Issue link: https://iconnect007.uberflip.com/i/1544707
42 SMT007 MAGAZINE I MAY 2026 mount component, regardless of whether it is underfilled with a "reworkable" or "non-rework- able" material. Each available rework method is tasked with breaking the bond between the PCB and the underfilled surface mount component. These methods include: • Hot air rework: Utilizes a stream of hot air to heat the surface mount component and PCB. • Infrared rework: Uses infrared emitters to target the surface-mount component, mini- mizing thermal impact on surrounding areas • Manual removal: Typically used only for "reworkable" underfill material and requires skilled and highly trained technical operators • Chemical agents: Involves the use of a spe- cialized softening agent to reduce the adhe- sive strength of the underfill material, thereby facilitating easier removal of the underfilled component • Laser ablation: Utilizes focused laser beams for precise heating, allowing selective reflow while minimizing damage to adjacent components • Precision milling: Used for removing under- filled surface mount components, this process employs high-precision milling equipment to remove the component one layer at a time Potential Issues With Underfill Rework Rework methods that rely on heat are generally not recommended for underfilled surface-mount components. When the underfill is heated to near-reflow temperatures, it can soften or become fluid, interfering with the formation of reliable solder connections and potentially compromising product integrity. • Hot air rework: Heating the solder beneath the component to a liquidus state can also cause the underfill to soften or reflow. As a result, adjacent underfilled components may be displaced from their pads during removal. • Infrared rework: Infrared emitters apply heat directly to the component, creating a risk of excessive localized overheating. This can also cause adjacent underfilled components to be displaced from their pads during removal. • Manual removal: Although highly flexible, this method is generally unsuitable for "non- reworkable" underfill materials and may dam- age the board if not performed by skilled, highly trained operators. • Chemical agents: "Non-reworkable" un- derfills are often difficult to remove through chemical processing. In addition, some OEMs object to the use of chemical soften- ing agents because they may aggressively attack components and/or the board. • Laser ablation: Effective use of laser ablation requires careful selection of the laser source and wavelength to match the material's absorption characteristics. If the beam is not properly controlled or focused, underfilled components can be damaged. • Precision milling: This "cold" removal process offers a significant advantage over heated rework methods for underfilled components. Although it is destructive to the component being removed, precision milling allows for subsequent component placement in the tar- get area and is a low-risk option when compo- nent salvage is not the primary objective. In general, component removal processes that do not rely on heat are preferred for underfilled components. Heated rework methods introduce greater unpredictability and increase the risk of K N O C K I N G D OW N T H E B O N E P I L E Figure 1: Example of BGA location with pad lifting and solder mask damage.