[sdiy] SMD soldering technique

cheater00 cheater00 cheater00 at gmail.com
Thu Mar 23 09:00:36 CET 2017


Hi,
I have recently bought an SMD learning kit to try out some techniques.
I've had some really good results that were stunning for a person who
tried real SMD soldering for the first time, so I thought I'd share
what I did and what I used.

I got one that looks like this, but I think I got mine on Amazon:

https://www.aliexpress.com/item/DIYmall-SMT-SMD-Component-Welding-Practice-Board-Soldering-DIY-Kit-Resitor-Diode-Transistor-By-start-Learning/32776255634.html

The 1206 were easy, as were the 0805 and 0603. Too bad they didn't
have smaller ones. I didn't have to use a microscope but I wear
contact lenses so my vision is OK. Good lighting was crucial (see by
the end of the email), as my eyes couldn't resolve the detail without
it. With the light the work was really comfortable.

I've used my Hakko-clone soldering station Aoyue Int2903 with this
Hakko-clone T12 tip type JL-02:

https://www.aliexpress.com/store/product/Hot-Hakko-T12-Soldering-Tips-T12-JL02-Series-Iron-Solder-Tip-For-Hakko-Fx-951-high/1486111_32574864414.html

The tip I used worked pretty good.

I used AmTech Tacky Flux, model NC-559-V2-TF. I bought it from Insat
on http://www.bga-reworking.co.uk/. They have other good soldering
stuff so check them out. I made enough of an order that they sent me a
set of tweezers and cutters. The tweezers are ESD and very precise,
the cutters have really nice blades but the spring shifts around which
is annoying.

It's important to buy the flux from an authorized distributor listed
on this page:

http://www.inventecusa.com/reps---distributors.html

You can find AmTech knockoffs nearly everywhere and obviously they're
not going to have the same chemical composition as the original.
Amazon has the knockoff, so does eBay. The flux is really important.

I first put the board in a "helping hand" stand, although I am
awaiting the delivery of an inexpensive pcb holder vise. Does anyone
know where to get aligator clips for the helping hand that don't have
the teeth? Much rather rubber jaws or no teeth at all? That would be
so much better. I might put some heat shrink on these.

I start soldering by applying a tiny amount of the flux to the board.
Then I'd add some Stannol SN60Pb39Cu1 to the pads. I have a 1.00mm
diameter 500g spool that'll last me, my children, and my children's
children a lifetime. I could use some finer solder though, maybe
0.2mm, because 1mm really applies very quickly. I'm holding my
soldering iron in my right hand.

Next I'll take a pair of ESD tweezers and, holding the tape in my
right hand, I'll pry it open with the tweezers and pick out the part.
I'll put it on the board and apply heat to the top pad with the
soldering iron, then to the other pad. The part will not have settled
yet, so once it's held securely by the joints I'll let go with the
tweezer and heat both pads alternating between them until the part
settles. If it needs pushing in place I'll use the tweezer or a
spudger. I'm going to buy a magnetic knife holder thing for my
tweezers and spudgers which should make the process easier.

At this point the resistor pads will have gratuitous balls of solder
on them, so I'll remove nearly all of it with Pollin 1mm wick, order #
840 030:

http://www.pollin.de/shop/dt/OTY5OTUxOTk-/Werkstatt/Loettechnik/Entloetgeraete/Entloetlitze_1_0_mm_1_5_m.html

it comes out of the spool condensed so I twist it around until it
separates into a mesh. This way it'll absorb much more solder for the
same length.

At this point I might have to realign the resistor so I'll use some
heat and a spudger. I use these spudgers:

https://www.aliexpress.com/item/6Pcs-Hand-Tool-Professional-Steel-Solder-Assist-Electronic-Components-Repair-Welding-Auxiliary-Tools-Set-FULI/32780051115.html

or at least ones that look the same. I don't know where I bought them
any more. ("Welding" is Aliexpress for "Soldering" and "Auxiliary
tool" is for "accessory", useful when searching for something)

The flux makes all the difference. I did the first resistor with the
flux, and it worked well. I did the neighbouring one without applying
flux, I just used flux from the previous one, and that was pretty good
too. I tried the third pad watching out not to apply any flux, and the
results were really bad. As soon as I applied a little flux the joints
cleaned up, and the resistor applied well. The flux also smells really
nice. I later cleaned it off with some 70% ethanol and normal q-tips.

I don't have a good light set up yet so during the process I used the
Black Diamond Revolt head-mounted lamp which I bought several years
ago, use all the time, and it remains like new.

http://blackdiamondequipment.com/en_US/headlamps-and-lanterns/revolt-BD620613_cfg.html

It has an adjustable angle mount which was very important for soldering.

The nice thing about this soldering technique is that it gave me
really perfect results without much of a fight. I might still have to
practice to leave more solder on the pads, but the initial results are
very promising.

The one improvement I'd like is a different tweezer. A sideways
tweezer would be better, where the jaws curve in on themselves out of
the plane of the sheet metal the tweezer is made of. I haven't been
able to find one with a nice angle (say 75 degrees) and a fine tip and
ESD coating. If anyone has a suggestion, I'd love to hear about it.

After cleaning with 70% ethanol, the board still seems to have a bit
of a film on it, so if someone has a suggestion for a better solvent
for the AmTek flux, let me know please.

Hope this helps someone. If not, at least I had fun documenting what I
did in case I forget in the future :)



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