Gold cap IC

[Nemo]

I have always had this question, but couldn't really get a good answer searching about it on the Google.

Does anyone know why these old/MIL-SPEC ICs came with gold-plated (I suppose it's plated, since it'd be ridiculously expensive to use pure gold) caps? I can somewhat understand the gold pins, but gold cap doesn't make any sense to me.

Is there any specific reason to this? or is it solely for aesthetics?

(Please refer to the attached image, for some reason the forum editor image function isn't working)

[han]

to prevent corrosion, that can affect chip wafer below..
maybe....

[Nemo]

to prevent corrosion, that can affect chip wafer below..
maybe....

I suppose oxidation could be a reason, but then why didn't they use zinc plating (galvanising) instead? or just aluminum. I think those would have been cheaper than heavily gold plating the cap.

[Psi]

Does anyone know why these old/MIL-SPEC ICs came with gold-plated (I suppose it's plated, since it'd be ridiculously expensive to use pure gold)

Yep, lots of electronics is gold plated, it's only 1000 atoms thick or so.

[han]

I search the gold plating is for radiation protection (see Radiation hardening) and  MIL-SPEC IC is not cheap, so gold plating is not increasing the price significantly, they use gold in bond wire afterall

[deth502]

I search the gold plating is for radiation protection (see Radiation hardening) and  MIL-SPEC IC is not cheap, so gold plating is not increasing the price significantly, they use gold in bond wire afterall

i would guess for some kind of shielding purposes myself.

military contracts go to the lowest bidder, so i can guarantee you that its not there for looks.

[free_electron]

The gold flash is because of the sealing process used. You dont want too many metals in the mix.
A silver particle paste is stenciled on the rim, the lid is placed on top of that and the part is sent through the oven. The silver solders the lid on the cavity. If done correctly this creates a hermetic seal
The cavity is gassed out during rampup and the actual soldering happens under pure nitrogen atmosphere.

[amyk]

I search the gold plating is for radiation protection (see Radiation hardening) and  MIL-SPEC IC is not cheap, so gold plating is not increasing the price significantly, they use gold in bond wire afterall

Gold is not any good at radiation shielding.

[BravoV]

So the gold basically to ensure long term mechanical integrity of the metal lid from getting corroded thru time, since the chamber is pressurized ?

[han]

my bad...

The gold only protect from UV and IR radiation...

http://info.goldavenue.com/Info_site/in_glos/in_glos_foil.html

[N2IXK]

The base metal is Kovar or similar alloy chosen for a similar coefficient of thermal expansion as the ceramic package. The gold plating is to enhance conductivity, aid solderability, and protect the Kovar from corrosion.