Using special soldering iron tips or a hot air gun to desolder surface mount chips in a TQFP package carries the risk of overheating the chip and / or printed circuit board. Below is a method for safely removing chips in a TQFP package – without overheating and with the ability to reinstall the desoldered chip. It does not require any special soldering equipment.
Remove a surface mount chip in a TQFP package from PCB is not that difficult. The method is to sequentially unsolder the leads located in a row on each of the four sides of the TQFP case and leave them raised above the surface of the printed circuit board, as shown in Photo 1. When all four rows of chip leads are formed like this, it remains only to remove it with a pincette.
Step 1 – remove excess solder.
You’ll need a soldering iron, a piece of a copper braid (tinned or not, for example taked of a shielded wire). The piece of a copper braid should first be dipped in an alcohol solution of rosin. Then remove excess solder from the leads and their corresponding contact pads as shown in Photo 2:
The result of this operation is clearly visible in Photo 3:
Step 2 – pull a piece of wire under the row of leads.
Under the row of leads freed from excess solder, pull a piece of enameled winding wire. One end of the wire must be stripped of enamel and soldered to the board as shown in Photo 4:
The diameter of the wire must be at least 0,2 mm, as a wire with a smaller diameter usually breaks. While unsoldering surface-mount chips, it is advisable to use a wire with heat-resistant enamel.
Step 3 – unsolder the leads from the pads.
The red arrow shows the direction in which it is necessary to pull the enameled wire threaded under the row of leads – parallel or at a slight angle to the plane of the printed circuit board and at an angle of 45° to the side of TQFP package. At the same time, with a soldering iron, it is necessary to heat the soldered lead closest to the loose end of the wire. As soon as it is unsoldered, the wire stretched with some effort will lift this lead above the printed circuit board and, coming out from under lead, immediately then move the soldering iron tip to the next lead, and so on. The direction of movement of the soldering iron tip is shown in Photo 5 with a yellow arrow. Thus, the unsoldering of the leads from the pads occurs “semi-automatically”. The result is shown above in Photo 1.
Copyright © Sergii Zadorozhnyi, 2012