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80 SMT007 MAGAZINE I OCTOBER 2026 interposer-to-PCB joints. Careful thermal characterization is still essential. Thermocouples should be used to verify tempera- tures at both interfaces because the actual solder- joint temperature will depend on the component, interposer construction, PCB thermal mass, heater configuration, and dwell time. The key benefit is the ability to control the two soldering events indepen- dently rather than repeatedly bringing both inter- faces through liquidus. X-ray Inspection Challenges Interposer assemblies can also be more difficult to evaluate using X-ray inspection than a conventional BGA installation. Because the assembly contains multiple vertically stacked solder-ball interfaces, the upper and lower solder joints may overlap in the X-ray image, making it harder to isolate and eval- uate an individual connection. This overlap can make defects such as opens, bridging, voiding, or inconsistent joint formation more difficult to interpret from a single top-down image. Oblique-angle X-ray inspection can help separate the interfaces visually, but the effective- ness of the inspection depends on the interposer design, ball pitch, material density, and capabilities of the X-ray system. Equipment Commonly Used Depending on the assembly, interposer rework may require: • Precision hot-air or infrared BGA rework equipment with bottom-side heating • Optical alignment and component-placement capability • PCB preheating equipment • Reballing fixtures and stencils • Solder paste, solder spheres, and flux com- patible with each interface • Interposer alignment or support fixtures • Stereo microscopy • X-ray inspection • Thermocouples and profiling equipment Alternatives to Interposer Rework An interposer should not automatically be consid- ered the preferred solution for every BGA-related failure. Depending on the failure mode, board construction, reliability requirements, and assembly value, a simpler repair may be more appropriate. Alternatives can include bonded replacement pads, jumper-wire repair to an accessible trace or via, PCB trace repair, conventional BGA removal and replacement, or complete PCB replacement when the damage or risk is too extensive to justify repair. Conclusion Interposer rework provides an additional option when conventional BGA rework, localized PCB repair, or board replacement does not adequately address the needs of an assembly. It can be espe- cially valuable for high-cost electronics, difficult- to-replace multilayer PCBs, engineering changes, prototype modifications, and specialized advanced- packaging applications. The process also introduces additional solder joints, alignment requirements, thermal consider- ations, and inspection challenges. For that reason, interposer rework should be approached as an engi- neered process rather than simply an extension of standard BGA rework. The interposer design, alloy selection, reflow sequence, thermal profile, inspection method, and reliability requirements should all be evaluated together before the repair strategy is finalized. When properly designed and controlled, an inter- poser can provide a practical way to recover valu- able hardware, implement difficult design changes, and extend the useful life of assemblies that might otherwise require replacement. SMT007 Nash Bell is president of BEST, Inc. To read past columns, click here. K N O C K I N G D OW N T H E B O N E P I L E