DFT means Design for testability, where logic will be implemented or inserted in the core design at RTL stage(Now a days most of the company prefer at RTL stage) or Netlist stage. This test circuit verifies that core design does not have manufacturing defects focusing on circuit structure rather than functional behavior.
Manufacturing defects may include
- Short circuits
- Open interconnects
- Power and ground shorts
Manufacturing defects remain undetected by functional testing and these can cause undesirable behaviour during circuit operation. DFT helps to find the manufactured defects and improves the quality, yield of products.
Now you may wonder what is the use of Functional testing.Functional testing verifies your circuit performs .For example assume that your design is an Half adder circuit , Functional test verifies that circuit performs the addition operation and computes the correct results over the range of patterns