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Tutorial: Soldering SMDs

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Devil_H@ck

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Hi again,

I made another tutorial. This one's about how to solder tiny SMDs with nothing but a standard soldering iron.
Check it out here: **broken link removed**
 
I would like to add an observation... the blob all pins method, then use desolder wick, works, but may severly stress the IC heat wise.

I frequently work on tiny IC's with pin pitches of 0.5mm, but tend to stay away from applying solder directly.

The trick I use is to pre-tin the pads with a small amount of solder, spray the pads with solder-flux laquer, (Kontakt-Chemie SK10) locate the ic, then solder the pins with a 'clean' iron tip only, reflowing the existing solder. This avoids any bridging, as flux has been pre-added, dry joints don't happen.

As I do this type of soldering a lot in my company, for prototyping, I had to invest in a pretty cool soldering station (Metcal) which uses RF to heat the tips, plus for SMD work use, I mainly use 0.4mm tips. These units are very expensive though, (£350, with no tips) used by the likes of NASA etc. I used to use Weller stations, but they don't even come near to the Metcals in performance & power. The aforementioned 0.4mm tip warms up, and melts solder in 3 Seconds :shock: from stone cold.

Yup, I realize, not many hobbiests are likely to have Metcals, but even with normal irons, the above method should still get good results.

It is possible to file down standard iron tips to thin rectanglular point to achieve similar results, using the pre-tin method, allowing single-pin re-flowing.

Just a few ideas that maybe helpful?

Steve
 
Crofty said:
I would like to add an observation... the blob all pins method, then use desolder wick, works, but may severly stress the IC heat wise.

I frequently work on tiny IC's with pin pitches of 0.5mm, but tend to stay away from applying solder directly.

The trick I use is to pre-tin the pads with a small amount of solder, spray the pads with solder-flux laquer, (Kontakt-Chemie SK10) locate the ic, then solder the pins with a 'clean' iron tip only, reflowing the existing solder. This avoids any bridging, as flux has been pre-added, dry joints don't happen.

As I do this type of soldering a lot in my company, for prototyping, I had to invest in a pretty cool soldering station (Metcal) which uses RF to heat the tips, plus for SMD work use, I mainly use 0.4mm tips. These units are very expensive though, (£350, with no tips) used by the likes of NASA etc. I used to use Weller stations, but they don't even come near to the Metcals in performance & power. The aforementioned 0.4mm tip warms up, and melts solder in 3 Seconds :shock: from stone cold.

Yup, I realize, not many hobbiests are likely to have Metcals, but even with normal irons, the above method should still get good results.

It is possible to file down standard iron tips to thin rectanglular point to achieve similar results, using the pre-tin method, allowing single-pin re-flowing.

Just a few ideas that maybe helpful?

Steve
Thanks for the tip! I got the same solder flux. I was a bit worried about heat too. I'll try it someday and make another tutorial ;).
 
We had a tutorial run by the IEEE Student Branch on campus here a few months ago, and we did basically this, except we used flux. Basically, we put the IC down on the board with tweezers, used a few drops of flux to make sure that all the pins&pads were covered, and then put a tiny bit of solder on your tips and quickly dragged it across. The flux sucked in all the solder and there was an almost perfect amount of solder on each pin/pad.
 
Have soldered SMC stuff for several years repairing boards the robot stuffed up so I don’t know how my method would work with a newbie but here is how I solder.

Soldering an IC
Find the pad where pin one will sit, half fill or less that pad with solder.

Now place your IC on the pads (by getting in the habit of always starting on pin one you don’t have to think too hard about what way round the IC goes when your hands are full) touch the iron on the pin one pad and use your finger (or twisters for the fraidy cats) to align the IC while the solder is fluid on that one pad. Once the chip is in position remove the iron.

You now should have the chip tacked on with minimal solder via a single pad, this will hold it in place while you solder the rest. Start at the other end of the chip and press the leg down with the iron onto the pad (not hard just enough to heat the leg and pad at the same time) apply solder from the side touching the leg and pad, not the iron, as soon as the solder starts to take pull the solder away and then the iron, with practice you should get this down to a fine art. If you bridge two legs together with solder (using too much solder) heat this bridge until it melds and then give the side of the circuit board a sharp tap on the bench, if that fails find your desoldering wick.

Don’t forget to solder pin one properly.
 
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