Encapsulation method

Abstract

The present invention relates to a method for encapsulating an electrical component (2) arranged on a circuit board (3), comprising the steps of: providing a circuit board (3) having a first substrate layer (4) comprising or essentially consisting of a thermoplastic LCP material, wherein the first substrate layer (4) forms a top surface area (40) with the electrical component (2) arranged thereon, the electrical component (2) being electrically connected to at least one electrically conducting contact structure (5) of the circuit board (3), wherein a frame structure (6) comprising or essentially consisting of a second thermoplastic material is arranged on the top surface area (40) and particularly connected to the at least one substrate layer (4), so that a recess (60) is formed on the circuit board (3), wherein the electrical component (2) is arranged in the recess (60), and filling a third thermoplastic material in a moldable state into the recess (60) to encapsulate the electrical component in the third thermoplastic material.

Description

[0001] Encapsulation Method

[0002] The present invention relates to a method for encapsulating an electrical component arranged on a circuit board, particularly printed circuit board, and a circuit board assembly.

[0003] US 2004 / 0262782 Al discloses encapsulated, overmolded and / or underfilled electrical components having a complete encapsulation, wherein overmolding and / or underfilling with a coefficient of thermal expansion that is uniform and substantially free of gradients includes a polymeric matrix and an inorganic filler having a platelet geometric structure. The platelet structure of the filler allows a desirable coefficient of thermal expansion to be achieved using a very low level of filler material. This low level of filler material facilitates lower viscosity during forming of the encapsulation and / or overmolding, thereby facilitating complete filling of a mold cavity and underfilling of space between a circuit board and a semi-conductor chip electrically connected to the circuit board.

[0004] Furthermore, encapsulation in thermoplastics, e.g., LCP (liquid crystal polymer), by pressing in film structures is known in the art, wherein however, depending on the product, the films have to be extensively recessed and registered. Further, such films may have limited adhesion values after pressing, thus interfaces may remain, which may weaken the diffusion barrier. Furthermore, such films are only available in certain thicknesses, which means that the structures often cannot be adapted as required. Further, the films may flow after pressing, resulting in an undefined shape in some cases.

[0005] Furthermore, encapsulation of electronic components based on the dam and fill process is generally known in the art. Here, dosing of liquid, mostly UV-curing adhesive systems is performed to encapsulate the respective component. This is a common packaging method. However, the afore-described materials are usually not biocompatible which is mandatory for applications in implantable medical devices. Furthermore, there is a fundamental risk inherent in a build-up with different materials (different mechanical properties, expansion coefficients, etc.). Furthermore, standard dam and fill processes are also limited in the amount of packaging possible.

[0006] Based on the above, the problem to be solved by the present invention is to provide a method for encapsulating an electrical component that is cost effective and helps to realize a high- quality encapsulation of components that can be easily adapted to the dimensions of the product.

[0007] This problem is solved by a method having the features of claim 1 and a circuit board assembly having the features of claim 15. Preferred embodiments of these aspects of the present invention are stated in the corresponding dependent claims and are described below.

[0008] According to claim 1, a method for encapsulating an electrical component arranged on a circuit board is disclosed, the method comprising the steps of:

[0009] - providing a circuit board having at least one substrate layer comprising or essentially consisting of a first thermoplastic material, which substrate layer forms a top surface area with the electrical component arranged thereon, the electrical component being electrically connected to at least one electrically conducting contact structure of the circuit board, wherein a frame structure comprising or essentially consisting of a second thermoplastic material is arranged on the top surface area and particularly connected to the at least one substrate layer, wherein the frame structure at least partially surrounds the electrical component so that a recess is formed on the circuit board, wherein the electrical component is arranged in the recess, and

[0010] - filling a third thermoplastic material in a flowable state into the recess to encapsulate the at least one electrical component in the third LCP material.

[0011] In one embodiment, the first thermoplastic material is a first LCP material. In one embodiment, the second thermoplastic material is a second LCP material. In one embodiment, the third thermoplastic material is a third LCP material. In one embodiment, the third thermoplastic material is provided in a flowable state by heating, i.e., by melting the third thermoplastic material into a molten state.

[0012] In one embodiment, the third thermoplastic material, particularly the third LCP material, is provided in flowable state by heating the third thermoplastic material to a temperature in the range of 250°C to 400°C, and particularly filled into the recess having a temperature in the range of 250°C to 400°C.

[0013] In one embodiment, prior to and / or during filling the third thermoplastic material, particularly the third LCP material, in a flowable state into the recess, the circuit board is heated, particularly to a temperature in the range of 100°C to 200°C. Advantageously, by heating the circuit board prior to and / during filling the third thermoplastic material, particularly the third LCP material, the circuit board is soften to improve the joining of the third thermoplastic material to the material of the circuit board, thereby reducing or eliminating an unfavorable interface between the third thermoplastic material and the material of the circuit board.

[0014] Within the meaning of the present invention, the term "liquid crystal polymer" or „LCP” is used in the meaning known to and commonly used by a person skilled in the art. A "liquid crystal polymer" refers in particular to an aromatic polymer, which has highly ordered or crystalline regions in the molten state or in solution. Non-limiting examples include aromatic polyamides such as aramid (Kevlar) and aromatic polyesters of hydroxybenzoic acid, such as a polycondensate of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid (Vectran).

[0015] In one embodiment, the frame structure is arranged on the top surface of the at least one substrate layer after the electronic component is arranged on the top surface of the least one substrate layer. Advantageously, the frame structure may be precisely oriented and dimensioned to the actual position and size of the electronic component in that manner.

[0016] In one embodiment, the electrically conducting structure comprises a first conductor pattern arranged on a bottom surface area opposite to the top surface area. In one embodiment, the electrically conducting structure further comprises one or more vias and optionally one or more electrically conducting pads or tracks arranged on the top surface area of the first substrate layer, wherein particularly the electronic component is electrically connected to the first conductor pattern via the one or more via and optionally by the one or more electrically conductive pads or tracks. In one embodiment, the printed circuit board comprises a second substrate layer being arranged on the bottom surface area of the first substrate layer such the first conductor pattern is arranged between the first substrate layer and the substrate layer, wherein the first conductor pattern is preferably at least partly, particularly entirely, enclosed by the first and second substrate layer.

[0017] According to an embodiment of the method, the frame structure forms a circumferential lateral wall of the recess.

[0018] Furthermore, according to an embodiment of the method, the lateral wall is continuous and completely surrounds the at least one electrical component.

[0019] According to yet another embodiment of the method, the lateral wall is interrupted by one or several gaps, wherein particularly the respective gap is at least partially filled with the third thermoplastic material upon said filling of the third thermoplastic material into the recess to anchor the third thermoplastic material to the frame structure in a hardened state of the third thermoplastic material.

[0020] Furthermore, according to an embodiment of the method, the lateral wall comprises one or several notches that are filled with the third thermoplastic material upon said filling of the third thermoplastic material into the recess, to anchor the third thermoplastic material to the frame structure in a hardened state of the third thermoplastic material.

[0021] Furthermore, in an embodiment of the method, the circuit board comprises a circumferential outer edge, wherein the frame structure extends up to said outer edge and is flush with said outer edge or is spaced apart from said outer edge. Furthermore, according to an embodiment of the method, the first and the second thermoplastic materials are identical in their chemical or material composition or differ in their chemical or material composition. Particularly, the composition may be different so that the first and the second thermoplastic material have different properties, for example different melting points.

[0022] The method according to one of the preceding claims, wherein the third thermoplastic material is identical in chemical or material composition to the first and / or second thermoplastic material, or wherein the third thermoplastic material differs in composition from the first and / or second thermoplastic material.

[0023] Further, in an embodiment, the electrical component is one of: an integrated circuit (IC), particularly an Application-Specific-Integrated-Circuit (ASIC), a sensor, a diode.

[0024] According to yet another embodiment of the method, the frame structure comprises a height in a direction normal to the top surface are that is equal to or larger than a height of the electrical component in the same direction.

[0025] Preferably, the second and / or third thermoplastic material is dispensed onto the circuit board by means of a suitable process. Either conventional methods may be used here, such as a dispensing device having e.g., a mechanical or pneumatic dispensing unit, or by means of a dispensing device in form of a 3D printer. To ensure that the second and / or third thermoplastic material is in a moldable, e.g., liquid or flowable form, during the dispensing process, the respective dispensing device is preferably configured to be temperature- controlled accordingly.

[0026] In case the circuit board, particularly the printed circuit board, is used without a frame structure being already present, the frame structure may first be produced in a first dispensing / printing step, and once this has cured sufficiently, the thermoplastic encapsulation of the electrical component based on the third thermoplastic material may be carried out in a second step. The frame structure (second thermoplastic material) and the encapsulating third thermoplastic material may be applied with the same dispensing device or via two separate dispensing devices, whereby the dispensing quantities and materials can be the same or different - specifically adapted to the application.

[0027] Particularly, according to an embodiment of the method, the frame structure is generated prior to said filling of the third thermoplastic material in the recess, wherein the frame structure is generated by dispensing the third thermoplastic material in a molten state onto the at least one substrate layer using a first dispensing device.

[0028] According to a further preferred embodiment of the method, the filling of said recess with the third thermoplastic material to encapsulate the electrical component is conducted by the first dispensing device or by a separate second dispensing device.

[0029] Furthermore, in an embodiment, the third thermoplastic material after having been filled into the recess formed by the frame structure is then pressed into a defined shape by means of a stamping tool.

[0030] Depending on the type of the third thermoplastic material, viscosity, dispensing volume and dispensing speed, the encapsulation of the at least one electrical component may be in a more or less cured form directly after the dispensing process. Above a certain temperature, the third thermoplastic material is still readily moldable. This state of the third LCP material may be used in a process directly succeeding the filling of the third thermoplastic material into the recess to produce a defined 3D shape of the encapsulation, for example to compensate for height tolerances, to flatten the encapsulation, or to emboss structures in the encapsulation. The stamping tool used for this purpose can also be temperature-controlled.

[0031] According to yet another aspect of the present invention, a circuit board assembly is disclosed, the circuit board assembly comprising an electrical component arranged on a circuit board, wherein the electrical component has been encapsulated with the third thermoplastic material by the method according to the present invention.

[0032] According to yet another aspect of the present invention, a circuit board assembly is disclosed, the circuit board assembly comprising an electrical component arranged on a circuit board, wherein the circuit board comprises a first substrate layer comprising or essentially consisting of a first thermoplastic material, particularly a first LCP material, wherein the first substrate layer forms a top surface area with the electrical component arranged thereon, the electrical component being electrically connected to at least one electrically conducting contact structure of the circuit board, and a frame structure comprising or essentially consisting of a second thermoplastic material, particularly a second LCP material, is arranged on the top surface area of the first substrate and particularly connected to the first substrate layer, so that a recess is formed on the circuit board, wherein the at least one electrical component is arranged in the recess, and a third thermoplastic material, particularly a third LCP material, is arranged in the recess and encapsulates the electrical component.

[0033] According to yet another aspect of the present invention, a device for encapsulating an electrical component arranged on a circuit board is disclosed, the circuit board having a first substrate layer comprising or essentially consisting a first thermoplastic material, particularly a first LCP material, wherein the first substrate layer forms a top surface area with the electrical component arranged thereon, the electrical component being electrically connected to at least one electrically conducting contact structure of the circuit board, wherein a frame structure comprising or essentially consisting of a second thermoplastic material, particularly a second LCP material, is arranged on the top surface area and particularly connected to the first substrate layer, so that a recess is formed on the circuit board, wherein the electrical component is arranged in the recess, wherein the device comprises a dispensing device configured to fill thermoplastic material, particularly a third LCP material, in a moldable state into the recess to encapsulate the at least one electrical component in the third thermoplastic material.

[0034] Furthermore, according to an embodiment, the device is configured to generate the frame structure prior to said filling of the third thermoplastic material into the recess, wherein the device is configured to dispense the second thermoplastic material in a moldable state onto the first substrate layer of the circuit board to form the frame structure. Furthermore, in a further embodiment, the device comprises a first dispensing unit configured to generate the frame structure and a second dispensing unit configured to fill said recess with the third thermoplastic material. According to an alternative embodiment the device comprises a single dispensing device configured to form the frame structure and to fill the recess. The device can use second and third thermoplastic materials that may be different or identical in composition.

[0035] Furthermore, according to yet another embodiment of the device, the device comprises a stamping tool configured to press the third thermoplastic material filled into the recess into a defined shape. Preferably, the device is configured to control a temperature of the stamping tool.

[0036] In the following embodiments of the present invention as well as further features and advantages of the present invention shall be described with reference to the Figures, wherein

[0037] Fig. 1 shows a cross-sectional view (left-hand side) and a top view (right-hand side) of a circuit board having an electrical component mounted on a top surface area of the circuit board that shall be encapsulated by a liquid crystal polymer material,

[0038] Fig. 2 shows a cross-sectional view (left-hand side) and a top view (right-hand side) of the circuit board of Fig. 1 having an additional frame structure connected to a top substrate layer of the circuit board to laterally contain the liquid crystal polymer that shall encapsulate the electrical component,

[0039] Fig. 3 shows a cross-sectional view (left-hand side) and top views (middle and righthand side) of further embodiment of the circuit board, wherein the frame structure is spaced apart from an outer edge of the circuit board and can further comprise gaps (middle) and / or notches (right-hand side), e.g., for anchoring the liquid crystal polymer material that shall encapsulate the electrical component to the frame structure. Fig. 4 shows cross-sectional views of an embodiment of a method for encapsulating an electrical component arranged on a circuit board in a liquid crystal polymer material, wherein the component to be encapsulated is arranged in a recess defined by a frame structure of the circuit board,

[0040] Fig. 5 shows cross-sectional views of a further embodiment of a method for encapsulating an electrical component arranged on a circuit board in a liquid crystal polymer material, wherein the component to be encapsulated is arranged in a recess defined by a frame structure of the circuit board, wherein the frame structure is formed by applying a liquid crystal polymer material to the circuit board to create the recess which is then filled by a liquid crystal polymer to encapsulate the electrical component sitting in the recess defined by the frame structure.

[0041] Fig. 6 shows cross-sectional views of a further embodiment of a method for encapsulating an electrical component arranged on a circuit board in a liquid crystal polymer material, wherein here a stamping tool is used to press against the liquid crystal material encapsulating the electrical component to give a surface of the encapsulating material a defined shape.

[0042] The present invention particularly relates to packaging method for encapsulating electronic components mounted on a circuit board, wherein the method particularly includes dosing of a thermoplastic material, particularly a liquid crystal polymer material (LCP) into a defined frame structure by means of e.g. conventional dosing methods and / or 3D printing methods.

[0043] Fig. 1 shows a circuit board 3, particularly a printed circuit board (PCB), comprising a first substrate layer 4 formed out of a first LCP material and e.g. further components 5 of interconnection technology, e.g. electrically conducting contact structures such as conductor tracks, vias and / or pads etc. Furthermore, an electrical component 2, such as an IC, a sensor, diode or other component, is contacted to the corresponding connection points of the circuit board 3 using e.g., usual bonding methods known in the art, e.g., thermo-compressing bonding or reflow soldering. The electrically conducing structure may be formed by an electrically conducting pad arranged on the top surface area, a via extending from the top surface area to an opposite side of the first substrate layer and a conductor pattern arranged on the opposite side of the first substrate layer 4. The circuit board may comprise a second substrate layer 4a arranged on the opposite side of the first substrate layer 4 such the conductor pattern is arranged, and particularly embedded, between the first 4 and second 4a substrate layer.

[0044] The component 2 may be contacted on a flat top surface area 40 formed by said substrate layer 4 (cf. Fig. 1), and particularly recessed in or surrounded by a frame structures 6 arranged on the top surface are 40 (cf. Fig. 3), which is positioned either fully (cf. Fig. 2), or partially (cf. Fig. 3), or respectively with notches 63 (cf. Fig. 3) around the component 2.

[0045] Particularly, as shown e.g., in Fig. 2 (right-hand side) and Fig. 3 (middle), the frame structure 6 may form a circumferential continuous lateral wall 61 of the recess 60 without being interrupted by gaps 62. Furthermore, as shown particularly in Fig. 3 (right hand side) the lateral wall 61 formed by the frame structure 6 may be interrupted by one or several gaps 62 and may in addition (or alternatively) comprise one or several notches 63, wherein particularly the respective gap 62 or notch 63 is configured to be at least partially filled with an LCP material that shall encapsulate the component 2 which allows for a better anchoring of the encapsulating LCP material.

[0046] The first substrate layer 4 of the circuit board 3 and the frame structure may be made of the same LCP material, or of LCP material with different properties, for example different melting points. Here, the material of the circuit board 3 is denoted as first LCP material, while the material of the frame structure 6 is denoted as second LCP material. Furthermore, a height H2 and the shape of the frame structure 6 may be adapted to the height and shape of the component 2 as desired, wherein preferably the height H2 of the frame is equal to or larger than the height Hl of the component 2.

[0047] Furthermore, Fig. 4 shows an embodiment of a method for encapsulating an electrical component 2 arranged on a circuit board 3 according to the present invention, comprising the steps of providing the circuit board 3, wherein the circuit board 3 comprises a first substrate layer 4 formed out of a first LCP material, wherein the first substrate layer 4 forms a top surface area 40 with the electrical component 2 arranged thereon, the electrical component 2 being electrically connected to at least one electrically conducting contact structure 5 of the circuit board 3, wherein a frame structure 6 formed out of a second LCP material is arranged on the top surface area 40 and connected to the first substrate layer 4, so that a recess 60 is formed on the circuit board 3, wherein the electrical component 2 is arranged in the recess 60, and filling a third LCP material in a moldable state into the recess 60 to encapsulate the electrical component 2 in the third LCP material LCP3.

[0048] In other words, by means of a suitable process, the third LCP material LCP3 is dispensed onto the circuit board 3 by either conventional methods, such as a dispensing device 8 with mechanical or pneumatic dispensing unit, or a 3D printer. To ensure that the third LCP material is in liquid form during the dispensing process, the dispensing device 8 is preferably configured to be temperature-controlled accordingly.

[0049] Particularly, the third LCP material LCP3 is dispensed onto the circuit board 3 while having a temperature in the range of 250°C to 400°C. Advantageously, prior to and / or during dispensing the third LCP material, the circuit board is heated, preferably to a temperature in the range of 100°C to 200°C.

[0050] As shown in Fig. 5, in the case of a circuit board 3 without a frame structure 6 that forms a lateral wall 61 for containing the third LCP material LCP3 (or the corresponding cured encapsulation 10), the frame structure 6 / lateral wall 61 may first be produced in a first dispensing / printing step, and once this has cured sufficiently, the LCP encapsulation 10 by means of the third LCP material LCP3 can be carried out in a second step. Frame structure 6 and encapsulation 10 may be applied with one dispensing device 8 or via two successively operating dispensing device 7, 8, whereby the dispensing quantities and materials (i.e. second and third LCP materials) can be the same or different - specifically adapted to the application. For circuit boards 3 that already comprise frame structures 6, only the third LCP material for the encapsulation 10 is dispensed over the component 2 (cf. Fig. 4). The third LCP material LCP3 can be the same or different from the second (frame) LCP material LCP2.

[0051] Generally, the frame structure 6 is intended to prevent the applied encapsulation material LCP3 from flowing over the desired area 40. If the frame structure has notches 63 and / or gaps 62, the process and viscosity of the third LCP material LCP3 may be adjusted so that the liquid third LCP material flows exactly into these notches 63 / gaps 62 - or is dispensed or printed.

[0052] As further shown in Fig. 6, depending on the type of third LCP material, viscosity, dispensing volume and dispensing speed, the LCP encapsulation 10 is in a more or less cured form immediately after the dispensing process. Above a certain temperature, the third LCP material is still readily moldable. This state may be used in a process directly adjacent to the metering station to produce a defined 3D shape of the encapsulation 10 by pressing a stamping tool against the encapsulation material 10, for example to compensate for height tolerances, to flatten the encapsulation 10, or to emboss structures in the encapsulation 10. Preferably, a stamping tool 9 used for this purpose may also be temperature-controlled.

[0053] Advantageously, the present invention achieves a simplification of current approaches to a process of encapsulation of components on a circuit board (e.g. PCB) in LCP. The method according to the present invention particularly achieves a better adaptation of the encapsulation 10 to the product / component 2 and further allows a reduction of interfaces of different materials to increase product quality, especially regarding biocompatibility / permeability. Furthermore, the solution according to the present invention yields a cost- effective solution allowing a biocompatible encapsulation with high quality and at the same time can be ideally adapted to the PCB substrate and the component to be encapsulated.

Claims

Claims1. A method for encapsulating an electrical component (2) arranged on a circuit board (3), comprising the steps of: providing a circuit board (3) having a first substrate layer (4) comprising or essentially consisting of a first thermoplastic material, particularly a first LCP material, which the first substrate layer (4) forms a top surface area (40) with the electrical component (2) arranged thereon, the electrical component (2) being electrically connected to at least one electrically conducting contact structure (5) of the circuit board (3), wherein is by a frame structure (6comprising or essentially consisting of a second thermoplastic material, particularly a second LCP material, is arranged on the top surface area (40) and particularly connected to the first substrate layer (4), wherein the frame structure at least partially surrounds the electronic component so that a recess (60) is formed on the circuit board (3), wherein the electrical component (2) is arranged in the recess (60), and filling a thermoplastic material, particularly a third LCP material, in a moldable state into the recess (60) to encapsulate the electrical component in the third thermoplastic material.

2. The method according to claim 1, wherein the frame structure (6) forms a circumferential lateral wall (61) of the recess (60).

3. The method according to claim 2, wherein the lateral wall (61) is continuous.

4. The method according to claim 2, wherein the lateral wall (61) is interrupted by one or several gaps (62), wherein particularly the respective gap 62 is at least partially filled with the third LCP material upon said filling of the third LCP material into the recess to anchor the third LCP material to the frame structure in a hardened state of the third LCP material.

5. The method according to one of the preceding claims, wherein the lateral wall (61) comprises one or several notches (62) that are filled with the third thermoplasticmaterial upon said filling of the third thermoplastic material into the recess (60) to anchor the third thermoplastic material to the frame structure (6) in a hardened state of the third thermoplastic material.

6. The method according to one of the preceding claims, wherein the circuit board (3) comprises a circumferential outer edge (30), wherein the frame structure (6) extends up to said outer edge (30) and is flush with said outer edge or is spaced apart from said outer edge (30).

7. The method according to one of the preceding claims, wherein the first and the second thermoplastic materials are identical in their chemical or material composition or differ in their chemical composition.

8. The method according to one of the preceding claims, wherein the third thermoplastic material is identical in chemical or material composition to the first and / or second thermoplastic material, or wherein the third thermoplastic material differs in chemical composition from the first and / or second thermoplastic material.

9. The method according to one of the preceding claims, wherein the at least one electrically conducting contact structure (5) is designed in form of a conductor track, a via, and / or an electrically conducting pad.

10. The method according to one of the preceding claims, wherein the electrical component (2) is one of an integrated circuit (IC), a sensor, or a diode.

11. The method according to one of the preceding claims, wherein the frame structure (6) comprises a height (Hl) in a direction normal to the top surface area (40) that is equal to or larger than a height (H2) of the electrical component (2) in the same direction.

12. The method according to one of the preceding claims, wherein the frame structure (6) is generated prior to said filling of the third thermoplastic material in the recess (60), wherein the frame structure is generated by dispensing the third thermoplastic materialin a flowable state onto the at least one substrate layer (4) using a first dispensing device (7).

13. The method according to one of the preceding claims, wherein the filling of said recess (60) with the third thermoplastic material is conducted by the first dispensing device (7) or by a separate second dispensing device (8).

14. The method according to one of the preceding claims, wherein the third thermoplastic material after having been filled into the recess is then pressed into a defined shape by means of a stamping tool (9).

15. A circuit board assembly comprising circuit board (3) having a first substrate layer (4) comprising or essentially consisting of a first thermoplastic material, particularly a first LCP material, which the first one substrate layer (4) forms a top surface area (40) with the electrical component (2) arranged thereon, the electrical component (2) being electrically connected to at least one electrically conducting contact structure (5) of the circuit board, wherein a frame structure (6) comprising or essentially consisting of a second thermoplastic material, particularly a second LCP material, is arranged on the top surface area (40) and particularly connected to the first substrate layer (4), so that a recess (6) is formed on the circuit board (3), wherein the electrical component (2) is arranged in the recess (60), wherein a third thermoplastic material, particularly a third LCP material, is arranged in the recess (60) encapsulates the electrical component (2).

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