Helium Atmosphere Processing Furnace Hoods
Publication Date: 2005-Apr-15
The IP.com Prior Art Database
Conventional open-ended solder reflow furnaces, designed to employ air or Nitrogen based processing atmospheres, are typically horizontal conveyor belt type furnaces. Objects, or “populated” circuit boards, are usually placed on one end of a moving horizontal conveyor belt and are transported into a heated enclosure (containing a processing atmosphere which also acts as a heat exchange medium between electrically driven heat sources and the objects to be heated) wherein the object heating and solder reflow process is completed. After this part of the processing step, the heated objects continue onward in their horizontal path as they cool and move out of the enclosure at the other end of the reflow furnace. During this process, air or Nitrogen based processing atmospheres, typically employed within these furnaces, are circulated by natural convection, or by forced gas circulation fans in order to produce relatively uniform heating rates in the objects or electronic assemblies that are processed.
When air or Nitrogen based atmospheres are employed in these kinds of furnaces, the cost of using either of these atmospheres is typically a negligible part of the overall production cost of the objects or electronic assemblies that are processed in this way. This is true even if there is a leakage of the gas processing atmosphere out of each end of the furnace or other more significant losses due to the ventilation/exhaust gas systems designed to get rid of contaminated gas atmospheres (due to off-gassing of noxious components in the solder pastes during the reflow process). However, in some furnace processing applications, relatively pure Helium atmospheres can be used more advantageously instead of air or Nitrogen because of its ability to act as a much more efficient gaseous heat exchange agent than all other gases except for Hydrogen. But, the costs associated with Helium processing atmospheres may not be negligible. So, every possible method of reducing Helium consumption rates and/or contamination of the Helium atmospheres (typically due to air infiltration and/or due to the introduction of solder paste off-gassing contamination during the reflow process), should be employed in these applications or potential users will seek other more cost effective methods.
Some have proposed solutions to this problem:
U.S.published patent application
US2002/0073574 A1, and
U.S.patents 5,076,487 and 5,364,007.
SUMMARY OF THE INVENTION
This invention concerns Helium atmosphere processing and furnace hood configurations that allow a minimum quantity of Helium to be used as an efficient heat exchange medium between heated elements (or surfaces, in furnaces) and objects that must be rapidly annealed, soldered, fused, or otherwise heated at relatively high temperatures within Helium atmospheres (or in gaseous mixtures containing Helium). A particular objective of this ID is to de...