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AN-1035 Datasheet(PDF) 10 Page - International Rectifier |
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AN-1035 Datasheet(HTML) 10 Page - International Rectifier |
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10 / 42 page  DirectFET ® Technology AN-1035 Board Mounting Application Note www.irf.com Version 28 (revision history), April 2016 Page 10 of 42 Rework guidelines Modern rework stations for ball grid array and leadless packages often use two heating stages. The first heats the substrate, either with a conventional hot-plate or a hot-air system. The second stage uses a hot-air system for localized heating, often with the option of unheated air for faster cooling of the solder interconnections on the replaced device; this improves the solder grain structure. The device placement mechanism or arm usually has a hot-air de-soldering gun as part of the pick head, equipped with a vacuum cup and thermocouple. Once the solder reflow temperature has been reached, the vacuum is automatically engaged to allow the device to be removed from the substrate. This reduces the risk of causing damage by premature removal. International Rectifier does not recommend reusing devices removed from a substrate. Dispose of the old device and use a new replacement. To replace a DirectFET device: Note: If you usually bake to remove residual moisture before rework, insert your normal procedure here. 1. Heat the site to approximately 100°C (150°C for lead-free assembly) using the substrate heating stage. Note: Pb devices are qualified for a maximum reflow peak temperature of 230°C (260°C for PbF devices). To avoid overheating the device or substrate, adjust the settings on your equipment to achieve a maximum air temperature of 300°C. 2. Lower the placement arm to bring the de-soldering tool into contact with the device. When the device and the solder interconnects reach reflow temperature, lift the placement arm to remove the device from the substrate. Discard the device. 3. Clear residual solder from the site using a blade- type de-soldering tool and de-soldering braid. Clear residual flux using a flux-reducing agent. Take care in cleaning the site: damage to the solder-resist may produce undesirable results. 4. When the site is ready, apply new solder paste with a micro-stencil and squeegee. 5. Position a new device on the vacuum tip of the placement head and lower the placement arm until the device is in contact with the solder paste. 6. Switch off the vacuum on the placement head and retract the placement arm, leaving the device in place. 7. Heat the site to approximately 100°C (150°C for lead-free assembly) using the substrate heating stage. 8. Use the de-soldering tool to heat both device and solder interconnects to reflow temperature, waiting until all the solder has reflowed. 9. Retract the arm, leaving the device in place. Cool as quickly as possible. Mechanical test results International Rectifier has subjected board-mounted DirectFET devices to extensive mechanical tests, conducted in accordance with industry standards and practices. The devices tested were of medium can size, one MQ-outline and one MT-outline. Given that all DirectFET devices are made in the same way, other can sizes should perform to the same high standard. This section contains summarized results for bend tests, compression tests, drop tests and vibration tests. Full reports are available on request. Bend tests Method These tests were carried out in accordance with BS EN 60068-2-21:1999 Test U: Robustness of terminations and integral mounting devices. To gauge relative performance, DirectFET devices were tested against ceramic capacitors of a similar size. Substrates were initially tested over knife edges set at 90mm pitch but, as few devices failed, the pitch was changed to 70mm. This meant that the same deflection formed a more acute radius, increasing the strain and reducing the deflection needed to cause failure (13-14mm deflection over 70mm pitch causes approximately the same strain as 25mm deflection over 90mm pitch). The speed of deflection was 1mms -1 for all tests. The test board measured 100x40mm and was manufactured from FR4 2oz copper, finished in nickel gold. The solder used was Sn63 Pb37. Devices were mounted both longitudinally and transversely, and were tested with the devices mounted on both front and back of the board. |
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