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28 SMT007 MAGAZINE I AUGUST 2022 Drag Soldering Drag soldering is a manual soldering pro- cess that uses a special soldering iron tip with a concave surface "spoon" or "hoof " shape to hold molten solder (Figure 2). is ball of mol- ten solder is then "dragged" across the leads of the QFP, letting the surface tension and nat- ural wetting forces of the solder deposit the correct amount of solder on each of the leads. When using the drag soldering technique, it is most effective with multi-leaded, very- fine pitched components. As with the point- to-point soldering technique, make sure the opposite corners of a package are tacked into place such that the component is aligned and cannot be moved off the pads. Apply enough solder to cover approximately one-third of the tip. For finer pitch parts apply less solder. Now flux the leads on each side of the component. Start from a row that has not been tacked in position. Bring the tip down at an angle to the point where the tip of the lead meets the land so that the edge with the solder on it is on the land, but the face is tilted away from the com- ponent. Hold the tips so the sha runs parallel to the row of the leads. e angle between the side of the tip and the side of the component can be up to 30 degrees (Figure 3) depending on operator preferences. Start running the tip down the toes of the leads. e variables to control are pressure (very light) and speed. e operator should glide across the leads with no pressure, with the speed determined by the thermal mass of the board. Follow this process on all sides, cleaning and inspecting aer soldering to the appropriate inspection criteria and class. Make sure the tip is tinned prior to putting it back into the holster. Adhesive-backed Stencil In some applications, less experienced solder- ing technicians can place an adhesive-backed stencil and solder a fine-pitched gull wing device in place (Figure 4). To begin, make sure Figure 2: Using a "hoof" tip to drag solder a fine pitched QFP (IPC 7711 Method 5). Figure 3: Drag soldering angle. Figure 4: Adhesive-backed stencil aligned and placed onto PCB (IPC 7711 Method 5).