Electrical Testing

Question 1

What electrical tests are carried out on the wafer?

Answer 1

The bare wafer is tested to measure its sheet resistance. This is used to ensure that the wafer is doped uniformly.

Question 2

What is parametric testing? Where is it carried out?

Answer 2

Testing for measurable elements such as thickness, width, resistivity, etc. These tests are carried out on test structures that are deposited on the scribe line (the space between die that is later cut).

Question 3

What tests do the die undergo during wafer sort?

Answer 3

During the sorting process, each die undergoes electrical tests to ensure that only known good die move on to packaging.

Question 4

What are the “class” tests?

Answer 4

The final tests of the device after packaging. While the die have already been tested, this tests for failures within the packaging.

Question 5

When is electrical testing carried out?

Answer 5

1. Before fabrication (on the wafer)
2. During fabrication
3. After fabrication - wafer sort
4. After packaging - class

Question 6

What is burn-in?

Answer 6

After assembly and packaging, the chips are exposed to harsh conditions (high temperature, voltage) in order to cause accelerated failure. This eliminates the chips that would fail early on.