Repair of Defects on High Melt Interconnect C4s
Original Publication Date: 2007-Jan-25
Included in the Prior Art Database: 2007-Jan-25
A method for repair of Interconnect bridges in Computer Chip Manufacture
Repair of Defects on High Melt Interconnect C 4s
Currently defects that are found at wafer final visual inspection (Grp B or RVSI) are
characterized as yield detractors and or reliability detractors and subsequently rejected.
These die are generally electrically good prior visually inspecetion and are a direct
impact to outgoing yield based on these visual criteria. Two defects that historically are rejected are C4 Bridges and Oversized C4s. The bridge is an electricaly conductive path between two C4s (or more) that causes an electrical short. This short can be a full
thickness bridge of the entire C4 or the underlying BLM material which is designed to help the C4 self allign and shape into a ball during a reflow process post test probing. The Oversized C4 can have an excess of Material for the ball with or without an oversized
BLM. These defects are typically associated with shorts in the module build process.
The idea is to use a material removal process to seperate the c4s that are bridged or reduce the size of the Overasized C4 The novelty of the approach is to us a commercialially available tool set to remove the full thickness materal down to the protective polymide layer. The aggressiveness of the method is dictated by the composition of the bridge and whether the BLM is present.
2 scenarios exist.
1) Full thickness BLM material and solder/plated material. If this is the case the entire stack must be removed to electrically isolate the c4s. Recall the BLM material is a self centering material so when the die...