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72 SMT Magazine • April 2015 residue on the board. This was easily cleaned with alcohol and a soft brush. results and analysis The temperature measurements below are for each of the shielding materials with the ref- erence IC temperatures between 232–240ºC for an accurate comparison. Conclusion Through the repeated measurement of out- lying component temperatures during the re- flow process, the clay/water gel (as seen in this YouTube video) was determined to be the best performing heat shield material. More testing, however, is needed to prove its suitability for electronics manufacturing (ionic cleanliness, SIR and reliability testing). The best perform- ing material that would have little impact on the electronic assembly was the ceramic fiber material. The next closest performing mate- rials in order were the copper tape, stainless steel, and polyimide tape. Polyimide tape sim- ply lacked the thickness and thermal resistance and was found to be the least effective shield- ing material thereby debunking the myth that this is the best material to use for PCB rework shielding. SMT references: 1. "Thermal Considerations for Surface Mount Layouts," Charles Mauney, Texas Instru- ments. 2. "Heat Management in Printed Circuit Boards," Jakob Dieterle Project Report 2010 MVK160 Mass Transit May 11, 2010. 3. "Thermal Considerations for Surface Mount Layouts," Charles Mauney, TI seminar. 4. Dytec Services Inc., Material Safety Data Sheet ColdShield Gel. Greer, South Carolina: Dytec Services, Inc., 7 Aug. 2012. 5. J-STD-075, "Classification of Non-IC Elec- tronic Components for Assembly Processes," IPC 2010. 6. IPC-9504 "Assembly Process Simulation for the Evaluation of Non IC Components," IPC 2011. Thanks to Adam Gaynor, EE student at Miami of Ohio who performed the experiments for this work. figure 6: Maximum temperature for various shielding materials at select locations on a pcb. bob Wettermann is the quality manager of BEST Inc. FeAture pOlyiMiDE TapE iS NOT THE ONly aNSWEr DuriNG rEWOrK continues