Integrated circuit protected by a resin

(54) Integrated circuit protected by a resin.

@ Applicant (s): ELECTRONIQUE SERGE DASSAULT, Société anonyme. - FR.

(72) Inventor (s): Richard Besson; Gérard Lecuyer.

(73) Holder (s) (74) Agent (s): Cabinet Netter.

(57) An integrated circuit forming a logic controller comprises in a box 1 a chip 2 comprising a processing unit and a programmable memory and security bits or fuses. A window 3 allows the erasure of the memory by ultraviolet. The location of this window 3 is covered with an opaque resin, possibly provided with a charge of dispersed conductive particles.

FR 2 608 317

D

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Integrated circuit protected by a resin.

The invention relates to computer security.

Computer systems may be required to contain protected or even highly protected data. This is data which is necessary for the functioning of the IT system, but the knowledge of which by unauthorized users could create serious damage.

A simple example is that of financial transactions. 10 We can cite as protected data the law of correspondence making it possible to establish a confidential code from more general identification data of the holder, or else this confidential code itself.

We now encounter the following difficulty: these computer systems are becoming widely used; the risk that protected data is intercepted is all the more serious.

It has been proposed to use monolithic circuits called logic controllers. These circuits include, in a housing, a microchip or chip comprising a processing unit and a programmable memory.

25 During production, the data can be entered into the programmable memory. One or more bits are also provided in the integrated circuit, also called fuses, the breakdown of which then prohibits the reading of the programmable memory from outside the integrated circuit. Only the processing unit then has access to the programmable memory.

For technological reasons, these integrated circuits forming a logic controller have a window allowing

10 notably the erasure of the programmable memory by ultraviolet. Once it has been erased, the programmable memory can then be entered or rewritten with the data it must contain. These are not only the protected data, but also other information and programs intended for the operation of the processing unit. This erase window gives access not only to the programmable memory itself, but also to the rest of the chip or chip. It follows that one thus sees all the elements of this chip.

The Applicant has noted that it is then possible to selectively attack the safety bits or fuses mentioned above. This done, it will be possible to bypass the protection of the programmable memory by these safety bits or fuses. That is to say, we recover access to the programmable memory, and thereby to the protected data stored therein.

The main object of the present invention is to provide a solution to this problem.

According to the invention, the location allowing the action on the programmable memory, which is generally an uncovered location such as a window for erasing the programmable memory by ultraviolet, is covered with an opaque resin. This resin is advantageously chosen and placed in such a way that its removal results in damage to the integrated circuit.

Very advantageously, the resin is placed after removal of the window transparent to ultraviolet light, or more generally to other electromagnetic radiation.

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compatible with chip materials.

According to another aspect of the invention, the resin is, at least in part, charged with dispersed conductive particles.

According to another aspect of the invention, the resin comprises a filler which makes it opaque to X-rays.

Other characteristics and advantages of the invention will appear on examining the detailed description below,

25 and attached drawings, in which:

- Figure IA is a top view of a logic controller integrated circuit of known type;

30- Figure IB is a side view, in partial cutaway, of the circuit of Figure 1; and

- Figures 2A and 2B are respectively a top view and a side view of a circuit equipped according to the invention.

The housing 1 of the integrated circuit is provided with output connection lugs 5. The chip located inside the housing is shown in 2. This chip includes, for a logic controller, a processing unit, a programmable memory, various auxiliaries, and interconnections therebetween.

Among the auxiliaries are the elements defining the security bit or bits.

A N o diagram of this chip is given here, and we do not donlOnera not more detail on the provision of security bits. The reasons will be obvious to those skilled in the art.

It suffices simply to recall that the Applicant has been able to determine, for such integrated circuits, how to bypass the protection that the security bits are supposed to provide to prohibit the reading of the programmable memory from outside the integrated circuit.

We recognize in Figure IB at 6 an extra thickness in which is housed the window 3 which allows the erasure of the programmable memory by ultraviolet.

The invention provides, in principle, for removing the extra thickness 6 where this window 3 is housed. The removal can be done mechanically (chiselling or grinding of the welded edges) or in a more advanced manner (ultrasonic desoldering, by example).

After that, a resin 4 is injected inside the housing (for example using a syringe -microdispenser- manually or automatically) which will overflow widely until it covers the entire cavity containing the puce 2. Some integrated circuits do not have such an additional thickness 6, but only the window 3. The means can be applied in the same way by mechanically removing the window 3 (grinding or drilling for example) and by injecting the resin into the cavity thus opened.

The resin used can for example be the epoxy resin HYSOL ES 4228 available from HYSOL but the person skilled in the art will easily determine other resins which can be used and which are compatible with contact on a monolithic integrated circuit chip.

The polymerization of the resin takes place in an oven, according to the manufacturer's specifications.

Advantageously, the resin '4 is loaded with conductive particles, at least in its upper part located at the level where the excess thickness 6 was, that is to say at some distance from the chip 2 itself, to avoid short -circuit it.

Such a conductive charge makes it possible to avoid inspection of the chip 2 using X-rays, or other efficient investigation techniques. But one can also use for this purpose other means than the insertion of the conductive charges dispersed inside the resin

4.

Thus, it is conceivable, in particular, to place in the resin coating 4 an X-ray screen, possibly carrying electrical connections and / or chips or other dummy circuit elements.

The invention applies in particular, but not limited to, in the following case: protection of a system of electronic payment terminals, including any concentrators and especially their confidential code composition boxes, against investigations tending to search for protected data, as defined above.