When depots go bad!

Getting the chips out of the package (De-encapsulation) and preparing them for the microscope is in theory a pretty simple process. The chips are usually potted in a plastic compound that to remove requires soaking in hot acid. I use 70% Nitric acid heated to 100-110°C which is at or just below its boiling point. I am still fairly new to this and working on the optimum times, and best techniques for extracting the die. But basically I heat the acid up, plunk the package in and watch it fizz and turn brown for ~10 mins, take it off the heat to cool down, then decant the acid and you are left with a die that can be cleaned with acetone and ready for the microscope.

And then there was this….

It was an RFMD RF3448 which is a LNA (or PA I was not able to find a datasheet or any information.)  I am 99% sure this is a Gallium Arsenide (GaAs) chip.  When I tried to pick up the die with tweezers it appear to fold up and have no structure. Instead of a nice die photo I appear to have a piece of gold foil with some die attached that is crinkled up.  In fact that is exactly what it is – Gallium Arsenide is a poor thermal conductor, the transistors generate quite a significant amount of heat. To enable the heat to dissipate the die are thinned, extremely thinned, down to 100 μm or less.  In addition the chips often contain through-substrate vias (Basically holes through the die) that are coated with gold to conduct heat directly from the front metal to the die-backside.  So when the die are this thin they are pretty flexible like a piece of foil.

Not sure how I am going to successfully depot a very thin GaAs die with through substrate vias.  I will have to try and find a different technique.

This entry was posted in Die Photo and tagged , , . Bookmark the permalink.