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Title:
AUTOMOTIVE LAMINATE WITH HOLES
Document Type and Number:
WIPO Patent Application WO/2019/186512
Kind Code:
A1
Abstract:
The increase in the electronic content of automotive glazing has expanded, from just components that are mounted to the glass, to components which are an integral permanent part of the glass. Some examples include antennas, sensors, LED lighting, displays and defroster circuits. Laminates comprising these and other thin components are becoming more common. Electrical connections are usually accomplished by means of a notch in the glass, extended to the edge, or with a thin flat lead that is brought out at the edge of glass. Both methods present drawbacks. Holes in laminated glass have not typically been used due to their tendency to break during the bending and lamination process as well as in service. The method of the invention creates holes in the glass with minimal surface damage and then seals the holes restoring the surface to near its original integrity and strength.

Inventors:
MANNHEIM ASTETE, Mario Arturo (Av. Guillermo Dansey 1846, Cercado de Lima, Lima, PE)
SARMIENTO SANTOS, Andres Fernando (Av. Guillermo Dansey 1846, Cercado de Lima, Lima, PE)
GRANADOS CARO, Laura (AV. Guillermo Dansey 1846, Cercado de Lima, Lima, PE)
Application Number:
IB2019/052639
Publication Date:
October 03, 2019
Filing Date:
March 30, 2019
Export Citation:
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Assignee:
AGP AMERICA S.A. (MMG Tower, piso 23 Avenida paseo del Mar, Ciudad De Panamá, PA)
International Classes:
B32B17/10; H05B3/86
Foreign References:
US20150236491A12015-08-20
US3866232A1975-02-11
EP0835743A21998-04-15
US20130140847A12013-06-06
Other References:
None
Attorney, Agent or Firm:
URDANETA, Daniel (MMG Tower, piso 23 Avenida paseo del Mar, Ciudad De Panamá, PA)
Download PDF:
Claims:
CLAIMS

What is claimed is:

1. A laminated automotive glazing comprising:

at least two glass layers, outer and inner glass layers;

at least one plastic interlayer disposed between said at least two glass layers; a sealing means;

at least one through hole formed in at least one glass layer;

at least one electrical conductor routed through at least one hole; and a sealing means applied to said at least one through hole;

2. The laminate of claim 1 wherein the hole diameter is less than 12 mm, preferably less than 6 mm, more preferably less than 3 mm.

3. The laminate of claim 1 wherein the hole diameter is less than 2 mm, preferably less than 1 mm.

4. The laminate of claim 1 wherein surface roughness of the hole is less than 12 pm, preferably less than 6 pm, more preferably less than 3 pm.

5. The laminate of claim 1 wherein surface roughness of the hole is less than 2 pm. preferably less than 1 pm.

6. The laminate of claim 1 wherein the sealing means is conductive.

7. The laminate of claim 6 wherein the sealing means is a silver filled resin which forms two vias.

8. The laminate of claim 7 further comprising a set of spring-loaded contact to make an electrical connection to the vias.

9. The laminate of claim 6 wherein the sealing means is a conductive glass frit.

10. The laminate of claim 6 wherein the sealing means is a conductive adhesive or a conductive via paste.

11. The laminate of claim 1 wherein the sealing means resistant to water.

12. The laminate of claim 1 wherein the sealing means has good adhesion to glass.

13. The laminate of claim 1 wherein the sealing means remains pliable at low temperatures.

14. The laminate of claim 1 wherein the sealing means has a coefficient of thermal expansion that is within 50% of the glass.

15. The laminate of claim 1 wherein components attached to the embedded electrical conductors passing through the holes are attached to the glass surface.

16. The laminate of claim 1 wherein components embedded within the laminate are attached to the embedded conductors passing through the holes are attached to the glass surface.

17. The laminate of claim 1 wherein components attached to the glass surface and/or embedded in the laminate are connected to each other by means of the embedded conductors passing through the holes.

Description:
AUTOMOTIVE LAMINATE WITH HOLES

Field of the invention

This invention relates to the field of laminated automotive glazing.

Background of the invention

One important tend in the automotive industry that we have seen for several years now, is the steady increase in the glazed area of the vehicle. This helps to reduce weight, by displacing heavier materials, while improving vision and letting in more natural light. At the same time, the electronic content of the vehicle has also been growing at an even greater rate as the industry moves toward full autonomous vehicles. As a result, components are increasingly being mounted to or incorporated into the glazing. Camera systems are just one example of a component that is mounted to the glass. The increase in the electronic content of automotive glazing has expanded from components mounted to the glass to components which are an integral permanent part of the glass. The defroster circuit, used to keep the camera field of view free of snow and ice, is an example of a component that is an integral permanent part of the glass. Some other examples include antennas, sensors, LED lighting and displays. Laminates comprising these and other thin components are becoming more common.

As a general rule of thumb, a component can be laminated if the thickness is no more than 1/3 of the total thickness of the interlayer. During the lamination process, the interlayer is treated at an elevated temperature and will at least partially flow to accommodate the component. The maximum thickness will depend upon other factors such as the other dimensions of the object, the thickness of the glass, the strength of the glass, the specific interlayer and the time, temperature and pressure of the lamination cycle. If the component is too thick, the glass may break. Objectionable distortion can also occur. With all other factors remaining the same, thinner is always better with respect to the risk of breakage and distortion.

The power and signal electrical connections are usually made by means of a notch in the glass or with a thin flat lead that extends from the laminate at the edge of glass. Both of these methods present drawbacks. When a notch cut in just one of the glass layers to expose the electrical connection points, this leaves a single thin annealed glass layer exposed which is weak and is easily damaged.

Thin flat leads tend to be expensive and are labor intense to install. They are also fragile and easily tom off at the point where they exit the edge of glass. They are much wider than a round conductor of the same cross-sectional area. As a result, during the lamination process, they can present problems during deairing and the autoclave cycle. Thin flat connectors when used for signal have the additional drawback in that they must pass in close proximity to the sheet metal as they exit the edge of glass. Signal is lost due to capacitive coupling to the sheet metal. In addition, due to the change in the thickness of the laminate, distortion and high residual stress can also result.

It is possible to drill holes in the annealed laminated glass for electrical connections. This has been done but is not a common practice. Holes in laminated glass have not typically been used due to their tendency to break during the bending and lamination process as well as in service.

It would be desirable overcome these limitations providing a superior method for making electrical connection in laminated glazing.

BRIEF SUMMARY OF THE INVENTION

The method of the invention creates holes in the glass by means of a femtosecond LASER or equivalent. The holes made in this manner have low surface roughness and have far fewer and less severe surface defects in the glass. After the electrical conductors have been routed, the holes are sealed in a manner such as to restore the surface to near its original integrity and protect it from deterioration from exposure to moisture.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

These features and advantages of the present invention will become apparent from the detailed description of the following embodiments in conjunction with the accompanying drawings, wherein:

Figure 1A shows a cross section of a typical automotive laminate.

Figure 1B shows a cross section of a typical automotive laminate with coating and performance film.

Figure 2A shows a panoramic windshield with camera defroster. Figure 2B shows a close-up view of holes in glass and wires.

Figure 3 shows an exploded view: LED lights with embedded wire power feeds.

Figure 4 shows an LED lights with embedded wire power feeds.

REFERENCE NUMERALS

2 Glass

4 Bonding layer (plastic Interlayer)

6 Obscuration

8 Sealant

12 Film

14 Wire

16 Embedded wire defroster

18 Coating

20 LED Light

24 Hole

30 Camera Field of View

101 Exterior side of glass layer 1, surface one.

102 Interior side of glass layer 1, surface two.

103 Exterior side of glass layer 2, surface three.

104 Interior side of glass layer 2, surface four.

201 Exterior glass layer

202 Interior glass layer

DETAILED DESCRIPTION OF THE INVENTION

The following terminology is used to describe the laminated glazing of the invention. A typical automotive laminate cross section is illustrated in Figures 1A and 1B. The laminate is comprised of two layers of glass, the exterior or outer 201 and interior or inner 202 that are permanently bonded together by a bonding layer 4 (interlayer). The glass surface that is on the exterior of the vehicle is referred to as surface one 101 or the number one surface. The opposite face of the exterior glass layer 201 is surface two 102 or the number two surface. The glass 2 surface that is on the interior of the vehicle is referred to as surface four 104 or the number four surface. The opposite face of the interior glass layer 202 is surface three 103 or the number three surface. Surfaces two 102 and three 103 are bonded together by the plastic bonding layer 4 An obscuration 6 may be also applied to the glass. Obscurations 6 are commonly comprised of black enamel frit printed on either the number two 102 or number four surface 104 or on both. The laminate may also comprise a coating 18 on one or more of the surfaces. The laminate may also comprise a film 12 laminated between at least two plastic bonding layers 4

The plastic bonding layer 4 (interlayer) has the primary function of bonding the major faces of adjacent layers to each other. The material selected is typically a clear thermoset plastic. For automotive use, the most commonly used bonding layer 4 (interlayer) is polyvinyl butyral (PVB). PVB has excellent adhesion to glass and is optically clear once laminated. It is produced by the reaction between polyvinyl alcohol and n-butyraldehyde. PVB is clear and has high adhesion to glass. However, PVB by itself, it is too brittle. Plasticizers must be added to make the material flexible and to give it the ability to dissipate energy over a wide range over the temperature range required for an automobile. Only a small number of plasticizers are used. They are typically linear dicarboxylic esters. Two in common use are di-n-hexyl adipate and tetra-ethylene glycol di-n-heptanoate. A typical automotive PVB interlayer is comprised of 30-40% plasticizer by weight.

In addition to polyvinyl butyl, ionoplast polymers, ethylene vinyl acetate (EVA), cast in place (CIP) liquid resin and thermoplastic polyurethane (TPU) can also be used. Automotive interlayers are made by an extrusion process with has a thickness tolerance and process variation. As a smooth surface tends to stick to the glass, making it difficult to position on the glass and to trap air, to facilitate the handling of the plastic sheet and the removal or air (deairing) from the laminate, the surface of the plastic is normally embossed contributing additional variation to the sheet. Standard thicknesses for automotive PVB interlayer at 0.38 mm and 0.76 mm (15 and 30 mil) from the vessel into a thin ribbon on the flat glass float line.

A wide variety of films are available that can be incorporated into a laminate. The uses for these films include but are not limited to: solar control, variable light transmission, increased stiffness, increased structural integrity, improved penetration resistance, improved occupant retention, providing a barrier, tint, providing a sunshade, color correction, and as a substrate for functional and aesthetic graphics. The term“film” shall include these as well as other products that may be developed or which are currently available which enhance the performance, function, aesthetics or cost of a laminated glazing. Most films do not have adhesive properties. To incorporate into a laminate, sheets of plastic interlayer are needed on each side of the film to bond the film to the other layers of the laminate.

Metals and many other types of materials have an ultimate yield strength at which point the material will fail. However, with glass we can only specify a probability of breakage for a given value of stress. Looking at glass at the molecular level, we would expect the strength to be very high. In fact, what we find in practice is that glass has a very high compressive strength, as expected, but very low tensile strength.

For a given set of glass test specimens, with identical loading, the point of failure at first glance might appear to be a random variable. In fact, the yield point follows a Weibull distribution and the probability of breakage can be calculated as a function of, stress, duration, surface area, surface defects and the modulus of glass.

To the naked eye, float glass appears to be near perfect. Any defects that may be present as so small as to not be visible. But, in fact, at the microscopic level, the surface appears rough and can be seen to be dotted with flaws. When the glass is placed in tension, these surface defects tend to open and expand, eventually leading to failure. Therefore, laminated automotive glass almost always fails in tension. Even when not in tension, the surface defects react with the moisture in the environment and slowly“grow” over time. This is known as slow crack growth.

The types of glass that may be used include but are not limited to: the common soda-lime variety typical of automotive glazing as well as aluminosilicate, lithium aluminosilicate, borosilicate, glass ceramics, and the various other inorganic solid amorphous compositions which undergo a glass transition and are classified as glass included those that are not transparent. The glass layers may be comprised of heat absorbing glass compositions as well as infrared reflecting and other types of coatings.

Most of the glass used for containers and windows is soda-lime glass. Soda-lime glass is made from sodium carbonate (soda), lime (calcium carbonate), dolomite, silicon dioxide (silica), aluminum oxide (alumina), and small quantities of substances added to alter the color and other properties. The glass layers may be annealed or strengthened. There are two processes that can be used to increase the strength of glass. They are thermal strengthening, in which the hot glass is rapidly cooled (quenched) and chemical tempering which achieves the same effect through an ion exchange chemical treatment.

Annealed glass is glass that has been slowly cooled from the bending temperature down through the glass transition range. This process relieves any stress left in the glass from the bending process. Annealed glass breaks into large shards with sharp edges. When laminated glass breaks, the shards of broken glass are held together, much like the pieces of a jigsaw puzzle, by the plastic layer helping to maintain the structural integrity of the glass. A vehicle with a broken windshield can still be operated. The bonding layer also helps to prevent penetration by objects striking the laminate from the exterior and in the event of a crash occupant retention is improved.

The glass layers are formed using gravity bending, press bending, cold bending or any other conventional means known in the art. In the gravity bending process, the glass flat is supported near the edge of glass and then heated. The hot glass sags to the desired shape under the force of gravity. With press bending, the flat glass is heated and then bent on a full of partial surface mold. Air pressure and vacuum are often used to assist the bending process. Gravity and press bending methods for forming glass are well known in the art and will not be discussed in detail in the present disclosure.

Laminates, in general, are articles comprised of multiple sheets of thin, relative to their length and width, material, with each thin sheet having two oppositely disposed major faces and typically of relatively uniform thickness, which are permanently bonded to one and other across at least one major face of each sheet.

Laminated safety glass is made by bonding two sheets (201 & 202) of annealed glass together using a plastic bonding layer comprised of a thin sheet of transparent thermos plastic bonding layer 4 as shown in Figure 1.

A panoramic windshield is a windshield on which the top edge has been substantially extended such that it comprises a portion of the vehicle roof. A panoramic roof is a vehicle roof glazing which comprises a substantial area of the roof over at least a portion of both the front and rear seating areas of the vehicle. A panoramic roof may be comprised of multiple glazings and may be laminated or monolithic.

Resistive heating circuits are commonly provided on automotive backlites to assist vision and enhance safety by melting snow and ice and clearing fog. Heated circuits are also provided on some windshields. On vehicles that have wipers that are hidden below the hood line when not in use, a heated wiper rest area is needed to keep the wipers clear of snow and ice when not in use and to prevent the buildup of snow in ice in the rest area when in use. Windshields that have safety cameras also require a heated circuit that can quickly clear the portion of the windshield in the camera field of view.

Silver frit is the most common type of heated circuit used for backlites, heated wiper rests and camera defrosters. It is also the most cost effective. Finely silver powder is mixed with carriers, binders and finely ground glass. Other materials are also sometimes added to enhance certain properties: the firing temperate, anti-stick, chemical resistance, etc. The silver frit is applied to the glass using a silk screen or ink jet printing process prior to the heating and bending of the glass. As the flat glass is heated during the bending process, the powdered glass in the frit softens and melts, fusing to the surface of the glass. The silver frit print becomes a permanent part of the glass. The frit is said to be“fired” when this takes place. This is a vitrification process which is very similar to the process used to apply enamel finishes on bathroom fixtures, pottery, china and appliances. Resistances as low as 2 milliohms per square and line widths as narrow as 0.5 mm are possible. The primary drawback to silver print is the aesthetics of the fired silver which has a dark orange to mustard yellow color depending upon which side of the glass it is printed on, the air side or the tin side. Busbars are printed silver but may be reinforced electrically with copper strips or braids. Screen print silver circuits cannot be used on the windshield as the lines are too wide and would interfere with vision.

An embedded wire resistive heated circuit is formed by embedding fine wires into the plastic bonding layer of a laminate. The wires are embedded in the plastic using heat or ultra-sound. Tungsten is a preferred material due to its tensile strength, which is lOx that of Copper and it flat black color. Heated windshields typically use tungsten wire that is in the 18 - 22 um range at which point the wires are virtually invisible. The wires are embedded using an oscillating sinusoidal like pattern to reduce glare that can occur under certain lighting conditions. For positions of the glazing other than the windshield, larger wire diameters can be used. Wire are typically embedded utilizing some sort of CNC machine. Thin flat copper is used for busbars with two layers being typically used. The first layer is applied to the plastic layer prior to the embedding of the wires. The second layer is applied over top of the first layer and the two are joined by soldering or using a conductive adhesive. For some applications it may only be required to use a single layer of copper. Of course, conductors other than copper can be used.

While wire heated windshields have been produced in large quantities for many years, acceptance has been limited. Even at a diameter of 18 um, the wires are visible under certain lighting conditions. Due to the limited power that can be achieved with a 12-volt electrical system, they do not develop that power needed for rapid deicing. The added cost is also relatively high. Very few vehicles have a wire heated windshield available as an option. Some of the automotive OEMs do not offer wire heated windshields on any models.

To make the connection of the electronic circuits, the invention proposes making holes through the glazing. Nevertheless, one of the main problems with annealed glass with holes drilled through the glass is that the holes tend to create weak spots which act as stress concentrators. This can lead to premature breakage. This is in part because holes in glass are typically made by grinding rather than the traditional material removal methods that can be used with non-brittle metals and plastics. It should be highlighted that the term hole, as used, applies to any perforation or opening through and in at least one of the glass layers. The shape of hole is not limited to circular but may be of any other shape including but not limited to rectangular and oval.

Glass is a brittle material. While it exhibits almost perfect elastic behavior it does not undergo plastic deformation under stress. Under stress, glass will bend but not deform unless it is pushed to the point of failure. Prior to that point, the glass will flex back to its original shape when the force is removed. As a result, it cannot be cut, drilled or otherwise worked by the same methods that are used for plastics, wood and metals. The glass will shatter. Holes need to be made by grinding away the glass. In addition, it is desirable to use two drill/grinding bits that meet in the middle of the glass thickness to avoid chipping that occurs when a single drill/grinding bit emerges through the opposite side. This dual bit method also contributes defects at the surface and in the walls of the hole which can lead also to breakage. Due to the constraint of the process, it is not practical to make very small holes. The minimum diameter is on in the 6-12 mm range. Smaller holes can be made but not economically on large scale series production parts.

One of the other problems caused by holes in annealed glass is caused by a phenomenon known as slow crack growth. The grinding process leaves behind surface defects. These small defects or cracks in the glass surface tend to grow over time due to exposure to moisture. The water reacts with the molecules of the glass composition forcing the cracks to open wider. In this manner, with no impact or added loading, glass tends to fail if left exposed to moisture long enough.

In the method of the invention, a LASER is used to cut an opening through the inner glass layer in an area outside of the camera field of view. Methods of LASER cutting and drilling through glass are known in the art. A nanosecond pulsed LASER or preferably a femtosecond pulsed LASER is used in conjunction with an optical means with provides a focal point that is at or below the exterior surface of the glass. As the glass is removed by the LASER the focus is adjusted or the LASER itself is moved to deepen the opening. In this manner, holes with low surface roughness can be produced. Surface roughness is important as it is a measure of the quality of the glass surface. A smoother surface has fewer and less severe surface defects. A smoother surface has a lower probability of breakage. Another advantage is that with the LASER this is no restriction on the minimum hole size other than the spot size of the beam (~25 um in one case). Thus, the size of the hole can be kept to the minimum needed for the wire to pass and to allow for expansion and contraction. The smaller size possible also improves the durability of the product by reducing the probability of breakage as the affected areas is correspondingly reduced.

With this method, the face of the hole and edges can be produced with a surface roughness of less than 2 um, orders of magnitude better than the best that can be achieved by traditional grinding.

The second step of the method is to seal the hole. Rather than leaving the abraded edges and surface of the hole exposed, a material is used to fill and seal the hole. The UV cured resins commonly used for windshield repair work well. However, as can be appreciated, there are many other materials that can be used including those which are not transparent and those with various other cure mechanisms. The primary properties include good adhesion to the glass and the ability to serve as a moisture barrier. Unless the coefficient of thermal expansion is close to that of glass, the material must also remain pliable at low temperatures so as to not create stress in the glass.

One of the issues with creating laminates in which components are a permanent part of the laminate is that the components must last for the life of the vehicle. Conversely, the laminate must last for the life of the component. While an LED may have an expected life expectancy of 50,000 hours, that may not always be sufficient, especially in an autonomous vehicle operating around the clock. There also will always be defective components that fail prematurely. And, if the laminate should fail, all of the components must be replaced as they are a permanent part of the laminate.

One of the other advantages of the method of the invention is that it enables the components to be mounted on the surface of the glazing with the electrical conductors used to provide signal and power, routed within the laminate. This also allows the use of components that cannot be laminated. In one embodiment, a conductive metal filled resin is used to seal and fill the hole, in effect creating a via in the glass layer. In a preferred embodiment, conductive glass frit is deposited in the hole and dried at temperatures lower than 450°C and fired at bending temperature to bond it to the glass. Conductive glass frit can be but is not limited to metal oxides mixed with conductive materials such as silver in such manner that a predetermined resistance is obtained. In an additional preferred embodiment, conductive material such as a metal is introduced in the hole and bonded to glass by using a non- conductive glass frit dried at temperatures lower than 450°C and then fired at bending temperatures.

In some embodiments, the sealing material is a metal filled polymer such as a conductive adhesive or conductive via paste.

Components can then be easily attached to signal and power by making direct contact with the via. In the event of failure of the glazing, the components can be transferred to the replacements. In the event of the failure of a component, the component can be replaced. DETAILED DESCRIPTION OF THE EMBODIMENTS

1. The panoramic windshield, illustrated in Figure 2A and 2B, is comprised of a clear, 2.3 mm thick, soda-lime glass outer glass layer, a solar green, 2.1 mm, soda-lime glass inner glass layer, two layers of PVB interlayer and a solar performance film layer. The film is positioned between the two PVB interlayers which serve to bond each of the glass layers to the film layer. In the installed windshield, a set of cameras is mounted on centerline towards the top of the windshield. The windshield is equipped with an embedded wire defroster 16 circuit in the camera field of view 30. The wire 14 is comprised of black 40 um diameter tungsten. The wire 14 is embedded into the surface of the PVB layer that faces the outer glass layer. Two 2 mm holes 24 are created in the flat inner glass layer, prior to bending, using a femto second LASER, as illustrated in Figure 2B. The walls of the hole 24 produced have a surface smoothness of < 2 um. The two glass layers are gravity bent to shape. During assembly of the laminate, the wires 14 to the defroster are threaded through the two holes 24 as the laminate is assembled. A standard laminating process is used to laminate the assembly. After lamination, the holes 24 are filled with a resin or a sealant 8 commonly used to repair cracks and chips in windshields, the air is evacuated from the hole 24, that the resin in cured by means of UV light. The protruding conductor is then crimped to an electrical connection means.

2. The panoramic windshield, illustrated in Figure 2A y 2B, is comprised of a clear, 2.3 mm thick, soda-lime glass outer glass layer, a solar green, 2.1 mm, soda-lime glass inner glass layer, two layers of PVB interlayer and a solar performance film layer. The film is positioned between the two PVB interlayers which serve to bond each of the glass layers to the film layer. In the installed windshield, a set of cameras is mounted on centerline towards the top of the windshield. The windshield is equipped with an embedded wire defroster 16 circuit in the camera field of view 30. The wire 14 is comprised of black 40 um diameter tungsten. The wire 14 is embedded into the surface of the PVB layer that faces the outer glass layer. Two 2 mm holes 24 are created in the flat inner glass layer, prior to bending, using a femto-second LASER, as illustrated in Figure 2B. The walls of the holes 24 produced have a surface smoothness of < 2 um. The two glass layers are gravity bent to shape. During assembly of the laminate, the wires 14 to the defroster are threaded through the two holes 24 as the laminate is assembled. A standard laminating process is used to laminate the assembly. After lamination, two vias are created by filling the holes 24 with a silver filled resin commonly used to repair breaks in screen print silver lines on heated backlite circuits. The air is evacuated from the hole, then the resin in cured by means of UV light. The electrical connection means utilizes a set of spring-loaded contact to make an electrical connection to the vias so formed. The laminate shown in exploded view in Figure 3 and in an ISO view in Figure 4, is comprised of two glass layers 201, 202 and a PVB bonding layer 4. A set of six 3 mm holes 24 are drilled by means of a femtosecond LASER. The walls of the holes 24 produced have a surface smoothness of < 2 um. Six 0.2mm copper wires 14 are embedded in the PVB bonding layer 4. The wires 14 are routed through the six holes 24. The assembly is assembled and processed through a standard lamination process. The holes in the laminate are filled with a silver filled conductive epoxy and then the epoxy is thermally cured. An assembly comprising five LED lights 20 is attached to the glass by a mounting means. Spring loaded contacts are used to contact the holes

24 (vias) filled with conductive epoxy resin or sealant 8. The sixth wire is used as the ground.