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76 SMT007 MAGAZINE I OCTOBER 2026 introduces another substrate, added solder joints, increased stack height, tighter alignment require- ments, and new thermal considerations. It can also affect signal integrity or impedance in high speed applications if not properly engineered. Common Applications Interposers are most useful when conventional BGA rework or localized board repair is not practical, reliable, or cost-effective. They provide another way to modify the electrical path between a component and the PCB without redesigning the complete assembly. Common uses include: • Bypassing damaged internal vias or connec- tions near a BGA footprint • Implementing engineering change orders that require signal rerouting • Adapting an existing PCB to a replacement component with a different pinout or connec- tion scheme • Recovering high-value assemblies where re- placing the PCB would be difficult or prohibi- tively expensive • Supporting prototype modifications and de- sign validation without committing to a new PCB revision Interposers are also used in semiconductor packaging as an intermediate routing layer between one or more integrated circuit dies and the package substrate. Organic materials such as FR-4 and polyimide are common in board-level or flexible applications, while silicon and glass are more closely associated with advanced pack- aging requiring very high interconnect density or demanding electrical performance. Interposer Rework At the board level, interposer rework is used when a conventional BGA removal-and-replacement process does not adequately address the electrical or mechanical requirements of the assembly. The interposer is introduced between the BGA and the PCB to reroute connections, accommodate design changes, or create an alternative interface between the component and its original footprint. A typical process may include: • Remove the BGA using a controlled hot-air or infrared rework process. • Clean and inspect the original PCB footprint • Re-ball the BGA or interposer if required • Prepare the PCB and interposer for assembly • Apply solder paste or flux as required K N O C K I N G D OW N T H E B O N E P I L E Figure 2: X-ray images of BGA-interposer-PCB from top and oblique angles.