As mentioned in TFA, the most important factor for successfully joining a metal and a glass is to match their thermal expansion coefficie...
As mentioned in TFA, the most important factor for successfully joining a metal and a glass is to match their thermal expansion coefficients. Most pure metals have a much greater thermal expansion than any glass, which will cause cracks. In the nineteenth century, the first successful joinings of metal with glass were done using platinum, but that is obviously too expensive for normal applications. Eventually a special alloy of iron-nickel-cobalt was developed, which is named kovar and whose thermal expansion is matched to that of a certain type of borosilicate glass. The use of kovar was widespread in electronics, starting with the vacuum tubes and gas tubes, and then continuing with the first generations of transistors and integrated circuits, which used metal packages. All the old transistors and operational amplifiers that were packaged in metal cans had pins and package bases made of kovar. When kovar had to be joined with a different kind of glass than the type with which it is matched in thermal expansion, that glass was coated in one or more layers of different kinds of glasses, with that matched to kovar in contact with the metal and the intermediate layers having intermediate thermal expansion coefficients, interpolating between the bulk glass and kovar. Kovar is not a good thermal or electrical conductor, which is why the modern power transistors that use plastic packages (e.g. TO-247) and copper bases and pins (which are plated with nickel or tin, to avoid corrosion) can easily dissipate much greater powers than the old transistors in TO-3 metal cans, which had the same size. On the other hand, the old transistors in metal packages were pretty much immune of environmental influences.
Posted by adrian_b on Jun 15, 2026, 4:34 PM
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Raise real-world problems, find people facing the same issue, and discuss solutions.2,000 issues0 comments
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Yeah, the plan is far too expensive for what it provides.
NewCrashed demand after one of the big AI labs (probably Anthropic because they focus way too hard on expensive frontier models) become inso...
New/dev/random is much too expensive for this.
Yeah, this always bugged me.
A year ago, I had the opinion that it'd be too expensive for developers to support offline mode, peer to peer, or community servers after...
The weird thing about this product is that its biggest competitor is "an old ipad." I feel like most of their target customer base alread...
There's a talk from Travis Kalanick recently on a podcast about this.
>nobody ever bought German cars for their low prices, except the Beetle Huh?
As mentioned in TFA, the most important factor for successfully joining a metal and a glass is to match their thermal expansion coefficie...
As mentioned in TFA, the most important factor for successfully joining a metal and a glass is to match their thermal expansion coefficients. Most pure metals have a much greater thermal expansion than any glass, which will cause cracks. In the nineteenth century, the first successful joinings of metal with glass were done using platinum, but that is obviously too expensive for normal applications. Eventually a special alloy of iron-nickel-cobalt was developed, which is named kovar and whose thermal expansion is matched to that of a certain type of borosilicate glass. The use of kovar was widespread in electronics, starting with the vacuum tubes and gas tubes, and then continuing with the first generations of transistors and integrated circuits, which used metal packages. All the old transistors and operational amplifiers that were packaged in metal cans had pins and package bases made of kovar. When kovar had to be joined with a different kind of glass than the type with which it is matched in thermal expansion, that glass was coated in one or more layers of different kinds of glasses, with that matched to kovar in contact with the metal and the intermediate layers having intermediate thermal expansion coefficients, interpolating between the bulk glass and kovar. Kovar is not a good thermal or electrical conductor, which is why the modern power transistors that use plastic packages (e.g. TO-247) and copper bases and pins (which are plated with nickel or tin, to avoid corrosion) can easily dissipate much greater powers than the old transistors in TO-3 metal cans, which had the same size. On the other hand, the old transistors in metal packages were pretty much immune of environmental influences.
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