2FUNDAMENTALS OF ELECTRICAL TESTING 1. What Is Electrical Testing? 2. Why Is Electrical Testing Necessary? 3. Anatomy of System-Level Electrical Testing 4. Fundamentals of Electrical Tests
3WHAT IS ELECTRICAL TESTING? A systematic process involves testing at every step to guarantee the functionality and performance of the component before it is committed to the next step and ultimately to the final product.
5WHY IS ELECTRICAL TESTING NECESSARY? When faulty chips pass an improperly designed test, they can cause system failures and enormous difficulty in system debugging.Debugging cost increases by about tenfold from chip level to board level, and also from board level to system level.Thus, it is of great importance to detect faults as early as possible.
6COST OF TESTINGAll these combined make for a lot of testing and associated cost. This figure illustrates the product development cycle and approximate distribution of total cost.Design-for-testTest developmentProduct testingThese all testing phases can constitute as much as 45% of the total cost.
7Fault Types and ModelsPhysical Defects can cause Electrical and Logical Faults:Physical Defects include:Defects in silicon substratePhotolithographic defectsMask contamination and scratchesProcess variations and abnormalitiesOxide defects
8Electrical and Logical Faults Electrical FaultsLogical FaultsShorts (bridging faults)OpensTransistors stuck-on, stuck-openResistive shorts and opensExcessive change in threshold voltageExcessive steady-state currentsLogical stuck-at-0 or stuck-at-1Slower transition (delay faults)AND-bridging, OR-bridging
12FUNDAMENTALS OF ELECTRICAL TESTS A system-under-test placed within a controlled environment that may include interactions and interfaces with other units.The response is one or more output electronic signals or simply a ‘‘pass/fail ’’indication.If the measured response matches the expected response (within an allowed margin of error) then the circuit ‘‘passes ’’the test.
16One possible SSF is characterized by the output of gate 1 being stuck-at logic zero (s-a-0).The fault is activated by applying a logic 1 at the inputs of gate 1.The only direct observation point is at the output of gate 4, the fault effect must be propagated through that gate. This is done by ‘‘sensitizing ’’a path through gate4, in this case by applying logic zeros to its other inputs.One way to accomplish that is to set (D,E,F,G) (0,0,1,0). So the input test pattern for this fault is (A,B,C,D,E,F,G) (1,0,1,0,0,1,0) and the OUTPUT 1 in the fault-free case, or OUTPUT 0 if the fault exists.