Method for printing conductive layer on surface of three-dimensional electronic assembly and related three-dimensional 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 a 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 nowadays common to insulate and protect electronic components, and even complete electronic circuits, such as systems in packages (SIPs), in polymer encapsulants. The polymer encapsulant may, for example, comprise a molding compound, more specifically an epoxy molding compound. Due to the high density of electrical functions integrated into complete electronic circuits, electromagnetic or electrical interference (EMI) can cause the electronic circuits to fail completely. For this reason, it is necessary to shield these electronic circuits to suppress both EMI radiation from being emitted from the electronic circuits and EMI radiation from being received by the electronic circuits.

[0003] Conventionally, metal housings are used in SIP modules, for example for EMI shielding purposes. However, metal housings do not meet the objective of miniaturization. Instead of using metal housings, the functional layers can be applied, for example by PVD processes. Alternatively, for example, an inkjet printer can be used to deposit a silver-containing inkjet ink on the surface of the SIP module. 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 means for curing are conceivable, such as oven curing, IR irradiation or plasma. 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 inks on the surfaces of 3D electronic assemblies, such as SIP modules, the ink tends to flow downwards on inclined or vertical surfaces due to gravity. 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 not to be precisely defined. Instead, they exhibit a wavy shape, and as a result, the ink layers cannot be printed in close proximity to the conductive components of the 3D electronic assemblies. Safety margins must be observed to prevent electrical shorts. Moreover, printing on surfaces that are not plane-parallel to the printhead of the inkjet printer also results in inaccurate and wavy printed edges.

[0007] It is an object of the present invention to provide a method for depositing a conductive layer on a surface of a 3D electronic assembly, such as a SIP, which reduces or overcomes the disadvantages of the 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 kind of conductive layer (or conductive print pattern) on a 3D electronic assembly. The conductive layer may be any kind of layer. When applied, this layer preferably achieves an EMI shielding function from electromagnetic interference (EMI) caused by electromagnetic induction or electromagnetic radiation emitted from electronic devices in the 3D electronic assembly or from external sources. However, this layer can also preferably be formed to perform the function of an antenna in an Antenna-in-Package (AIP).

[0010] The conductive layer may be composed 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 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 an 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 can also include a non-conductive layer, such as a protective layer, that protects the conductive layer underneath from damage and / or other deleterious environmental effects, such as excessive heat and corrosion-inducing substances (e.g., oxygen).

[0013] Using the method according to the invention, the conductive layer can be deposited only on certain parts or on the entire exposed surface(s) of the 3D electronic assembly, and the layer thickness can be selectively manipulated to be either variable or very uniform and homogeneous over the entire deposited part 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 adapted to the needs and requirements of the user.

[0014] In the method of the present invention, it is preferred to use SIP.However, in general, any 3D electronic assembly that needs to be at least partially covered by a conductive layer, such as 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 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 requirements of the user. The method of the present invention is preferably carried out using an inkjet printer having one or more printheads. Each printhead has a number of print nozzles arranged in a print nozzle plane. The printing width of the printheads 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 function. For example, curing can be achieved using UV light. Other means of curing are also conceivable, such as oven curing, IR irradiation or plasma. Before the printing process, the surface of the 3D electronic assembly may undergo a pretreatment process, for example using plasma, for cleaning purposes.

[0018] After each printing step or a certain number of printing steps, the conductive layer can be cured. If an ink requiring crosslinking is used, the crosslinked ink may further undergo a 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 comprising at least one electronic device embedded in a solid polymer material, the method comprising 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 polymeric 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 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 performed 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, the conductive layer being 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, a conductive layer being 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] When the 3D electronic assembly is arranged 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 polymeric 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, 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 moulding compound.

[0036] The above features of the first and second aspects of the invention may be combined in any manner, and therefore the invention is not limited to the feature combinations described below with reference to preferred embodiments of the invention. [Brief description 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 present invention, and are in no way intended to limit the present invention, but merely to illustrate preferred embodiments thereof, in which: [Figure 1] FIG. 1 is a diagram showing a conventional Standard-in-Package (SIP). [Diagram 2] FIG. 2 illustrates a SIP according to a preferred embodiment of the present invention. [Diagram 3]FIG. 2 illustrates another SIP according to another preferred embodiment of the present invention. [Figure 4] FIG. 13 illustrates a further SIP according to yet another preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] It is pointed out again 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. 1-4, the same reference numbers 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 parts 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. Since high-viscosity inks are difficult to process by inkjet printing, low-viscosity inks are the first choice for the conductive layer. Low-viscosity inks tend to flow downwards due to gravity, and therefore the edge(s) of the conductive layer are uneven, imprecise, and wavy. The wavy (blurred) edge(s) result in a variation in the layer thickness of the conductive layer. In particular, the layer thickness near the edge of the sidewall tends to be thinner than other parts, resulting in poorer EMI shielding in the areas with thinner layer thickness. When multiple layers of ink are printed, the thickness deviation of the wavy (blurred) edge tends to be larger.

[0042] To reduce or eliminate this problem, FIG. 2 shows a SIP 10A according to a preferred embodiment of the present invention. As shown in FIG. 1, a number of 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 sharpness of the conductive layer at the sidewalls, recesses 18 are formed on some or all of the vertical sidewalls to act as ink flow barriers. The recesses 18 may preferably extend continuously, i.e., without any interruptions or gaps, around the periphery of the polymer molding compound 16. Wet ink is allowed to flow into the recesses 18 and accumulate therein until the ink is sufficiently cured, at which point the ink will no longer flow downwards due to gravity, thus resulting in precise and sharp edge(s) of the conductive layer 20A. It should be noted 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 recess, but instead may stop abruptly before reaching the bottom of the recess. 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 the SIP 10A of FIG. 2, inter alia, in that a conductive layer 20B is deposited only on a portion of the top surface of the polymer molding compound 16. Again, a recess 18 is formed on one, preferably three, vertical sidewalls of the polymer molding compound 16, and another recess 18 is formed on the top surface of the polymer molding compound 16 to prevent ink from flowing into areas of the top surface of the molding compound 16 that should not be covered by ink. The sidewall recess 18 may preferably extend continuously along all three sidewalls of the polymer molding compound 16. However, it may also extend along only one sidewall of the polymer molding compound 16, resulting in the three sidewalls of the cubic polymer molding compound 16 being devoid 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 may preferably extend 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 structured 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 may range from 5 to 50 μm, and the width of the at least one recess 18 may range from 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 a ring 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, the conductive layers 20A, 20B, 20C are at least partially defined by at least one recess 18. "Defined" in this context can be interpreted as the edge of the conductive layers 20A, 20B, 20C being defined by the upstream edge in the ink flow direction. Thus, the sharpness of the edge of the conductive layers 20A, 20B, 20C is improved regardless of whether the ink completely fills the at least one recess 18 or only partially fills it. The at least one recess 18 can be formed, for example, by laser ablation, sawing, milling, and embossing.

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

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

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

[0050] The waviness can be measured using a suitable imaging technique, for example, 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 number of printed 3D electronic assemblies (e.g., 400 pieces) to obtain an average value of the waviness of the printed edge of the conductive layer. An average value 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] Although the preferred embodiment of the invention has been described in relation to a SIP, as shown in Figures 2-4, the invention may also be applied to an AIP. The antenna preferably snakes 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 (inboard) 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 said surface of said solid polymer material (16) of said 3D electronic assembly (10A, 10B, 10C); and depositing a conductive layer (20A, 20B, 20C) on at least a portion of said surface of said solid polymeric material (16) such that said conductive layer (20A, 20B, 20C) is at least partially defined by said at least one flow barrier (18).

2. 2. The method of claim 1, wherein when the 3D electronic assembly (10A, 10B, 10C) is arranged 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).

3. The method of claim 1 or 2, 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).

4. The method according to any one of claims 1 to 3, wherein said at least one flow barrier is a recess (18).

5. The method of claim 4, wherein the at least one recess (18) is formed by laser ablation, sawing, milling, or embossing.

6. A method according to any one of claims 4 or 5, 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.

7. 7. The method according to any one of claims 4 to 6, further comprising a 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 for forming the at least one recess (18).

8. The method according to any one of claims 1 to 7, wherein the step of depositing the conductive layer is performed by inkjet printing or spray coating.

9. The method of any one of claims 1 to 8, 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.

10. 1. A three-dimensional (3D) electronic assembly (10A, 10B, 10C) comprising at least one electronic device (14) embedded in a solid polymeric material (16), said 3D electronic assembly (10A, 10B, 10C) comprising at least one flow barrier (18) on a surface of said solid polymeric material (16), said conductive layer (20A, 20B, 20C) being provided on at least a portion of said surface of said solid polymeric material (16) such that said conductive layer (20A, 20B, 20C) is at least partially defined by said at least one flow barrier (18).

11. 11. The 3D electronic assembly (10A, 10B, 10C) of claim 10, wherein 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) when the 3D electronic assembly (10A, 10B, 10C) is arranged on a horizontal surface.

12. 12. The 3D electronic assembly (10A, 10B, 10C) of claim 10 or 11, wherein the at least one flow barrier (18) is a continuous ring-shaped flow barrier (18) that extends completely around the solid polymeric material body (16).

13. The 3D electronic assembly (10A, 10B, 10C) according to any one of claims 10 to 12, wherein the at least one flow barrier (18) is formed as a recess (18).

14. The 3D electronic assembly (10A, 10B, 10C) of claim 13, 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.

15. 3D electronic assembly (10A, 10B, 10C) according to any one of claims 10 to 14, wherein the conductive layer (20A, 20B, 20C) has a layer thickness in the range of 0.0001 μm to 100 μm, preferably in the range of 1 to 4 μm.

16. 16. The 3D electronic assembly (10A, 10B, 10C) of any one of claims 10 to 15, 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) comprises a conductive ink.

17. The method of any one of claims 1 to 9 or the 3D electronic assembly of any one of claims 10 to 16, wherein the 3D electronic assembly is a System-in-Package (SIP) or Antenna-in-Package (AIP) and the solid polymer material is a moulding compound.

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