Method for printing a conductive layer on the surface of a 3D electronic assembly and related 3D electronic assembly

Abstract

To provide a method for depositing a conductive layer on a surface of a three-dimensional (3D) electronic assembly 10A that includes at least one electronic device 14 embedded in a solid polymeric material 16.SOLUTION: A method includes the steps of (i) providing a 3D electronic assembly 10A, (ii) forming at least one flow barrier 18 on a surface of a solid polymer material 16 of the 3D electronic assembly 10A, and (iii) depositing a conductive layer 20A on at least a portion of the surface of the solid polymer material 16 such that the conductive layer 20A is at least partially defined by the flow barrier 18.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for depositing a conductive layer on the surface of a 3D electronic assembly such as a System-in-Package (SIP).Furthermore, the present invention relates to a 3D electronic assembly.

[0002] It is common today to insulate and protect electronic components, and even complete electronic circuits, such as systems in packages (SIPs), in polymer encapsulants. The polymer encapsulant may include, for example, molding compounds, more specifically, epoxy molding compounds. Due to the high density of electrical functions integrated into complete electronic circuits, electromagnetic or electrical interference (EMI) can cause complete failure of the electronic circuit. Therefore, these electronic circuits must be shielded to suppress both EMI radiation from being emitted by the electronic circuit and EMI radiation from being received by the electronic circuit.

[0003] Traditionally, SIP modules have used metal housings for EMI shielding, for example. However, metal housings are not suitable for miniaturization. Instead of using metal housings, functional layers can be applied, for example, by a PVD process. Alternatively, a silver-containing inkjet ink can be deposited on the surface of the SIP module using, for example, an inkjet printer. Once the inkjet ink is printed on the surface of the SIP module, it is cured, for example, using UV light, to form a continuous functional layer on the surface of the SIP module. Other curing methods, such as oven curing, IR irradiation, or plasma, are also possible. Before the printing process, the surface of the SIP module may be subjected to a pretreatment process for cleaning purposes. Again, plasma can be used for this purpose.

[0004] US Patent Application Publication No. 2021 / 227697(A1) and US Patent Application Publication No. 2015 / 068787(A1) disclose generating grooves by laser ablation and filling the grooves with a conductive material, e.g., a conductive ink, thereby obtaining precisely contoured tracks, e.g., on a printed circuit board.

[0005] US Patent Application Publication No. 2012 / 055013 A1 relates to laser ablation of selected areas to create, for example, antennas by depositing silver ink in the ablated areas. Summary of the Invention [Problem to be solved by the invention]

[0006] When inkjet printing conductive ink onto the surface of a 3D electronic assembly, such as a SIP module, the ink tends to flow downward due to gravity on inclined or vertical surfaces. This problem can be mitigated by applying only a thin layer at a time and repeating the printing process several times to achieve sufficient layer thickness. However, the edges of the printed layers tend to be inaccurate. Instead, they exhibit a wavy shape, and as a result, ink layers cannot be printed close to the conductive components of the 3D electronic assembly. A safety margin must be maintained to prevent electrical shorts. Furthermore, printing on surfaces that are not plane-parallel to the inkjet printer's printhead also results in inaccurate, wavy printed edges.

[0007] It is an object of the present invention to provide a method for depositing a conductive layer on the surface of a 3D electronic assembly, such as a SIP, which reduces or overcomes the drawbacks of prior art methods. In particular, it is an object of the present invention to improve the edge sharpness of the deposited conductive layer, especially when the layer is deposited by an inkjet printer or a spray coater. [Means for solving the problem]

[0008] These objects are achieved by the subject matter of independent claims 1 and 10. Optional and preferred features of the invention are the subject matter of the dependent claims.

[0009] The present invention is generally suitable for depositing any type of conductive layer (or conductive print pattern) on a 3D electronic assembly. The conductive layer may be any type of layer. When applied, this layer preferably performs an EMI shielding function against electromagnetic interference (EMI) caused by electromagnetic induction or electromagnetic radiation emitted from electronic devices within the 3D electronic assembly or from external sources. However, this layer may also preferably be configured to function as an antenna in an antenna-in-package (AIP).

[0010] The conductive layer may be comprised of a conductive ink, which is a type of ink that becomes conductive when printed and preferably cured. Examples of such types of ink include silver, gold, titanium, bismuth, nickel, chromium, or copper inks, or silver-, gold-, titanium-, bismuth-, nickel-, chromium-, or copper-containing inks, preferably inks containing metal organic decomposition (MOD) compounds (also known as MOD inks). The conductive ink may also be a type of ink that includes conductive particles, such as silver, gold, titanium, bismuth, nickel, chromium, or copper particles.

[0011] For a conductive ink to function as an EMI shield, for example, the conductive ink must be printed so as to form a continuous layer over at least a portion of the exposed surface of a 3D electronic assembly, without gaps greater than a quarter wavelength of the frequency of the external or internal electromagnetic radiation to be blocked.

[0012] The conductive layer may also include a non-conductive layer, such as a protective layer, that protects the underlying conductive layer from damage and / or other harmful environmental influences, such as excessive heat and corrosion-inducing substances (e.g., oxygen).

[0013] Using the method according to the present invention, a conductive layer can be deposited only on specific portions or the entire exposed surface(s) of a 3D electronic assembly, and the layer thickness can be selectively manipulated to vary or be very uniform and homogeneous across the deposited portion of the exposed surface(s) of the 3D electronic assembly. The final layer thickness can, of course, be achieved in one or more subsequent deposition steps, depending on the absolute thickness value. Thus, a highly effective conductive layer can be realized with properties that can be specifically tailored to the needs and requirements of the user.

[0014] In the method of the present invention, it is preferable to use a SIP. However, in general, any 3D electronic assembly that needs to be at least partially covered by a conductive layer, such as an AIP, may be used in the method of the present invention. The shape of the 3D electronic assembly may be, for example, a cube or a rectangular parallelepiped.

[0015] The present invention can in principle be used in any digital printing process, preferably a digital inkjet printing process, by which conductive and non-conductive coatings (layers, printed patterns) can be deposited with selectively adjustable thickness, high structural uniformity and homogeneity, and high throughput.

[0016] Inkjet printers are commonly known and may have different setups specifically adapted to the user's requirements. The method of the present invention is preferably carried out using an inkjet printer having one or more print heads. Each print head has a number of print nozzles arranged in a print nozzle plane. The printing width of the print heads used in the method of the present invention can be selected depending on the size of the 3D electronic assembly, for example, 30.5 cm (12 inches) or more.

[0017] When the printed conductive layer is cured, a functional layer is obtained that preferably exhibits EMI shielding functionality. For example, curing can be achieved using UV light. Other curing methods are also possible, such as oven curing, IR irradiation, or plasma. Prior to the printing process, the surface of the 3D electronic assembly may be subjected to a pretreatment process, for example, using plasma, for cleaning purposes.

[0018] After each printing step or a predetermined number of printing steps, the conductive layer can be cured. If an ink requiring cross-linking is used, the cross-linked ink may undergo a further chemical reduction step, resulting in the precipitation of metal in the form of nanoparticles. Any solvent is evaporated and the printed ink is sintered. The curing step is understood to include all of these chemical processes occurring for a particular type of ink.

[0019] A first aspect of the present invention relates to a method for depositing a conductive layer on a surface of a three-dimensional (3D) electronic assembly that includes at least one electronic device embedded in a solid polymer material. The method includes the steps of: (i) providing a 3D electronic assembly; (ii) forming at least one flow barrier on a surface of the solid polymer material of the 3D electronic assembly; and (iii) depositing a conductive layer on at least a portion of the surface of the solid polymer material such that the conductive layer is at least partially defined by the at least one flow barrier.

[0020] Preferably, when the 3D electronic assembly is disposed on a horizontal surface, at least one flow barrier is formed on a non-horizontal and / or non-planar, preferably vertical, surface of the solid polymer material.

[0021] More preferably, the at least one flow barrier is a continuous ring-shaped flow barrier that extends completely around the solid polymeric material.

[0022] It is advantageous if at least one flow barrier is a recess.

[0023] According to a preferred embodiment of the present invention, the at least one recess is formed by laser ablation, sawing, milling or embossing.

[0024] Preferably, at least one recess has a depth in the range of 5 to 50 μm and a width in the range of 5 to 50 μm.

[0025] More preferably, the method further comprises the step of laser marking the 3D electronic assembly, wherein a laser for laser marking the 3D electronic assembly is also used to form the at least one recess.

[0026] More preferably, the step of depositing the conductive layer is carried out by inkjet printing or spray coating.

[0027] It is advantageous if the conductive layer is an electromagnetic interference shield covering at least one electronic device, and the conductive layer is printed using a conductive ink.

[0028] A second aspect of the present invention relates to a three-dimensional (3D) electronic assembly comprising at least one electronic device embedded in a solid polymer material, the 3D electronic assembly comprising at least one flow barrier on a surface of the solid polymer material, and a conductive layer provided on at least a portion of the surface of the solid polymer material such that the conductive layer is at least partially defined by the at least one flow barrier.

[0029] If the 3D electronic assembly is placed on a horizontal surface, it is preferred that at least one flow barrier is provided on a non-horizontal and / or non-planar, preferably vertical, surface of the solid polymer material.

[0030] It is further preferred that at least one flow barrier is a continuous ring-shaped flow barrier that extends completely around the solid polymeric material.

[0031] Advantageously, at least one flow barrier is formed as a recess.

[0032] More advantageously, at least one recess has a depth in the range of 5 to 50 μm and a width in the range of 5 to 50 μm.

[0033] According to a preferred embodiment of the present invention, the layer thickness of the conductive layer is in the range of 0.0001 μm to 100 μm, and preferably in the range of 1 μm to 4 μm.

[0034] Preferably, the conductive layer is an electromagnetic interference shield covering at least one electronic device, and the conductive layer comprises a conductive ink, preferably comprising or consisting of silver, gold, titanium, bismuth, nickel, chromium, or copper.

[0035] More preferably, in the method of the first aspect of the invention or the 3D electronic assembly of the second aspect of the invention, the 3D electronic assembly is a system-in-package (SIP) or an antenna-in-package (AIP) and the solid polymer material is a molding compound.

[0036] The above features of the first and second aspects of the invention may be combined in any way, and therefore the invention is not limited to the feature combinations described below with reference to preferred embodiments of the invention. [Brief explanation of the drawings]

[0037] The present invention will now be described by way of example with the aid of the accompanying drawings, in which: The drawings are for illustrative purposes and serve only to provide exemplary embodiments of the invention; The drawings do not limit the invention in any way, but merely illustrate preferred embodiments thereof; [Figure 1] FIG. 1 is a diagram showing a conventional Standard-in-Package (SIP). [Figure 2] FIG. 1 illustrates a SIP according to a preferred embodiment of the present invention. [Figure 3]FIG. 10 illustrates another SIP according to another preferred embodiment of the present invention. [Figure 4] FIG. 10 illustrates a further SIP according to yet another preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] It is again pointed out that although the preferred embodiment described below and shown in Figures 1 to 4 relates to a standard-in-package (SIP), the present invention may be applicable to any kind of 3D electronic assembly in which at least one electronic device is embedded or encapsulated in a polymer material.

[0039] In the following description and in FIGS. 1 to 4, the same reference numerals in all embodiments indicate the same or technically similar parts.

[0040] FIG. 1 shows an exemplary conventional SIP 1 including a number of electronic devices 3, such as integrated circuits, disposed on a substrate 2. The substrate 2 provides sufficient rigidity to the SIP 1. The electronic devices 3 are embedded in a polymer molding compound 4, such as epoxy. To electromagnetically shield the electronic devices 3 from electromagnetic interference (EMI) caused by electromagnetic induction or electromagnetic radiation, a conductive layer (printed pattern) 5 is applied to selective portions of the surface of the polymer molding compound 4. In the example shown in FIG. 1, the conductive layer 5 is deposited on the entire top surface and portions of both side walls of the approximately cubic-shaped polymer molding compound 4.

[0041] The conductive layer is conventionally printed onto a polymer molding compound, preferably using an inkjet printer. Because high-viscosity inks are difficult to process using inkjet printing, low-viscosity inks are the first choice for the conductive layer. Low-viscosity inks tend to flow downward due to gravity, resulting in uneven, imprecise, and wavy edges of the conductive layer. The wavy (blurred) edge(s) results in variations in the layer thickness of the conductive layer. In particular, the layer thickness near the sidewall edges tends to be thinner than in other areas, resulting in poorer EMI shielding in areas with thinner layer thickness. When multiple layers of ink are printed, the thickness deviation of the wavy (blurred) edges tends to increase.

[0042] To reduce or eliminate this problem, FIG. 2 illustrates a SIP 10A according to a preferred embodiment of the present invention. As shown in FIG. 1, multiple electronic devices 14 are disposed on a substrate 12 and embedded in a polymer molding compound 16. A conductive (functional) layer 20A is deposited on the top surface of the polymer molding compound 16 and on a portion of the sidewalls of the polymer molding compound 16. To improve the edge definition of the conductive layer at the sidewalls, recesses 18 that function as ink flow barriers are formed in some or all of the vertical sidewalls. The recesses 18 preferably extend continuously around the periphery of the polymer molding compound 16, i.e., without any interruptions or gaps. Wet ink flows into the recesses 18 and is allowed to accumulate therein until the ink is sufficiently cured, at which point gravity prevents the ink from flowing downward, resulting in precise, sharp edges of the conductive layer 20A. Note that depending on the type of ink, the thickness of the layer to be printed, and other process parameters, the wetted ink may not flow into the recesses but instead may abruptly stop before reaching the bottom of the recesses. In that case, edge sharpness is also improved. Figure 2 also shows an inkjet printer printhead 30 having a number of print nozzles (not shown) arranged in a print nozzle plane 32.

[0043] 3 shows another SIP 10B according to another preferred embodiment of the present invention, which differs from SIP 10A of FIG. 2, inter alia, in that a conductive layer 20B is deposited on only a portion of the top surface of polymer molding compound 16. Again, a recess 18 is formed in one, preferably three, vertical sidewalls of polymer molding compound 16, and another recess 18 is formed in the top surface of polymer molding compound 16 to prevent ink from flowing into areas of the top surface of polymer molding compound 16 that should not be covered by ink. Sidewall recess 18 preferably extends continuously along all three sidewalls of polymer molding compound 16. However, it is also possible for a recess 18 to extend along only one sidewall of polymer molding compound 16, thereby leaving all three sidewalls of a cubic polymer molding compound 16 free of recess 18.

[0044] Referring to FIG. 4, a SIP 10C is shown having a dome-shaped polymeric molding compound 16. A conductive layer 20C is printed on the non-planar top surface of the dome-shaped molding compound 16 using a conductive ink. The conductive layer 20C is defined by a recess 18 located near the bottom of the dome-shaped molding compound 16, adjacent the substrate 12. The recess 18 prevents the ink from flowing into areas that should not be covered by the ink. The recess 18 preferably extends continuously, i.e., without gaps, around the circumference of the dome-shaped polymeric molding compound 16.

[0045] Generally, at least one, i.e., one or more, flow barriers 18 may be formed in the polymer molding compound 16 at selected locations. The at least one flow barrier may be a recess 18 or a platform (shoulder), not shown, either of which may be configured to prevent ink from flowing into areas that should not be covered by the ink. The at least one recess 18 may preferably have the form of a trench having a planar bottom and two sidewalls extending perpendicularly from the bottom. The depth of the at least one recess 18 may be in the range of 5 to 50 μm, and the width of the at least one recess 18 may be in the range of 5 to 50 μm. The depth and / or width of the at least one recess 18 may vary along its length. The present invention is not limited to a particular shape of the recess 18. Instead, it is contemplated that the recess 18 may have any shape, including symmetrical and asymmetrical shapes in vertical or horizontal cross section. The recess 18 may be, for example, arc-shaped, semicircular, polygonal, or V-shaped. The at least one recess 18 may be continuous in that it is ring-shaped with no gaps between them and no free ends. The at least one recess 18 may extend around the entire circumference of the polymeric molding compound 16.

[0046] In all preferred embodiments of the present invention, conductive layers 20A, 20B, 20C are at least partially defined by at least one recess 18. "Defined" in this context can be interpreted as meaning that the edge of conductive layers 20A, 20B, 20C is defined by the upstream edge as viewed in the ink flow direction. Therefore, the edge definition of conductive layers 20A, 20B, 20C is improved regardless of whether the ink completely fills or only partially fills at least one recess 18. At least one recess 18 can be formed by, for example, laser ablation, sawing, milling, and embossing.

[0047] Preferably, the at least one recess 18 can be formed by the same laser as that used to mark the 3D electronic assembly. For this purpose, an infrared laser with an emission wavelength of 1064 nm can be used. However, other types of lasers, such as a green laser with an emission wavelength of 532 nm, can also be used for this purpose. For example, when using an infrared laser, the scanning speed of the laser can be 350 to 1350 mm / s, the frequency can be 10 to 200 Hz, and the power output of the infrared laser can be in the range of 20 mW to 100 W.

[0048] Low-viscosity conductive ink on non-horizontal walls flows down due to gravity. According to the present invention, the ink flow is stopped by the recess before it hardens, creating a sharp, well-defined edge. The recess can be partially or completely filled with ink, resulting in a thicker layer thickness within the recess than outside the recess. In an ideal situation, the ink does not flow past the recess, resulting in a relatively sharp edge on the printed ink, reducing the undulations present in prior art.

[0049] In the prior art, where the polymer molding compound is not recessed, the edge of the conductive layer can vary by as much as 150 μm, whereas in the present invention, where the polymer molding compound is recessed in selected portions, the edge of the cured conductive layer can vary by only 50 μm. Because the edge waviness is reduced, a more uniform layer thickness can be achieved across the entire conductive layer.

[0050] Waviness can be measured using a suitable imaging technique, such as a microscope or an automatic optical inspection (AOI) system. For example, the average waviness can be determined by measuring the distance between the peak and trough of the wavy edge of the conductive layer relative to a reference position, preferably a printer setting where the edge should ideally be, and averaging the measurements for a large number of printed 3D electronic assemblies (e.g., 400) to obtain an average value for the waviness of the printed edge of the conductive layer. Average values ​​can also be obtained for each surface of the polymer molding compound; for example, four average values ​​can be obtained for a cubic polymer molding compound.

[0051] The thickness of the conductive layer is preferably in the range of 0.0001 μm to 100 μm, more preferably in the range of 0.001 μm to 50 μm, even more preferably in the range of 0.1 μm to 5 μm, and even more preferably in the range of 1 μm to 4 μm.

[0052] While preferred embodiments of the present invention have been described in connection with SIPs, as shown in Figures 2-4, the present invention is also applicable to AIPs. The antenna preferably serpentines on the domed surface of the polymer encapsulant of the AIP and may be formed with precise antenna edges by forming two spaced recesses that define a raised polymer mound between them. The adjacent (inner-located) edges of the two recesses define the width of the antenna. The sharpness of the antenna edges is important with respect to the frequency accuracy of the antenna.

Claims

1. A method for depositing a conductive layer on a surface of a three-dimensional (3D) electronic assembly (10A, 10B, 10C) comprising at least one electronic device (14) embedded in a solid polymeric material (16), comprising: Providing a 3D electronic assembly (10A, 10B, 10C); forming at least one flow barrier (18) on the surface of the solid polymer material (16) of the 3D electronic assembly (10A, 10B, 10C); depositing a conductive layer (20A, 20B, 20C) on at least a portion of the surface of the solid polymer material (16) such that the conductive layer (20A, 20B, 20C) is at least partially defined by the at least one flow barrier (18); the at least one flow barrier is a recess (18); When the 3D electronic assembly (10A, 10B, 10C) is disposed on a horizontal surface, the at least one flow barrier (18) is formed on a non-horizontal and / or non-planar, preferably vertical, surface of the solid polymer material (16).

2. 2. The method of claim 1, wherein the at least one flow barrier (18) is a continuous ring-shaped flow barrier (18) that extends completely around the solid polymeric material (16).

3. The method of claim 1 , wherein the at least one recess (18) is formed by laser ablation, sawing, milling, or embossing.

4. The method of claim 1, wherein the at least one recess (18) has a depth in the range of 5 to 50 μm and a width in the range of 5 to 50 μm.

5. 10. The method of claim 1, further comprising the step of laser marking the 3D electronic assembly (10A, 10B, 10C), wherein a laser for laser marking the 3D electronic assembly (10A, 10B, 10C) is also used to form the at least one recess (18).

6. The method of claim 1 , wherein the step of depositing the conductive layer is performed by inkjet printing or spray coating.

7. 2. The method of claim 1, wherein the conductive layer (20A, 20B, 20C) is an electromagnetic interference shield (20A, 20B, 20C) covering the at least one electronic device (14), and the conductive layer (20A, 20B, 20C) is printed using a conductive ink.

8. A three-dimensional (3D) electronic assembly (10A, 10B, 10C) comprising at least one electronic device (14) embedded in a solid polymer material (16), said 3D electronic assembly (10A, 10B, 10C) comprising at least one flow barrier (18) on a surface of said solid polymer material (16), said conductive layer (20A, 20B, 20C) being disposed on at least a portion of said surface of said solid polymer material (16) such that said conductive layer (20A, 20B, 20C) is at least partially defined by said at least one flow barrier (18); the at least one flow barrier (18) is formed as a recess (18); A three-dimensional (3D) electronic assembly (10A, 10B, 10C), wherein when the 3D electronic assembly (10A, 10B, 10C) is positioned on a horizontal surface, the at least one flow barrier (18) is provided on a non-horizontal and / or non-planar, preferably vertical, surface of the solid polymer material (16).

9. 9. The 3D electronic assembly (10A, 10B, 10C) of claim 8, wherein the at least one flow barrier (18) is a continuous ring-shaped flow barrier (18) that extends completely around the solid polymer material molding (16).

10. 9. The 3D electronic assembly (10A, 10B, 10C) of claim 8, wherein said at least one recess (18) has a depth in the range of 5 to 50 μm and a width in the range of 5 to 50 μm.

11. 9. The 3D electronic assembly (10A, 10B, 10C) according to claim 8, wherein the layer thickness of said conductive layer (20A, 20B, 20C) is in the range of 0.0001 μm to 100 μm, preferably in the range of 1 to 4 μm.

12. 9. The 3D electronic assembly of claim 8, wherein the conductive layer is an electromagnetic interference shield covering the at least one electronic device, the conductive layer comprising a conductive ink.

13. 9. The 3D electronic assembly of claim 8, wherein the 3D electronic assembly is a system-in-package (SIP) or an antenna-in-package (AIP), and the solid polymer material is a molding compound.