Application of Face-Centered Central Composite Design for the Optimization of Chemical Etching Process of QFN-mr Package Using Alkaline-Based Chemical Solution

Abstract

Quad-Flat No Lead Multi-row (QFN-mr) is a common type of integrated circuit (IC) package that is leadless and plastically encapsulated in build. Before being cut into units through singulation process, QFN-mr packages are in Cu leadframe strip form and typically subjected to chemical wet etching treatment to remove Cu metal in areas between lead and pad and eventually, prevent metal shorting issue during soldering of individual units. The objective of this work is to establish optimum parameter combination for the chemical etching of QFN-mr package using face-centered central composite design as experimental design and alkaline-based solution as chemical etching agent. Experimental runs were carried out in a conveyorized, horizontal wet etching line. From the results, it was found out that the amount of material etched increases as conveyor speed and etching nozzle spray pressure are decreased and increased, respectively. Optimum setting was predicted to be at 55 cm/min conveyor speed and 1.67 bar etching spray pressure. This produced the target lead and pad dimensional response, as proved by the results of the actual confirmatory test performed.