Thermomechanical
Use of a heated package combined with sanding techniques. Heating makes the package soft. Some success with using a Dremel to rapidly remove the top layer until chip was just showing. Major issues have been scratching of the die due to particulates. It may be possible to mitigate this issue by switching to a finer grinder or by pouring a high temperature liquid (mineral oil?) for lubrication.
Procedure
Under development
Notes
Advantages
Disadvantages
Thermomechanical + nitric aicd
This technique takes advantage of the following:
The layers above a die can be effectively removed by sanding
The layers below a die can be effectively removed by heating the glue onto the carrier island and pulling up pins
The remaining die with minimal epoxy can be finished off with nitric acid (best results)
Procedure
Heat chip
Using rotary tool (Dremel), sand down until bond wires are present.
Should be able to be done in a few minutes
Sanding down until the die is visible is possible, but if will be followed with nitric bath anyway, is not worth the risk
Squirting with fluid or using magnification may help to show the bond wire
Pull up external leads towards the ground surface. This should deteriorate the top layer and leave the die on a small island in the middle
If package cracks during this, should not be a problem
Combination of glue on carrier island to die being soft from heat and missing epoxy around die should allow die to separate from package with minimal epoxy attached
Turn off heat
Use nitric acid techniques to finish off the sample
Notes
Advantages
Low chemical use
Quick turnaround time
Fairly reliable
Disadvantages
Not suitable for live analysis
Still requires caustic chemicals
Multiple areas for failure
Risk of sanding down too far and damaging die
Risk of cracking die during package breakup
