Packaging Interconnect
Advanced packaging technology locates tiny interconnects between stacked semiconductor dies to enable high-density electrical paths. Within these multi-chip modules, a micro bump functions as the physical and electrical bridge that connects the active circuitry of one layer to another. These miniature solder joints are typically spaced at pitches below forty micrometers, representing a substantial reduction from traditional flip-chip interconnects.
They are formed using electroplating processes followed by thermal reflow.
Metrological Inspection
Verifying the coplanarity and volume of these tiny structures requires high-resolution optical metrology systems before the bonding process. Height variations across the wafer must remain within strict sub-micron tolerances to prevent open circuits or solder bridging during assembly. Automated inspection systems utilize white-light interferometry to measure every interconnect with extreme precision.
Thermal Stress
Mismatch in thermal expansion between the silicon die and the substrate induces mechanical stress on these contacts during temperature changes. This stress can lead to micro-cracking and eventual signal loss.
Manufacturing Control
Reliability evaluation involves subjecting the bonded packages to accelerated thermal cycling to monitor resistance changes over time. Any rise in contact resistance points to mechanical degradation or void formation within the solder joint. Continuous monitoring ensures that the assembly processes remain optimized for high-volume manufacturing.
