Adhesion Enhancing Structures for a Package

Abstract

A package includes an electronic chip having a pad. The pad is at least partially covered with adhesion enhancing structures. The pad and the adhesion enhancing structures have at least aluminium in common.

Claims

1. A package comprising an electronic chip having a pad, wherein the pad is at least partially covered with adhesion enhancing structures, and wherein the pad and the adhesion enhancing structures have at least aluminium in common.

2. The package of claim 1, further comprising a dielectric structure at least partly covering the electronic chip.

3. The package of claim 2, wherein at least a part of the adhesion enhancing structures is covered directly by the dielectric structure, and/or wherein the dielectric structure comprises a mold compound which at least partially encapsulates the electronic chip.

4. The package of claim 1, wherein the adhesion enhancing structures comprise at least one of aluminium oxide and aluminium hydroxide.

5. The package of claim 1, wherein the pad comprises at least one of pure aluminium, aluminium-copper, aluminium-silicon-copper, and copper with an aluminium oxide coating.

6. The package of claim 1, wherein the adhesion enhancing structures form a substantially homogeneous layer.

7. The package of claim 1, wherein the adhesion enhancing structures have a height in a range between 50 nm and 1000 nm.

8. The package of claim 1, wherein the adhesion enhancing structures comprise at least one of nanofibers and microfibers.

9. A package, comprising: a chip carrier; an electronic chip mounted on the chip carrier; and a dielectric structure covering at least part of a surface of at least one of the chip carrier and the electronic chip, wherein at least part of the covered surface comprises hydrothermally formed adhesion enhancing structures.

10. The package of claim 9, wherein at least one of the adhesion enhancing structures and the surface comprises aluminium.

11. The package of claim 9, further comprising a connection element electrically coupling the electronic chip with the chip carrier and having a surface which is at least partially covered by the dielectric structure, wherein the covered surface of the connection element comprises hydrothermally formed adhesion enhancing structures.

12. A method of forming a semiconductor package, the method comprising: providing an aluminium based surface; and roughening the surface by forming adhesion enhancing structures by a hydrothermal process.

13. The method of claim 12, wherein the adhesion enhancing structures comprise aluminium.

14. The method of claim 12, the adhesion enhancing structures are formed on an electrically conductive surface.

15. The method of claim 12, further comprising converting material of the surface into at least part of the adhesion enhancing structures.

16. The method of claim 12, further comprising providing an electronic chip with a pad, wherein the pad forms at least part of the surface.

17. The method of claim 12, wherein forming the adhesion enhancing structures comprises placing the surface in a heated aqueous solution.

18. The method of claim 17, further comprising at least one of: heating the aqueous solution to a temperature in a range between 50 C. and 90 C.; providing at least one of purified water, deionized water or distilled water as the aqueous solution; and maintaining the surface in the heated aqueous solution for a time interval between 1 minute and 10 hours.

19. The method of claim 12, further comprising at least partially encapsulating the surface with the adhesion enhancing structures by a dielectric structure.

20. The method of claim 12, wherein the hydrothermal process comprises hydrothermally converting material of the surface into the adhesion enhancing structures.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0046] The accompanying drawings, which are included to provide a further understanding of exemplary embodiments and constitute a part of the specification, illustrate exemplary embodiments.

[0047] In the drawings:

[0048] FIG. 1 shows a surface morphology of an aluminium-based pad before carrying out a hydrothermal process according to an exemplary embodiment.

[0049] FIG. 2 shows a surface morphology of the aluminium-based pad of FIG. 1 after having carried out the hydrothermal process according to an exemplary embodiment.

[0050] FIG. 3 shows a side view of adhesion enhancing structures on an aluminium pad manufactured according to an exemplary embodiment after a hydrothermal process.

[0051] FIG. 4 shows a top view of adhesion enhancing structures on an aluminium pad manufactured according to an exemplary embodiment after a hydrothermal process.

[0052] FIG. 5 shows an aluminium-based surface with adhesion enhancing structures according to an exemplary embodiment before attaching a tape in terms of an adhesion test.

[0053] FIG. 6 shows the aluminium-based surface with adhesion enhancing structures of FIG. 5 with attached tape in terms of the adhesion test.

[0054] FIG. 7 shows the aluminium-based surface with adhesion enhancing structures of FIG. 6 after removing the type in terms of the adhesion test.

[0055] FIG. 8 shows a cross-sectional view of a package according to an exemplary embodiment.

[0056] FIG. 9 to FIG. 13 show top views of an aluminium pad surface after exposure times of 10 (FIG. 9), 20 (FIG. 10), 30 (FIG. 11), 60 (FIG. 12) and 180 minutes (FIG. 13), respective1y.

[0057] FIG. 14 to FIG. 18 show side views of the pad surface of FIG. 9 to FIG. 13 after exposure times of 10 (FIG. 14), 20 (FIG. 15), 30 (FIG. 16), 60 (FIG. 17) and 180 (FIG. 18) minutes, respectively.

[0058] FIG. 19 shows a top view and FIG. 20 shows a side view of a pad surface after exposure of 20 minutes of an Al.sub.2O.sub.3 layer covered copper pad using an ALD (Atomic Layer Deposition) deposition process.

[0059] FIG. 21 shows a top view and FIG. 22 shows a side view of AlOH dendrites on copper pads covered with an Al.sub.2O.sub.3 layer formed by ALD after 10 minutes of spray-on of 70 C. hot deionized water.

[0060] FIG. 23 illustrates a cross-sectional view of a package according to an exemplary embodiment.

[0061] FIG. 24 illustrates a cross-sectional view of a package according to another exemplary embodiment.

[0062] FIG. 25 is a flowchart illustrating a method of forming a semiconductor package according to an exemplary embodiment.

DETAILED DESCRIPTION

[0063] The illustrations in the drawings is schematic. Before describing further exemplary embodiments in further detail, some basic considerations of the present invention will be summarized based on which exemplary embodiments have been developed.

[0064] According to an exemplary embodiment, adhesion enhancing structures (in particular aluminium oxide dendrites) may be grown on a (in particular aluminium comprising) surface such as a pad to enable good mold compound adhesion on this surface.

[0065] In terms of semiconductor packages, a high reliability is required. One of the major issues is the mold compound adhesion in the package especially for the adhesion between metal pad areas and mold compound. At this interface, it is advantageous to render a surface as rough as possible to enable, descriptively speaking, an interdiffusion area between mold compound resin and the surface.

[0066] According to an exemplary embodiment, a reliable protection against undesired delamination of the package can be accomplished by a very simple process with simple chemistry. It has turned out that a proper homogeneity of the growth of adhesion enhancing structures may render proper adhesion possible without facing quality issues. Apart from the simple processing, a process according to an exemplary embodiment has also advantages in terms of work security and health restrictions due to healthy and non-hazardous components. The simple process and the corresponding simple tools allow the manufacture with low effort because of cheap material and simple tools with small space consumption.

[0067] An exemplary embodiment manufactures aluminium hydroxide adhesion enhancing structures (in particular adhesion enhancing fibers) grown in a hydrothermal process providing a low effort and healthy solution. Results have shown a very good conformity and reproducibility of the dendrite growth. Within experiments, samples with aluminium based pads as well as pads with an ALD-manufactured Al.sub.2O.sub.3 layer covered copper pads have been investigated. The dendrites were grown by placing bare chips or assembled chips on leadframe into for instance 75 C. hot water for an appropriate time.

[0068] Exemplary embodiments allow the manufacture of robust packages with zero or extremely low tendency of delamination. At the same time, exemplary embodiments can be advantageously carried, out without adding further materials to the system and. avoiding complicated hazardous processes.

[0069] More generally, and also referring to FIG. 5 described, below in further detail, a manufacturing process of forming a semiconductor package 100 according to an exemplary embodiment may be as follows:

[0070] Firstly, an electronic chip 102 may be provided with one or more contact pads 104 comprising aluminium and having an exposed electrically conductive surface 112. For example, a respective contact pad 104 may be made of pure aluminium, aluminium-copper, or aluminium-silicon-copper. It is also possible that a respective contact pad 104 is composed of a copper base with a thin aluminium oxide coating. Aluminium oxide is electrically insulating, so that the surface 112 on which adhesion enhancing structures 106 will be grown later may be also electrically insulating rather than electrically conductive.

[0071] Thereafter, the method may comprise roughening a surface 112 of the one or more contact pads 104 using a hydrothermal process. In terms of this hydrothermal process, it is possible to grow adhesion enhancing structures 106 (in particular adhesion enhancing fibers or dendrite structures which may have dimensions in the order of magnitudes of nanometers to micrometers) on the pad 104 and on the basis of material of the pad 104. In other words, the pad 104 itself may be the source of material which forms the adhesion enhancing structures 106 integral with the pad 104. Therefore, the hydrothermal process hydrothermally converts material of the surface 112 into the adhesion enhancing structures 106 to thereby intrinsically grow rather than deposit the adhesion enhancing structures 106. As a consequence, the adhesion enhancing structures 106 formed based on the pad 104 (comprising aluminium) may comprise aluminium as well. Thus, the adhesion enhancing structures 106 and the pad 104 may both comprise aluminium, i.e. may have at least one chemical element (in particular Al) in common. Thus, the adhesion enhancing structures 106 may be formed by modifying or converting material of the surface 112 of the respective pad 104 into the adhesion enhancing structures 106.

[0072] In terms of the mentioned hydrothermal process for forming the adhesion enhancing structures 106, the electronic chip 102 with the one or more pads 104 having the electrically conductive surface 112 may be placed in a hot aqueous solution, more specifically may be immersed in heated water. Preferably, the aqueous solution may be heated to a temperature preferably between 7 C. and 80 C., for instance to 75 C. This temperature selection may ensure an efficient formation of the adhesion enhancing fibers. As the aqueous solution, deionized water or distilled water may be used. The electronic chip 102 with the at least one pad 104 having the electrically conductive surface 112 may be kept immersed in the heated aqueous solution for a selectable time interval of for instance between 10 minutes and 3 hours. The duration for which the electronic chip 102 remains immersed in the purified water determines the thickness of the layer of adhesion enhancing structures 106 being integrally formed on the surface 112 of the respective pad 104. After formation of the adhesion enhancing structures 112, the surface 112 has an increased roughness which improves the adhesion properties of a mold compound or another encapsulant to be formed subsequently.

[0073] Thus, the method comprises subsequently encapsulating the electronic chip 102 with the one or more pads 104 having the surface 112 covered with adhesion enhancing structures 106 by an encapsulant as dielectric structure 108 such as a mold compound by carrying out a molding procedure,

[0074] FIG. 1 shows a surface morphology of an aluminium-based pad 104 before an exposed surface 112 of the pad 104 is made subject of a hydrothermal process according to an exemplary embodiment. FIG. 2 shows a surface morphology of the aluminium-based pad 104 of FIG. 1 after the hydrothermal process according to an exemplary embodiment has formed adhesion enhancing structures 106 on the surface 112, i.e. after having formed the adhesion enhancing structures 106 in form of nanofibers. Thus, FIG. 1 and FIG. 2 illustrate the surface morphology of an aluminium based pad 104 before (FIG. 1) and after (FIG. 2) the above-described hydrothermal process. FIG. 1 and FIG. 2 show scanning electron microscope (SEM) images.

[0075] As can be taken from FIG. 2, a homogenous coverage of the surface 112 by the adhesion enhancing structures 106 has been found after the described treatment.

[0076] According to the exemplary embodiment of the method to which FIG. 1 and FIG. 2 refer, a Teflon (polytetrafluoroethylene) beaker was overflowed with deionized water (DI water) for 30 minutes. After that, the beaker was filled with 80 ml of deionized water at room, temperature. The beaker including its water was heated on a hotplate to 75 C., and a sample on which adhesion enhancing structures were to be formed was immersed in the water. After an appropriate exposure time, the beaker was removed from, the hotplate and was allowed to cool to room temperature. The sample was taken out of the beaker.

[0077] FIG. 3 shows a side view of adhesion enhancing structures 106 on an aluminium pad 104 manufactured according to an exemplary embodiment after a hydrothermal process. FIG. 4 shows a top view of the adhesion enhancing structures 106 on the aluminium pad 104 manufactured. according to this exemplary embodiment after the hydrothermal process. Thus, FIG. 3 and FIG. 4 show the adhesion enhancing structures 106 on experimentally captured images (SEM, TRIM, transmission electron microscope).

[0078] Analysis via SEM, TEM and EDX (energy dispersive X-ray spectroscopy) indicate that the adhesion enhancing structures 106 grow very homogenously, for instance with an approximate thickness of 200 nm. As can be taken in particular from FIG. 3, the adhesion enhancing structures 106 form a substantially homogeneous layer. It can also be seen experimentally that the interface between pad 104 and the adhesion enhancing structures 106 is very smooth without signs of inhomogeneous corrosion. It can also be confirmed experimentally that the composition is as well homogenous and that the adhesion enhancing structures 106 are aluminium-(hydro)-oxides.

[0079] FIG. 5 to FIG. 7 show results of an adhesion test of an aluminium-based surface 112 with adhesion enhancing structures 106 according to an exemplary embodiment.

[0080] FIG. 5 shows the aluminium-based surface 112 with adhesion enhancing structures 106 according to an exemplary embodiment before attaching a tape in terms of the adhesion test.

[0081] FIG. 6 shows the aluminium-based surface 112 with the adhesion enhancing structures 106 of FIG. 5 with attached tape 170 in a portion 172 only in terms of the adhesion test. Another portion 174 has not been covered by the tape 170.

[0082] FIG. 7 shows the aluminium-based surface 112 with the adhesion enhancing structures 106 of FIG. 6 after removing the tape 170 in terms of the adhesion test, i.e. after having removed tape 170 from portion 172. As can be taken from FIG. 7, glue residues 176 are visible which indicate proper adhesion properties.

[0083] The described adhesion test with sticky tape 170 shows that the adhesion enhancing structures 106 increase the adhesion while the adhesion enhancing structures 106 are not breaking easily, see FIG. 5 to FIG. 7.

[0084] FIG. 8 illustrates a cross-sectional view of a package 100 configured as an encapsulated electronic chip 102 on a chip carrier 110 according to an exemplary embodiment. The electronic chip 102 may have one or more pads 104. More specifically, FIG. 8 illustrates a cross-sectional view of the package 100, which is embodied as a Transistor Outline (TO) package, according to an exemplary embodiment. The package 100 is mounted on a mounting base 118, here embodied as printed circuit board (PCB).

[0085] The mounting base 118 comprises an electric contact 134 embodied as a plating in a through hole of the mounting base 118. When the package 100 is mounted on the mounting base 118, electronic chip 102 of the electronic component 100 is electrically connected to the electric contact 134 via electrically conductive chip carrier 110, here embodied as a leadframe, of the package 100.

[0086] The electronic chip 102 (which is here embodied as a power semiconductor chip) is mounted adhesively or soldered (by e.g. electrically conductive adhesive, solder paste, solder wire or diffusion soldering) on the chip carrier 110 (see reference numeral 136). An encapsulant (here embodied as mold compound) forms a dielectric structure 108 and encapsulates part of the leadframe-type chip carrier 110 and the electronic chip 102. As can be taken from FIG. 8, pad 104 on an upper main surface of the electronic chip 102 is electrically coupled to the partially encapsulated leadframe-type chip carrier 110 via a fully encapsulated clip-type or bond wire type connection element 114.

[0087] During operation of the power package 100, the power semiconductor chip in form of the electronic chip 102 generates heat. For ensuring electrical insulation of the electronic chip 102 and removing heat from an interior of the electronic chip 102 towards an environment, an electrically insulating and thermally conductive interface structure 152 is provided which covers an exposed surface portion of the leadframe-type chip carrier 110 and a connected surface portion of the encapsulant-type dielectric structure 108 at the bottom of the package 100. The thermally conductive property of the interface structure 152 promotes a removal of heat from the electronic chip 102, via the electrically conductive leadframe-type chip carrier 110, through the interface structure 152 and towards a heat dissipation body 116. The heat dissipation body 116, which may be made of a highly thermally conductive material such as copper or aluminium, has a base body 154 directly connected to the interface structure 152 and has a plurality of cooling fins 156 extending from the base body 154 and in parallel to one another so as to remove the heat towards the environment.

[0088] Conventionally, a package 100 of the type shown in FIG. 8 may suffer from delamination between mold material of the dielectric structure 108 on the one hand and material of the various components (in particular pad 104, chip carrier 110, connection element 114) of the package 100 encapsulated within and directly contacting dielectric structure 108 on the other hand. Highly advantageously, the package 100 reliably prevents any tendency of the delamination or poor adhesion within the dielectric structure 108 by providing hydrothermally formed adhesion enhancing structures 106 at an interface between the dielectric structure 108 on the one hand and one or more of the mentioned constituents on the other hand. This will be described in the following in further detail:

[0089] Firstly referring to detail 180, it is shown in FIG. 8 that the dielectric structure 108 covers an electrically conductive surface 112 of the pad 104 of the electronic chip 102. In order to improve the roughness and therefore the adhesion properties, the electrically conductive surface 112 is provided with adhesion enhancing structures 106 which are configured as intermingled nanofibers. For instance, the pad 104 may be made of aluminium and the adhesion enhancing structures 106 may comprise aluminium as well, for instance may comprise aluminium oxide or aluminium hydroxide as a result of a hydrothermal manufacturing process, as described above. As a result, the dielectric structure 108 directly covers exposed portions of the adhesion enhancing structures 106 on the pad 104 and therefore properly adheres to the pad 104 via its adhesion enhancing structures 106. The adhesion enhancing structures 106 may have a height, h, of for instance 500 nm.

[0090] Now referring to a further detail 182, the package 100 also comprises hydrothermally formed adhesion enhancing structures 106 comprising aluminium at an interface between the leadframe-type chip carrier 110 and the dielectric structure 108. In order to form the adhesion enhancing structures 106 in a corresponding manner as described above on the chip carrier 110, it is advantageous that the chip carrier 110 is made of aluminium or has at least aluminium material on the surface 112 on which the adhesion enhancing structures 106 are grown hydrothermally. The material on the surface of the chip carrier 110 can then be modified or converted into the adhesion enhancing structures 106 thereon during the hydrothermal process.

[0091] Yet another detail 184 in FIG. 8 snows the (for instance clip-type or bond wire type) connection element 114 electrically connecting the chip carrier 110 with the pad 104 of the electronic chip 102. As shown, the package 100 comprises further hydrothermally formed adhesion enhancing structures 106 comprising aluminium, at an interface between the connection element 114 and the dielectric structure 108. In order to form, the adhesion enhancing structures 106 in a corresponding manner as described, above on the connection element 114, it is advantageous that the connection element 114 is made of aluminium or has at least aluminium material on the surface 112 on which the adhesion enhancing structures 106 are grown hydrothermally. The material on the surface of the connection element 114 can then be modified or converted into the adhesion enhancing structures 106 during the hydrothermal process. Thus, the connection element 114 electrically coupling the electronic chip 102 with the chip carrier 110 also has a surface 112 covered by the dielectric structure 108 and being provided with hydrothermally formed adhesion enhancing structures 106.

[0092] With embodiments, it may be possible to form, on a pad area for Al-based pads 104 and for Cu pads 104 covered, with ALD, adhesion enhancing structures 106. The homogenous dendrite layer leads to a homogenous optical appearance enabling a visual check of the process efficiency.

[0093] FIG. 9 to FIG. 13 show top views of the aluminium pad surface after exposure times of 10, 20, 30, 60 and 180 minutes, respectively. In other words, FIG. 9 to FIG. 13 show the surface morphology of aluminium, based, pads 104 after different durations. FIG. 14 to FIG. 18 show side views of this pad surface after exposure times of 10, 20, 30, 60 and 180 minutes, respectively. In the side views, the AlOH dendrites or adhesion enhancing structures 106 on aluminium based pads 104 are shown after different durations (images of 10-60 min taken of broken wafer with SEM, image of 180 min taken with TEM).

[0094] FIG. 19 shows a top view and FIG. 20 shows a side view of the surface after exposure of 20 min of an Al.sub.2O.sub.3 layer covered copper pad 104 using an ALD deposition process. The top- and side views of the AlOH dendrites on protected copper pads 104 after 20 minutes are shown (captured by TEM).

[0095] Both pads 104 show dendrite growth in the top view, while the thicknesses are varying with the exposure time, and the thickness for the ALD formed Al.sub.2O.sub.3 layer covered copper pad 104 is thinner. While the aluminium based pad 104 has about 600 nm thick dendrites, the latter case resulted in a 50 nm thick layer of adhesion promoting structures 106. In all cases the dendrite growth is very homogenous. The interface between the pad metal and the dendrites is very smooth without any signs of inhomogeneous corrosion and that the composition is as well.

[0096] Based on these analytical findings, it is possible to implement AlHO dendrites grown via temperature hydrolysis as adhesion promoter for robust packages. The analysis and evaluations have proven that it is possible to grow homogeneous dendrites as well on aluminium based metal areas as on ALD Al.sub.2O.sub.3 layer covered copper areas.

[0097] In view of this growth procedure, it is also possible to implement the hydrolysis on leadframe (or more general chip carrier 110) level. The copper areas of a package 100 may be covered by an ALD Al.sub.2O.sub.3 layer which can be deposited on the single package components (for instance copper pad 104, copper leadframe or other chip carrier 110) or after a wire bond process, for instance on the finished package 100.

[0098] FIG. 21 shows a top view of AlOH dendrites on ALD Al.sub.2O.sub.3 layer covered copper pads 104 after 10 minutes of spray-on of 70 C. hot deionized water. FIG. 22 shows a corresponding side view. FIG. 21 and FIG. 22 shows the result of an investigation where a wafer with an ALD-type Al.sub.2O.sub.3 layer protected copper pad 104 was exposed to humidity under high temperatures on a wet chemical etch tool. It shows that out of a 6 nm thin layer, thick dendrites are grown.

[0099] FIG. 23 illustrates a cross-sectional view of a package 100 according to an exemplary embodiment.

[0100] The package 100 of FIG. 23 comprises an electronic chip 102 having pads 104 covered with adhesion enhancing structures 106. The pads 104 and the adhesion enhancing structures 106 have a chemical element, for instance aluminium, in common.

[0101] FIG. 24 illustrates a cross-sectional view of a package 100 according to another exemplary embodiment.

[0102] The package 100 of FIG. 24 comprises a chip carrier 110, an electronic chip 102 mounted on the chip carrier 110, and a dielectric structure 108 covering a surface 112 of the chip carrier 110 and the electronic chip 102. The covered surface 112 comprises hydrothermally formed adhesion enhancing structures 106.

[0103] FIG. 25 is a flowchart 190 illustrating a method of forming a semiconductor package 100 according to an exemplary embodiment.

[0104] The method comprises providing an aluminium based surface 112 (see box 192), and roughening the surface 112 by forming adhesion enhancing structures 106 by a hydrothermal process (see box 194).

[0105] It should be noted that the term comprising does not exclude other elements or features and the a or an does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs shall not be construed as limiting the scope of the claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

[0106] Although specific embodiments have been illustrated and. described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.