boundary scan

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boundary scan

This technology should be discussed as early as the product design stage, because it needs special components to perform this task. In the UUT based on digital circuits, devices with IEEE 1194 (boundary scan) support can be purchased, so that most diagnostic problems can be solved with little or no detection. Boundary scan will reduce the overall functionality of UUT, because it will increase the area of each compatible device (add 4-5 pins and some lines to each chip), so the principle of selecting this technology is that the cost should be able to improve the diagnosis results. It should be remembered that boundary scan can be used to program flash memory and PLD devices on UUT, which further increases the reason for choosing this test method.

How to deal with a limited design?

If the UUT design has been completed and determined, the options are limited. Of course, you can also ask for modification in the next revision or new product, but process improvement always takes a certain time, and you still have to deal with it.

The main idea here is how many tests you can do. It may be enough according to the expected fault type, but if it is not enough, a delicate balance is usually needed between more expensive test systems, and a more accurate detection method is selected after balancing the product sales cost (COGs) of UUT with the marginal profit. So the answer is that there is no simple answer.

The best reference for future design is the completion of function test when it is limited. When faced with these limitations, you should record the tests that can be completed within the specified time range of production line speed, as well as the number of testers on the production line. Time limit is very important, because it is impossible to let the production yield give way to you, so your job is to sacrifice test coverage for time, so you will ask for improvement so that these restrictions can be lifted in the future!