Application of dry ice surface treatment technology in system level package
Time：2023-09-11 Category：【DSJet technology】Read：319
With the development of miniaturization and system integration, System-in-Package (SiP) has rapidly become a solution to package miniaturization and multifunctionality. However, as SiP volume decreases and operating frequencies increase, chips become more susceptible to electromagnetic interference from the external environment, which can seriously affect the normal functioning of the chips. To protect the integrated circuits in the package, electromagnetic shielding coating technology is commonly used to form Faraday cages.
The main factors affecting electromagnetic shielding performance are the surface continuity of the shielding and the absence of conductors that can directly penetrate the shielding. The adhesion and integrity of the electromagnetic shielding coating are essential for ensuring shielding effectiveness. The surface quality before the sputtering process greatly affects the bonding strength of the coating. During the separation process of the package, when the Cu metal in the PCB substrate is subjected to energy excitation, it evaporates into gas. Some Cu unavoidably adheres to the side surface of the package, making it difficult to remove by wiping or cleaning. The embedded Cu particles in the molecular structure of the material surface reduce the roughness and decrease the bonding area between the shielding layer and the package, thereby reducing the bonding strength. In severe cases, it can cause coating delamination and result in the failure of electromagnetic shielding functionality. Therefore, improving the surface quality of the package after separation is crucial for enhancing the reliability of the shielding film.
Currently, commonly used pre-coating treatment methods in the semiconductor packaging field include hot chemical roughening polishing, deionized water cleaning, and plasma polishing. Hot chemical roughening polishing involves high temperatures, which can corrode the product and leave residual chemical substances on the surface. Deionized water cleaning has low cleaning efficiency, significant water resource waste, and can only remove surface dust and impurities, with little capability to remove Cu impurities generated during the separation process. Plasma polishing has high investment costs and cannot selectively target specific surfaces.
This article proposes a new method for surface treatment of semiconductor packages, which is dry ice (solid carbon dioxide) treatment. As early as 1945, the United States began researching the comprehensive utilization of CO2, but to this day, dry ice treatment technology is limited to industrial sectors with larger sizes and lower precision requirements. Dry ice treatment technology has been widely used in industries such as food, machinery, agriculture (greenhouse cultivation), automotive, aerospace, and other large-scale manufacturing. However, there have been few research reports on its application in the semiconductor packaging field, which requires miniaturization, high precision, and higher surface requirements.
