Issue link: https://iconnect007.uberflip.com/i/1424540
88 SMT007 MAGAZINE I NOVEMBER 2021 component. Some of the most common prob- lems include: • Twisting motion to break board/device bond during the component removal process may damage board or neighboring devices • Using a sharp tool to "cut" the underfill so the component can be removed may damage neighboring components or the PCB • Mechanically scraping or cutting away the underfill may cause damage to PCB or neighboring components • e mechanical bond of the underfill to the PCB may cause the liing of pads, laminate damage, or solder mask damage (Figure 1) • e time-consuming nature of removing the underfill makes the rework process beyond economic repair • Heating the solder underneath the BGA/ CSP/QFN to a liquidus temperature for removal causes the underfill to begin to reflow, "pushing" solder out from the designated pad areas • Neighboring underfilled components can be pushed off their pads during the removal process ere are numerous methods which can be used to rework these underfilled devices. Each method has both advantages as well as draw- backs. e method used most oen for reworking underfilled devices involves the use of a heat source to reflow the BGA while simultaneous- ly creating a parting line in the underfill be- tween the component and the PCB. is will release the component from the pads on the PCB, as the soened material still adheres to both the component and the board. Either the BGA rework system has a twisting motion to get the component removed or a bimetallic re- flow nozzle "grabs" the suspect component for removal. Aer component removal, the site is dressed using a hot air source along with a tool such as a solder extractor or a hobby knife, or by utilizing a specific soldering iron chisel tip along with solder braid. If no BGA rework sta- tion is available, then a non-controlled heat source such as a heat gun can be used to re- move the component from the board followed by clean up. ese processes require care and skill by the operator to not damage the board or neighboring components. Another method which can be used to re- move the BGA by breaking the adhesive force of the underfill is via a soening agent. A sol- vent-based chemical—formulated by the un- derfill vendor—comes into contact with the underfill and soens it. is allows for easier removal of the underfill, thereby reducing the likelihood of component, mask, or pad dam- age. One of the drawbacks to this methodolo- gy is being able to get the soening agent to all areas of the underfill, as the hardened underfill blocks the liquid from getting to all areas. Furthermore, depending on how Figure 1: BGA site location after removal of underfilled BGA indicating both pad lifting and mask damage.