Beginner SMD

Today I soldered some “real” SMD for the first time of my life. Here comes my beginner experiences. Maybe they are helpful for other beginners. I have some experience with TTH but SMD was new to me.

  1. A 3mm soldering tip is fine enough. Actually it does not matter to much to have a fine tip. But see (2).
  2. Flux is your friend. The more the better. If everything is soaked with flux the solder is just sucked under the pins. Although I read about this I did not expect that it works that well.
  3. Spare parts are mandatory. Whatever 2 pin SMD part falls to the floor is basically gone.
  4. Good fixation is helpful.
  5. Good tweezers might have been helpful but it was possible without.
  6. I should have glued most parts into place. Most probably this would have saved a lot of time.
  7. Flux is your friend. The more the better.
  8. Try to use the biggest possible SMD parts. 1206 is in reality much smaller than it appears in Eagle.
  9. For the chips you need to double check every solder joint. Visual inspection works poor. A multimeter, preferably with a beeper works much better.
  10. Flux is your friend the more the better.
  11. Traces that lead away from a chip before they bend are much easier to solder. I will take care with the next revision of my board layout.
  12. Solder mask is not really necessary. My board was etched using the toner transfer method and I was woried that lack of solder mask would be an issue. However it is not. Did I mention that a flux pen is your friend?

Udo

Solder paste - that’s the way to do it.

How do you apply it? Or would it wick between the pins of the chips as well?

Udo

I’ve used all sorts of methods, from paint brush to using a pin.
Just wave a hot iron over the pins, and surface tension does the rest.

I see. Do you glue you parts in place? If so, which kind of glue do you use?

Udo

No, no glue, the paste is sticky enough for most components

Got it. Do you then prefer an iron or hot air?

Udo

I don’t have hot-air (except at work), so an iron does it for me.
No use for BGA, or packages with pads on the underside, though.

Thanks a lot. Next time I will then try solderpaste and stick to my iron.

Udo

Tried flux pens, didn’t like it, i now use a fine paint brush to apply flux, fine solders helpfull too oh and in my case a 3x eye loupe

I’ve only done a little SMD soldering, and I tried it without flux.

It was a NIGHTMARE. What kind of flux do you guys prefer? I like the convenience of a pen, but maybe a brush would work better?

Also, I use a 45x magnifier, which makes it easy to visually inspect the joints.

In the latest copy of Everyday practical electronics here in the uk, July copy, theres a realy good article on home smd soldering. It doesnt sound nearly as daunting after reading it. They also talk about how good a particular snack oven was to reflow as it matched the temperature gradient needed without any modification.
I might give it a go myself sometime.

Gordon

Can one reflow without a stencil?

Every video I’ve ever seen on reflowing involves a stencil :P.

I used a Stannol No-clean X32-10i Flux pen. Reason for choosing this particular pen is that it was the cheapest one that said “no clean” on the label.
Using lots of flux surface tension pulls the solder under the pins. Much easier than expected. The only issue is that I can not see if the solder joints are good. To fine detail for my eyes. So I used a multimeter to double check each joint. Had two without contact and one unintended bridge. This was easy to fix.
The hardest part was aligning the pins to the board.
The other parts (resistors and caps) were just pretty small but easy to solder as well. My experience was: whenever something would not work: more flux and it works fine :slight_smile:

Btw: does anyone know a source for reasonable priced flux. The flux pen had a rather hefty price tag.

Udo

How hefty was it?

Here’s one for US$7.49.

digikey

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=KE1804-ND

5 bucks

Comparable price. I consider this is a lot of money for just 10ml flux.

Udo

You dont need a stencil.
In the EPE article he showed how the solder paste can be spread across the pads to a thickness and that when it is heated it pulls itself onto the pads. You have to get the thickness right which takes a bit of practice and a very small spreader.

Gordon

Comparable price. I consider this is a lot of money for just 10ml flux.

for hobby use it goes a loooooooooooooong way (i have some cheaper 3$ rosen flux stuff from the same people, dont think I have even put a dent in the pen yet, but for the price I am not wasting it either)

TchnclFl; I often do production without a stencil using 0806 parts. On one of my boards I had 6 resistors and 2 caps in a row. So I got a phone screen protector out of the packet(acetate works well too), cut off a piece that was far too big and stuck it over the pads. I then got a CD marker pen and a small ruler and drew a line across all the pads from 1 end to the other, I then peeled it off, took my scalpal and cut out the ink sections.

Now you have a basic stencil, just lay it back over the pads and squeegee the paste over. The plastic retains its stickyness for around 15 boards(but can still be used afterwards, just need to hold it yourself). Then I place the parts and throw them in the oven :slight_smile: