Note: Descriptions are shown in the official language in which they were submitted.
IMPROVEMENTS TO MEMORY CARDS
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This invention relates to portable memory cards
and more particularly to cards containing an electronic
circuit in the form of an integrated circuit eomprising a
memory and date processing circuitry.
It is known to use such cards as identification
or access control cards, credit or payment cards, or more
generally as transaction cards for keeping account of
banking or commercial operations. Hereinafter, the term
"memory card" will be used to refer to a card of the above
type, whatever its purpose may be.
In a memory card, the chip forming the electronic
circuit is embedded in an insulating plastic material
constituting the card proper with standardised dimensions.
The circuitry contained in the chip is provided with
eonduetors ending at contact terminals, external or
internal, for example as described in Canadian Patent
Application No. 365.505 filed by the present applicant on
the 26th November 1980, to enable this circuitry to be
electrically connected to a transfer apparatus for the
reading and/or writing of date in the card memory.
It can happen that, as a result of rubbing for
example, electrostatie eharges are indueed on the surfaee
and in the plastie material eonstituting the eard and that
these localised charges cause electrostatic potentials
which are dangerous not only in relation to the use of
data in the card, but also for the eleetronic circuit
itself which can be damaged, in particular if this cireuit
is fabrieated using the MOS semieonduetor technique.
Thus the invention has as its objeet a memory
eard of the type deseribed above in whieh there is
provision for avoiding the appearance and development of
sueh eleetrostatie potentials.
Aeeording to this invention there is provided a
portable memory card of the type eomprising an eleetronic
eireuit in the form of an integrated eireuit embedded in
an insulating plastie material, the said circuit having
eonduetors eoupled to eontaet terminals
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1 enabling the card to be electrically connected with a
data transfer apparatus, characterised in that it ~urther
comprises means for producing a conductive equipokential
region at least partly surrounding the said electronic circuit
and within which parasitic electrostatic charges tend to
distribute themselves equipotentially.
The said means for producing a conductive equip-
otential region around the electronic circuit can comprise
either a coating of plastic material containing conductive
material, or a screen formed by a conductive jacket embedded
in the plastic material of the card, or a combination of these
two arrangements.
The use of a material containing conductive material,
that is to say conductive in the mass, permits parasitic
electric charges to flow and distribute themselves equipotentially
thereby avoiding localised charges sufficiently large to affect
the integrated circuit in the card and perturb in particular
the data memory. Likewise, the use of a conductive jacket
also enables the formation of an equipotential region within
it~ protecting the circuit from the influence of static electric
charges.
Various memory cards in accordance with this ~-
inYention will now be described, by way of ex~mple, with
reference ~o the accompanying drawings, in which:-
Figure 1 shows schematically in longitudinal section
a first embodiment of a memory card, with
internal contac~ terminals,
Figure 2 shows a first embodiment of a memory card, -
with external contact terminals;
Figure 3 shows schematically another embodiment of
a memory card7with internal contact terminals;
Figure 4 shows a memory card as in the embodiment
3~ of Figure 3, but with external contact terminals;
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1 Figures 5 and 6 sho~s a memory card incorporating
both the arrangements of the
preceding embodiments; and
Figure 7 shows yet another embodiment of the invention.
Referring to Fig~ure 1, there is shown a memory card
10 in longitudinal section, in which an electronic circuit 11~
such as an integrated circuit in the form of a chip, connected
by conductors 12 to internal contact ter~inals 13, is coated
in a plastic material 14. This material 14 is for example
formed of polyurethane foam, or more generally of an anti-
static and electrically-conductiYe elastomer. The terminals
13 have been previously covered with a perforable plastic
material 15, as described in the aforementioned patent
application. The assembly of parts 11 to 15 is then embedded
or coated in a plastic meterial 16 which forms the actual card
10 of standardised dimensions. The material 14 produces around
the circuit 11 and its associated parts 12 and 13 a conductive
region to avoid localised accumulation of electrostatic charges
by facilitating the flow and equipotential distribution of
these charges.
The conductivity of the material 14 is chosen to
be sufficient to avoid such accumulation, but nonetheless to
be too low to cause a short-circuit between neighbouring
` 25 conductors or contact terminals for the Yoltages normally
used in the transfer apparatus enabl;ng processing of data
contained in the circuit 11. The resistivity of the material
14 is for example chosen to produce a resistance of the order
of 1 to 10 kilohms between neighbouring terminals.
Figure 2 shows a memory card of the same form as
that preceding, but with external contact terminals. In this
figure and those that follow, the same reference numerals
will be used to indicate corresponding parts. As in the
; 35 case of Figure 1, the circuit 11 with its contact terminals
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1 13 and their perforable covering 15 is first coated in the
conductive material 14, but such that this material is
flush with the level of the covering 15 of the terminals 13
and forms in plan a surface surrounding at the same time the
S circuit 11 and its terminals 13. This first assembly is then
partially embedded in the material 16 giving the card 10
its final form, while leaving the conductive material 14
free of an~ covering in the central part of the card in its
upper part.
Figure 3 shows another embodiment of memory card
in which an electrostatic screen is used to produce the
conductive equipotential region around the electronic circuit
of the card. The circuit 11 and its associated parts 12, 13
and 15 are placed within a conductive jacket 17 comprising
one or several thin foils of a good electrical conductivity
metal or of a metallised insulator, before being embedded
in the material 16 to form the card to its final size.
The conductive jackethas of ~ourse openings 18 formed over the
terminals 13 and perm~tting movable contacts of the transFer
apparatus to a pass through and come into contact with the
corresponding terminals of the card 10. The jacket 17 thus
produces around the circuit 11 and its associated parts a
conductive equipotential region acting as a Faraday cage and
protecting it from external parasitic electrostatic potent;als.
In Figure 4 there is shown a memory card with
surface contacts and formed in the same way as the precading
example, the upper part of the jacket 17 extending flush in
this case with the surface of the card 10.
Figure 5 shows a memory card with internal contacts
in which the arrangements of Figures 1 and 3 are used together,
that is to say in which the conductive material 14 is itself
enclosed in a conductive jacket 17 before being embedded in
the material 16, so as to augment thereby the protection against
external electrostatic charges.
Figure 6 shows a memory card with external contacts
having the double protective arrangement- of the preceding
figure.
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l Where the integrated circuit chip is mounted on a
flexible insulating film, commonly called TAB (tape automated
bonding), to which it is joined by conductors obtained by chem-
ical etching of metallisation deposited on this ~i~m, another
ihlplementation of the conductive jacket advantageously comprises
retaining the metallisation of the film in a zone surrounding
the chip and its conductors to form, on one of the faces o~
the circuit, part of the conductive jacket acting as electro-
static screen. Figure 7 shows schematically a plan view of
`this implementation. In this figure, the circuit ll is shown
joined by its conductors 12 to the terminals 13 which lie at
the edges of an opening 21 formed in a substrate consisting
of a flexible film 20, for example of polyamide material,
such as Kapton (trade mark) made by the firm du PDnt de Nemours.
The conductors 12 and the terminals 13 are formed, ;n known
manner, by an initial metallisation of the film 20 and by the
selective removal of this metallisation, for example by
chemical attack, according to the configuration of the
conductive tracks which it is desired to keep.
In using the present invention the initial
metallisation of the film 20 is further retained in a
zone 22 surrounding the terminals 13 and the opening 21
so that this auxilary metallisation 22 forms the first
part of the electrostatic 6creen on the upper surface of
the circuit ll. Preferably, the metallisation 22 is coupled
by a conductive track 25 to a voltage reference point, such
as the terminal 130 at zero volts. The second part of the
electrostatic screen on the lower surface of the circuit ll
can-be proYided either by an additional metallisation on
the other side 23 of the film 20 in a zone corresponding to
the zone 22, or by the application of a thin metallised
plastic foil 24. The two upper and lower metallisations
22 and 23 or 24 are connected together by a conductive link
26 extending through the film 20 such that both are connected
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1 to the same potential, for e~ample zero volts. It will be
understood that the assembly, having been metallised on both
sides, is then embedded in the plastic material making the
card into its final form as in the preceding examples.
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