Good Quality Comes From Good Design for Test

Adrian Cheong
Agilent Technologies
Singapore

Product quality can be improved through proper application of design for test (DFT) strategies. With today's shrinking product sizes and increasing functionality, it is difficult to get good test coverage of loaded printed circuit boards due to the loss of test access. Advances in test techniques, such as boundary scan, help to recover this loss of test coverage. However, many of these test techniques need to be designed into the product to be effective.

This paper will discuss how to maximize the benefits of boundary scan test, including specific examples of how designers should select the right component, connect multiple boundary scan components in chains, add test access to the boundary scan TAP ports, etc. A discussion of DFT guidelines for PCB layout designers is also included. Finally, this paper will include a description of some advanced test methods used in in-circuit tests, such as vectorless test and special probing methods, which are implemented to improve test coverage on printed circuit boards with limited test access.

Advanced test methods such as boundary scan, vectorless testing or special probing methods, derived from test innovations are constantly being developed to overcome the issues with implementing proper testing on today's products. However, the products need to be designed specifically for the implementation of these advanced test methods. Design engineers should think ahead about how the product is to be tested. Collaboration between R&D and test is crucial to ensure that products are tested adequately in mass production so that there is enough confidence in their quality before they are shipped customers. This is how good product quality comes from good design for test strategies.