FIELD OF THE INVENTION

The invention relates in general to thermal management components, and more specifically to a heat sink for electronic components such as light emitting diodes (LEDs).

BACKGROUND OF THE INVENTION

LED lighting modules require cooling for increased light emission and prolonged LED life time. Typically, LED modules are mounted to thermal management components.

Heat sinks are passive thermal management components designed to carry off heat from the LED module by dissipating the heat to the ambient atmosphere off the surface of the heat sink. Heat sinks are typically based on materials with a good thermal conductivity such as aluminum, copper, or aluminum nitride (A1N). Owing to the high price of these materials, and the comparatively large material volume needed for certain applications, heat sinks infer a considerable cost for lighting systems and electronic devices in general.

Further, for heat sinks based on metallic, i.e., electrically conducting, materials, electrical safety issues arise in addition to an antenna effect which may have a disturbing effect in certain applications. SUMMARY OF THE INVENTION

It is an object of the present invention to provide a more efficient alternative to the above techniques and prior art.

More specifically, it is an object of the present invention to provide an improved heat sink and a method for manufacturing a heat sink.

These and other objects of the present invention are achieved by means of a heat sink having the features defined in independent claim 1 , and by means of a method for manufacturing a heat sink defined in independent claim 8. Embodiments of the invention are characterized by the dependent claims. According to a first aspect of the invention, a heat sink is provided. The heat sink comprises a first member and a second member. The first member is arranged for being in thermal contact with an object from which heat is to be dissipated. The second member is in thermal contact with the first member.

According to a second aspect of the invention, a method for manufacturing a heat sink is provided. The method comprises the steps of providing a first member and molding a second member around at least part of the first member. The first member is arranged for thermal contact with an object from which heat is to be dissipated.

The present invention makes use of an understanding that a heat sink, i.e., a passive thermal management component, may comprise two members, which members are based on two different materials. The first member is arranged for being in thermal contact with the heat source, and the second member is in thermal contact with the first member. In other words, the object from which heat is to be dissipated is mounted to the first member such that a sufficient thermal contact is achieved. When in use, heat from the object can be dissipated into the first member and further into the second member.

A heat sink according to the first aspect of the invention, which heat sink comprises two members, is advantageous since the amount of material required for the first member is reduced as compared to a monolithic heat sink, i.e., a heat sink solely based on one material. If the material used for the first member is more expensive than the material used for the second member, a heat sink according to the first aspect of the invention is less expensive than a heat sink comprising only the material used for the first member. By a proper choice of materials for the first and the second member, as well as a suitable design, a less expensive heat sink with comparable thermal properties as a monolithic heat sink may be achieved. The thermal properties of a heat sink according to the first aspect of the invention may be achieved by a proper choice of materials for the first and the second member, as well as a suitable design. In particular, the relative volume of the first and the second member may be chosen such that a trade-off between cost and thermal properties is achieved.

According to an embodiment of the heat sink according to the first aspect of the invention, the first member has a higher thermal conductivity than the second member. Since the cross sectional area of a heat sink typically increases along the direction of heat flow, i.e., with increasing distance from the heat dissipating object, it is sufficient to have a material with a lower thermal conductivity further away from the heat dissipating object, the lower conductivity being, at least in part, compensated by an increased cross sectional area. Such a heat sink is advantageous since a good heat dissipation from the object, which object is mounted to the first member, can be achieved while at the same time the heat sink is less expensive, owing to the fact that part of the required volume of the heat sink is based on a material with a lower thermal conductivity, and, typically, a lower price.

According to an embodiment of the heat sink according to the first aspect of the invention, the second member encompasses at least part of the first member. Having the second member encompass at least part of the first member is advantageous since a mechanically more reliable interface can be achieved as compared to an interface between two flat surfaces. A permanent compressive stress at the interface may be achieved by using materials with suitable thermal expansion coefficients. In that way a mechanical interlocking interface may be obtained. The mechanical reliability of the interface may further be improved by parts extending from the first member into the second member, or vice versa.

According to an embodiment of the heat sink according to the first aspect of the invention, the second member is molded around at least part of the first member. The second member can, e.g., be insert injection molded. Molding the second member is advantageous since molding, or casting, is an easy way to attach the second member to the first member. A further advantage is that the second member easily can be adapted to the application at hand, e.g., the thermal requirements or size restrictions, by tailoring the mould. In that way a variety of second members can be molded onto a single, or a few different, first members. Thus, many different heat sinks can be designed based on a few first members. Further, the object from which heat is to be dissipated may be mounted to the first member before the second member is molded onto the first member, and further assembling may be performed before the second member is molded.

According to an embodiment of the heat sink according to the first aspect of the invention, the second member is based on a thermal polymer. Using a thermal polymer is advantageous since it is moldable and has a good thermal conductivity, typically about 10- 20 W/Km.

According to an embodiment of the heat sink according to the first aspect of the invention, the first member is based on aluminum nitride (A1N). Using A1N is

advantageous since it has a good thermal conductivity, typically about 150-200 W/Km. Further, A1N is a dielectric material, an antenna effect does therefore not arise.

According to an embodiment of the heat sink according to the first aspect of the invention, the object from which heat is to be dissipated is an electronic component. The object may, e.g., be a light emitting diode (LED) or a surface mounted device (SMD). Using a heat sink according to the first aspect to the invention to dissipate heat from an electronic component, the heat sink comprising a thermal polymer based member, is advantageous since, at least, the second member is electrically insulating, thereby reducing the antenna effect of the heat sink. Further, the risk for electric hazards is mitigated.

According to an embodiment of the method according to the second aspect of the invention, the method further comprises the steps of fitting the first member with a mold, pre-heating the first member, pre-heating a thermal polymer, and injecting the thermal polymer into the mold.

Even though some embodiments, and advantages thereof, have been discussed with respect to a heat sink according to the first aspect of the invention, corresponding argumentation applies to embodiments of the method according to the second aspect of the invention.

Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non- limiting detailed description of embodiments of the present invention, with reference to the appended drawings, in which:

Fig. 1 is a perspective view of a heat sink, in accordance with an embodiment of the invention.

Fig. 2 shows cross sections of different heat sinks, in accordance with embodiments of the invention.

Fig. 3 illustrates a method for manufacturing a heat sink, in accordance with an embodiment of the invention.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested. DETAILED DESCRIPTION

Fig. 1 shows a heat sink 100 according to an embodiment of the invention. Heat sink 100 comprises a first member 101 and a second member 102. Also shown in Fig. 1 is an integrated circuit (IC) 103 from which heat is to be dissipated.

The first member 101 and the second member 102 may be made of any material having a thermal conductivity sufficiently high for the application at hand. The design of heat sink 100, and in particular the volume ratio between the two members 101 and 102, may also be adapted to the intended use of the heat sink, in particular the type and dimension of the heat dissipating object 103, the amount of heat to be dissipated, as well as the environment in which the heat sink is to be used.

The first member 101 may, e.g., be made of aluminum nitride (A1N), boron nitride (BN), silicon carbide (SiC), aluminum oxide (A1203), aluminum, or copper.

The second member 102 may, e.g., be made of a thermal polymer comprising a filler material such as A1N, BN, SiC, A1203, glass, diamond, graphite, aluminum, or copper.

As an example, the first member 101 may be made of A1N by ceramic powder injection molding and end sintering. Subsequently, the second member 102 may be made of a thermal polymer which is injection molded onto the first member 101. Typically, A1N has a thermal conductivity of 150-200 W/Km, whereas thermal polymers have a thermal conductivity of 10-20 W/Km. Thus, the first member 101, which is in thermal contact with the heat dissipating object, has a higher thermal conductivity than the second member 102.

In Fig. 2, cross sections of different heat sinks according to embodiments of the invention are shown.

Heat sink 210, shown in Fig. 2a, comprises a box shaped first member 211 embedded in the second member 212 such that at least one of the faces of the first member 211 is accessible for thermal contact with a heat dissipating object.

If the two members 211 and 212 are made of two different materials, a combination of materials may be chosen with respective thermal expansion coefficients such that the interface 213 between the two members 211 and 212 is always under compressive stress. In that way an interlocking interface 213 is obtained. If the second member 212 is molded around, or at least part of, the first member 211, an interlocking interface 213 is typically obtained due to the shrinking of the second member 212 during cool down.

Heat sink 220, shown in Fig. 2b, comprises a first member 221 which has the shape of a sphere segment and which is embedded in the second member 222 such that at least one of the faces of the first member 211 is accessible for thermal contact with a heat dissipating object.

Heat sink 230, shown in Fig. 2c, comprises a box shaped first member 231 which is in contact with the second member 232 only through a single face of each member.

Heat sink 240, shown in Fig. 3d, is similar to heat sink 230 but differs from the latter by a sphere segment 243 extending from the first member 241 into the second member 242. The sphere segment 243 amounts to more than half of a sphere such that an interlocking interface between the two members is obtained.

Heat sink 250, shown in Fig. 2e, comprises a box shaped first member 251 having tapered holes 353 such that an interlocking interface between the two members is obtained when the second member 252 is molded and the holes 353 are filled with material.

Heat sink 260, shown in Fig. 2f, is similar to heat sink 250 but differs from the latter by the fact the tapered holes 263 do not extend entirely through the first member 261. An interlocking interface between the two members is obtained when the second member 262 is molded and the holes 263 are filled with material.

Even though particular shapes of the first and second members, and the resulting heat sinks, have been illustrated in Fig. 2, the members may have any shape suitable for the application at hand.

With reference to Fig. 3, a method 300 for manufacturing a heat sink according to an embodiment of the invention is described.

First, in step 310, a first member 301 is provided. The first member 301 may, e.g., be made of A1N by molding and sintering. Then, in step 320, the first member 301 is fit with a mold 302 adapted for molding the second member 305 by injection molding. Mold 302 comprises a hole 303 for injecting liquid material. Subsequently, in step 330, liquid material 304, e.g., a thermal polymer, is injected through the hole 303 into the mold 302, thereby forming the second member 305. Finally, in step 340, after the liquid material has solidified, the mold 302 is removed.

If a thermal polymer is used for molding the second member 305, the first member 301 may be pre-heated to typically 80°C, and the thermal polymer 304 may be pre- heated to typically 250°C, before the thermal polymer 304 is injected into the mold.

The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, instead of molding the second member around the first member, the second member may be cast around the first member. The members of a heat sink according to an embodiment of the invention may also comprise more than one part. For instance, two thermal polymer parts may be molded around the first member. Vice versa, a single second member may be molded around a first member comprising more than one part. Further, the heat sink may be configured with references, such as holes or threads, for mounting the object from which heat is to be dissipated. The heat sink may also be configured with references for mounting further components, such as optics, electrical conductors, or housing. References and extra components may also be incorporated into the second member during the molding step by fitting them with the mold prior to injecting the liquid material. Finally, a heat sink according to an embodiment of the invention may be used to dissipate heat from objects other than the integrated circuit described with reference to Fig. 1.

In conclusion, heat sink comprising a first member and a second member is provided. The first member is arranged for thermal contact with an object from which heat is to be dissipated. The second member is in thermal contact with the first member. According to an embodiment of the invention, the second member consist of a thermal polymer molded around the first member. Further, a method for manufacturing a heat sink is provided.