Mounting and dismantling of microcircuits in small-sized packages with plenary leads
Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies
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The proposed method allows you to quickly and accurately mount and dismantle microcircuits in TQFP, SOIC and similar packages without special soldering equipment. One of the microcircuits in the TQFP-32 package is shown in fig. 1 mounted on an adapter printed circuit board for installation on the main board of the device instead of a similar microcircuit in a DIP-28 package.
For soldering plenary leads of miniature microcircuits, a soldering iron with a tip called Microwav is convenient. Such a tip (Fig. 2) can be purchased ready-made or made independently by drilling a small recess in its working surface, it will contain a small supply of solder. You can also use an old sting with a burnt-out working surface, which is enough to process with a file so that only a small depression remains from the large recess formed on it
It is recommended to solder using the following technology:
- in the place intended for the microcircuit, place a little glue from the glue stick
- put a microcircuit in this place, checking the placement of its first output
- by moving the microcircuit (glue will not allow it to move arbitrarily) and slightly bending its leads, achieve an exact alignment of all the leads with the contact pads intended for them
- solder one of the extreme pins (for example, the lower right one) to the contact pad - if the microcircuit has moved during soldering, correct its position
- solder one more terminal located diagonally relative to the first one soldered, and again check the position of the microcircuit
- say with a thick solution of rosin in alcohol or other liquid flux over the microcircuit leads and contact pads under them
- make sure that the solder covers the entire working surface of the soldering iron tip and fills the recess on it, without, however, forming a drop on the tip
- run the soldering iron tip along the right row of pins from top to bottom at a speed of approximately one pin per second (Fig. 3). Let me remind you that the lower right output was soldered earlier, so the movement of the soldering iron will not cause the microcircuit to shift, and the flux will prevent the solder from filling the gaps between the contact pads
- repeat the operation with the remaining rows of leads, each time replenishing the supply of solder in the deepening of the tip.
Perhaps reliable soldering will not work right away, experiment with the angle of the tips? It is desirable that when moving, it touches both the pins and pads on the board.
It was easier to dismantle microcircuits with plenary leads than with holes mounted in holes. You can do this without special nozzles. You should start by "pushing" an enameled wire (for example, PEV-2) with a diameter of 0,2 .. 0,25 mm under one of the rows of pins of the microcircuit. This can be prevented by flux residues remaining under the microcircuit and its leads. Determine where the wire met with an obstacle, and heat the nearby microcircuit leads with a soldering iron while advancing the wire.
One of the ends of the wire, for example, the right one, must be fixed, as shown in fig. 4, bending and soldering to the contact pad or printed conductor, or simply passing it through the hole on the board, then, heating the microcircuit leads with a soldering iron tip, pull the wire from under them by the free end. The leads will rise slightly, and the gaps formed between them and the contact pads will be cleaned from solder.
The operation, starting with "pushing" the wire, repeat with all the rows of conclusions.
Author: V. Baranov, Kharkov, Ukraine; Publication: radioradar.net
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