Patente US5107078 - Electric connection or disconnection element, integrated circuit including ...

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ELECTRIC CONNECTION OR DISCONNECTION ELEMENT, INTEGRATED CIRCUIT INCLUDING SUCH ELEMENTS AND THE CORRESPONDING CONNECTION OR DISCONNECTION METHOD 5

FIELD OF THE INVENTION

The invention concerns an electric connection or disconnection element, as well as an integrated circuit 10 including such elements and a method for connecting or disconnecting these elements.

BACKGROUND OF THE INVENTION

More particularly, the invention concerns the irre- 15 versible electric connection or disconnection between two conductive tracks laid on an integrated circuit support. Up until now, the most commonly used techniques to establish a disconnection consist of cutting a conductive link between the tracks by means of the 20 energy of a laser (flash) and, so as to establish additional connections, consist of locally depositing a conductive material by using a mask (anti-flash).

SUMMARY OF THE INVENTION 25

The invention renders it much easier to carry out electric connections and disconnections. It uses the surface tension properties of certain materials in their liquid state, such as indium, generally used to set up connections and disconnections. 30

The electric disconnection between two conductive tracks laid on an integrated circuit support includes two surfaces able to be wetted by an electric conductive material heated to its liquid state, each surface being laid on one track, as well as a connection disk extending 35 between the tracks and, at two extreme and opposing zones, on the wettable surfaces, the disk being made from the conductive material.

The connection element includes on each track a surface able to be wetted by an electric conductive material brought to its liquid state, as well as one disk made from the conductive material, the disks each including one extreme zone on one of the wettable surfaces and extending from this extreme zone in a direc- 4J tion opposite the other wettable surface.

These elements are used by virtue of two complementary aspects of a given phenomenon, but the disconnection or connection method with the aid of these elements is identical: it consists of melting the disks by Jq heating them and of then allowing them to cool and solidify.

BRIEF DESCRIPTION OF THE DRAWINGS

There now follows a more detailed description of the 55 invention with the aid of the following accompanying figures, given by way of illustration and being in no way restrictive:

FIGS. 1 and 2 represent a side view and a top view of a disconnection element; 60

FIG. 3 represents the same element after disconnection;

FIGS. 4 and 5 represent a top view of a connection element;

FIG. 6 represents the same element after connection; 65 FIG. 7 represents a device with integrated circuits and provided with connection and disconnection elements;

FIG. 8 represents the final state of a repair of the device of FIG. 7; FIG. 9 represents another larger device; and FIGS. 10 and 11 represent two stages of a method to repair the device of FIG. 9.

DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS

FIGS. 1 and 2 show two electric conductive tracks 1 and 2 on a support 3 able to carry one or more integrated circuits. The tracks 1 and 2 end face-to-face and are provided at their extremity with a gold film 4 and S. One indium disk 6 connects the two tracks 1 and 2 by extending them; the two extremities of the disk 6 rest on the films 4 and 5. The upper face of the disk 6 opposite the support 3 is flat.

The disk 6 has been obtained, for example, by depositing with a mask. FIG. 2 shows a rectangular disk 6, but it is possible to use disks with other shapes.

So as to cease the electric connection established by the disk 6 between the tracks 1 and 2, it merely suffices to heat the disk 6 until it has melted. In its liquid state, the surface tension forces modify the shape of the disk 6. As gold is a wettable material for the indium, it can be observed that the droplet obtained by melting the disk 6 tends to spread over the films 4 and 5. The droplet thus expands, its material moving slightly towards the left of the film 4 located on the left and towards the right of the film 5 located to the right on the drawing. A contraction of the droplet finishes by being produced, then is totally separated and finally (FIG. 3) two indium balls 7 and 8 are obtained respectively centered on the films

4 and 5 and in the shape of truncated spheres at the location of these films 4 and 5. The connection between the tracks 1 and 2 is definitively broken.

The support 3 is left to cool; the balls 7 and 8 solidify without changing shape.

The support 3 and the films 4 and S are found on the tracks 1 and 2, as shown on FIGS. 4 and 5. The connection element is composed of two separate plain indium disks 9 and 10 each having one extremity section respectively 11 and 12 disposed on the film 4 or 5, and one additional section, respectively 13 and 14, adjacent to the extremity section 11 or 12 and extending from the latter in a direction opposite the other film, respectively

5 and 4.

So as to establish the electric connection between the tracks 1 and 2, the disks 9 and 10 are heated until they melt. The freed surface tension forces rearrange the material of the disks 9 and 10 into two truncated balls 15 and 16 (FIG. 6) similar to those of FIG. 3, but in this instance their volumes are sufficiently large so that they join together. The modification of the surface tension forces resulting from this joining leads to coalescence of the two balls 15 and 16 into a single droplet 17 which thus now unites the tracks 1 and 2 and provides an electric connection. As in the case with the disconnection element, the droplet 17 is then left to cool and solidify.

The use of such connection and disconnection elements is possible on a large device bearing the elementary integrated circuits to be interconnected, such as aligned memories and where there is a need to verify the integrated circuits one after the other so as to replace them when they are found to be defective.

The large device includes (FIG. 7) on a support 19 integrated circuits 20 connected to connection lines 22. Interconnection lines 21 extend between the integrated

3 4

circuits 20 and their extremities end close to the extrem- situated above the connection elements 43, but the wetides of the connection lines 22 so that the interconnec- table surface pads 49 and 50 of the repair circuit 47 are tion lines 21 lengthen the connection lines 22. spaced further apart than the wettable surfaces 4 and 5

Connection elements 23, similar to those of FIGS. 3 on the interconnection line 41 and the connection line

and 4, are laid on the extremities of the interconnection 5 42 and extend above sections of the disks 9 and 10 laid

21 and connection 22 lines, which thus correspond to at the side of the lines 41 and 42.

the tracks 1 and 2 of these figures. In addition, the con- The connections required to put the device into ser

nection lines 22 are provided with an element 23 for vice are obtained by means of a single stage for heating

connection to the integrated circuit 20, a verification the entire device, which causes the disks of the connec

block 24 and a welding block 25. 10 tion elements 43 to melt. The droplets thus produced

Upon start up, the integrated circuits 20 are thus freeiy recover and undergo coalescence when they are

separated and verification consists of placing the termi- not overhung by a repair circuit 47: the phenomenon nals of a measuring device on the verification blocks 24 described here is pictured on FIG. 6 and which thus

and of testing the integrated circuits 20 one after the results m connecting the integrated circuits 40 in repair

other. The connection elements 23, which have not 15 t0 the interconnection lines 41. But the situation is dif

been melted, prevent electnc interference by the inter- ferent for the connection elements 43 below the repair

connection lines 21. circuits 47: the droplets are intercepted by the wettable

The defective integratedI circuits 20 need to be re- surface ds 49 ^ ^ of the ^ circuit „msomas

placed by repair circuits 27 provided with wettable they recover and spread over them. When solidification

surface pads 28 disposed so as to be opposite the weld- 20 {wo baUs ^ M) 5, an(J „ m ... ^

m^_ocs ,. „, ,. ^ it_ , . . . being slanted opposite the other, the first one 51 con

The connection lines 22 leading to the defective mte- Jr • . »• r 1+ * i

. j • ->n r *i + *i. i . nectmg an interconnection line 41 to a connection line

grated circuits 20 are firstly cut with the laser so as to „ , . f. , , . .. ..

f *i. Ij- ui i -ie Tu 53 laid below the repair circuit 47 and in contact with

separate them from the welding blocks 25. The cutting .. .. ,„ i_ iL , , „

■ • ,„„ t. „f„„_ „„ ex/- n -n,„„ tu i« the wettable surface 49, whereas the second ball 52

zone is given the reference 26 on FIG. 7. Then the 25 ^ ^. ,. .„ , ,

wettable surface pads 28 of the separation circuits 27 are ^ L ?v ♦"'u, J J5".?6 ^T"

aligned on the welding blocks 25 and then, by heating device » to wettable surface pads 50, which is

the device, the indium disks are melted covering the electrically isolated from the rest of the repair circuit

welding blocks 25 which thus wetten the surfaces of * .

pads 28 and, after having solidified, establish a mechani- 30 TMe connection elements 43 may also be used as

cal and electric connection of the repair circuits 27 to weldm« elements in this embodiment; the balls 52 not

the support 19 and to the connection lines 22. The repair havinS anv electnc connection role are nevertheless

circuit 27 covers the elementary circuit 20 without useful m strengthening the mechanical linking of the

being in contact with the latter, as shown on FIG. 8. rePmr circuits 47 on the support 39.

During the same overall heating operation, the connec- 35 °f course, the invention may also be extended to all

tion elements 23 reclose, thus joining the correct inte- the materials having similar properties already used in

grated circuits 20 and the repair circuits 27 between tn,s technique,

them via the interconnection lines 21. What is claimed is:

Another device bearing integrated circuits is shown 1 Process for putting into service a device comprison FIG. 9 and has been designed so as to allow for 40 m8: a substrate; a plurality of integrated circuits placed easier implementation and repair operations. The sup- on said substrate; a plurality of electrical connecting port is given the reference 39, the integrated circuits the lines placed on said substrate and respectively connectreference 40, the interconnection lines the reference 41 mS integrated circuits; first pads wettable by a and the connection lines the reference 42; as in the pre- soldering material, said first pads being arranged in ceding device, the interconnection lines 41 each extend 45 Pairs, the pads of each pair being respectively located between two integrated circuits 40 but without reach- on adjacent portions of two different electrical connecting them, but here the connection lines 42 each extend mg lines; a plurality of flat ingots of said soldering matefrom one integrated circuit 40 parallel to one associated rial, each of said ingots respectively covering one of interconnection line 41 and close to this line 41. The said first pads of said pairs and extending substantially connection elements, referenced here by 43 and estab- 50 away from the other first pad of the same pair, said lished both on one interconnection line 41 and one con- process comprising the steps of probing said integrated nection line 42, thus have disks 9 and 10 extending from circuits to find among them deficient circuits; placing the films 4 and 5 perpendicular to said lines 41 and 42. In repair circuits above said deficient circuits, said repair addition, the interconnection lines 41 are provided with circuits comprising second electrical connecting lines verification blocks 44 at each of their extremities and 55 and second pads wettable by said soldering material, similarly each connection line 42 is ended by one verifi- each second pad extending respectively above one of cation block 46. said first pads; heating said substrate so that said ingots

During a preliminary stage for putting the device into of each of said first pads of a pair melt and become

service, the verification blocks 44 and 46 make it possi- droplets that coalesce either with one of said second

ble to respectively control the continuity of the inter- 60 pads or with the other said first pad of the same pair; connection lines 41 and the sound and proper state of and allowing said substrate to cool down and the drop

the integrated circuits 40. As for the preceding device, lets to solidify.

the incorrect integrated circuits 40 are replaced by 2. Process according to claim 1, wherein said second

repair circuits 47 placed above them, but the disposition pads are arranged in second pairs, the pads of each of

of the welding zones is different. As can be seen on 65 said second pairs being spaced further apart than said

FIG. 10, the lower face of the repair circuits 47 is pro- first pads of said pair below said second pair,

vided with pairs of wettable surface pads 49 and 50 * » » » *

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Electric connection or disconnection element, integrated circuit including ...