WARNING: These methods are destructive, meaning, your chip will not function after you uncap it or remove its die. If you want to still use the chip after uncapping, consider using reactive etching or acid jet etching, this can be done by various failure analysis labs for a reasonable fee.
HEALTH WARNING: Some chip packages may contain materials which are toxic. One example is beryllium oxide which is sometimes found in RF power products. It is a good idea to take measures to minimize exposure such as dust mask/respirator, lab coat and gloves. (Thanks for the reminder Bill.)
So if the chip won’t work afterward, why do this at all? Integrated circuits are very hard to design properly, so many people put substantial effort into doing layout, mask and process engineering. With this in mind, one rationale for uncapping chips is to look at the artwork that is otherwise concealed inside the package. For students who are interested in IC design, looking at dies can provide some insight into already proven designs. There is also some excitement in finding various easter eggs that the designers put in the masks. Finally, for simple enough chips, it is sometimes fun to see how the device works from a gate/transistor level.
Ceramic Dual Inline Packages – These packages are characterized by two ceramic plates that are held together by an adhesive, typically epoxy. The pins usually protrude from between the two plates and bend downward, complying with the DIP spacing standard. Although there are chemical means to attack the adhesive, they are time consuming due to limited surface area. The easiest way to get to the die is by brute force: with a chisel and hammer. One easy method is to put the chip in a vice and put a chisel directly between the two plates and then tap it a few times. With luck, the top will fly off and all that remains is to blow the debris off with compressed air and the die is open to examination.
Ported Packages – These packages can be either quad or dual inline packages, however, their characteristic is a metal plate in the center of the package covering the port hole. On most DIP packages, removing the cover will uncover the top of the die. The quad packages are more tricky, if the metal pad is intended to conduct heat, it is probably connected to the back substrate of the integrated circuit. The easiest way to remove this is to use a heat gun to melt the solder that holds the plate on and then gently lift it up with some tweezers. Since the packages are generally hermetically sealed, care must be taken not to scratch the die when you initially force the cover off to let some air in.
Metal Can Packages - Some chips, particularly op amps, are still packaged in metal can enclosures to minimize noise. There are some less obvious performance benefits, but those are for another post. The easiest way to open these devices is to use a specially designed can opener that presses the outside metal against the hard inner ceramic cylinder which holds the chip. The other way is to put the chip in a vice, being careful not to crush the can, and sawing most of the way around the can with a hand saw and then bending the top of the can back. The resulting image is very similar to the cover of the 1997 edition of Microelectronic Circuits by Sedra and Smith.
Plastic Packages – Although most common, these are the least straightforward to cleanly uncap. The first, and easiest method, is to heat the package with the heat gun until the epoxy that holds the package together becomes brittle and the package can be picked apart by tweezers. The downsides are that the fumes from this process are not very good for you and that the success rate really depends on how the top of the die is interfaced to the plastic mold. An AD711 that I opened had something that looked like hot glue between the top of the die and the rest of the chip which made it easy to remove (the die is on the microscope slide in the collective picture). Another logic gate that I uncapped by this method refused to come clean and cracked slightly.
WARNING: This last section deals with sulfuric acid. This MUST be performed by someone who know how to handle such a substance in an appropriate lab setting or the results may be catastrophic. Please use common sense when handling this material, and if you don’t know how to do something, ask someone who does. I am not responsible for any accidents that occur.
Another way to remove the plastic package from the chip is to melt it with a strong acid that is particularly effective at destroying organic compounds. The acid of choice in this case is sulfuric acid and the organic compounds are the resins in the chip packaging. Nitric acid can also be used, but it is harder to come by. First, I tried to use a pair of modern ICs, one from Analog Devices and one from National Semiconductor to see how well the process worked. I put the chips in a Pyrex dish, filled it with the acid and then put it on a hot plate set to about 80C. The increased temperature increased the acid’s activity and thereby effectiveness. After about twenty minutes, I noticed that chips showed some sign of disintegration, however, I didn’t want to sit all night by the fume hood to get a result. I decided to cheat and used a logic circuit from the early 90′s which I knew was fabricated with a weaker plastic case. The package of this chip melted in about ten minutes exposing the bare die. To put things in perspective, shaking the chip dry and then dipping it into a beaker of water brought the water pH down to 1.6, so a base was slowly added to neutralize the acid in the water. The chips were then rinsed in deionized water and put out for display. A final note, latex and thin nitrile gloves will not protect you from sulfuric acid. The only reason in this case to wear them is that they will promptly discolor when brought in contact with the acid, so you know that you touched it and hopefully give you enough time to take them off before the acid eats through.