Plasma
ELECTRONICSPlasma is used in the electronics industry for a wide variety of applications ranging from adhesion promotion of encapsulants and adhesives, to enhancing the release properties of optical disc master stampers. The power of plasma to precision clean surfaces prior to metallization and solid state bonding has been recognized by industries such as automotive, where it is used prior to spot welding, and printed circuit board fabrication where it is used to clean drill smear prior to metallization. Electronic connectors and feedthroughs rely on plasma to promote surface wetting properties of adhesives, encapsulants and sealants. This insures leak free devices in products such as water meters and submersible connectors, and is especially used for critical devices such as implantable cardiac defibrillators and pacemakers
Plasma Cleaning prior to Wire Bonding
In chip packaging, plasma cleaning is essential for improving the cleanliness of bond pads prior to wirebonding. Ball shear and stitch pull strengths are dramatically enhanced by surface plasma cleaning. Ideally, during the pull test the wire should remain welded to the bond pad while it is broken midspan. PVA TePla's unique microwave plasma efficiently removes organic contaminants and thin oxide layers from the bond pads with unparalleled throughput. Microwave plasma processing allows for tailored surface cleaning and conditioning through the application of our proven and cost effective systems.
Improve adhesion of potting compounds
Plasma activation prior to potting ensures a good hermetic seal, reduces current leakage and provides stronger physical bonding to the device. The protection of electronic or electrical devices by an encapsulating resin is referred to as "potting". Potting provides electrical insulation and protection from moisture, high/low temperatures, and physical and electrical stress. It can also function as a flame retardant, shock absorber and heat sink. Poor "wetting" of the potting material to the device is common, particularly to low surface energy polymers. This can result in poor bonding and voiding. Plasma activation raises surface energies and ensures good wettability, and more complete flow of resins onto almost all low energy polymer materials, including PTFE, silicone rubber and Kapton.
In one case study, a major manufacturer of discrete electrical components produced several million potted electrical parts per month. Their defect rate due to 'leakers' was as high as 5%. PVA TePla was reduced their defect rate to 0.5% using plasma treatment to improve the bond between the potted compound and the Veloxa housing. Due to the large volume and small sizes of the components, PVA TePla America developed a rotary basket plasma reactor for this application. The system has been operating reliably for several years with minimal down time.
Desmear
Plasma desmear and etch-back by plasma is an established practice in the PCB industry. Drilling vias through multilayer PCB's leaves residue, or smear, on the via walls. This smear must be removed before metallization (to establish electrical connectivity) can occur. Gas plasma readily cleans smear in through-vias by the activation of oxygen and fluorinated compounds such as CF4. The plasma released oxygen and fluorine radicals attacks the resinous smear by a chemical etch process. The result is clean vias completely free of smear. Competing technologies using wet chemical methods fall short when it comes to fine through-vias, Teflon core material, or acrylic adhesives used on polyimide based interposers. For those applications, low pressure gas plasma has proven to be the superior cleaning method. PVA TePla's unique electrode design also ensures excellent plasma treatment uniformity, not only across each board, but also from one board to another and from process to process.
