Page "Joint Test Action Group" Paragraph 2

JTAG was an industry group formed in 1985 to develop a method to test populated circuit boards after manufacture.

At the time, multi-layer boards and non-lead-frame ICs were becoming standard and connections were being made between ICs which were not available to probes.

The majority of manufacturing and field faults in circuit boards were due to solder joints on the boards, imperfections in board connections, or the bonds and bond wires from IC pads to pin lead frames.

JTAG was meant to provide a pins-out view from one IC pad to another so all these faults could be discovered.