interposer
An electrical interface between one connection or socket and another, used to spread a connection to a wider pitch or to reroute it.
interposer: adapter that translates between incompatible pin layouts
An interposer is a thin circuit board or substrate that sits between two incompatible electrical interfaces, converting the pin pattern, spacing, or signal routing of one to match the other. It acts as a physical and electrical translator, allowing components with different footprints or connector types to work together without modifying either the source or destination device.
The most common use is pitch conversion: a chip or connector with 0.5 mm pin spacing might need to interface with a socket designed for 1.27 mm spacing. The interposer bridges this gap, with traces routing the finer pitch down to the coarser one. Interposers are also essential in test environments, where they allow probing or measurement of signals between a component and its socket without soldering directly to the board.
Interposers come in several forms. Rigid PCB interposers are the simplest and cheapest, using standard copper traces on FR-4 or similar laminate. Flex interposers use polyimide film to fold and route signals in three dimensions, useful where space is tight. High-end interposers in semiconductor testing or high-frequency RF work use ceramic substrates or thin-film technology to minimize inductance and capacitance. In advanced packaging, silicon interposers act as a redistribution layer (RDL) between chiplets or between a die and substrate, offering much finer feature resolution than PCB technology.
Signal integrity issues arise when interposer traces are too long, introduce impedance mismatches, or create uncontrolled loop areas in high-speed designs. Thermal problems occur if the interposer blocks airflow or isolates heat from the primary component. Mechanical failures happen when the interposer is too rigid (breaking solder joints under thermal cycling) or too flexible (causing contact bounce or creep). Crosstalk between routed signals on a dense interposer can corrupt data, especially in parallel bus applications.
The term interposer comes from the verb interpose, meaning to place something between two other things. In electronics, it has been in use since the 1980s in the context of test fixtures and socket adapters. Today it spans from simple single-layer adapters costing a few dollars to sophisticated multi-layer silicon redistribution structures integral to modern chiplet packaging and 3D die stacking.