October, 2017
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Efficient Convection Soldering with Vacuum and Pyrolysis Continued from previous page
face load of 0.1 MPa. The simulation results showed that
the greatest deformation, of 0.014 in. (0.36 mm), occurred in the longest cham- ber walls. The greatest load, 30.04 MPa, occurred at the chamber’s radii, due to the bending of its sides. The results of the simulation indicated that with a yield point of at least 90 MPa at a temperature of 500°F (260°C), the vacuum chamber has a safety factor of 3, before permanent plastic deformation. The vacuum chamber is subjected to
a cyclical load, caused by the generating of vacuum and its subsequent venting. A comparison of the stresses revealed that at maximum elongation of 0.037 percent at the radii, the aluminum-based vacuum chamber design was highly durable. Though the temperature caused slight changes to the microstructure, the chamber did not crack or fail.
Thermal Pyrolysis Outgas is released into the
atmosphere from the solder paste, the PCB and the components during the soldering process. There are also diverse fine particles that need to be cleared out. Rehm developed an effi- cient system to eliminate both kinds of residue. Known as “cracking” in the field
of petrochemistry, the residue elimi- nation system is based on thermal pyrolysis. During cracking, long- chain hydrocarbon compounds are made to oscillate by increasing the temperature of the process atmos- phere. Once hot enough, typically above 932°F (500°C), the long-chains break into smaller pieces. These smaller compounds are then collected in condensation and filtered out of the system. Cracking is also influenced by
dwell time and partial pressure. Due to the fact that pressure in a thermal pyrolysis unit for a convection solder- ing system can only be adapted to a limited extent at reasonable cost, temperature and throughput are decisive factors in the layout of the pyrolysis unit. The use of a catalyst is another
option for influencing the cracking process. Catalysts can reduce decom- position temperature and dwell time, resulting in time and energy savings. The disadvantage of the process is that it is difficult to match the cata- lyst to the solder vapor, which has to be exact.
Since the chemical composition
of the solder vapor varies greatly depending on the type of solder paste, components and PCB, it doesn’t make sense to use catalysts for sys- tems built for flexible production. However, even without a catalyst, thermal pyrolysis is a robust removal process.
Performance and Energy Consumption
After the functionality of the
vacuum chamber and pyrolysis unit had been tested at the PCB level, the system’s overall performance was evaluated. Rehm conducted FID (flame ionization detection) measure- ments to examine the distribution of the residues in the process chamber and the effectiveness of the removal system. FID is a widely used measur- ing method for the detection of volatile hydrocarbon compounds. The gas to be analyzed is passed
over a flame and ionized with a carri- er gas. If the test gas contains hydro-
with the VisionX-Series
Distribution of hydrocarbon concentration in zones of the vacuum convection soldering system.
carbons, electrons are released during ionization. The current is then meas- ured in picoamperes (pA). In actual production, residues
occur while soldering electronic com- ponents, which contaminate the sys- tem. This is difficult and time-consum- ing to recreate in the lab. FID meas- urements make it possible to shorten the required amount of time and to compare the degree of removal (clean- ing power) of different methods. A solder paste mixture was
applied to the PCBs for outgassing measurements. The mixture consisted of a variety of solder pastes. Roughly 0.06 oz (1.7g) of this solder paste was applied to each PCB, which is an aver-
Continued on next page
VisionX-Series Convection Soldering
For more information visit or call + 1 770 442 8913
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November 14–17, 2017
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