June, 2016
www.us-
tech.com
Continuous Temperature Monitoring During Reflow Soldering
By D. Uhlemann, pro-micron, Dr. H. Bell and S. Schorner, Rehm Thermal Systems, and A. Kraus, Kraus Hardware T
he expansion of monitoring and traceability to the soldering process is long overdue. Not only required by OEMs in the automotive in-
dustry, but also manufacturers from the fields of medical technology, aviation and aerospace place high demands on their suppliers to document and trace processes and materials. This is usually asso- ciated with extensive effort and high costs, because new processes and trained employees, as well as software for digital documentation, are frequently required. Kraus Hardware, an EMS company based in Grossostheim, Germany, has raised its production facilities to a new level by launching a comprehensive traceability program. The WPS 2.4 technology is an
innovative measurement system from wireless transmission expert pro-micron (
www.pro-micron.de) that is installed in Rehm Thermal Sys- tem’s CondensoX series of vapor phase soldering systems. Kraus Hardware is the world’s first EMS provider to use the wireless tempera- ture measuring system in produc- tion. As a result, the company can now monitor its entire surface-mount soldering process.
Tracing the Solder Profile As part of this process, Rehm’s
CondensoXM vapor phase soldering system was retrofitted with a passive, wireless temperature measuring sys- tem for monitoring and documenting soldering profiles. The entire profile is measured with previously unachiev- able degrees of accuracy, and trans- mitted in real-time to the system soft- ware, without interrupting or influ- encing production. By including the temperature
profile in the manufacturing docu- mentation, traceability has been ex- panded at Kraus to include the ther- mal soldering process as well. In ad- dition to machine settings and process parameters, such as pressure in the process chamber and the amount of Galden®, a heat transfer fluid, the temperature and time curves for each soldering process are also saved. Due to a 5 Hz sampling rate, enough data is generated for de- tailed, automatic evaluation of the soldering profiles. For example, capa- bility coefficients (Cp
, Cpk ), as well as
heat-up and cool-down gradients can be calculated, and individual alarms can be set for deviations. The temperature sensor is at-
tached to the soldering system’s workpiece carrier at the same height as the PCBs to be soldered. This cuts out the time-consuming preparation and connection of thermocouples. Actual measuring effort, start-
ing and ending a measurement or connecting the data logger to a PC,
The entire soldering
profile is measured with previously unachievable degrees of accuracy and transmitted in real-time.
for example, is eliminated because each process cycle is measured and saved automatically. This ensures that each manufacturing batch is monitored, which provides uninter- rupted documentation of soldering profiles. The WPS 2.4 wireless tempera- ture sensor accompanies the PCBs on
the workpiece carrier throughout the entire solder- ing process, from preheating and the peak zone,
right up to the end of the cool-down phase. This re- sults in a continuously reproducible profile.
Continous Sensor Function The temperature measuring system is based
Workpiece carrier with temperature sensor (on the right strut) in the loading position.
on surface acoustic wave (SAW) technology at a fre- quency of 2.5 GHz. The name of the system is de- rived from the frequency band it uses, which en- ables it to function worldwide in the ISM (industri- al, scientific and medical) band. The sensor gathers data with a receiving and transmitting antenna in both the cooling zone and the process chamber and transmits the response signal back to the measur-
Continued on next page
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