next topic »

[on:]

I have looked at many design recently--like all the Arduino clones on Kickstarter and pretty much any prototype circuit--they either use breadboards and Arduino shields or complete SMD components. I understand that SMD components are used because they are smaller and cheaper DIP components. I also completed a board recently where the cost of the PCB was more than all the components combined. That's a little ridiculous. I want to move to SMD parts. However, I am at a standstill.

It is difficult to hand solder even a relatively large SOIC-24 even with a nice Hakko-FX888 with a curved tip, although my solder was pretty thick. I tried to flux the pads and drag solder, but I seem to create many bridges and removing even just one is miserable. For this reason, I want to move to non-iron based methods such as the reflow skillet with solder paste, however I do not know where to buy it. I heard that it must be kept cold or it will lose its chemical properties, and I hear it is applied with a syringe. Is there a tutorial and accompanying product that I may buy to hopefully solder TQFPs 32s, LQFP 100s, and maybe QFNs?

[Reply #1 on:]

Lots of tutorials available: http://lmgtfy.com/?q=how+to+surface+mount+solder+paste

[Reply #2 on:]

I bought a hot-air station and that's been pretty easy. Just run a line of solder past along the pads, hit it with the air, and clean up with braid if necessary.

Also one advantage to having the hot-air station is that you can remove components.

______
Rob

[Reply #3 on:]

Alright then. I have access to a hot air station. Where would I obtain solder paste and an appropriate syringe?

[Reply #4 on:]

Alright then. I have access to a hot air station. Where would I obtain solder paste and an appropriate syringe?

The solder paste intended for hand rework comes in a syringe.

Chip Quik SMD291SNL10 Rework Solder Paste, 10CC, Lead Free
Chip Quik SMD291AX10   Solder Paste, 10CC, 63/37 SN/PB

The prices seem to be in the low to mid $20 range.

[Reply #5 on:]

SMD Hand Soldering

[Reply #6 on:]

You can also use the skillet reflow method.  SparkFun has a great tutorial.  This is how I create my custom boards now.

[Reply #7 on:]

Hay there heres a photo of my PCB i solderd with a soldering iron. all SMD some are 0805s
I have had years practice so im realy good at SMD now its sooo easy.
Just get in there and try it.

[Reply #8 on:]

Many different ways to do it. My preferred approach is to source a stencil from Pololu. That makes it super easy to get the right amount of paste where I want it. Simply select a 4-mil thick stencil for normal work, and 3-mil for a fine job (i.e. where you have microprocessors that have pins with a 0.5mm pitch, for example).

Simply surround the board with other spare boards, tape down, then position the stencil carefully, tape as well. spread the solder paste with a thin stainless steel applicator blade or putty knife. Place all components, run through you favorite reflow technique - I happen to use a re-purposed toaster oven with the rocket scream reflow controller.

The components come out clean, the solder is usually perfect and requires no additional work. This is especially important for chips with finely-pitched pins as those are very easy to bend during subsequent cleaning-related touch ups. I use no lead, no clean Kester NXG1 solder paste that I bought (I think) at Techni Tool.

[Reply #9 on:]

A cheap solder might be the source of your problems as well; as you can see from Lakes' example it should be pretty straightforward. What are you using?

[Reply #10 on:]

I use a flux pen, solder paste and a hotplate. See http://www.hobbytronics.co.uk/hotplate-smd-soldering. The trick is to get just the right amount of solder paste on the pads for ICs, so that surface tension pulls all the solder on to the pads, leaving no solder bridges. I find that warming the solder paste first helps. If you do get solder bridges, I use desolder braid to remove them; but I don't put solder on the desolder braid as shown in then tutorial, I run the flux pen over the braid instead.

[Reply #11 on:]

One thing I forgot to mention is that you can make a cheap "Hot Air Station" from a Radio Shack desoldering tool and an aquarium air pump.  The desoldering tool has a heater like a soldering iron, a hollow tip, and a squeeze bulb to apply suction.  Inside the hollow tip is a chamber to catch the solder.  You pack the chamber with copper wire to provide a large surface area to heat air and replace the squeeze bulb with a cheap aquarium air pump.  The result is a stream of hot air coming out the tip.

[Reply #12 on:]

I have my stencils lasercut and use soldering paste, a steady hand, and a toaster oven. This method is covered all over the web and works well if your only doing a few.