Method and laser system for electrically contacting connection surfaces of two substrates
Through the three-stage laser loading method, the substrate is preheated by the first laser device, and the problems of energy loss and temperature unevenness in the prior art are solved, and stable and efficient substrate connection is achieved.
Patent Information
- Application Number
- CN202411797824.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-12-14
- Filing Date
- 2024-12-09
- Publication Date
- 2025-06-17
AI Technical Summary
The prior art has problems of energy loss and uneven temperature when connecting two substrates, resulting in unstable connections and potential damage to the substrate.
Three-stage methods are adopted: positioning stage, first loading stage and second loading stage. The substrate is preheated by the first laser device at the first loading stage, improving the absorption capacity of the substrate and flux, reducing the reflection of laser radiation, thereby inputting the melted flux at a lower energy during the second loading stage.
It realizes efficient connection of two substrates at low energy consumption, avoids substrate damage, and improves connection stability and efficiency.
Smart Images
Figure CN120155656A_ABST
Abstract
Description
Field of the Invention
[0001] The present invention relates to a method for electrically contacting the joining surfaces of two substrates. Furthermore, the present invention relates to a laser system for loading at least one substrate with laser energy. Background Art
[0002] Various methods are known for joining or contacting the joining surfaces of two substrates arranged in an overlapping state, in which laser energy is used to generate the heat required for the connection in the region of the contact pairs formed by the joining surfaces. For example, methods or devices for thermally connecting the joining surfaces of two substrates are known, in which an optical fiber is used to introduce laser energy into the contact pairs of the joining surfaces, the cross-section of which is dimensioned such that all contact pairs can be simultaneously loaded with the laser radiation emitted from the end cross-section of the optical fiber. However, this method does not allow for targeted loading of individual contact pairs. Furthermore, in this method, the joining surfaces of the substrates are fastened to each other in their relative positions only by the self-weight of the upper substrate without additional pressure loading. It is also known that, in order to thermally connect the joining surfaces of two substrates, one substrate can be loaded from behind through a transparent pressure plate, and the joining surfaces of these substrates are pressed against each other by means of the pressure plate. A transparent glass plate is used as the pressure plate here.
[0003] Furthermore, methods for directly mounting semiconductor chips on carrier substrates are known from the general prior art. Thus, there are methods in which the semiconductor chip is directly fixed on the carrier substrate or circuit board by means of its joining surface facing the carrier substrate and a solder previously applied to the joining surface of the chip. Here, in the case of reflow soldering, the solder coating melts again in the soldering furnace and connects to the joining surface of the carrier substrate. This method has become very complex both in terms of its process and with regard to the equipment required therefor.
[0004] It is also known that, in order to connect the connecting contact portions of two substrates, a solder flux is distributed as spherical solder balls onto the weldable connecting contact portion of one of the substrates by means of a solder ball delivery device of a laser welding system and at least partially melted by means of a laser device, such that a material-fit connection can be formed between the connecting contact portions of the substrates. Alternatively, the solder flux located on the connecting contact portion can also be at least partially melted by heating one of the substrates, in order to form a material-fit connection between the connecting contact portions of the substrates after the first substrate has been applied to the second substrate. However, by introducing thermal energy onto the surface of the substrate, especially in the case of temperature-sensitive substrates, undesired ablation of the substrate can occur. Depending on the absorption capacity of the solder flux or the substrate, only a small fraction of the laser radiation can be used to heat the solder flux in such methods, while a large fraction of the radiation is reflected by the solder flux or the substrate and does not contribute to its heating. This results in significant energy losses in practice, such that the amount of energy required for melting the solder flux is significantly increased. Summary of the Invention
[0005] Therefore, the object on which the present invention is based is to provide a method and a laser system which enable reliable connection of two substrates by melting a solder flux with low energy consumption. In addition, the contact of the connection surfaces of the substrates should be improved and damage to the substrates to be connected should be avoided.
[0006] The object is achieved by a method having the features of an embodiment according to the invention and by a laser system having the features of an embodiment according to the invention.
[0007] According to the method for electrically contacting the connection surfaces of two substrates, wherein the first substrate is electrically and mechanically connected to the connection surface of the second substrate with its connection surface facing the second substrate, can be divided into at least three stages, namely a positioning stage, a first loading stage and a second loading stage. In the positioning stage, the first substrate is positioned with its connection surface relative to the connection surface of the second substrate. Therefore, for the contact or connection of the first substrate and the second substrate, the connection surfaces of the first substrate and the second substrate can be arranged in an overlapping state. In the first loading stage, at least one of the substrates, namely the first substrate or the second substrate, is loaded with a first laser radiation on the back side by means of a first laser device. "On the back side" refers to the back side of the substrate within the scope of the present invention, which corresponds to the side of the substrate facing away from the other substrate. That is to say, in other words, the back side of the first substrate is the side of the substrate facing away from the second substrate, and the back side of the second substrate is the side of the substrate facing away from the first substrate. The connection surface of the substrate is arranged at the front side of the substrate opposite to the back side, wherein a flux is arranged between the connection surfaces of the first substrate and the second substrate. In the first loading phase, although the solder and the substrates are heated by the first laser radiation applied to one of the substrates by means of the first laser device, in particular the substrates applied by means of the first laser device, the solder has not yet melted. By heating the substrates and the solder to an increased temperature level, the absorption capacity of the substrates and the solder is increased. This achieves an advantageous effect, so that after the change to the second loading phase, in which at least one of the substrates is applied with the second laser radiation by means of the second laser device, only the amount of energy required to heat the solder from the temperature level reached in the first loading phase to the melting temperature must be additionally input, wherein due to the increased absorption capacity of the substrates and the solder after the first loading phase, the reflected portion of the laser radiation is reduced, thereby increasing the efficiency of the application of the second laser radiation. In the second loading phase, the solder provided between the substrates is melted at least to such an extent that the connecting surfaces of the first substrate and the second substrate facing each other are electrically contacted. Preferably, in addition to the electrical contacting of the connecting surfaces facing each other, the first substrate is also mechanically fastened to the second substrate. Preferably, the first substrate with its connection surface facing the second substrate is directly electrically and mechanically connected to the connection surface of the second substrate by fixing the connection surface of the first substrate with solder previously applied to the connection surface of the first substrate directly to the second substrate.
[0008] In the context of the present invention, the term "flux" also refers to copper pads, sintering pastes and / or copper pads (so-called Cu-pillars) for Cu-Cu mixed bonding, in addition to solderable, in particular solderable metal connections used, for example, in the form of solder pastes or solder balls. The term "sintering paste" refers to a suspension, wherein the suspension comprises particles consisting of at least one solderable and electrically conductive material and a solvent.
[0009] It is known within the scope of the present invention that, in addition to dividing the method for electrically contacting the connecting surfaces of two substrates according to the present invention into a positioning phase, a first loading phase, and a second loading phase, it is also advantageous that, in the first loading phase, loading can be carried out with a first laser radiation having a wavelength different from that of the second laser radiation. Thus, the wavelength of the corresponding laser radiation can be matched to the requirements in the first loading phase and / or the second loading phase, because it has been recognized that effective preheating of the connecting fitting can be carried out by loading with a first laser radiation having a first wavelength, and effective melting of the solder can be carried out by loading the connecting fitting with a second laser radiation having a second wavelength different from the first wavelength. This provides the following advantages: economical heating with a first laser radiation that can be easily absorbed by a variety of materials can be carried out in the first loading phase, and the second laser radiation is only used in the second loading phase, and the second laser radiation induces a greater deep thermal effect in the material of the connecting fitting, especially in the solder. Thereby, thermal damage can be prevented, especially during the first loading phase. In addition, due to the preheating, the required laser power of the second laser device can be designed to be lower from the beginning with respect to such laser devices. On the one hand, this can achieve a reduction in equipment costs, and on the other hand, it can also achieve miniaturization of the laser system used in the method. Preferably, the first laser radiation can have a smaller wavelength than the second laser radiation. For example, in the first loading phase, the first laser radiation can be in the ultraviolet wavelength range, and in the second loading phase, the second laser radiation can be in the near-infrared wavelength range.
[0010] It is also conceivable that, compared with using the second laser device during the second loading phase, the first laser device requires a smaller laser energy input during the first loading phase. It is also conceivable that the second laser device can have a higher power than the first laser device in order to melt the solder. Due to the increased absorption capacity of the connecting fitting within the scope of the first loading phase, the power of the second laser device can thus be significantly reduced with respect to such methods having only one loading phase. Thereby, the second laser device can be adjusted more precisely, and thermal damage to the substrate can be prevented. Due to the preferably smaller laser energy input into the solder and / or the first substrate, the second laser device can have a significantly smaller laser power compared to the case where the first laser device is not used in the first loading phase. Since in principle, the power of the laser source can be adjusted more precisely in a lower power range compared to a higher power range, a more precise adjustment of the second laser device is thus feasible. On the other hand, thermal damage can be prevented, which especially occurs in the case of high laser power. In particular, the required laser power of the second laser device can also be designed to be lower from the beginning. On the one hand, this can achieve a reduction in equipment costs, and on the other hand, it can also achieve miniaturization of the laser system used in the method.
[0011] It has been recognized as advantageous within the scope of the present invention that the transition from the first loading phase to the second loading phase is controlled by means of a control device as a function of the duration of the first loading phase, the laser energy in one of the input substrates, the temperature of one of the substrates, and / or the temperature of the solder. In other words, the control device is configured to activate the second laser device based on different measured values or sensor data, thereby triggering the transition from the first loading phase to the second loading phase.
[0012] The control device can control the transition from the first loading phase to the second loading phase as a function of the duration of the first loading phase. That is, as soon as one of the substrates has been loaded with the first laser radiation by means of the first laser device for a sufficient length of time, the transition from the first loading phase to the second loading phase is triggered by means of the control device. Since, under the assumption of a constant laser power throughout the first loading phase, the laser energy input can be determined based on the loading duration and the laser power of the first laser device. As soon as sufficient laser energy input has been effected into the connection partners, that is, the first substrate, the second substrate, and the solder, the transition from the first loading phase to the second loading phase can be triggered by means of the control device.
[0013] Alternatively or additionally, the control device can control the transition from the first loading phase to the second loading phase as a function of the laser energy in one of the input substrates and / or the solder. Control based on the input laser energy offers the advantage, compared to control based only on the duration of the first loading phase, that the adjustment or variation of the laser power can also be taken into account during the first loading phase. It has been recognized here that the detection of the laser power at each point in time during the first loading phase allows an accurate calculation of the laser energy input into the connection partners even in the case of a varying laser power during the first loading phase.
[0014] Also alternatively or additionally, the transition from the first loading phase to the second loading phase can be controlled by means of the control device as a function of the temperature of one of the substrates and / or the temperature of the solder. For this purpose, the temperature of one of the connection partners can be monitored at least at regular time intervals or continuously. In the case where the temperature of the connection partner is sufficient and thus the absorption capacity of the connection partner is increased sufficiently, the transition from the first loading phase to the second loading phase can be effected. Preferably, the temperature of the first substrate and / or the solder is detected and the transition from the first loading phase to the second loading phase is controlled based on its temperature value. It is also conceivable to measure the temperature of one of the substrates and, taking into account the construction and material of the substrate, the temperature of the solder can be determined.
[0015] Within the scope of the present invention, the term "substrate" is understood to include all devices provided with a printed conductor structure and external connection surfaces for contacting. Thus, within the scope of the present invention, the substrate can be, for example, a chip, a circuit board or a carrier substrate. A preferred field of application of the method proposed here or the scope of use of the system proposed here lies in flip-chip technology and also within the scope of SMD (Surface-mounted device) technology.
[0016] Within the scope of the present invention, the term "connection fitting" denotes the first substrate, the second substrate and the solder.
[0017] Here, the term "laser device" can be understood only as a laser emitting device for emitting laser radiation or also as a laser emitting device combined with a radiation conducting device, by means of which the laser radiation is guided from the laser emitting device to the connection fitting. Lenses and / or devices with mirrors are known as radiation conducting devices.
[0018] Thus, the method proposed can be used extremely generally, since different substrates, such as also metallized chips, can be connected to other substrates. The general use of the method is mainly based on the fact that these two loading phases can be very precisely matched to the connection fitting. Furthermore, the energy efficiency of the method can thereby be increased and damage to the connection fitting can be minimized. In particular, material fractures, such as occur when heating chips often composed of different materials, can be avoided. In context, it has been recognized as advantageous that the heating of the chip is carried out without gradation but follows a gradient.
[0019] Within the scope of the present invention, it has also been recognized that, by means of the first laser device during the first loading phase, in addition to the connection fitting, the environment is also heated, thereby improving and simplifying the contact of the connection surfaces of the first substrate and the second substrate with each other during the second loading phase. It has also been recognized that the adhesive can be cured by means of the first laser device and / or the second laser device. In particular, by energy input and the resulting heating of the adhesive, the adhesive can be cured. As adhesives, for example but not exhaustively, epoxides, dry films, benzocyclobutene compounds (BCB), polyimide compounds and / or UV-curing compounds can be used.
[0020] Advantageous embodiments of the present invention are the subject matter hereof. Within the scope of the present invention, there are also included all combinations consisting of at least two features disclosed in the description and / or the drawings. It goes without saying that all features and embodiments disclosed for the method, in an equivalent manner and method, although with different wording, also relate to the laser system according to the present invention. Herein, in particular, it should be understood that customary language conversions and / or meaningful substitutions of the corresponding terms within the scope of normal language practice, in particular the use of synonyms supported by generally recognized language literature, are included in this disclosure, without being explicitly mentioned in their respective formulations.
[0021] The temperature of the connection fitting can be measured in a contactless and advantageous manner. By means of a temperature sensor, it is possible to measure at least the radiant temperature of at least one in the substrate and / or the solder during at least the first loading phase. By means of a control device, the transition from the first loading phase to the second loading phase can then be controlled based on the radiant temperature of one of the substrates in the substrate and / or based on the radiant temperature of the solder. Advantageously, the temperature sensor can be configured as an infrared pyrometer. Such an infrared pyrometer can measure highly accurately and quickly and, due to its compact construction, is suitable for applications with limited installation space. The infrared pyrometer also has a relatively small weight due to its compact construction and can be positioned extremely flexibly. For example, the infrared pyrometer can be arranged within the joining tool of a laser system for electrically contacting two substrates at the connection surface. In particular, compared to known infrared cameras for temperature detection, which are extremely large and heavy compared to the infrared pyrometer, the infrared pyrometer offers various advantages. In particular, the rapid temperature detection, advantageously carried out in less than 1 ms, more preferably in less than 0.3 ms, is a major advantage compared to the relatively slow temperature detection of infrared cameras (usually in the range of 25 ms). Preferably, by means of the temperature sensor, it is possible to measure at least the radiant temperature of the first substrate and / or the solder during at least the first loading phase, and the transition from the first loading phase to the second loading phase can be controlled by means of the control device based on the radiant temperature of the first substrate and / or based on the radiant temperature of the solder.
[0022] In the second loading phase, in addition to the loading with the first laser device, the second laser device is also used for loading. Thus, in the second loading phase, the connection fitting is simultaneously loaded with laser radiation by means of the first laser device and the second laser device. Since the loading with the first laser device is retained, the second laser device can be operated with a lower power.
[0023] If the radiant temperature of at least the first substrate, the second substrate, and / or the solder flux is measured by means of a temperature sensor during a first loading phase, the radiant temperature of at least the first substrate, the second substrate, and / or the solder flux can also be measured by means of the temperature sensor during a second loading phase. Then, the second loading phase can be terminated based on the measured radiant temperature of at least the first substrate, the second substrate, and / or the solder during the second loading phase. Therefore, the method can be carried out with a minimum of equipment and control technology costs.
[0024] The switching temperature that triggers the transition from the first loading phase to the second loading phase can be selected according to the characteristics of the substrate to be contacted and / or the soldering. Therefore, in order to determine the switching temperature, when defining the switching temperature, the material-specific absorption capacity of the substrate and / or the solder flux that changes with the material temperature can be considered separately.
[0025] The first laser device can be switched on in a clock-controlled manner for a defined on-duration in the standby mode and switched to the operating mode by means of a control device based on the current temperature of at least one substrate measured by means of a temperature sensor. Within the scope of the present invention, the "standby mode" means the operational readiness of the first laser device, in which the original function of the laser device, i.e., the emission of laser radiation, is temporarily deactivated but can be activated at any time without preparation or a long waiting time. Within the scope of the present invention, the "current temperature" of the substrate is the temperature or temperature change that results once the substrate is placed within the measurement area of the temperature sensor. Therefore, it is feasible to use the temperature sensor not only for triggering the transition between the first loading phase and the second loading phase and, if necessary, also for terminating the second loading phase, but also for detecting at least one substrate, because the measurement of the substrate temperature presupposes the presence of the substrate. Therefore, the temperature sensor can be configured to trigger the method once the substrate is within the measurement area of the temperature sensor. In particular, if the temperature of the first substrate can be measured by means of the temperature sensor during the clock-repeated on-duration of the first laser device, during which the first laser device is in the standby mode, the method can be triggered. Because the temperature of the first substrate can only be measured when the first substrate is present, the temperature value determined by the temperature sensor or the temperature change determined by the temperature sensor indicates the presence of the first substrate.
[0026] According to a preferred embodiment, in the first loading phase, the first substrate can be loaded on the back side with a first laser radiation by means of a first laser device, and in the second loading phase, the first substrate can be re-loaded on the back side with a second laser radiation by means of a second laser device. That is, the first laser radiation and the second laser radiation are incident on the first substrate on the back side, whereby the device for carrying out the method can be constructed compactly.
[0027] According to another preferred embodiment, in the first loading phase, the first substrate can be loaded on the back side and the second substrate can be loaded on the front side with first laser radiation by means of a first laser device. Subsequently, in the second loading phase, the first substrate can be loaded on the back side with second laser radiation by means of a second laser device. In the first loading phase, the first substrate and the second substrate are thus loaded with the first laser radiation. This can be done in such a way that, for example, the first substrate is configured smaller than the second substrate and the focus of the laser radiation transverse to the loading direction is configured larger than the first substrate, whereby the first laser radiation hits not only the first substrate but also the second substrate. This also has the positive effect that the environment of the connection fitting, in particular the environment of the first substrate, can be preheated during the first loading phase. In the second loading phase, the focus of the second laser radiation can then be oriented such that the second laser radiation only hits the first substrate, so that energy is only input into the first substrate.
[0028] According to another embodiment, in the first loading phase, the second substrate can be loaded on the back side with first laser radiation by means of a first laser device, and in the second loading phase, the first substrate can be loaded with second laser radiation by means of a second laser device. This offers the advantage that no costly deflection devices or radiation conduction devices are required, since the second substrate can be loaded, for example, from below in the first loading phase and the first substrate can be loaded from above in the second loading phase. Thus, the loading with the first laser radiation can be carried out in a simple manner and method not only in the first loading phase but also in the second loading phase.
[0029] At least by means of the first laser device, the activation of a process gas can be carried out or supported in the first loading phase. In particular, the process gas can be heated by means of at least the first laser radiation. As process gases, for example but by no means exhaustively, argon, oxygen, nitrogen, hydrogen or helium can be used. The process gas can be used to achieve a low-reactive and / or reducing environment. The process gas can also be used to discharge reactive gases after and / or before a process step.
[0030] In a second aspect, the invention relates to a laser system for loading at least one substrate with laser energy, wherein the laser system comprises the following:
[0031] - at least one first laser device that emits first laser radiation, and - at least one second laser device, wherein the second laser device emits laser radiation having a wavelength different from that of the first laser radiation, and
[0032] - a control device that is configured to activate the second laser device, wherein the control device has a temperature sensor and / or a time sensor.
[0033] Thus, in a first loading phase, at least one substrate in the substrate stack can be loaded with a first laser radiation on the back side by means of a first laser device, and in a second loading phase, at least one substrate in the substrate stack can be loaded with a second laser radiation by means of a second laser device in order to cause electrical contact of the facing joining surfaces of the first substrate and the second substrate. As already described for this method, due to the preheating of the joining partners, in particular of the substrate loaded with the first laser radiation in the first loading phase, the absorption capacity of the joining partners can be increased, so that the power of the laser device used in the second loading phase can be reduced with respect to such devices and methods having only one loading phase. The first laser device can already preheat the substrate and the solder, however the solder is not yet melted. During the second loading phase, during which at least one substrate in the substrate stack is loaded with the second laser device, the electrical contact of the facing joining surfaces of the first substrate and the second substrate takes place, wherein the solder is melted for the contact. By means of a temperature sensor and / or a time sensor, the control device can activate the second laser device, that is to say control the transition from the first loading phase to the second loading phase. By means of the temperature sensor, the transition from the first loading phase to the second loading phase can be controlled according to the temperature of the substrate and / or according to the temperature of the solder. By means of the time sensor, the control device can activate the second laser device according to the laser energy in one of the input substrates and / or according to the duration of the first loading phase, thus controlling the transition from the first loading phase to the second loading phase.
[0034] It is conceivable that the laser system comprises at least one further laser device, wherein the further laser device can emit a further laser radiation, which has a different wavelength from the first laser radiation and / or the second laser radiation. Preferably, the laser system can have a third laser device, wherein the third laser device can emit a third laser radiation, and wherein the third laser radiation has a different wavelength from the first laser radiation and / or the second laser radiation. Loading the joining partners with the third laser radiation can take place in a third loading phase. In addition to the third laser device, the laser system can have a fourth laser device, wherein the fourth laser device can emit a fourth laser radiation, and wherein the fourth laser radiation has a different wavelength from the first laser radiation, the second laser radiation and / or the third laser radiation. Loading the joining partners with the fourth laser radiation can take place in a fourth loading phase. The laser system can comprise any number of further laser devices.
[0035] The first laser device can have an ultraviolet laser (UV laser) and thereby emit UV laser radiation. The second laser device can have a near-infrared laser (NIR laser) and thereby emit NIR laser radiation. It is known that an ultraviolet laser emits laser radiation in the wavelength range from 200 nm to 400 nm. It is also known that a near-infrared laser, also known by the name Near-Infrared-Laser (NIR), emits laser radiation in the wavelength range from 785 nm to 1550 nm. It has been recognized within the scope of the present invention that the ultraviolet laser and the laser radiation emitted thereby are particularly well-suited for preheating the connecting fitting. The near-infrared laser, whose emitted laser radiation is in a wavelength range different from that of the UV laser, is advantageously suited for melting the solder for the contact joint surface in the second loading phase.
[0036] It is also conceivable that the first laser device has a diode laser as the radiation source and the second laser device has a pulsed laser as the radiation source, such that special advantages resulting from the implementation of the method according to the invention have been taken into account when selecting the laser devices, namely that for the first laser device, a radiation source with a relatively low power, for example, is used, which only has to be sufficient to bring the connecting fitting to a temperature level with increased absorption capacity, and the second laser device is configured as a "power laser" compared to the first laser device.
[0037] The laser system can include a joining tool for positioning and joining a first substrate on a second substrate. Within the joining tool, a beam channel for the first laser radiation and / or for the second laser radiation can be configured. With the aid of the joining tool, the first substrate can be positioned with its joint surface relative to the joint surface of the second substrate. For this purpose, the joining tool can have a receiving portion for detachably fixing the first substrate at the joining tool. With the aid of the receiving portion, the first substrate can be received and positioned relative to the second substrate, in particular forming an overlapping state with the second substrate. It is also conceivable that pressure can be applied to the first substrate with the joining tool in order to improve the connection between the first substrate and the second substrate. Since a beam channel for the first laser radiation and / or the second laser radiation is configured within the joining tool, the loading of at least one substrate can be carried out in a simple manner and method through the joining tool. Therefore, the equipment can be constructed with less expense, and the laser radiation applied through the beam channel of the joining tool can be directly applied to the back side of the substrate fastened at the joining tool. Therefore, it is not necessary to consider additional laser devices or additional beam channels separately formed from the joining tool in the surrounding area of the connecting fitting, whereby the joining tool can move significantly more simply because there is no need to consider conflicts with additional beam channels. In other words, significantly more space is provided for the joining tool, whereby the movement stroke and position deviation can be minimized.
[0038] A temperature sensor for detecting the radiant temperature can be arranged in the optical path of the reflected radiation of the first substrate, the second substrate and / or the solder. The temperature sensor can be configured as an infrared sensor, preferably as a pyroelectric infrared sensor. Thus, the temperature of the connecting fitting from which the reflected radiation is to be detected can be measured contactlessly. It is conceivable that the reflected beam originally obtained from the laser radiation loading is used for temperature measurement by means of the infrared sensor.
[0039] The temperature sensor can be arranged within the laser system such that the optical path of the reflected radiation designed for temperature measurement and the optical paths of the first laser radiation and the second laser radiation extend at least partially simultaneously in the beam path. Thereby, it is possible to advantageously shield all optical paths from the environment in the case of constructing only one beam path. Preferably, the beam path in which the optical path of the reflected radiation and the optical paths of the first laser radiation and the second laser radiation extend at least partially simultaneously can be formed within the joining tool. The infrared sensor can be arranged within the joining tool at the end of the beam path spaced apart from the substrate. The end of the beam path facing the substrate can be formed by a receiving portion which can be used to receive the first substrate. However, it is also conceivable that the optical path of the reflected radiation and the optical path of the first laser radiation extend at least partially simultaneously in a common beam path, while the optical path of the second laser radiation extends in a separate beam path.
[0040] The laser system can have a substrate support on which the back side of at least one of the substrates can be fastened. Preferably, the back side of the second substrate can be fastened on the substrate support. Depending on the fastening of the back side of one of the substrates on the substrate support, the positioning of the first substrate relative to the second substrate can be simplified. Preferably, the first substrate or the second substrate is held form-fittingly on the substrate receiving portion such that the underside of the held substrate abuts against the substrate receiving portion. It is also conceivable that the substrate to be held is held on the substrate receiving portion by generating a holding force. In order to generate the holding force, negative pressure loading of the substrate abutting on the substrate receiving portion can be carried out. Thus, the substrate receiving portion can realize a positioning receiving portion for the substrate.
[0041] An optical window can be introduced into the substrate support, and the optical window has an optically transparent window body portion to allow laser radiation and / or reflected radiation to pass through unobstructed into and / or out of at least one substrate. Within the scope of the present invention, the term "optical window" refers to an optically transparent plate, which is typically designed such that it provides maximum transmission of optical radiation, preferably laser radiation, within a specific wavelength range, and at the same time reduces reflection and absorption. In addition, the optical window can act as a thermal insulator so that the maximum possible amount of heat can be transmitted through the optical window. The optical window can be arranged in the optical path of one of the laser radiations and / or in the optical path of the reflected radiation detectable by means of a temperature sensor. In other words, the first laser radiation, the second laser radiation and / or the reflected radiation can penetrate the optically transparent window body portion of the optical window. By means of the optical window, additional laser radiation can be introduced into the substrate, in particular into the underside of the second substrate, and / or the reflected radiation can be reflected and detected through the optical window. Thus, it is possible to load laser energy through the optical window via the underside of the second substrate, especially during the first loading phase. In addition, the first substrate to be arranged on the second substrate can be positioned in a simple manner and method without considering the second laser device, and thus significantly more space is provided for the joining tool due to the application of the second laser radiation from below onto the connecting fitting. Therefore, it is also possible to minimize the travel required, for example, when changing or orienting the joining tool, the first laser device and / or the detection device above the connecting fitting, thereby preventing position deviations during the joining process and / or during the positioning phase.
[0042] The bonding tool can have a receiving part with a negative pressure device for applying negative pressure to the first substrate, where the first substrate can be fastened to the opening of the pressure chamber of the negative pressure device. The first substrate is preferably detachably fastened to the opening of the pressure chamber of the negative pressure device, and the substrate can be detached by canceling the negative pressure. By fastening the substrate to the bonding tool by means of negative pressure, the substrate can be carefully held at the bonding tool, especially without deformation, and positioned relative to the second substrate. A negative pressure can be formed in the pressure chamber of the first substrate at its opening, such that the negative pressure is applied to the substrate and the substrate is held at the receiving part. The pressure chamber can have at least one side wall part, and the other wall parts enclosing the pressure chamber can be formed by the optical window and the first substrate. That is to say, opposite to the opening of the pressure chamber, the optical window can be arranged at a distance from the second substrate. Advantageously, for positioning, it is sufficient that only the side wall part of the pressure chamber abuts against the substrate, whereby the substrate can be carefully held again and deformation occurring when the optical window abuts directly against the substrate can be prevented. Therefore, the following possibility is also provided, that a three-dimensional substrate is fixed at the bonding tool. It has proven to be particularly advantageous that the side wall part of the receiving part abuts against the back side of the first substrate. Thereby, the laser radiation emitted by the receiving part onto the first substrate can be focused onto the first substrate, and for example, surface tension or ablation of the second substrate surrounding the substrate can be excluded. It is conceivable that the negative pressure device of the receiving part also generates a negative pressure by means of which the second substrate can be held on the substrate support part. Therefore, structural space can also be advantageously saved, because the substrate support part and the receiving part jointly utilize the negative pressure device.
[0043] The beam channel extending at least partially within the bonding tool can be at least partially arranged within the pressure chamber, and / or the pressure chamber can form at least one section of the beam channel. Preferably, the pressure chamber forms the last section of the beam channel, that is to say, the section of the beam channel abutting against the substrate.
[0044] The laser system can include a radiation conduction device having at least one mirror and / or lens for conducting the laser radiation to one of the substrates. In particular, when two laser radiations are to be conducted through a single beam channel, the radiation conduction device can have at least one semi-transparent optical mirror. Subsequently, the laser radiation of one of the two laser devices can penetrate the semi-transparent mirror, such that the laser radiation hits the back side of the substrate, and the laser radiation of the other laser device is deflected by the semi-transparent mirror, such that the optical path of the other laser radiation is also deflected onto the back side of the substrate.
[0045] It goes without saying that the embodiments and examples mentioned above and those to be described below can be implemented not only individually but also in any combination with each other without departing from the scope of the present invention. It is also self-evident that the embodiments and examples mentioned above and those to be described below relate to the method according to the present invention in an equivalent or at least similar manner and method, and are not separately mentioned for the said method.
[0046] Embodiments of the present invention are schematically illustrated in the drawings and are described below by way of example. Description of the Drawings
[0047] The drawings show:
[0048] Figure 1 showing a first embodiment of a laser system according to the present invention;
[0049] Figure 2 showing a second embodiment of a laser system according to the present invention; and
[0050] Figure 3 showing a third embodiment of a laser system according to the present invention. Detailed Description of the Invention
[0051] Figure 1 showing an embodiment of a laser system 01 according to the present invention, the laser system being adapted to apply laser energy to at least one of substrates 02, 03, wherein the laser system 01 is adapted to perform a method according to the present invention for electrically contacting the joining surfaces of the two substrates 02, 03. In Figure 1 the illustration shown, the first substrate 02 is disposed on top of the second substrate 03 in an overlapping state with the second substrate 03 by means of a bonding tool 11. A solder 07 is provided between the first substrate 02 and the second substrate 03. The solder 07 is provided at the joining surfaces of the substrates 02, 03, wherein the joining surfaces are respectively formed on the front sides of the substrates 02, 03. In contrast, the back side 31 of the second substrate 03 faces away from the solder 07 and can be positioned on a substrate support 12 not shown here. As in Figure 1 and Figure 3As shown, the back side 21 of the first substrate 02 can be abutted against the receiving portion 14 of the bonding tool 11. A negative pressure can be applied to the first substrate 02 for fixation at the receiving portion 14, and the negative pressure is formed within the pressure chamber 15, which is connected via a pressure pipeline 17 to a negative pressure pump of a negative pressure device (not shown here). It can be seen that the pressure chamber 15 is formed by the side wall portion of the bonding tool 11 and the optical window 13 or the receiving portion 14 of the bonding tool, wherein the opening of the pressure chamber 15 is formed by the opening of the receiving portion 14 and can be closed by the first substrate 02, so that when a negative pressure is applied to the pressure chamber 15, a negative pressure is also applied to the substrate 02 for fixation and positioning at the receiving portion 14. Through the optical window 13 provided within the beam channel 10 provided in the bonding tool 11, the back side 21 of the first substrate 02 can be irradiated with the first laser radiation 41 emitted by the first laser device 04 and the second laser radiation 51 emitted by the second laser device 05. Therefore, during the first loading stage, the first substrate 02 can be irradiated with the first laser radiation 41, and during the second loading stage, the second substrate 02 can be irradiated with the second laser radiation 51. It is also conceivable that during the second loading stage, the first substrate 02 is irradiated with the first laser radiation 41 and the second laser radiation 51. In order to perform the transformation between the loading stages or activate the second laser device 05 and trigger the irradiation with the second laser radiation 51, a control device 06 and a temperature sensor 08 are included. The temperature sensor 08 is arranged in the beam channel 10 such that the temperature sensor 08 detects the reflected radiation 81 reflected by the back side 21 of the first substrate 02 and can transmit the temperature measurement value to the control device 06. For transmitting the energy supply and / or the temperature measurement value of the temperature sensor, the temperature sensor 08 and the control device 06 are connected via a data connection 18 shown by a dotted line. In addition, the control device 06 can be connected to the first laser device 04 and the second laser device 05 via a data connection 18 shown by a dotted line. In addition, the control device 06 has a time sensor (not shown here) in addition to the temperature sensor 08. The control device 06 is configured to control the transformation from the first loading stage to the second loading stage according to the duration of the first loading stage, according to the laser energy input into the first substrate 02, or according to the temperature of the first substrate 02. It is also conceivable that the control device 06 is configured to determine the reflected radiation received by the temperature sensor 08 of the first substrate according to the temperature of the first substrate 02 and determine the temperature of the solder 07 according to the characteristics of the first substrate 02. It can also be seen that the optical path 42 of the first laser radiation 41 emitted by the first laser device 04 is turned towards the direction of the first substrate 02 by means of the semi-transparent mirror 161 of the radiation conduction device 16. While the optical path 52 of the second laser radiation 51 emitted by the second laser device 05 extends through the semi-transparent mirror 161 of the radiation conduction device 16 without being turned towards the direction of the first substrate 02. In order to focus the laser radiation, the radiation conduction device 16 also has a lens 162.
[0052] Figure 2 Shows a second embodiment of a laser system 01 according to the present invention, the laser system having a first laser device 04 and a second laser device 04. It can be seen that the first laser radiation 41 emitted by the first laser device 04 and following the optical path 42 is not only focused on the back side 21 of the first substrate 02, but also irradiates the area adjacent to the substrate 02. Therefore, the first laser radiation 41 irradiates not only the first substrate 02, but also the second substrate 03, thereby preheating the environment of the first substrate 02 as well as the second substrate. In addition, different from the first embodiment, the temperature sensor 08 is arranged such that it detects the reflected radiation 81 from the solder 07, so that the temperature of the solder 07 can be measured non-contactingly. The radiation conduction device 16 having the semi-transparent mirror 161 redirects the first laser radiation 41 along the optical path 42 and the second laser radiation 51 having the optical path 52 and emitted by the second laser device 05 is focused on the back side 21 of the first substrate 02 by means of the lens 162. The radiation conduction device 16 may have additional lenses not visible here to focus the first laser radiation 41 on the connection fitting and the defined environmental area. That is, the laser system 01 shown in Figure 2 can preheat the first substrate 02, the second substrate 03 and the environment of the first substrate 02 by means of the first laser radiation 41 in the first loading stage and load the second laser radiation 52 on the first substrate 02 in the second loading stage, so that the solder 07 melts and the electrical contact of the facing connection surfaces of the first substrate 02 and the second substrate 03 is made. The control device 06 may additionally have a time sensor in addition to the temperature sensor 08, so that the control device 06 can control the transformation from the first loading stage to the second loading stage according to the duration of the first loading stage, according to the laser energy in one of the input substrates 02, 03, or according to the temperature of the solder 07.
[0053] In Figure 3 the embodiment of the laser system 01 according to the present invention shown corresponds as much as possible to the embodiment shown in Figure 1 However, the difference is that the first laser radiation 41 emitted by the first laser device 04 irradiates the back side 31 of the second substrate 03. For this purpose, the second substrate 03, in particular the back side 31 of the second substrate 03, is positioned on the substrate support 12 such that the back side 31 of the substrate 03 abuts against the optical window 13 introduced into the substrate support 12. Through the optical window 13, the optical path is redirected by means of the mirror 161 of the radiation conduction device 16. Loading the first substrate 02 in the second loading stage according to Figure 3It is carried out from above the connecting fitting. The first substrate 02 can be positioned relative to the second substrate 03 by means of the joining tool 11. The laser radiation 51 follows the optical path 52 through the lens 162 for focusing and the optical window 13 of the joining tool 11 to the back side 21 of the first substrate 02. A negative pressure can be applied to the pressure chamber 15 formed at the end of the joining tool 11 pointing to the first substrate 02 via the pressure line 17 so that the first substrate 02 is fixed at the receiving part 14 of the joining tool 11. In order to shield the second laser radiation 51, the second laser radiation 51 is conducted through the beam channel 10 of the joining tool 11 after focusing. The control device 06 is in turn used to control the change between the first loading phase and the second loading phase and can have a time sensor (not shown here) in addition to the temperature sensor 08 shown here. The temperature sensor 08 detects the reflected radiation 81 that is emitted from the back side 21 of the first substrate 02. The temperature sensor 08 can be arranged at or in the region of the laser device 05. The control device 06 can control the change from the first loading phase to the second loading phase according to the duration of the first loading phase, according to the laser energy input into the second substrate 03 by means of the first laser device 04, or according to the temperature of the first substrate 02. According to the Figure 3 illustrated embodiment, different from Figure 1 is that a costly radiation conduction device 161 is not provided above the connection pairing member. In addition, the joining tool 11 provides significantly more free space during the movement of the joining tool 11 because the first laser device 04 is arranged below the substrate support 12 and thus not in the movement space of the joining tool 11.
Claims
1. A method for electrically contacting connection surfaces of two substrates (02, 03), wherein the first substrate (02) is electrically and mechanically connected with the connection surface of the second substrate (03) with its connection surface facing the second substrate (03), wherein - positioning the first substrate (02) with its connection surface facing the connection surface of the second substrate (03), and - in a first loading phase, loading at least one of the substrates (02, 03) with a first laser radiation (41) on the back side by means of a first laser device (04), - in a second loading phase, at least one of the substrates (02, 03) is loaded with a second laser radiation (51) by means of a second laser device (05) and a solder (07) disposed between the substrates (02, 03) is melted at least to such an extent that the connecting surfaces of the first substrate (02) and the second substrate (03) facing each other are brought into electrical contact, and - wherein in the first loading phase a first laser radiation having a different wavelength than the second laser radiation is loaded, and - Controlling the change from the first loading phase to the second loading phase by means of a control device (06) depending on the duration of the first loading phase, depending on the laser energy input into one of the substrates (02, 03), depending on the temperature of one of the substrates (02, 03), and / or depending on the temperature of the flux (07).
2. The method according to claim 1, It is characterized in that By means of a temperature sensor (08), preferably configured as an infrared pyrometer, the radiation temperature of at least one of the substrates (02, 03) and / or the flux (07) is measured at least during the first loading phase, and by means of the control device (06), the change from the first loading phase to the second loading phase is controlled according to the radiation temperature of one of the substrates (02, 03) and / or according to the radiation temperature of the flux (07).
3. The method according to claim 1 or 2, It is characterized in that In the second loading stage, in addition to loading with the first laser device (04), loading is also performed with the second laser device (05).
4. The method according to claim 2 or 3, It is characterized in that By means of a temperature sensor (08), during the second loading phase, the radiant temperature of at least one of the substrates (02, 03) and / or the flux (07) is measured, and the second loading phase is terminated according to the radiant temperature of at least one of the substrates (02, 03) and / or the flux (07).
5. The method according to any one of the preceding claims, It is characterized in that In standby mode, the first laser device (04) is switched on in a clocked manner for a defined switch-on period and is switched into operating mode by means of the control device (06) as a function of the current temperature of at least one of the substrates (02, 03) measured by means of the temperature sensor (08).
6. The method according to any one of the preceding claims, In the first loading phase, the first laser radiation (41) is applied to the first substrate (02) on the back side by means of the first laser device (04), And in a second loading phase, the first substrate (02) is loaded with the second laser radiation (51) on the back side by means of the second laser device (05).
7. The method according to any one of the preceding claims, It is characterized in that In the first loading phase, the first substrate (02) is loaded on the back side and the second substrate (03) is loaded on the front side with the first laser radiation (41) by means of the first laser device (04), And in the second loading phase, the first substrate (02) is loaded with the second laser radiation (51) on the back side by means of the second laser device (05).
8. The method according to any one of the preceding claims, It is characterized in that In the first loading phase, the second substrate (03) is loaded on the back side with the first laser radiation (41) by means of the first laser device (04), And in the second loading phase, the first substrate (02) is loaded with the second laser radiation (51) by means of the second laser device (05).
9. The method according to any one of the preceding claims, It is characterized in that At least in the first loading phase the process gas is activated.
10. A laser system (01) for loading at least one substrate (02, 03) with laser energy, wherein the laser system comprises the following: - at least one first laser device (04), and - at least one second laser device, wherein said second laser device emits laser radiation having a wavelength different from said first laser radiation, and A control device (06) configured to activate the second laser device (05), wherein the control device (06) has a temperature sensor (08) and / or a time sensor.
11. The laser system according to claim 10, It is characterized in that The first laser device (04) has an ultraviolet laser and the second laser device (05) has a near infrared laser.
12. The laser system according to claim 10 or 11, It is characterized in that It comprises a joining tool (11) for positioning and joining the first substrate (02) to the second substrate (03), wherein a beam channel (10) for an optical path (42) of the first laser radiation (41) and / or an optical path (52) of the second laser radiation (51) is formed within the joining tool (11).
13. The laser system according to any one of claims 10 to 12, It is characterized in that The temperature sensor (08) is provided for detecting the radiation temperature in the beam path of the reflected radiation (81) of the first substrate (02), the second substrate (03) and / or the solder (07) and is designed as an infrared sensor, preferably as a pyroelectric infrared sensor.
14. The laser system according to any one of claims 10 to 13, It is characterized in that It comprises a substrate support part (12), on which the back side of at least one of the substrates (02, 03) can be fixed, preferably the back side (31) of the second substrate (03) can be fixed.
15. The laser system according to claim 14, It is characterized in that An optical window (13) having an optically transparent window portion is introduced into the substrate support portion (12) to allow laser radiation (41, 51) and / or reflected radiation (81) to pass through unimpeded into at least one substrate (02, 03) and / or to leave at least one substrate (02, 03), wherein the optical window (13) is arranged in the optical path (42, 52) of one of the laser radiations (41, 51) and / or in the optical path of reflected radiation (81) that can be detected by means of the temperature sensor (08).
16. The laser system according to any one of the preceding claims, It is characterized in that The joining tool (11) has a receiving portion (14) having a vacuum device for applying vacuum to the first substrate (02), wherein the first substrate (02) can be fixed at an opening of a pressure chamber (15) of the vacuum device.