Climate monitoring of solder paste storage

There is a saying that the cobbler's children have no shoes, and the plumber's tap drips. So what about the automation of an automation technology provider? Manufacturers are rarely able to implement every innovation immediately in their own production. After all, new solutions must be tailored to current challenges, and the timing must be right in order to implement new solutions during ongoing operations. At its Beierfeld site, TURCK has now been able to directly implement a recently introduced innovation and automate the handling of solder pastes in electronics manufacturing.

In Beierfeld, the company operates an SMT production facility for printed circuit boards, in addition to many other production lines. SMT stands for Surface Mounted Technology and refers to a production process in which components such as resistors or capacitors are soldered directly onto a printed circuit board – in contrast to the traditional THT (Through Hole Technology) process, in which components with small wire pins are inserted through holes in the printed circuit board and then soldered. In the SMT process, solder paste is applied very thinly (<150 micrometers) to the printed circuit boards by printers. The printed circuit board is then assembled with the components and soldered in the subsequent reflow process.

Climate conditions of solder pastes influence quality 

To achieve the best possible solder joint quality, the solder paste must be stored within a specific temperature range. In addition, opened containers may not be used for longer than 30 days. Before processing in the printer, they must be stored at room temperature for at least four hours before the containers may be opened. Following this acclimatization, which prevents condensation, the paste must be mixed for 60 to 90 seconds – shaken, not stirred. On average, the paste may only be processed at 23–27 degrees Celsius – with a humidity of 40–60 percent (depending on the manufacturer). After printing the circuit boards, no more than eight hours may elapse before the circuit boards are soldered in the oven.

All in all, there are a number of parameters that must be adhered to, and manual control of these parameters requires a great deal of attention and care when taking handwritten notes. As with all human processes, there is no such thing as 100 percent certainty when it comes to manual solder paste control. If the specifications are not adhered to exactly, there is a risk of quality losses. The paste then does not optimally fulfill its task of facilitating the melting process and preventing oxidation, resulting in more waste. The production managers in Beierfeld wanted to automate and thus optimize the tracking of solder pastes. Not least within the framework of ISO 9001 and IATF 16949 certification, to which Turck Beierfeld is subject as a supplier to the automotive industry, continuous tracking of processes and preliminary products is mandatory.

Manual tracking of solder pastes

Until now, the times at which items were stored in the refrigerator were recorded manually by scanning the paste containers. Removal and opening were recorded by notes on the containers or documentation sheets. The refrigerators already had internal temperature monitoring, but this did not record trends; it simply triggered an email to logistics when the temperature fell below or exceeded the defined range.

Together with his team and project manager Linda Galle, Christian Seliger, who is responsible for the Research and Development division at the Beierfeld site, planned and implemented the automated recording and documentation of paste handling. "In order to achieve rapid project success even during ongoing operations, we divided the project into several sections," says Linda Galle. "With our Plan-Do-Check-Act approach, we ensure that each section is successfully completed before the next one is started."

In the first section, the initial task was to monitor and centrally document the climate conditions of the refrigerators, printers, and workstations for preheating. The system must generate appropriate messages or alarms when critical values are reached. In the next project section, RFID-supported recording of solder paste cans and a connection to a Manufacturing Execution System (MES) are to be implemented.

The climate inside the refrigerators is monitored using TURCK's IM18-CCM50 condition monitoring system. Each of the five refrigerators contains one of these control cabinet monitors with an integrated Linux computer. Their integrated sensors measure the distance to the refrigerator door and the temperature inside the cabinet. The devices can also measure humidity, but this is not relevant in this application as only closed paste containers are stored in the refrigerators.

The temperature and humidity in the printers, on the other hand, are certainly relevant, so the combined temperature and humidity sensor CMTH records these variables there. Each of the three separate solder paste printers has one of these condition monitoring sensors, while another records the conditions at the workstation where the pastes are stored for acclimatization. Each CMTH sensor is connected to a compact TBEN-S IO-Link master, which transmits the data to the production network. The managed IP67 switch TBEN-L5-SE-M2 also integrates all IM18-CCM50s into the production network.

With their open Linux operating system, the IM18-CCM50 are designed for the installation of OEM-specific software, allowing users to implement their own software solutions. They form the brain of the system, which stores and communicates with the sensors, the network, and the TURCK Cloud. To monitor the refrigerators, only network drivers and scripts for collecting sensor data are installed on the condition monitoring platform. The IM18-CCM50 transmits the data from the integrated sensors and the CMTH sensors directly to the TURCK Cloud via Ethernet.

Clear dashboards in the TURCK Cloud show climate conditions

This first phase of the solder paste tracking project now automatically ensures that the temperatures in the refrigerators, at the acclimatization workstation, and in the printers comply with the specifications. The times at which the pastes are stored and removed are currently still documented manually or recorded by scanning the QR codes on the containers. If humidity or temperature rises, employees can see this on the dashboard in the TURCK Cloud. In addition to the current values, long-term trends can also be identified. Trend detection and correlations between the data series could be analyzed in the future by the MES to be connected.

"The condition monitoring solution based on the IM18-CCM that has now been implemented was only the first step on the way to fully automated monitoring of the storage and use of solder pastes. In the follow-up project, we will connect our MES and thus complete the digitalization and automation of our production. This will enable us to maintain the highest level of quality even at maximum capacity and avoid unnecessary costs due to expired solder pastes," says Christian Seliger, summarizing the interim results.

Outlook: RFID-supported seamless solder paste tracking

In the second stage of expansion, the tracking of the pastes will be implemented directly with RFID tags on each can, which will also enable the correct acclimatization to be recorded before the containers are opened. Since the IM18-CCM devices then communicate directly with the MES, which controls the production orders for the printers, the system can immediately check whether the paste container used has been stored and acclimatized correctly before the circuit boards are printed or, in the event of violated conditions, block its use. If all data is available in the MES, further information could also be obtained from it, for example to identify weak points and sources of error.