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SIM cards in mobile phones can survive heat at up to
450 degrees Celsius (356 degrees Fahrenheit) and possibly beyond, a
finding that should help probes into terror attacks and other
crimes, scientists said on Wednesday.
The subscriber identity module (SIM)
card is the heart of a mobile phone, providing a record of numbers
received, numbers dialled and text messages.
So the fingernail-sized slice of
plastic and silicon can be a goldmine for detectives, provided they
get their hands on intact data.
For instance, investigations into
the March 11, 2004 Madrid train bombings, in which 191 people were
killed, made a breakthrough thanks to SIM cards recovered from
phones that were intended to trigger two unexploded bombs.
In an unusual investigation,
electronic engineers Benjamin Jones and Tony Kenyon from University
College London subjected SIM cards to trial by heat.
They collected 12 cards,
currently or recently in use, from members of the public in Britain,
Ireland and Sweden.
Using acid, the researchers
gently stripped the protective epoxy moulding surrounding each chip
in order to expose its circuitry.
The cards were then placed in
heated air for 10 minutes, were allowed to cool and the researchers
then sought to recover data by attaching tiny probes to the circuit
and reading its contents via an interface pad.
Six cards were heated to around
180 C (356 F) and could be read after rewiring with no loss of data.
Five were cooked to 450 C (842
F). Four of them could not be read by the researchers, but the fifth
one could, briefly.
The 12th card, heated to a
searing 650 C (1,202 F), could not be read.
Jones and Kenyon say the
experiment proves that SIM cards can survive to 450 C (842 F) -- and
quite possibly beyond that.
They point out that the rewiring
technique they used is not even the last resort for forensic experts
who want to delve into a damaged SIM card.
Other hi-tech data-reading
methods include probing the external connections to a processor and
monitoring power consumption during operation and using a so-called
electrical scanning probe microscope to read the electrical charge
at key "gates" in the SIM circuitry.
In addition, SIM cards may
survive for much longer in a blaze if they are close to the floor or
on a desk, for previous research has shown temperatures in a
building fire vary greatly according to the location, they say.
"A chip that has been
exposed to such temperatures may also be mechanically damaged, and
the data may not be retrieved by simple probing or rewiring. But the
data itself remains uncompromised and can possibly be read using
other techniques," say Jones and Kenyon.
Their paper appears in the latest
issue of the journal Forensic Science International.
 --AFP
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