Printed circuit board assembly (PCBA), starting with plated through hole, later evolve to surface mount assembly, have been planar in 2 dimension. Components are mounted onto PCBA in the x and y direction, where the height, z direction, is controlled by the component height.
On the assembly level, board to board and board to flexible printed circuit (FPC) are commonly used to interconnect two or more PCBAs together to create a three dimensional structure.
On the PCB level, we will look at several techniques aimed at reducing the number of components mounted on the surface.
On the PCBA level, certain 3D assembly techniques have been developed to address reduction in board available space or reduction in overall assembly thickness. These techniques include Package-on-Package (PoP) and Cavity assembly.
As the PCBA started with a two dimension assembly using one single FR4 rigid PCB, where plated thru hole and surface mount components are placed in the x and y direction, various methods are in use to interconnect multiple PCBAs together to create a three dimension assembly.
Board to Board (B2B) level connectors are the most common. These include connectors using PTH or SMT. Some examples are daughter board mounted onto a motherboard, high speed/high density connection between backplane and functional cards, etc. B2B connections create a rigid three dimensional assembly structure where PCBA orientation has to follow the x, y, and z axis. It was difficult to interconnect PCBAs at various angles at will. PCBAs can either stack on top of each other, or be connected at 90 degrees to each other. The connector, whether PTH or SMT, also takes up valuable board surface area in today’s high density application.