The bond cycle
Every Wire Is Two Welds
A bonder welds one end of a wire to the die, loops it across to the package and welds the other end, then repeats for every pad.
Wire bonding connects each pad on the edge of a die to a lead or substrate trace with a thin wire, one wire per signal. Each wire is bonded twice: once on the die and once on the package. The bond itself is a solid-state weld; ultrasonic vibration, usually with heat (thermosonic bonding), scrubs through surface oxide and grows an intermetallic layer between wire and pad. That intermetallic is what survives a decade of temperature cycling.
| Stage | What happens | Main yield risk |
|---|---|---|
| First bond | Capillary presses the ball onto the die pad with ultrasonic energy and heat | Pad cratering into the dielectric below, weak intermetallic, pad peel |
| Loop | Capillary pays out wire along a programmed path to the lead | Sag into the next wire, loop too tall for the package, sweep during molding |
| Second bond | Wire is wedged onto the lead or trace and torn off | Poor adhesion on the plating, tail length variation |
| Repeat | Bonder indexes to the next pad | Capillary wear and alignment drift on high pin counts |
Lines watch bond pull strength, ball shear and intermetallic coverage continuously, because a weak bond usually passes final test and fails in the field.
Ball, wedge, ribbon
Ball Bonds Carry Most of the Volume
| Bond type | How it works | Where it is used |
|---|---|---|
| Ball bond | A spark (electronic flame-off) melts the wire tip into a ball; ball on the die, stitch on the lead. Works in any direction around the die | MCUs, analog, memory, mobile and automotive chips; most wires by count |
| Wedge bond | A flat wedge tool presses the wire at both ends; each bond must point the same way, so it is slower | RF, power modules and aerospace; aluminum wire; low loops |
| Ribbon bond | A flat ribbon replaces round wire, bonded wedge-style | High-current power devices and RF power amplifier outputs |
Wedge bonding is tied to power electronics, and that market turned down: Kulicke & Soffa reported wedge bonder sales down 34% for the first nine months of its 2026 fiscal year on weaker EV and industrial capacity spending, while ball bonder sales nearly tripled year on year in the July quarter (reported).
Wire metal
Gold's Price Moved the Industry to Copper
Gold was the default wire for decades because it bonds easily and does not corrode. Its price ended that. At $4,147 a troy ounce in October 2026, the gold in 100 wires 20 µm across and 2 mm long is worth about 16 cents, which is more than the selling price of many small analog chips. The same wires in copper hold less than a thousandth of a cent of metal.
| Wire | Strengths | Where it is used |
|---|---|---|
| Copper | About 20,000 times cheaper per wire than gold; better electrical and thermal conductivity; needs forming gas (nitrogen with a little hydrogen) at the bond head to stop oxidation; harder, so pads must tolerate more force | Most consumer, mobile, automotive and memory volume |
| Palladium-coated copper | Palladium skin protects the copper in storage and bonding; reliability close to gold | Automotive and high-reliability parts moving off gold |
| Gold | Easiest to bond, corrosion-proof, longest qualification record | Medical, aerospace, RF and legacy programs too costly to requalify |
| Aluminum | Bonds to aluminum pads with no intermetallic concern; wedge-bonds at room temperature; survives high temperature | Power modules, EV inverters, high-temperature parts |
| Silver alloy | Cheaper than gold, high reflectivity | LEDs and some low-cost consumer packages |
Wire runs from 15 µm for fine-pitch parts to 75 µm and thicker for power. The diameter sets the minimum pad pitch, the current each wire can carry and how far the loop moves when mold compound flows past it.
Pads and limits
Pads on the Edge Cap the Signal Count
The die side of the bond is the pad: an opening in the top passivation over aluminum or aluminum-copper, with a titanium or titanium nitride barrier underneath. Advanced-node dies with copper top metal add an aluminum cap to stay wire-bondable. Fragile low-k dielectric under the pad limits how much ultrasonic energy a bond can use, which is the main source of cratering.
Pads sit around the die edge, so a wire-bonded die's signal count grows with its perimeter, not its area. At about 40 µm pitch, the finest in production, a 5 mm die has room for roughly 500 pads; a flip-chip die of the same size can carry thousands of bumps across its face. That limit, not cost, is why every high-performance chip moved to flip-chip.
Bonders
Two Makers, and China Is Buying
Two companies build most of the world's wire bonders, and their order books moved sharply in 2026. Kulicke & Soffa reported $330 million in revenue for the quarter ended July 4, 2026, up from $148 million a year earlier, and guided about $375 million for the quarter ended October 3. Customers headquartered in China, including Huatian and JCET, supplied 56% of its revenue in the period (reported from its quarterly filing).
| Maker | Base | Position |
|---|---|---|
| Kulicke & Soffa | Singapore and Fort Washington, PA | Co-leader in ball bonders (RAPID and IConn platforms); wedge bonders from its Orthodyne line |
| ASMPT | Singapore and Hong Kong | Co-leader in ball bonders; broad back-end portfolio from die attach to molding |
| Hesse Mechatronics | Germany | Wedge and ribbon bonders for power modules and RF |
| F&K Delvotec | Germany | Heavy aluminum wedge bonders for power and hybrid modules |
| Shinkawa (Yamaha Robotics) | Japan | Ball bonders for Japanese and Asian volume lines |
China's packaging houses are the largest buyers of wire bonders, and the bonders they buy are still made by Kulicke & Soffa and ASMPT.
Consumables
Wire and Capillaries Come From Japan
| Consumable | What it does | Main suppliers |
|---|---|---|
| Bonding wire | Gold, copper, palladium-coated copper, aluminum or silver alloy drawn to 15 to 75 µm with tight purity and grain control | Tanaka, Heraeus, Nippon Micrometal, MK Electron, Tatsuta |
| Capillaries | Ceramic tips the wire feeds through; the tip shape sets bond size and pitch | SPT (Small Precision Tools), Kulicke & Soffa, PECO, Gaiser |
| Wedge tools | Tungsten carbide or ceramic tools for wedge bonding; wear limits bonds per tool | SPT, PECO, specialty tool houses |
| Forming gas | Nitrogen-hydrogen cover at the bond head for copper wire | Air Liquide, Linde, Air Products |
Wire is a small cost per package in copper but a slow one to change: each wire grade is qualified into each product, and switching supplier means requalifying. Japan is the center of wire supply, with Heraeus in Europe and MK Electron in Korea.
Where it runs
Wire Bonding Runs in Asia
Wire bonding runs where back-end labor and OSAT capacity are: China, Taiwan, Malaysia, the Philippines, Thailand and Vietnam. The rooms are looser than a wafer fab, Class 1000 to 10,000, because the die is already sealed except for its pads; vibration matters more than particles, and bonders sit on isolated slabs.
- Made in US
- US planned
- Made abroad
| Site | Location | Does | Status | US status |
|---|---|---|---|---|
| JCET | Jiangyin and Suqian, China | Wire bond and flip-chip assembly; largest Chinese OSAT | Operating | Made abroad |
| Tianshui Huatian | Tianshui and Kunshan, China | High-volume wire-bond assembly | Operating | Made abroad |
| Tongfu Microelectronics | Nantong, China | Wire bond and flip-chip; major AMD assembly partner | Operating | Made abroad |
| ASE | Kaohsiung, Taiwan, and Penang, Malaysia | Largest OSAT; wire bond across all package families | Operating | Made abroad |
| Amkor | Philippines, Malaysia and Korea | Wire-bond assembly for automotive and analog customers | Operating | Made abroad |
| Texas Instruments | Melaka and Kuala Lumpur, Malaysia | In-house assembly of TI analog and embedded chips | Operating | Made abroad |
| Placeholder: other wire-bond assembly rows from the fab dataset | ||||
No US site runs high-volume merchant wire bonding today; the US packaging projects under way, at Amkor in Peoria and SK hynix in West Lafayette, are for advanced flip-chip and HBM work. The full OSAT picture is on OSAT Landscape.
Wire bond or flip-chip
Flip-Chip Took the High End, Not the Volume
| Wire bond | Flip-chip | |
|---|---|---|
| Connections | Around the die edge; hundreds at most | Across the whole die face; thousands to tens of thousands |
| Path length and inductance | Millimeters of wire; higher inductance | Tens of micrometers of bump; much lower |
| Heat path | Through the die attach to the paddle | Through the die back to a lid and heat sink |
| Cost | Lowest per package; mature tools | Needs wafer bumping, a laminate substrate and underfill |
| Typical chips | MCUs, analog, power, sensors, memory, mature logic | CPUs, GPUs, AI accelerators, FPGAs, flagship mobile SoCs |
The two coexist inside many packages: a chiplet module joins its dies with micro-bumps or hybrid bonds, and a stacked memory package may wire-bond each die to the substrate. The density end of the range is on Advanced Die Interconnects.
Record
Page Record
This page also carries the material from Wire Bond and Flip-Chip Interconnect.
- Covers
- Wire bond cycle, bond types, wire metals, pad limits, bonder makers, consumables and assembly sites
- Sources
- Kulicke & Soffa third quarter fiscal 2026 results and 10-Q (August 2026); gold price, pricegold.net (October 19, 2026); copper price, Reporte Minero (October 2026); wire cost per package computed from wire volume and metal density
- Last verified
- October 2026