SMT007 Magazine

SMT-Apr2015

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66 SMT Magazine • April 2015 Some urban legends or myths have been developed over time to where they almost be- come "true" without any real basis in fact. For example, urban legend has it that Walt Disney wanted so much to finish the projects prior to his death that he had himself (or some believe just his head) cryogenically frozen so that his cancer could be healed at some future date. The infamous "Nessy" of Loch Ness monster fame was photographed showing a head and neck in the "physician's photograph" purporting that a sea monster or previously thought to be extinct dinosaur lives in a deep inland lake in Scotland. The electronics manufacturing industry has its own myth in polyimide tape being the most ef- fective way to shield neighboring components by Bob Wettermann BEST InC. Debunking the Myth: Polyimide Tape is Not the Only Answer During Rework from heat exposure. Legend has it that this thin, adhesive-backed "protector" will shield components from damage. Within the last year we undertook an ex- periment to determine how effective different materials including polyimide tape would be in protecting neighboring devices during local- ized heating. This unwanted heating of com- ponents is driven by a desire to reduce neigh- boring component damage, to eliminate the need for removing components near the de- vice being reworked which could be reflowed increasing the IMC layer thereby reducing the reliability of the interconnection. Historically, non-semiconductor components have been able to meet the heat withstand requirements of board assembly temperature conditions. For lead-free reflow, wave soldering components are qualified for 275°C for 10 seconds. Simi - larly, for SMT reflow soldering, components FeAture

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