Method and apparatus for optically transparent via filling

A method and apparatus for filling a via with transparent material is presented, including the steps of providing a panel having a via, occluding the via with transparent material in a workable state so that a portion of the occluding material is internal to the via and a portion of the material is external to said via. The external and internal portions are separated so the transparent filler material, when set, forms a smooth and featureless surface. This causes the filled via to have a substantially even and uniform appearance over a wide range of viewing angles when lit.

FIELD OF THE DISCLOSURE

The field of the technical subject matter relates to methods for filling a via with material and products produced through use of such methods. More particularly it relates to filling very small vias with optically transparent material. Even more particularly it relates to filling very small vias with optically transparent material so that the vias are largely unnoticeable when unlit and provide an even, uniform light when backlit.

BACKGROUND

Projecting a light through a housing to provide information is commonplace. Examples include but are not limited to computer keyboards that include indication lights for functions such as “Caps Lock” or “Num Lock”; computer monitors that include an “on/off” light, automobiles that include lights to indicate whether heated seats are on or off, or whether an air bag is on or off; televisions with indicator lights, and a whole host of other consumer electronics. A common way to provide for such lighting is to provide a projecting light that is visible when the light is off and brightly lit to indicate when the light is on. A collection of lights, or holes for lights, may be disruptive to the objectives of an industrial designer.

One method of attempting to make the holes for lights less visible is to drill very small, tapered holes and fill them with a transparent material. Holes or vias can be formed using mechanical drills, lasers, electrical discharge machining, or chemical etching. A method for producing optical vias is described in co-pending application Ser. No. 11/742,862 PROCESS FOR OPTICALLY TRANSPARENT VIA FILLING, assigned to the assignee of the instant invention. In this method, the vias are drilled, filled with workable transparent material, the filler transparent material set, and then the surface is cleaned to remove excess set transparent material from the visible surface of the article. By workable we mean that the material is in a plastic state, able to be poured or otherwise inserted into the via and conform to the interior shape of the via, thereby sealing it. This process is illustrated inFIGS. 1a-1d. InFIG. 1a, a substrate10, having a front or cosmetic side12and a back side14, the substrate10having a via16filled with a transparent filler18being irradiated with ultraviolet (UV) radiation20from an ultraviolet light source22to set the filler18.FIG. 1bshows the same substrate10and via16now filled with set filler24. Note that the UV radiation has penetrated and set filler that extends beyond front side12causing a “finger”26of cured filler to extend beyond front side12. InFIG. 1c, a mechanical device such as a blade is used to remove the finger26of set material from front side12of the substrate10. The finger26of set material can also sometimes be removed by simply wiping with a cloth if the fingers are small enough.FIG. 1dshows the substrate10with via16filled with set material24following removal of finger26.

FIG. 2shows a high resolution optical microscope image of a via30filled with cured filler32taken from the front or cosmetic side34of the substrate following removal of excess cured filler. As can be seen inFIG. 2, this process leaves a fractured surface in the cured transparent material32on the visible side of the article which can make the via unsightly, more visible when unlit and impairs the lit appearance, all of which are undesirable. Accordingly, there remains a need for a method and apparatus for filling vias with a transparent material without surface fractures to improve their aesthetics both when lit and unlit.

SUMMARY OF THE INVENTION

Disclosed are improved methods for occluding a via in a relatively thin substrate or panel with a material that permits the transmission of light through the transparent filler material and products that are made by such methods. By via we refer to a hole formed in a panel or substrate extending from one surface to another characterized by an interior volume bounded by the interior walls of the via and planes which extend the surfaces penetrated by the via. By occlude we mean to introduce material into the interior volume of the via in such a fashion as to completely fill a cross-section of the via. Note that the entire via volume of the via may or may not be completely filled, however, excess material that extends beyond the volume of the via at one surface is typically present. It is one of the goals of the instant invention to disclose methods and apparatuses for removing this excess material in such a fashion as to leave the surface smooth and debris-free and thereby provide an improved filled, light-transmissive via. Panels or substrates to be filled in this manner are typically made of metal, although other materials such as plastic or composite materials may be used. Transparent filler material is introduced into the via in workable form and then made or allowed to set or cure into a hard, optically transparent material that typically adheres to the inside walls of the via to assist in remaining in place in the via. Exemplary materials that may be used include UV-settable polymers, or other polymers that set by exposure to radiation, epoxies or other multi-part compounds that set through chemical reactions, compounds that set through cooling or application of heat and compounds that set by evaporation of solvents or otherwise harden. Any of these materials may be used advantageously in the instant invention.

An exemplary light transmissive material is AHS-1100 Developmental Material manufactured by 3M Company, St. Paul, Minn. Other transparent fillers may be used advantageously, including fillers that can be set by means other than UV radiation. Set refers to the process whereby transparent filler transforms from a substantially liquid or workable state to a solid or relatively hardened state. Transparent fillers can be set by chemical reactions, heat or other electromagnetic radiation, exposure to air, evaporation of solvents or other means. The embodiments described herein can be adapted to use these other setting methods. For example, in the case where the filler is a two-part epoxy that is mixed prior to application to the via and will set in a determined amount of time, the residue can be quickly removed by mechanical or compressed air before the filler sets completely. It is also contemplated that, in the alternative to the materials described above, thermoplastic materials can form the transparent fillers. In this case the excess material would have to be removed prior to the setting by cooling of the thermoplastic materials.

According to one embodiment of the instant invention, the method comprises providing a panel including at least one via and occluding the via with an optically transmissive material, then removing the excess material prior to it becoming set through curing, cooling, evaporation of solvent or otherwise hardened. Removing the excess material prior to setting leaves the exposed surface of the transparent material smooth and unfeatured, thereby making it less visible when unlit and provides more even, uniform illumination when lit. The excess material can be removed by wiping the surface by mechanical means, such as a blade or a squeegee or the excess material can be removed with compressed air. These steps can be followed by wiping with a solvent or vacuum suction or combinations of these methods to remove any remaining excess material. Additionally, light-transmissive vias made according to methods described herein are also disclosed. For example, taught herein is a via having a light transmissive properties wherein the light transmissive via in an article is filled with an optically transmissive material, where the excess optically transmissive material is at least partially removed from the surface of the article prior to the material setting.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An object of the instant invention is to provide methods and apparatuses for creating improved filled holes in surfaces.FIG. 3ashows a schematic diagram of a substrate10with a front or cosmetic side or surface12and a back side or surface14having a via16occluded with a transparent filler18. The transparent filler18is partially set using a UV light source50emitting UV light52. Note that the UV light is being directed to the substrate at an angle close to parallel with the back side14of the substrate to prevent radiation from penetrating through the via16and setting the portion of filler54that extends beyond the front surface12.FIG. 3bshows the substrate10and partially set filler48in the via16. Since the portion of the partially set filler48that extends beyond the front surface12is not set, it can be removed using a mechanical blade or squeegee56wiped across the surface, removing excess filler58from the immediate vicinity of the via16.FIG. 3cshows the substrate10with the partially set filler48and the excess unset filler58on the top surface12of the substrate10. In this embodiment, UV light source60is placed more perpendicular to the back surface14so that the UV light rays62penetrate the partially set filler48all the way to the top surface12and thereby complete the setting process. In other embodiments the excess filler material can be removed prior to any setting taking place.FIG. 3dshows the substrate10with the completely set filler64after being cleaned to remove the unset filler remaining on the top surface12. This cleaning can be accomplished by either vacuum or solvent wash or other equivalent methods and can be performed either before or after the material in the via has been finally set.

Another embodiment of the instant invention is illustrated inFIGS. 4a-4c.FIG. 4ashows a substrate10with a front side12and a back side14with a via16. Via16is occluded with workable transparent filler18. InFIG. 4b, an air knife80is used to direct a compressed air stream82onto the top surface of the substrate12to remove excess filler58from the immediate vicinity of the via16. In this embodiment of the invention, a vacuum nozzle,86removes the excess filler58from the top surface12once it has been moved away from the via.FIG. 4cshows the partially set filler48in the via16being set using UV radiation62from a UV source60from the back surface14of the substrate10. It is also contemplated that the setting could be by heating, cooling, evaporation of solvents, chemical reaction or other means. Following setting, the front surface10may be wiped with solvent to remove any remaining traces of excess filler.

FIG. 5shows an optical microscope picture of a filled via30produced by the instant invention taken from the cosmetic or front side34. Note the smooth appearance of the filler90, which makes the filled via less noticeable when unlit and makes the via appear more evenly illuminated from a wider range of viewing angles.

FIG. 6shows a scanning electron microscope image of a via30taken from the front side34of a panel, filled with transparent material92that has been prepared according to an embodiment of the instant invention using a mechanical means to remove the excess unset filler. While the appearance of the filled via is greatly improved over the prior art, for example as shown inFIG. 2, a small amount of debris and surface texture is apparent on the set filler.FIG. 7shows a scanning electron microscope image of a via30with a transparent filler94taken from the front side34of a panel, processed according to an embodiment of the instant invention that uses compressed air and vacuum to remove excess filler from the via. This picture shows that the filler94has no detectable residue and no apparent surface texture.

It will also be appreciated that details of the preferred embodiments can be interchanged and still be within the bounds of the teachings of this invention.