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Hello everyone, in this lesson we will take a look at the soldering of QFN chips

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Let's talk about removing the QFN chip first

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When removing the QFN chip, first use tweezers to hold the chip firmly

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While clamping the chip firmly, give the tweezers a force towards the palm of your hand

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In this way, when the chip is melted, it can be observed at the first time, and the chip can be removed

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We next use the air gun to heat the chip

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The temperature and wind speed are 450 degrees, 60 degrees

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When disassembling the QFN, it must be heated evenly, and at the same time,

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it must be heated straight up and down

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Here is just for the convenience of demonstration, so blowing diagonally

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It can be seen that the chip has moved

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We remove the chip

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In this way, the disassembly of the QFN chip is completed.

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Next, let me take a look at the soldering of the QFN chip

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First we need to apply a little flux to the pad

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Then we need to align the direction of the chip

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You can see that there is a bar at this position of the motherboard,

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which represents the first pin of the chip.

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So, the mounting direction of the chip should be like this

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Next we use an air gun to heat the pad

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The temperature and wind speed of the air gun are constant

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Continue to heat the pad until all the tin on the pad melts

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You can see that the tin on the ground has now melted

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After melting, we can clamp the chip, put it on the pad, and then align the chip

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This way the chip is soldered

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But it doesn't necessarily mean it's welded.

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We also need to check the soldering of the chip

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After inspection, it was found that the 3 pins on the right were obviously lacking tin

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In this case, we can use a soldering iron to solve it

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Drag solder the pins with a soldering iron and tin wire

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After drag soldering, the situation of tin deficiency will be significantly improved

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Let's take a look at the pins after soldering

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Each pin must be bright and full, and there is no lack of tin, even tin, or false soldering

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This kind of QFN is welded

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Just now we used an old chip to solder

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Older chips are generally less difficult to solder

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Next we use the new chip to solder

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It can be seen that each of its pins is relatively dim and not shiny

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Pins like this cannot be soldered directly, we need to tin the pins first

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Use a soldering iron and tin wire to tin all the pins on all four sides

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The effect after tin plating should be as shown in the figure

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Every pin is shiny

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This is the only way to weld

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At the same time, we also need to plate a little tin on the ground in the middle

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It should be noted here that the tin on the ground must not be added too much

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If you add too much, it will affect the welding

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The next welding process is the same as before, let's fast forward a little

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After the welding is completed, we still need to check the welding condition of the chip

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After inspection, it is found that the third pin from right to left has a false soldering

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We can use the method of dragging tin with the soldering iron just mentioned to solve the problem.

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But here I want to introduce you a different solution

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Use tweezers to pick up a little tin paste and apply it to the place where the solder is weak

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If you can't observe the false soldering, you can also apply tin paste to the four sides

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After the solder paste is applied, heat the chip directly with an air gun to melt the solder paste

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It can be seen that after the tin paste melts, there is linked tin

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Linked tin is very easy to handle

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We use a soldering iron to touch it a little bit, and even the tin is gone

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After dealing with the linked tin, let's clean the chip

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Finally, let's observe the welding effect

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It can be seen that each pin is very full and bright, and there is no lack of tin, tin connection, etc.

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This kind of QFN is welded