Patent Application
20200164598
This application claims priority under 35 USC 119 of German Application No. DE 10 2018 129 802.1, filed on Nov. 26, 2018, the disclosure of which is herein incorporated by reference.
The invention relates to a method for joining a first join part, in particular a cover glass, with a second join part, in particular a housing and/or a display layer of a cover glass display assembly, for example of a smartphone, a mobile computer or the like,
Smartphones, wearables, mobile computers such as notebooks or tablet computers and the like usually have a cover glass display assembly, which is part of a touch-sensitive display unit, for example. Generally, such cover glass display assemblies can (also) be found in devices for outdoor use and/or in devices for use under water such as (waterproof) watches, trackers and/or measuring devices, in particular tachometers.
In such an assembly, a cover glass is joined with a housing and/or with a display layer of the device in question and in particular glued to it or them. The adhesion runs, in particular, along an edge region of the device in question.
A comparable situation also exists, for example, with regard to rear-view mirrors in motor vehicles, in particular interior rear-view mirrors or exterior rear-view mirrors, in particular with illuminated surfaces, as well as with regard to cameras and the like.
For this purpose, an adhesive is introduced into a joining zone between the cover glass and the housing or the display layer, in particular along its peripheral edges.
In addition to so-called pressure-activated adhesives (PSA), in particular thermoplastic, laser-activated adhesives (LAA) and thermally activated adhesive films with crosslinking constituents (TAA) have increasingly been used as adhesives in recent years. LAAs as well as TAAs both require heat and pressure to form the particular joining properties that are desired.
These thermosensitive adhesives can be heated by irradiation with light, in particular by means of a laser or a laser scanner. To optimize the absorption of the light, a dye layer may be formed in the joining zone. This dye layer is heated by the incident light. The heat is transferred by heat conduction to the adhesive, which is adjacent to the dye layer, causing the adhesive to heat up as well.
Such heating is very time consuming, however. Although, in principle, the adhesive can be heated faster by higher outputs of the laser or higher intensities of the laser light, it may overheat, which may cause, for example, the dye layer to be damaged or destroyed. Furthermore, considerable thermal scattering losses occur as well due to thermal conduction effects.
Furthermore, the thermal scattering losses may also damage components adjacent to the join parts, for example electronic components.
The object of the present invention is therefore to provide a method and a device for joining a first join part with a second join part by means of a thermosensitive adhesive, which makes a safe and at the same time rapid joining of the two join parts possible.
The object is achieved by a method for joining a first join part, in particular a cover glass, with a second join part, in particular a housing and/or a display layer of a cover glass display assembly, for example of a smartphone, a mobile computer or the like,
A planar emitter can be understood as a light source which is configured to irradiate the one or more join parts in a planar manner. A planar emitter can thus be understood as a light source whose light pattern on a surface to be illuminated is—in difference to a usual laser—not or at least substantially not in a punctiform shape. In particular, the size of the light pattern may correspond to the size of the joining region or a joining zone or at least substantially to the size of the joining region or the joining zone or at least a substantial part of the joining region or the joining zone.
By using a planar emitter as the light source, a high light or heat output can be transmitted onto or into the join parts at a low intensity, i.e. despite a low output per unit area. The low intensity reduces the risk of damage to, for example, a dye layer. The dye layer can be heated across a large area, which means that the adhesive can be heated across a large area as well.
Due to the overall higher heat output, the process time can be reduced. Heat losses caused by heat conduction can be minimized. Unlike, for example, when heating an outer side of the assembly with, for example, a heatable joining punch, the heat can be introduced directly into the joining zone. The parts to be joined can thus be treated with care.
While, for example, there is an increased risk of local overheating, especially an overheating of the dye layer, when using a conventional, punctiform-acting laser due to its high intensity of the laser light, such local overheating can be avoided when using a planar emitter. Curved surfaces can be irradiated or radiated through as well without the light reaching or exceeding locally critical intensity limits of the light due to lens effects of the surface.
Furthermore, the light pattern of the light source may be adapted to the respective requirements and properties of the join parts, for example to their shape. Thus, it is conceivable to adapt the light pattern from the light source to the spatial course of the adhesive.
Sensitive elements outside the joining area can be protected against undesired heating.
Due to the planar irradiation, complex and thus costly mechanics as required, for example, for a laser scanner are not necessary.
Consequently, a strip light source may be used as the light source. A strip light source is a light source which produces a substantially rectangular, in particular a striped or line-shaped, light pattern. The light source may be designed as a stationary light. Alternatively or additionally, the light source may be designed to run across an area to be illuminated. The light source may be designed to radiate a predefined amount of energy onto the area to be illuminated. For this purpose, the light source may, for example, if the adhesive is an LAA, also be configured to vary its irradiation intensity and/or its speed of travel when passing over the area to be illuminated, in particular as a function of the respective (local) width of the area.
Particularly in the case of smartphones, tablet computers and the like, the cover glass display assemblies to be processed are often rectangular or at least substantially rectangular. Thus, if the light source is designed as a strip light source, the light source or the light pattern of the light source may be focused into an area along one of the edges of the join parts. If the light source has several strip light sources, several of the edges may be covered at the same time.
It is conceivable for the first join part, the second join part and/or their joining zones to be irradiated with light having a light intensity, in particular measured as pulse peak intensity, of 10 W/mm2 at the most, preferably 1 W/mm2 at the most. As a result, overheating can be avoided in conventional cover glass display assemblies and in the dye layers commonly used for them. In particular, the light intensity may, compared to a punctiform light source, be reduced by using the planar irradiation, for example below a material-specific process limit. Alternatively or additionally, the speed of the process may be increased. In general, it is conceivable that the light intensity is selected on the basis of the material of one or more light-absorbing layers, in particular on the basis of the dye layer.
In particular, a thermoplastic, a substance with crosslinking constituents and/or an adhesive having such a substance may be used as adhesive. The thermoplastic may be, for example, an LAA. In particular, the thermoplastic may be meltable several times. The substance with a crosslinking composition may be a TAA. In particular, the substance with a crosslinking composition may be activated once, for example, with increased heat. Such adhesives require, inter alia, controlled or controllable heat or temperature conditions that can be met when using the method according to the invention.
Since the method according to the invention is able to avoid local overheating, a light-absorbing or at least partially light-absorbing dye layer can be irradiated, in particular for the purpose of heating the adhesive. The dye layer is able to improve the absorption of the incident light, in particular within the joining zone. The dye layer may be an ink, comprise an ink and/or be made by means of an ink. The dye layer may be nontransparent to visible light or at least substantially nontransparent. This results in an additional visual protection so that the layers located under the dye layer are not visible from the outside or covered by the dye layer. Alternatively or additionally, the dye layer may, for example, in a cover glass display assembly to be manufactured of a device such as a smartphone, optically hide one or more areas that should not be visible to a user of the device.
It is also conceivable that at least two individual light sources, for example at least two LEDs, are used as the light source. Thus, a powerful planar emitter can be produced from inexpensive individual components. It is also conceivable that at least one individual light source is designed as an infrared emitter, in particular with a focusing device, and/or comprises such an emitter. Alternatively or additionally, at least one individual light source may be configured as a laser and/or comprise a laser, in particular with a low beam power and preferably with a beam-shaping device.
The light source used may be a matrix light source, in particular a vertical cavity surface-emitting laser (VCSEL) array. VCSEL arrays comprise a plurality of planar-emitting individual light sources arranged in matrix form. These make it possible to generate a particularly homogeneous, planar light pattern in an inexpensive manner. It is possible to generate high light outputs, in particular in the range of 100 W-10 kW.
VCSEL arrays also make it possible to control the individual light sources of the array separately from each other. Thus, a light distribution adapted to the shape of the joining zone or to the adhesive may be generated during production, i.e. within the light source.
The light may be masked along its beam path by a masking device. As a result, the light pattern may be adapted more precisely to the shape or the course of the joining zone. Sensitive areas of the assembly or adjacent elements may be shaded and thus protected.
In particular, the method may provide that the size and/or the position of a masking window of the masking device are adjusted. For this purpose, the masking device may be configured to be variable in shape. In particular, the masking device may consist of four slit masks, in particular rectangular slits, arranged so as to be displaceable relative to each other. By means of such a masking device, a rectangle masking may take place in adjustable dimensions. Alternatively or additionally, radii or curvature masking elements, in particular those formed for a specific application, may be provided for masking one or more curvilinear regions.
Alternatively or additionally, the light source may also be movably arranged, in particular relative to the first and/or second join part.
It is also conceivable that the beam path of the light is shaped and/or directed by a lens assembly and/or by a mirror device. In particular if the light source has a plurality of individual light sources, the individual light sources may be arranged in a spatially distributed manner and still produce a continuous, in particular seamless, light pattern.
It is therefore particularly advantageous if at least one, preferably each, individual light source is assigned a part and/or a portion of the lens assembly and/or the mirror assembly. This makes it possible to separately control and/or shape the beam path of the light emitted by the at least one or by each individual light source.
In a variant of the method according to the invention, the light source is operated during the joining with at least two different power levels. Alternatively or additionally, the duty cycle of the light source and/or—especially in a pulse width modulated operation of the light source—their pulse width may be varied for example.
By operating the light source with at least two different power levels, it is possible to use the same light source for several process phases of the joining process. As a result, different types of adhesives may be used as well. If, for example, the adhesive is a TAA, then the joining process can take place in two different stages. In a first heating phase with, for example, 1 W/mm2 over a period of less than one second, a specific temperature level can be set, and in a second heating phase in a period of one or more seconds, the adhesive can be heated to a higher temperature level. Subsequently, in a post-heating phase, the temperature in the joining zone may be kept approximately at the same level by irradiating the zone with a reduced power.
At least one individual light source may be operated with a higher individual light power than at least one other individual light source. For this purpose, the light source may be configured to produce an adjustable light distribution. This also makes it possible to adapt the light distribution to the shape of the adhesive material or the joining zone to be heated beforehand. Individual light sources arranged in a central region of the light source may, for example, be operated with a lower power to obtain a light distribution which irradiates substantially along the edge regions of the join parts and/or which takes component-specific heat outflows into consideration, for example during a longer joining process.
In order to achieve a permanent connection, the two join parts may be pressed against each other before, during and/or after the irradiation with light, in particular with a joining punch, particularly preferably with a deformable joining punch.
For this purpose, the joining device used may have, in particular, a deformable, joining punch. The joining punch may press against a join part, for example against the first join part, while the other, for example, the second, join part is mounted on a workpiece carrier. The workpiece carrier may be deformable. In particular, the workpiece carrier may be configured to adapt to the shape of the workpiece it carries, in particular the second join part. The joining device may have, for example, a plurality of joining punches for this purpose. Each join part may be pressed against the respective other join part by a joining punch assigned to it, for example. The joining punches may be configured to be adaptable in their shape and/or in the distribution of the pressure applied by them onto the respective join parts to be joined.
Furthermore, included in the context of the invention is a joining device, in particular a device for carrying out the method according to the invention, for joining a first join part, in particular a cover glass, with a second join part, in particular a housing and/or a display layer of a cover glass display assembly, for example of a smartphone, a wearable, a mobile computer or the like, by means of a thermosensitive adhesive, with a light source for the direct and/or indirect heating of the adhesive by irradiating the adhesive with light, in particular with infrared and/or visible light, wherein the light source is formed as a planar emitter, in particular as a VCSEL array.
The joining device may have, in particular a deformable, joining punch for pressing the first join part and the second join part against each other.
Such a deformable joining punch can be obtained, in particular, when the joining punch has at least one force-receiving part which can be acted upon by a contact force F and at least two pressing parts for putting pressure on the first join part, wherein the at least two pressing parts are tiltably arranged and/or configured on the joining punch independently of one another relative to the force-receiving part.
Additional features and advantages of the invention may be found in the following detailed description of the embodiments of the invention, on the basis of the figures of the drawing, which show details essential to the invention, and in the claims.
The features shown in the drawing are shown in such a way that the features of the invention can be made clearly visible. The different features may each be realized in variants of the invention either in isolation or together in any desired combinations.
A dye layer 18 is applied to the underside of the first join part 12 and adjacent to the adhesive 16. The adhesive 16 and the dye layer 18 are thus located in a joining zone 19.
While the first join part 12 is substantially transparent to light in the wavelength ranges of visible light and near infrared, in particular in the range 800-1100 nm, the dye layer 18 is nontransparent in these wavelength ranges. It thus absorbs light from these wavelength ranges.
Light 20, in particular in the aforementioned wavelength ranges, may be generated by a light source 22 designed as a strip light source and irradiated in the direction of the assembly 10. The light source 22 in particular generates a strip-shaped light. For this purpose, the light source 22 is designed as a VCSEL array. The light output it generates as well as the radiated light distribution may be adjusted.
It can be seen that in order to join the two join parts 12, 14, the light 20 passes through the first join part 12 and is absorbed by the dye layer 18. The dye layer 18 heats up and thus the adhesive 16 heats up as well. Alternatively, it is also conceivable that the dye layer 18 is dispensed with. In such a case, it is advantageous if at least one layer below the dye layer 18, for example the adhesive 16, is configured to absorb the light 20.
By means of a joining punch 24, the first join part 12 may be pressed against the second join part 14 with a contact force F. To do so, the second join part 14 is fixed on a workpiece carrier 26. The workpiece carrier 26 may be arranged in a stationary manner. The joining punch 24 is, in particular, configured to uniformly apply the contact force F across a wide area, i.e. across a larger area of the first join part 12.
The light source 22, the joining punch 24, as well as the workpiece carrier 26 are components of a joining device 28. Apart from the parts mentioned, the joining device 28 also comprises further parts, which are not shown in
In the embodiment shown in
For shading areas to be protected of the assembly 10 or, respectively, of the smartphone, a masking device 32 is arranged in the beam path of the light 20, in particular close to the assembly 10. The masking device 32 has a masking window 33 through which light 20 can pass. The masking window 33 may have a slit-like design and/or have a varying slit width, in particular transversely to the image plane of
In the embodiment according to
In a preferred embodiment of the invention, a glass pane which is transparent, in particular for the light 20 (not shown in
The joining device 28 according to
In the embodiment of the joining device 28 shown in
In the joining device 28 shown in
In this embodiment, the light source 22 is formed from a plurality of individual light sources 36. The individual light sources 36 are arranged at regular intervals and, in particular, distributed across a wide area. As a result of this arrangement, it is possible, as can be seen in
In order to make this arrangement of the individual light sources 36 possible in terms of space, the masking device 32 and the mirror device 34 are each constructed from a plurality of individual elements. In particular, each individual light source 36 is assigned a single mask 38 and a single mirror surface 40 or respectively arranged in the respective beam path of the respective individual light source 36. Each individual mask 38 thus delimits or respectively masks the beam path of the individual light source 36 assigned to it. In this exemplary embodiment, the individual masks 38 are each designed in two parts so that a slit-shaped masking window is formed between their individual mask parts. However, it is also conceivable to form the individual masks 38 in one piece with a, in particular slit-shaped, preferably centered, masking window.
The individual elements 38, 40, in particular, make it possible that all the individual light sources 36 irradiate into the assembly 10 or into the joining zone 19 virtually without any scattering losses.
A further development of the joining device 28 according to
It can be seen, in particular, that the mirror device 34 with its individual mirror surfaces 40 extends along a horizontal direction x at most to an edge K of the joining zone 19. In other words, the mirror device 34 does not protrude beyond the edge K. To this purpose, the individual mirror surfaces 40 are suitably curved, in particular more curved in comparison with
As will be explained in more detail below, a plurality of such arrangements or joining devices 28 can be positioned side by side and collision free as partial joining devices 42 and be used as a joining device 28 adaptable to different assemblies 10 (
Consequently,
It can be seen that the assemblies 10 to be processed according to
The joining device 28 has four partial joining devices 42, which respectively correspond to the partial joining device 42 according to
Each partial joining device 42 and thus each strip of light 20 can be displaced in one direction each. As indicated in
Because the individual mirror surfaces 40 (
Thus, by moving the partial joining devices 42 and thus the strips of light 20, the size and shape of the generated light pattern can be adapted to the particular assembly 10 to be processed.
The embodiment of a joining device 28 illustrated in
This joining device 28 in turn has four partial joining devices 42, which in turn are arranged to be displaceable, in particular collision free, in parallel or at least substantially parallel to the upper side of an assembly 10 to be joined.
Each of the partial joining devices 42 is in turn configured as a strip light source and projects light 20 onto the assembly 10. In the assembled state, i.e. in the original state that the flat pattern view shown in
In addition, as shown particularly in
As can be seen as well, for example, in
In this joining device 28, the mirrors within the partial joining devices can be dispensed with. Intensity gradients of the light 20 which may occur, in particular at the edges of the respective beam paths, may be avoided or removed by suitable masking devices 32 (see
The joining device 28 may, in particular in the embodiments described above, have at least one, in particular deformable, joining punch 24 (
Such a deformable joining punch 24 is shown in
The joining punch 24 has a force-receiving part 44 which can be acted upon by the contact force F along a direction z orthogonal to the direction x. The force-receiving part 44 is formed as a bar and has approximately in the middle a force-receiving point 46 onto which the contact force F is applied in a joining operation.
Below the force-receiving part 44, a plurality of load-guiding parts 48 is hierarchically arranged in several planes, in this case in two planes. The load-guiding parts 48 are also designed as bars.
The load-guiding parts 48 are tiltably arranged via hinge parts 50 on the respective element located above them, i.e. on a load-guiding part 48 or on the force-receiving part 44 located above them. They are thus tiltably arranged relative to the force-receiving part 44 on the joining punch 24.
Two pressing parts 52 are arranged on each of the load-guiding parts 48 in the lowest plane. In the situation shown in
Due to the tiltable arrangements of the load-guiding parts 48, the pressing parts 52 are tiltably arranged on the joining punch 24, at least independently of the pressing parts 52 that are arranged on the respective other load-guiding parts 48, relative to the force-receiving part 44. It is conceivable that, as an alternative or in addition, the pressing parts 52 are directly tiltably arranged, in particular mounted, on the respective load-guiding parts 48 of the lowest plane.
This capacity to tilt causes the joining punch 24 to be deformable. It may, when the two join parts 12, 14 are pressed against each other, adapt in particular to the surface geometry of the first join part 12, which may have changed itself and may be irregular under certain circumstances due to the joining process, and thus cause a more evenly distributed or adjustably distributed introduction of the contact force F or, respectively, of generated contact pressures; to this purpose, the distributions of the contact force F or of the contact pressures may be adjusted in particular by making adaptations to the shape and/or dimensions of the components of the joining punch 24.
For clarity reasons, the deformations of the first join part 12 during the joining process are significantly enlarged in
It can be seen that when the force-receiving part 44 is acted upon by the contact force F, the pressing parts 52 press with partial forces F1 to F8 onto the first join part 12 at their respective contact points or transfer the respective partial forces F1 to F8 to it.
As a result of the tiltable arrangements of the load-guiding parts 48, the load-guiding parts 48 can tilt in such a way that all the pressing parts 52 rest on the first join part 12 despite its deformations. Thus, it is possible to apply a uniform force onto the first join part 12.
In a first step 102, the assembly 10 of the joining device 28 to be processed, which, for example, has the embodiment according to
The required contact pressure F or the required pressure distribution is built up in this step 102 by means of the joining punch 24.
Then, in a step 104, the masking device 32 is set up, in particular adjusted; in particular, the size of its masking window 33 is adapted to the assembly 10 to be processed. Alternatively or additionally, the masking device 32 may also be set up in advance, in particular during an initial setup step.
Furthermore, the light distribution or the emission characteristic of the light source 22 is adjusted. The adjustments of the masking device 32 and/or the light distribution of the light source 22 may be carried out, for example, analogously to the procedure illustrated in
If the adhesive 16 is an LAA or a TAA, it must first be heated to a wetting temperature T1 or up to a melting temperature, and this wetting temperature T1 should be kept at least approximately over a wetting time dt1. At this wetting temperature T1, the adhesive initially wets the two join parts 12, 14 adjacent to it.
To ensure that the chemical reactions required for the establishment of the connection properties are triggered or take place in such an adhesive 16 designed as a TAA, such an adhesive 16 must subsequently be heated to a reaction temperature T2. The reaction temperature T2 must then at least approximately be held over a reaction time dt2. Then, the adhesive 16 is cooled over a cooling time dt3 until it reaches a removal temperature T3.
The temperatures T1, T2, T3 and the times dt1, dt2, dt3 are selected, in particular, depending on the materials used, in particular the adhesive 16 and/or the join parts 12, 14.
In a step 106, therefore, the light source 22 is operated for a short time with high power or intensity, causing the adhesive 16 to be heated indirectly by irradiating the dye layer 18 with light 20 until the adhesive 16 reaches the wetting temperature T1. An intensity of about 1 W/mm2 is generated, for example. After reaching the wetting temperature T1, the power or intensity of the light source 22 is temporarily reduced in order to at least approximately maintain the wetting temperature T1 over the wetting time dt1.
If the adhesive 16 is a TAA, the light source 22 is reused during a next step 108 until the adhesive 16 reaches the reaction temperature T2. In particular, the light source 22 can be operated with increased power. This increased power or intensity is, in turn, used for a comparatively short period of time. Then, the power or intensity of the light source 22 is again reduced to at least approximately keep the reaction temperature T2 over the reaction time dt2. Meanwhile, the two join parts 12, 14 are still pressed against each other or, respectively, the contact force F is still maintained by means of the joining punch 24.
If the adhesive 16 is a thermoplastic, for example a LAA, step 108 may be omitted and the method continued immediately at step 110.
Finally, in a last step 110 the temperature is reduced from the reaction temperature T2 to the removal temperature T3 over the cooling time dt3. The assembly 10 may then be removed from the joining device 28 and processed further, for example.
In a variant of the method, a plurality of method steps, in particular method steps 106 and 108, are not performed on the same joining device 28 and/or at least not by means of the same light source 22, but a plurality of joining devices 28 and/or different light sources 22 are used. A laser or a laser scanner may be used, for example, instead of a light source 22 in the form of a planar emitter for the heating to the temperatures T1 and/or T2.
It is also conceivable in order to maintain a temperature, in particular the wetting temperature T1 and/or the reaction temperature T2, to provide a thermal insulation and/or to supply thermal energy from the outside, for example via the workpiece carrier 26 and/or the joining punch 24 instead of or in addition to a reduced power supply by the light source 22.
Furthermore, a joining device 28 is conceivable which is adapted to join more than one assembly 10 or more than one pair of join parts 12, 14 to be joined together. In connection with such a joining device 28, a variant of the method 100 according to the invention is to join several assemblies 10 or pairs of join parts 12, 14 to be joined together simultaneously or alternately.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2018 129 802.1 | Nov 2018 | DE | national |
