Off-The-Top– is package architecture in which high-speed data signals are routed to the top of the package then taken directly to a flex cable transmission line – in some cases through a connector. Taking the high speed signals off the top eliminates the vias that would otherwise degrade the signal even before it left the package. The Off-The-Top transmission oath begins at the bond from the IC bonding pad and ends at the destination, which may be another IC, a connector, or any other component configured for a similar termination. Besides improved data transmission, Off-The-Top reduces package to PC board I/O count by the number of data lines taken from the top of the package, simplifies package substrate complexity and can reduce the number of routing layers required in the PC board.

 

Stairstep– is package architecture in which a stepped package is mated with a stepped PC board to create a direct interconnecting path through the PCB. Control signals are routed through the package substrate as before, but the Stairstep architecture routes the high-speed signals across the PCB on a direct path that includes no vias or stubs.

 

Stairstep is a viable either as a flip chip or wire bonded type packages. Stairstep designs can utilize more than one PCB layer for high-speed signals.