Ceramic non gold cap

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Yes just remove the caps.
The cap is just a way to support heat exchange from the chip inside.
I have heard the solders or brazing possibly may have some low percent of silver.
Personally have never chased after it though.
 
Snip off some piece and dissolve it. Then test with stannous. As it was said, there can be some silver present, but I do not expect much. These solders can contain indium, but that is whole another league to chase, process and then sell.
 
Slochteren said:
Yes these have gold bondwires, hard to see at the pictureView attachment 63972
Click to expand...

Very nice, thank you! I would definitely check that braze for gold content also. Not so sure about silver though. Usually chip braze is a gold/silicon or gold/tin alloy. I forget which was used for what purpose, attaching lid, die, or pins. If I remember correctly, GoldSilverPro used to say that even if the braze didn’t look gold colored it might still be gold bearing.

I had some of those Fujitsu PGA chips around. I’ll have to see if I still do or if I did something with them already? I’m pretty sure I’ve got some of the 40 pin DIP ones at least.
 
FYI, I found the below which is part of an old post by GSP. Although he was talking about ceramic DIP packages with gold plated caps, the materials used would be the same for a PGA package. The only question is whether a different braze might have been used for attaching non-gold plated caps?

GSP:
“On a sealed package, like that one, about 60%, or maybe more, of the value is in the 2 different gold brazes, neither of which looks much like gold. The 80%Au/20Sn, under the lid, is a pasty dark gray color, especially when heated in air, and the 96Au/4Si braze is a very light yellow color. Don't figure you have all the gold unless the chip is free to slide around. This only occurs after all the gold braze under the chip has been dissolved with aqua regia.‬”
 
macfixer01 said:
FYI, I found the below which is part of an old post by GSP. Although he was talking about ceramic DIP packages with gold plated caps, the materials used would be the same for a PGA package. The only question is whether a different braze might have been used for attaching non-gold plated caps?

GSP:
“On a sealed package, like that one, about 60%, or maybe more, of the value is in the 2 different gold brazes, neither of which looks much like gold. The 80%Au/20Sn, under the lid, is a pasty dark gray color, especially when heated in air, and the 96Au/4Si braze is a very light yellow color. Don't figure you have all the gold unless the chip is free to slide around. This only occurs after all the gold braze under the chip has been dissolved with aqua regia.‬”
Click to expand...
I completely forgot about this... You are right. Worth to check. Dip-tin covered lids could be previously plated as well. I experienced this a lot in the past when working with old "eastern block" "dip-tinned" metal-cap DIP ceramic IC´s. Even the top of the lid was "silver" in colour, it contained nice gold underneath.

Still don´t know why they dip-tinned the lid, if it was once gold plated...
 
I was reading about why gold is used, when I had assumed that any conductive metal could provide RF interference protection. The crux of it is that gold apparently stays very highly conductive at very high frequencies. This finally makes sense to me about why this lid, which is not obviously connected to anything on the chip, is often gold plated.

No clue why to cover it with tin. Would gold layer dissolve into the tin, like how we understand ENIG plating to dissolve into the solder? Seems like that would defeat the purpose, if the purpose is to have a layer of gold for preventing RF interference.
 

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