Patent Description:
An optical or electrical article may comprise a hermetically sealed cavity, which contains a sensitive electrical component. The hermetically sealed cavity may e.g. protect the sensitive electrical component from atmospheric humidity. It is known that a hermetically sealed cavity may be formed by positioning a layer of filler material between a first glass piece and a second glass piece, and by heating the combination in an oven. The filler material may be molten in the oven and subsequently cooled to hermetically join the first glass piece to the second glass piece.

<CIT> forming the basis for the preamble of claim <NUM> discloses a packaging method for a sodium-sulfur battery. The method comprises placing the battery in a sealed container, evacuating the sealed container, pressing a bottom cover into a shell of the battery with a hydraulic press, taking the battery out from the sealed container, and performing laser welding under atmospheric conditions.

<CIT> discloses a method for sealing a sodium-sulfur battery. The method comprises placing a container of the battery into a case, reducing the pressure inside the case to a first set pressure, supplying gas into the case up to a second set pressure, closing an opening of the container with a cover of the battery, and welding a contact interface between the cover and the container.

<CIT> discloses producing double glazed glass, in which a gap between two glass plates is in a vacuum state. A first sealing material layer is formed from ultraviolet-curable resin on an outer periphery of a sealing region of a first glass plate. A second sealing material layer is formed from sealing glass material on an inner periphery of the sealing region. The first glass plate and a second glass plate are placed in a vacuum chamber, and the vacuum chamber is evacuated. The first glass plate and the second glass plate are laminated together so that the sealing material layers face the surface of the second glass plate. The first sealing material layer is cured by ultraviolet treatment, thereby forming a first sealing layer. Next, the laminate of the first glass plate and the second glass plate is exposed to an air atmosphere, and the second sealing material layer is irradiated with laser light.

The embodiments relate to a method for forming an article, which comprises a hermetically sealed cavity.

According to an aspect, there is provided a method for producing an article (<NUM>) by welding a first piece (<NUM>) to a second piece (<NUM>) according to claim <NUM>.

wherein the first sealing surface (SRF1) and the second sealing surface (SRF2) are substantially planar, wherein the preliminary joint (S0) allows a sliding movement of the second sealing surface (SRF2) with respect to the first sealing surface (SRF1) after opening the chamber (<NUM>) before forming the welded seam (J1), and wherein the laser beam (LB1) is focused to the interface (IF1) through the first piece (<NUM>) and/or through the second piece (<NUM>).

The pressure of the cavity is reduced by using the chamber. The chamber may be called e.g. as a vacuum chamber. The laser welding takes place after the vacuum chamber has been opened. The laser welding may take place after the vacuum chamber has been opened such that the vacuum chamber does not restrict positioning of the laser welding unit with respect to the pieces. In particular, the laser welding may take place outside the vacuum chamber. The method may facilitate focusing of the laser beam to desired points of the common interface of the pieces. The pieces may be welded together with the focused laser beam such that there is no need to guide the laser beam into the vacuum chamber. The method may provide substantial freedom to move the laser welding unit with respect to the semi-manufactured article during forming the hermetic seam. For example, it is not necessary to guide the laser beam through a wall of the chamber.

The article may be formed substantially without heating the surface of the cavity. This may facilitate e.g. hermetic encapsulation of a sensitive component inside the cavity. This may increase operating reliability of the component encapsulated in the cavity. The temperature of the surface of the cavity may remain lower than e.g. <NUM> during forming the seam e.g. in order to reduce the probability of damaging the component. The temperature of the surface of the cavity may remain lower than <NUM> during forming the seam in order to improve operating reliability of the component. The temperature of the surface of the cavity may remain substantially equal to the normal room temperature (e.g. near <NUM>) during forming the seam.

It is not necessary to spend time for heating and/or cooling the pieces. The method may allow production of articles at a high rate. Keeping the temperature of the cavity below the predetermined limit may reduce or minimize the risk of releasing harmful substances from the pieces to the hermetically sealed cavity.

At least one of the pieces is substantially transparent at the wavelength of the laser beam. At least one of the pieces is substantially transparent in the infrared, visible and/or ultraviolet wavelength range, so as to allow transmission of the laser beam through the piece to the interface.

The material of the first piece may be e.g. glass, silicon, sapphire, or ceramic. The material of the second piece may be e.g. glass, silicon, sapphire, or ceramic. The use of these materials may provide a dimensionally stable and gas-tight hermetic structure. The permeability of glass to gases may be substantially lower than the permeability of plastics or the permeability of epoxy resins, for example.

The use of glass, silicon, sapphire, and/or ceramic and keeping the temperature of the pieces below a predetermined limit may reduce or minimize the risk of releasing harmful substances from the material of the piece to the hermetically sealed cavity and/or to a component enclosed in the cavity. The use of glass, silicon, sapphire, and/or ceramic and keeping the temperature of the pieces below a predetermined limit may reduce or minimize the risk of releasing a harmful substance out of the sealed cavity. The use of glass, silicon, sapphire, and/or ceramic and keeping the temperature of the pieces below a predetermined limit may reduce or minimize the risk of releasing a harmful substance out of a component enclosed in the cavity. Outgassing may be reduced or eliminated.

The welded seam may be formed from the material of the first piece and from the material of the second piece without using a filler material between the pieces. The article may be manufactured by using a reduced number of materials. The welded seam may fully encircle the cavity so as to provide a hermetically sealed structure.

The laser beam may cause localized fusion of the mating surfaces of the pieces such that a large portion of the mating surfaces may remain solid during the welding. A large portion of the mating surfaces may remain solid during the welding such that the dimensions of the article are not changed due to the welding. Consequently, the final thickness of the article may be accurately defined by the initial dimensions of the pieces.

The pressure difference between exterior and interior of the article may hold the second piece in place during the laser welding such that it is not necessary to press the second piece against the first piece by a pressing tool during the laser welding. Performing the welding without the pressing tool may provide increased freedom to select the position of the laser welding unit with respect to the pieces. Said pressure difference may also reduce or minimize internal stresses of the article, thereby increasing the operating reliability of the produced article.

Keeping the temperature of the pieces near an intended operating temperature of the article during the laser welding may reduce internal stress of the pieces and may improve operating reliability of the article e.g. when the thermal expansion coefficient of the material of the first piece is substantially different from the thermal expansion coefficient of the material of the second piece. The ratio of the thermal expansion coefficient of the material of the first piece to the thermal expansion coefficient of the material of the second piece may be e.g. lower than <NUM>/<NUM> or higher than <NUM>. The intended operating temperature may be e.g. substantially equal to the room temperature (e.g. <NUM>).

In the following examples, several variations will be described in more detail with reference to the appended drawings, in which.

Referring to <FIG>, the produced article <NUM> comprises a hermetically closed cavity CAV1. The article <NUM> is produced by welding a first piece <NUM> to a second piece <NUM> with a laser beam. The first piece <NUM> is joined to the second piece <NUM> by a welded seam J1. p<NUM> may denote the internal pressure of the cavity CAV1. p<NUM> may denote the external pressure of gas on the outer surface of the article <NUM>. The pressure p<NUM> may be equal to the ambient pressure p<NUM>, e.g. substantially equal to <NUM> kPa.

The article <NUM> may be a device. The article <NUM> may be e.g. an optical device and/or an electronic device.

SX, SY and SZ denote orthogonal directions.

Referring to <FIG>, a production apparatus <NUM> may be arranged to produce the article <NUM> by altering internal pressure of a vacuum chamber and by using laser welding.

The apparatus <NUM> may be arranged to produce the article <NUM> by welding a first piece <NUM> to a second piece <NUM>. The first piece <NUM> has a first sealing surface SRF1, and the second piece <NUM> has a second sealing surface SRF2. The first piece <NUM> may comprise e.g. glass, silicon, sapphire and/or a ceramic material. The second piece <NUM> may comprise e.g. glass, silicon, sapphire and/or a ceramic material. The sealing surface SRF1 may consist essentially of glass, silicon, sapphire and/or a ceramic material. The sealing surface SRF2 may consist essentially of glass, silicon, sapphire and/or a ceramic material.

The apparatus <NUM> may comprise e.g. a base <NUM> and a cover <NUM>. The base <NUM> may operate as a part of a low-pressure chamber <NUM>. The low-pressure chamber <NUM> may also be called e.g. as a vacuum chamber.

The article <NUM> comprises the first piece <NUM> and the second piece <NUM>. The first piece <NUM> has a first sealing surface SRF1, and the second piece <NUM> has a second sealing surface SRF2. The piece <NUM> and/or <NUM> may initially comprise one or more open cavities OCA1, wherein the first piece <NUM> comprises an open cavity OCA1. The first piece <NUM> may have a concave portion, which may at least partly define a closed cavity CAV1 when the second piece <NUM> is pressed against the first piece <NUM>. The second piece <NUM> is positioned with respect to the first piece <NUM> such that the cavity is initially open. The open cavity OCA1 is converted into a closed cavity CAV1 by closing the open cavity OCA1. The geometry of the pieces <NUM>, <NUM> is selected such that the open cavity OCA1 is converted into a closed cavity by bringing the first sealing surface SRF1 of the first piece <NUM> into contact with the second sealing surface SRF2 of the second piece <NUM>. The second sealing surface SRF2 may be positioned against the first sealing surface SRF1 e.g. by moving the second piece <NUM> with respect to the first piece <NUM>.

G0 denotes a gap between the first sealing surface SRF1 and the second sealing surface SRF2. d0 denotes the height of the gap G0. The gap G0 allows a flow F1 of a gas GAS1 (or GAS0) from the open cavity OCA1 through the gap G0 (<FIG>). An initial position of the second piece <NUM> is selected such that the cavity OCA1 is open when the pressure of the chamber is reduced. An initial position of the second piece <NUM> is selected such that there is a gap G0 between a portion of the first sealing surface SRF1 and a portion of the second sealing surface SRF2. The height d0 may be greater than zero. The height d0 may be e.g. greater than <NUM>, or even greater than <NUM>.

p<NUM> may denote gas pressure of the cavity OCA1, CAV1 at a first side of the piece <NUM>. p<NUM> may denote gas pressure at the second (other) side of the piece <NUM>. The pressure p<NUM> may be called e.g. as cavity pressure, and the pressure p<NUM> may be called e.g. as external pressure. p<NUM> may denote an ambient pressure. The external pressure p<NUM> may be substantially equal to the ambient pressure p<NUM> when the vacuum chamber is open. The ambient pressure p<NUM> may be e.g. in the range of <NUM> kPa to <NUM> kPa. The ambient pressure p<NUM> may be substantially equal to the atmospheric pressure. The ambient pressure p<NUM> may be e.g. substantially equal to <NUM> kPa.

The pieces <NUM>, <NUM> are initially surrounded with a gas GAS1. The cavity OCA1 is initially filled with the gas GAS1. The gas GAS1 may be e.g. air. The gas GAS1 may also be e.g. inert gas, e.g. argon or nitrogen. The pieces <NUM>, <NUM> may be initially surrounded with inert gas GAS1. For example, the apparatus <NUM> may be arranged to operate in a room or confined space, which is filled with the inert gas GAS1.

The first piece <NUM> may be supported e.g. by the base <NUM>. The position of the first piece <NUM> may be optionally defined with respect to the base <NUM> e.g. by using one or more positioning elements <NUM>. One or more positioning elements <NUM> may be optionally arranged to operate as clamps. The piece <NUM> may be optionally clamped to the base <NUM> e.g. by one or more clamping elements <NUM>. The base <NUM> may optionally comprise e.g. a recess (not shown) to define the transverse position of the piece <NUM> with respect to the base <NUM>. The use of the clamping elements or recess is not necessary. The first piece <NUM> may be kept stationary with respect to the base <NUM> also without clamping the first piece <NUM>. The piece <NUM> may also be held in place e.g. by gravity and friction.

The apparatus <NUM> may comprise one or more actuators <NUM>. The one or more actuators <NUM> may be arranged to close the cavity by moving the first piece <NUM> and/or by moving the second piece <NUM>. The one or more actuators <NUM> may be arranged to cause a relative movement between the first piece <NUM> and the second piece <NUM> when the chamber <NUM> is closed. The second piece <NUM> may be temporarily supported by one or more supporting elements <NUM>. The supporting elements <NUM> may also be called e.g. as contact elements. The cavity CAV1 may be closed by moving one or more contact elements <NUM>. The second piece <NUM> may be brought into contact with the first piece <NUM> by moving one or more contact elements <NUM>. The apparatus <NUM> may comprise one or more actuators <NUM> for moving the contact elements <NUM>. The actuators <NUM> may comprise contact elements <NUM> for contacting with the second piece <NUM>. The piece <NUM> may be supported by one or more contact elements <NUM>. The second piece <NUM> may be temporarily clamped by using one or more contact elements <NUM>. The piece may be clamped between two or more contact elements <NUM>.

The first piece <NUM> may comprise one or more open cavities OCA1 and/or the second piece <NUM> may comprise one or more open cavities OCA1. The first piece <NUM> and/or the second piece <NUM> may comprise one or more concave portions to define one or more open cavities OCA1.

The chamber <NUM> may comprise the base <NUM> and a cover <NUM>. The chamber <NUM> may be closed e.g. by moving the cover <NUM> with respect to the base <NUM>. The chamber <NUM> may be closed such that the first piece <NUM> and the second piece <NUM> remain inside the chamber <NUM>.

The chamber <NUM> may comprise one or more openings <NUM>, <NUM> for guiding gas out of the chamber <NUM>. The chamber <NUM> may optionally comprise one or more openings <NUM>, <NUM> for guiding gas into the chamber <NUM>.

The apparatus <NUM> may comprise a pump PUMP1 for removing gas from the chamber <NUM>. The pump PUMP1 may cause a gas flow QPUMP out of the chamber <NUM>. The pump PUMP1 may be arranged to reduce the internal pressure p<NUM> of the chamber <NUM> with respect to the ambient pressure p<NUM>.

The apparatus <NUM> may comprise a pressure sensor M1 for monitoring pressure inside the chamber <NUM>.

The production apparatus <NUM> may optionally comprise a valve CV1 for controlling a first gas flow QGAS0 of a gas guided into the chamber <NUM>. For example, the valve CV1 may control the flow rate of an inert flushing gas GAS0. The chamber <NUM> may be optionally flushed with a flushing gas GAS0 before closing the cavity OCA1. The composition of the flushing gas may be selected to provide a desired gas composition in the closed cavity of the article <NUM>. The chamber <NUM> may be flushed e.g. with inert gas. The inert gas may be e.g. nitrogen (N<NUM>) or argon (Ar). The gas may be provided e.g. from a gas cylinder via the valve CV1. The composition of the gas inside the cavity OCA1 may become substantially similar to the composition of the gas GAS0 of flushing gas flow QGAS0.

The apparatus <NUM> may optionally comprise a valve CV2 for controlling a second gas flow of a gas guided into the chamber <NUM>. For example, the valve CV1 may control the flow rate when the pressure of the chamber is increased, after the cavity has been closed, before opening the chamber.

The apparatus <NUM> may comprise a control unit CNT1 for controlling operation of the valves CV1, CV2, and for controlling operation of the pump PUMP1. The apparatus <NUM> may comprise a control unit CNT1 for timing operation of the valves CV1, CV2 and the pump PUMP1. The apparatus <NUM> may comprise a control unit CNT1 for controlling operation of the valves CV1, CV2 and the pump PUMP1 e.g. based on measured internal pressure of the chamber <NUM>. The apparatus <NUM> may optionally comprise one or more actuators for opening and/or closing the chamber <NUM>.

The chamber <NUM> may comprise a sealing SEAL1 to form a pressure tight seal between the base <NUM> and the cover <NUM> when the chamber <NUM> is closed.

Referring to <FIG>, gas GAS1 (or GAS0) is drawn out of the chamber <NUM> in order to change the internal pressure p<NUM> of the chamber <NUM> and in order to remove gas from the open cavity OCA1. The pump PUMP1 may draw gas GAS1 out of the chamber <NUM>. Gas GAS1 may be simultaneously drawn out of the open cavity OCA1 and from the interior of the chamber <NUM>. The interior of the open cavity OCA1 is in fluid communication with the interior of the chamber <NUM> e.g. via the gap GAP1. The interior of the open cavity OCA1 is in fluid communication with the interior of the chamber <NUM>. The internal pressure p<NUM> of the chamber <NUM> is substantially lower than the ambient pressure p<NUM>. The pressure p<NUM> of the open cavity OCA1 may be substantially equal to the internal pressure p<NUM> of the chamber <NUM>. The pressure p<NUM> of the cavity is changed by changing the internal pressure p<NUM> of the chamber <NUM>.

The internal dimensions of the chamber <NUM> may be selected according to the external dimensions of the article <NUM>. The internal volume of the chamber <NUM> may be small when producing a small article <NUM>. Consequently, the internal pressure of the chamber <NUM> may be reduced at a high rate.

A transverse dimension of the article <NUM> (e.g. in the direction SX or SY) may be e.g. in the range of <NUM> to <NUM>. For example, the transverse dimensions of the article <NUM> may be e.g. in the order of <NUM> x <NUM>. For example, a circular silicon wafer may be used as one of the pieces <NUM>, <NUM>. The diameter of the wafer may be e.g. in the range of <NUM> to <NUM> (<NUM> inch to <NUM> inch). The thickness (in the direction SZ) of the second piece <NUM> may be e.g. greater than or equal to <NUM>. The total thickness of the article <NUM> may be e.g. in the range of <NUM> to <NUM>.

Referring to <FIG>, the gap G0 may be closed by using one or more actuators <NUM>. For example, the actuators <NUM> may move the second piece <NUM> with respect to the first piece <NUM>. MV1 may denote a movement of the piece <NUM>. The pressure p<NUM> of the open cavity OCA1 may be substantially equal to the internal pressure p<NUM> of the chamber <NUM> when the cavity is closed. The internal pressure p<NUM> of the chamber <NUM> is substantially lower than the ambient pressure p<NUM> when the gap G0 is closed. The open cavity OCA1 is converted into a closed cavity CAV1 by covering the open cavity OCA1 by the piece <NUM>.

The open cavity OCA1 is converted into the closed cavity CAV1 by closing the gap G0.

Referring to <FIG>, the internal pressure p<NUM> of the chamber <NUM> may be increased after the cavity has been closed. The internal pressure p<NUM> of the chamber <NUM> may be increased before opening the chamber so as to facilitate opening of the chamber <NUM>. For example, a gas flow QEQ may be guided into the chamber e.g. via a valve CV2. The internal pressure p<NUM> of the chamber <NUM> may be equalized with the ambient pressure p<NUM>. The internal pressure p<NUM> of the chamber <NUM> may be increased such that the internal pressure p<NUM> of the chamber <NUM> becomes substantially equal to the ambient pressure p<NUM>.

The sealing surface SRF1 of the piece <NUM> is in contact with the sealing surface SRF2 of the piece <NUM> so as to form a preliminary joint S0. The three-dimensional shape of the sealing surface SRF1 substantially matches with the three-dimensional shape of the sealing surface SRF2 such that the preliminary joint S0 is gas tight to a certain degree. The preliminary joint S0 encircles the cavity CAV1. The shape of the surface SRF1 and the shape of the surface SRF2 are substantially planar such that the surfaces SRF1, SRF2 form a substantially gas-tight temporary joint when the first surface SRF1 is pressed against the second surface SRF2.

The shape of the surface SRF1 matches with the shape of the surface SRF2 such that the surfaces SRF1, SRF2 together form a temporary substantially gas-tight joint when the first surface SRF1 is pressed against the second surface SRF2. The surface SRF1 is planar. The surface SRF2 is planar.

For example, the RMS height of the closed gap between the pieces may be smaller than <NUM>, advantageously smaller than <NUM>. RMS means root mean square. For example, the surface SRF1 and/or the surface SRF2 may be planar surfaces. For example, the flatness of the surface SRF1, SRF2 may be better than <NUM>, advantageously better than <NUM>.

The preliminary joint S0 between the pieces <NUM>, <NUM> may be formed without welding and without using an adhesive.

The sealing surface SRF2 is in contact with the sealing surface SRF1, and the shape of the surface SRF2 matches with the shape of the surface SRF1 such that the second piece <NUM> may be held against the first piece <NUM> also by van der Waals forces.

The preliminary joint S0 allows small relative movement of the surface SRF1 with respect to the surface SRF2. For example, the surface SRF2 may slide by a few micrometers in a transverse direction, with respect to the surface SRF1. The surface SRF2 may slide by a few micrometers in a transverse direction, which is perpendicular to the surface SRF2.

In principle, the piece <NUM> could also be pulled apart from the piece <NUM> in order to open the preliminary joint, without causing visually detectable damage to at least one of the pieces <NUM>, <NUM>. The preliminary joint S0 allows relative movement of the first sealing surface SRF1 with respect to the second sealing surface SRF2 after opening the chamber <NUM>. The preliminary joint S0 allows relative movement of the first sealing surface SRF1 with respect to the second sealing surface SRF2 before forming the welded seam J1.

The preliminary joint S0 is gas tight to a certain degree. The internal pressure p<NUM> of the chamber <NUM> is increased wherein the pressure p<NUM> of the cavity CAV1 remains lower than the pressure p<NUM> of the chamber <NUM>. Consequently, the second piece <NUM> may be held against the first piece <NUM> also by a pneumatic force F<NUM> caused by the pressure difference p<NUM>-p<NUM>.

The preliminary joint S0 allows small relative movement of the surface SRF2 with respect to the surface SRF1 also after opening the chamber, before performing the welding. In case of the substantially planar surfaces SRF1, SRF2, the surface SRF1 may be e.g. in a plane defined by the directions SX and SY, and the surface SRF2 may slide along the planar surface SRF1 e.g. in the direction SX. The planar surface SRF2 may be held against the planar surface SRF1 mainly by the pressure difference p<NUM>-p<NUM> such that surface SRF2 could be moved along the planar surface SRF1 e.g. in the direction SX. The planar surface SRF2 may be held against the planar surface SRF1 by the pressure difference p<NUM>-p<NUM> such that surface SRF2 is movable along the planar surface SRF1 e.g. by a few micrometers e.g. in the direction SX (after opening the chamber, before performing the welding).

Referring to <FIG>, the chamber <NUM> is opened after the cavity CAV1 has been closed by forming the preliminary joint S0 between the pieces <NUM>, <NUM>. The external pressure p<NUM> outside the semi-manufactured article <NUM>' is substantially equal to the ambient pressure p<NUM>. The semi-manufactured article <NUM>' comprises the stacked combination of the pieces <NUM>, <NUM>.

The preliminary joint S0 allows small relative movement of the piece <NUM> with respect to the first piece <NUM> after the chamber <NUM> has been opened, before performing the welding.

Referring to <FIG> and <FIG>, the second piece <NUM> is welded to the first piece <NUM> by using a laser beam B1. The apparatus <NUM> may comprise a laser welding unit <NUM> for forming a welded hermetic seam J1 between the first piece <NUM> and the second piece <NUM>. The first piece <NUM> and the second piece <NUM> have a common interface IF1. In particular, the first sealing surface SRF1 may be in contact with the second sealing surface SRF2 so as to define a common interface IF1 between the first piece <NUM> and the second piece <NUM>. A laser welding unit <NUM> may comprise focusing optics <NUM> for focusing the laser beam B1 to the common interface IF1. The focusing optics <NUM> may provide a focused laser beam B1 by focusing light of a primary beam B0. The primary beam B0 may be provided e.g. by using light of a fiber laser. The laser beam B1 is focused to the interface IF1 through the piece <NUM> and/or through the piece <NUM>. The piece <NUM> and/or the piece <NUM> is substantially transparent at the wavelength of the laser beam B1. The laser beam B1 may be pulsed e.g. in order to provide high instantaneous optical intensity at the focal point and/or in order to minimize heating of the material outside the focal spot.

Forming of the hermetic seam J1 may comprise locally melting material of the first piece <NUM> at a focal point of the laser beam B1 and locally melting material of the second piece <NUM> at a focal point of the laser beam B1. The laser beam B1 may cause localized fusion of both pieces at the interface IF1. The seam J1 may be formed by re-solidification of the material of the pieces <NUM>, <NUM>.

The high intensity of the laser beam B1 may cause nonlinear absorption at the focal point.

The focal point of the laser beam B1 may be moved with respect to the semi-manufactured article <NUM>' such that the seam J1 may encircle the cavity CAV1. The laser unit <NUM>, an optical component of the unit <NUM>, and/or the article <NUM>' may be moved so as to cause the relative movement of the focal point. The seam J1 may be unbroken (contiguous). One or more seams J1 may together encircle the cavity CAV1. One or more seams J1 may together form a closed loop around the cavity CAV1.

The second piece <NUM> may be held against the first piece <NUM> by the pneumatic force F<NUM> such that it is not necessary to use a contact element for pressing the second piece <NUM> against the first piece <NUM> during the laser welding. For example, the contact elements <NUM> may be optionally moved away from the second piece <NUM>. This may allow substantial freedom to move the semi-manufactured article <NUM>' with respect to the laser welding unit <NUM> during the laser welding. The laser beam B1 may have unhindered access to substantially all points of the interface IF1. Welding of the interface IF1 with the laser beam B1 is started after the chamber <NUM> has been opened.

The second piece <NUM> may be permanently fastened to the first piece <NUM> with a part of the seam J1 almost immediately after start of the laser welding, such that the second piece <NUM> cannot be separated from the first piece <NUM> without causing visually detectable damage to at least one of the pieces <NUM>, <NUM>. Forming of the seam J1 may substantially prevent relative movement of the first sealing surface SRF1 with respect to the second sealing surface SRF2. Forming of the seam J1 may permanently fasten the second piece <NUM> to the first piece <NUM> such that the second piece <NUM> cannot be separated from the first piece <NUM> without causing visually detectable damage to at least one of the pieces <NUM>, <NUM>.

An actuator <NUM> may be arranged to move the semi-manufactured article <NUM>' with respect to the laser welding unit <NUM>. The actuator <NUM> may be e.g. a translation stage or a robot. An actuator <NUM> may be arranged to move the laser beam B1 with respect to the semi-manufactured article <NUM>'. The actuator <NUM> may comprise e.g. a robot, a translation stage and/or a scanning optical element.

The semi-manufactured article <NUM>' may be supported e.g. by the base <NUM> during the laser welding. Alternatively, the semi-manufactured article <NUM>' may be transferred to a different supporting element before starting the welding.

Referring to <FIG>, the article <NUM> is formed from the semi-manufactured article <NUM>' by forming the welded seam J1. The cavity CAV1 of the article <NUM> is in a hermetically closed state after the seam J1 has been formed. The absolute pressure p<NUM> of the cavity CAV1 of the article <NUM> may be e.g. lower than <NUM> kPa, lower than <NUM> kPa, lower than <NUM> Pa, or even lower than <NUM>-<NUM> Pa.

The welded seam J1 hermetically joins the first piece <NUM> to the second piece <NUM>. The welded seam J1 acts as a hermetic joint between the first piece and the second piece. The welded seam J1 may act as a permanent hermetic vacuum joint. The method comprises forming a hermetic joint J1 between the first piece <NUM> and the second piece <NUM>. The apparatus may be arranged to form a hermetic joint J1 between the first piece <NUM> and the second piece <NUM>.

Referring to <FIG>, the manufactured article <NUM> may optionally comprise one or more parts <NUM>, which are located in the cavity CAV1. The hermetically closed cavity may protect the part <NUM> e.g. from atmospheric humidity, from oxygen and/or from aerosol particles. The parts <NUM> may be mounted or formed in the cavity CAV1. The article <NUM> may be produced e.g. by using the chamber <NUM> shown in <FIG>. The part <NUM> may be mounted or formed in the open cavity OCA1 before the cavity OCA1 is closed. The part <NUM> may be e.g. an electric component, an optical component and/or a mechanical component. The part <NUM> may comprise an electrical circuit. The part <NUM> may be e.g. a semiconductor component. The part may comprise e.g. a photodetector. The part may comprise e.g. a laser diode and/or a light emitting diode. The part may comprise an antenna. One or more components <NUM> may be mounted or formed in the cavity OCA1 before the chamber <NUM> is closed.

The closed cavity CAV1 may also be arranged to protect other external components from a harmful substance contained in the closed cavity CAV1.

For example, the cavity may contain a battery, which may contain corrosive substance.

The part <NUM> may remain the hermetically closed cavity CAV1 after the hermetic seam J1 has been formed by laser welding. The absolute pressure p<NUM> of the cavity CAV1 of the article <NUM> may be e.g. lower than <NUM> kPa, lower than <NUM> kPa, lower than <NUM> Pa, or even lower than <NUM>-<NUM> Pa.

The position of the welded seam J1 may substantially coincide with the position of the preliminary joint S0. The welded seam J1 may be adjacent to the position of the preliminary joint S0. The finished article <NUM> may comprise one or more welded seams J1. The finished article <NUM> may comprise two or more welded seams J1.

The thickness d100 of the article <NUM> after the welding may be substantially equal to the thickness of the semi-manufactured article <NUM>'.

<FIG> shows method steps for producing the article <NUM>. The pieces <NUM>, <NUM> are provided (step <NUM>). The chamber <NUM> is closed such that both pieces <NUM>, <NUM> are located inside the chamber <NUM> (step <NUM>). The pressure of the open cavity OCA1 is reduced after closing the chamber, before closing the cavity (step <NUM>). The preliminary joint S0 is formed by bringing the mating portions of the sealing surfaces SRF1, SRF2 into contact with each other, after the pressure has been reduced (step <NUM>). The pressure of the chamber <NUM> is increased after the cavity has been closed (step <NUM>). The chamber <NUM> is opened (step <NUM>). The hermetic seam J1 is formed by laser welding after the chamber <NUM> has been opened (step <NUM>).

The method may optionally comprise one or more additional method steps between opening the chamber <NUM> (step <NUM>) and performing the laser welding (step <NUM>). For example, the method may comprise removing a protective film from an outer surface of the piece <NUM>, <NUM> after opening the chamber but before starting the laser welding.

<FIG> shows, by way of example, temporal evolution of cavity pressure p<NUM> and temporal evolution of external pressure p<NUM> during manufacturing of the article <NUM>.

The pressure p<NUM> of the open cavity OCA1 and the external pressure p<NUM> may initially be equal to the ambient pressure p<NUM>. The chamber <NUM> may be closed at a time t<NUM>. Reduction of the chamber pressure p<NUM> may be started at the time t<NUM>. The pressure p<NUM> may refer to the internal pressure of the chamber <NUM> during the time period when the chamber <NUM> is in the closed state.

The external pressure p<NUM> may reach a minimum value pMIN e.g. at a time t<NUM> Gas (GAS0 or GAS1) may be removed from the open cavity OCA1 during the time period from t<NUM> to t<NUM> such that the pressure p<NUM> of the cavity may be substantially equal to the external pressure p<NUM> at the time t<NUM>. The minimum value of the cavity pressure p<NUM> may also be substantially equal to pMIN. The gap G0 may be closed at the time t<NUM>. The preliminary joint S0 may be formed at the time t<NUM>. The pressure p<NUM> may be increased during a time period from t<NUM> to t<NUM>, after the preliminary joint S0 has been formed. The chamber <NUM> may be opened at a time t<NUM>. The laser welding may be performed during a time period from t<NUM> to t<NUM>, after the chamber <NUM> has been opened. The hermetic seam J1 may be fully completed at the time t<NUM>. pF may denote the final internal pressure of the hermetically closed cavity CAV1.

The second piece <NUM> may be held against the first piece <NUM> by van der Waals forces and/or by the pneumatic force F<NUM> caused by the pressure difference p<NUM>-p<NUM>.

A relative pressure difference ((p<NUM>-p<NUM>)/p<NUM>) between external pressure (p<NUM>) and the pressure (p<NUM>) of the cavity (CAV1) may be e.g. greater than <NUM>% when the chamber (<NUM>) is opened. The pressure difference (p<NUM>-p<NUM>) between outer and inner surfaces of the second piece <NUM> may be e.g. greater than <NUM> kPa during forming the welded seam J1.

The preliminary joint S0 is gas tight to a certain degree, but the preliminary joint S0 is not hermetic. The preliminary joint S0 may allow a small leakage of ambient gas into the closed cavity CAV1 when the chamber <NUM> is opened. The preliminary joint S0 may allow a small leakage of ambient gas into the closed cavity CAV1 during the time period from t<NUM> to t<NUM>. The difference PF-PMIN between the final pressure pF and the minimum pressure pMIN may be e.g. smaller than <NUM>%, or even smaller than <NUM>% of the ambient pressure p<NUM>.

The preliminary joint S0 may be a partially gas tight joint before forming the welded seam J1 such that the relative rate of change (Δp<NUM>/Δt)/(p<NUM>-p<NUM>) of pressure (p<NUM>) of the closed cavity (CAV1) is e.g. smaller than <NUM>/s immediately after the chamber (<NUM>) has been opened. The shapes of the sealing surfaces SRF1, SRF2 may be selected such that the preliminary joint S0 is a partially gas tight joint.

The opening of the chamber <NUM> and/or the laser welding may be performed at the ambient pressure p<NUM>. In particular, opening of the chamber <NUM> and/or the laser welding may be performed at the ambient pressure p<NUM> and in an inert gas atmosphere so as to ensure that only inert gas is allowed to leak into the closed cavity CAV1 before the hermetic welded seam J1 is fully completed.

The welding may be performed soon after the chamber <NUM> has been opened, in order to reduce or minimize leakage through the preliminary joint S0. A time period (t<NUM>-t<NUM>) between opening the chamber <NUM> and forming the hermetic seam J1 may be e.g. shorter than <NUM>, shorter than <NUM>, or shorter than <NUM>. The time period (t<NUM>-t<NUM>) may be e.g. shorter than <NUM>, shorter than <NUM>, or even shorter than <NUM> in order to minimize leakage. A time period (t<NUM>-t<NUM>) between start of pressure increase and completion of the hermetic seam J1 may be e.g. shorter than <NUM>, shorter than <NUM>, or shorter than <NUM>. The time period (t<NUM>-t<NUM>) may be e.g. shorter than <NUM>, shorter than <NUM>, or even shorter than <NUM> in order to minimize leakage.

The temperature of the pieces may be kept near an intended operating temperature of the article during the laser welding, e.g. in order to reduce outgassing and internal stress. The temperature of the cavity may be kept in a predetermined temperature range during the laser welding. The temperature of the surface of the cavity may be kept e.g. below <NUM> during the welding. The temperature of the surface of the cavity may be kept e.g. in the range of <NUM> to <NUM> during the welding. The temperature of the surface of the cavity may be kept near the intended operating temperature during the laser welding. The intended operating temperature may be e.g. substantially equal to the room temperature (e.g. <NUM>).

The spatially averaged temperature of the first piece and the spatially averaged temperature of the second piece may remain below <NUM> during the welding. The spatially averaged temperature of the first piece and the spatially averaged temperature of the second piece may remain in the range of <NUM> to <NUM> during the welding. The spatially averaged temperature of the first piece and the spatially averaged temperature of the second piece may remain substantially equal to <NUM> during the welding. A change of spatially averaged temperature of the first piece and a change of spatially averaged temperature of the second piece may remain e.g. smaller than <NUM> during the welding with the laser beam.

Performing the welding near the intended operating temperature may improve operating reliability of the article also when the thermal expansion coefficient of the material of the first piece is substantially different from the thermal expansion coefficient of the material of the second piece. The ratio of the thermal expansion coefficient of the material of the first piece to the thermal expansion coefficient of the material of the second piece may be e.g. lower than <NUM>/<NUM> or higher than <NUM>.

Thermal expansion coefficients of the pieces <NUM>, <NUM> may also be matched in order to reduce internal stress during use of the article <NUM>. The article <NUM> may be used e.g. in conditions where the article <NUM> experiences thermal cycling. Matching of the thermal expansion coefficients of the pieces may further improve operating reliability of the article <NUM>.

<FIG> shows, by way of example, an article <NUM> produced by the method steps discussed with reference to <FIG>.

<FIG> shows, by way of example, geometric deformation of the article <NUM> caused by the pressure difference p<NUM>-p<NUM>. The pressure difference p<NUM>-p<NUM> may cause the pneumatic force F<NUM>, which may also slightly bend the pieces <NUM>, <NUM>. Bending of the piece <NUM> may cause a microscopic transverse displacement of the second piece <NUM> with respect to the first piece <NUM> (e.g. in the direction SX). Performing the laser welding under the deformed state may facilitate minimizing internal stress of the article <NUM>. Performing the laser welding such that the cavity pressure p<NUM> is lower than the external pressure p<NUM> during the welding may facilitate reducing or minimizing residual internal stress of the material of the article <NUM>. Performing the welding substantially at the ambient pressure (p<NUM>=<NUM> kPa) and utilizing the pressure difference p<NUM>-p<NUM> during the welding may improve operating reliability of the article <NUM> for operating conditions where the article <NUM> will be subjected to said ambient pressure (p<NUM>=<NUM> kPa).

The article <NUM> may be formed from two or more pieces. <FIG> shows, by way of example, forming an article <NUM> by joining three pieces <NUM>, 120a, 120b together by laser welding. The article <NUM> may comprise pieces <NUM>, 120a, 120b, and a component <NUM>. The first piece <NUM> may e.g. a spacer piece. The spacer piece may have one or more openings, i.e. open cavities. The second piece 120a may be e.g. a first cover. The third piece 120b may be e.g. a second cover. One or more components <NUM> may be mounted in the open cavity. The open cavity of the piece <NUM> may be closed after the pieces <NUM>, 120a, 120b have been positioned in the chamber <NUM> and after gas has been removed from the open cavity. A first preliminary joint may be formed by bringing a sealing surface of the second piece 120a into contact with a first sealing surface of the piece <NUM>. A second preliminary joint may be formed by bringing a sealing surface of the third piece 120b into contact with a second sealing surface of the piece <NUM>. The chamber <NUM> may be opened after the cavity has been closed. A first seam J1a may be formed by the laser welding to permanently join the second piece 120a to the first piece <NUM>. A second seam J1b may be formed by the laser welding to permanently join the third piece 120b to the first piece <NUM>.

One or more of the pieces may comprise electronic feedthrough FEED1. The feedthrough FEED1 may provide a galvanic electrical connection from the outside of the article <NUM> to the hermetically encapsulated component <NUM>.

<FIG> shows an article <NUM>, which may be formed e.g. by the method shown in <FIG>. The article <NUM> may comprise one or more components <NUM>, which are hermetically enclosed in the cavity CAV1 of the article <NUM>. The pressure of the cavity CAV1 may be e.g. lower than <NUM> kPa. The cavity CAV1 may optionally comprise inert gas. The article <NUM> may comprise substantially planar covers 120a, 120b, which have been joined to a spacer piece <NUM> by laser welding.

The article <NUM> may be e.g. a display, which comprises an array of Organic Light Emitting Diodes (OLED). The component <NUM> may comprise an array of light emitting diodes. The component <NUM> may be hermetically encapsulated by joining together two or more pieces <NUM>, 120a, 120b.

Referring to <FIG>, the article <NUM> may be an elongated and/or cylindrical object. The article <NUM> may be produced by joining two or more pieces <NUM>, 120a, 120b together by laser welding. The first piece <NUM> may be e.g. a tube section, and the pieces 120a, 120b may be plates. The pieces <NUM>, 120a, 120b may be positioned in the chamber <NUM> in order to remove gas GAS1, GAS0 from the interior OCA1 of the tube <NUM>. The interior OCA1 of the tube <NUM> may be optionally flushed with inert gas GAS0.

The cavity OCA1 may be closed at the reduced pressure of the chamber <NUM>. A first actuator 310a and a first supporting element 311a may move the piece 120a so as to close a first end of the tube <NUM>. A second actuator 310b and a second supporting element 311b may move the piece 120b so as to close the second end of the tube <NUM>.

The chamber <NUM> may comprise two or more parts <NUM>, 220a, 220b. For example, a base part <NUM> of the chamber <NUM> may be closed by a first end part 220a, and by a second end part 220b. The closed chamber <NUM> may be sealed e.g. by seals SEAL1a, SEAL1b. The chamber <NUM> may be opened after the cavity OCA1 of the tube <NUM> has been closed. The tube <NUM> may be held in place e.g. by positioning elements <NUM>.

After opening the chamber <NUM>, the semi-manufactured article <NUM>' may comprise a first interface IF1a and a second interface IF1b. The first interface IF1a may be defined by mating contact surfaces of the pieces <NUM>, 120a. The second interface IF1a may be defined by mating contact surfaces of the pieces <NUM>, 120b. The pieces <NUM>, 120a may together form a first preliminary joint. The pieces <NUM>, 120b may together form a second preliminary joint.

Referring to <FIG>, a first seam J1a may be formed by the laser welding to permanently join the second piece 120a to the first piece <NUM>. A second seam J1b may be formed by the laser welding to permanently join the third piece 120b to the first piece <NUM>.

Referring to <FIG>, the article <NUM> may be e.g. a (long) cylindrical object. The article <NUM> may be formed e.g. according to <FIG>. The article <NUM> may be produced e.g. by closing both ends of a glass tube <NUM> with circular plates 120a, 120b, wherein the glass tube may be used as the first piece, and a circular plate may be used as the second piece.

The article <NUM> may optionally comprise a component <NUM>, which may be positioned inside the piece <NUM> before the cavity is closed.

The second circular plate 120b may also be welded to the end of the tube <NUM> also before the tube <NUM> is inserted into the chamber <NUM>. In an embodiment, the piece <NUM> may also have a closed end already before the piece <NUM> is positioned into the chamber <NUM>.

In general, the open cavity OCA1 of a piece <NUM> may be closed by moving at least one of the pieces <NUM>, <NUM>. For example, the cavity may be closed by lowering or dropping the second piece <NUM> onto the first piece. For example, the cavity may be closed by lifting the piece <NUM> into contact with the second piece <NUM>. For example, the cavity may be closed by tilting the piece <NUM> and/or <NUM>.

The article <NUM> may be e.g. an optical device, and/or electrical device. The article may be e.g. a solar cell. The article <NUM> may be e.g. an OLED display.

The size of the focal spot of the laser beam B1 may be e.g. in the range of <NUM> to <NUM>. The height dimension of the seam J1 may be e.g. in the range of <NUM> to <NUM> (in the direction perpendicular to the surface SRF1), and a transverse dimension of the seam J1 may be e.g. in the range of <NUM> to <NUM>.

The method may be used for mass production of a plurality of articles. For example, pieces for forming a plurality of articles may be simultaneously located the same chamber <NUM> when the chamber is closed and opened. For example, gas may be removed from a cavity OCA1 of a second article <NUM> in the vacuum chamber <NUM> during laser welding of a first (previous) article <NUM>.

The pieces <NUM>, <NUM> may be substantially homogeneous or the piece <NUM>, <NUM> may comprise two or more different materials. The pieces <NUM>, <NUM> may comprise two or more different materials such that the sealing surfaces SRF1, SRF2 consist essentially of glass.

The first piece <NUM> may comprise glass. The second piece <NUM> may comprise glass. The first piece <NUM> and/or the second piece <NUM> may consist essentially of glass. The first piece <NUM> and the second piece <NUM> may consist essentially of glass. The glass may be e.g. fused silica or borosilicate glass. The glass may consist of non-crystalline amorphous solid. The softening temperature of the glass may be e.g. higher than <NUM>.

The glass pieces <NUM>, <NUM> may comprise two or more different materials such that more than <NUM>% of the mating surface area of the sealing surfaces SRF1, SRF2 consists essentially of glass. For example, more than <NUM>% of the mating surface area of the sealing surfaces SRF1, SRF2 may consist essentially of glass such that the remaining mating area of the sealing surface SRF1 and/or SRF2 may be essentially metallic. The welded seam J1 may comprise one or more portions where glass is welded to a metal. The metal may be e.g. gold or silver.

The material of the first sealing surface SRF1 may be selected from a group consisting of glass, silicon, sapphire, and ceramic. The material of the second sealing surface SRF2 may be selected from a group consisting of glass, silicon, sapphire, and ceramic.

A material of the first piece may be glass, silicon, sapphire, or ceramic. A material of the second piece may be glass, silicon, sapphire, or ceramic. The seam may be formed from said material of the first piece and from said material of the second piece.

One or more outer surfaces of the article <NUM> and/or the inner surface of the cavity may further comprise other material than glass. An outer surface of the article <NUM> and/or the inner surface of the cavity may comprise e.g. metallic material.

An article <NUM> produced by the method may also comprise two or more cavities which are hermetically isolated from each other.

The piece <NUM> and /or the piece <NUM> may also be called e.g. as substrates.

The article <NUM> may be e.g. an optical device, and/or electrical device. The article may be e.g. a solar cell. The article <NUM> may be e.g. a display. The component <NUM> may comprise an array of light emitting diodes. The article <NUM> may be e.g. a display, which comprises an array of Organic Light Emitting Diodes (OLED). The article <NUM> may be e.g. an OLED display. The component <NUM> may be hermetically encapsulated by joining together two or more pieces <NUM>, <NUM>, 120a, 120b.

The component <NUM> may comprise one or more light emitting elements. The component <NUM> may comprise a single light emitting element or a plurality of light emitting elements. The component <NUM> may comprise an array of light emitting elements. The light emitting element or elements may be e.g. a light emitting diode (LED), or a laser emitter. The laser emitter may be e.g. a semiconductor laser. The laser emitter may be e.g. a vertical-cavity surface-emitting laser (VCSEL). The light emitting diode may be e.g. an organic light emitting diode (OLED).

The article <NUM> may be e.g. an image sensor. A digital camera may comprise an image sensor <NUM> for capturing digital images. The image sensor <NUM> may comprise an encapsulated component <NUM>, which may convert an optical image into a digital image. The component <NUM> may comprise e.g. an array of CMOS detectors or an array of CCD detectors. CMOS means Complementary Metal Oxide Semiconductor. CCD means Charge-Coupled Device.

The article <NUM> may be e.g. a temperature measurement device, a MEMS device, an atomic clock device, and/or an implantable medical device. MEMS means a microelectromechanical system.

The encapsulated component <NUM> may be e.g. an optical element. The optical element may comprise e.g. one or more reflective layers, one or more wavelength-selective layers, one or more diffractive microstructures, and/or one or more optical multilayer coatings.

The piece <NUM> and/or the piece <NUM> may comprise one or more reflective layers, one or more wavelength-selective layers, one or more diffractive microstructures, and/or one or more optical multilayer coatings.

The article <NUM> may be e.g. a pressure measurement device. The article <NUM> may be arranged to monitor temporal variations of external pressure p(t). The symbol t may denote time. The article <NUM> may be used as a pressure sensor for monitoring external pressure p(t) after the article <NUM> has been produced. The piece <NUM> and/or <NUM> may be slightly deformed when exposed to external pressure p(t). The degree of bending of the piece <NUM> and/or <NUM> may depend on the pressure difference p(t)-p<NUM> between external pressure p(t) and internal pressure p<NUM>. The relative position of a surface of the piece <NUM> or <NUM> may depend on the pressure difference p(t)-p<NUM>, wherein the relative position may be determined e.g. with respect to the other piece (<NUM> or <NUM>). The article <NUM> may optionally comprise a component <NUM>, which may be arranged to monitor the pressure-dependent position of the piece <NUM> or <NUM>. The component <NUM> may be arranged to form an electrical signal, optical signal and/or radio frequency electromagnetic signal indicative of the pressure difference p(t)-p<NUM>. The component <NUM> may be encapsulated inside the article <NUM>. Producing the article <NUM> according to the present method may reduce internal stress of the pieces <NUM>, <NUM> and/or may improve operating reliability of the article <NUM>.

Claim 1:
A method for producing an article (<NUM>) by welding a first piece (<NUM>) to a second piece (<NUM>), the method comprising:
- providing the first piece (<NUM>), which comprises an open cavity (OCA1) and a first sealing surface (SRF1),
- providing the second piece (<NUM>), which comprises a second sealing surface (SRF2),
- providing a chamber (<NUM>), which has controllable internal pressure (p<NUM>),
- closing the chamber (<NUM>) such that the first piece (<NUM>) and the second piece (<NUM>) are inside the closed chamber (<NUM>),
- changing the internal pressure (p<NUM>) of the chamber (<NUM>) so as to cause a flow (F1) of a gas (GAS1) from the open cavity (OCA1),
- closing the open cavity (OCA1) by moving at least one of the pieces (<NUM>, <NUM>) such that the first sealing surface (SRF1) forms a partially gas tight preliminary joint (S0) together with the second sealing surface (SRF2), and such that the first piece (<NUM>) and the second piece (<NUM>) define an interface (IF1),
- opening the chamber (<NUM>) after the preliminary joint (S0) has been formed, and
- forming a welded seam (J1) by focusing a laser beam (B1) to the interface (IF1) after the chamber (<NUM>) has been opened,
characterized in that the first sealing surface (SRF1) and the second sealing surface (SRF2) are substantially planar, wherein the preliminary joint (S0) allows a sliding movement of the second sealing surface (SRF2) with respect to the first sealing surface (SRF1) after opening the chamber (<NUM>) before forming the welded seam (J1), and wherein the laser beam (LB1) is focused to the interface (IF1) through the first piece (<NUM>) and/or through the second piece (<NUM>).