Method and system for separating an assembly

Abstract

The invention relates to a method for separating an assembly (1), wherein the assembly (1) comprises at least one component (2) and a circuit board (3), wherein the at least one component (2) is connected to the circuit board (3) by means of at least one solder connection (4), wherein the method has at least the following steps: - thermally conditioning the at least one solder connection (4), comprising the steps of: o heating the at least one solder connection (4), o after heating, cooling the at least one solder connection (4) at a cooling rate such that the at least one solder connection (4) becomes rigid, wherein the cooling rate is greater than 6°C / s, - separating the at least one component (2) from the circuit board (3) by way of the application of a force (F) such that there is a brittle fracture of the at least one solder connection (4). The invention also relates to a system (5) for separating an assembly (1).

Description

[0001] Method and system for separating an assembly

[0002] The invention relates to a method for separating an assembly, wherein the assembly comprises at least one component and a circuit board, wherein the at least one component is connected to the circuit board by means of at least one solder connection. The invention further relates to a system for separating an assembly.

[0003] A solder joint is obtained by a soldering process which creates a material-tight connection using a thermal process.

[0004] Printed circuit boards with components soldered to them are used in a wide variety of automation field devices manufactured and distributed by the Endress+Hauser Group. Field devices are used to determine and / or monitor process variables. In principle, field devices refer to all devices that are used close to the process and that provide or process-relevant information. These include, for example, level measuring devices, flow measuring devices, pressure and temperature measuring devices, pH / redox potential measuring devices, conductivity measuring devices, etc., which measure the corresponding process variables such as level, flow, pressure, temperature, pH value or conductivity. Field devices often have a sensor unit that is in contact with a process medium, in particular at least temporarily and / or at least partially, and which serves to generate a signal dependent on the process variable.Furthermore, these often have an electronic unit arranged in a housing, wherein the electronic unit serves to process and / or forward signals generated by the sensor unit, in particular electrical and / or electronic signals.

[0005] Electronic units often comprise at least one printed circuit board with components soldered to it using one or more soldering processes. Various soldering processes are known from the prior art, the selection of which is determined by the application, in particular the components to be soldered and / or the solder. A soldering process widely used in industrial production lines for the manufacture of printed circuit boards is reflow soldering, in which surface-mounted components (SMD components for short) are soldered directly onto designated contact surfaces. For this purpose, the SMD components are mechanically placed onto the contact surface of the printed circuit board coated with solder paste using placement machines and then soldered together with a reflow soldering process in a reflow soldering oven. This creates a multitude of solder connections simultaneously.

[0006] In addition to SMD components, there are special components that have larger dimensions due to their function. These components are preferably designed as through-hole technology components – THT components for short. THT components are typically soldered using a wave soldering process. The circuit board is moved over a so-called solder wave, which is created by pumping liquid solder through a narrow gap.

[0007] What both reflow soldering and wave soldering have in common is that the solder (or the soldering material) is exposed to a so-called temperature profile during the soldering process. This refers to a temperature-time progression during soldering. The temperature profile typically includes preheating the solder and / or the soldering material, reaching a maximum temperature that is above the liquidus temperature of the solder, and subsequent cooling. Current technology strives to achieve low cooling rates in order to produce solder joints of sufficiently high quality, for example, high-strength solder joints with sufficiently high mechanical resistance.

[0008] However, such solder connections have the disadvantage that the solder connection(s) must be remelted to remove the component from the contact surface. This is energy-intensive, and it can also generate toxic fumes. To protect the environment and improve the recycling of printed circuit boards, it is desirable to provide a simpler method for removing the components. This applies particularly to printed circuit boards used in devices with a comparatively short lifespan, such as between 2 and 10 years.

[0009] The invention is based on the object of specifying a method and a system for separating a component from the printed circuit board.

[0010] The object is achieved according to the invention by a method according to claim 1 and a system according to claim 6.

[0011] With regard to the method, the object is achieved according to the invention by a method for separating an assembly, wherein the assembly comprises at least one component and a printed circuit board, wherein the at least one component is connected to the printed circuit board by means of at least one solder connection, wherein the method comprises at least the following steps:

[0012] - performing a thermal conditioning of the at least one solder joint, comprising the steps of: o heating the at least one solder joint, o after heating, cooling the at least one solder joint at a cooling rate such that the at least one solder joint solidifies, wherein the cooling rate is greater than 6°C / s,

[0013] - Separating the at least one component from the circuit board by applying a force so that a brittle fracture of the at least one solder connection occurs.

[0014] According to the invention, an existing solder joint of an assembly is thermally conditioned in such a way that it becomes brittle. The thermal conditioning, i.e. the heating and rapid cooling of the solder joint, leads to a change in the mechanical properties, in particular the plastic properties, of the at least one solder joint. As a rule, soldering processes are designed in such a way that a solder joint that is stable over a longer period of time is obtained. The solder joint produced in the soldering process is therefore typically non-brittle or ductile, whereby non-brittle and ductile in the sense of this application mean that the solder joint cannot be separated by brittle fracture. In fracture mechanics, brittle fracture refers to a sudden material failure. Brittle materials orSolder joints are characterized in the stress-strain diagram by a steep rise of the Hooke's line, at the end of which fracture occurs without plastic deformation.

[0015] In order to create a solder joint that can be separated by brittle fracture, the existing solder joint can be subsequently thermally conditioned. Heating the at least one solder joint can result in a liquidus temperature of the at least one solder joint being exceeded. However, this is not a requirement; rather, heating can also involve heating the at least one solder joint to temperatures below a liquidus temperature of the at least one solder joint, in particular, for example, at least 20 °C, in particular at least 40 °C, below the liquidus temperature of the at least one solder joint. The decisive factor in conditioning is the rapid cooling of the at least one solder joint at a cooling rate of at least 6 °C / s. At this cooling rate, the properties of the at least one solder joint change in such a way that a brittle-fractured solder joint is created.This is then fractured brittlely under the application of force, so that the at least one component is separated from the circuit board. The process step of separating the at least one component from the circuit board can be carried out, in particular, at room temperature. Thermal conditioning of the at least one solder connection thus ensures that the at least one component can be easily separated from the circuit board.

[0016] In the case where the at least one component has multiple solder connections or where the circuit board is connected to multiple components, a majority of the components can advantageously be separated from the circuit board essentially simultaneously by means of brittle fracture under the action of a force on the respective solder connection. In particular, a cooling rate of greater than 8°C / s, in particular greater than 10°C / s, is used. The cooling rate can be less than 507s.

[0017] In one embodiment, the cooling rate is adjusted by supplying a liquid medium to the at least one solder joint. The liquid medium can be, in particular, liquid nitrogen, but other liquid media are also possible, such as water or oil, or media containing water or oil. The liquid medium serves, in particular, as a coolant.

[0018] In a further embodiment, a force of less than 40 N, in particular less than 30 N, in particular less than 20 N, in particular less than 10 N, is used to separate the at least one component from the circuit board.

[0019] Preferably, the at least one component is separated from the circuit board by means of twisting, vacuum, ultrasound, dry ice, an air knife, free fall, sudden mechanical stress, and / or a brush. Twisting refers in particular to deforming or bending the circuit board. An air knife is a nozzle from which a high-speed air jet emerges. With regard to free fall, a drop device can be used, into which the assembly is inserted and dropped over a defined distance under the influence of gravity until the assembly strikes an impact surface. The brush can be used to shear the at least one component from the circuit board.

[0020] With regard to the system, the object underlying the present application is further achieved by a system for separating an assembly, wherein the assembly comprises at least one component and a printed circuit board, wherein the at least one component is connected to the printed circuit board by means of at least one solder connection, with

[0021] - a heating region designed to heat the at least one solder joint, - a cooling region designed to cool the at least one solder joint after the heating process at a cooling rate such that the at least one solder joint solidifies, wherein the cooling rate is greater than 6°C / s,

[0022] - a separation region which is designed to separate the at least one component from the circuit board by means of the action of a force, so that a brittle fracture of the at least one solder connection occurs.

[0023] In the system according to the invention, an assembly is thermally conditioned and then separated into its components, i.e., the circuit board and component(s), by means of brittle fracture. The system is designed such that the assembly first passes through the heating zone, then the cooling zone, and finally the separation zone. The system according to the invention is particularly suitable for carrying out the method according to the invention.

[0024] In one embodiment, the heating area has at least one heating element.

[0025] In a further embodiment, the cooling area has at least one heat exchanger.

[0026] In one embodiment, the cooling zone has an opening through which a liquid medium can be fed into the cooling zone. The liquid medium can be, in particular, liquid nitrogen, but other liquid media are also possible, such as water or oil, or media containing water or oil.

[0027] Preferably, the system further comprises a transport means for receiving the printed circuit board, wherein the transport means is designed to transport the assembly through the heating area, the cooling area, and the separation area. The transport means can be designed in the form of a conveyor belt. The conveyor belt can be designed as a single piece or in the form of several modular sections. In particular, the transport means can be designed to transport the printed circuit board and the at least one component separately in the separation area after the at least one component has been separated from the printed circuit board. For example, the transport means can have two areas, one of which is designed to transport the printed circuit board and the other to transport the at least one component.

[0028] A further embodiment provides that the separating region has a separating agent which is designed to act on the force on the at least one solder connection.

[0029] In particular, the separating means is a brush, an air blade, an ultrasonic device, a drop device, a means for generating a negative pressure and / or a means for twisting the circuit board.

[0030] The invention will be explained in more detail below with reference to the following figures. They show:

[0031] Fig. 1a-b: schematic representation of the assembly before and after separating at least one component from the circuit board.

[0032] Fig. 2: an embodiment of a system according to the invention.

[0033] The method according to the invention and the system according to the invention are applicable to assemblies comprising at least one component and a printed circuit board, which are connected by means of at least one solder connection.

[0034] An assembly 1 is manufactured using a soldering process, e.g., reflow soldering. A solder, e.g., in the form of solder paste, is applied to a designated contact surface of the at least one component 2 or the circuit board 3. The at least one component 2 is then placed on the circuit board 3 and soldered to the circuit board 3 in a thermal process. Such an assembly 1 is schematically illustrated in Fig. 1a. After its manufacture, the assembly 1 can be used in a wide variety of electrical or electronic devices, such as field devices, measuring devices, laboratory devices, or consumer devices. At the end of the device's life cycle, it is generally disposed of. To recycle the assembly 1, it must be removed from the device and separated into its individual components, which requires the separation of at least one solder connection 4.

[0035] The method according to the invention provides that the at least one solder connection 4 of the assembly 1 is thermally conditioned by first heating it and then cooling it at a cooling rate of at least 6°C / s. Due to the high cooling rate, the mechanical properties of the at least one solder connection 4 change, so that it acquires brittle fracture properties. After thermal conditioning, the at least one component 2 is separated from the circuit board 3 under the action of a force F, so that a brittle fracture occurs at the at least one solder connection 4. During this separation step, a force F of less than 40 N, in particular less than 30 N, in particular less than 20 N, in particular less than 10 N, is used. Fig. 1 b shows a schematic representation of the assembly 1 after the separation step. The solder connection 4 has undergone brittle fracture; the at least one component 2 and the circuit board 3 are separate.

[0036] An embodiment of the system 5 according to the invention, in which the method according to the invention can be used, is shown in Fig. 2. The system 5 has three areas: a heating area 6 for heating the at least one solder connection 4, a cooling area 7 for cooling the at least one solder connection 4 and a separating area 8 for separating the at least one component 2 from the circuit board 3. The assembly 1 is placed on an optional transport means 12, which is designed to transport the assembly 1 through the heating area 6, the cooling area 7 and the separating area 8. The assembly 1 first passes through the heating area 6, which optionally has two heating elements 9 for heating the at least one solder connection 4.

[0037] The assembly 1 is then transported to the cooling area 7, which has two optional heat exchangers 10. The heat exchangers 10 are designed to cool the at least one solder joint 4 at a cooling rate of at least 6°C / s. The cooling area 7 can further have an opening 11 through which a liquid medium can be fed into the cooling area 7. The liquid medium is designed to assist the cooling process.

[0038] After the at least one solder connection 4 has been cooled and thermally conditioned in the cooling area 7, the assembly 1 is introduced into the separation area 8. There, for example, a separation means 13 is arranged, which is designed to exert or act on a force F on the at least one solder connection 4, so that the at least one solder connection 4 fractures brittlely and the at least one component 2 is separated from the circuit board 3. The separation means 13 can be a brush designed to shear the at least one component 2 from the circuit board 3. The separation means 13 can be an air blade for generating a high-speed air flow, an ultrasonic device for generating ultrasonic waves, a means for generating a negative pressure, such as a pump, a dropping device for dropping the assembly in a defined manner and causing it to impact an impact surface, and / or a means for twisting the assembly.

[0039] List of reference symbols

[0040] 1 assembly

[0041] 2 Component 3 Circuit board

[0042] 4 Solder connection

[0043] 5 Appendix

[0044] 6 Heating area

[0045] 7 Cooling area 8 Separation area

[0046] 9 Heating element

[0047] 10 heat exchangers

[0048] 11 Opening

[0049] 12 Means of transport 13 Release agents

[0050] F Force

Claims

Patent claims 1 . Method for separating an assembly (1), wherein the assembly (1) comprises at least one component (2) and a printed circuit board (3), wherein the at least one component (2) is connected to the printed circuit board (3) by means of at least one solder connection (4), wherein the method comprises at least the following steps: - performing a thermal conditioning of the at least one solder joint (4), comprising the steps of: o heating the at least one solder joint (4), o after heating, cooling the at least one solder joint (4) at a cooling rate such that the at least one solder joint (4) solidifies, wherein the cooling rate is greater than 6°C / s, - Separating the at least one component (2) from the circuit board (3) by applying a force (F) so that a brittle fracture of the at least one solder connection (4) occurs.

2. The method according to claim 1, wherein the cooling rate used is a cooling rate of greater than 8°C / s, in particular greater than 10°C / s.

3. Method according to one of claims 1-2, wherein the cooling rate is adjusted by supplying a liquid medium (14) to the at least one solder joint (4).

4. Method according to one of claims 1-3, wherein a force (F) of less than 40 N, in particular less than 30 N, in particular less than 20 N, in particular less than 10 N, is used to separate the at least one component (2) from the circuit board (3).

5. Method according to one of claims 1-4, wherein the at least one component (2) is removed from the circuit board (3) by means of twisting, suppression, ultrasound, dry ice, an air knife, free fall, sudden mechanical stress and / or a brush.

6. System (5) for separating an assembly (1), wherein the assembly (1) comprises at least one component (2) and a printed circuit board (3), wherein the at least one component (2) is connected to the printed circuit board (3) by means of at least one solder connection (4), with - a heating area (6) which is designed to heat the at least one solder connection (4), - a cooling region (7) which is designed to cool the at least one solder joint (4) after the heating process at a cooling rate such that the at least one solder joint (4) solidifies, the cooling rate being greater than 6°C / s, - a separation region (8) which is designed to separate the at least one component (2) from the circuit board (3) by means of the action of a force (F), so that a brittle fracture of the at least one solder connection (4) occurs.

7. System (5) according to claim 6, wherein the heating area (6) has at least one heating element (9).

8. Plant (5) according to one of claims 6-7, wherein the cooling region (7) has at least one heat exchanger (10).

9. Plant (5) according to one of claims 6-8, wherein the cooling region (7) has an opening (11) by means of which a liquid medium (14) can be fed into the cooling region (7).

10. System (5) according to one of claims 6-9, wherein the system (5) further comprises a transport means (12) for receiving the printed circuit board (3), wherein the transport means (12) is designed to transport the assembly (1) through the heating area (6), the cooling area (7) and the separating area (8).

11. System (5) according to claim 10, wherein the transport means (12) is designed to transport the circuit board (3) and the at least one component (2) separately in the separation area (8) after the separation of the at least one component (2) from the circuit board (3).

12. System (5) according to one of claims 6-11, wherein the separating region (8) has a separating means (13) which is designed to act on the force (F) on the at least one solder connection (4).

13. System (5) according to claim 12, wherein the separating means (13) is a brush, an air blade, an ultrasonic device, a drop device, a means for generating a negative pressure and / or a means for twisting the circuit board.

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