WO2008152575A1

WO2008152575A1 - Flexible electronics package and method for manufacturing such a package

Info

Publication number: WO2008152575A1
Application number: PCT/IB2008/052280
Authority: WO
Inventors: Koen Van Os; Arie H. Kentie; Thomas Schüler
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-06-14
Filing date: 2008-06-10
Publication date: 2008-12-18
Also published as: TW200916002A

Abstract

A flexible electronics package (1;40;50) comprising a flexible substrate (10), having an electronic component (3) connected thereto, and a flexible encapsulant (12) at least party embedding the flexible substrate(10). The flexible electronics package (1;40;50) further comprises at least a first textile sheet (13) provided on a first side (11) of the flexible substrate (10), the first textile sheet (13) being at least partly embedded by the flexible encapsulant (12).

Description

Flexible electronics package and method for manufacturing such a package

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a flexible electronics package and a method for manufacturing such a package.

TECHNICAL BACKGROUND

Due to the ever ongoing integration of electronics in new applications, such as in electronic textiles including clothing or domestic textiles with integrated sensors and/or displays, there is an increasing demand for flexible electronics packages and circuit boards.

In flexible electronics packages, electronic components are typically mounted on a flexible substrate, such as a very thin "ordinary" printed circuit board (PCB) substrate, for example FR-4, or a better adapted but generally more expensive polyimide (or similar) based flexible printed circuit board (FPC).

However, the electronic components mounted on the flexible substrate are generally unprotected and, especially in the case of the very thin "ordinary" substrates, the substrate itself is not very durable in respect of repeated bending, which is often encountered in the above-mentioned electronic textiles.

One method of protecting the electronic components mounted on the flexible substrate and increasing the durability of the substrate itself is to mold the populated flexible circuit board in a flexible encapsulant, such as silicone. The flexible electronics packages manufactured using this method have, however, turned out to be prone to delamination and cracking, and accompanying degraded performance and sensitivity to changes in the environment, such as elevated humidity and temperature.

SUMMARY OF THE INVENTION

In view of the above-mentioned and other drawbacks of the prior art, a general object of the present invention is to provide an improved flexible electronics package, especially having an improved robustness and life-time. According to a first aspect of the present invention, these and other objects are achieved through a method for manufacturing a flexible electronics package, comprising the steps of providing a flexible circuit board having an electronic component connected thereto; providing at least a first textile sheet on a first side of the flexible circuit board; and encapsulating the flexible circuit board and the textile sheet by means of a flexible encapsulant in such a way that the first textile sheet is at least partly embedded by the encapsulant.

By "textile sheet" should, in the context of the present application, be understood a sheet manufactured by textile fibers. The textile sheet may, for example, be manufactured by means of weaving, braiding, knitting, or felting. In particular, the textile sheet may be woven or non- woven.

The present invention is based upon the realization that the robustness of the flexible electronics package can be significantly increased, while sacrificing very little flexibility, by at least partly embedding a textile sheet, together with the populated flexible circuit board, in the encapsulant, to thereby form a sandwich construction.

In addition to being an additional, reinforcing layer, adding to the integrity of the electronics package, the textured and absorbing nature of the textile sheet improves the quality of the encapsulation by reducing the occurrence of bubbles or voids in the encapsulant. Furthermore, the adhesion of the encapsulant to the flexible substrate is improved, due to the very large surface area of the textile sheet with respect to the encapsulant.

Furthermore, when providing the textile sheet on the same side as the electronic components, the protection of these electronic components is improved compared to the case when they are only covered by the flexible encapsulant. Moreover, the manufacturing method according to the present invention enables the manufacture of a flexible electronics package which is easy to integrate in a textile application, such as a piece of clothing. By only partly embedding the first textile sheet in the flexible encapsulant, the flexible electronics package is provided with fastening means, in the form of the "free" portion of the first textile sheet, which can subsequently be integrated into the textile application by means of conventional textile processes, such as sewing, gluing, forming etc.

By providing a second textile sheet on a second side of the flexible substrate and additionally at least partly embedding this second textile sheet in the flexible encapsulant, the integrity and robustness of the flexible electronics package can be even further improved. Moreover, in case of double-sided mounting of electronic components, the electronic components on both sides of the flexible substrate can be protected through the provision of the additional second textile sheet. As discussed above for the first textile sheet, the second textile sheet may be completely or partly embedded by the flexible encapsulant. According to one embodiment, one or several of the electronic components mounted on the flexible substrate may be optical electronic components, such as light- sources and/or optical detectors. Suitable light-sources for use in electronic textile applications may typically include compact semiconductor light-sources, such as light- emitting diodes (LEDs) and semiconductor lasers. When optical electronic components are mounted on the flexible substrate, an optically transparent flexible encapsulant is typically selected. The optically transparent flexible encapsulant should be at least partly transmissive in the wavelength range which is relevant for the particular optical electronic component(s) utilized.

In case optical electronic components are mounted on the flexible substrate, the textile sheet covering the optical electronic components may, furthermore, be configured to alter at least one property of light passing through it. For example, the textile sheet may diffuse light emitted by a light-source, such as a LED, or the textile sheet may have one or several colored portions acting as color filter(s). Moreover, the textile sheet may be selectively transmissive and function as a mask for enabling output of a luminous pattern or symbol etc.

Alternatively, or in combination with the optical properties of the textile sheet discussed above, the textile sheet may include one or several apertures, and the method may then further include the step of aligning such apertures to corresponding optical electronic components provided on the flexible substrate. Such a textile sheet with apertures may, for example, be used when diffuse light is unwanted or a further optical element is added to the flexible electronics package.

Such an optical element may, for example, be provided by shaping the flexible encapsulant appropriately at a position corresponding to the optical electronic component.

The encapsulant can be shaped into the desired optical element by adapting the mold appropriately. Examples of such optical elements include various lenses, diffusers, gratings, etc.

Optical elements can also be implemented/realized by placing one or several discrete optical elements, such as lenses and/or reflectors, or an interconnected array of optical elements in the mold prior to adding the encapsulant, or they can be immersed in the encapsulant prior to curing thereof.

Furthermore, the textile sheet can be configured to function as one or several optical elements, such as a suitably shaped reflector for selected optical electronic components. For this purpose, one or several further textile sheets may be added to the flexible electronics package.

According to a second aspect of the present invention, the above-mentioned and other objects are achieved by a flexible electronics package comprising a flexible substrate, having an electronic component connected thereto; and a flexible encapsulant at least partly embedding the flexible substrate, wherein the flexible electronics package further comprises at least a first textile sheet provided on a first side of the flexible substrate, the first textile sheet being at least partly embedded by the flexible encapsulant.

Features and advantages of this second aspect of the present invention are largely analogous to those described above in connection with the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention, wherein:

Figs, la-b schematically illustrates an exemplary embodiment of the flexible electronics package according to the present invention, in the form of a LED-array light- output device;

Fig. 2 is a flow chart illustrating a method for manufacturing the flexible electronics package in Figs, la-b;

Fig. 3 schematically illustrates the molding of the flexible electronics package in Fig. 1;

Fig. 4 is a section view of an exemplary flexible electronics package according to an embodiment of the present invention having molded optical elements; and Fig. 5 is a section view of another exemplary flexible electronics package according to an embodiment of the present invention having a combination of the molded optical elements in Fig. 4 and embedded discrete optical elements. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the present detailed description, the present invention is mainly described with reference to a flexible electronics package comprising a flexible PCB populated with a plurality of optical electronic devices in the form of LEDs, which is embedded by a flexible and optically transparent encapsulant together with first and second textile sheets.

It should be noted that this by no means limits the scope of the invention, which is equally applicable to flexible electronics packages including other electronic components, a non-transparent flexible encapsulant, and/or a textile sheet provided on one side thereof only etc. Fig. Ia is a schematic top view of a flexible electronics package according to an embodiment of the present invention, where the flexible electronics package 1 is provided in the form of a flexible array 2 of LEDs 3 (only one of these is indicated by a reference numeral for ease of drawing), having a textile rim 4 surrounding the LED array 2 for facilitating integration of the flexible electronics package 1 into a textile application, such as a piece of clothing. As is also indicated in Fig. Ia, the LEDs 3 in the LED array 2 are connected to a power supply 5 via connecting wires 6a-b, and, consequently, emit light. The structure of the flexible electronics package 1 in Fig. Ia will now be described with reference to fig Ib, which is a schematic section view of the flexible electronics package 1 along the line I-I in Fig. Ia. It should be noted that the proportions of the flexible electronics package 1 have been distorted to enable a more informative illustration thereof.

As is illustrated in Fig. Ib, the flexible electronics package 1 comprises a flexible substrate 10, on which the LEDs 3 are mounted on a first side 11 thereof. The flexible substrate 10 is embedded by a flexible, optically transparent encapsulant 12. Also embedded by the encapsulant 12 are, as shown in Fig. Ib, a first textile sheet 13 on the first side of the flexible substrate, and a second textile sheet 14 on a second side 15 of the flexible substrate opposite the first side 11. The second textile sheet 14 is completely embedded by the encapsulant 12, while the first textile sheet 13 is partly embedded by the encapsulant 12. The portion of the first textile sheet 13 that is not embedded is the textile rim 4 for attachment of the flexible electronics package 1 to a textile, such as a piece of clothing or domestic textile.

In the following, a method for manufacturing the flexible electronics package 1 shown in Figs, la-b will be described with reference to the flow chart in Fig. 2 and the schematic illustration of the molding step in Fig. 3. With reference to Fig. 2 and Fig. 3, a textile sheet 14 is placed in a cavity 20 in a lower part 21 of a mold 22 in a first step 100. This lower textile sheet 14 has a smaller extension than the cavity 20 and fits therein as illustrated in Fig. 3.

Subsequently, in step 101, the populated flexible printed circuit board 25 (including a flexible substrate 10 and optical electronic components in the form of LEDs 3 mounted on the first side 11 thereof) is suspended in the lower part 21 of the mold 22 by aligning holes 26a-b provided in the flexible PCB 25 with pins 27a-b provided in the lower part 21 of the mold 22, and on a moveable ruler 28, respectively. The flexible PCB 25 is kept flat and suspended by exerting a pulling force on the ruler 28, thereby tensioning the flexible PCB 25. Although not specifically illustrated here, the flexible substrate 10 may advantageously be perforated in order to increase flexibility and also to improve the adhesion of the encapsulant 12 to the flexible PCB 25.

In the next step 102, an upper textile sheet 13 having a larger extension than the mold 22 is provided on top of the flexible PCB 25 which is suspended in the lower mold part 21. This upper textile sheet 13 may preferably be configured to diffusively transmit the light emitted by the LEDs 3 mounted on the flexible substrate 10, while being sufficiently opaque to conceal the other electronics and circuit traces of the flexible PCB 25. Hereby, the function of the LED array 2 is enhanced, while concealing the "technology" from the user. As described above in connection with Fig. Ia, the portion 4 of the upper textile sheet 13 which is outside the mold 22 can function as means for attaching the flexible electronics package 1 to a textile electronics application.

Thereafter, in step 103, the lower mold part 21 is filled with a liquid, transparent encapsulant 12. The encapsulant may, for example, be a transparent silicone, such as Silgard^® 184. During filling of the mold 22, the textile sheets 13, 14 will absorb the liquid encapsulant 12 through capillary action and thereby facilitate the formation of a bubble free encapsulant. The mold 22 is then closed by attaching a covering upper mold part 29 thereto, so that the excess liquid encapsulant 12 flows out of the mold 22 through the overflow holes 30a-b provided in the upper mold part 29.

Finally, in step 104, the encapsulant 12 is cured, for example, through heating, the mold 22 is opened, and the finished flexible electronics package 1 is removed from the lower mold part 21.

Through the embedding of the textile sheets 13, 14 in the encapsulant 12, the thus manufactured flexible electronics package 1 has been reinforced to become more durable, has received a more appealing appearance, and has received means, in the form of the textile rim 4, for integration into a textile application.

It should be noted that the manufacturing method described above merely represents an example, and that many variations to this method are apparent to the skilled person. For example, a molding procedure adapted for mass production would typically involve filling the mold under vacuum etc.

In the procedure described above, integral textile sheets 13, 14 were used, and no step of precise alignment to the LEDs 3 comprised in the flexible PCB 25 was performed. In other embodiments, certain or all of the LEDs 3 may not be covered by the upper textile sheet 13 and/or additional optical elements may be incorporated in the flexible electronics package 1. Two such exemplary embodiments are schematically illustrated by Figs. 4 and 5. In Fig. 4, which is a section view of an exemplary flexible electronics package 40, an aperture 41 in the upper textile sheet 13 has been aligned with one 3c of the LEDs 3a-c mounted on the flexible substrate 10. In the section illustrated in Fig. 4, one of the perforations 42 in the flexible substrate 10 discussed above is also visible. Furthermore, it is illustrated by Fig. 4 that the flexible and optically transparent encapsulant 12 has been locally shaped into optical elements 43a-c at positions corresponding to the LEDs 3a-c. The optical elements 43a-c are here shown as convex domes, but may be provided in many other shapes depending on how the upper mold part 29 (referring to Fig. 3) is configured. Another exemplary flexible electronics package 50 is schematically shown in

Fig. 5. This flexible electronics package 50 differs from the electronics package 40 in Fig. 4 in that the upper textile sheet 13 has one aperture 51a-c for each LED 3a-c, and that a discrete optical element 52a-c, here in the form of a reflector, has been positioned in the mold 22 prior to filling encapsulant 12 therein. Accordingly, the reflectors 52a-c have been embedded by the encapsulant, and optical devices 53a-c, each comprising a LED 3a-c, a reflector 52a-c, and a convex dome 43a-c have thus been formed.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments. For example, other elements may be included in the flexible electronics package other than the optical elements described above. Such other elements may, for example, include fastening means, such as buttons etc for facilitating mechanical integration of the flexible electronics package in applications, such as electronic textiles. Moreover, such other elements may include activation means, for example switches, buttons etc for enabling user control of the electronic components included in the flexible electronics package.

Claims

CLAIMS:

1. A method for manufacturing a flexible electronics package (1; 40; 50), comprising the steps of: providing (101) a flexible circuit board (25) having an electronic component (3a-c) connected thereto; providing (102) at least a first textile sheet (13) on a first side (11) of said flexible circuit board (25); and encapsulating (103) said flexible circuit board (25) and said textile sheet (13) by means of a flexible encapsulant (12) in such a way that said first textile sheet (13) is at least partly embedded by said encapsulant (12).

2. A method according to claim 1 further comprising the step of: providing (100) a second textile sheet (14) on a second side (15) of the flexible circuit board (25) opposite said first side (11) of the flexible circuit board.

3. A method according to claim 1 or 2, wherein said electronic component is an optical electronic component (3).

4. A method according to claim 3, wherein said optical electronic component (3a-c) is mounted on said first side (11) of the flexible circuit board (25), said first textile sheet (13) includes an aperture (41), and said step of providing (101) said first textile sheet (13) comprises the step of: aligning said aperture (41) to said optical electronic component (3 c).

5. A method according to claim 3 or 4, wherein said step (103) of encapsulating comprises the step of: shaping said flexible encapsulant (12) to function as an optical element (41a-c) at a position corresponding to said optical electronic component (3a-c).

6. A method according to any one of claims 3 to 5, further comprising the step of: providing an optical element (52a-c) at a position corresponding to said optical electronic component (3a-c), wherein said step of encapsulating (103) includes: encapsulating said optical element (52a-c) in such a way that said optical element is at least partly embedded by said encapsulant (12).

7. A flexible electronics package (1; 40; 50) comprising: a flexible substrate (10), having an electronic component (3) connected thereto; and a flexible encapsulant (12) at least partly embedding said flexible substrate (10), characterized in that said flexible electronics package (1; 40; 50) further comprises at least a first textile sheet (13) provided on a first side (11) of said flexible substrate (10), said first textile sheet (13) being at least partly embedded by said flexible encapsulant (12).

8. A flexible electronics package (1; 40; 50) according to claim 7, wherein only a portion of said first textile sheet is embedded by said encapsulant (12).

9. A flexible electronics package (1; 40; 50) according to claim 7 or 8, further comprising a second textile sheet (14) provided on a second side (15) of said flexible substrate (10) opposite said first side (11) of the flexible substrate, said second textile sheet (14) being at least partly embedded by said flexible encapsulant (12).

10. A flexible electronics package (1; 40; 50) according to any one of claims 7 to 9, wherein said flexible encapsulant (12) is optically transparent.

11. A flexible electronics package (1; 40; 50) according to claim 10, wherein said electronic component is an optical electronic component (3).

12. A flexible electronics package (1; 40; 50) according to claim 11, wherein said optical electronic component (3) is mounted on said first side (11) of the flexible substrate (10).

13. A flexible electronics package (1; 40; 50) according to claim 12, wherein said first textile sheet (13) is configured to diffusely transmit light.

14. A flexible electronics package (1; 40; 50) according to claim 7, comprising: a flexible substrate (1; 40; 50) having a plurality of light-emitting devices (3a-c) mounted on said first side (11) thereof; a first, diffusely optically transparent textile sheet (13) provided to cover said light-emitting devices (3a-c); a second textile sheet (14) provided on a second side (15) of said flexible substrate (10), opposite said first side (11) thereof; and a transparent flexible encapsulant (12) at least partly embedding said flexible substrate (10), said first textile sheet (13), and said second textile sheet (14).