Claims

1. A method of manufacturing a backplane electronic card (20) having an internal face (142) adapted to be connected to connectors (13) of electronic cards (12) and an external face (143) adapted to be connected. connected to an external connector (15), a series of first blind holes (146) opening out on the one hand on the internal face (142) of the backplane electronic card (20) and a series of second blind holes (148 ) opening out on the one hand on the external face (143) of the backplane electronic card (20), the backplane electronic card (20) comprising:

- a first printed circuit (21) having a first face and a second face intended to form the internal face (142) of the backplane electronic card (20);

- a second printed circuit (22) having a first face and a second face intended to form the outer face (143) of the backplane electronic card (20) and;

- a third printed circuit (23) having a first face (231) facing the first face of the first printed circuit (21) and a second face (232) facing the first face of the second printed circuit (22), the third printed circuit (23) constituting an electrical insulator between its first face (231) and its second face (232);

said first blind holes (146) passing through the first printed circuit (21) but not passing through the third printed circuit (23) and said second blind holes (148) passing through the second printed circuit (22) but not passing through the third printed circuit

(23);

characterized in that the method comprises the following steps:

- deposition on the first face of the third printed circuit (23) of a first bonding layer (31), said first bonding layer (31) having first areas (41) free of material distributed on the first face (231) of the third printed circuit (23), and depositing a second bonding layer (32) on the second face (232) of the third printed circuit (23), said second bonding layer (32) having second areas (42) free of material distributed on the second face (232) of the third printed circuit (23);

- assembly on the first adhesive layer of the first face of the first printed circuit (21), said first printed circuit (21) having a series of first through holes (146 ') intended to form the first blind holes (146), each first through-hole (146 ') opening into a first zone free of material from the first adhesive layer (31) on the first face (231) of the third printed circuit (23) to form the first blind holes (146), and assembly on the second bonding layer of the first face of the second printed circuit (22), said second printed circuit (22) having a series of second through holes (148 ') for forming the second blind holes (148), each second hole through (148 ') opening into a second zone (42) free of material from the second adhesive layer (32) on the second face (232) of the third printed circuit (23) to form the second blind holes (148).

2. The method of claim 1, wherein a first through hole (146 ') has a diameter, and a first area free of material into which opens said first through hole (146') has a diameter greater than the diameter of the first through hole. (146 ') of at least 100 mhi; and wherein a second through-hole (148 ') has a diameter, and a second area clear of material into which emerges said second through-hole (148') has a diameter greater than the diameter of the second through-hole (148 ') of at least minus 100 pm.

3. Method according to any one of the preceding claims, in which the bonding material comprises a fabric impregnated with uncured resin.

4. The method of claim 3, wherein the resin has a dynamic viscosity greater than 5000 poises between 80 ° C and 180 ° C.

5. Method according to any one of the preceding claims, wherein the first bonding layer (31) has the first areas (41) released from material before it is deposited on the first face (231) of the third printed circuit (23) and / or the second bonding layer (32) has the second areas (42) free of material before it is deposited on the second face (232) of the third printed circuit (23).

6. Method according to any one of the preceding claims, wherein the third printed circuit (23) comprises first conductive pads (35) distributed on the first face, the first adhesive layer (31) being arranged on the first face ( 231) of the third printed circuit (23) so that the first conductive pads (35) are located in first areas (41) free of material from the first adhesive layer (31), and that said first conductive pads (35) face after assembly to premiers through holes (146 ’) of the first printed circuit (21) to form the bottom of the first blind holes (146) of the internal face (142) of the backplane electronic board (20); and / or the third printed circuit (23) comprises second conductive pads (36) distributed on the second face (232), the second adhesive layer being arranged on the second face of the third printed circuit (23) of the third printed circuit ( 23) so that the second conductive pads (36) are located in second areas (42) free of material from the second bonding layer (32), and that the second conductive pads (36) face after assembly to second through holes (148 ') of the second printed circuit (22) to form the bottom of the second blind holes (148) of the external face (143) of the backplane electronic board (20).

7. The method of claim 6, wherein the conductive pads (35, 36) have a central recess (37, 38) facing the through holes (146 ', 148 ") of the first printed circuit (21) and / or the second printed circuit (22) intended to form the blind holes (146, 148).

8. Method according to one of claims 6 or 7, wherein the conductive pads (35, 36) result from the prior etching of a conductive layer of the third printed circuit (23).

9. A method according to any preceding claim, wherein the first through holes (146 ') and / or second through holes (148') for forming the blind holes (146, 148) have a metallic coating (46). , 48) of their walls having a first flange (461, 481) extending over the first faces (211, 221) of the first and second printed circuits (21, 22).

10. Method according to any one of the preceding claims, wherein the assembly on the first bonding layer (31) of the first face (211) of the first printed circuit (21) comprises a positioning of the first face of the first printed circuit (21) on the first adhesive layer (31) with the first through holes (146 ') intended to form the blind holes (146, 148) facing the first zones (41) free of material, and a pressing the first printed circuit (21) on the first adhesive layer (31) with heating to a temperature between 140 and 200 ° C; and / or the assembly on the second adhesive layer (32) of the first face (221) of the second printed circuit (22) comprises a positioning of the first face (221) of the second printed circuit (22) on the second adhesive layer (32) with the second through holes (148 ') intended to form the blind holes (146, 148) facing second areas (42) free of material, and a pressing of the second printed circuit (22) on the second bonding layer (32) with heating to a temperature between 140 and 200 ° C.

The field of the invention is that of electronic computers and in particular computers for on-board systems in avionics. More specifically, the invention relates to the method of manufacturing a backplane electronic card for a computer for on-board systems in avionics.

STATE OF THE ART

In modern airplanes, it is known practice to interconnect the piloting and / or control modules of functional components of the airplane through one or more main buses of the airplane. These buses are currently buses specific to the field of aviation, and in particular buses using distributed serial bus protocols of ARINC 429 or other types. Thus, by way of example, for the management of the mobile elements of the landing gear of an airplane, several piloting and / or control modules are used, the latter each being connected to the main buses of the airplane. .

Each control module comprises a computer 1 implementing a suitable program in order to ensure the control function to which it is dedicated, as well as a communication interface adapted to the protocol of the main bus allowing the exchange of data between the computer and the main buses of the plane.

FIG. 1 shows the simplified diagram of an electronic computer 1. This comprises a mechanical frame 11, one or more electronic cards 12 and a card 20 called a “backplane” card in English.

Each electronic card 12 is mechanically held in the frame 11 by slides and connected to the backplane electronic card 20. The backplane electronic card 20 comprises card connectors 13 adapted to be connected to a complementary connector 74 carried. by the electronic card 12.

The backplane electronic card 20 comprises, for each control module, an external connector 15 adapted to cooperate with a complementary connector carried by the associated module.

As illustrated in Figure 1, it is known to connect the external connector 15 to the backplane electronic board 20 by son 71 wound on square pins 72 of the components, according to the so-called 'Wrapping' method according to English terminology. -saxonne.

The wrapping technique has many drawbacks including excessive cost, obsolescence of components and skills, and poor electromagnetic compatibility performance.

Another drawback of wrapping is that the lack of impedance matching and noise can generate reflection phenomena at high frequencies and electronic failures on critical signals.

Another drawback of wrapping is that it requires a large wiring area which penalizes the compactness of computer 1.

As illustrated in Figure 2, it has been proposed to use a web 16 which is a flat electrical strip (flexible printed circuit board), consisting of copper wires bonded to each other, provided with a connector to each of its ends to connect the external connector 15 and the backplane electronic board 20.

As illustrated in FIG. 3, it has also been proposed to connect the external connector 15 to a connection printed circuit 19 connected to the backplane electronic board 20 by means of a flexible printed circuit 18 and connectors d. 'Complementary interconnections 17.

All of these solutions are complex, expensive and bulky.

Electronic cards are also known, such as that described in document US 2005/109532 (Dl), comprising two printed circuits bonded to one another by a layer of resin and having a series of first blind holes opening onto the first face of the electronic board and a series of second blind holes opening onto the second face of the electronic board allowing the direct reception of connectors using a force-fitted pin technology in metallized holes and being mounted directly on either side other on each side of PCB.

However, in such electronic boards, there is a risk that the resin will rise up into the blind holes during the assembly of the printed circuits, which means that the pin-shaped connection elements can no longer be inserted into the blind holes. Even when the pin-shaped connection elements can be inserted into the blind holes, there is the risk of an electrical contact fault due to the presence of the resin.

With reference to FIG. 4, patent application WO2016151053 describes an electronic backplane board 20 having an internal face 142 adapted to be connected to electronic card connectors and an external face 143 adapted to be connected to an external connector. The backplane electronic board 20 comprises a first printed circuit 222 having a face intended to form the face internal 142 of the backplane electronic board 20, a second printed circuit 223 having a face intended to form the external face 143 of the backplane electronic board 20 and a third printed circuit 224 between the first printed circuit 222 and the second printed circuit 223.

The backplane electronic board 20 comprises a first waterproof membrane

102, and the first printed circuit 222 has a series of first blind holes 146 opening out on the one hand on the internal face 142 of the backplane electronic board 20 and on the other hand on the first waterproof membrane 102.

The backplane electronic board 20 includes a second waterproof membrane

103, and the second printed circuit 223 has a series of second blind holes 148 opening out on the one hand on the outer face 143 of the backplane electronic board 20 and on the other hand on the second waterproof membrane 103.

The first and second blind holes 146, 148 are adapted to receive force-inserted connection elements and to form an electrical connection point with them. The first waterproof membrane 102 is disposed between the first printed circuit 222 and the third printed circuit 224; the second waterproof membrane 103 is disposed between the second printed circuit 223 and the third printed circuit 224. The first and second waterproof membranes prevent the resin used in the bonding material from rising up into the blind holes 146, 148 during the manufacture of the backplane electronic board 20.

However, the presence of these waterproof membranes induces additional sizing constraints. Such a backplane electronic card must in fact have a very small thickness, for example between 3.5 and 6 mm, while the pin-shaped connection elements typically have a length of between 1.7 mm and 2 mm. . Thus, the presence of these watertight membranes leads to predicting as accurately as possible the thickness dimensions of the elements of the backplane electronic card. Any deviation may result in blind holes not deep enough to properly accommodate the pin-shaped connection elements. On the other hand, the manufacturing process described by application WO2016151053 provides for the formation of blind holes in the first printed circuit and the second printed circuit after assembly of the three printed circuits, which implies strict control of the holes. These constraints complicate manufacturing, increase costs and increase non-compliance issues.

PRESENTATION OF THE INVENTION

The invention aims to allow a simple and easy manufacture of such a backplane electronic card, which makes it possible to prevent the resin of the bonding material from rising up into the blind holes, and therefore makes it possible to obtain blind holes. present a maximum useful depth for the connection pins intended to be accommodated in these blind holes.

To this end, the invention provides a method of manufacturing a backplane electronic card having an internal face adapted to be connected to electronic card connectors and an external face adapted to be connected to an external connector, a series first blind holes opening on the one hand on the internal face of the backplane electronic card and a series of second blind holes opening on the one hand on the external face of the backplane electronic card, the electronic backplane board backplane comprising:

• a first printed circuit having a first face and a second face intended to form the internal face of the backplane electronic card;

• a second printed circuit having a first face and a second face intended to form the external face of the backplane electronic card and;

• a third printed circuit having a first face facing the first face of the first printed circuit and a second face facing the first face of the second printed circuit, the third printed circuit constituting an electrical insulator between its first face and its second face said first blind holes passing through the first printed circuit but not passing through the third printed circuit and said second blind holes passing through the second printed circuit but not passing through the third printed circuit;

the method comprising the following steps:

• deposition on the first face of the third printed circuit of a first bonding layer, said first bonding layer having first areas free of material distributed on the first face of the third printed circuit, and deposition on the second face of the third printed circuit a second adhesive layer, said

second bonding layer having second areas free of material distributed on the second face of the third printed circuit;

• assembly on the prem 1st bonding layer of the first face of the first printed circuit, said first printed circuit having a series of first through holes intended to form the first blind holes, each first through hole opening into a first area free of material from the first bonding layer on the first face of the third printed circuit to form the first blind holes, and assembly on the second bonding layer of the first face of the second printed circuit, said second printed circuit having a series of second through holes intended to form the blind holes, each second through-hole opening into a second zone free of material to form the second blind holes of the second adhesive layer on the second face of the third printed circuit to form the second blind holes.

In order to form the blind holes, the areas free of material from the bonding layers in front of each hole in the printed circuits makes it possible to prevent the rise of the bonding material such as resin in these blind holes, by absorbing the creep of this resin during assembly, which at least partially fills these areas free of material.

Typically, the bonding material comprises a fabric impregnated with uncured resin. Preferably, the resin of the sizing material has a dynamic viscosity greater than 5000 poises between 80 ° C and 180 ° C, and preferably greater than 10,000 poises below 100 ° C. The use of such a bonding material makes it possible to limit the creep of the bonding material in the areas free of material from the bonding layers, and therefore makes it possible to further limit the risk of the rise in the bonding material such as the resin in the blind holes. Furthermore, the low creep of the material constituting the bonding layers makes it possible to manipulate these bonding layers before deposition on the third printed circuit, and in particular to pierce the areas free of material therein before deposition.

Preferably, the areas free of material which face the through holes of the printed circuits intended to form the blind holes have a diameter greater than the diameters of these through holes of at least 100 mhi, and preferably of at least 250 mhi, and more preferably at least 500 mhi. The flow of the material of the bonding layer during assembly at least partially fills these areas free of material. Due to the greater diameter of the areas free of material, these areas free of material have a higher volume absorption capacity, which therefore allows better

absorb the creep of the resin and therefore prevent the resin from rising in the blind holes. In addition, the resin is initially located further from the through holes of the printed circuits intended to form the blind holes, which further limits this risk.