Washable Coatings for Packaging Practices

Many packaging processes require the protection of components while another application is conducted. This may include a planarizing coat over large topography while a deposition, bonding, or curing step is completed. Washable coatings are materials that protect the substrate during thermal or mechanical activities and are simply washed away using readily available and green products, such as water or detergent. Washable products are not new, an example includes laser washable coatings that remove debris from the heat activation zone (HAZ) during scribe and break processes. In such cases, thermal resistance is of coatings is preferred as high as possible. While many products used for such applications include polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP), such materials are not good choices for thermal resistance as they cross-link when exposed to temperature or to metals, leaving residue that is difficult or impossible to remove. While these are water soluble, they were designed for industrial and consumer packaging applications such as laundry packets, vitamins, or other non-thermal processes. Using thermal sensitive materials as PVA and PVP for laser processes creates a narrow process window that requires special washing tools that use high-pressure nozzels or heat. Alternatively, thermal resistant washable products are available that provide protection to 300°C or more, and upon being exposed to such conditions and metal contact, will simply rinse away without the aid of mechanical tooling.[1] Planarizing coatings commonly require thermal resistance, as they can be thick (>300um) and perform in encapsulating solder bumps while a dielectric or another die is solder attached and temperatures in excess of 250°C are needed. This has been proven in the case of protecting C4 bumps while bonding micro-bumped die onto FPGA interposers.[2] Bonding and curing is conducted with water or detergent washable UV-cured adhesive coatings. Similar coatings have been proven for EMI/RFI shielding where coatings are applied to porous substrates followed by temporarily affixing die to be processed in a PVD tool. When completed, the die are removed while the coating is washed away in a cleaner.[3] The success in these and related temporary applications depend upon the use of the proper washable coating. Our experience in creating solutions for these and other industry needs will be discussed as well as the criteria for using temporary washable coatings.