Vacuum Tube Contamination Warning
It has been brought to our attention that a certain number of assembled pc boards have been subject to accidental contamination with vacuum tubes. It is not known at this time if the tubes are original manufacturer devices from the 1950's or reproductions recently imported from Russia. (Ref: US DOCpet0820-492.45gh.99ac138). Clearly, however the suspect vacuum tubes are not wanted and were not specifed in the original electronic design.
As shown in the photograph in the left, vacuum tubes are glass envelopes with metal plates, grids and filaments. While mostly harmless on their own, when connected to an electronic circuit, such devices have been found to consume valuable coulombs that are needed in other areas of the electronic circuit.
The contamination tends to be more extreme and more prevalent with circuits that utilize compact packages such as 0201s, Micro BGAs and QFN parts. The US Department of Commerce has estimated that upwards of 82.3% of all circuits that utilize CSP (chip scale package) devices have some level of vacuum tube contamination. Further, it is not believed that these vacuum tubes are fully RoHS compliant.
In most cases, the contamination is clearly visible and quite easy to identify. However, in some of the more extreme infestations, you may need to dim the room lights and look for glowing filaments, as seen in the photo below.
Mitigation: If you do find that your pc boards contain unwanted vacuum tubes, remediation involves a simple three step process. Fortunately, vacuum tubes tend to utilize sockets rather than thru-hole or surface mount solder. Step one, is to remove power from the circuit. Step two is to wait five minutes to allow the glass envelopes to cool. Step three is to carefully grasp the glass envelope and pull up to remove it from the circuit board.
Sorry. Couldn't resist the april fools tradition. :-)