SOLDER HERARCHY FOR LEAD FREE SOLDER JOINT

摘要

A LEAD FREE SOLDER HIERARCHY FOR USE IN THE SECOND LEVEL SOLDER CONNECTION OF ELECTRONIC COMPONENTS SUCH AS JOINING AN ELECTRONIC MODULE TO A CIRCUIT BOARD. AN OFF-EUTECTIC SOLDER CONCENTRATION OF SNCU OR SNAG IS USED FOR THE MODULE SIDE CONNECTION. THIS OFF-EUTECTIC SOLDER CONTAINS SUFFICIENT INTERMETALLICS TO PROVIDE THE MODULE SIDE CONNECTION WITH A ROBUST SECOND LEVEL ASSEMBLY AND REWORK PROCESS. THE OFF-EUTECTIC COMPOSITION PROVIDES AN INTER-METALLIC PHASE STRUCTURE IN THE MODULE SIDE FILLET DURING ASSEMBLY. THE INTER-METALLIC PHASE STRUCTURE ELIMINATES PROBLEMS OF TILT AND COLLAPSE DURING SECOND LEVEL ASSEMBLY AND AIDS IN REWORK BY PROVIDING A MORE COHESIVE JOINT ALLOWING REMOVAL OF THE COLUMNS FROM THE BOARD WITHOUT SIMULTANEOUS REMOVAL FROM THE MODULE.(FIG. 1F)