Panasonic KX-FC255CX-S Service Manual page 201

17.2.3. Flat Package IC Installation Procedure
1. Temporarily fix the FLAT PACKAGE IC, soldering the two marked pins.
*Check the accuracy of the IC setting with the corresponding soldering foil.
2. Apply flux to all pins of the FLAT PACKAGE IC.
3. Solder the pins, sliding the soldering iron in the direction of the arrow.
17.2.4. Bridge Modification Procedure
1. Lightly resolder the bridged portion.
2. Remove the remaining solder along the pins using a soldering iron as shown in the figure below.
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KX-FC255CX-S