Chip on Board - Encapsulation
Encapsulation is the process of covering Chip-On-Board or Flip Chip components in a protective shell in order to prevent physical damage following Die and Wire Bond. There are two basic types of encapsulation: Glob Top and Dam-and-Fill.
Glob Top is simply the process of depositing the encapsulant on top of the component. The encapsulant is of a low viscosity which allows it to flow and conform to the shape of the component without damaging the fragile wires present in Chip-On-Board applications. Because of the low viscosity however, the encapsulant can potentially run beyond the desired cover area and into adjacent components before it is cured.
Dam-and-Fill encapsulation utilizes a dam around the periphery of the component for the purpose of preventing flow of the encapsulant to adjacent components. There are several different types of dams to choose from. Mechanical dams are essentially physical walls that are built into the substrate around the die placement area. Silicone and Double Viscosity dams consist first of a line of silicone or high-viscosity encapsulant that is dispensed around the periphery of the component. Next a low viscosity encapsulant is dispensed on top of the component and fills the area of the dam.
Encapsulation dams are usually square in shape so that stress is evenly distributed after cure. Dams should be at least 0.010" higher than the highest wire loop being covered.
Examples of all three encapsulation methods.