PCB Yield Example

A product contains 10 PCBs, and a goal of 95% turn on yield was 3et for each PCB at in-circuit test (ICT). The product final test turn-on yield will be as follows:

A turn-on yield of 61% is disappointing, especially when 95% in-circuit PCB yield could be difficult to achieve. To achieve a 95% final product turn-on, what should the PCB ICT test goal be?

When a final test DPU of 95% is required for a product of 10 PCBs, the individual PCB ICT yield goals should be set at 99.5%.

It can be seen that the test yield for each component making the final product has to increase substantially in order to increase the turn on yield of a large electronic product. The manufacturing process has to increase its quality level in order to match increased product complexity. Several methodologies and tools can be used for each part of the PCB assembly process. These steps do not necessarily require the use of more sophisticated inspection methods and equipment, but simple problem solving techniques such as:

• Incoming electronic component quality can be improved with better supplier certification and supplier process control methods.

 PCB assembly process quality can be enhanced with better employee training, the use of more automation such as autoinsertion through hole (TH) and auto placement of SMT components, and improving the design guidelines of PCBs. Design guidelines might include standards for component polarity indicators, component placement and orientation in one axis, pad, hole and line geometry, and graphic placement aids.

• Soldering quality can be improved by continuously upgrading soldering materials and processes with the latest technology available, and performing design of experiment (DoE) techniques to optimally meet the soldering process parameters.