Why Wire-Bond?
Lower thermal load, graceful failure behavior, and automation-friendly assembly, ideal for many EV and industrial battery systems.
Wire-Bonding in Action
Precision ultrasonic bonding process
Low Heat Input
No molten pool; minimal heat into the cell during bonding.
Safer Failure Modes
Multiple bonds share current; individual bonds can act like fuses.
Flexible Automation
Reprogrammable paths, easy multi-bond strategies, clean rework.
Proven QC
Objective pull/shear tests + inline process monitoring.
How Ultrasonic Wire-Bonding Works
A wedge tool presses aluminum (or copper) wire/ribbon to the terminal and vibrates at ultrasonic frequencies. Oxides are dispersed, metal lattices interdiffuse, and a solid-state bond forms, without melting. Typical process temperature is near ambient to ~100 °C, well below fusion welding.
Because the joint isn’t a melt pool, there’s no spatter and heat into the cell is limited. The wire is then looped and bonded at a second point, creating a compliant connection that tolerates vibration and thermal cycling.
Quick visual
- Place wedge on cleaned terminal surface
- Apply force + ultrasonic energy → solid-state bond (no melt)
- Form loop and make second bond (optional parallel bonds)
Visual deformation profile
Each bond is inspected by the bond-head camera. The machine is taught the “good” deformation ear geometry; a typical acceptance window is ~110–150% of wire diameter measured at the ear width. Bonds outside limits are flagged for further inspection or rework.
Inline pull testing
After each ultrasonic weld, the bond head applies a controlled pull (force & dwell) to verify strength in-process. Industry practice targets ~50% of the mean break load from the wire datasheet. Example: 500 µm wire → 450 cN for 250 ms. Out-of-family results trigger inspection/rework.
Pattern recognition
Vision-based pattern recognition locates each module and registers bond sites before every run. This ensures precise placement, reduces operator touch time, and minimizes downtime between cycles.
Precision at Scale
Collector plates are laser cleaned right before they go through the bonding process
Every bond is precisely placed and verified for consistent, reliable connections
Wire-Bond vs Laser vs Resistance
All three are proven. Choose by heat budget, geometry, throughput, and quality controls.
| Attribute | Wire-Bond (Ultrasonic) | Laser (Fusion) | Resistance (Spot) |
|---|---|---|---|
| Heat into cell | Very low; no melt phase | Localized melt; HAZ to control | Local melt via current |
| Fit-up / gap | Tolerant; needs clean, flat pads | Zero-gap + clamping preferred | Electrode force provides contact |
| Spatter risk | None (no melt) | Manage with process/fixture | Possible; depends on setup |
| Reworkability | High: individual bonds removable | Low–moderate | Low–moderate |
| Per-joint current | Tens of amps; parallel bonds scale | High per seam/spot dependent | Moderate; limited by conductivity & thickness |
| Throughput | High; parallelizable | Very high with scanning heads | Good; indexing + electrode wear |
| Inline QC | Pull/shear + electrical checks | Melt-pool/vision/PD monitoring | Resistance/nugget checks |
Notes: Laser welding often requires intimate contact and clamping; scanning-head lasers achieve very high speeds but demand tight process control. Resistance welding is cost-effective, but electrodes are consumables and copper’s high conductivity can complicate heat generation.
Quality & Standards
- Bond verification: pull and shear per established methods (e.g., MIL-STD-883 Methods 2011/2017).
- Inline data: pattern recognition, force/ultrasonic/time logs, traceability to MES (common in mass production).
- Pack-level safety: validation to UL 1973 for stationary/industrial systems and UN 38.3 for transport (cells/packs), with vibration testing to automotive norms where applicable.
Process Documentation
We maintain bond recipes, test plans, and acceptance criteria per product line. Ask us for a sample quality report or to witness a pull/shear test.
Where We Use Wire-Bonding
Lithium Block™ Modules
Primary cell-to-busbar interconnect with multi-bond redundancy and loop compliance. Optimized pad design for repeatable bond quality.
MonoLith™ Packs
Targeted use where low thermal input and reworkability matter. We combine with laser/joining methods where high-current seams are advantageous.
Wire-Bonding FAQ
How much current can a single bond carry?
It depends on wire/ribbon gauge, material, and pad metallurgy. Designs use multiple bonds in parallel to hit the target current with margin, then derate. For high power, ribbon or multiple round wires are used; we never rely on a single joint for the main current path.
What’s the purpose of the loop?
The loop provides mechanical compliance, absorbing vibration and differential expansion. We tune loop height and span so strain stays off the welds and terminals while keeping inductance reasonable.
How do you verify the weld shape?
We use visual deformation profile inspection with the bond-head camera. The machine is taught a “good” ear geometry; a typical acceptance is ~110–150% of wire diameter measured at the ear width. Out-of-bounds welds are flagged for review or rework.
Do you pull test every weld?
Yes. Inline pull testing is performed in process. After the weld, the bond head applies a controlled pull (force & dwell) to verify strength according to the wire’s datasheet. Industry practice targets ~50% of mean break load. Example: 500 µm wire → 450 cN for 250 ms. Out-of-family results are investigated.
How do you ensure consistent bond placement?
Pattern recognition locates each module and registers bond sites before each run. This maintains precise placement, reduces operator touch time, and minimizes downtime between cycles.
What surface prep and flatness are required?
Ultrasonic bonds need clean, flat pads. No oils, flux, or oxide films; surface energy and roughness must be within spec. Flatness affects energy coupling and ear formation; warped pads or burrs will degrade weld quality.
Aluminum vs copper? Ribbon vs round wire?
Aluminum wire/ribbon is common for cell terminals due to oxide behavior and bonding energy.Copper can be used with the right surface and parameters but is more demanding. Ribbon provides more cross-section and lower profile for high current; round wire is flexible and fast for general use.
What happens if a bond is overloaded?
Bonds exhibit fuse-like behavior under severe overcurrent; they separate rather than propagating damage. Designs use parallel bonds so a single failure doesn’t create a hard open; the BMS and protection strategy handle the event at the system level.
Can wire bonds be reworked?
Yes: one advantage of ultrasonic wire bonding is clean reworkability at the joint level. Rework follows a documented procedure and re-inspection (visual + pull) to return the site to an acceptable state.
What standards or methods do you reference for QC?
We align to industry practices (e.g., MIL-STD-883 methods 2011/2017 for pull/shear concepts) adapted for power interconnects. We retain inline process logs (force/energy/time), visual profiles, and traceability to build records.
How do bonds hold up to vibration and temperature?
The loop provides compliance and reduces stress transfer to the weld. With correct loop geometry and parameters, ultrasonic bonds perform well under environmental and vibration testing; specifics are validated per program.
When would you choose laser instead of wire-bond?
Laser excels at long seams, very high per-joint current, or when structural seam requirements dominate. It demands tight fit-up (zero-gap) and process control. Wire-bond wins when low heat, compliance, and reworkabilityare priorities. Many packs mix techniques deliberately.
Explore "Why Wire-Bond" for your program
We'll compare options against your current densities, thermal budget, and test plan.
Talk to Engineering