Characterization of the thermal performance of modern convection reflow ovens is important in
ascertaining the process window for a particular product or application. This is especially true
for lead free processes. Using typical manufacturing materials such as FR4 can be problematic
in that the product changes thermal characteristics after a relatively short number of thermal
Other potential test vehicles such as a stainless steel or aluminum plate are more
robust and able to withstand repeated thermal cycles, however, introduce significantly different
thermal conductivities that masks potential weaknesses in oven design. Trying to match these
physical properties within a single test vehicle is necessary in order to characterize the various
oven parameters. Such materials exist in composites with highly insulating properties similar to
typical FR4 material as well as a high tolerance to numerous thermal excursions.
investigates the performance of three different ovens by measuring the uniformity of gas
temperature and the heat transfer characteristics using a commercially available test vehicle
specifically designed for this purpose. Using this test vehicle, it is possible to characterize
specific physical properties of a given oven design. The results indicate dramatic differences in
oven performance, specifically, the uniformity across the width and length of the tunnel as well
as the heat transfer capacity. Using this test vehicle, it is possible to characterize specific
physical properties of the oven. Oven design significantly impacts the steady state operation of
the individual zones as well as the entire heated length.
The uniformity or lack thereof in the
measured air temperature along the length of the tunnel and across the width of the tunnel will
have an impact on the ability to consistently and uniformly heat the product to be run. The
difference in temperature as measured between the air and the high mass sensors demonstrates
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the efficiency of the oven to transfer heat, or heat transfer value. A higher heat transfer value
allows for tighter control over the reflow process. This proportionality is related to the heat
transfer coefficient, however, is not the exact heat transfer coefficient for any particular oven.
Several tools exist to characterize the heat transfer coefficient as well as defining the portion of
heating associated with infrared energy.
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