CASE System

Californium Assessment for Single event Effects

The spontaneous fissioning ²⁵²Cf sources used have typical activities of 1 - 2 µCi (40-50kBq) with the following properties :

• Half-life of 2.645 years
• Decays by alpha emission (96.9%) to ²⁴⁸Cm or spontaneous fission (3.1%)
• An average of 3.7 neutrons per fission with an average energy of 2.3MeV.
• 1 µCi emits 4.4e³ neutrons/second.
• Cf-252 has a very high specific activity (ie 1 gram equals 20TBq (537Ci)).
• At 1m a 1 µCi source produces a dose equivalent of 23.3 µSv/hr (n's)& 1.6 µSv/hr (γ's).
• The average Linear Energy Transfer (LET) of the fission products is 43 MeV/(mg/cm² ).

To increase the fission product fluence at the device under test (DUT) the device itself needs to be decapsulated and the CASE system operated in an evacuated bell jar. As memory density and processor complexity increases more and more metallisation layers are being used which makes it more difficult for the fission products to penetrate through to the sensitive volume. As the CASE system is a low rate pre-test facility that cannot be focussed onto particular regions of interest on the chip studies are now being carried out into the use of laser-based test systems. These laser-based systems will be able to map the chip topography and will not carry with them the inherent radiation hazards associated with the partially-sealed Cf-252 sources.

 

^{The ESTEC CASE System}

^{Common Parameters :}

• ^{Bell jar :27cm diameter base, 20 cm high (+ 10 cm radius dome)
  hence maximum board size 18 X 18 cms (including any plugs & sockets)
  board should have feet of at least 5cm to allow for cabling.
  boards should sit horizontal and NOT mounted vertically.}
• ^{Standard connectors :
  BNC bulkhead vacuum connectors (socket to socket)
  FMC} 
• ^{All plates have the provision to place the source adjust rod at the centre or mid-point or edge of the bell-jar.}
• ^{Source holder : from height adjust rod to source centre : 8 cms.
  (Rod diameter approx 1 cm - ie hole in DUT board must be at least 1cm if the device is more than 8 cms from the edge of the board)}