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Product-Specific Drying and Curing Systems
By Dr. Hans Bell and Paul Wild, Rehm Thermal Systems GmbH
tems used in the electronics industry. Such diversi- ty makes it difficult to create a categorical system which represents the many variants. The generic term “dryer” usually applies to thermal systems that are not used for soldering, sintering or diffusion sol- dering — those that do not produce a firmly bonded joint. This may involve actual drying processes, such as paste drying and the curing of coatings, or such processes as burn-in testing and tempering. Everything from automotive airbags and
H
onboard flight computers and sensors to simple traf- fic signals are required to operate reliably in any conditions. Complex PCBs and connections are needed in these devices, and in order to ensure their operation, a lacquer coating is applied to the assem- bled board or to certain components. The dried and cured coating protects the electronics from prema- ture failure due to corrosion, moisture, dust, vibra- tion, and from other ambient influences.
The generic term “dryer” usually applies to thermal systems that are not used for soldering, sintering or diffusion soldering — those that do not produce a firmly bonded joint.
Dryers are equipped with technology deter-
mined by the products to be processed and antici- pated throughput requirements. In the field of photovoltaics, for example, a throughput time of
orizontal dryers, vertical dryers, infrared dryers, ultraviolet dryers, and nitrogen dry- ers are just a few of the types of thermal sys-
two seconds per wafer is common, which places special demands on the conveyor system. By con- trast, long dwell times are not unusual for other
problem is to apply heat to accelerate curing. This is demonstrated by the Arrhenius equation, which is a formula that describes how various reactions are affected by temperature. Coated PCBs can be heated through methods
including convection and infrared radiation. Together with the challenges of throughput rates, energy efficiency, homogenous temperature distri- bution and flexibility, these basic physical princi- ples still result in new difficulties for drying sys- tems. Other factors, such as a lack of space in a manufacturing facility, must also be taken into consideration. To meet these needs Rehm devel- oped its RVDS vertical drying system. The RVDS provides many temperature profil-
Interior of the RDS magazine dryer.
applications, such as the tempering process. In order to give the systems the smallest possible footprint, depending on the application, dryers can be set up vertically or horizontally.
Vertical Dryer Solvents and additives are mixed into the
encapsulating compounds and lacquers to improve handling and processing. After encapsulation, the solvents must be expelled to permit drying of the protective coating. The volatile elements in the sol- vents escape from the materials at room tempera- ture, albeit slowly. A well-known solution to this
ing options and consumes little energy and meets small space requirements due to its upright design. With a length under 4m (13.1 ft), the ver- tical conveyor can replace a comparable horizontal dryer with a length of 40m (131.2 ft). This concept permits efficient use of valuable space. If long drying times are necessary, a vertical
system containing two processing towers can easi- ly be equipped with a third, with only a minimally increased footprint. The dryer is also furnished with anti-drip mechanisms to avoid contamination of the mechanical system and the PCBs with droplets from the coatings in process. A drying or curing process must take into the
account the following: maximum temperature, process duration at maximum temperature, devia- tion from maximum temperature, and tempera- ture homogeneity, e.g. over the surface of the
Continued on next page
August, 2016
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