Field of the invention

The present invention relates to a LED module comprising an insulated metal substrate. In particular the invention relates to an integrated LED module with insulated metal substrate and advanced circuitry having stress reducing means .

Background of the invention

In the prior art, LED Modules comprising an insulated metal substrate (IMS) are known, on which substrate one or more LED Chips are arranged. The insulated metal substrate usually comprises a metal sheet base covered by an insulating layer of dielectric material such as resin or ceramic material. The dielectric material ensures the insulation of electric components arranged thereon from the metal sheet of the IMS and additionally enables heat dissipation from the electric components to the metal sheet base.

For connecting the LED Chips onto the IMS carrier, chip- on-board technique is usually applied. In addition to LED Chips, circuitry for current provision and current control for the LED Chips may be provided on the IMS carrier. A known solution is hereby the provision of the circuitry by means of surface mounted devices (SMD) on the carrier.

A problem that arises in such solutions is the restricted arrangement possibility of the electric parts on the IMS carrier. This is in particular due to the fact that the electric parts are usually connected to a surface of the IMS carrier after the provision of the LED Chips, as there exists the risk of the bond pads for the LED Chips on the carrier being contaminated in a soldering process for the electric parts. Accordingly, the area on the IMS carrier on which electric parts such as SMD parts may be arranged, as well as their particular orientation on the IMS carrier is limited. Therefore, complex circuitry and high populated circuits cannot be realized on these LED modules .

The present invention thus seeks to provide an enhanced IMS LED Module with complex circuitry, and which may be manufactured economically while at the same time a reliable connection between the individual parts of the IMS module is to be provided.

Summary of the invention

In a first aspect, the invention relates to a LED Module comprising a first carrier with at least one LED Chip arranged thereon and a second carrier on which electric components for being connected to the at least one LED Chip are arranged, wherein the first carrier is an insulated metal substrate comprising a metal base material and a dielectric layer on which the at least one LED Chip is arranged, wherein the second carrier is a sheet-shaped circuit board arranged to at least partially cover a top surface of the first carrier and which is electrically connected to the first carrier, and wherein the second carrier comprises stress reducing means which arranged to at least partially surround or encompass electric connection means of the first and second carrier. The first and second carrier may thus be prefabricated individually and then joined together in order to form the LED module. Due to the independent manufacturing of the first and second carrier, the constraints as present in particular to the spatial arrangement of the electric components on the LED module are overcome. Moreover, the first and second carrier comprising the at least one LED chip respectively constituting the circuit board for the electric components of the LED module may be manufactured and tested individually before joining. Accordingly, more sophisticated and complex circuitry can be provided on the LED module without the necessity of increasing the dimensions of the LED module.

As the LED module comprises stress reducing means, a fixed and reliable connection between the first and second carrier is provided. Accordingly, material stresses that may be caused when soldering the first and second carrier together can be minimized. Such temperature caused stresses may in particular occur in case of the first and second carrier being made of different material and having different thermal expansion coefficients. For example in case of the metal base material of the first carrier being made from aluminium and the second carrier being made from FR4 material, the thermal expansion coefficients of these materials essentially differ which may cause stresses within the first and/or second carriers during and/or after the soldering process.

The stress reducing means of the LED module are preferably dilatation means designed to enable an at least partial dilatation of the first and/or second carrier with respect to each other. The second carrier is preferably arranged on the top surface of the first carrier such as to cover at least 50%, more preferably at least 65%, most preferably at least 75% of the top surface of the first carrier.

The second carrier is preferably arranged such as to at least partially surround the at least one LED Chip on the first carrier. In a preferred embodiment, the second carrier is essentially ring-shaped or rectangular. The second carrier preferably comprises at least one opening or through hole through which the at least one LED Chip of the first carrier protrudes. The at least one opening is preferably arranged in a central portion of the second carrier. The second carrier may comprise a plurality of openings or through holes through which a plurality of LED Chips of the first carrier protrude.

The second carrier constitutes a circuit board for mounting electric components thereon. The second carrier is preferably made from a material different than the material of the first carrier. The second carrier is preferably made from FR4 material. The electric components are preferably surface mounted devices (SMD) which are mounted onto the second carrier.

The first carrier is constituted by an insulated metal substrate. Thereby, the metal base layer material is preferably made by aluminium. The dielectric layer is preferably made from a ceramic material or an insulating resin material. The LED Chip is preferably arranged on the dielectric layer.

The at least one LED Chip is connected to the first carrier by means of chip-on-board technique. In a preferred embodiment, a plurality of LED chips is arranged on the first carrier. The LED Chips are preferably arranged in a central portion of the first carrier.

The at least one LED Chip is preferably encapsulated by a color conversion material. Thereby, a resin material such as a silicone matrix comprising color conversion particles may be applied onto the surface of the LED Chip. Accordingly, at least a portion of the primary light emitted by the LED chip is converted into a light of another wavelength. The light emitted by the color converted LED Chip is preferably white light.

The at least one LED chip is preferably covered by a dam- and-fill arrangement that may be formed on the top surface of the first carrier by means of a dispensing technique. Thereby, a surrounding dam is provided on the top surface of the first carrier, which is then filled by a color conversion material as described above.

In a preferred embodiment, the first carrier and the second carrier are connected such as to form a sandwichlike structure or laminate. Preferably, the outer contours of the second carrier essentially correspond to the outer contours of the first carrier. In a particularly preferred embodiment, the first and second carrier are preferably of essentially circular or rectangular shape.

The first and second carrier are preferably connected by at least partially flexible connecting means. In a preferred embodiment, the first and second carrier are connected by means of an adhesive foil. The adhesive foil may be a double-sided adhesive foil. The adhesive foil preferably comprises outer contours conformal to the first and/or second carrier. The adhesive foil may further comprise openings or recessions for enabling a connection between the first and second carrier. The openings or recessions may be provided in the portions in which the LED chips are arranged and/or in which an electric connection between the first and second carrier is present .

The first and second carrier may alternatively or additionally be connected by means of an electric connector, clamp or plug. The clamp may be arranged at a lateral side of the first and second carrier thereby clamping the two carriers together.

The first and second carriers are electrically connected to each other. Thereby, the electric components of the second carrier are preferably connected to the at least one LED Chip of the first carrier.

The first and second carrier may be connected by means of a soldering connection. The first carrier preferably comprise soldering pads or points that are connected to conformably arranged soldering pads or points of the second carrier.

The soldering connection of the first and second carrier enables an electric connection of the carriers without the necessity for bulky connectors. Therefore, an integral and compact LED module is provided whereby the outer dimensions such as the width and the height of the LED module are reduced to a minimum. Thereby, the soldering connection merely requires for soldering pads or points in the bottom surface of the second carrier. Accordingly, no wires or connection means have to protrude from the top surface of the second carrier. The soldering pads or points in the second carrier are designed to be soldered together with soldering pads or points in an upper surface of the first carrier.

The soldering pads or points of the first and second carrier are arranged in close vicinity to each other. A lateral maximum distance between the respective soldering points of the first and second carrier is preferably below 3mm and may lie between 0.1 and 2 mm, more preferably between 0.2 and 1 mm. According to such an arrangement, the temperature caused stresses due to soldering the first and second carrier together are minimized. The first and second carriers are preferably soldered together by means of a low temperature solder. The melting point of the used solder is preferably lower than a melting point of a solder used for arranging the electric components on the second carrier. The low temperature solder used for connecting the first and second carrier preferably comprises a melting point of below 150°, preferably below 140° .

The stress reducing means preferably comprise at least one linear and/or curved groove. The at least one groove preferably extends from an upper to a lower surface of the second carrier and thus presents a cut-out portion. The stress reducing means may as well comprise at least one or preferably a plurality of through holes.

The at least one linear and/or curved groove is preferably a continuous groove of predefined length. The length of the at least one linear and/or curved groove preferably lies between 2 and 9mm, preferably between 3 and 8mm.

The linear and/or curved groove may comprise a thickness or lateral width of between 0.5 and 3mm, preferably between 1 and 2mm, more preferably between 1.2 and 1.5mm. The thickness of the linear and/or curved groove is preferably constant. The linear and/or curved groove may comprise different sections of varying thickness.

The stress reducing means may extend from a lateral side or edge of the second carrier. Thereby, the stress reducing means may extend from an inner aperture or through hole of the second carrier through which the at least one LED chip protrudes. The stress reducing means may as well extend from an outer lateral side or edge of the second carrier.

In an alternative embodiment, the stress reducing means are arranged at an inner portion of the second carrier which is distanced from a lateral side or edge of the second carrier. Thereby, the stress reducing means do not extend towards the later side or edge of the second carrier .

The stress reducing means are preferably arranged at a maximum lateral distance of below 2mm, more preferably at a distance between 0.1 and 1mm, most preferably at a distance between 0.1 and 0.8mm to the respective soldering point .

In a further aspect, the invention also relates to a lighting device such as preferably an LED Spotlight comprising an LED Module as outlined above.

Brief description of the drawings

Further features, advantages and objects of the present invention will become apparent for a skilled person when reading the following detailed description of embodiments of the present invention, when taken in conjunct with the figures of the enclosed drawings.

Fig. 1 and 2 are perspective exploded assembly drawings of a preferred embodiment of the LED module according the invention.

Fig. 3 is a perspective exploded assembly drawing of another preferred embodiment of the LED module.

Fig. 4a and 4b are perspective side views of another preferred embodiment of the LED module. Fig. 5a is a perspective side view of a further preferred embodiment of the LED Module.

Fig. 5b is an exploded assembly drawing of the embodiment according to fig. 5a.

Fig. 6a is a perspective side view of a further preferred embodiment of the LED Module.

Fig. 6b is an exploded assembly drawing of the embodiment according to fig. 6a.

Detailed description of the figures Fig. 1 and 2 relate to a perspective assembly drawing of a preferred embodiment of the LED module 10 according to the invention .

The LED module 10 comprises a first carrier 1 being an insulated metal substrate (IMS) . The IMS carrier 1 preferably comprises a metal base material (not shown) , preferably aluminum, and a dielectric layer la arranged to cover the metal base material. The dielectric layer may be made from ceramics or an insulating resin material. The IMS carrier 1 is preferably sheet-shaped, i.e. of homogenous thickness. The thickness of the first carrier 1 preferably lies between 1 and 5mm. The IMS carrier 1 is preferably of essentially circular shape when seen in top view. Notably, the carrier 1 may be of various shape such as rectangular or squared (see fig. 5a, 5b).

At least one LED Chip 3 is arranged in chip-on-board technigue on the IMS carrier 1 and preferably on the top dielectric layer la thereof. In a preferred embodiment, a plurality of LED Chips 3 is arranged on the first carrier 1. The at least one LED Chip 3 respectively the plurality of LED chips 3 are preferably encapsulated by a color conversion material 9. The color conversion material 9 is preferably held by a dam 9a which surrounds the at least one LED chip or the plurality of LED chips 3. The color conversion material 9 and the dam 9a are preferably applied onto the first carrier 1 by means of a dam-and- fill process, in which the surrounding dam 9a is dispensed onto the surface of the first carrier 1 and the resulting recess within the dam is then filled with color conversion material 9 such as a phosphor particles comprising resin material .

The at least one LED Chip 3 is electrically contacted to the circumference of the color conversion material 9 by means of dedicated circuitry provided on the first carrier 1. The circuitry for the LED Chip 3 preferably comprises soldering pads or points 7b. The soldering pads 7b are thus arranged outside of the color conversion material 9. The at least one LED chip 3 is preferably arranged in a central portion of the first carrier 1.

The LED module further comprises a sheet-shaped second carrier 2 which constitutes a circuit board for supporting electric components 4 thereon. The second carrier 2 preferably comprises a homogenous thickness, which preferably lies in the range of 0.5 to 2mm.

The second carrier 2 is preferably made from a different material than the first carrier 1, such as e.g. FR4 material. The circuit board carrier 2 is preferably designed to comprise complex circuitry for supplying and controlling electric current for the LED chips 3 arranged on the first carrier. The circuitry of the second carrier comprises the mentioned electric components 4 and wiring for connecting the components. The electric components 4 are preferably surface mounted devices (SMD) . The circuitry of the second carrier 2 may further comprise an electric connector or clamp 6 for connecting the LED module 10 to an external power supply. The second carrier 2 further comprises electric connection means for connecting the second carrier 2 to the first carrier 1. The electric connection means preferably comprise soldering pads or points 7a which are designed for being connected to dedicated soldering pads or points 7b of the first carrier. Accordingly, an electric connection between the first and second carrier 1,2 may be established by means of a soldering process. The soldering pads or points 7a are formed in a lower bottom portion or surface of the second carrier 2 and may extend through the whole carrier 2.

In the assembled state, the second carrier 2 preferably covers the top surface la of the first carrier 1 at least partially. In particular, the second carrier 2 is preferably arranged on the top surface la of the first carrier such as to cover at least 50%, more preferably at least 65%, most preferably at least 75% of the top surface la of the first carrier 1.

The second carrier 2 is preferably of conformal outer shape to the first carrier 1. This means that the outer contours of the first and second carrier 1,2, when seen in top view, preferably correspond. Thereby, the second carrier 2 is preferably of essentially circular shape. A central opening or through hole 2a is preferably provided in the second carrier 2, through which the LED chip 3 of the first carrier 1 protrudes in the assembled state of the first and second carrier 1,2. The second carrier 2 may comprise a plurality of openings or through holes through which the LED Chips 3 of the first carrier 1 protrude (see fig . 5a, 5b) .

The first and second carrier 1,2 are preferably connected to each other by means of an adhesive foil 5. Accordingly, the LED module 10 comprises a sandwich-like structure in which a bottom layer is constituted by the first carrier I , a middle layer is constituted by the adhesive foil 5 and the top layer is constituted by the second carrier 2.

The adhesive foil 5 is preferably at least partially flexible. The foil 5 is preferably of conformal outer shape to the first and/or second carrier 1,2 as shown in figure 1. Thereby, the adhesive foil 5 may comprise dedicated openings 5a, 5b, 5c which correspond to openings provided in the first and/or second carrier 1,2. In particular, the adhesive foil 5 preferably comprises a central opening 5a for the LED chip or chips 3. The foil 5 preferably also comprises openings 5b which are formed such that the soldering pads of the first and second carrier 1,2 may be connected. The foil 5 may additionally comprise openings 5c conformably shaped to fixation openings 11 in the first and second carrier 1,2. By means of said fixation openings or holes 11, the LED module 11 may be fixedly connected to a housing of a lighting device such as an LED spotlight by means of screws or other suitable connecting members.

The first and second carrier 1,2 are thus connected by means of the adhesive foil 5. Thereby, the electric components and circuitry is preferably arranged solely on an upper surface of the second carrier 2, opposite to the surface of the carrier 2 to which the foil 5 is connected.

The first and second carrier 1,2 are additionally connected by means of the soldering connection of the solder pads 7b of the first carrier 1 and the solder pads 7a of the second carrier 2. Thereby, in order to reduce the temperature caused stress in the LED module 1, the solder pads 7a, 7b of the first and second carrier 1,2 are preferably arranged in close vicinity to each other. In particular, a lateral maximum distance between the respective solder pads 7a, 7b in the first and second carrier 1,2 is preferably below 3 mm, and more preferably between 0.1 and 2 mm, most preferably between 0.2 and 1mm.

As shown in particular in Fig. 2, the LED module 10 comprises stress reducing means 8 that are arranged to at least partially surround the or encompass the electric connection means 7a of the second carrier 2. The stress reducing means are preferably dilatation means 8 designed to minimize the temperature caused stress in the first and second carrier 1,2 obtained e.g. during a soldering process for connecting the first and second carrier 1,2. The stress reducing means 8 comprise at least one groove, preferably a plurality of grooves that essentially surround or encompass the soldering pads 7a of the second carrier 2. The at least one groove extends through the whole carrier 2, i.e. from its upper surface to its lower surface. Accordingly, an expansion of the material of the solder pads 7a of the first carrier 2 in the soldering process may be compensated by the stress reducing means 8. These stress reducing means 8 in conjunction with the provided adhesive foil 5 thus enable to provide a certain flexibility of the laminated LED module 10 which compensates for temperature induced stress within the first and/or second carrier 1,2.

The stress reducing means 8 are preferably arranged at a lateral maximum distance of below 2mm, more preferably at a distance between 0.1 and 1mm, most preferably at a distance between 0.1 and 0.8mm to the respective soldering point 7a.

The grooves preferably comprise a lateral width respectively thickness of between 0.5 and 3mm, more preferably between 1 and 2 mm. The thickness of the grooves is preferably constant. The stress reducing means 8 may as well comprise several sections with grooves of different and/or constant thickness. The grooves 8 are arranged linear and/or curved. In the preferred embodiment shown in fig. 2, the grooves 8 are arranged in an essentially rectangular or squared pattern about the circumference of the soldering pads 7a.

The stress reducing means 8 are arranged at an inner portion of the second carrier 2 which is distanced from a lateral side or edge 2a, 2c of the second carrier. This means that the grooves, or through holes of the stress reducing means 8 do not extend to the outer lateral side or edge 2c of the second carrier 2 or to the lateral side or edge of the opening 2a. The stress reducing means 8 are thus arranged between the opening 2a and an outer lateral side or edge 2c of the second carrier 2.

Figure 3 relates to another preferred embodiment according to the invention, in which the second carrier 2 comprises another preferred arrangement of the stress reducing means 8. The rest of the structure of the LED module 10 according to this embodiment essentially corresponds to the structure according to the embodiment in figure 1 and 2. In this embodiment, the stress reducing means 8 comprise at least two linear grooves respectively cutouts. The linear grooves extend from a lateral side or edge of the second carrier 2. In particular, the linear grooves extend from a central opening 2a of the second carrier 2 towards the outer circumference of the second carrier 2 such that the solder pads 7a are situated between the linear grooves 8. The linear grooves extend preferably radially from the central opening 2a. As outlined above with respect to fig. 1 and 2, the grooves preferably comprise a lateral width respectively thickness of between 0.5 and 3mm, more preferably between 1 and 2 mm. The thickness of the grooves is preferably constant.

The stress reducing means 8 are preferably arranged at a lateral maximum distance of below 2mm, more preferably at a distance between 0.1 and 1mm, most preferably at a distance between 0.1 and 0.8mm to the respective soldering point 7a.

Fig. 4a and 4b relate to a further preferred embodiment of the LED module according to the invention. In this embodiment, the first and second carrier 1,2 are preferably held together by means of mechanical connection means . In particular, a mechanical connector or plug 6 is laterally arranged and designed to exert a clamping force onto the first and second carrier 1, 2, thereby holding the carriers 1,2 together- The mechanical connector or plug 6 preferably engages the first and second carrier 1,2 via an outer lateral edge lc,2c thereof. The connector 6 preferably exerts a clamping force onto an outer lateral portion of the first and second carrier 1,2. Thereby, preferably no adhesive foil is arranged between the first and second carrier 1,2.

In a lateral portion of the second carrier 2, opposite to the connector 6, a preferably linear groove or cut-out 12 is formed. In order to enable a slightly flexible connection between the first and second carrier 1,2, the linear groove 12 is preferably filled with a resin material 12a such as a silicone material (see fig. 4b) . The resin material 12a may be applied into the linear groove 12 and thus onto the surface la of the first carrier 1 in a dispensing process. The resin material 12a then protrudes from the upper top surface la of the first carrier 1 into the recess 12. When hardened respectively cured, the resin material 12a is restricted by the inner contours of the recess 12 such that a lateral movement of the first and second carrier 1,2 with respect to each other is essentially prevented. However, due to the nature of the used resin material, a certain flexibility of the first and second carrier 1,2 is maintained such that temperature induced stress due to the soldering of the first and second carrier 1,2 can be compensated.

The LED module 10 according to this embodiment additionally comprises stress reducing means 8 formed in the second carrier 2 and which comprise a linear groove 8' extending from the central opening 2a towards the connector 6. Thereby, the solder pads 7a may be arranged on both sides of the linear groove 8' . Further, the stress reducing means comprise at least one further groove 8 which extends from the central opening 2a and is arranged to partially surround or encompass the electric solder pads 7a with the liner groove 8'. Thereby, the at least one further groove 8 preferably comprise two connected linear sections. The linear sections are arranged at an angle with respect to each other such as to at least partially surround the electric solder pads 7a.

Fig. 5a and 5b relates to another preferred embodiment of the LED Module 10 according to the invention. Therein, the first and second carrier 1, 2 are of essentially rectangular shape. The second carrier 2 is arranged to essentially cover the upper surface of the first carrier 1 in the assembled state as shown in fig. 5a.

On an upper surface of the first carrier 1 a plurality of LED Chips 3 is arranged, which in the assembled state protrude through openings respectively through holes 2a of the second carrier 2.

The second carrier 2 preferably comprises electric components 4 which may be surface mounted devices (SMD) . The second carrier 2 further preferably comprises an electric connector or clamp 6 for connecting the LED module 10 to an external power supply. The connector or clamp 6 is preferably arranged at a first end portion of the rectangular shaped LED module 10.

The second carrier 2 further comprises electric connection means 7a for connecting the second carrier 2 to the first carrier 1. The electric connection means 7a are preferably arranged at a second end portion of the rectangular shaped LED module 10 which is situated opposite of the first end portion. The electric connection means preferably comprise soldering pads or points 7a which are designed for being connected to dedicated soldering pads or points 7b of the first carrier 1. The soldering pads or points 7a may extend through the whole substrate of the first respectively second carrier 1,2.

The second carrier 2 is further equipped with stress reducing means 8 which are arranged to at least partially surround or encompass the electric connection means 7a. Thereby, the stress reducing means comprise at least one groove 8 of essentially T-shaped form, which extends from an outer later side surface or edge 2c of the second carrier 2. The T-shaped groove 8 preferably extends throughout the whole substrate of the second carrier 2. The T-shaped groove preferably extends around at least one corner portion of the soldering pads or points 7a.

According to this embodiment, a very compact and flat arrangement for in particular linear luminaires is provided. Thereby, no external converter is needed as the electronic components of the converter are preferably arranged on the second carrier 2. Hence, the line power may be directly applied to the LED module 10.

Fig. 6a and 6b relate to a further preferred embodiment of the invention which essentially corresponds to the embodiment as depicted and described with respect to fig. 5a and 5b. Thereby, the second carrier 2 is slightly shorter in its length such as to only partially overlap with the first carrier 1. In particular, the end portion of the second carrier 2 at which the soldering pads or points 7a are provided is retracted respectively shortened with respect to the underlying first carrier 1. Accordingly, the soldering pads or points 7a of the second carrier 2 may be contacted to the soldering pads or points 7b of the first carrier via dedicated bond wires 7c. This enables a facilitated soldering process of the first and second carriers 1,2.