ELECTRICAL CONNECTION PAD WITH ENHANCED SOLDERABILITY AND CORRESPONDING METHOD FOR LASER TREATING AN ELECTRICAL CONNECTION PAD

Abstract

The invention concerns an electrical connection pad (10′) for providing an electrical connection between components of an electronic system, wherein the electrical connection pad comprises: a metallic layer (12); and a laser induced periodic surface structure (20), LIPSS, formed on an external surface (16) of the electrical connection pad (10) and exposing the metallic layer (12) and a method for correspondingly laser-treating an electrical connection pad (10).

Claims

1-22. (canceled)

23: An electrical connection pad for providing an electrical connection between electronic components, wherein the electrical connection pad comprises: a metallic layer; and a laser induced periodic surface structure formed on an external surface of the electrical connection pad and exposing the metallic layer.

24: The electrical connection pad of claim 1, wherein the laser induced periodic surface structure has a period from 100 nm to 10 μm.

25: The electrical connection pad of claim 1, wherein the laser induced periodic surface structure has a modulation amplitude from 10 nm to 100 μm.

26: The electrical connection pad of claim 1, wherein the metal layer has a thickness from 1 μm to 10 mm.

27: The electrical connection pad of claim 1, wherein the metal layer comprises copper, zinc, tin, lead, brass, platinum, gold, silver and/or aluminium or combinations, compounds and/or alloys thereof.

28: The electrical connection pad of one of claim 1, further comprising a dielectric layer arranged on the metallic layer, wherein the laser induced periodic surface structure is further formed in the dielectric layer.

29: The electrical connection pad of claim 6, wherein the dielectric layer comprises a metal oxide, carbon and/or an organic material.

30: The electrical connection pad of claim 7, wherein the dielectric layer is a metal oxide layer comprising copper oxide, zinc oxide, tin oxide, lead oxide, brass oxide, platinum oxide, gold oxide, silver oxide, and/or aluminium oxide.

31: The electrical connection pad of claim 6, wherein the dielectric layer has a thickness between 1 nm and 5 μm, preferably between 1 nm and 1 μm, more preferably between 5 nm and 30 nm.

32: The electrical connection pad of claim 1, wherein the electrical connection pad is a solder pad.

33: A circuit board comprising an electrical connection pad for providing an electrical connection between electronic components, wherein the electrical connection pad comprises: a metallic layer; and a laser induced periodic surface structure formed on an external surface of the electrical connection pad and exposing the metallic layer.

34: A method for laser-treating an electrical connection pad, wherein the electrical connection pad comprises: a metallic layer; and a dielectric layer arranged on the metallic layer forming an external surface of the electrical connection pad; wherein the method comprises: laser-treating the external surface with polarised ultrashort-pulse pulsed laser light, thereby forming a laser induced periodic surface structure exposing the metal layer.

35: The method of claim 12, wherein the external surface is laser-treated with laser light pulses having a pulse length from 30 fs to 100 ns.

36: The method of claim 12, wherein the external surface is laser-treated with laser light pulses having a wavelength from 193 nm to 10.6 μm.

37: The method of claim 12, wherein the laser light has a fluence from 0.01 J/cm2 to 10 J/cm.sup.2.

38: The method of claim 12, wherein laser-treating the external surface comprises laser-treating from 10% to 90% of the external surface.

39: The method of claim 12, wherein laser-treating the external surface comprises scanning at least a part of the external surface with the laser light using a laser light deflection system.

40: The method of claim 12, wherein the laser light is configured such that a modulation amplitude of the laser induced periodic surface structure is equal to or greater than a thickness of the dielectric layer.

41: The method of claim 12, wherein laser-treating the external surface comprises completely removing the dielectric layer.

42: The method of claim 12, wherein the external surface is laser-treated with an incidence angle from 0° to 45°.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0042] FIG. 1 shows an electrical connection pad before undergoing laser treatment according to an embodiment of the invention.

[0043] FIG. 2 illustrates the laser treatment of an electrical connection pad with a laser light at a given incidence angle according to an embodiment of the invention.

[0044] FIG. 3 illustrates the laser treatment of an electrical connection pad with a laser light at a given incidence angle according to an embodiment of the invention using a laser light deflection system.

[0045] FIG. 4 shows an electrical connection pad with a LIPSS according to an embodiment of the invention.

[0046] FIG. 5 shows an electrical connection pad with a LIPSS according to another embodiment of the invention.

[0047] FIG. 6 shows the height profile of a LIPSS according to embodiments of the invention.

[0048] FIG. 7 shows a circuit board incorporating an electrical connection pad with a LIPSS according to an embodiment of the invention.

[0049] FIG. 8 shows top views of electrical connection pads according to embodiments of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0050] For the purposes of promoting an understanding of the principles of the invention, reference will now be made to preferred embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, alterations and further modifications in the illustrated devices and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur now or in the future to one skilled in the art to which the invention relates.

[0051] FIGS. 1 to 3 illustrate a method for laser treating an electrical connection pad 10 comprising a metallic layer 12 and a dielectric layer 14, wherein the dielectric layer 14 is arranged on top of the metallic layer 12 forming an external surface 16 of the connection pad 10. In the embodiment shown, the dielectric layer 14 is a metal dielectric layer. Before the laser treatment, the dielectric layer 14 has, in the example shown, a thickness H2 of about 30 nm. The metallic layer 12 has, in the example shown, a thickness H1 i of about 30 μm. In the embodiment shown, the metallic layer 12 comprises copper, and the dielectric layer 14 comprises copper oxide formed as a consequence of the electrical connection pad 10 being exposed to the atmosphere for some time. Thus, before the laser treatment, the upper surface of the dielectric layer 14 forms the external surface 16 of the electrical connection pad 10.

[0052] The method of the invention comprises laser-treating the external surface 16 with a pulsed laser light 32 generated by a laser device 30. In the example shown, the laser device 30 is an ultrashort solid state laser device, for example a Ytterbium-doped fiber laser, configured to generate linearly polarised ultrashort-pulse laser light having a pulse length of about 200 fs, a wavelength of about 1030 nm and a fluence of about 0.5 J/cm.sup.2. However, any other values within the previously described ranges are possible within the context of the present invention.

[0053] As shown in FIG. 2, the external surface 16 can be laser-treated with an incidence angle θ, i.e. an angle between the incidence direction of the laser light 32 and a direction perpendicular to the plane of the external surface 16, with the incidence angle θ being in the range of 0° to 45°, for example being around 45°, as shown in FIG. 2. As shown in FIG. 3, a laser light deflection system 34 can be used for scanning the laser light 32 throughout the external surface 16 or a part thereof, for example using a rotatable mirror or the like.

[0054] As a result of the laser treatment with the indicated parameters, an electrical connection pad 10′ with an enhanced solderability comprising a LIPSS 20 on the external surface 16 is formed.

[0055] FIG. 4 shows an example in which, before the laser treatment, the dielectric layer 14 had a thickness of about 3 nm and the metallic layer 12 had a thickness of 30 μm. Laser light with a fluence of 0.1 J/cm.sup.2, a wavelength of about 1030 nm, and a pulse length of 200 fs was used for forming the LIPSS 20. As a result of the laser treatment, the dielectric layer 14 is completely ablated or removed, such that the electrical connection pad 10′ no longer comprises, after the laser treatment, the dielectric layer 14. In this case, the LIPSS 20 is entirely formed in the metallic layer 12, which also forms the external surface 16. As a result of the laser treatment, the metallic layer 12 now has a thickness H1′ that can be equal to or smaller than the thickness H1 of the metallic layer 12 before the laser treatment, depending on the particular settings of the laser treatment. In the example shown, the (maximal) thickness H1′ of the metallic layer 12 after the laser treatment is about 30 μm. The LIPSS 20 has an amplitude modulation A and a period P. In the example shown in FIG. 4, the amplitude modulation is about 300 nm and the period is about 900 nm.

[0056] FIG. 5 shows an example in which, before the laser treatment, the dielectric layer 14 had a thickness of 30 nm and the metallic layer 12 had a thickness of 30 μm. Laser light with a fluence of 0.1 J/cm.sup.2, a wavelength of 1030 nm, and a pulse length of 200 fs was used for forming the LIPSS 20. As a result of the laser treatment, the dielectric layer 14 is only partly ablated or removed, such that the electrical connection pad 10′ comprises, after the laser treatment, a remnant of the dielectric layer 14 formed on top of the metallic layer 12. In this case, the LIPSS 20 is formed in the metallic layer 12 and the dielectric layer 14, which form in combination the external surface 16. The profile of the LIPSS 20 substantially corresponds to an approximate sinusoidal wave profile. The thickness of the electrical connection pad 10′ takes maximal values at the upper peaks of the sinusoidal wave profile, where the remnants of the dielectric layer 14 are arranged, while the metallic layer 12 is exposed at the external surface 16 and the metallic layer 12 at the lower peaks of the sinusoidal wave profile, where the dielectric layer 14 has been totally removed. In other embodiments, the LIPSS 20 formed on the external surface 16 may have a wave profile other than a sinusoidal wave profile.

[0057] FIG. 6 shows an exemplary wave profile of the LIPSS 20 formed on the external surface 16 of an electrical connection pad 10′ according to embodiments of the present invention, illustrating the periodic variation in the thickness of the electrical connection pad 10′, i.e. in the metallic layer 12 and/or the dielectric layer 14 arranged on the metallic layer 12.

[0058] As a result of the laser treatment, the metallic layer 12 of the electrical connection pad 10′ of FIG. 5 now has a thickness H1′ that can be equal to or smaller than the thickness H1 of the metallic layer 12 before the laser treatment, depending on the particular settings of the laser treatment, and the dielectric layer 14 has a thickness H2′ that can be equal to or smaller than the thickness H2 of the dielectric layer 14 before the laser treatment, depending on the particular settings of the laser treatment.

[0059] In the example shown, the thickness H1′ of the metallic layer 12 after the laser treatment is about 30 μm and the thickness H2′ of the dielectric layer 14 after the laser treatment is about 3 nm. The LIPSS 20 has an amplitude modulation A and a period P. In the example shown in FIG. 5, the amplitude modulation is about 200 nm and the period is about 950 nm.

[0060] FIG. 7 shows a printed circuit board 50 according to an embodiment of the invention comprising an electrical connection pad 10′ acting as a solder pad to establish an electrical connection between a conductive substrate structure 52 of the printed circuit board 50 and a conductive wiring 40 via solder material 42, which may comprise lead, tin or any other suitable solder material. The solder material 42 may partially or completely cover the electrical connection pad 10′. Through the electrical connection pad 10′, a durable electrical connection between the conductive substrate structure 52 and another electronic component connected thereto through the conductive wiring 40 is formed, which thanks to the principles of the present invention is explained above, has an improved solderability due to the presence of a LIPSS and can be formed with a simplified manufacturing method in a workflow resulting in electrical connection pads having practically no caducity date or storage/transportation time limit before becoming useless.

[0061] FIG. 8 shows exemplary top views of electrical connection pads 10′ arranged on a substrate structure 52, after the electrical connection pad 10′ has been laser-treated. The solder material 42 is arranged on the electrical connection pad 10′ and, in the example shown, defines a circular profile partially covering the external surface 16 of the electrical connection pads 10′.

[0062] FIG. 8a illustrates an electrical connection pad in which the external surface 16 has been completely laser-treated, for example by using laser light with a spot size S to linearly scan the external surface 16 over a first direction, indicated as direction “y” in FIG. 8, at different positions along a second direction, indicated as direction “x” in FIG. 8. In FIG. 8a, said different positions are spaced apart from each other by a distance equal to or smaller than the spot size S, such that 100% of the external surface 16 is covered by the resulting LIPSS. The area of the external surface 16 covered by the LIPSS is indicated in FIG. 8 as lined areas.

[0063] FIG. 8b illustrates an electrical connection pad 10′ in which the external surface 16 has been partially laser-treated, for example by linearly scanning the external surface 16 over the direction “y” at different positions along the direction “x” mutually spaced apart by a distance greater than the spot size S. As a result, in FIG. 8b, about 50% of the external surface 16 is laser-treated and contains the resulting LIPSS, as illustrated in the figure by the lined areas, which in the example shown form stripes extending along the direction “y”.

[0064] Although preferred exemplary embodiments are shown and specified in detail in the drawings and the preceding specification, these should be viewed as purely exemplary and not as limiting the invention. It is noted in these regards that only the preferred exemplary embodiments are shown and specified and that all variations and modifications should be protected, which presently or in the future lie within the scope of protection of the invention as defined in the claims.

LIST OF REFERENCE SIGNS

[0065] 10 electrical connection pad (before laser treatment) [0066] 10′ electrical connection pad (after laser treatment) [0067] 12 metallic layer [0068] 14 dielectric layer [0069] 16 external surface [0070] 20 laser induced periodic surface structure [0071] 30 laser device [0072] 32 laser light [0073] 34 laser light deflection system [0074] 40 conductive wiring [0075] 42 solder material [0076] 50 circuit board [0077] 52 conductive substrate [0078] H1 thickness of the metallic layer (before laser treatment) [0079] H2 thickness of the dielectric layer (before laser treatment) [0080] H1′ thickness of the metallic layer (after laser treatment) [0081] H2′ thickness of the dielectric layer (after laser treatment) [0082] P period of the laser induced periodic surface structure [0083] A modulation amplitude of the laser induced periodic surface structure [0084] θ incidence angle of the laser [0085] x, y directions