What is "interposer"

Interposer \In`ter*pos"er\, n. One who, or that which, interposes or intervenes; an obstacle or interruption; a mediator or agent between parties.
--Shak.

n. 1 One who interposes. 2 An electrical interface between one socket or connection and another, used to spread a connection to a wider pitch or to reroute it.

An interposer is an electrical interface routing between one socket or connection to another. The purpose of an interposer is to spread a connection to a wider pitch or to reroute a connection to a different connection.

Interposer comes from the Latin word "interpōnere", meaning "to put up between".

A common example of an interposer is an integrated circuit die to BGA, such as in the Pentium II. This is done through various substrates, both rigid and flexible, most commonly FR4 for rigid, and polyimide for flexible. Silicon and glass are also evaluated as an integration method.

Another example of an interposer would be the adapter used to allow a SATA drive to work in a SAS environment. An interposer would allow a SATA drive to plug into a SAS backplane, providing pseudo path redundancy.