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Reduce Pollution of Process Gasses in an Air Reflow Oven
Reduce Pollution of Process Gasses in an Air Reflow Oven
This paper gives detailed information of catalyst systems designed and implemented in SMD production lines to reduce pollution of process gasses.
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Authored By:
Gerjan Diepstraten
Vitronics Soltec B.V

Summary
The introduction of lead-free solders resulted in a selection of different chemistries for solder pastes. The higher melting points of lead-free alloys required thermal heat resistant rosin systems and activators that are active at elevated temperatures. As a result, more frequent maintenance of the filtration systems is required and machine downtime is increased. Last year a different method of cleaning reflow ovens was introduced. Instead of cooling down the process gasses to condensate the residues, a catalyst was used to maintain the clean oven. Catalytic thermal oxidation of residues in the nitrogen atmosphere resulted in cleaner heating zones. The residues were transformed into carbon dioxide. This remaining small amount of char was collected in the catalyst.

In air ovens the catalyst was not seen as a beneficial option because the air extracted out of the oven was immediately exhausted into the environment. When a catalyst is used in an air environment there is not only the carbon dioxide residues, but also water. When a catalyst is used in an air reflow oven the question is where the water is going to. Will it condensate in the process part of the oven or is the gas temperature high enough to keep it out of the process area? A major benefit of using a catalyst to clean the air before it is exhausted into the environment is that the air pollution is reduced dramatically. This will make environmental engineers happy and result in less pollution of our nature. Apart from this, the exhaust tubes remain clean which reduces the maintenance of air ovens. This paper will give more detailed information of catalyst systems during development and performance in production lines.

Conclusions
A catalytic thermal oxidation unit has been designed and implemented in SMD lines successfully using the Design for Six Sigma project methodology. A catalyst is an excellent device to crack the carbon molecules at a low temperature of approximately 225 Celsius. This temperature is ideal for cleaning reflow process gasses that have similar temperatures in the process zones. The returning gasses from the catalyst are clean and have no impact on the reflow process temperatures of the zones.

The pyrolysis responds differently in an air and nitrogen environment. In nitrogen the returning gasses are clean and dry which makes it possible to recycle the nitrogen in the oven and have a reduced nitrogen consumption. In air ovens the air coming out of the catalyst is wet. Returning this gas back into the oven would condensatein the baffles. In air ovens the gas is exhausted into the environment after being cleaned by the catalyst.

Initially Published in the IPC Proceedings

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