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Reflow Oven Evaluation Using The ECD OvenRIDER

Posted on Mar 20, 2002


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 excursions. 

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.

This paper 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 4 Vitronics Soltec Company Confidential 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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