National Physical Laboratory, NPL, has created an interactive assembly and soldering defect database, each month readers can add other defect solution to their own collection. Also available from the database is free access to over 100 process and reliability reports on soldering technology, Download Here
This termination was seen after the top component was mechanically removed to examine for open connections and shows the solder ball on a TSV cavity. There was evidence of some form of residues on the surface ball. This indicated that either dip flux or flux from the dip paste was present on the top package balls prior to placement and reflow. In this case the flux medium was in contact with both balls but failed to allow the two surfaces to reflow together to form a joint
This may be a problem with some form of contamination on the surface of the balls that the flux could not overcome or for some reason the package could not sink down evenly allowing the metal to metal contact prior to reflow. In a case like this where both the ball interfaces were slightly flattened with no residues it may be the oxide surfaces not being removed by the flux. The x-ray image also shows the open connection, the complete reflow cycle of TSV packages has been observed in x-ray to investigate these types of fault by the author see our YouTube Video Channel
To complement our “Defect of the Month” editorial Circuits Assembly now features “Defect Video of the Month” presented online by Bob Willis. This covers different failure modes with many video examples of defect occurring in real time and supported by IPC
