I don't think it is useful to think of absolutes here. Tamper proofing is something that is done in degrees. What is more useful is to think of the level of tampering that is possible, and the level of determination a user needs to show in order to reverse engineer your product. Is the tamper proofing supposed to stop against grade school kids, industrial spies, or nation states? The methods differ accordingly.
For instance, consider the simple blob. A gooey blob of plastic that sits atop ICs to help prevent identification and tampering. The blob will definitely keep an uniformed attacker, who is not very persistent at bay. He may even destroy a few ICs trying to deblob them. However, a reverse engineer supported by a company, or with sufficient spare time and expertise can remove it. Someone working for a nation state may have a custom tool for the job.
Likewise, an exploding box is certainly not going to be a popular home product, though it is supposedly tamper resistant. People manage to tamper with land mines you know? As others have said, this is an arms race.
People have even had good luck pulling ICs out of their packages and getting information that way. If your product has sensitive info in it, expect it to get x-rayed too, so add "lead box" to the parts list.
If you have infinite time and money, just make things as expensive as you can for the attacker. In that case, only the truly dedicated will try. There are no absolute guarantees.
One little asterisk to my opinion on this is that complexity in microelectronics is itself a hurdle to tempering with them on a finite level. As in, no, you will most likely not be able to physically tamper with the individual transistors of an Intel CPU (I mean with a physical implement, not be interacting with them electronically of course), nor will you be able to trivially reverse engineer them. There are equipment, and logistics hurdles, and the understanding of chips like that on a fine grain level is very complex.