Wire Bonding
A reliable wire bond needs clean metal-to-metal contact between the wire and the bond pad or lead frame. Thin films of organic residue (photoresist, flux, outgassing from die-attach adhesives, handling and storage contamination) can weaken that contact, lowering pull and shear strength and causing non-stick failures. Plasma cleaning removes these films without solvents and without touching delicate wires or die. Production lines use inline plasma systems for this step; a Harrick Plasma Cleaner brings the same low-temperature treatment to R&D labs, prototyping, failure analysis and low-volume packaging.
How plasma treatment is used in wire bonding and packaging
Bond pad and substrate cleaning. Air or oxygen plasma removes thin organic films from gold and aluminum bond pads and from substrates just before bonding. Argon is often preferred for copper, silver-plated lead frames and other metals that oxidize easily.
Die attach and underfill. Cleaning the die and the board raises surface energy so die-attach adhesives, underfill and no-flow flux adhesives wet the surface and bond well.
Encapsulation and molding. A plasma step before glob-top, potting or mold compound improves adhesion at the package interfaces and helps reduce delamination.
Failure analysis and reliability testing. Wire-bonded packages are plasma cleaned to remove surface contamination before inspection, corrosion screening and other reliability tests.
Developing a packaging or bonding process? Tell us your pad metallization, substrate and part size and we will point you to published conditions and the right configuration. Request a Quote or email info@harrickplasma.com.
Why Harrick Plasma for wire bonding
- No electrode inside the chamber. RF is coupled from an external coil, so no electrode material is sputtered onto bond pads or wires.
- Isotropic treatment. The plasma reaches every exposed surface of the part, including pads beside raised components and the sides of bonded wires.
- Cold plasma. Parts stay near room temperature, which suits polymers, adhesives, flexible substrates and assembled devices.
- Gas choice. Run air through the metering valve with no cylinder needed, or oxygen, argon or nitrogen when the metal calls for it. The PlasmaFlo gas flow mixer adds repeatable flow and pressure control.
- Sized for development work. The Basic Plasma Cleaner fits individual die and small substrates; the Expanded Plasma Cleaner fits boards, packages and batches of parts up to about 5 inches (130 mm) across.
Frequently asked questions
Why plasma clean before wire bonding? Organic films only a few nanometers thick can keep the wire from bonding to the pad. Plasma removes them, giving a clean, high-energy surface for a stronger, more consistent bond.
Which gas should I use? Air or oxygen is effective at removing organic residue from gold and aluminum. Argon is a common choice for copper and silver, where oxygen could oxidize the surface.
How long should I clean? Cleaning times typically run from about 1 to 10 minutes, depending on the level of contamination. Confirm your settings with wire pull or ball shear tests, or with a quick water contact angle check.
How soon after cleaning should I bond? As soon as practical. Clean surfaces pick up contamination again from the air, so bond, attach or encapsulate within hours of treatment, ideally sooner.
Which Harrick Plasma Cleaner should I choose? The Basic Plasma Cleaner suits single die and substrates up to about 2 inches (50 mm). The Expanded Plasma Cleaner fits boards, packages and batches up to about 5 inches (130 mm) across. Long lead-frame strips will not fit; contact us with your part sizes and we will recommend a configuration.
