[time-nuts] beryllium oxide

[Bruce Griffiths]

Robert Atkinson wrote:
> I've personally seen three applications of BeO in electronics. Two, including the most common, are a possible hazzard.
> The most common application is RF power devices (transistors and terminating resistors). These hace a "washer" or slab of BeO between the semiconductor device and the mounting stud or flange. Asthis is trypically below the electrical connecting leads (often wide strips or tabs), application of excessive force between heatsink and PCB can fracture the BeO causing dust an chips/splinters. Splinters onder the skin or in the eye can cause problems as well as inhaled dust. force can be applied during manufacture / service or in an accident or if the item containing the unit is crushed. Next most common is the use in metal can semiconductors. One example are early LM78Hxx TO3 regulators. These are fairly safe as the can has to be ruptured. The third is as a block of solid BeO bonded to metal plates used to insulate conduction cooled vacuum tubes. Some power tubesmay use it internally. A big problem is that it looks like any other ceramic. In some UK equipment
>  devices containing BeO will be marked with "cornflower blue" paint dot. A non-electronic application is in some (eg argon-ion) lasers.
> on a side note some vacuum tubes (especially cold cathode types) contain various radioactive materials.
>
> Robert G8RPI.
>
>
> --- On Fri, 16/1/09, Mike S <mikes at flatsurface.com> wrote:
>
>   
>> From: Mike S <mikes at flatsurface.com>
>> Subject: Re: [time-nuts] beryllium oxide
>> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
>> Date: Friday, 16 January, 2009, 6:28 PM
>> At 12:45 PM 1/16/2009, Lux, James P wrote...
>>     
>>> More realistically, the dangeris dust when something is
>>>       
>> physically 
>>     
>>> overstressed (dropped, mounting overtightened, thermal
>>>       
>> shock). That, 
>>     
>>> and if it gets ground up in trash disposal... Say
>>>       
>> someone throws it in 
>>     
>>> the shredder.
>>>       
>> So, if some electronics have an IC with a BeO package, and
>> it sits 
>> undisturbed, what's the problem? It seems to me that
>> most, if not all, 
>> such uses would be additionally contained by heatsinks and
>> compound, 
>> since it's the thermal conductivity properties which
>> caused it to be 
>> used in the first place.
>>
>> Hard to say how much dust might be produced by dropping or 
>> overtightening. In my experience, ceramics tend to break
>> pretty 
>> cleanly. Maybe BeO is different.
>>
>> Granted, the manufacturer can be expected to be biased, but
>> Brush 
>> Ceramics claims "Beryllium oxide (BeO), in solid form
>> and as contained 
>> in finished products, presents no special health
>> risks." They also 
>> claim "Under federal regulations and most state
>> regulations, BeO 
>> ceramic or products containing BeO
>> ceramics that are no longer recyclable and declared solid
>> wastes are 
>> not classified as hazardous waste due the content of BeO
>> ceramic." 
>>
>>
>>     
The OCXO in question doesn't have the usual foam insulation that is
easily removed, but has cast in place insulation of somewhat higher density.
Its impossible to remove without cutting or dissolving, and there is no
easy way to know if beryllia powder was used selectively as a thermal
conduction enhancement additive rather than beryllia sheets were used
internally within semiconductor packages or as thermally conductive
washers. I have no data on the pin connections or any other specs.

It appears to be a General Radio 1158-4010 with 7 teflon insulated
feedthrough insulators.

Bruce