Tergeo and Tergeo-plus tabletop plasma cleaner
Thermasonic wire bonding is one of the critical packaging processes, especially for aerospace and automotive industry, where the bonding joint can be stressed under extreme conditions. Surface contaminations on bond pads including epoxy bleed-out from the die attach step can severely weaken the bonding strength due to poor interfacial adhesion. Oxygen plasma treatment is widely used to remove surface contaminants prior to wire bonding. However, the thin gold film on bonding pad may be sputtered away by energetic ions in traditional direct immersion mode plasma cleaning. Ion sputtering damage is especially severe for plasma systems using KHz rf power supply because ions can be accelerated to very high energy in KHz electric field. Tergeo plasma cleaner use MHz rf power supply to reduce ion energy and plasma potential, thus minimize the ion sputtering damage. In addition, Tergeo plasma cleaner integrate a separate remote plasma source that enables real ion-free downstream mode plasma cleaning. In downstream mode plasma cleaning, plasma is generated in separate remote plasma source. Only reactive atomic oxygen can diffuse into the sample chamber and chemically oxidize the surface contaminant. Ion free downstream mode plasma clean is very useful feature for bonding pad with thin gold coating.
Underfill void formation during reflow drives interconnect yield down and degrades reliability. Vacuum plasma treatment with oxygen gas has multiple benefits for flip chip application. Frist, the vacuum environment reduces moisture in the substrate and device. Second, oxygen plasma treatment reduce contaminations. Third, plasma treatment activates surface, adds hydroxyl functional groups on the surface and increase surface wettability for liquid adhesive and improve bonding strength. Plasma treatment can reduce void formation in underfill, increase filet height and improve filet uniformity around the device.
Good adhesion between adhesive and substrate is of great importance for plastic-encapsulated microcircuits. Plasma treatment can remove surface contamination and increase surface roughness through chemical reaction with oxygen or fluorine radicals and physical ion sputtering process. Activated surface promote better adhesion and increase surface wettability. Plasma treatment can provide better contact, improve heat transfer and minimizing void formation.
Tergeo plasma cleaner can also be used to remove polymer encapsulants and expose interconnects for failure analysis.