Assume that, you are a college student. Your teacher handles the class for a specific subject.  During the course, the teacher gives the materials for the respective subject. During the class, the teacher may conduct the test. The teacher will compare the answers of the students with the correct one. The objective of the class test is to evaluate the students’ performance based on the class test. Quality of class test is good than effectiveness in the evaluation also it depends upon the quality of the subject content. If any student may fail the test, he/she need to take the subject again to improve the knowledge on the specific subject. Retest may be conducted to check the quality of those students.

Testing of an integrated circuit: A certain procedure is needed to be followed to check the performance of an IC after the fabrication. If the performance of the IC is not good, then the IC has to be redesign until it meets the performance. 

Think that you are going to prepare your own dish. First, you collect all the relevant material that is required for the dish. Then add the ingredients one by one while cooking. In the end, you test the quality of your food. If it meets your customer’s expectations you supply it into the market. Otherwise, you need to modify your dish with a different ingredient. Customers may give some suggestions to add a new ingredient or increase or decrease some specific ingredients. Again, you need to modify the dish. Here dish is nothing but your experiments on a certain design. Ingredients are nothing but an IC ie. if the quality of an IC is good, the design becomes successful.  So the IC has to be tested before starting the experiment.

How to test an IC? What to test? That we will see in the next session.

An IC needs some inputs to test its function. For example, to test an OR gate we need one of the inputs should be logic 1 and the other may be any of the two logic states. These logic inputs are applied at the input pin of an OR gate IC to check whether the OR gate is working properly or not. Like the OR gate, we need to apply different combinations of input to check the functionality of an IC. These input combinations are also called test patterns or test vectors.

During the IC laboratory session, your lab instructor may use an IC Tester, to test the small ICs. Is the instructor test the Microprocessor / ARM Processor/ Microcontroller? Probably the answer is No. Then how to test this processor or controller IC’s. Why IC tester doesn’t play its roll here. The reason is the IC tester can test only small IC’s. i.e. IC tester can able to test the IC with a minimal number of inputs.

If the microprocessor or controller has more number of inputs IC tester may not be effective to test its functions. In this case, this type of IC can be tested with Automatic test equipment (ATE). Figure1 shows the ATE of g systems.  ATE testing usually happened on the industry side. An ATE can store the test patterns of IC to be tested in its memory. From the memory, test vectors are applied to the IC to check its performance.  Tessolve semiconductor is the leading industry in India in the field of testing. This industry is known well for analog design and test, SOC testing, Digital testing, and Embedded design and test.

On what basis this ATE decide the performance of an IC? or What is the purpose of test patterns?

During the manufacturing of an IC, faults may occur. It may be a misalignment of mask layer or faults in the silicon wafer side or during the metallization process. There are many causes for the appearance of the faults. This fault has to be detected at an earlier stage mainly before selling in the market. Otherwise, it may lead to the design of a faulty product. So, testing the IC is necessary before it reaches the market.

The cost of an IC is directly dependent on the cost of testing an IC. Faults may occur at any stage of IC design. Consider the food scenario again. You are preparing for food. You forget to add one important ingredient. What will you do? You have to restart your preparation. A similar type of problem may occur at any stage of preparation. If you found the problem at the final stage, the cost of ingredients, cost of time everything is worthless. Similarly, the fault has been created at any stage of design. Detecting the fault at the earlier stage is very much crucial.

While doing experiments or projects, the designer has to be very careful about their logic for their work. IC’s plays a major role in logic. So, IC has to be tested before starting the experiments.