Early Design Review of Boundary Scan To Enhancing Testability

Sivakumar Vijayakumar - Keysight Technologies

With complexities of PCB design scaling and manufacturing processes adopting to environmentally friendly practices raise challenges in ensuring structural quality of PCBs. This makes it essential to have a good 'Design for Test' (DFT) to ensure a robust structural test.

A good structural test implementation starts right at the design of an ASIC wherein, the system application and, the ASIC design itself should be kept in mind for implementing the features to enable testability.
Answers to the below four questions are the essence of the first part of this paper.

What are the aspects to be considered for enhancing 'DFT'?
How effectively can the 'DFT' be reviewed?
Is there an intelligent and automated way of doing this?
At which phase of Product Life Cycle should the DFT review be done, to obtain best value for structural test?

During the course of the DFT review, can we realize a good test strategy for the PCBA? How can the test strategy of the PCBA be partitioned as to what portions of the design can be covered structurally and what is covered functionally, in a way that provides best diagnostics to discover faults? Answers to the above two questions will be addressed in the second part of this paper.

A good overall DFT enables identifying defects early in the process. You do not want to find these defects to percolate into customer base. A good DFT equips for a comprehensive testability. This maximizes defect detection and in reducing NTF bone pile. The rework on the defects to fix happens in lesser strikes. All of these help in reducing the scrap cost which will add back to savings as an ROI. After adopting this scheme as a well-oiled machinery, the RMA logistics costs will come down. The brand equity will rise.