SMT soldering technic question

[Mendoza666]

I was practicing my soldering skill over wasted board and I realized something : It is very easy to put too much solder over smt pin and clean it with the wick after. I made a very clean job and it was very easy...maybe too easy. Is it a good technic or not.

Thanks

 

[ME]

I don't think this is a good technique.
Why put too much solder on in the first place?
With some pratice and some very thin solder it is not too hard to apply the rigth amount.
I have soldered a lot of 0603 SMD's and SMD IC's without problems.
Of course you have to remove some solder once in a while, but if you are carefully this shouldn't happen too often.

 

[Al Farouk]

for fin pitch chips (0.5 and 0.65) the method that Mendoza666 explained is the preferred one for most of people work in this field and gives good results without causing deforming of the chip pins. Regarding the heating that applied to the chip, it is within the range that the chip can sustains. the only disadvatage is the wasting of alloy and shield.

 

[Fragrance]

hi


please read out this topic

**broken link removed**

 

[fuzcub]

I've found that even the messyist flux can be tidied up with a tiny paintbrush dipped in acetone. (just watch out for connector shells and other disolveable parts)

 

[ME]

I've found that even the messyist flux can be tidied up with a tiny paintbrush dipped in acetone. (just watch out for connector shells and other disolveable parts)

It's much better to use isopropyl alcohol (also known as isopropanol) to remove flux.

 

[Big Boy]

The method I use work well for even finest pitch.

You start by centering chip as precizely as you can, then, you solder two opposite corner. Just put some solder in the corner, don't bother if pads link togetter for the moment. The goal is just to put the chip in place.

Now, take liquid flux, and pour across all pins of one side. Then, put some solder on your iron tips. With experience, you'll know how much solder to put on the tip.

Now, sweep slowly across all fluxed pins. If you go too fast, sloder will bond across multiple pins. But don't be too slow to overheat the chip. Again, experience will tell the optimal sweep speed! Do a few sweeps if some pins are not soldered, adding some solder if needed.

Now, the flux will make solder stick to pads easily. After sweeping, you may get some pins bonded togetter, look carefully, and when you find such solder bonds across pins, just do a quick sweep on those pads, outward from the chip.

Repeat process for other sides of the chips.

You should not wick-out the solder unless there is too much. If you do wick-out extra solder, do a final sweep without adding extra selder. This is because when you wick-out solder, this can leave some pins with very little solder, and you may run into problems afterward (solder bound that break and pads that end-up floating).

It's really something you have to look after with a magnifier.

After, to remove flux, there is some stuff that are sold that are made especially for removing flux. It's better than isopropyl alcool. Is very abbrasive and good at doing it's job, yet, contact with skin is not generally much of a problem. Just make sure you don't spray this stuff on plastics as it will react with it (plastics will tarnish).

 

[grlgrlin]

start with small Components like Resisitors ,caps, and then go for soldering small IC's,since first time learners it is easier to solder the pins than removing. then gradually practice removing the SOIC ,double sided, then go for fine pitch, don't just junp into fine pitch, its is verry dangerous . and more imp. better to have temp controlled station.

 

[4C]

I regularly place 0.5mm pitch QFP's (100 to 208 pins).
I use the method described by Mendoza666.

A few things to add:-

1. Dont try to use tiny iron tips, they tend not to hold temperature very well. Use a medium sized tip that is about the width of 3 to 4 pin pitches.

2. Be careful if there are any vias just inside the row of pads, the solder will tend to ball up behind the pin - usually shorting two or three pins together. These are usually visible if you focus your view behind and between the pins. They usually happen when removing the flood of solder too quickly. To remove apply a moderate amount of solder to the group of 3-4 pins, give a few seconds for the heat to conduct through to the ball at the back of the pins, then remove with wick.

3. I find a strip of masking tape approx 4mm wide and 100mm long is the best way to position the device. Fix the centre of the tape to the device, hold the ends and move the device into position, once happy with the position press the ends of the tape onto the board. If the device moves the tape can sometimes be slid accross the board, or just remove and retry.

4. Dont just do a 208 pin device in one go, it will probably overheat and damage it. Solder one edge, then rest or solder other parts to allow the device to cool.

Well that's my 10p worth, anyone got a good way to solder BGAs?????

 

[JohnJ]

Hey, super advice from all of you! That same thing works for Leadless chips as well!
I regularly solder 0402s and 0201 here at work. The big advantage we have here is a microscope at each of our benches.
A few additional hints and tricks:

To remove fine pitch ICs we just mask the area around the chip with KAPTON tape (high temperature) and heat the area with a heat shrink gun until the chip falls off. A razor knife or small tipped tool can be used to apply a SMALL amount of upward pressure to help it (too much will bend any pins not yet free). Many of the fine pitch chips have a pad on the underside that is soldered to the board to act as a heat sink (small leads don't carry heat away from the chips very well). With these chips that's the only way you are going to get it off. (Check the data sheet or the replacement part to see if one exists.) Since you are heating the area it should come away all at once. DON'T be in a hurry! I've spent 2 or 3 minutes waiting for the chip to come away with a very hot gun.

Some notes:
- Watch for discoloration of the silk screen and the solder mask, they give you a good warning that you are overheating a spot.
- The chips themselves are pretty heat resistant: I just quickly looked at a data sheet for a plastic TSOP and the lead solding temperature is +300°C and the storage temperature is +160°c. As long as you spread the heat around evenly, the solder will melt long before you reach those temperatures

The previous advice for soldering the new ones in is great except if your chip has the heat sink pad on the bottom. For that type I clean the pads with solder wick (carefully they do lift!). I then add a small amount of solder to several pads spaced around the footprint. Add flux to all the pads including the heat sink area and drop a short piece of fresh solder off the roll on the heat sink pad (flattening it first helps). Then just hold chip in place (non-matalic tool is best since this takes awhile and the handle of your razor knife will get quite hot before you're done, my lesson is healing quite nicely ) and start heating with your gun. You will feel it start to squish down as the solder melts. This will not take as long as removing the chip since the hot air can now get under the chip. MAKE SURE YOU REALIGN THE CHIP WITH THE PADS BEFORE YOU STOP HEATING! :!: Now you can go in solder the leads as the other guys mentioned.

Oh.. for 0402s, 0201s, and 01005s (1/2 of a 0201) I use exactly the technique you asked about, since it's impossible to feed the right amount of solder from a roll at those sizes. My other 2 leaded SMT trick is to leave a small amount of solder on ONE of the pads and press down on the part while heating that pad. Make sure the other pad is clean, otherwise you will break the cap off the first end when you try to solder the other end the same way!

Sorry to be so long winded!