A method of and a system and soldering station for electrically connecting an electrical contact terminal to an electrical contact patch of a photovoltaic device.

Cross-reference to related applications

The present document is related to and claims priority and benefit from the Netherlands patent application document NL 2008714 filed on 26 April 2012, entitled "A method of and a system and soldering station for electrically connecting an electric contact terminal to an electric contact patch of a photovoltaic device". The content of this Netherlands patent application document NL 2008714 is herein incorporated by reference. Technical Field

The present invention relates to Photovoltaic, PV, devices and, in particular, to electrically connecting such devices. Background

PV devices convert optical energy, such as solar radiation, into electrical energy. A PV device is comprised of a single PV cell or of a PV module or solar panel comprised of a layered structure comprising a plurality of PV cells and interconnect and fusible foils for contacting and fusing the PV cells into a laminated structure. Individual PV cells or solar cells are series connected to obtain a higher output voltage and PV cells are parallel connected to provide a higher output current.

PV cells of the so-called back or rear contact type comprise a plurality of electrical contacts arranged at their back or rear side surface opposite a radiation or light receiving front side surface of the PV cells. A PV module is formed by adjacently arranging a plurality of PV cells in an array or matrix arrangement. At their back or rear surface, the PV cells are electrically interconnected by electrically conductive tracks positioned at an electrically isolating back layer of the PV module. The conductive tracks comprise electrical contact patches for electrically connecting contact terminals of a junction box, a load or an electrical inverter, for example.

PV cells of the non-back contact type are provided with electrical contact patches at both the front and rear side of the cells. Besides the connections to the terminals of a junction box, a load or an inverter system, or the like, in a PV module the contact patches of adjacent PV cells are electrically interconnected by contact terminals in the form of small metal strips ("ribbons") or tabs. In practice, these electrical connections are made by soldering. Soldering is the process of bonding a contact terminal and contact patch using a solder alloy or solder paste.

The connections of the contact patches and the contact terminals have to be mechanically durable, must have a low electrical resistance and must be cost effective to produce, both in terms of production costs and material costs. Faulty solder joints remain one of the major causes of device failure, such that high standards of workmanship in soldering are vital. A sufficient low electrical resistance of the solder connection and mechanical reliability thereof require temperatures of the contact terminal, the contact patch and the solder material at or above their wetting temperature. Applying too much heat, however, may cause the PV cell or PV module to become thermally overstressed or overheated, thereby causing damage to the PV cell and/or delamination of the PV module. Delamination bears the risk of corrosion of the solder joints due to the penetration of moisture between the delaminated layers of the PV module, thereby causing accelerated degradation of the solder joints. When applying too less heat no proper wetting action and bonding may take place, with the risk of faulty solder joints over time.

WO2008/105026 discloses interconnection of several adjacent PV cells by flat electrical conductive lines to form a solar module. The conductive lines and electrical contacts of the PV cells are interconnected by means of a spot-welding heating appliance.

JP201 1 -1 14205 discloses a solar module of the back-contact type having electrically connected internal and external wiring. Summary

It is an object of the present invention to provide a mechanically and electrically reliable and durable solder joint of a contact terminal and a contact patch in PV devices, thereby minimizing the risk of locally overheating PV cells or PV modules and preventing malfunctioning thereof.

In a first aspect, there is provided a method of electrically connecting an electrical contact terminal to an electrical contact patch of a Photovoltaic, PV, device, the contact terminal comprising a contact part having a substantially U-shaped cross section comprising a substantially flat base part one surface side of which comprises an electrical contact surface, and two oppositely spaced raised leg parts extending from the base part at a surface side opposite the contact surface, the method comprising the steps of:

- positioning the base part with the contact surface at the contact patch,

- providing solder material for soldering the contact surface and the contact patch,

- heating the contact part by applying heat to at least one raised leg part at a position remote from the base part thereby causing the solder material to melt and bonding the contact terminal and contact patch, and

- applying a mechanical force for holding the contact surface at the contact patch till the contact terminal and the contact patch are bonded.

The invention is based on the insight that soldering requires localized heating of the contact terminal and the contact patch to prevent the PV cell and in particular the layer or layers of organic material in the PV module to become locally thermally overstressed or overheated. By heating the contact part of the contact terminal from a leg part that is raised with respect to the contact part, i.e. the contact surface thereof, in accordance with the invention, on the hand heat is applied to the leg part at a distance of the contact patch at which the contact surface is positioned, thereby effectively avoiding direct contact of a heat source and the contact patch, while on the other hand localised heating is achieved in that the heat is transferred from the leg part to the contact surface of the base part of the contact terminal which is in contact with the contact patch.

The mechanical force for holding the contact surface at the contact patch till the contact terminal and the contact patch are bonded can be provided by a heating appliance used for heating and/or a separate holding appliance providing a sufficient holding force at the contact terminal. When using the heating appliance for the purpose of applying a holding force, it will be appreciated that same has to be turned off and/or sufficiently cooled down below the wetting temperature of the solder joint.

In an embodiment, the heat is applied sideways at the at least one raised leg part at a position remote from the base part.

In another embodiment, the heat is applied at an end of at least one of the raised leg parts remote from the base part. The mechanical force for holding the contact surface at the contact patch may be applied by a heating appliance applying pressure force from the end of the or each raised part in the direction of the contact surface. In a further embodiment, to promote the transfer of heat to the contact surface of the contact terminal, the contact part of the contact terminal is heated by applying heat from both raised leg parts simultaneously.

The U-shaped contact part may be formed integral with and near an end of a strip of electrically conducting material.

Heating of the base part of the contact terminal may be applied from one or both of contact heating and non-contact heating of the at least one raised leg part. With contact heating, heat is directly transferred by conduction from one body to another, such as by a conventional soldering iron, for example. Non-contact heating makes use of radiation heating, laser heating or RF induction heating by eddy currents induced in the contact part of the contact terminal by an RF energy source.

The method according to the invention is by excellence suitable for RF heating, in that the RF source is kept at a distance remote from the PV cells, thereby effectively preventing or reducing unwanted induction of eddy currents in the conductors and electrically conducting layers as well as contact points inside or directly outside a PV cell. Which eddy currents, for example, may damage the PN junctions of the cell. By applying RF heating simultaneously to two spaced leg parts of the contact part of a contact terminal, a closed RF loop including the contact terminal for inducing eddy currents therein can be formed, providing a relatively quick heating of the contact surface, the contact patch and the soldering material.

While contact heating suffers from wear and oxidized material of and at the tip of a soldering iron, for example, thereby impeding the transfer of heat and causing contamination of the solder joint, non-contact heating and in particular RF induction heating is free of combustion gasses and combustion waste, for example, while avoiding safety hazards and, in most cases costly, protection measures which may occur with laser heating, for example.

In an embodiment, the heating is controlled by measuring the temperature of the base part, and/or the time duration of applying heat to the base part, and/or the amount of heat applied, for example. With RF induction, heating of the contact part, the contact patch and the solder material can be suitably controlled dependent on any of the above parameters, such to provide a durable and reliable solder joint, while avoiding local thermal overstress in a contact patch. The temperature of the base part is typically measured by a non-contact optical pyrometer, for example, while the amount of heat applied by an RF heating appliance is measured from the power applied to the RF energy source and/or the time duration of applying the power and/or a particular powering cycle or the like.

Those skilled in the art will appreciate that the method according to the invention is particularly suitable for automatic or semi-automatic operation. To avoid heating at non-contact positions of a PV cell or PV module and to prevent faulty solder joints by misalignment of the contact surface of a contact terminal and the contact patch of the PV device, in an embodiment, a heating appliance providing the heating and the contact terminal are positioned at the contact patch using laser guidance.

Adequate positioning of a heating appliance and the contact terminal is supported, in an embodiment, by providing the heating appliance and the contact terminal with matching shapes for self-aligned positioning of the heating appliance and the contact terminal. Arranging raised leg parts in a sloping manner with respect to the base part, such to provide an open top triangular or delta shaped, L shaped, or trapezium shaped cross section, for example, and by applying the heating from a circular or semi-circular ring shape heating appliance sideways from at least one of the raised leg parts at a position remote from the base part, excellent self-aligning properties are achieved.

In the method according to the invention, the solder material or solder paste can be either pre-applied at one or both of the contact surface and the contact patch prior to positioning of the base part with its contact surface at the contact patch, and/or during the heating of the contact part of the contact terminal.

By applying, in an embodiment, the solder material in an overdose for bonding the contact terminal and contact patch, the quality of the solder joint can be judged from a visual inspection of the amount of solder material circumferentially extending outwardly of the contact surface and the contact patch after bonding. Gaps in or fluctuating amounts of the solder material extending from the joint, may indicate bonding faults which, over time, may develop into malfunctioning of the solder joint. As known to those skilled in the art, wetting can only occur properly if the contact surface of the base part of the contact terminal and the surface of the contact patch to be soldered are free of contamination and free from an oxide film that is formed when the surfaces are exposed to air. Accordingly, in an embodiment, soldering flux is applied at one or both of the contact surface and the contact patch prior to the heating. The type and composition of the constituents of the soldering flux are known to those skilled in the art and commercially available.

The contact terminal may be shaped in any suitable form, such as a contact strip, a connector, a contact terminal integral with a junction box, and a contact terminal of an electronic component, for example.

It can be advantageous to prevent exposure of the contact patches to air, or other atmospheric gasses, as long as possible prior to the soldering operation. Accordingly, in an embodiment wherein the PV device is a PV module comprising a plurality of PV cells having a light receiving front side and a back side and a plurality of electrical contacts electrically connected to electrically conductive tracks of the PV module, the method further comprises exposing electrical contact patches at the conductive tracks from an external surface side of a back layer of the PV module, and soldering electrical contact terminals to the contact patches.

With this embodiment contamination and oxidation of the contact patches due to exposure thereof to the ambient atmosphere is as much as possible delayed to immediately prior to the actual soldering of the contact terminals. Less contaminated contact patches require less use of chemical aggressive cleaning agent, compared to more heavily contaminated or oxidised contact patches. Less contaminated contact patches can be effectively pre-cleaned using a brush or other abrasive tool, for example. If exposure of the contact patches immediately prior to the soldering action is not applicable, it is advised to cover the contact patches after exposure by an Organic Surface Protection, OSP, agent or the like.

In the case of a PV module, for example, it is advantageous to fix a junction box at the isolating back layer, i.e. at the external surface side thereof opposite the electrically conducting tracks, and to electrically connect the contact terminals to electrical connector elements of the junction box.

The junction box generally comprises electronic components such as semiconductor diodes, for example. However, the junction box may also comprise electronic circuit components making up an electronic inverter for converting DC power supplied by the PV cells of the PV module into AC power for connecting a load or connecting the PV module to the power network or grid. In a second aspect, there is provided an electrical contact terminal for use in the method according to the invention disclosed above, which contact terminal comprises a contact part having a substantially flat base part, one surface side of which comprises an electrical contact surface, and two oppositely spaced raised leg parts extending from the base part at a surface side opposite the contact surface, providing a contact part having a substantially U-shaped cross section, wherein the U-shaped contact part is formed integral with and near an end of a strip of electrically conducting material. In a third aspect, there is provided a Photovoltaic, PV, module, comprising a plurality of PV cells having a light receiving front side and a back side, a plurality of electrical contacts electrically connected to electrically conductive tracks of the PV module comprising electrical contact patches, and contact terminals electrically connected to the electrical contact patches at a back layer of the PV module, in accordance with the method disclosed above according to the first aspect.

In an embodiment, the PV module is a PV module of the back contact type, wherein the back layer is an electrically isolating back layer and the electrically conductive tracks are arranged at the internal surface side of the back layer opposite the electrical contacts of the PV cells.

In a fourth aspect, there is provided a system for electrically connecting electrical contact terminals to electrical contact patches at a back layer of a Photovoltaic, PV, module in accordance with the method disclosed above, the system comprising:

- an assembling station, arranged for assembling a PV module comprising a plurality of PV cells, the PV cells having a light receiving front side and a back side, a plurality of electrical contacts electrically connected to electrically conductive tracks of the PV module comprising the electrical contact patches,

- a soldering station, arranged for electrically connecting electrical contact terminals to the contact patches, and

- a mounting station, arranged for electrically connecting the contact terminals to electrical connector elements of a junction box. In an embodiment, the system further comprises an exposing station, arranged for exposing electrical contact patches at the electrically conductive tracks from an external surface side of the said back layer. Exposure of the electrical contact patches may be provided by removing part of the back layer and/or any intermediate layer using laser ablation or by a mechanical grinding or removal technique, known per se to the person skilled in the art.

In an embodiment the system further comprises a material deforming station, arranged for forming electrical contact terminals comprising a contact part having a substantially flat base part, one surface side of which comprises an electrical contact surface, and two oppositely spaced raised leg parts extending from the base part at a surface side opposite the contact surface, providing a contact part having a substantially U-shaped cross section, wherein the U-shaped contact part is formed integral with and near an end of a strip of electrically conducting material.

In a fifth aspect there is provided a soldering station, arranged for electrically connecting electrical contact terminals to electrical contact patches of a Photovoltaic, PV, device in accordance with the method and system disclosed above.

The expression substantially U-shaped or U-shaped cross section used in the description and the claims in connection with the contact part of a contact terminal, is to be construed, in the light of the present invention and the attached claims, in its broadest sense, including open top triangular or delta shaped and trapezium shaped cross sections and the like, whether or not with raised legs of the same or different dimensions, in particular of the same or different length.

The expression substantially flat base part used in the description and claims in connection with the contact part of a contact terminal, is to be construed, in the light of the present invention and the attached claims, in its broadest sense, including a base part having a flat, slightly curved, dimpled or any other non-smooth surface area.

In the method, in the electrical contact terminal, in the PV module, in the system for electrically connecting electrical contact terminals, and in the soldering station of the preceding aspects, wherever applicable, the contact part may comprise a single leg part raised with respect to the base part, replacing the substantially U- shaped cross section. That is a contact part having a substantially flat base part, one surface side of which comprises an electrical contact surface, and comprising only one spaced raised leg part extending from the base part at a surface side opposite the contact surface.

The invention will now be described in more detail by means of specific embodiments, with reference to the enclosed drawings, wherein equal or like parts and/or components are designated by the same reference numerals. The invention is in no manner whatsoever limited to the embodiments disclosed.

Brief Description of the Drawings

Fig. 1 shows schematically, not to scale, in a cross section view, part of a prior art Photovoltaic, PV, module.

Fig. 2 shows schematically, not to scale, in a cross section view, part of a prior art Photovoltaic, PV, module of the back contact type.

Fig. 3 shows schematically, not to scale, in a perspective, partly exploded view, a prior art PV module of the back contact type according to Fig. 2.

Fig. 4 shows schematically, not to scale, the prior art PV module of Fig. 3 viewed at the back side thereof.

Fig. 5 shows schematically, not to scale, in a perspective view an embodiment of an electrical contact terminal according to the invention.

Figs. 6 - 9 illustrate schematically, not to scale, the method according to the invention with reference to the electrical contact terminal of Fig. 5.

Fig. 10 shows schematically, not to scale, in a top view, the electrical contact terminal of Fig. 5 soldered to a contact patch, in accordance with the method of the invention.

Figs. 1 1 - 15 illustrate schematically, not to scale, the method according to the invention with self-aligning contact terminals and heating appliances.

Fig. 16 shows schematically, not to scale, in a cross section view, the PV module of Fig. 2 comprising a contact terminal according to Fig. 5.

Fig. 17 shows, in a very schematic and illustrative form, a system for electrically connecting electrical contact terminals to electrical contact patches at a back layer of a PV module according to the invention. Detailed Description

Fig. 1 shows, in a schematic cross-section view, not to scale, part of a prior art Photovoltaic, PV, device in the form of a PV module or solar module 1 comprising a junction box 2 attached to the PV module 1 at an external back side 12 opposite a light receiving front side 1 3 of the PV module 1 for receiving optical radiation, i.e. solar radiation. The PV module 1 comprises a plurality of plate-shaped or planar polygonal PV cells or wafers 3, adjacently arranged in an array or matrix of PV cells and embedded in a layer 4 of organic material such as, for example, Ethylene Vinyl Acetate, EVA. At its light receiving front side 13, the PV module 1 comprises a transparent cover layer or panel 5 of, for example, glass and a support or back layer 6 at its back side 12.

The PV cells 3, at each their light receiving front side 14 and back or rear side 15, comprise a plurality of electrical contacts (not shown) electrically connected to electrically conductive tracks 7, 8 at both the front and back side 14, 15, respectively. Adjacent PV cells 3 are series connected by electrical contact terminals or strips or ribbons 16 of electrically conductive material, interconnecting the electrically conductive tracks 7 and 8. Electrical contact terminals or strips or ribbons 17 of electrically conductive material connect the series connected PV cells to connector terminals 1 1 of the junction box 2, via an opening or slit 10 in the back layer 6 and the layer 4 of organic material. The contact terminals 16 and 17 are soldered to the conductive tracks 7 and 8 at contact patches 18, 19, respectively. The electrically conductive tracks 7, 8 and the contact terminals 16, 17 are typically formed of copper, silver, aluminium or another electrically conductive material.

Fig. 2 shows, in a schematic cross-section view, not to scale, part of a PV module or solar panel 21 of the so-called back or rear contact type, comprising plate- shaped or planar polygonal PV cells or wafers 22, adjacently arranged in an array or matrix of PV cells, and each having a light receiving front side or front surface 23 and a back or rear side or surface 24 opposite the front surface 23. The PV cells 22 are of the back contact or rear contact device type, which means that the electrical contacts 25 for electrically connecting the PV cells 22 are only provided at the back side 24 of a PV cell 22. The electrical contacts 25 may be shaped as dot-like contact points, for example, generally produced from solder alloys or electrically conductive pastes comprising, for example, copper or silver material, aluminium and mixtures thereof.

The array of PV cells 22 forms a first planar layer of the PV module 21 , embedded in a second planar layer 26 layer organic material which is formed by a first fusible foil or first encapsulant of a thermoplast or thermosetting material, capable of fusing when heated above a certain threshold temperature, such as EVA or an alternative material, such as, for example, a thermoset foil material. The second layer 26 comprises holes or cut outs for the contacts 25 of the PV cells

22 that electrically connect to conductive traces, wires or tracks 27 at a surface side of an electrically isolating planar interconnect foil or back foil or back layer 28, constituting an outer third planar layer of the PV module 21 . Typical interconnect or back foil material is a laminate of polyethylene terephthalate, PET, and TEDLAR® on which the electrically conductive tracks 27 are fixed. This laminate may comprise a layer for providing a required mechanical strength and support, because the interconnect foil should be highly non-stretchable. Additionally, the laminate may comprise a layer acting as a moisture barrier and/or a solder mask layer acting as an isolation layer (not shown). The electrically conductive tracks 27 are typically formed of copper, silver, aluminium or another electrically conductive material including mixtures of electrically conductive material.

Opposite the front side 23 of the PV cells 22, a fourth planar layer 29 of organic material is positioned. This fourth layer 29 is transparent and formed by a second fusible foil or second encapsulant of a thermoplast or thermosetting material capable of fusing when heated above a certain threshold. A typical second encapsulant material is also EVA or an alternative material, such as, for example, a thermoset foil material.

A fifth layer 30, comprised of a transparent or translucent, i.e. a light transmissive, cover panel, such as a glass material, forms an external layer protecting the PV cells and the electrical connections against dirt, moisture and other contaminants and provides sufficient physical rigidness to the PV module 21. The fifth layer 30 may comprise anti- reflection properties or structured surfaces to trap impinging light inside the PV module 21 . The electrically conductive tracks 27 electrically connect by electrically conductive strips, ribbons or contact terminals 33 to connector terminals 1 1 of a junction box 2 arranged at an external or outer or back side 31 of the back layer 28 of the PV module 21 , opposite the light receiving front side 32 thereof. The electrical contact terminals 33 extend through a slit or opening 34 in the back layer 28 and the second layer 26, and are soldered to contact patches 35 of the conductive tracks 27.

Fig. 3 shows, not to scale, a PV module 39 of the back contact type according to Fig. 2, in a perspective, partly exploded view from the light receiving front side 32 thereof. The second and fourth layers 26 and 29, respectively, are omitted in Fig. 2 for sake of clarity. Although just four PV cells 22 are shown, those skilled in the art will appreciate that in practice the length and width dimensions of a PV module may vary between about 0.3 and 2 m, whereas the length and width of a PV cell are in the range of 5 - 30 cm. A PV module of general dimensions typically comprises up to about 50 PV cells.

Fig. 4 shows, not to scale, the PV module 39 of Fig. 3 viewed at the back side 31 thereof, showing the conductive tracks 27 for soldering the electrical contact terminals 33. The contact patches 35 are exposed from the back layer 28 by a respective slit or opening 34 provided in the back layer 28. For clarity sake, the electrical contact terminals 33 and the junction box 2 are not shown in this figure. In practice more than two contact patches 35 may be exposed for soldering contact terminals 33. An embodiment of an electrical contact terminal 40 for use with the method according to the invention is schematically shown, in a perspective view, not to scale, in Fig. 5.

The contact terminal 40 comprises a contact part 41 having a substantially U- shaped cross section, comprised of a substantially flat base part 42, an outer surface side 43 of which comprises an electrical contact surface, and two oppositely spaced raised leg parts 44, 45 extending from the base part 42 at a surface side 46 thereof opposite the outer surface side 43. From the leg part 44 an elongate flat strip portion 47 extends in the direction away from the other leg part 45. Similarly, from the leg part 45 an elongate flat strip portion 48 extends in the direction away from the leg part 44. In the embodiment shown, the strip portion 47 is substantially longer than the strip portion 48. The electrical contact terminal 40 is formed in one, integral piece from an electrically conductive material such as, but not limited to, copper, silver, aluminium or alloys thereof. In a practical embodiment, for connecting the conductive patches 35 of a PV module 39 of the back contact type shown in Figs. 2, 3, 4, the contact terminal 40 has a thickness of about 150 - 250 micron, whereas the strip portion 47 is about 4-5 cm long and the strip portion 48 has a length of about 0.5 cm, both having a width of about 0.5 cm, while the raised leg parts 44, 45 are about 1 -3 mm in height. Those skilled in the art will appreciate that other dimensions are feasible, dependent on a particular type of PV device.

The method according to the invention will now be generally illustrated in Figs. 6 - 10, with reference to the particular embodiment of the electrical contact terminal 40 shown in Fig. 5. Figs. 6 - 9 show the contact terminal 40 from a side view, each time soldered to an electrical contact patch 35, also shown in side view. The solder material is indicated by reference numeral 50.

In all the figures shown, first the electrical contact surface 43 of the base part 42 of the electrical contact terminal 40 is positioned opposite the contact patch 35, and solder material 50 is provided for connecting the contact terminal 40 with its base part 42, i.e. the electrical contact surface 43 thereof, by a soldering operation to the contact patch 35. As illustrated with reference to Figs. 1 and 2, it will be appreciated that the contact patch 35 is formed by part of a surface side of the electrically conductive tracks

Soldering is the process of bonding a contact terminal and contact patch using a solder alloy or solder paste, such as a combination of tin and lead, for example in a tin/lead ratio of 50/50, 60/40 or 63/37, by heating the contact terminal 40, the contact patch 35 and the solder material 50 at or above their wetting temperature. Dependent on the type of solder material or solder paste 50, temperatures in the range of well over 190 °C and even up to approximately 300 °C are required for providing a sufficient low electrical resistance of the solder connection and an adequate mechanical reliability thereof. However, in particular with PV modules of the type shown in Figs. 1 and 2, at such temperatures delamination may occur between the back layer 6 and the layer 4 of organic material as shown in Fig. 1 , or between the back layer 28 and the layer 26 of organic material shown in Fig. 2, for example. Delamination bears the risk of corrosion of the solder joints due to the penetration of moisture and other contaminants between the delaminated layers of the PV module, thereby causing accelerated degradation of the solder joints. Applying too much heat may also cause the PV cell to become locally thermally overstressed or overheated, thereby causing damage to the PV cell. In the case of a back contact type PV module 21 , for example, by applying too much heat the electrically conductive tracks 27 may become detached from the back layer 28, with an increased risk of damaging or breakage of the conductive tracks. Obviously, when applying too less heat no proper wetting action and bonding may take place, with the risk of faulty solder joints over time.

In accordance with the invention, by heating the base part 42, the solder material 50 and the contact patch 35 from at least one of the raised leg parts 44, 45 of the contact terminal 40, by applying heat to at least one or both of the raised leg parts 44, 45 at a position remote from the base part 42, the heat source may be kept at a proper distance from the back layer 6 or 28 of the PV module 1 , 21 or 39 while the heat applied is effectively, locally transferred from the raised leg part or leg parts 44, 45 to the base part 42 of the contact terminal 40, the solder material 50 and the contact patch 35, thereby effectively avoiding or at least effectively reducing heat transfer to the back layer or the layer of organic in which the PV cells are embedded. It will be appreciated that the risk of delamination of these layers by local overheating is considerably reduced or even avoided.

Fig. 6 illustrates application of heat by a heat source or heating appliance 51 to both raised leg parts 44 and 45 from the respective strip portions 47 and 48 of the contact terminal 40. That is at the ends of the raised leg parts 44, 45 remote from the base part 42. Fig. 7 shows application of heat by a heating appliance 51 to both raised leg parts 44 and 45 from an outer side thereof, wherein the heating appliance 51 is located just below the strip portions 47 and 48 of the contact terminal 40, remote from the base part 42. Fig. 8 illustrates application of heat by a heating appliance 51 to both raised leg parts 44 and 45 from an inner side thereof, that is the side inwardly of the substantially U-shaped contact part 41 of the contact terminal 40 near the respective strip portions 47 and 48 of the contact terminal 40. Fig. 9 shows the application of heat from a heat source or heating appliance 52 located against a single raised leg part 44 (or 45), wherein the heat source 52 is located near the strip portion 47 (or 48).

To arrive at a reliable solder joint, after the solder material 52 has melted and the heating appliance 51 , 52 is moved away from the contact terminal 40 or switched off, for example, the solder material 50, the base part 42 and the contact patch 35 have to cool down. At least during this phase, a mechanical force has to be applied for holding the base part 42, i.e. the contact surface 43 thereof to the contact patch 35 till the base part 42, i.e. the contact terminal 40, and the contact patch are bonded. This mechanical force is schematically indicated by arrows 53.

In Fig. 6, the mechanical force 53 can be directly applied by the heating appliance 51 at the raised leg parts 44, 45 from the strip portions 47, 48, for example. In Figs. 7 - 9 the mechanical force 53 can be applied in a same manner, however using a separate mechanical appliance, schematically indicated by reference numeral 54, which can be attached to or be separate from the heating appliance 51 , 52. The mechanical force 53 may be applied in addition to or as an alternative of at the surface side 46 of the base part 42.

As already discussed in the summary part above, heating of the base part 42 of the contact terminal 40 may be applied by contact heating, non-contact heating or both. With contact heating, heat is directly transferred to the raised leg part or parts 44, 45 by conduction from the heating appliance 51 , 52 in direct mechanical contact with the raised leg part or parts 44, 45. Non-contact heating makes use of radiation heating, laser heating or RF induction heating by eddy currents induced in the contact part 42 of the contact terminal 40 by an RF energy source as heating appliance.

By applying RF heating simultaneously to two spaced leg parts 44, 45 of the contact part 41 of a contact terminal 40, a closed RF loop including the contact part 41 for inducing eddy currents therein can be formed, providing a relatively quick heating of the contact surface 43, the contact patch 35 and the soldering material 50.

The method according to the invention is by excellence suitable for RF heating, in that the RF heating appliance is kept at a distance remote from the contact surface 43 and the contact patch 18, 19, 35 and the PV device 1 , 21 , 39, thereby effectively preventing or reducing unwanted induction of eddy currents in the conductive tracks 7, 8, 27, other than locally required for soldering purposes, or the contacts 25 or contact points inside or directly outside a PV cell 3, 22. Which eddy currents, for example, may damage the PN junctions of a PV cell.

Fig. 10 shows schematically, not to scale, in a top view, the contact terminal 40 soldered to the contact patch 35. In accordance with a preferred embodiment of the invention, wherein the solder material 50 is applied in an overdose for bonding the contact terminal 40 and the contact patch 35. When soldered, the solder material will extend outwardly, sideways from the base part 42 of the contact terminal 40. The quality of the solder joint can now be judged to a certain extent from a visual inspection of the amount of solder material 50 extending from the base part 42. If none or less solder material 50 extends outwardly from the base part 42, the solder joint may not be sufficient. Of course, one can also measure the electrical resistance between the contact terminal 40 and the contact patch 35 and/or apply a certain mechanical force to test the mechanical strength of the solder joint, for example.

Those skilled in the art will appreciate that said solder material 50 may be applied during and/or before heating of the contact terminal, at one or both the contact surface 43 and the contact patch 35, prior to positioning of the base part 42 with its contact surface 43 at the contact patch 35.

Before positioning of the contact terminal 40, the contact patches 35 may be pre-cleaned by brushing or abrasion thereof, for example using a glass fiber brush or glass fiber abrasive paper. It is recommended to remove any fiber parts left after pre- cleaning by a vacuum cleaner, for example. Soldering flux 49 may be applied at one or both of the contact surface 43 and the contact patch 35 prior to heating thereof. This to improve the cleaning and wetting action. It is preferred to have the contact patches 18, 35 exposed as short as possible prior to the soldering action. This to avoid contamination of the contact patches as much as possible. Exposure of the contact patches may be provided by laser ablation or any other grinding technique, such as milling, or by a chemical etching technique to locally remove the back layer 6, 28.

Fig. 1 1 shows schematically, in side view, not to scale, a further embodiment of a contact terminal 55 for use with the invention. In this embodiment, a contact part 56 is formed by two raised leg parts 57, 58 extending at an obtuse angle from a substantially flat base part 60, forming a substantially U-shaped contact part 56 with self-aligning properties. A flat strip portion 59 extends from the raised leg part 57 in a direction away from the other raised leg part 58. The dimensions of the parts may be identical to the respective ones of contact terminal 40.

In this embodiment, an RF heating appliance 61 is used for heating the base part 60. The heating appliance comprises a semi-circular hollow electrically conductive loop or winding 62 through which water or an other cooling liquid may flow for rapidly cooling down the appliance and the contact part 56 after the solder material has been melted.

Due to the angled U-shape of the contact part 56, when moving the heating appliance 61 vertically, seen in the plane of the drawing, in the direction of the contact patch 35, the contact part 56 will automatically line up with the heating appliance 61 . That is, the contact terminal 55 self-aligns with the heating appliance 61 .

By positioning the heating appliance 61 exactly with respect to the contact patch 35, for example using laser guidance or any other suitable guidance means, schematically indicated by arrow 67 in Fig. 1 1 , the contact part 56 of the contact terminal, i.e. the base part 60 thereof having the contact surface to be connected to the contact patch 35, will automatically and properly align with and above the contact patch 35, thereby avoiding bad solder joints in that the base part 60 is positioned halfway above the contact patch 35, for example. With the heating appliance 61 , the mechanical force for holding the contact terminal 55 at the contact patch 35 during cooling down can be applied. With RF heating, the contact part 56 forms part of the RF loop of the heating appliance 61 . Fig. 12 shows the contact terminal 55 according to Fig. 1 1 and an RF heating appliance 66, having an RF loop 62 mounted in a body 63 of electrically isolating material. The body 63 has an outer shaped which can be optimally matched to the shape of the contact part 56 of the contact terminal 55, for improving the self- alignment properties thereof. In the body 63 a through hole 64 is provided for receiving temperature measurement means, schematically indicated by arrow 65, such as a pyroptometer, for example. With this pyroptometer, the temperature of the base part 60 can be measured for automatically controlling the temperature and the amount of heat applied during a pre-set, fixed or variable time duration. Those skilled in the art will appreciate other manners for measuring the temperature of the base part 60, i.e. the contact patch 35 and solder material 50.

Figs. 13 - 15 illustrate other examples of contact terminals 70; 80; 90 having self-alignment positioning properties with a heating appliance 51 , due to the particular shape of the contact parts 71 ; 81 ; 91 respectively.

The respective raised leg parts 71 , 72; 81 , 82; 91 , 92 form a substantially U- shaped contact part and extend from a substantially flat base part 75; 85; 95. The contact terminal 70; 80; 90 each comprise a strip portion 74; 84; 94 extending from a raised leg part for electrically connecting the contact terminal to a connector of, for example, a junction box 2.

The contact terminals 50; 70; 80; 90, due to their angled raised leg parts, exhibit a spring action force when the heating appliance 51 , or a separate mechanical appliance, is used for keeping the contact part 56; 71 ; 81 ; 91 at the contact patch 35, which spring action operates in improving the quality of the solder joint.

Although not explicitly referred to in Figs. 6 - 15, each of the base parts 60; 75; 85 and 95 of the contact terminals 55; 70; 80 and 90, respectively, comprise a surface side forming an electrical contact surface 43 for electrically connecting the contact terminal to a contact patch 35, and a surface side 46, opposite the contact surface 43, from which the respective raised leg parts 57, 58; 71 , 72; 81 , 82; and 92, 93 extend, as disclosed in detail with respect to contact terminal 40.

Fig. 16 shows a PV module 100, comprised of the PV module 21 of Fig. 2, wherein a contact terminal 40 of Fig. 5 is applied using the method according to the invention as disclosed above, connecting the conductive track 27 to the connector terminal 1 1 of the junction box 2. The elongate strip portion 47 of the contact terminal 40 connects to the connector terminal 1 1 . It will be appreciated that any electrical contact terminal providing heating form at least one raised leg part may be used in accordance with the invention, inclusive the electrical contact terminals 17 and 33 of Figs. 1 and 2, respectively. In the PV module 1 of Fig. 1 the contact terminals 16 series connecting the

PV cells 3 may also be of the type for use with the present invention. That is, the contact terminals 16 may be soldered to the conductive tracks 7, 8 in accordance with the method of the invention, discussed and illustrated above. Fig. 17 shows, in a very schematic and illustrative form, a system 1 10 for electrically connecting electrical contact terminals to electrical contact patches at a back layer for forming the PV module 100 as shown in Fig. 16, for example, in accordance with the present invention. The system 1 10 comprises an assembling station 1 1 1 , among others arranged for assembling a PV module 100 of the type such as shown in Fig. 16 by applying heat 1 18, a soldering station 1 14, for example an RF 121 soldering station, arranged for soldering electrical contact terminals to contact patches of the PV module, as illustrated and disclosed above in accordance with the method of the invention, and a mounting station 1 15, arranged for electrically connecting the thus soldered contact terminals to electrical connector elements of a junction box 2. The junction box 2 is generally mounted at the outer or external side of the back layer of the PV module 100, for example by gluing or the like. Alternatively, the system 1 10 may comprise an exposing station 1 13, arranged for exposing 120 electrical contact patches at the electrically conductive tracks of the PV module 100 from an external surface side of the back layer of the PV module, for example by laser ablation. Further, the system 1 10 may comprise a material deforming station 1 12, arranged for forming 1 19 a contact part for soldering using the method according to the invention, for example a contact part illustrated in any of the Figs. 5-15.

Arrows 1 17 indicate transport means for transporting the PV module 100 from one station to another. Dependent on the type of junction box 2, the mounting station 1 15 may be visited before the soldering station 1 14.

In particular the soldering station 1 14 may be provided as a separate station arranged for electrically connecting electrical contact terminals to electrical contact patches of a PV device. Such as a PV cell or PV module, either fully automated or manually, in accordance with the method of the invention.

The invention may be practiced otherwise than as specifically described herein, and the abovementioned embodiments and examples are merely intended as an illustration to the skilled reader. The scope of the invention is only limited by the appended claims.