Printed circuit board, associated electronic device and manufacturing method
The nested via structure on PCBs with distinct electrical potentials addresses the vulnerability to edge attacks by reducing the intrusion diameter, enhancing security through complex via connections.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- THALES SA
- Filing Date
- 2025-12-11
- Publication Date
- 2026-06-18
AI Technical Summary
Existing printed circuit boards (PCBs) are vulnerable to edge attacks due to the large geometry of vias, which can be easily accessed and short-circuited by attackers, allowing unauthorized connections between neighboring vias, despite standard manufacturing methods requiring a minimum spacing of several hundred micrometers.
The PCB design incorporates nested metal shafts within each via, with each shaft connected to a different electrical potential, making it difficult for attackers to access the inner cylinder without affecting the outer signal, and the manufacturing process involves drilling, metallization, and polymer resin filling to create these nested structures.
The nested via structure significantly reduces the possible intrusion diameter from 500 µm to 350 µm, enhancing protection against edge attacks by ensuring each via has distinct electrical potentials, thereby improving security.
Smart Images
Figure EP2025086628_18062026_PF_FP_ABST
Abstract
Description
[0001] TITLE: Printed circuit board, electronic device and associated manufacturing process
[0002] The present invention relates to a printed circuit board, as well as an electronic device comprising such a printed circuit board. The invention also relates to a method for manufacturing such a printed circuit board.
[0003] A printed circuit board, also called a PCB (Printed Circuit Board), is made up of several layers of an insulating substrate. Conductive traces, usually made of copper, are etched onto the surface of these substrate layers. One or more electronic components are mounted on the surface of the PCB and are electrically connected to the conductive traces located either on the surface of the PCB or between the substrate layers. A printed circuit board on the surface of which at least one electronic component is mounted is called an electronic board. The absence of a component on such a board will be referred to as a printed card and also constitutes a use case of the invention. Hereafter, both configurations will be referred to as "boards."
[0004] To prevent edge attacks, it is known, for example, to create several vias side-by-side, often in rows, around the components to be protected. This forms a plurality of vias in the vicinity of the protected component. Generally, a via is formed by a hole drilled through the PCB, the hole being covered with a layer of metal, usually copper, deposited by metallization. This creates a metallic shaft. It is also known, to prevent edge attacks, to set the neighboring vias of the same plurality of vias to different electrical potentials using a method called instantiation, so that in the event of a micro-drill, the micro-drill short-circuits two neighboring vias, thus allowing the physical attack to be detected.
[0005] However, these vias have a relatively large geometry; in particular, standard manufacturing methods require spacing them with a pitch of several hundred micrometers. As a representative example, vias with an internal diameter of 300 µm must be spaced with a pitch close to 800 µm. It is thus possible to drill through a via without affecting neighboring vias, with an intrusion diameter of up to 500 µm. Consequently, a well-equipped attacker can access these vias, allowing them to connect vias of the same potential together before drilling through the shorted via undetected. In this case, a possible intrusion diameter is close to 800 µm. The invention specifically aims to address these problems by providing a device that offers improved protection against edge attacks on printed circuit boards.
[0006] To this end, the invention relates to a printed circuit board, in which:
[0007] - the card has two opposite faces, the two opposite faces including a top face and a bottom face and being orthogonal to an axis of height,
[0008] - The card comprises several layers laminated one on top of the other, the several layers including a top layer and a bottom layer, the top layer being closer to the top face than the bottom layer,
[0009] - the map includes a via, which is provided across the map and extends along a main axis parallel to the vertical axis,
[0010] - the via includes a first shaft, which is made of metal, which extends along the main axis and which has an upper end and a lower end, the lower end being located opposite the upper end along the main axis, the upper end of the first shaft being closer to the upper face than the lower end of the first shaft,
[0011] - the via includes a second shaft, which is different from the first shaft, which is made of metal and is arranged in a first internal volume of the first shaft, the second shaft having a high end and a low end opposite to the high end, the high end of the second shaft being closer to the high face than the low end of the second shaft,
[0012] - the second drum is joined to the first drum using a first polymer resin,
[0013] - the upper end of the second barrel is closer to the upper face than the upper end of the first barrel, the first barrel being suitable for connection to a first conductive element so as to be brought to a first electrical potential, while the second barrel is suitable for connection to a second conductive element so as to be brought to a second electrical potential, different from the first electrical potential, the card comprises a plurality of vias, the plurality of vias including a first via and a second via, which are arranged in close proximity to each other, each via comprising respectively one instance of the first barrel and one instance of the second barrel, in which:
[0014] • the first barrel of the first via is electrically connected to the second barrel of the second via, and • the second barrel of the first via is electrically connected to the first barrel of the second via.
[0015] Thanks to the invention, each via comprises two nested shafts with two different potentials. Access to the inner cylinder, carrying a different potential, without affecting the signal present on the outer cylinder, is made much more difficult by this geometry of one cylinder surrounding another. For example, with adjacent vias spaced 900 µm apart, the first shaft having a diameter of 600 µm and the second shaft a diameter of 300 µm, the possible intrusion diameter is reduced to 350 µm, which is significantly less than the 500 µm or even 800 µm mentioned in the case of prior art. Protection against edge intrusion is thus improved.
[0016] According to advantageous but not mandatory aspects of the invention, such a printed circuit board may incorporate one or more of the following features taken individually or in any technically permissible combination:
[0017] The card includes an electronic component, for example a microprocessor, which is mounted on the card in the vicinity of the plurality of vias, the plurality of vias being arranged so as to restrict access to a portion of the card located below the electronic component in a direction transverse to the card.
[0018] The invention also relates to an electronic device, comprising a card as described above.
[0019] According to another aspect, the invention relates to a method for manufacturing a printed circuit board, the method including the following steps: a step of supplying a printed circuit board, the board comprising at least one layer having a top face; next, a first drilling step, during which the board is drilled along the height axis, so as to form a first hole opening onto the top face of the board; next, a first metallization step, during which the first hole is metallized, so as to form the first shaft, the first shaft delimiting a first substantially cylindrical internal volume centered on the main axis, one upper end of the first shaft being flush with the top face of the board; next, a first filling step, during which:
[0020] • The first internal volume is filled using a first polymer resin, and
[0021] • An additional layer is applied to the top surface of the card, so that the card has a top surface oriented in the same direction as the top surface. Next, a second drilling step is performed, during which the additional layer and the first internal volume filled with the first polymer resin are drilled, so as to form a second hole. This second hole has a diameter smaller than the diameter of the first internal volume and opens onto the top surface. Then, a second metallization step is performed, during which the second hole is metallized, so as to form a second shaft coaxial with the first shaft. One upper end of the second shaft is closer to the top surface than the upper end of the first shaft. The first and second shafts together form a via. Each of these steps is repeated at least once, so as to provide at least one first via and a second via in close proximity to each other and to form a plurality of vias.while the process also includes a connection step, in which:
[0022] • the first drum of the first via is electrically connected to the second drum of the second via, by means of a first transfer via, and
[0023] • the second barrel of the first via is electrically connected to the first barrel of the second via, by means of a second transfer via, which is different from the first transfer via.
[0024] This process induces the same advantages as those mentioned above regarding the electronic board of the invention.
[0025] Advantageously:
[0026] Transfer vias are created by a laser or mechanical drilling step, followed by a metallization step.
[0027] The process includes a second filling step, during which a second internal volume delimited by the second drum is filled with a second polymer resin, the second filling step being subsequent to the second metallization step.
[0028] The invention will be better understood, and other advantages thereof will become more apparent in the light of the following description of an embodiment of an electronic circuit board, an electronic device, and a manufacturing process, conforming to its principle, given solely by way of example and with reference to the accompanying drawings, in which:
[0029] - [Fig 1] Figure 1 represents respectively, on two insets a) and b), a perspective view and a partial section of an electronic device according to the invention, the electronic device comprising a printed circuit board also according to the invention, - [Fig 2] Figure 2 represents, on four insets a) to d), manufacturing steps of the printed circuit board of Figure 1;
[0030] - [Fig 3] Figure 3 shows, in four insets a) to d), other manufacturing steps of the printed circuit board of Figure 1, and
[0031] - [Fig 4] Figure 4 represents a perspective view of a detail of the printed circuit board of Figure 1.
[0032] An electronic device 10 according to the invention is shown in Figure 1a). The electronic device 10 is schematically represented by a parallelepiped in dashed lines. The electronic device 10 comprises a card 12. The card 12 is a printed circuit board, also known as a PCB. The card 12 has two opposite faces, each including a top face 14A and a bottom face 14B, and is orthogonal to an axis of height Z12. Generally, the terms "top," "bottom," "right," and "left" are used in relation to the orientation of the elements as illustrated in the drawings, although this may differ in reality.
[0033] Card 12 also features a slice 14C, which here is formed of four rectangular faces parallel to the height axis Z12.
[0034] As is known, the card 12 is formed by laminating several layers 15 of insulating substrate one on top of the other, with metallic layers, in particular copper, located on faces of the substrate layers 15. The metallic layers are etched to form printed circuits on the surface of the layers 15. The layers 15 are shown in Figures 2 and 3. As explained below, in the context of the invention, the card 12 comprises at least two layers 15; in other words, the card 12 is a multilayer card.
[0035] The card 12 preferably includes an electronic component 16, for example here a microprocessor, which is mounted on the upper face 14A of the card 12. The electronic component 16 is thus a surface-mount component, also called SMT in French, so as to be connected to the printed circuit located on the upper face 14A, and / or to printed circuits located between two adjacent layers 15.
[0036] Map 12 advantageously comprises a plurality of vias 18, which includes at least two vias 20 located in close proximity to one another. In the illustrated example, the plurality of vias 18 comprises four vias 20. Each via 20 extends along its own principal axis A20, the principal axis A20 being parallel to the height axis Z12. In the non-limiting example shown, the vias 20 of the plurality of vias 18 are aligned; in other words, the plurality of vias 18 is a row of vias. Other configurations are, of course, possible. In an alternative not shown, the vias 20 of the plurality of vias 18 are not aligned but are arranged along a curve, at an angle, in a staggered pattern, etc., or even randomly.
[0037] The electronic component 16 is here mounted on the card 12 in the vicinity of the plurality of vias 18, the plurality of vias 18 being arranged so as to limit access to a portion of the card 12 located under the electronic component 16 in a direction transverse to the card 12, in other words in a direction parallel to a plane orthogonal to the height axis Z12.
[0038] In Figure 1b), the plurality of vias 18 is shown in cross-section along a plane orthogonal to the height axis Z12. Advantageously, the vias 20 of the same plurality of vias 18 are similar, preferably identical to each other. The following describes the leftmost via 20 in Figure 1, bearing in mind that what is valid for one of the vias 20 is applicable to the other vias.
[0039] The via 20 comprises a first shaft 21, which extends along the main axis A20 and is made of metal. The first shaft 21 is formed by drilling through the card 12, preferably using a drill bit. The resulting hole is then metallized to form the first shaft 21. Metallization deposits a layer of metal, preferably copper. Metallization is carried out, for example, by electrolytic deposition. The first shaft 21 thus has a substantially cylindrical shape with a circular cross-section.
[0040] Via 20 includes a second barrel 22, which is different from the first barrel 21, which is made of metal and which is arranged in the first barrel 21, preferably coaxially with the first barrel 21.
[0041] We now describe a manufacturing process for via 20, with reference to figures 2 and 3.
[0042] The process includes a step 101 of supplying the printed circuit board 12, as illustrated in Figure 2a). Initially, the board 12 comprises at least one layer 15 and has a top face 15A covered with a conductor (usually copper), which here corresponds to a top face of layer 15 located at the top of Figure 2a). Other conductors may also be present on the faces of the other layers 15 inside the board 12. In Figures 2 and 3, the board 12 is partially shown.
[0043] The process then comprises a first drilling step 102, during which the card 12 is drilled along the height axis Z12, so as to form a first hole 30 opening onto the upper face 15A as illustrated in Figure 2b). For the implementation of the invention, it is not essential that the first hole 30 open onto the lower face 14B of the card 12. Depending on the configuration, the first hole passes through the card 12, or is left blind. In practice, the first hole 30 is drilled using a drill bit. The first hole 30 has, for example, a diameter between 450 µm and 600 µm. The first hole 30 has a generally cylindrical shape with a circular cross-section centered on the main axis A20.
[0044] The process then comprises a first metallization step 103, during which the first hole 30 is metallized to form the first barrel 21, as illustrated in Figure 2c). The first barrel 21 defines the first internal volume V21, which is substantially cylindrical and centered on the main axis A20. The first metallization step 103 allows for the application of a metal thickness ranging, for example, from 20 to 30 µm. It is understood that the first internal volume V21 then corresponds substantially to the hole 30, minus the metal thickness of the barrel 21.
[0045] The first shaft 21 has an upper end 24A, which rests on the upper face 15A, and a lower end 24B, which is located opposite the upper end along the main axis A20. The lower end 24B is shown in Figure 3d). The lower end 24B is thus located on the side of the lower face 14B. The upper end 24A of the first drum 21 is suitable for connection to a printed circuit board formed on the upper face 15A, the connection advantageously being made during the manufacture of the first drum 21, that is to say during the first metallization step 103. In addition or as an alternative, the lower end 24B of the first drum 21 is suitable for connection to a printed circuit board formed on another layer, different from the upper face 15A, of the card 12. For example, when the first hole 30 opens onto the lower face 14B, the lower end 24B of the first drum 21 is suitable for connection to a printed circuit board formed on the lower face 14B.Thus, generally speaking, the first barrel 21 is configured to be connected to a first conductive element so as to be brought to a first electrical potential. The first conductive element is not shown.
[0046] Next, the process includes a first filling step 104, during which:
[0047] The first internal volume V21 is filled using a first polymer resin 32, and
[0048] An additional layer 15' is provided on the upper face 15A of the card 12, so that the card 12 presents the upper face 14A. The upper face 14A is thus oriented on the same side as the upper face 15A. The upper face 14A has a conductive layer (generally made of copper).
[0049] After hardening, the polymer resin 32 forms a solid plug 33, which seals the first internal volume V21, as illustrated in Figure 2d). According to non-limiting examples, the first polymer resin 32 is, for example, an epoxy resin implemented before the preparation of the layer 15', or the polymer resin 32 is produced by the creep of the layer 15' during its preparation, or the polymer resin 32 is produced by a combination of the two.
[0050] In the illustrated example, the cap 33 and the additional layer 15' are shown as originating from the material, being formed by the first hardened polymer resin 32. In a preferred variant, the additional layer 15' is preformed, i.e., the already hardened additional layer 15' is laminated onto the upper face 15A, the first polymer resin 32 serving both as a filler material for the first internal volume V21 and as an adhesive between the additional layer 15' and the layer 15 presenting the upper face 15A.
[0051] The additional layer 15' has a similar, preferably identical, structure to the other substrate layers 15 of the card 12. Thus, as a result of the first filling step 104, the additional layer 15' forms one of the substrate layers 15 of the card 12. In other words, the card 12 then comprises at least two substrate layers 15. The additional layer 15' masks the upper end 24A of the first barrel 21. The additional layer 15' and the cured polymer resin 32, in other words the plug 33, are electrically insulating.
[0052] The process then comprises a second drilling step 105, during which the additional layer 15' and the first internal volume V21, previously filled with the first polymer resin 32, are drilled to form a second hole 34. This second hole 34 has a diameter smaller than one diameter of the first internal volume V21 and opens onto the upper face 14A, as illustrated in Figure 3a). Preferably, the second hole 34 is centered on the main axis A20. Preferably, the drilling of the first internal volume V21 is carried out using a drill bit. According to an alternative not shown, the drilling of the first internal volume V21 is carried out using a laser. This method is commonly used to create small-diameter vias called "micro-vias." Micro-vias are generally used to create vias that penetrate only a limited thickness of substrate, for example, a single layer.Preferably, a laser is used for controlled ablation of the material, creating a limited thickness and forming a blind hole. The hole is then metallized, forming an electrical connection between the metallic circuits located on either side of the drilled thickness. Such a micro-via is also called a transfer via. Alternatively, the transfer via is created by a mechanical drilling step.
[0053] The process then comprises a second metallization step 106, during which the second hole 34 is metallized to form the second barrel 22, as illustrated in Figure 3b). The second barrel 22 is thus joined to the first barrel 21 by means of the first polymer resin 32, which fills a portion of the first internal volume 21 located between the second barrel 22 and the first barrel 21. The second barrel 22 has a substantially cylindrical shape with a circular cross-section. The second barrel 22 defines a second internal volume V22. It is understood that the second internal volume V22 corresponds substantially to the second hole 34, minus the thickness of the second barrel 22. Preferably, the second barrel 22 is coaxial with the first barrel 21.
[0054] The second shaft 22 has a top end 26A and a bottom end 26B, which is opposite the top end 26A. The top end 26A is closer to the top face 14A than the bottom end 26B. The bottom end 26B is shown in Figure 3d). The bottom end 24B is thus located on the side of the bottom face 14B. The first shaft 21, which surrounds the second shaft 22, is set back from the second shaft 22 relative to the top face 14A. In the illustrated example, the top end 26A of the second shaft 22 opens onto the top face 14A, while the top end 24A of the first shaft 21 opens onto the top face 15A, now covered by the additional layer 15'. It is understood that the upper end 26A of the second drum 22 is suitable for being connected to a printed circuit board provided on the upper face 14A, the connection being advantageously made during the manufacture of the second drum 22, that is to say during the second metallization stage 106.Thus, the second barrel 22 is configured to be connected to a second conductive element held at a second electrical potential, different from the first electrical potential. The second conductive element is not shown.
[0055] Thus, as a result of the second metallization step 106, we obtain the via 20, which includes the first barrel 21 and the second barrel 22, arranged coaxially with the first barrel 21, as schematically illustrated in figure 3 d), where the substrate layers 15 / 15' are not shown.
[0056] Advantageously, the process includes a second filling step 107, which is subsequent to the second metallization step 106 and during which the second internal volume V22 is filled, by means of a second polymer resin 36. After hardening, the second polymer resin 36 forms a solid plug 37, which seals the second internal volume V22.
[0057] Each of the steps 102 to 107 is repeated several times in several locations of the map 12, so as to preserve the plurality of vias 18. With reference to figure 4, the plurality of vias 18 includes a first via 20A, shown on the left of figure 4, and a second via 20B, shown in the middle of figure 4. The plurality of vias 18 here includes a third via 20C. Each via 20A / 20B / 20C comprises respectively one example of the first drum 21 and one example of the second drum 22. The first drum 21 of the first via 20A is electrically connected to the second drum 22 of the second via 20B, preferably by means of a transfer via through the additional layer 15', while the second drum 22 of the first via 20A is electrically connected to the first drum 21 of the second via 20B, preferably by means of a second transfer via, which is different from the first micro-via and which passes through the additional layer 15'.Transfer vias are advantageously micro-vias.
[0058] Similarly, the first drum 21 of the second via 20B is electrically connected to the second drum 22 of the third via 20C, preferably by means of a third transfer via through the additional layer 15', while the second drum 22 of the second via 20B is electrically connected to the first drum 21 of the third via 20C by means of a fourth transfer via.
[0059] Thus, step by step, each via is connected to its neighboring via by cross-connections. For each via 20A / 20B / 20C, the first barrel 21 and the second barrel 22 end up at different electrical potentials. For pairs of neighboring vias, for example the pair 20A / 20B or the pair 20B / 20C, the first barrels 21 also end up at different electrical potentials.
[0060] It is understood that for the implementation of the invention, it is not necessary for the upper end 26A of the second barrel 22 to be located on an external face of the card 12, in other words it is not necessary for the upper end 26A of the second barrel to be on the surface of the card 12. It is sufficient in fact that the upper end 24A of the first barrel 21 is set back from the upper end 26A of the second barrel 22, with respect to the external face of the card 12, so that the first barrel 21, which surrounds the second barrel 22, does not prevent access to the second barrel 22.
[0061] According to an alternative, not shown but nonetheless advantageous, following the connection step, the card 12 is covered with a second additional layer of substrate, in addition to the additional layer 15' created during the filling step 104, so as to seal the second internal volume V22 and also, where applicable, the transfer vias created to connect the neighboring vias 20 to each other. In other words, the upper face 14A is masked by this second additional layer.
[0062] Preferably, the card 12 has a structure that is generally symmetrical with respect to a plane of symmetry, which is orthogonal to the height axis Z12. The plane of symmetry is not shown. This avoids bending deformations of the card 12 when it is subjected to temperature variations. Preferably, each via 20 advantageously has a structure that is symmetrical with respect to the plane of symmetry of the card 12. However, for implementation of the invention, it is not necessary for the lower end 24B of the first shaft 21 to be recessed from the lower end 26B of the second shaft 22 relative to the lower face 14B.
[0063] However, it is advantageous for the lower end 24B of the first barrel 21 to be set back from the lower end 26B of the second barrel 22 relative to the lower face 14B, because it is then possible to provide transfer vias on the side of the lower face 14B, so as to connect the first barrel 21 of a via 20 to the second barrel 22 of a neighboring via 20. The designer of the printed circuit board thus has more freedom.
[0064] The embodiments and variants mentioned above can be combined to generate new embodiments of the invention.
Claims
DEMANDS 1. Printed circuit board (12), wherein: the board (12) has two opposite faces, the two opposite faces including a top face (14A) and a bottom face (14B) and being orthogonal to a height axis (Z12), the board (12) comprises several layers (15, 15') laminated one on top of the other, the several layers (15, 15') including a top layer and a bottom layer, the top layer being closer to the top face (14A) than the bottom layer, the board (12) includes a via (20), which is formed through the board (12) and which extends along a principal axis (A20) parallel to the height axis (Z12), the via (20) includes a first shaft (21), which is made of metal, which extends along the principal axis (A20) and which has a top end (24A) and a bottom end (24B), the lower end (24B) being located opposite the upper end (24A) along the main axis (A20),the upper end (24A) of the first barrel (21) being closer to the upper face (14A) than the lower end (24B) of the first barrel (21), the via (20) comprises a second barrel (22), which is different from the first barrel (21), which is made of metal and which is arranged in a first internal volume (V21) of the first barrel (21), the second barrel (22) having an upper end (26A) and a lower end (26B) opposite to the upper end (26A), the upper end (26A) of the second barrel (22) being closer to the upper face (14A) than the lower end (26B) of the second barrel (22), the second barrel (22) is joined to the first barrel (21) by means of a first polymer resin (32), the upper end (26A) of the second barrel (22) is closer to the upper face (14A) than the upper end (24A) of the first barrel (21), the first barrel (21) being suitable for being connected to a first conductive element so as to be brought to a first electrical potential,while the second barrel (22) is suitable for being connected to a second conductive element, so as to be brought to a second electrical potential, different from the first electrical potential, the card (12) comprises a plurality of vias (18), the plurality of vias (18) including a first via (20) and a second via (20), which are arranged in the vicinity of each other, on the other, each via (20) comprising respectively one copy of the first drum (21) and one copy of the second drum (22), in which: the first drum (21) of the first via (20) is electrically connected to the second drum (22) of the second via (20), and the second drum (22) of the first via (20) is electrically connected to the first drum (21) of the second via (20).
2. Card (12) according to claim 1, wherein: the card (12) comprises an electronic component (16), for example a microprocessor, which is mounted on the card (12) in the vicinity of the plurality of vias (18), the plurality of vias (18) being arranged so as to limit access to a portion of the card (12) located below the electronic component (16) in a direction transverse to the card (12).
3. Electronic device (10), comprising a card (12) according to claim 2.
4. A method for manufacturing a printed circuit board (12), the method including the following steps: a step of supplying (101) a printed circuit board (12), the board (12) comprising at least one layer (15) having a top face (15A), then, a first drilling step (102), during which the board (12) is drilled along the height axis (Z12), so as to form a first hole (30) opening onto the top face (15A) of the board (12), then, a first metallization step (103), during which the first hole (30) is metallized, so as to form the first shaft (21), the first shaft (21) defining a first internal volume (V21) substantially cylindrical centered on the main axis (A20), a high end (24A) of the first shaft (21) being flush with the top face (15A) of the board (12), then, a first filling step (104), during which: • the first internal volume (V21) is filled using a first polymer resin (32), and • an additional layer (15') is applied to the upper face (15A) of the card (12), so that the card (12) has a top face (14A) oriented in the same direction as the upper face (15A); then, a second drilling step (105) is performed, during which the additional layer (15') and the first internal volume (V21) filled by the first polymer resin (32) are drilled, so as to form a second hole (34); 14. A second hole having a diameter smaller than a diameter of the first internal volume (V21) and opening onto the upper face (14A); then, a second metallization step (106), during which the second hole (34) is metallized so as to form the second shaft (22) coaxial with the first shaft (21), an upper end (26A) of the second shaft (22) being closer to the upper face (14A) than the upper end (24A) of the first shaft (21); the first shaft (21) and the second shaft (22) together forming a via (20), wherein: each of the steps (101, ..., 106) is repeated at least once, so as to provide at least one first via (20A) and one second via (20B) in close proximity to each other and to form a plurality of vias (18); the method also includes a connection step, wherein: • the first drum (21) of the first via (20A) is electrically connected to the second drum (22) of the second via (20B), by means of a first transfer via, and • the second barrel (22) of the first via (20A) is electrically connected to the first barrel (21) of the second via (20B), by means of a second transfer via, which is different from the first transfer via.
5. Method according to claim 4, wherein: the transfer vias are provided by a laser or mechanical drilling step, followed by a metallization step.
6. A method according to any one of claims 4 or 5, wherein: the method comprises a second filling step (107), during which a second internal volume (V22) delimited by the second drum (22) is filled with a second polymer resin (36), the second filling step (107) being subsequent to the second metallization step (106).