Advanced Packaging in GaAs –INL developed a “Temporary Wafer Bonding” (TWB) solution for GaAs wafers, scalable to volume production and multi-wafer panel level processing.
In TWB, the wafer is attached to a glass carrier to allow its handling throughout the “Re-Distribution Layer” process (RDL), one of the main phases of Advanced Packaging. The development of TWB for GaAs encompassed the search of the appropriated glass type for the carrier and adhesive, capable of withstanding the thermomechanical and chemical stress of RDL process; the method for wafer to carrier bonding and de-bonding; the demonstration of the mechanical robustness of the carrier-wafer stack on thermal stress cycles; and the assurance of high carrier-wafer electrical conductivity.
The figure shows a Æ150mm GaAs wafer mounted on a Æ200mm glass carrier. The surface of the set is covered with a thin film sputtered Cu (100nm), that acts as the cathode for the electroplating process. The critical issue is the electrical continuity of the thin film across the interface boundary between carrier and wafer, in order to guaranty a uniform electroplating process at the GaAs wafer surface.
