Trelic’s picture of the week 1/2018

What can you see here?


This is one of our test structures. You can see a ceramic substrate and a large silicon chip, attached with die attach adhesive and wire bonds. In this case we designed both the chip and the substrate by ourselves to optimize the test structure for the purposes of the project.  Testing the reliability of a whole product is often rather complicated and it can be difficult to analyse the failure mechanisms and to separate the effects of the different parts of a product. Therefore, various test structures can be used to simplify the product and to ensure reliable testing. With a well-designed test structure, only selected issues can be tested, and failures are easier to locate and analyse than from a whole product.

In this test structure the large silicon chip is attached onto the substrate using a die attach adhesive. The adhesive attaches the chip to the right location on the substrate, but it also has another important task: heat dissipation. Getting rid of the excessive heat can be especially important when such a large chip is used.

The electrical connection between the chip and the substrate in this test structure is managed with wire bonds. In this test structure two different wire lengths were used to study how the length affected the reliability of the interconnections. Wire bonds are very commonly used in electronics, even though they can have reliability issues. Thin wires are easily damaged leading to failures. Consequently, wire bonds are typically protected from mechanical shocks by protecting them with polymer materials such as dam + fill materials and glop-tops.

But boy those wires are pretty!