Heat-curable epoxy resin is mostly used for the resin used in semiconductor sealing. Functionality including heat dissipation and thermal expansion is given to the resin by mixing silica particulate SiO2, silica dioxide).
The semiconductor die and substrate or lead frame are electrically bonded through bonding wires after the semiconductor assembly process. When doing so, it is necessary to protect the semiconductor die and bonding wire mechanically and chemically. Although they were previously sealed using metallic covers or ceramics in a vacuum condition, resin sealing is the common method in the present day.
Resin sealing requires various properties, including the ability to adhere to the semiconductor die and substrate, heat tolerance, heat dispassion, thermal expansion, and mechanical strength.
There are two types of sealing resin for semiconductors: solid type and liquid type.
The solid-type sealing material is called transfer molding. Molding methods similar to mold injection are adopted. In transfer molding, after a pellet-type material is heated and softened in the plunger, resin is put into a mold, cooled, and solidified. The liquid-type sealing material is called potting. The resin is deposited onto the semiconductor die (bonded to the substrate) and thermal curing is performed.
Many sealing resins for semiconductors contain 10 to 20% of thermal curing resin (such as epoxy), and 80 to 90% of silica filler. This is to improve the thermal conductivity and match the thermal-expansion coefficient of the silicon semiconductor to be sealed. Most of the current semiconductors are packaged with this sealing resin.
In the BGA (Ball Grid Array) and QFN (Quad For Non-lead package) processes, which seal multiple semiconductor packages, DISCO dicing saws (dicing with dicing blades) are used to dice the sealed packages. In recent years, wafer-level CSP (Chip Size Packages) are sealed at the wafer level. Thus, in addition to DISCO dicing saws for singluation, DISCO grinders (grinding equipment using grinding wheels) for the low-profiling of sealing resin are also often used.