Much of the Gold Value will be Under the Chip

Much of the gold value will be under the chip, if it's attached with gold/silicon solder. I believe the solder makeup is 96Au/4Si. About the only thing that will dissolve it is true hot aqua regia.The acid can only dissolve the solder starting at the edges of the chip. It can literally take take days for the hot acid to completely undermine a large chip.

The main reason for breaking up the CPU is to break up the chip. This provides much more chip edge area for the acid to penetrate. It will still go slow. When the gold is gone, you'll be able to slide the pieces around on the pad.

We used to speed this up on all-gold side braze packages by heating the part up to the melting point of the solder, on a heating block, and removing the chip with a vacuum probe. A sharp pointed knife, like an Z-Acto will work. We then put chip and package in the aqua regia.I think the solder melts around 700-800 F. There are several possible sources of gold on these parts. The percentages are educated guesses and only apply to all-gold parts - gold in every category below.

High value: 60%

- Gold(80%)/Tin(20%) eutectic braze used to attach the gold plated metal lid to the ring

- Gold(~96%)/Silicon(~4%) eutectic braze used to attach the chip to the pad

Medium value: 30%

- Gold plating on the legs

- Gold plating on the metal lid

Medium Low value: 10%

- Gold plating on the inside fingers

- Gold plating on the inside pad - the flat square area where the chip is is mounted

- Gold plating on the bottom of the chip

- Gold plating on the ring where the lid is attached

Very Low value: 2%

- Pure gold bonding wires going from the chip to the fingers - about a mile (1 mil dia.), or two (.7 mil dia.), of wire to the troy oz. This figures out to $.005 to $.01 per inch of wire.