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Recently I built a SMD reflow oven using a toaster oven and a controller kit. This has made it really easy to solder up SMD PCBs (surface mount device printed circuit boards). You simply put blobs of solder paste on the pads, drop the SMD parts into place, put in the reflow oven and bake. You don't even have to be all that precise in positioning the SMD parts as the surface tension of the melted solder tends to pull parts into alignment with the pads. Here is a good Adafruit article on SMD/SMT (surface mount technology).

The paste can be applied several ways:

You can get it in a syringe and simply squeeze blobs of paste where you need it. This is fine for small projects but your hand will get tired (the paste is thick) and controlling the size of blobs tends to be difficult (and gets very much more so as your hand gets tired).

You can get a stencil and use a squeegee to wipe a layer of paste on the board. Its like silkscreening a T-shirt. While this is great for large board runs, you do need to get the stencil made (if you are having a PCB made you can often get the fab house to also make the stencil). You also need to make up some sort of jig to accurately (and repeatedly in the case of multiple boards) locate the stencil on the PCB. The great thing is that you get the perfect amount of solder (assuming of course the stencil is designed correctly). Here is a Sparkfun tutorial on it.

Since most of the stuff I do are one offs, I like the syringe method, but do find getting small blobs is difficult and my hand does get tired. I looked for better ways.

I found this cool little caulking gun like contraption on Tindie that looked great. But it's quite expensive to actually get sent to Canada (where I live).

I saw this project on making a dispenser using a small stepper and some 3d printed parts. It looked quite interesting and I actually ordered some stepper motors off AliExpress with it in mind (and I am very slowly working on a 3D printer). But the designer is not selling the PCBs anymore so I kept on looking.

One of my associates at the local maker space (VHS) happened to pick up an automatic glue dispenser while in Shenzhen, China. These are made to apply glue via a compressed air driven syringe but they work well with solder paste.

The idea of using these glue dispensers for solder has been around for some time. You'll find some more information here and here. And more information here.

You could even build your own as this article describes. This may be the cheapest solution especially if you have a well stocked spare parts box. You can get the needed air power syringes on AliExpress like these.

Essentially the solder paste dispenser is a box with a micro-controlled air solenoid valve. When you trigger it (either from a foot pedal or syringe mounted button) it sends a controlled pulse of air to the syringe. This pushes down the plunger pad and pushes out a bit of solder. Adjusting the amount of air pressure and the duration of the pulse, controls the size of the blob of solder paste.

Naturally there are several caveats you should be aware of:

  • These are inexpensive and therefore very very very cheaply made. Don't expect precision or high-end parts.
  • They need a source of compressed air to function. Great if you have a compressor but what if you don't. (I tested using a portable air tank instead and this is quite feasible.)

This Instructable will look at getting a glue dispenser, making some possibly needed modifications, setting up an air source and everything else you may need to use it for a solder dispenser. It will also cover some basic SMD soldering.

Please note that I am located in Canada so I am looking at everything from a North American perspective. You will need to make what ever local allowances are required for things like mains voltage, compressed air connector, pressure measurement, etc.

DISCLAIMER!! This project may deal with high voltages, high temperatures, compressed gases, dangerous tools, processes and/or chemicals. Any of these have the possibility to injure or kill you (and/or people around you) and damage or destroy your property.

Do not attempt this project if you are not competent in the various tasks required and able to do them safely. You will need to make various design decisions during a project of this nature and you need to be able to evaluate the various potential safety issues involved.

In my examples, I usually try to show safe ways of doing things but it is up to the user to decide on the suitability and safety of using any design, process or tool presented in this Instructable project.

Don't say I didn't warn you...

Also be aware that you will potentially void your warranty if you open the case...

Step 1: SMD Overview

As much as I like the old school through hole parts, you can't really stay away from SMD parts now. They allow for a much smaller PCB size and some parts are not even available in through hole style anymore.

An example is the Bus Pirate. A member of my local maker space (VHS) put together a Bus Pirate kit and it is mostly SMD parts. In the pictures you can see that I used a solder paste dispenser (this was the one the same member brought back from China) to paste up the board. Then I simply dropped on the parts and baked it in the reflow oven I had made earlier. While this board is not overly complicated, it would get very tiring pasting it all by hand. The solder paste dispenser makes it a breeze and you can get a PCB pasted up, and parts dropped on and baked in no time at all.

Note that this ability doesn't take away issues with user error.

On this board I initially installed one of the large caps (C10 if you are curious) backwards. I was fine for the first few minutes (just enough for me to assume I had done everything properly). Later I had it hooked up to a PC and was holding it in my left hand. I smelled something burning and was busy looking everywhere else in the shop (naturally assuming it could not be the Bus Pirate) until I noticed the smoke and a small flame coming from from one of the capacitors. Scared the %^&$ out of me and I dropped the board and yanked out the USB cable. Unfortunately, the cat's litter box was also to my left. Fortunately the cat litter box was pretty clean.

The Bus Pirate did survive. I hand-soldered a replacement cap with the correct orientation and it is now working fine.

But I always think of the litter box when I use it....

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More by packetbob:How to make a solder paste dispenser for SMD projects... Making A SMD Reflow Oven 
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