wire for high-current power loops — and ribbon bonding. They differ in how the bond is formed, what pad metals they suit, and how much current the finished interconnect can carry.
What is thermosonic wire bonding?
Thermosonic bonding forms a gold ball bond using three things at once: ultrasonic energy, bond force, and a moderately heated stage — typically well below the temperatures a purely thermocompression bond would need. The combination is what lets gold ball bonding run fast and gently enough for fine-pitch work on sensitive die. We run it in-house as a service, not as equipment.
What is the difference between ball bonding and wedge bonding?
A ball bond starts by melting the wire tip into a free-air ball, which is then bonded to the pad; the tool can then move in any direction for the second bond, so layout is flexible. A wedge bond deforms the wire directly against the pad with ultrasonic energy and no ball, which means the bond is directional — the tool has to be oriented along the wire path. Wedge runs at lower temperature and suits aluminum pads and heavy wire; ball is faster and more flexible for dense, fine-pitch gold work.
When should you use aluminum wedge bonding?
When the pads are aluminum, when the assembly cannot take added heat, or when the loop has to carry real current. Ultrasonic aluminum wedge bonding needs no elevated stage temperature, and heavy aluminum wire gives a cross-section that fine gold wire cannot match for power paths. It is also the natural choice on substrates where a gold ball bond would need metallisation that is not there.
When is ribbon bonding the right choice?
Where cross-section matters more than footprint. A flat ribbon presents more conductor area for a given height than a round wire, which helps at RF — lower inductance for the same span — and for current-carrying links. We offer ribbon bonding with sizes on request, matched to the span and the electrical requirement.
Do you offer copper wire bonding?
No. We run gold and aluminum only. Copper wire bonding is a legitimate process and widely used in high-volume commercial packaging, but it is not one we run, and we would rather say so than take a build we are not set up for.
What wire diameters do you run?
Fine wire from 15µm to 50µm in both gold and aluminum, plus heavy aluminum wire for power loops and ribbon on request. Minimum achievable bond-pad pitch is set by the bonder and the specific pad geometry rather than by a single published number — ours runs on an ASM AERO Eagle, and the honest answer to a pitch question is that it depends on your pad layout.
How is wire bond strength verified?
By destructive pull testing to MIL-STD-883 Method 2011, the standard wire-bond pull method. Method 2011 sets a minimum; production bonds typically run 3-4x that minimum rather than sitting just above it. We report the multiple rather than a raw force figure, because the multiple is what tells you how much margin the process is actually holding.