The process of PCBA functional testing involves creating a simulated operating environment (excitation and load) for the PCBA board to test its various design states and to obtain parameters for each state to verify the board’s function. Essentially, a suitable stimulus is loaded onto the PCBA board, and the response of the output terminal is measured to ensure it meets requirements. There are two methods of PCBA functional testing: wired testing and wireless testing.
Wired test fixtures have been the industry standard, providing an economical approach for lower probe count PCBAs or prototypes to avoid non-engineering (NRE) costs. However, wired fixtures can face challenges as the signal frequency increases, leading to issues like crosstalk and coupling due to wire routing.
To address the limitations of wired test fixtures, engineers developed wireless test fixtures. In wireless fixtures, a multi-layer PCB called a transition board (T-board) replaces the set of signal wires on the underside of a wired probe card. Automatic PCB design software is used to route circuit traces when changing wires. Wireless fixtures offer increased reliability, as the PCB designer can precisely control how each trace is routed, which helps isolate troublesome signals. They also provide consistent electrical parameters and reduce ground and crosstalk noise, making the signal bounce faster, which is particularly important in low voltage test applications.