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Long ago it was used as a heat sink compound in (among other things) power transistors. It was very good at it's job. Unfortunately, it is horribly toxic. Is it still used anywhere an EE might come across it unaware?

Glorfindel
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Dirk Bruere
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    By unaware you mean when someone has peeled of the "warning, contains toxic material" sticker? – PlasmaHH Jul 14 '17 at 13:40
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    I believe it is used as ceramic insulating material in a lot of applications. As a ceramic it is not hazardous, but machining it would produce hazardous dust. –  Jul 14 '17 at 14:13
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    @PlasmaHH Old transistors with BeO had no warning stickers – Dirk Bruere Jul 14 '17 at 14:13
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    @DirkBruere: I don't know how it is in your country, but here BeO must be labeled for at least 30 years, so probably most of the time of its commercial use. But since you make that remark, is your question more "can I still stumble over 50 year old transistors" and the answer is obviously yes, nobody went around collecting them all because they are bad. – PlasmaHH Jul 14 '17 at 14:20
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    @CharlesCowie: already breaking that ceramic will produce hazardous dust, hence the requirement to label it properly in most places. – PlasmaHH Jul 14 '17 at 14:20

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Yes, it's still used in Apex's range of high voltage amplifier ICs - still a current and popular line of chips for driving, among other things, piezoelectric transducers. For example, the PA95; its datasheet says:

The exposed substrate contains beryllia (BeO). Do not crush, machine, or subject to temperatures in excess of 850°C to avoid generating toxic fumes.

These chips can drive large currents at high voltages and therefore need great cooling capability. I guess BeO is just too good a heat conductor to replace, despite its toxicity.

Sean
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    As with anything, the PA95 datasheet specifications and the price has a proportional OMG factor. – Dejvid_no1 Aug 08 '17 at 21:11
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    @Dejvid_no1 Tell me about it. I had to buy some for a project and found a few of the batch (bought from a well known but non-approved supplier) were dead on arrival. I heard from a colleague who had spoken to an Apex representative who had said that it is common to find old, broken Apex chips onto which fraudsters have soldered new pins and sandblasted to pass off as new. I guess the £100+/unit cost is quite attractive to those wishing to make a quick buck! – Sean Aug 08 '17 at 21:46
  • they're good though. I had to build some test gear with very compact 70V line amps back about 1999. I used pairs of Apex power opamps in bridge mode. They took some real punishment that year and AFAIK are still going strong 20 years later. – danmcb Sep 28 '21 at 07:57
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You can buy resistors with BeO substrates (Johanson). Not a single warning about the toxicity of BeO in the datasheet!

Bas
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