TO package capping technique

[blueskull]

I'was born in 1992, and I've never lived in the age where metal cans are commonly used to house transistors.
That being said, I am interested to know how a TO package is capped.
I tried to search, but I didn't find much information.

To my understanding, the GTMS is only used on pin feedthrough, but not cap sealing.
Soldering is an apparent option, but is there a way that I can get around with that? My design houses an MCM in a TO can, not just a single chip, and the MCM is soldered with SAC305, so I will risk reflowing the internal if I globally solder the cap.
Laser soldering or welding is out my reach, so let's put that aside.

Is there a low temperature GTMS process that is below 217C, or is there some other ways to seal the cap?
Stud welding or epoxy sealing are appealing, but I need hermetic seals.

Another way I can think of is to use Nanofoil, but to cut that thing to a continuous ring shape without a Q switched laser is a challenge.

[T3sl4co1l]

I thought those were always welded.  That is, a spot welder with probably a bit more current than usual, and a hollow ring shaped electrode.  I'd read that weld spatter was an early reliability problem, so it needs to be done a little more carefully than ordinary fabrication welding would do.

The height of the "coin" would help block spatter.  Also, TO-39s are welded, and I think they can have an emboss or coin on the base, for the same benefits?

A blob of silicone goo, encapsulating the chip, would also help.

This explains the popularity of steel bodies over aluminum or copper, though aluminum was fairly common too (I want to say Motorola used them a lot?).  Aluminum can be spot welded, but doing it without overheating the chip would be a bit more challenging.

I suppose you can't get Pb90 or the like for the MCM?

As to speculation... what is this, challenging APEX at their own game?  Shouldn't be hard to compete if you get even modest production quantities.

Tim

[floobydust]

The TO can is also used for high speed optical use, so GTMS would be used on the cap with the lens.
It can be stamped, shelled or soldered.
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