Another soldering station inquiry

I've done this, but I'm no expert by any means.

If you have a steady hand, good vision and a good pair of tweezers, you can solder some SMD devices using a soldering iron.

It can help to daub some flux onto the pads you'll be soldering beforehand, then melt a small slab of solder onto one pad, position the part with the tweezers holding the part's "pin" onto the solder while aligning the part so that all of the other "pin"s and pads line up properly and then touch the iron to the soldered pad and part side to melt the solder and attach that "pin". Then apply solder and iron to the other "pin"s and pads once the first pad has been attached. It's usually a good idea to check and re-solder the first pad after the rest of the "pin"s have been soldered.

I think that a hot air station would require you to use a custom solder paste and applicator to add the paste to the pads before applying the hot air gun. You might also need to hold the part down while applying the hot air.

I observed QFPs being soldered by hand in China. They were roughly 100 pin devices. The soldering iron had a flat tip with a dimple. The operator used wire solder to put a small ball of solder in the dimple. The solder ball was then pulled across one side of the QFP. It was only a couple of seconds per side to solder the part.  If memory serves me they had brushed flux on prior to this. I  recall writing a report long ago and mentioning this after visiting this factory. In general I was not impressed with their workmanship but found this very clever.  The majority of the board was through hole components.

*** Changing gears to more convention soldering.

Solder paste can be applied to individual pads using a syringe.  Most common is applying it with a stencil. Often parts are glued to the board.

If soldering with an iron the part needs to be held down so it doesn't leave with the iron. In hot air it may be blown off. Tweezers can be used in lieu of glue as can a vacuum pick-up device for holding the part down.

In general, I agree with Will's comments on the process.

Larry

Before you invest in anything you may want to get a few of the SMD practice kits on Amazon or Ebay. Only $5 or $10 and a great way to learn/practice technique at no risk. Also, there are a lot of SMD videos on YouTube with some good tips.

With a reasonably fine solder tip and very thin solder, it is not as hard as it looks at first glance. Some of the kits don’t actually “do” anything but let you practice soldering resistors, caps, diodes and perhaps a few ICs of various sizes. But if you look at the circuit board traces, you’ll notice that there are various combinations of serial and/or parallel circuits so it is fairly easy (with a meter and a little math) to figure out how many of your solder joints are good. For your second try, you might want to try a simple kit that flashes LEDs in a “waterfall” pattern or something similar. 

I would also recommend picking up one of the “tweezer type SMD meters” since  a lot of the “included free” parts aren’t marked well. Adafruit has a perfectly serviceable one for about $30 as I recall.

IMHO, a little skill in SMD soldering is very useful. Especially since some newer chips are only available in SMD form, but you can easily find tiny PCB boards with headers to adapt SMD chips for breadboard use.

@will @larry-manson @steve-cross

Thanks for all your thoughts, all good points and I think I concur that I don't really need to get a hot air soldering station.  

However, as I perused them on the internet, some of the cheaper ones seemed to fair OK in some reviews, and one had a little sucker to pick and place the SMD components.  And I admit I was sucker'd into hitting the buy button. 🤨  

I thought unless I buy one I will never really know if it will proved to be of much use.   If nothing else it will be good for shrinking the heat shrink tubing 😎 

I haven't come across the 'tweezer type SMD meters' so I will be perusing those too.  

One important thing to consider in how well you have soldered is VISUAL INSPECTION!

Think magnifiers, magnifying glass, ring light with magnifier, reading glasses (for some), digital microscope, or.....

Just because electrically the joint tests good today, it doesn't ensure it will be good tomorrow or after a little stress. Stress can be from vibration or thermal. 

Visual isn't everything, but it along with an electrical test is all most of us can afford.

I once had a lab under me that subjected boards to vibration and thermal shock in the design stage and first parts validation. We identified failure modes that would happen in the future.

@larry-manson

I find one of those headband magnifying lenses with a little light works well to inspect my circuit boards, and for the soldering of pins and the like.  I also have a small usb microscope to show a nice big picture on my monitor, but I have not really found a need to use it.   I haven't  actually done much soldering of pcb's, 3 or 4 times a year maybe, but maybe I will be doing a bit more when I get my electronics hobby room properly set up, and I have a better grasp on all this electronics malarky. 😀