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Today's video is about surface mount soldering using a hot air rework station.

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The model I'm using is the 852A Plus from AOU, however you pronounce that.

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This is a common model available worldwide.

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We're going to solder the components used in our own LCD backpack.

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There is a 20-pin microcontroller, a MOSFET transistor, and a variable resistor, all surface

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mount components.

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We will also be using a laser cut stencil for adding the solder paste to the circuit

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board.

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The stencil is 0.1mm thick, which may not seem thick enough to apply sufficient solder

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paste, but it is.

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So let's get rid of the components for now and we'll apply our solder paste.

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Line up the stencil holes with the component pads and add a blob of solder paste, either

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from a syringe or from a little tub.

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The perfect tool for spreading the paste is a craft knife blade.

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Once your stencil is lined up correctly, hold it down to stop it moving and spread the paste

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with the blade.

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Lift off the stencil and check that the paste has transferred to the pads correctly.

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Any problems, just wipe it off and start again.

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We can clean up the stencil with the blade, scrape off the unused solder paste and then

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wipe with a cloth.

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Now we can add the components to our board.

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A pair of SMD tweezers is useful here.

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Drop the chip onto the solder paste.

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Make sure the pads are aligned and give it a gentle press.

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the solder paste will hold it in position. Now we add the transistor. Drop it into place

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and a little press will hold it. Don't worry if it is not perfectly aligned. When the solder

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paste heats up it will be pulled into position. Add the last component and we are ready for

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the hot air station. I use a heat proof mat for the board to sit on. The hot air is coming

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out at 350 degrees centigrade so don't do it on anything that will burn. The hot air

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rework station is easy to use. Turn on the power and then turn on the hot air. Set the

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required temperature, we use 350 degrees. The air flow can be left to the default. It

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only takes a few seconds to heat up. Use the hot air gun about a centimetre from the board

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and for transistors like this, move the gun in a circular motion. The solder paste soon

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melts and the transistor is pulled into the correct alignment. For the chip, go up and

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down each row of the pins. It will be obvious when the paste has melted. Give the chip a

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little press to seat it firmly in the solder. Again, a circular motion is used for the variable

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resistor.

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And that's it. Check the board under a magnifying glass and rework any joints if you need to.