Un-fill electronics packaging material

• Main Author: Soh, Pei Xuan
• Other Authors: Gan Chee Lip
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering
• Online Access: https://hdl.handle.net/10356/176057
• Institution: Nanyang Technological University

This project examines the methodologies used to weaken or remove underfill and allow for successful component desoldering from the Printed Circuit Board (PCB). With increasing usage of underfill to ensure solder joint reliability, especially for use in Integrated Circuit (IC) packaging such as Ball Grid Arrays (BGA), and Chip Scale Packages (CSP), there is an underlying challenge to rework the PCB due to the strength of the underfill which bonds the PCB substrate and the component together. The effect of different rework methods on underfill was investigated. Samples of non-reworkable underfill of unknown properties on PCBs and known properties on glass slides were prepared. Rework methods used include the soldering iron, hot air gun, Infrared (IR) heater, onyx24 semi-automatic rework station, laser ablation and Microwave Induced Plasma (MIP). Rework methods used were able to remove the underfill successfully. The use of soldering iron was only able to remove exposed underfill. Hot air gun method demonstrated that specific components can be targeted and removed. The hot air first weakens the hold of the underfill onto the component and the board. With the addition of an applied force, it further weakens the hold and allows for successful component removal. IR heater method showed that it should not be used if the objective was to remove only a component from the board because the method involves heating up the entire board, which causes multiple component displacements. Onyx24 semi-automatic rework station revealed that component desoldering from the PCB is only possible if the bond of the underfill is weak. Laser ablation shown that it can ablate away both electronic components and underfill. The efficiency of removal depends on the material absorption and the laser wavelength. On the other hand, MIP was able to chemically etch away the underfill through oxygen plasma with argon as carrier gas. Observation of samples using optical microscopy showed that laser ablation using UV was the most effective method in removing underfill cleanly. Soldering iron and MIP were also effective in removing underfill but are very time-consuming processes. Component removal with underfill is also effective using hot air and a shearing force applied to the component.