IC Failure Analysis: Case Studies in Success

The benefits of failure analysis may not be immediately apparent to some critics. It may seem pointless to invest time and money in developing technologies that are inherently broken and won’t be sold to consumers. Failure analysis is most useful, though, when it can find patterns that could lead to more failures, which would cost a business a lot of money and hurt its reputation with customers. Here are two device case studies that both have several abnormal electrical openings. Even though both devices did similar things when they broke, the reasons why they broke were very different. To find these causes, we had to do a detailed IC failure analysis, which led us to find big problems with the processes in both cases.

Device A is a high-speed switching part that is used in high-speed communication systems. Using flip-chip connection technology, the gadget glues the die to its ceramic substrate, which is made to handle thermal stress. The company that made the device, Wile E. Coyote Microelectronics (hereafter WEC Micro), got a lot of complaints from customers who said the device stopped working as soon as they put it in their goods. WEC Micro discovered that electrical failures were the root cause of the failures and sent a sample of these defective products to an outside lab for failure analysis. The outside lab did a number of non-destructive tests on the broken units, such as x-ray and acoustic microscopy, which is what is recommended. Through acoustic microscopy, it was found that there was more than 75% delamination at the first subsurface interface between the device die and the underfill material that was used to fill the gap between the die and the ceramic substrate. An x-ray showed that some of the flip-chip solder joints between the die and the ceramic substrate were broken or missing. Using the information from non-destructive testing, the analyst decided to cross-section the device in place without taking the die off of its substrate. The problem could be seen in the cross-section. It looked like the die bump solder had melted again after processing and seeped into the area where the die surface and underfill material had separated. This wicking process didn’t leave enough solder for the die and substrate to make a good connection. WEC Micro evaluated the findings of the investigation and came to the conclusion that their procedure needed to be altered to prevent this kind of delamination, or else they would encounter several further failures.

Read more: IC Failure Analysis Lab Flow – Defects From A to Z

Real Genius Integrated Circuits or RGIC, created Device B, a microcontroller that manages a high-power laser system. A plastic-encapsulated ball grid array or pBGA, is used to package the device using conventional gold wire bond connection techniques. In the device’s initial production testing, RGIC noticed unusual behavior and asked for a failure study to identify the underlying cause of the issue. Early non-destructive testing and visual inspection did not detect any evident flaws; however, electrical testing identified electrical openings on a number of signal pins. The analyst concluded that the failure was probably somewhere on the die because the non-destructive testing had not revealed any issues with the device’s packaging. To get rid of the plastic covering the device’s surface, the gadget was decapsulated. The analyst used an electron microscope to do passive voltage contrast imaging and discovered many metal traces that were “glowing,” possibly representing open circuit spots. Cross-sectioning these locations revealed vias between metal layers that had been poorly treated, resulting in an open circuit. Once RGIC found out what went wrong, they were able to change their process and stop the strange behavior in future production runs.

Electrical openings were the same failure mode in both of these case studies. The true reason for these device failures, however, was entirely different, with one device failing because of a packing flaw and the other because of incorrect die processing. This case makes IC failure analysis even more important because the real reason why both of these devices failed would not have been found without a full investigation. This would have stopped the manufacturers from streamlining their production and bringing a reliable, usable product to market.

Video 01: Integrated Circuit Failure Analysis Lab