WO2014067784A1

WO2014067784A1 - Method for producing an led module comprising a heat sink

Info

Publication number: WO2014067784A1
Application number: PCT/EP2013/071669
Authority: WO
Inventors: Georg Rosenbauer
Original assignee: Osram Gmbh
Priority date: 2012-10-30
Filing date: 2013-10-16
Publication date: 2014-05-08
Also published as: DE102012219879A1; CN104781940A

Abstract

The invention relates to a method for producing an LED module, in which a laser weld (5.1) is produced between a heat sink (1) and a printed circuit board (2) carrying at least one LED (3).

Description

description

Method for manufacturing a LED module with heat sink

Technical area

The present invention relates to a method for manufacturing an LED module with a heat sink.

State of the art

LEDs (light emitting diodes) as light-emitting semiconductor components are known for decades and in use and can also be found currently still growing dis ^¬ tung. The actual semiconductor device, the sogenann ^¬ th chip is equipped as standard with a "Package" (for example, ceramic, plastic or Metallträgerma- material including solder pads, possibly phosphor layers for converting UV-radiation into light and possibly transparent lenses or optics from polycarbonate or Sili ^¬ kon). the semiconductor device including package is referred to as a LED diode and associated material including a printed circuit board as Trägerma-. the board may for example consist of FR4, an epoxy resin-impregnated glass fiber mat material, or the circuit board may also include a metal ^¬ core board in. a common circuit board can also be used for more than one LED diode. known in the prior art also is the use of heat sinks for dissipating heat from the LED diode and the circuit board. Although LEDs relatively good efficiencies Errei ^¬ chen, they produce waste heat anyway. Such heatsinks can be complex three-dimensional structures have to dissipate the heat particularly well and radiate. In the state of the art, the boards are fastened with screws, attached, double-sided adhesive sheets or adhesives on the heat sink.

The assembly of at least one LED diode, the board (or more than one board) and the heat sink, which is hereinafter referred to as LED module, can then be installed in un ^¬ ferent different devices, for example, in light sources such as So-called retro fitlampen, so LED bulbs, which correspond with their approximate design and its socket classic bulbs such as incandescent. The LED modules can also be installed in complete luminaires.

Presentation of the invention

The present invention is based on the problem of specifying an improved manufacturing method for a LED module with a heat sink. The problem is solved by a method for producing an LED module in which a mechanical connection for producing or improving a heat coupling between a heat sink and a PCB carrying at least one LED is produced by laser welding, and by a correspondingly manufactured LED module itself.

The inventor has come to the conclusion that the vorbe ^¬ known connection methods are another costly in terms of the assembly of the heat sink and board and is not particularly suitable for machine automation ^¬ tion. He also stated that by local concentrated energy coupling with a laser and corresponding melting of material areas a very good mechanical connection between the heat sink and board can be produced. Laser welding can be relatively easily au ^¬ automate, because no separate components such as rivets, screws, double-sided adhesive films or adhesives must be handled, which can also be used that can be easily guided by laser movable mirrors or other optical elements and laser thus the spot weld can be easily and quickly localized. The energy input can also be so short that the heat input for the LED module and in particular the LED diode itself is not a problem. Furthermore, in the laser welding of the associated with the production of more mechanical connection points set effort to ^¬ is comparatively low, that is, for example, much less than when setting several screws with a screwing or by hand, which also has advantages for the mechanical connection of services still to be refined reasons , The purpose of the mechanical connection is the production of a heat coupling between the heat sink and the board in order to efficiently dissipate the forwarded from the LED diode in the board heat. Finally, the procurement and logistics cost of additional components can be avoided and the process can be completely contact-free and extremely fast Runaway ^¬ leads.

In a preferred embodiment, the heat sink and the board are directly connected during laser welding, the ie means without the interposition of an intermediate part. In other words, material parts of the heat sink and material ^{parts of} the board merge with each other during laser welding. This does not necessarily exclude a solder, as long as material parts of the heat sink and the board are melted with and mixed with each other. Preferably, however, an immediate welding oh ^¬ ne additional solder is provided.

In principle, fusible materials can be welded by laser welding, ie, for example, also thermoplastics, or materials with a fusible fraction, that is, for example, reinforced plastics with thermoplastic binder or thermoplastic matrix. For example, a metal core board could be welded with plastic coating with a plastic ^¬ heat sink, which owes its thermal conductivity, for example ^¬ thermally conductive fillers such as glass fibers or carbon additives. Preferably, however, metal ^¬ metallic material parts are fused together. That, metallic coatings, as well as "massive" component parts ^¬ or metal cores.

In particular, and independently thereof, metal core boards are preferred. First, the metal core can also be used for welding, for example, by having a non-metallic coating sufficiently thin, absent or removed at the appropriate location. On the other hand, the metal core ensures a good thermal conductivity of the board, which indeed has a heat transport function between the LED diode and the heat sink. Preferred materials of the metal core are aluminum including aluminum alloys and copper including copper alloys.

Furthermore, regardless of the metallic welding, a heat sink with a metal core or made entirely of metal is preferred. Of course, this is also about the thermal conductivity. With regard to the metallic welding in the case of a metal-core heat sink, the above statements on the metal-core board and its coating apply mutatis mutandis. Incidentally, the heat sink preferably has a three-dimensional shape aligned with its function, so it is not simply a flat plate. For example, it may have ribs or otherwise be structured in three dimensions in favor of improved heat transport and / or heat radiation.

The board in turn is, as already mentioned, in direct ^¬ ter heat and power to the LED diode. Preferably, between the board and the LED diode materials are provided only for the attachment and / or the heat transfer, for example, solder, adhesive or Wärmeleitmassen. The LED diode and the board can also abut each other directly.

In a preferred embodiment, the laser beam is directed from the side to the board on which the LED is mounted on the board. The laser beam is directed into an LED-free area, so for example with two mounted LED diodes between them. He then hits the board itself and the LED diodes are not or negligibly affected. Depending on the strength and material, the laser beam From this side, the board completely melts the board with respect to the depth (of course not in relation to the area, that is to say extending transversely to the thickness direction) and then also melts a part of the heat sink under the board in order to establish the welded connection.

In this context, a position of the board can be selected which is diluted or even specially diluted for this purpose (about 20% to 80%)

30% to 70% or 40% to 60% of the thickness). Thus, the penetration of the board is simplified up to the interface with the heat sink.

In addition, in this variant of the invention, an edge of the board can be used, for example, an outer edge on which the heat sink is flush or laterally projecting something, or even the edge of a provided in the board for this purpose or other reasons hole , At this edge then the board can be melted and (by the laser beam itself or by the molten board material) a part of the Kühlkör ^¬ pers.

In other embodiments, the laser beam is directed from the opposite side to the heat sink. In this case too, the heat sink can in principle be completely penetrated, with heat sinks in many cases being so thick that it is particularly appropriate here to choose or produce a thinned spot. In addition, the laser can also be directed from this side onto an edge of the heat sink at which the circuit board is flush or protrudes. For illustration, reference is made to the ^exemplary embodiments.

Finally, the laser welding according to the invention can also be combined with other measures with regard to the coupling between the board and the heat sink. In particular, between the blank and the heat sink, a contact material which conforms to the shape can be provided, which is thin (compared to its areal extent) and lies in-between. This may be an adhesive or a thermally conductive material ("thermal interface material").

Of course, the thermally conductive material improves the heat transfer in addition to the direct mechanical coupling (which in practice is associated with unavoidable air gaps).

In the case of an adhesive, in addition to or instead, an improvement of the mechanical coupling can be achieved. For example, thus the number of laser welding ^¬ points or distances can be reduced. This is especially true for otherwise possibly to be feared bulges between laser welding attachment points, such as if they are provided only on the edge. The additional Verbin ^¬ dung by adhesive (or by filling the thermally conductive material) may then avoid due to buckling between the circuit board and heat sink distances or eliminate their disadvantages.

In another combination, pin fasteners may be provided. For example, this generic term refers to screws or rivets which act as fastening elements between the printed circuit board and the heat sink itself are previously known. It has been found that advantages can be achieved despite the laser welding with rivets or rivets according to the invention, for example because the number of laser welding points or lines can be reduced and a screw or rivet (perhaps only individually or in small numbers) for other reasons anyway makes sense, for example, to attach the entire LED module to a housing or to attach optical elements to the LED module. The same applies mutatis mutandis to other pin fasteners, such as locking pins or clamp mounting pins, the dowel-like terminals or can work with spreading elastic elements. These can in particular also consist of plastic.

Brief Description of the Drawings Figures 1 to 11 each show a schematic sectional view in side perspective view of an invented LED module to illustrate the erfindungsge ^¬ MAESSEN manufacturing process, corresponding to a first to eighth embodiments.

Preferred Embodiment of the Invention Figure 1 shows the first embodiment. Therein be ^¬ records the reference numeral 1 is a metal heat sink whose three-dimensional structure has cooling fins and is considerably more complex than drawn. However, this structure is known as such and is also familiar to the person skilled in the art. On the heat sink 1, a board 2 is planar manner ^¬ sets, namely, a metal core board having an aluminum core ^¬ (a copper core would also be preferred) and an insulating coating, are printed on the electrical conductor tracks. On the board 2, two LED diodes 3 are soldered, in a conventional manner. The LED diodes 3 essentially consist of the soldered epitaxial substrate of a preceding epitaxy process, in which the actual active semiconductor layers of the LED are formed, and a package.

The heat sink in this case is an aluminum die cast alloy, but could also be rolled steel, aluminum, copper or other metal sheets that have been formed into a heat sink. Typical wall thicknesses for diecast cooling bodies are 1 mm to 6 mm, for sheet metal cooling bodies 0.5 mm to 3 mm. In particular, in sheet-metal cooling bodies coatings come with an insulator on at least one side into consideration, ^¬ that the heat sink can be mounted isolated. Thermoforming processes are for reshaping particularly in Be ^¬ costume. Die-cast alloy cooling bodies can also be injection-molded with plastic, in particular on the surface which does not touch the printed circuit board (pointing downward in FIG. 1). For example, a plastic coating of the board may provide an insulator on an aluminum base, typically 1.6 mm thick, onto which, for example, 35 μm thick copper layers for the tracks, a solder mask, and a solder resist (for reflow solder mounting of the LEDs) are deposited , Typical thicknesses of the metal core boards ^¬ between 0.4 mm and 3 mm. The arrow in the center symbolizes a vertically downward laser beam 4 of an infrared laser, for example a pulsed Nd: YAG laser (wavelength 1.06 ym). For example, it may have a pulse energy of between 10 J and 100 J, in the present case about 40 J, with pulse widths of the order of 10 ms to 100 ms, for example 20 ms. Typical pulse powers are between 1 kW and 9 kW, for example 2 kW.

The laser beam melts the metal core of the board 2, and the fusion penetrates through the board 2 to the metal or metal core of the heat sink 1. The plastic coating of the board 2 is possibly damaged locally, but this is unproblematic in consideration of the ladder ^¬ web structure and of course the LEDs 3, because a suitable range can be selected. In the (approximately conical) melting region, which is denoted by 5 in the figure, metallic material constituents of the plate 2 and of the heat sink 1 mix and form a solid local mechanical bond after solidification.

It would, as I said, as a heat sink and a metal ^¬ core cooling body (made of an aluminum die-cast or sheet metal alloy) with a plastic coating conceivable; The plastic coating would then locally destroyed in a similar manner as in the circuit board 2 or would be green for ^¬ the thermal conductivity in the relevant Kontaktbe ^¬ rich between heat sink 1 and board 2 anyway not available.

The laser also includes other IR lasers, such as C02 lasers (10.6 ym) diode lasers, fiber lasers, disk lasers, or other solid-state lasers into consideration. When welding plastic-coated heat sinks, non-pulsed (CW) lasers have proven their worth.

An advantage of this embodiment is that the laser beam impinges in the usual mounting direction, so the LED module does not have to be turned over or processed from below. As far as a certain particle contamination arises when the laser beam strikes, gravity does not direct it to the optics of the laser. Through the "top" incoming laser welding ^¬ SEN the welding points can in a simple manner on the circuit board 2 and the LEDs 3 adjusted (i.e. positio ^¬ defined) are. Here, in correspondingly simple manner, a plurality welds 5 possible, for example several times consecutively te on a moving (linear verfahrendes or rotating) LED module, where ^¬ linienhaf- when depending on repetition of Laserpulsung or spaced welds can be produced. with scanner optics, mechanical shutter and / or movable workpiece holders also areal grid or distributions may be generated become.

The method is particularly suitable for thin circuit boards, although relatively high laser energies on the order of, for example, 40 J or more per pulse may be required. Associated with this, in comparison to other embodiments, larger quantities of smoke or scratches can occur on the LED lenses (not shown), for which reason appropriate precautions, for example a good suction, may be necessary. It is favorable if, in the area of the future laser welding connection 5, no solder resist is present in advance appropriate pollution of the atmosphere by the smoke to avoid. Due to the board thickness relatively large welding lenses occur, so that the number of welding spots can remain small. The achievable strength can certainly be comparable to previously known methods.

Moreover, the process can also be improved by an inert gas purge to protect from a heat input betrof ^¬ fene areas from oxidation. In principle, the LEDs 3 are themselves not jeopardized by the Kurzzeitigkeit and Loka ^¬ le limit of the heat input, as long as they are not taken or will not work in its immediate neighborhood.

The following exemplary embodiments each differ in specific form from the first exemplary embodiment and are explained with regard to these differences. Incidentally, the above statements apply mutatis mutandis.

2, a depression 6 is provided in advance in the blank 2 in order to facilitate the welding connection at the point of impact of the laser beam 4.

As a result, the remaining thickness of the board 2 is significantly lower, for example by about 50%.

This is done by another mechanical step in the production of the board, for example by a milling step. Although this additional step is in itself a certain disadvantage, it is not particularly great because of its automatability and low cost relevance. As a result, smaller laser energies are required, less smoke and risk of spattering are created, and the resulting weld nuggets are smaller, which can facilitate their placement. An extraction is still advisable and because of the smaller version of the welded joint 5.2 (both in the area and in depth), the number of individual welds with respect to the first embodiment also et ^¬ something can be increased. (In general, however, the invention is also conceivable for small welded joints with small numbers of welded joints or only with individual welded joints, not only but also in conjunction with other conventional fastening systems.)

The third exemplary embodiment in FIG. 3 corresponds in part to the second embodiment; However, here is not only a recess in the board 2 vorgese ^¬ hen, but a hole. This hole can also be generated by a mechanical step in the Platinenferti ^¬ supply, for example by simply piercing, which is compared to the milling step even less problematic, because it does not have to pay attention to the depth.

In this case, the laser beam 4 is angled irradiated from above in order to meet an edge of the Kühlkör ^¬ pers 1 can be melted together in the material regions of the board 2 and material regions. This is indicated in Fig. 3 by the welded joint 5.3. Due to the clear previous distinction of the hole against the ^¬ over the remaining board area in this embodiment, the risk of accidental separation of conductor tracks is particularly low. Through the di- rect welding on the interface between the board 2 and the heat sink 1 are created even compared to the second embodiment, particularly little Schmauch and we ^¬ nig spatters and is only a low laser energy necessary. Here, too, more spot welds are typically compared to the ^¬ ers th embodiment advisable. For example, as in the second embodiment, it may be between 3 and 10 spot welds, whereas in the first embodiment, typically 2 to 6 are preferred.

In the fourth embodiment in FIG. 4, instead of the edge within the hole 7 in FIG. 3, the outer edge of the board is the target of the laser beam 4. In this way, the welded connection is to be kept particularly well out of the strip conductor area and it does not have to extend to the hole 7 ^{¬ be} targeted. Again, a little more welding points should be set than in the first embodiment, as ^¬ preferably between 3 and 10. In order to take into account the difference ^¬ Liche inclination of the laser beam relative to the LED module, the LED module, for example, rotated about a vertical axis be so that without changing the laser beam, the two drawn in Fig. 4 welding areas 5.4 can be made. Incidentally, this embodiment is particularly suitable for the combination with an additional central attachment, for example, with the third embodiment or in kon ^¬ conventional form with a screw, rivet or a locking or clamping attachment pin. A ^¬ adhesive material between board 2 and the heat sink 1 can be advisable (or a good heat-conducting material with good Haftei- characteristics) to avoid problems due to a bulge between board 2 and heat sink 1.

The fifth embodiment shown in FIG. 5 differs as well as the sixth, seventh and eighth embodiment of the first four exporting explained thereafter ^¬ approximately embodiments in that the laser beam 4 here from "below", ie from the board 2 side remote from the heat sink 1 is directed to the latter. in the ers ^¬ th variant of FIG. 5 while the overall strength of the heat sink is melted. Therefore, this variant is suitable for rather small material thickness of the heat sink 1, for example, in one embodiment from deep-drawn sheet metal. the basic disadvantage of a working On the side facing away from the usual mounting side and the need for relatively high laser energies, it is advantageous to prevent the development of smoke and the development of scratches on the side facing away from the LEDs 3. Care must be taken that particles falling down do not pollute the optics of the laser because (here with usual arrangement) the gravity downwards and thus basically points in the direction of the laser optics. Incidentally, in this embodiment, there is a need for a relatively accurate control of the reflow depth so as not to cut through the possibly comparatively thin board 2.

The next embodiment in Fig. 6 differs from the fifth embodiment in Fig. 5 in analo ^¬ ger manner as the second embodiment in Fig. 2 differs from that in FIG. 1. Here, therefore, a recess 8 was provided in the heat sink 1 from below, for example, by a milling process or by a corresponding shaping during die casting.

The seventh embodiment in Fig. 7 corresponds in an analogous manner to the third of Fig. 3, the heat sink 1 is thus pierced or more generally provided with egg ^¬ nem hole 9, which can be prepared, for example, by taking into account in die casting. Incidentally, the corresponding welded connection 5.7 is very similar to the welded connection 5.3 from FIG. 3, although the remarks relating to the laser alignment "from below" apply to the fifth and sixth exemplary embodiments.

Accordingly, the last eighth exemplary embodiment in FIG. 8 corresponds to the fourth from FIG. 4, wherein, unlike FIG. 4, the printed circuit board 2 must protrude somewhat beyond the heat sink 1 (and not vice versa as in FIG. 4). At the edge in between a weld 5.8 is provided. The comments on the fourth exemplary embodiment apply, taking into account the special features of working from below. In particular, this also applies to the risk ei ^¬ ner buckling and the particular suitability for combination with a mechanical connection "in the area" between board 2 and heat sink 1. For this purpose (but also for a combination with other embodiments of the invention) are, for example Adhesives In combination with the invention, however, their curing or drying times do not necessarily have to be a significant disadvantage for the production, because the mechanical connection between board 2 and Heatsink 1 can already be made by one or a few laser welding points. The provided between board 2 and heat sink 1 adhesive can then harden during storage or at the latest during operation of the LED module and the elevated temperatures then occur, provide additional support and prevent buckling. The adhesive may also bridge an air gap, thereby improving thermal contact. This is particularly true in view of occasionally unavoidable rather unevenness in the surfaces, especially in those of the heat sink 1. Here also so-called thermal interface materials can be used, which either improve only the heat transfer or additionally adhesion-improving properties (such as adhesive with additional heat conduction additives).

Similarly, a combination with mechanical fasteners such as screws or rivets is possible, which can be used advantageously for other connection ^¬ purposes, for example, for attachment of optical parts, Abdecklinsen or housing parts. In particular, can solve the described Woël ^¬ exercise problem-one or a small number of more centrally arranged fastening elements, so especially for a combination overall with the fourth or the eighth embodiment is suitable. The same applies to rivets and specially shaped plastic fasteners that clamp in dowel-like ^¬ form or form-fitting (by spreading the elements) connect. All these fasteners are basically previously known and therefore not shown in detail. An example is shown in FIG. 9 with a central screw or rivet or a dowel-like fastening element 10, which centrally penetrates and connects the heat sink 1 and the printed circuit board 2. Incidentally, the Anmer- only pertains to the fourth embodiment in Figure 4, in particular ^¬ sondere with respect to the welded joints 5.4.

Two further examples are shown in FIGS. 10 and 11 with an adhesive connection 11 between the heat sink 1 and the circuit board 2, on the one hand in FIG. 10 in combination with welded connections 5. 4 as in FIG. 4 and in FIG. 11 in connection with a welded connection 5. 8 according to FIG. 8.

Claims

claims

Method for producing an LED module (1-3), in which a mechanical connection (5.1-5.8) for producing or improving a heat coupling between a heat sink (1) and a board (2) bearing at least one LED (3) by means of laser welding will be produced.

The method of claim 1, wherein in a melted by the laser welding region (5.1-5.8) material parts of the heat sink (1) and material parts of the board (2) are fused together.

The method of claim 2, wherein the fused together material parts are metallic.

A method according to any preceding claim, wherein the board (2) is a metal core board.

Method according to one of the preceding claims, in which the heat sink (1) is metallic or has at least one metal core.

6. The method according to any one of the preceding claims, wherein the board (2) in direct thermal coupling to a nem substrate (3), and this carries, on which substrate at least one LED active layers abge ^¬ are eliminated.

Method according to one of the preceding claims, in which the laser beam (4) is directed from an LED side to a region of the board (2) which is LED-free, to the printed circuit board (2).

Ge is directed ^¬ method of claim 7, wherein the laser beam (4) diluted to a relative to adjacent areas of the board (2) point (6) of the board (2).

9. The method of claim 7, wherein the laser beam (4) is directed to an edge of the board (2).

Method according to one of claims 1 to 6, wherein the laser beam (4) from a LED side of the board (2) opposite side of the heat sink (1) is directed to the heat sink (1).

A method according to claim 10, wherein the laser beam (4) is applied to an opposite region of the

Heatsink (1) is diluted point (8) of the heat sink (1) is directed.

Method according to Claim 10, in which the laser beam is directed onto an edge of the heat sink (1). Method according to one of the preceding claims, wherein between the circuit board (2) and the heat sink (1) prior to the laser welding, a thin and flat conformal in the form of contact material is provided, in particular an adhesive or a thermal Leit ^¬ material.

Method according to one of the preceding claims, in which the circuit board (2) and the cooling body (1) additionally connected to at least one pin fastener mecha ^¬ cally, in particular a screw (10), a rivet (10) or a latching ^¬ or Clamp fixing pin (10).

15. LED module (1-3), produced by a method according to one of the preceding claims with a heat sink (1) and a LED (3) carrying the circuit board (2), which are connected by a laser welding connection (5.1-5.8) and in thermal coupling with each other.