What is QFN packaging?Manual soldering QFN packaging method
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What is QFN packaging?Manual soldering QFN packaging method

Posted Date: 2024-01-13

What is QFN packaging? QFN (Quad Flat No-lead Package) is an emerging surface mount chip packaging technology with small pad size, small volume, and plastic as sealing material. Because the large exposed pad in the bottom center is soldered to the PCB's heat dissipation pad, the QFN has excellent electrical and thermal performance.

It's on the bottom, these pads.

Generally, the first type is more common. The long pad at the back is lengthened by personal proofing for hand soldering, but it is easy to short circuit.

Of course the best way is to open a steel mesh, but that is too wasteful. . .

The tools you need first are:

Non-magnetic precision tweezers, a glue needle with a diameter of 22 or above, highly fluid solder paste, a heat gun, a magnifying glass, a desk lamp, flux, cotton swabs, alcohol, washing water, and a clamping board.

It’s not that poor students have too much stationery, it’s that they really need so much.

The first step is to clean the board with washing water and a toothbrush.

Then clamp it on the board:

Then use solder paste to apply to the heat sink, do not apply to the surrounding pins

Many videos require you to paint all these areas. After practicing it myself, I felt it was inappropriate because it felt uneven.

Then apply a layer of flux evenly on the entire pad to ensure even heating.

Then, drop flux in an empty space and stick it on the reverse side of the chip. In order to fix the chip, use the solder paste on the needle at this time. Make sure it is even. If it is uneven, wipe it and re-apply it. Then also apply it on the heat sink. Apply, but sparingly.

Next, blow the solder pad first to melt the top of the heat sink. Then you can check the amount of solder resist and add a little. Generally, I see that the heat sink in the middle is blown out, and the surrounding pins are fine as well.

At this time, use tweezers to hold the chip and blow it quickly with an air gun. At this time, you can see that the solder paste is perfectly retained on the pins, which is actually tin implantation.

At this time, turn the chip over and align it. Pay attention here. The chip may be too small and you cannot see where the alignment point is, or the flux may contaminate the chip surface. You must remember the direction in advance.

At this time, the temperature on your soldering pad should have just dropped a little. Then you pinch the chip and continue to blow the soldering pad with the hot air gun. Continue to raise the temperature, mainly blowing the heat sink. At this time, the chip is placed on it. But don't fall, keep blowing.

After blowing for about five or six seconds, put it down and put it as neatly as possible. At this time, you need to carefully make fine adjustments, that is, touch the corners of the chip with the head of tweezers. If there are no errors, you should be able to see the reset action of the chip. If you place it accurately, the reset action will be very small.

At this time, use tweezers to gently squeeze the top of the chip to make it fit better.

This is what it looks like when finished

I can't take pictures anymore. At this time, I quickly remove the air gun. Check to see if the solder joints around the chip are regular.

Looks perfect under the microscope

No need for repair welding

Such

A large part of this success is due to this super-fine needle

The above may seem complicated, but it’s actually not simple at all, hhhhh

First, you need to treat the soldering pad. The heat dissipation part should be thinly layered, and the surface should be evenly covered with flux for rapid heat conduction.

The next step is to implant tin on your small chip. The key is to make it even.

Next, heat the pad first, and the middle heat dissipation part will be tinned. Then heat the chip, pay attention to the time.

Then it's time to drop and continue to blow. The key is to aim.

This is followed by a slight squeeze of the chip.

Here I will write about the welding of 0402.

Prepare materials first

Apply the solder slurry evenly, and be sure to use a small amount. If any excess flows out from the needle, wipe it immediately. Do not squeeze the solder gun, and let it flow out directly.

upper component

No problem, but it may be that the soldering is not good and needs to be tested. This LED does not seem to be of high quality.

Identify this way

The top is negative

That's it

But most are good

One problem here is actually the temperature of the air gun. I personally need 330~360. This temperature is actually very high.

A tweet from Teacher Zhuo Qing said that the temperature of the hot air gun should be calibrated.

This reflow temperature profile is then simulated by moving the air gun from far to near. But I can't do it. The chip should not be damaged by scalding at 300+ temperatures for a short period of time.

In fact, I can also solder many such chips using this method.






Review Editor: Liu Qing


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