Predictive Maintenance – Effective Residue Management through Integrated Filter Monitoring

Convection soldering system VisionXP+ from Rehm Thermal System enables predictive maintenance and safe, stable processes

Optimum soldering results depend not only on the actual melting process of the solder paste. Cooling the assembly to be soldered plays an important role in soldering highly complex electronic components. The filter monitoring – including volume flow control integrated in the convection soldering systems of the Vision series from Rehm Thermal Systems – ensures effective residue management and constant cooling capacity, thereby supporting stable and safe performance of the soldering process.

When the solder paste melts inside the process chamber, process gases are produced which cause contamination of the cooling modules and the fine filter. The volume flow of the cooling process, which should be as constant as possible, is reduced by these contaminants. Less volume flow means less cooling capacity at the same time, which can lead to an increase in the outlet temperature or to a changed cooling gradient at the assemblies. However, for a safe and stable process, the correct run-out temperature and a constant cooling gradient of the soldered assembly are of great importance.

The filter monitoring with active readjustment automatically detects via the integrated control system when the volume flow falls below the level individually set by the customer to meet his production requirements. This is an indication that the filter is about to be changed. Until this change is made, the system automatically readjusts the volume flow by means of active readjustment in order to continue cooling the assemblies within the specified process window by increasing the cooling capacity. For this purpose, the set gas flow rate in the cooling zones is continuously compared with the value actually determined.

The filter monitoring with active readjustment thus guarantees a high level of process reliability and ensures an optimum reflow soldering process with constant flow conditions. In addition, the data from the filter monitoring with active readjustment can be collected and used to predict the next filter replacement with external data analysis programmes.

Attached is a graphic of the volume flow control of the cooling section (graphic: Rehm Thermal Systems).

Rehm Thermal Systems offers various types of cooling for the VisionXP+ convection soldering system

The standard cooling system installed in all Vision convection soldering systems consists of up to four individual cooling modules. These allow a precisely controlled cooling process as well as individual adjustment of the cooling gradient. For the cooling process, a small part of the warm and charged air volume present due to the soldering process is first extracted into the lower part of the system. It is then cleaned over several cooling modules and cooled to the desired temperature (usually below 20 °C). The air is then blown back from above onto the assembly, which results in the cooling. The “closed loop principle” guarantees a closed atmosphere cycle. The standard cooling section consists of active and passive cooling modules. The active cooling modules are supplied with water via a heat exchanger. The cooling filters can be easily cleaned and serviced at the rear of the system: the process chamber does not need to be opened to do this.

Gentle cooling with Power Cooling Unit

For gentle cooling, especially for complex assemblies, an extended cooling section can be connected to the VisionXP+. This can be implemented as an extension to standard cooling zones under a nitrogen atmosphere or as a separate, downstream module (“Power Cooling Unit”) in an air atmosphere for higher cooling performance for insensitive materials. Advantage of the air-cooled variant: while nitrogen is needed in the process section of the convection unit to prevent oxidation, the extended cooling section no longer needs to be flooded with nitrogen, resulting in nitrogen savings.

Underside cooling for uniform cooling from above and below

For particularly massive or large assemblies or boards with product carriers, the VisionXP + can also be equipped with underside cooling. The actual cooling process is identical to that of the standard cooling section, but the extracted, cleaned and cooled air flows not only from above onto the module, but also from below.

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Gradual cooling for energy saving

Rehm also offers an energy-saving cooling variant for the VisionXP+ convection soldering system: the air is extracted at several points rather than just one. This results in gradual cooling and offers significant energy saving potential.

Rehm CoolFlow: reduced energy usage with liquid nitrogen

Along with their partner Air Liquide, Rehm has developed a cooling system (“Rehm CoolFlow”), which uses the nitrogen used for inertia even more efficiently. The -196°C liquid nitrogen releases its energy in the cooling section, then evaporates and can then be used in its gaseous state for inerting the process atmosphere. The cooling water, which previously required high energy use for cooling, including cooling unit and refrigerant, is completely eliminated.

Rehm Thermal Systems offers various types of cooling for the VisionXP+ convection soldering system

The standard cooling system installed in all Vision convection soldering systems consists of up to four individual cooling modules. These allow a precisely controlled cooling process as well as individual adjustment of the cooling gradient. For the cooling process, a small part of the warm and charged air volume present due to the soldering process is first extracted into the lower part of the system. It is then cleaned over several cooling modules and cooled to the desired temperature (usually below 20 °C). The air is then blown back from above onto the assembly, which results in the cooling. The “closed loop principle” guarantees a closed atmosphere cycle. The standard cooling section consists of active and passive cooling modules. The active cooling modules are supplied with water via a heat exchanger. The cooling filters can be easily cleaned and serviced at the rear of the system: the process chamber does not need to be opened to do this.

Gentle cooling with Power Cooling Unit

For gentle cooling, especially for complex assemblies, an extended cooling section can be connected to the VisionXP+. This can be implemented as an extension to standard cooling zones under a nitrogen atmosphere or as a separate, downstream module (“Power Cooling Unit”) in an air atmosphere for higher cooling performance for insensitive materials. Advantage of the air-cooled variant: while nitrogen is needed in the process section of the convection unit to prevent oxidation, the extended cooling section no longer needs to be flooded with nitrogen, resulting in nitrogen savings.

Underside cooling for uniform cooling from above and below

For particularly massive or large assemblies or boards with product carriers, the VisionXP + can also be equipped with underside cooling. The actual cooling process is identical to that of the standard cooling section, but the extracted, cleaned and cooled air flows not only from above onto the module, but also from below.

.

Gradual cooling for energy saving

Rehm also offers an energy-saving cooling variant for the VisionXP+ convection soldering system: the air is extracted at several points rather than just one. This results in gradual cooling and offers significant energy saving potential.

Rehm CoolFlow: reduced energy usage with liquid nitrogen

Along with their partner Air Liquide, Rehm has developed a cooling system (“Rehm CoolFlow”), which uses the nitrogen used for inertia even more efficiently. The -196°C liquid nitrogen releases its energy in the cooling section, then evaporates and can then be used in its gaseous state for inerting the process atmosphere. The cooling water, which previously required high energy use for cooling, including cooling unit and refrigerant, is completely eliminated.

The new ProMetrics monitoring tool from Rehm Thermal Systems offers optimal control and top quality when soldering electronic assemblies

With ProMetrics, Rehm Thermal Systems has developed an instrument for monitoring thermal profiles during soldering. It checks how well the previously created profile corresponds to the required, predefined specifications. The process window index (PWI) ascertained in this way is a statistical measure that quantifies the quality of a thermal process. This is mostly determined by the specification of the solder paste and the most heat-sensitive component. The following applies as a general rule: The lower the PWI, the better the profile and thus the more efficient and stable the process.

The generation of real-time data for each component allows the exact determination of the assembly position and reliably detects any deviations or delays in the soldering system. Process changes can thus be detected immediately. This leads to the greatest possible reliability in the calculation of the temperature profile of an assembly.

By integrating ProMetrics into the ViCON software, errors in data transmission to a higher-level system, such as MES, can be excluded and are available centrally in the MES for each assembly. Uniform logging in ViCON ensures the necessary transparency and traceability. Repeated maintenance of data is not necessary and the susceptibility to errors is significantly reduced.

A representation of the envelope curve visualises any deviations of the soldering profile from the specified parameters. Alarm messages in the ViCON show these deviations from the temperature profile outside the

envelope curve.

In order to be able to use ProMetrics from Rehm Thermal Systems effectively, both software and hardware components are required for optimal quality control of the soldering profile. The Solderstar software with the associated licence dongle is used to record the data. The Solderstar software is integrated into the ViCON and helps with thermal profiling. Using a measurement data logger from Solderstar, temperatures of a reference board are recorded in order to be able to check the process stability of the system. The system is equipped with monitors to record the temperatures; in addition, the temperatures in the heating zones are recorded by sensors.

Temperature profiling with Solderstar equipment

With Solderstar, Rehm Thermal Systems gains from a competent partner boasting many years of expertise in this area for the creation and optimisation of temperature profiles during reflow soldering. The Solderstar PRO thermal profiling systems contain a compact data logger with Solderstar Smartlink connectors. The system transmits live profile data directly to Solderstar’s AutoSeeker software.

ProMetrics can be used for single and dual lane systems and is the first system in the world that is also suitable for vacuums.

The cycle time of the VisionXP+ Vac convection soldering system by Rehm Thermal Systems is defined by the time which is required to complete the vacuum step. This includes the transportation of the product into the vacuum chamber, the closing of the vacuum chamber, the time until the target pressure has been achieved, the dwell time at the target pressure, the ventilation of the chamber and the opening of the chamber. However, productivity can be further increased using a two-track system with central support, scalable vacuum chamber sizes for optimum adaptation to the respective product and an optimised temperature/pressure/time profile. This is possible with the VisionXP+ Vac. With regard to profiling, the ViCON software by Rehm Thermal Systems enables the combined temperature/pressure/time profile to be created in a convenient manner. In this regard, we should not lose sight of the fact that pressure gradients which are too high during the creation of the vacuum may increase productivity but may also lead to process errors such as solder beads or components which slip out of place. Therefore, profiling enables the combination of maximum productivity and maximum process reliability to be found. In summary, the VisionXP+ Vac enables large-scale production on an inline reflow soldering system and features an optional vacuum for void-free processes.

Resource efficiency and CO₂ footprint

In addition to the total cost of ownership, CO₂ footprints are becoming increasingly important. Consumption of electricity, nitrogen and coolant, as well as heat loss, should therefore not just be reduced for economic reasons but also to promote environmentally-friendly and climate-friendly production. With respect to the local energy mix in Germany, 1 kWh corresponds to an equivalent of 0.49 kg CO₂ emissions and 1 m³ nitrogen corresponds to approx. 0.5 kg CO2 emissions. An energy saving of 30% by replacing AC motors with EC motors therefore corresponds to a reduction of the CO₂ footprint by approx. 5%. Precise regulation is required to reduce nitrogen consumption. On top of this, the innovative option of Rehm CoolFlow facilitates the optimisation of cooling and nitrogen consumption. Liquid nitrogen is used in the cooling zone for more efficient cooling and the gaseous nitrogen that is created is used for inerting the process chamber. This means that less energy is required to provide the coolant, while the nitrogen is used twice, leading to a reduction of CO₂ emissions by 15% in total.

Another aspect of resource efficiency is the maintenance intervals and service times. In order to keep the maintenance intervals as long as possible, functions such as vibration measurement on the transport system are used to identify contamination and wear on the chain. The pyrolysis unit typically reduces the contamination in the machine, while the heat loss from pyrolysis is returned to the heating zones. For the VisionXP+ Vac by Rehm Thermal Systems, the current energy and nitrogen consumption is very easy to monitor with the ViCON software. Furthermore, all data on resource efficiency can be recorded and logged, as well as transmitted directly to the management execution system (MES).

In conclusion, the resource-friendly consumption of energy is a primary goal of the most recent developments in order to reduce running costs and CO₂ footprints. Innovative features combine the reduction of energy and nitrogen consumption to achieve the best process results with as low a CO₂ footprint as possible for inline reflow soldering systems both with and without a vacuum.