Patent Description:
It is often necessary to attach electrical connectors on to the surface of glazings to provide electrical power to devices associated with the glazing or to electrically connect devices on the glazing. Such electrical devices may include heaters which need electrical power or antennae which need connection to other devices. Electrical connections to glazings are often used in automotive glazings such as windscreens, rear windows or side windows.

<CIT> discloses an element for contacting a conductive surface with a soldering foot shaped in an approximate figure of eight.

<CIT> discloses an electric connector for connecting to a conductive element in a glazing part i.e. automobile glazing which has elements extending between feet without increasing the distance between the feet.

<CIT> discloses adhering a terminal using solder by baking silver paste on a conductive element and applying a metal terminal comprising tin and lead.

It is known to solder electrical connectors on to the surface of an electrically conductive coating on the surface of a glazing (most often glass). Lead-containing solders have traditionally been used because they have high ductility that can adjust for the mechanical stresses existing between an electrical connector and a glass substrate to which the electrical connector is soldered.

However, there have been concerns about the use of lead containing solders in many countries and, in Europe, under European Union Directive <NUM>/<NUM>/EC, lead-containing solders are to be replaced by lead-free solders.

The use of lead-free solders to attach connectors to glass surfaces can, unfortunately, be problematic because lead-free solder can introduce high mechanical stress in the glass leading to glass cracks and breakage either during the soldering process or subsequently during temperature fluctuations in service.

There have been attempt to modify connectors and soldering processes to avoid or reduce such problems.

<CIT> discloses an electrical connector and a compensator plate, the compensator plate being connected to a pane with a conductive structure on the surface with lead-free solder.

<CIT> discloses glazing panes having at least one electrical connection element. The panes have a substrate, an electrically conductive structure on a region of the substrate, a layer of a solder material on a region of the electrically conductive structure, and at least two soldering points of a connection element on the solder material. The soldering points have contact surfaces between the connection element and the electrically conductive structure, and the shape of contact surface has a segment of an oval, an ellipse, or a circle with a central angle of at least <NUM>°.

<CIT> discloses a method of producing a pane having an electrical connection element that is said to avoid problems with components having different thermal expansion coefficients.

<CIT> discloses glazings comprising a ply of glazing material having a first electrically conductive component mounted thereon, and a second electrically conductive component, joined to the first by a lead-free solder. The second component has a thickness t and comprises first and second connector feet linked by a bridge portion, the bridge portion being at a height h above each of the connector feet. t and/or h are chosen to minimise the occurrence of stress faults in the glass in the region of the solder.

<CIT> discloses glazings comprising a ply of glazing material having a first electrically conductive component mounted thereon, and a second electrically conductive component, joined to the first by a solder. The second component comprises first and second connector feet linked by a bridge portion, the bridge portion being at a height h above each of the connector feet, and each of the feet comprises at least one protrusion having a height (d). At least one of h or d is chosen to maximise the adhesion between the second electrically conductive component and the first electrically conductive component.

<CIT> discloses an improved electrical connector for use with a glazing. The glazing comprises a ply of glazing material having a first electrically conductive component mounted thereon, and a second electrically conductive component, joined to the first by a solder. The second component has a thickness t and comprises first and second connector feet linked by a bridge portion, the bridge portion being at a height h above each of the connector feet, and each of the feet comprises at least one protrusion having a height d. At least one of t, h or d is chosen to minimise the occurrence of stress faults in the glass in the region of the solder. <CIT> also discloses an electrical connector according to the prior art.

There is nevertheless still a need to provide an electrical connector which mitigates the stress associated with the use of solder, especially lead-free solder. It is an aim of the present invention to address such a need.

The present invention according provides, in a first aspect, an electrical connector for a glazing, the electrical connector comprising a first connector foot for soldering to the glazing and a second connector foot for soldering to the glazing, and a bridge portion comprising sheet metal having a thickness in the range <NUM> to <NUM> linking the first connector foot and second connector foot, wherein the first connector foot and the second connector foot each are shaped so that <NUM>% or more of the perimeter of each foot is curved, and wherein the first connector foot and the second connector foot are connected to the bridge portion by a first neck portion and a second neck portion respectively and the first neck portion and the second neck portion each have a narrower width than the bridge portion and, in a side view, the electrical connector has a step-like profile or "Z" shaped profile or "S" shaped profile.

This is greatly advantageous because the thickness of the sheet metal in combination with the curvature of the feet when soldered on a glazing has been shown to result in significantly less stress occurring in the glazing (even when lead-free solder is used) reducing the likelihood of breakage of glass substrates either during the soldering process or during use.

The first connector foot and the second connector foot are connected to the bridge portion by a first neck portion and a second neck portion respectively, and the first neck portion and the second neck portion each have a narrower width than the bridge portion. A narrower neck portion is advantageous because it reduces still further stress on the glazing when the connector feet are soldered to the glazing. Even less stress may be induced in the glazing when the sides of the first and second neck portion are curved, especially wherein the curved sides of the first and second neck portion are concave.

A perimeter of the connector feet having a curved portion is advantageous because temperature differences may arise at corners or straight edges of connectors leading to stress in the glazing and even cold spots where the solder does not flow or wet as easily or even does not melt. These issues may lead to poor adhesion of the connector feet and/or to mechanical stresses being induced in the glazing. Thus, it is advantageous if the first connector foot and the second connector foot each are shaped so that <NUM>% or more, preferably <NUM>% or more, more preferably <NUM>% or more, of the perimeter of each foot is curved. Curved perimeters aid in efficient and even distribution of flowing solder, more even distribution of heat, and once the connector feet are soldered on the glazing, lead to more even electrical contact.

The first connector foot and the second connector foot may each be shaped so that the perimeter of each foot forms a closed curve.

It is preferred that the curved portion of the perimeter of the first connector foot and the perimeter of the second connector foot each form a convex curve.

In use, when the first and second connector feet are positioned on a glazing, the bridge portion may at a height h above the first and/or second connector feet, wherein h is preferably in the range <NUM> to <NUM>, more preferably <NUM> to <NUM>, most preferably <NUM> to <NUM>. A height below about <NUM> may result in relatively poor performance.

A suitable height, h, is achieved by the electrical connector further comprising a double fold comprising an A fold and a B fold between each connector foot and the bridge, so that in side view, the electrical connector may have a step-like profile or "Z" shaped profile.

The angle of the A fold and B fold are generally independently selected.

The angle of the A fold (e.g. subtending an angle between the connector foot and the A fold to B fold portion of the electrical connector) may be right-angled or acute, that is preferably having an angle in the range <NUM>° to <NUM>°.

The A fold may, alternatively, have an angle that is obtuse, preferably in the range <NUM>° or <NUM>° to <NUM>°, more preferably <NUM>° to <NUM>°, more preferably <NUM>° to <NUM>°, even more preferably <NUM>° to <NUM>°, and most preferably <NUM>° to <NUM>°.

Whether the angle of the A fold is acute, right-angled or obtuse, it is preferred that the angle of the A fold is such that the bridge portion is, as discussed above, at a height h above the first and/or second connector feet, wherein h is preferably in the range <NUM> to <NUM>.

The angle of the B fold (that may subtend an angle between the A fold to B fold portion of the electrical connector and the bridge portion) may be right-angled or acute preferably in the range <NUM>° to <NUM>°, or may be obtuse preferably in the range <NUM>° or <NUM>° to <NUM>°.

The A fold and a B fold may each have a radius of curvature in the range <NUM> to <NUM>, preferably <NUM> to <NUM>.

If the folds of the double fold have a generally larger radius of curvature, the double fold may form a generally S-shaped profile.

The A fold may be situated directly above the connector foot which advantageously further reduces stress. In this case, the projection of the portion of the connector between the A and B fold would intersect with the connector foot.

It is convenient if the first connector foot and the second connector foot also comprise the sheet metal. The electrical connector may, therefore, be produced by stamping / cutting the shape of the connector out of sheet metal of appropriate thickness and composition and then, optionally, bending the correct parts of the electrical connector to form the shape of the electrical connector.

The sheet metal preferably has a thermal conductivity in the range <NUM> to <NUM> W/m°C, preferably <NUM> to <NUM> W/m°C, more preferably <NUM> to <NUM> W/m°C which has great benefits in ensuring that the soldering process is efficient and the heating of the connector is even thereby reducing the chance of hot and/or cold spots.

It is preferred if the sheet metal of the connector has a coefficient of thermal expansion which is close to (i.e. matched) to the coefficient of thermal expansion of the substrate (usually the glass substrate) because thereby mechanical stresses during heating and cooling are reduced. Glass usually has a coefficient of thermal expansion in the range <NUM> × <NUM>-<NUM> /° C to <NUM> × <NUM>-<NUM> /° C in a temperature range from <NUM>° C to <NUM>° C.

Thus, preferably, the sheet metal has a thermal expansion coefficient in the range <NUM> × <NUM>-<NUM> /°C to <NUM> × <NUM>-<NUM> /°C, preferably <NUM> × <NUM>-<NUM> /°C to <NUM> × <NUM>-<NUM> /°C, more preferably <NUM> (or <NUM>) × <NUM>-<NUM> /°C to <NUM> × <NUM>-<NUM> /°C, even more preferably <NUM> × <NUM>-<NUM> /°C to <NUM> × <NUM>-<NUM> /°C, most preferably <NUM> × <NUM>-<NUM> /°C to <NUM> × <NUM>-<NUM> /°C.

Preferably, the sheet metal has an electrical conductivity in the range <NUM> × <NUM><NUM> S/m to <NUM> × <NUM><NUM> S/m, preferably <NUM> × <NUM><NUM> S/m to <NUM> × <NUM><NUM> S/m, more preferably <NUM> × <NUM><NUM> S/m to <NUM> × <NUM><NUM> S/m, most preferably <NUM> × <NUM><NUM> S/m to <NUM> × <NUM><NUM> S/m. This provides suitable electrical conductivity to ensure correct electrical contact between the power supply of the vehicle (if used in an automotive glazing) and the electrical components on the glazing.

The sheet metal may comprise steel, copper, aluminium, or titanium, preferably steel, more preferably mild steel or an alloy of, for example, iron optionally comprising Mn and/or Ni.

An example of an advantageous alloy is an iron/Ni alloy, preferably having a Ni content of 25wt% to 55wt%, more preferably 27wt% to 51wt%, optionally containing Co and/or Mn. Examples of advantageous Fe/Ni alloys include Invar (FeNi36), Kovar (Fe with 29wt% Ni and 17wt% Co) and FeNi49 (Fe with 49wt% Ni).

It is useful if the connector feet are provided with solder in the appropriate amount/weight. Thus, preferably, the electrical connector further comprises a solder deposit adhered to each foot of the connector, preferably a substantially lead-free solder deposit. Generally, the solder deposit may be a substantially annular solder deposit.

The solder is preferably a lead-free solder i.e. contains no lead. By no lead is meant having a lead content of <NUM> wt% or lower, preferably <NUM>. 05wt % or lower. This is particularly advantageous because of environment benefits.

Lead-free solders often have lower ductility than lead-containing solders which can lead to high mechanical stresses between a connector and a glass substrate. One of the great advantages of connectors according to the present invention is that mechanical stress is reduced.

The solder may contain one or more of indium, tin, copper, silver, bismuth and zinc. The proportion of tin in the solder may be from <NUM> wt. % to <NUM> wt. %, preferably from <NUM> wt. % to <NUM> wt. %, more preferably from <NUM> wt. % to <NUM> wt. The proportion of bismuth, indium, zinc, copper, silver, in the solder composition may be from <NUM> wt. % to <NUM> wt. %, preferably <NUM> wt. % to <NUM> wt. The solder composition may contain nickel, germanium, aluminium, or phosphorus at <NUM> wt. % to <NUM> wt. A preferred solder composition is (in wt%) <NUM> Sn, <NUM> Ag, <NUM> Cu.

Preferably, at least a portion of each connector foot comprises a coating comprising copper, zinc, tin, silver, gold, or alloys or layers thereof, to improve wettability of the solder and protect the solder-contacting surface.

Preferably, each connector foot comprises a solder-contacting surface having at least one spacer to space the foot from the surface of the glazing. This is advantageous because it promotes even solder flow and wetting. The spacer may be an elevation spacer or one or more spacer stubs. The spacer may space the connector foot <NUM> to <NUM> from the glazing surface, preferably <NUM> to <NUM>, more preferably <NUM> to <NUM> and most preferably about <NUM>.

The substrate preferably comprises glass, more preferably float glass. The preferred glass material is soda lime glass.

Connectors according to the invention are suitable for soldering to a glazing surface even with lead-free solder.

Thus, the present invention provides, in a second aspect, a glazing comprising, a pane of glazing material, an electrically conductive layer on a surface of the pane, a solder deposit on the electrically conductive layer, and an electrical connector as discussed in relation to the first aspect on the solder deposit, wherein the electrical connector comprises a first connector foot and a second connector foot soldered to the glazing, and a bridge portion comprising sheet metal having a thickness in the range <NUM> to <NUM> linking the first connector foot and second connector foot, wherein the first connector foot and the second connector foot each are shaped so that <NUM>% or more of the perimeter of each foot is curved. Preferably, the solder comprises lead-free solder.

The electrically conductive coating on the glazing may have a layer thickness of <NUM> to <NUM>, preferably <NUM> to <NUM>, more preferably, <NUM> to <NUM> and, most preferably <NUM> to <NUM>. The electrically conductive coating will usually comprise silver, preferably, silver particles and a glass frit.

The layer thickness of the solder will usually be <NUM> or lower, preferably <NUM> or lower, more preferably <NUM> or lower and most preferably <NUM> or lower.

Preferably, the solder, electrically conductive layer and the first connector foot and/or the second connector foot are adapted so that the solder wets the electrically conductive layer and/or the solder-contacting surface(s) of the first connector foot and/or the second connector foot. More preferably the solder wets the electrically conductive layer and/or the solder-contacting surface(s) of the first connector foot and/or the second connector foot such that the solder contact angle is <NUM>° or below, even more preferably <NUM>° or below most preferably <NUM>° or below.

Good wetting of the electrically conductive layer or the solder-contacting surface(s) of the first connector foot and/or the second connector foot, advantageously both electrically conductive layer and the solder-contacting surface(s) of the first connector foot and/or the second connector foot, tends to reduce stress on the glass. Solder contact angle may be measured as is known to those skilled in the art by measuring the angle at the edge of a drop or mass of solder on a surface (an example of the method is as indicated in <NPL>).

In a third aspect, the present invention provides, a method of soldering an electrical connector to a glazing, the method comprising, providing a pane of glazing material with an electrically conductive layer on a surface of the pane, providing an electrical connector as discussed in relation to the first aspect preferably comprising a first connector foot and a second connector foot for soldering to the glazing, and a bridge portion comprising sheet metal having a thickness in the range <NUM> to <NUM> linking the first connector foot and second connector foot, wherein the first connector foot and the second connector foot each are shaped so that <NUM>% or more of the perimeter of each foot is curved, and there is a solder deposit on each connector foot, and fusing the solder.

The present invention will now be described by way of example only, and with reference to the accompanying drawings, in which:.

<FIG> shows a first type of a bridge-type electrical connector <NUM> according to the present invention. The connector <NUM> comprises a first connector foot <NUM> and a second connector foot <NUM>, the first <NUM> and second <NUM> connector feet being linked by a bridge <NUM>. The bridge <NUM> and first connector foot <NUM> are connected by a narrower (narrower in width than the bridge <NUM>) first neck portion <NUM> which has concave curves sides / edges each with a radius of curvature. The narrow neck portion improves stress distribution on the glazing during soldering. The bridge <NUM> and second connector foot <NUM> are similarly connected by a narrower second neck portion <NUM> which has concave curves sides / edges. The connector <NUM> may be formed by stamping/cutting the connector <NUM> from sheet metal, for example mild steel. In use the first and second connector feet <NUM>, <NUM> are soldered to the glazing, and the bridge <NUM> is positioned at a height h in the range <NUM> to <NUM> above the glazing surface. Positioning the bridge at a height above the surface is accomplished by double folding the connector <NUM> in the region of the first and second connector feet <NUM>, <NUM> along respective lines A (in a valley fold so that, in the top orientation as shown in <FIG>, the first connector foot <NUM> would be substantially in the plane of the paper and the bridge <NUM> would come out of the paper) and folding the bridge <NUM> along respective lines B in mountain folds. After the double folds A and B are made, in a side view, the connector <NUM> in the area of the first and second connector feet <NUM>, <NUM> has a step-like profile; the angles of the folds may be acute, approximately right angled or obtuse.

<FIG> shows a second type of a bridge-type electrical connector <NUM> according to the present invention. The connector <NUM> comprises a first connector foot <NUM> and a second connector foot <NUM>, the first <NUM> and second <NUM> connector feet being linked by a bridge <NUM>. The bridge <NUM> and first connector foot <NUM> are connected by a narrower (narrower in width than the bridge <NUM>) first neck portion <NUM> which has square sides / edges. This alternative form of the narrow neck portion also improves stress distribution on the glazing during soldering. The bridge <NUM> and second connector foot <NUM> are similarly connected by a narrower second neck portion <NUM> which has square sides / edges. As in the first connector <NUM> illustrated in <FIG>, the connector <NUM> is shaped in the region of first and second connector feet <NUM>, <NUM> with a double fold along respective lines A in a valley fold and along respective lines B in mountain folds. After the double folds A and B are made, in a side view, the connector <NUM> in the area of the first and second connector feet <NUM>, <NUM> also has a step-like profile; the angles of the folds may be acute, approximately right angled or obtuse.

<FIG> shows a third type of a bridge-type electrical connector <NUM> according to the present invention in (a) bottom plan view and (b) top plan view. The connector <NUM> as in <FIG> comprises a first connector foot <NUM> and a second connector foot <NUM>, the first <NUM> and second <NUM> connector feet being linked by a bridge <NUM>. The bridge <NUM> and first connector foot <NUM> are connected by a narrow first neck portion <NUM> which has square sides / edges and is in this connector <NUM> joined (e.g. by soldering or welding) to the top surface of the first connector foot <NUM>. This alternative form of the neck portion <NUM> improves stress distribution on the glazing during soldering and also, because it allows the first connector foot to have a perimeter that has no straight sides or corners (i.e. the perimeter is closed curve, generally in an elliptical shape), solder distribution and flow under the foot is much improved. The bridge <NUM> and second connector foot <NUM> are similarly connected by a second neck portion <NUM>. As in the first connector <NUM> illustrated in <FIG>, the connector <NUM> is shaped in the region of the first and second connector feet <NUM>, <NUM> in the form of a double fold along respective lines A in a valley fold and along respective lines B in mountain folds. After the double folds A and B are made, in a side view, the connector <NUM> in the area of the first and second connector feet <NUM>, <NUM> also has a step-like profile; the angles of the folds may be acute, approximately right angled or obtuse.

<FIG>, <FIG> show, highly schematically, cross-sectional side views of embodiments of the connector. The embodiments of <FIG> are not part of the claimed invention. The same reference numerals refer, in <FIG>, to similar or equivalent features.

<FIG> shows a connector with a bridge <NUM> joining two connector feet <NUM>. The connector feet <NUM> are soldered through solder fillets <NUM> to an electrically conductive coating <NUM> deposited on a glass substrate <NUM>. The electrically conductive coating <NUM> will usually comprise silver, preferably, silver particles and a glass frit. Each connector foot <NUM> is connected to the bridge <NUM> (and therefore connected electrically to the other connector foot <NUM>) via neck portions <NUM> and AB portions <NUM>. The connector is double folded in the region of each connector foot <NUM> by fold A between the neck portion <NUM> and AB portion <NUM> (subtending an angle <NUM> between the connector foot <NUM> and the AB portion <NUM>) and a fold B between the AB portion <NUM> and the bridge <NUM> (subtending an angle <NUM> between the AB portion <NUM> and the bridge <NUM>). In the embodiment of <FIG>, the angles <NUM> and <NUM> are acute, and approximately the same, so that the double folds form a step-like, Z shaped profile. In other embodiments, the A and B folds may be different so that angles <NUM> and <NUM> may be independently selected. In <FIG>, the A and B folds are sharp with very small radii of curvature.

The connector shown in <FIG> is generally similar to that of <FIG> and will not be described in detail. The A and B folds in the connector of <FIG> are each at approximate right angles.

<FIG> shows a connector where the A fold and B fold are of greater radius of curvature than those of the embodiment of <FIG>. Thus, the profile is generally of an "S"-shape.

<FIG> shows a connector which is not part of the claimed invention and where each neck portion <NUM> is bent back (forming a hairpin fold) so that the A fold between the neck portion <NUM> and AB portion <NUM> is directly above the connector foot <NUM>. The projection of the AB portion <NUM> towards the substrate <NUM> surface (when the connector is in use) therefore intersects with the connector foot <NUM> which has advantages in reducing stress in use. The angle of the A fold is obtuse as is the angle of the B fold.

<FIG> shows a connector which is not part of the claimed invention and generally as indicated in <FIG>, with the neck portion <NUM> joined (e.g. by soldering or welding) to the top surface of the first connector foot <NUM>. This has great advantages in terms of reducing stress and allowing the connector foot <NUM> to have a perimeter that has no straight sides or corners (i.e. the perimeter is closed curve, generally in an elliptical shape) so that solder distribution and flow under the foot is much improved. As in the connector of <FIG>, the projection of the AB portion <NUM> towards the substrate <NUM> (when the connector is in use) intersects with the connector foot <NUM> which has advantages in reducing stress in use. The angle of the A fold is obtuse as is the angle of the B fold.

A finite element analysis (FEA) simulation was conducted to evaluate changing the design of connector on the stress on the glass in a temperature cycling test between -<NUM> and +<NUM>.

In a comparative Example, a connector made of <NUM> thick copper soldered on to <NUM> thick glass with a <NUM> mmm thick solder layer (solder 50wt% Pb and 50wt% Sn: ASTM Sn50) and being simulated as a quarter symmetric finite element model having a rectangular shape (i.e. straight edges with no curvature), a foot of <NUM> length, an AB portion of <NUM> length and a bridge of <NUM> length with a bridge height <NUM>, angle of the A fold (i.e. angle between the A fold to B fold portion of the electrical connector and the bridge portion) <NUM>° (equivalent to an angle of <NUM>° from the glass surface to the AB portion) showed stress of <NUM> MPa at -<NUM> and of <NUM> MPa at +<NUM>.

Claim 1:
An electrical connector (<NUM>, <NUM>, <NUM>) for a glazing, the electrical connector comprising a first connector foot (<NUM>, <NUM>, <NUM>, <NUM>) and a second connector foot (<NUM>, <NUM>, <NUM>) for soldering to the glazing, and a bridge portion (<NUM>, <NUM>, <NUM>, <NUM>) comprising sheet metal having a thickness in the range <NUM> to <NUM> linking the first connector foot and second connector foot, wherein the first connector foot and the second connector foot each are shaped so that <NUM>% or more of the perimeter of each foot is curved and wherein the first connector foot and the second connector foot are connected to the bridge portion by a first neck portion (<NUM>, <NUM>, <NUM>, <NUM>) and a second neck portion (<NUM>, <NUM>, <NUM>) respectively and the first neck portion and the second neck portion each have a narrower width than the bridge portion characterised in that, in a side view, the electrical connector has a step-like profile or "Z" shaped profile or "S" shaped profile and a double fold comprising an A fold and a B fold between each connector foot and the bridge.