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Connector removal and replacement
Connector removal and replacement
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Connector removal and replacement

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SMT process

SMT process

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  • 1. Connector Removal and Replacement http://www.circuitrework.com/features/634.shtml Consider a typical scenario where a project is already overdue and you learn that a 150-pin connector needs to be replaced. Desoldering the connector one pin at a time using vacuum desoldering tools just won't cut it. Quickly removing and replacing a large multi-pin connector seems a daunting task, but it really isn't. Here's how it can be done. The solution, and likely the best method, is to reflow all the solder joints at once using a solder fountain system. This enables you to remove and Figure 1: Typical solder replace the connector in two quick operations. fountain system used to quickly and reliably remove and replace A solder fountain system generates significant heat, with molten solder in large through hole components, direct contact with the board. This is what a high-mass object like a including connectors. connector needs. However, it's important that the dwell over the molten solder be as brief as possible. The number of times that the connections are reflowed should be kept to a minimum to protect the board, the components, and the solderability of surfaces. The operator needs to exercise extra caution. This process uses molten solder and exposes the untrained operator to serious hazards. A thorough review of the solder fountain system and comprehensive training are mandatory. Solder Fountain System Most solder fountain systems have the same basic components. These include a solder pump and solder reservoir, interchangeable nozzles in Figure 2: Connector aligned various sizes, and controls for solder fountain height. Solder from the directly over the flowing molten solder. reservoir is driven up through the nozzle by the pump. Above the solder fountain head there is generally a light projected alignment mark that permits you to center the part to be removed over the nozzle. (See Figure 1) Ideally, the leads of a component should be immersed in the molten solder without having the solder wave exert any upward pressure on the circuit board. (See Figure 2) Insufficient immersion in the solder wave will prevent proper heat transfer and reflow. Excess pressure will cause solder to surge up through holes and to spill out onto the top side of the circuit board. There are a variety of removal tools to help extract the component once reflow has been achieved. Figure 3: Once full solder reflow has been achieved, remove the connector either by hand, or with an extractor tool.
  • 2. Circuit Board Preparation If components, or the circuit board surface, are susceptible to damage or exposure to solder, they must be protected. This can be done by applying high-temperature tape to any flat surfaces surrounding the rework area, or applying high-temperature flexible mask to protect irregular surfaces. The mask may need baking to properly cure prior to reflow. Pre-bake Circuit boards should be baked for 1 to 4 hours at 65 degrees C - 120 degrees C. Time and temperature requirements for pre-heat depend on board construction, age, exposure and moisture sensitivity specifications. Baking will drive out moisture from the circuit board to prevent delamination, reduce thermal shock to the board that may cause surface or internal damage and raise the temperature of the circuit board and components to allow for quicker component removal. Removal Procedure 1. Set up the solder fountain system and install the proper nozzle. Check the table height and solder wave height to be sure they are properly set for the circuit board. 2. Apply liquid flux to both the top and bottom side solder fillets of all the leads of the connector to be removed. 3. Place the circuit board over the nozzle. (See Figure 2) Check the position using the alignment light and activate the solder fountain. Once full solder reflow has been achieved, remove the connector either by hand, or with an extractor tool. (See Figure 3) Immediately drop the solder fountain to prevent over exposure. Operator skill and experience are required to prevent hole and pad damage caused by premature removal of the connector, or from heat damage due to delayed removal. 4. Allow the circuit board to cool before cleaning and inspection. Replacement Procedure 1. Preform connector leads if needed, and test on a practice board to be sure leads are properly aligned. 2. Set up the solder fountain system and install the proper nozzle. Check the table height and solder wave height to be sure they are properly set for the circuit board. 3. Apply liquid flux to both the top and bottom side of all the solder filled holes and to the leads of the connector. 4. Place the circuit board over the nozzle. Check the position using the alignment light and activate the solder fountain. Once full solder reflow has been achieved, insert the new connector. Immediately drop the solder fountain wave to prevent over exposure. A great deal of operator skill and experience are required to expect good results when inserting the connector during the solder fountain cycle. 5. Allow the circuit board to cool before cleaning and inspection.

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