We seem to maybe have a bit of disconnect here.
The CPU in a Cube is not directly on the logic board. It is rather on a "daughter card" that is attached via a 300 pin connector and held down by 3 screws in stand-offs. The card actually has the same dimensions and the same connector as many other G4 towers-the Sawtooth, Gigabit Ethernet, Digital Audio, and Quicksilver(although the QS stock cards have a 4th screw post that supplies an additional +12V to the card). This daughter card is about the size of small note pad, or maybe a couple of credit cards put together.
The CPU itself is only a small part of the CPU daughter card. The "package" it's mounted on is about 2"x2"(probably a bit smaller), while the actual silicon CPU is a few millimeters wide and a bit over a centimeter tall. The package is attached to the daughtercard via ball grid array(BGA) soldering, which means that there are a few hundred solder "balls" holding it in place and making electrical connections to the rest of the daughter card.
Some folks who frequent this forum-mainly the two that I've mentioned-have done a fair bit of work upgrading CPUs on daughter cards(or on logic boards where the CPU is on the board-that's no the case on Cubes). I'm GROSSLY oversimplifying the procedure, but basically they use either hot air or a hot place to heat the old CPU and lift it off, clean up the attachment site, and then use a similar procedure to solder the new one back in place.
This is ONLY possible when replacing CPUs that are "pin compatible." Some PowerPC 750 CPUs(G3s) can be replaced with 7400s(G4s). 7447As can sometimes be replaced with 7448s(which are in many cases a better CPU than the 7447A). There are probably other examples, but those are the only ones I know of.
If all you have is a bare BGA 7447A(i.e. a chip with BGA pads on the bottom) you are out of luck on fitting it to your Cube as is. If it's on a daughtercard, it MIGHT work in the Cube, but it might only work in other roomier G4 towers with better thermal management.
If it's a bare BGA chip, I'd discourage you from throwing it away as someone who does BGA work may be able to make use of it. If it's actually a 1.67ghz CPU(i.e the top of the CPU carries that marking in the silicone) it could probably be used as a nice, stable upgrade for something like a late iMac G4.
7447A based upgrades-again-are complete daughter cards with a 7447A CPU on them. They pop up for sale on Ebay, but make ABSOLUTELY sure that the one you're buying is compatible with Cubes. I suggest sticking with Sonnet for the fewest headaches, and avoid Gigadesigns at all costs(I have one Gigadesigns CPU that's made its rounds on this forum-I'm at least the 3rd owner on here-and I finally have it running stably, but not at its rated clock speed-it was sold to me inexpensive after the previous owner fought with it for a few years, and I managed to make a big improvement by lapping and polishing the heatsink). Expect to pay $100 or better for one.
BTW, I have an 800mhz Sonnet in one of my Cubes that was given to me by a member on here. It's actually quite a nice little CPU. It's 7450 based, not 7447A, and has L3 cache which makes it peppier than the clock speed would make you think. I mostly run it in OS 9, but it runs Leopard decently well, especially with a Geforce 3 GPU. That CPU uses the stock Cube heat spreader plate and heatsink assembly rather than its own heatsink, although I have a base fan in it(all my Cubes-even the stock 450mhz, have a base fan).
