Outline
This procedure is used to remove BGA devices that have been underfilled with non-reworkable epoxy underfill.
Minimum Skill Level - Expert
Recommended for technicians with advanced soldering and component rework skills and extensive experience in most repair/rework procedures.
Conformance Level - High
This procedure most closely duplicates the physical characteristics of the original, and most probably complies with all the functional, environmental and serviceability factors.
Tools and Materials
Cleaner
General purpose cleaner for removing contamination.
Desolder Braid
Woven copper wire designed to wick solder from surfaces and holes.
End Mills
Designed for end cutting and hole boring.
Microscope
Precision microscope with stand and lighting for work and inspection.
Milling Machine
Use for precision milling of circuit board materials.
Soldering Iron
Properly maintained soldering iron and properly sized soldering iron tips.
Procedure
Enclose the circuit board assembly in a static barrier bag. Cut an opening in the bag to expose the underfilled device to be removed and seal the edges to the circuit board with high temperature tape.
Secure the circuit board assembly with appropriate tooling and fixtures to the base of the milling machine. Setup a microscope to observe the milling operation.
Caution
Check to ensure the the circuit board is rigidly secured in place and parallel to the milling machine base. Proper fixturing to hold and support the circuit board assembly is critical.
Install the appropriate end mill into the chuck of the milling machine and set the speed as required.
Setup a vacuum system close to the milling area to remove dust and debris during the milling operation.
Begin machining off the BGA device body, removing approximately .010 inch per pass. Repeat the milling process removing .010 inch thick layers until the entire body of the device has been machined away and the underfill epoxy is exposed.
Begin machining off the underfill epoxy, removing .002 - .003 inch thick layers. Repeat the milling process removing .002 - .003 inch per pass until there is approximately .010 inch thick layer of underfill remaining on the circuit board surface. Vacuum all debris.
Remove the circuit board assembly from the milling machine.
Use Solder Braid and wick the solder that remains in each underfill pocket, exposing each of the pads on the circuit board surface.
Re-install the circuit board assembly to the base of the milling machine.
Continue machining the remaining underfill removing .001 inch per pass until there is approximately .003 - .005 inch think layer of underfill remaining.
Caution
Exercise care to avoid machining through the underfill damaging the soldermask, pads or surface traces.
Remove the board from the static bag and clean the area and circuit board as needed.
