Introduction: How to Make a Solder Paste Dispenser for SMD Projects...

About: technology hobbyist...

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....

Step 2: How to Get One....

As I mentioned my associate at VHS picked up a glue dispenser while he was visiting Shenzhen. I didn't want to have to go that far, so I shopped on the Internet.

You can find these glue dispensers at various vendors on Ebay and AliExpress. If you are brave (and can read Chinese) you can try TaoBao but then you have to arrange shipping. They all look quite similar and have a variety of brand names. I don't think there is much difference in the quality.

I got mine from a vendor on AliExpress based solely on the best price I could find. It got to me in 8 days and the package was pretty beat up by the time it got here.

There are the digital versions like the one I got, and simpler analog versions.

The package comes with a variety of parts as the picture shows. Different vendors may include different amount of accessories. You won't really need much more than a single syringe and some needles. You can get more bits on AliExpress like this assortment here. You can find lots of others on the web.

Step 3: Fixing the AC Wiring...

As I mentioned these are really cheaply made. The power supplies on these are not the auto-sensing units that can work on 110 or 220 VAC. These devices have a transformer and it has to match your mains voltage (110 VAC in North America).

Now depending on your unit, and who you get it from, you may need to make a modification to the transformer wiring to make it work on 110 VAC. The one my fellow VHS members brought from Shenzhen was wired for 220 VAC but the transformer primary had a centre tap and he was able to easily modify it for 110 VAC. You may be able to do this or simply replace the transformer with one meant for 120 VAC.

Though the unit I purchased was advertised as 220V, when it showed up you could see they had replaced the transformer with a 110V version. They even had written 110V on the back label. No CSA or UL sticker though.

However as soon as I unpacked the device I felt a "clunking" sound from inside whenever I jiggled it. I removed the top cover and discovered a few things with the 120 VAC wiring:

  • The original 220V transformer had been replaced with a 110V one but looks to have never been tightened properly. It was loose and its mounting flanges were actually bent. That explained the clunking noise.
  • One of the solder terminals on the fuse holder was melted into the holder (too much heat when soldering in the factory I guess).
  • Several of the AC wires had been damaged when being stripped and barely had any strands left soldered in place. Two of the wires broke just due to my moving them around when dealing with the bent transformer bracket.

Wasn't really expecting great QA on this anyway.

CAUTION: Remember you are working on line voltage here. Make sure the unit is unplugged when you are do any of this sort of work.

However I wanted to feel safe while using it, so I did the following:

  • Removed the transformer, fixed its flanges and mounted it back in place with proper machine screws and nuts (rather than the cheesy screw just threaded into the bottom of the case).
  • Replaced the fuse holder. Kept the 1/4 Amp fuse as this device doesn't draw much current.
  • Replaced all the 120V wiring connecting the power socket, fuse holder, power switch and transformer. Any connections were also covered in heat shrinkable tubing. Note the heat shrink pictures show my re-using some of the original wiring. Shortly after this, I broke them and that lead me to re-wire it all. Better safe than sorry...

While I do have a full size heat gun, I picked up this little SparkFun unit. Due to its small size it is easier to use in tight spaces without heating up everything.

Once you have completed the AC wiring give it all a once-over to make sure you have connected everything properly. When you turn it on the LED display should light up with what the "SET TIME" is configured for. If it starts cycling non-stop then the DIP switches may be incorrectly set. Turn it off and continue reading.

If it starts smoking then it's probably best to turn the power off...

Perhaps go have a drink to calm your nerves...

If, for whatever reason, you want to replace the transformer, the one in my unit measures 14V with no load and drops to about 10V when the solenoid is powered. The load with the solenoid powered is about 0.40 Amps.

Step 4: Fixing the Air Stuff...

Now that the AC wiring is good, you should check the solenoid. On mine I noticed it was held in place by a single (and loose) screw that looked like it had been picked out of the garbage. Once I removed the screw I saw that the solenoid actually had two mounting holes. It looked like the case actually had two holes also but where the second one was located would interfere with the PCB location.

I kept the solenoid in its location but marked out where the second hole should be. I then drilled this out to allow proper mounting. The screws are M4. I had some in my parts' bin but they were too long. It was easy enough to cut them down with a hack saw and file the edges off. I then screwed them in place. For any screw you should make sure you use lock washers or use some LockTite thread locker to make sure they don't come loose with vibration.

Now look at the various hoses in the control box. A couple of things I noticed were:

  • No clamps on any of the connections. Just press fit. Not sure how long these will hold up to 60 PSI air.
  • No slack in any hose. For every run they used the shortest length they could and this kept things pretty tight.

The hose connections didn't look too strong but I wasn't sure of the best sort of clamp to use. I thought of small wire ties but since these don't wrap in a full circle there was a chance for leakage. While I was getting parts for the compressed air connection I found some tiny hose clamps. These are 1/4" and don't really fit as tight as I would have liked but are better than nothing. I thought this would give extra protection against a hose coming loose. They were a bit pricey ($1.37 for two) at the big box hardware store. You can probably find them much cheaper at an auto parts store or possibly an appliance parts store.

I put the clamps on every hose barb in the controller. You will have to pull off each hose in order to put on the clamps. Make sure you do up a diagram and take some pictures before you start pulling off the hoses. You will not remember they connect. Trust me... I know.

Now another thing I noticed was that some of the hoses were pulled pretty tight. One in particular (from the left of the regulator) was too short to let me move the solenoid so I could screw it in properly.

The vinyl hose used in the control box is 6 mm. The connectors on the front and back panel and the internal regulator are push fit. You just push the tube into the connector. To release, push in the plastic collar and you can pull the tube out. The rest of the connectors are the barbed type.

I couldn't find 6 mm tube but I did find some 1/4" and tried replacing the internal hose. It seemed to connect fine but when I pressurized the system I found that it leaked from the push fit connectors. So 1/4" vinyl tube does not seem to work with the 6 mm fittings used in the controller.

I ended up cutting a section off of the 6 mm supply line that comes with the unit to replace the internal hose. This let me move the solenoid as I wanted.

CAUTION: Compressed air can be dangerous. Make sure you wear safety glasses.

Be advised that even with all the clamps installed and everything tightened up, I still hear air escaping from inside the box. Not a huge amount so I don't think I'll go any farther in hunting it down.

Before you close up the case you should also check the low-voltage cabling. Look for any bad solder joints of wires that have had strands cut through when being stripped. Hard to detect I know. Can't hurt to re-solder anything that looks suspect. I noticed the wiring in mine was pretty bad and the quality of the 3.5 mm jack for the trigger was equally so. I suspect I'll be replacing the jack after several uses...

Once this is done you can close up the case. Best to power it up and make sure things still operate.

Step 5: Fixing the Triggers...

The solder dispenser has three ways to trigger a shot:

  • Front panel push button (located on lower left side)
  • Syringe mount push button (connected to rear jack)
  • Foot pedal (connected to rear jack)

I prefer the foot pedal as I find when I use the syringe trigger it moves the syringe slightly and I don't like this. YMMV.

My syringe trigger was missing a cable to connect it. It appears you can just use a 3.5 mm stereo cable. However my switch assembly looked pretty cheesy. The jack was barely more than a hunk of plastic and some pieces of scrap metal. I decide to get rid of the jack and just hardwire a length of cable into the switch assembly. This let me get a length I was happy with and ensure the switch assembly would not fall apart. I used hot glue to lock the wire and switch into place before I screwed the assembly back together. I then added a 3.5 mm mono plug to the end of the cable.

As for the foot pedal, it appeared fine but the cable it came with was too short for the way I wanted to position things. I replaced it with a longer cable. Sorry, no pictures for this. However to open the foot pedal you do the following:

  1. Remove the 2 screws you see on the bottom of the base plate
  2. Remove the baseplate
  3. Remove the small screw near the edge of the pedal
  4. Carefully hold the pedal assembly in your hand
  5. With a pair of pliers pull the pivot rod out from the side near the screw you just removed
  6. Once the rod is free, the pedal will spring open so make sure you don't lose the spring

Do this in reverse to put it all together after you replace the wiring.

Of course you can use any N.O. (normally open) switch to activate a shot. If neither of the supplied triggers work for you feel free to rig up something interesting. Maybe an eye blink detector...

Step 6: All About Air.....

The solder dispenser needs compressed air. Not a huge amount of volume but at least 60-80 PSI. Naturally this means you need an air compressor. Since these are typically quite loud you will want one as far away from your desk as possible. I am quite lucky as mine is located in my garage but I have a hose running back to the basement of my house where my workshop is.

The biggest issue with getting air hooked up to the solder dispenser is that the supplied connector doesn't work with the standard 1/4" quick connect fittings typically used in North America. While you may be able to source an adapter, I just put together the following parts:

  • Quick Connect Male Fitting - Mates with end of existing air hose
  • Air Filter - Keeps crap and water from air hose getting into dispenser. This is optional but if you are using old hoses you may want one. It has a drain to release air and any water or oil it has captured.
  • Ball Valve - Shuts Off Air - Again this is optional. Since I don't have a whole lot of trust in the dispenser air connections, I wanted to be able to shut the air off without having to go to the garage.
  • 1/8" Hose Barb - You connect the 6 mm vinyl hose to this. I also used a hose clamp on this.
  • 1/4" Hose Clamp - I used the same style as I did inside the controller. These have very sharp edges so I may try to find nicer ones. Perhaps fro a car parts store.

All these parts should be available at Home Depot or stores like that.

From the pictures you should be able to see how I put this together. Make sure you use Teflon tape on all the connections (or some sort of pipe sealant) or else you will get air leaks. I wrap the tape around the thread in the opposite direction as the thread turns into the fitting to make sure the tape doesn't come loose when you tighten things.

Also make sure you keep the tape one thread up from the end of the fitting to make sure the tape doesn't actually block part of the pipe. I usually give four wraps of Teflon on each connection.

When you are done you should be able to push the end of the 6 mm connecting vinyl tubing into the back connector of the solder dispenser. I push it in till it bottoms out; then slowly apply air pressure and make sure nothing leaks. You should be able to push the front panel "SHOT" button and get a burst of air. Make sure there is nothing in front of the unit that can get blown around. Wearing eye protection would probably be a good idea.

As for the compressor itself, make sure you drain it every few days as the tank will fill with water and start to rust. Make sure you turn it off when not using it so it doesn't run unnecessarily.

On my air compressor I have a water trap/filter built into the pressure regulator. When I use the solder dispenser I set the compressors regulator for 60 PSI and then use the regulator on the dispenser to reduce it down as needed. And if you look at the compressor picture you'll see my garage is quite messy. Use this as an example as to how your shop should not look.

CAUTION: Again have respect for compressed air and wear safety glasses. The air can easily blow something into your face

Step 7: But I Don't Have a $%^# Compressor...

Of course if you don't have an air compressor you have to look at other options.

If you are a SCUBA diver and have your own tank you may be in luck. I've not been able to test but you can get an adapter like this that lets you connect normal 1/4" NPT pipe fittings (typically used on compressed air fittings) to your BCD (buoyancy compensator device). As I understand things this would give you access to the LP (low pressure) which is about 120-140 PSI. You would then want to connect a separate regulator to drop the pressure down to the 60-80 PSI needed by the solder dispenser. Certainly the advantage to this is that the SCUBA tank is filled to a really high pressure so it holds a lot of air. The disadvantage would be the cost.

Another option would be to use a CO2 (carbon dioxide) system (these are becoming more and more popular for home brew draft beer systems). I would strongly advise AGAINST this, as a CO2 leak (in a small room like a workshop) could asphyxiate someone.

The best option is a portable air tank. These are typically sold for inflating tires. You fill the tank up and then take it to where ever you need a source of air. The tank I had was able to be filled to 125 PSI via a Schrader valve (this is the fancy name for a tire valve). There is then a hose with a tire filler adapter so you can fill a flat tire. It also has a valve assembly to connects the hose, Schrader valve, pressure gauge, high pressure release valve and the tank. They come in 10 gallon or 5 gallon sizes. The one I tested with was 10 gallons and I recommend this size.

In order to make it work with the solder paste dispenser I made a few modifications. First you need to remove the hose. Then you need to add a pressure regulator and gauge to be able to lower the high pressure (120 PSI) of the tank to something lower for the input to the solder dispenser. This allows you to fill the tanks as much as possible (therefore getting the longest run time) without putting too much pressure into the solder dispenser. I used a small cheap regulator and valve I got for $9.00. Since the valve assembly on the tank is small you will see that I had to use some lengths of brass pipe to make room for the regulator otherwise it would hit the tank when you tried to screw it all together. My setup looks a bit strange as I just set it up for testing and used what I could find in the shop. Remember to use Teflon tape on all the connections. After the regulator I added a female quick-connect fitting to allow the adapter we made earlier to easily connect to it.

Now it was a simple matter to get the tank filled, take it into the shop and connect it to the solder dispenser. No compressor needed.

Of course the big question is what kind of run time (for lack of better words) will you get from the tank? Since solder is expensive and I did not want to waste any (not to mention it is toxic to dispose of) I went looking for something similar to test with.

Luckily my wife was painting some porch railings and we had a tube of caulking handy. While not quite as thick as solder it was the closest I could easily find. Since my dispenser came with a second syringe I filled it up to a similar level as a full solder tube. When filling the syringe try to leave the bottom hole clear so most of the air can escape when pushing in the plunger.

Now I just needed to do a test run with the air tank and see how many shots I could get. Luckily the dispenser control unit has several functions, one of which runs in an auto mode. It starts when you press the trigger, lets air out for the SET TIME, then waits the INTERVAL time, then repeats till you hit the trigger again. I set this up and played with a variety of the settings. I used an old piece of wood to leave dabs of caulking on.

For my test:

  • I filled the air tank to 110 PSI.
  • Set the tank regulator to 60 PSI.
  • Set the solder dispenser regulator to 50 PSI.
  • Set the dispenser SET TIME to a range between 0.2 - 0.3 sec and had the INTERVAL set for 0.5 sec.
  • Then I let it rip.

I got 1184 shots before the pressure in the tank dropped to 60 PSI. I'm sure I could have got another hundred or more till the pressure dropped below what was needed.

1184 blobs of paste would allow you to solder several hundred parts (minimum, as it depends on the number of pins/pads) and I think this is much more than anyone would try for hand-placed SMD soldering.

Based on my testing, I think the 10 gallon portable tank is quite viable to use instead of an air compressor. You should be able to fill it up at any place that has air for tires.

CAUTION: Again have respect for compressed air and wear safety glasses. The air can easily blow something into your face. Also be aware that a fully charged tank could potentially be dangerous. Keep it in a safe area where children, cats, etc cannot play with it.

Step 8: Something About Solder...

Let's talk about solder paste... Basically it is tiny lead balls mixed with flux to make a paste. When it is heated to melting point the lead balls flow into each other and join the metal's surfaces as the flux cleans the area.

Currently I use leaded (I plan to try lead-free eventually once I get a few more boards under my belt) CHIPQUIK SMD291AX that I get from DigiKey. It's a bit pricey compared to the much cheaper import stuff but a little goes a long way and I always get decent results. I think it's worth the extra money considering it's low cost compared to all the other equipment and your parts. Naturally YMMV.

When you order the paste from DigiKey it comes chilled in an insulated bag along with a freezer pack. This is to keep it cool during shipping. All the mainstream solder vendors insist you keep the paste refrigerated and give it a limited shelf life. They say the lead will separate from the flux if it gets too warm (or if it gets frozen). I don't worry too much about it, though I do try to keep it cool. I don't go as far as putting it into the fridge (don't want to contaminate our food with lead) but I try to store it in cooler areas of the house. Certainly for any production boards you want to follow the solder paste maker's recommendations.

CAUTION: You should know that lead is very poisonous. I have used rolls of lead solder for many many years with no issues (well... no known issues) but suspect you could easily inadvertently ingest the dried solder powder. Make sure to wash your hands after handling solder and pasting up a PCB. If you muck up a board and end up wiping off all the paste make sure you clean your work area and don't have globs of solder paste that may dry up and turn to lead dust. Keep little kids away from your work area as they are much more susceptible to lead poisoning.

Now my solder dispenser just came with one size of syringe, which is larger than the syringe that the solder comes in. I simply squirted all the solder into the larger syringe and used the needle that came with the solder paste. When you squeeze in the solder, try to put it all to the side and keep the bottom hole open. Then when you push the plunger in you can let as much of the trapped air out as possible. Too much air isn't the end of the world but it will make the action more springy than you may want. Another trick to get out air is to remove the tip, push a piece of wire (as thick as will fit through the hole) in through the solder to the air space. Then twist and wiggle the wire a bit to create a path out of the hole. Now you can fire a few shots and hopefully the trapped air will be able to vent out. You may have to do this a few times.

The syringe that the solder paste came with should have come with a tip and a cap to close it. Place the cap on the paste dispenser syringe you just filled with solder paste. Keep the tip in a safe place. I keep mine in a small jar with a bit of Alcohol to keep them from getting gummed up.

Step 9: A Holder for All the Bits...

The glue dispenser comes with a stand of sorts to hold the syringe. However it is quite large and tips over pretty easily. I was thinking of better ways to hold things when I saw a 3/4"' schedule 40 coupler laying on the floor (I had actually bought it for a laser tag project I'm also working on). Turns out it is a nice size to hold the syringe but wasn't quite deep enough to allow for the syringe tip.

However, I had a hunk of 2x4 also sitting on the floor (my shop is often really really messy) and I figured I could use the depth of the 2x4 to make something up. Basically, I used a hole saw to make a shallow hole in the 2x4 that was large enough for several of the 3/4" couplers to fit into. I used a smaller hole saw to make an inner cut and then used a chisel to remove the unwanted wood. This left a hole the coupler would fit into but I still needed extra depth for the syringe needle.

Next I used a forstner bit to make a smaller diameter hole. This provided the required depth inside to make room for the syringe needle.

Then I decided to get a bit more fancy. I used the table saw to chamfer the edges of the 2x4. During this process I happened to glance at my tool box and noticed a package of rare earth magnets I bought years ago and had not used. I though that putting some of these on the bottom of the syringe holder would stop it from moving as the magnets would stick to the top of the glue dispenser case. So that's what I did. I simply drilled small holes big enough for the magnets (with a small forstner bit) and glued them in with a bit of hot melt. Now I could place the holder on top of the glue dispenser and it wasn't going to move anywhere.

As you can see in the pictures I can place the syringe in one coupler and use the others for tweezers and other SMD tools.

Couple of caveats:

  • The magnets did not stick as well as I had though they would. It could be due to their age (probably as I bought them 15 years ago) or perhaps they needed a steel backer to get more power. It works fine but again doesn't stick as well as I thought it should.
  • After using it for a while I have decided to remake the holder. I'll just use two of the couplers (one for the syringe and one for the tweezers) and then make a hole to sit in a small jar of alcohol that I use to put the syringe tips into to make sure they don't dry out and gum up.

CAUTION: Power tools can also be dangerous. make sure you have no loose clothing around rotating machinery.

Step 10: Setting It Up...


We are finally ready to actually use the dispenser.

On the front panel you have the following controls:

  • POWER - Turns the dispenser on and off
  • SHOT - Sends the trigger command. The remote pedal and syringe trigger connect via a jack on the rear panel and duplicate this function
  • DISPLAY - Shows the SET TIME as XX.XX seconds
  • SET TIME - Adjusts the time the air solenoid stays open in seconds (adjustable from 00.01 to 99.99 seconds)
  • INTERVAL - Adjusts the delay between air solenoid activations (only used in some modes)
  • AIR PRESSURE - Sets the pressure of the air feeding the syringe
  • VACUUM - Adjusts the amount of vacuum or pull-back suction applied to the syringe when you are not sending it pressurized air. Just leave this shut as it is not needed for solder paste
  • AIR OUT - Not labelled but this is where the syringe air tube connects
  • PRESSURE DIAL - Shows the pressure of the syringe air

The back panel has the following:

  • AIR IN - This is where the compressed air source connects to
  • DRIP - I believe they meant to say DIP as these are the DIP switches used to select the various modes.
  • FOOT SWITCH - This is where you connect the foot pedal or syringe switch
  • POWER - The power cable connects here
  • FUSE - This is a 1/4 AMP fuse

First thing you need to do is setup the mode via the DRIP switches. Looking at the manual will not help you much (unless you can read Chinese) but I have created a spreadsheet (based on various web posts in other sites and plain old trial and error) that shows the various modes.

For our application you need to select "F5" as this will give you a single shot for each activation of the trigger. There are several other modes that while not applicable to our use, may be handy should you find other uses for the controller. I found the continuous (F3) mode handy for testing with the portable air tank.

Next plug in whatever trigger you plan to use.

Now we can setup the front panel controls.

First turn on the POWER.

Then set the TIME INTERVAL to say 00.20 seconds.

Then set the INTERVAL to 0.1 seconds (this setting doesn't really come into play for this mode except that you can't trigger the next shot till after this has timed out. So the lower the better, but it can't be 0.0.

Next set the AIR PRESSURE to 50 PSI. You will see this in the pressure gauge.

And turn the VACUUM right off. This controls the amount of air sent through a venturi. This creates a vacuum which is applied to the syringe air line when a shot of air is not being sent. It stops a thinner glue from dripping. You don't need this with the thick solder paste. Plus it make a lot of noise as it bleeds off the air it needs.

Now connect the syringe that you have filled with solder paste. Holding the syringe on a paper towel you can try a shot. It may take a while to clear the air out of the syringe but eventually you should get a blob of solder squeezed out on each shot. If you don't, there are several things to adjust:

  • Turn up the pressure (I would not go past 60 PSI to avoid stressing the dispenser plumbing)
  • Make the SET TIME longer
  • Change the tip size. The solder paste typically comes with a tip but you can try the ones you may have got with the dispenser

There is no magic setting, so you will just have to experiment. You should see the gauge move and the feel the syringe pulse with every shot. The brand, viscosity and temperature of the solder paste will all impact the performance. You will find that the heat from your hand holding the syringe will cause the paste to thin a bit, so realize you may have to adjust things as you go.

Once you get a small blob from the syringe on every shot, it is time to try pasting up a PCB...

However if you are really geeky (or you think you may find some other uses for the controller) then you may be interested in how accurate the settings really are. Below shows the measured pulse width at small range of settings:

SET TIME setting vs measured pulse width

00.10 = 0.101 sec

00.20 = 0.202 sec

00.30 = 0.304 sec

00.40 = 0.404 sec

INTERVAL setting vs measured pulse width

0.1 = 0.110 sec

0.2 = 0.210 sec

0.3 = 0.310 sec

0.4 = 0.410 sec

I don't have any way to measure across the whole range accurately, but this gives you an idea. The controller board outputs a 9.5 VDC pulse to the solenoid. The solenoid draws about 0.3 Amp. The controller uses a TIP122 transistor (with no heatsink) so you should be able to load it up a bit more (it depends on the transformer capacity). And while the wires to my solenoid are colour coded (black and red) the polarity is actually reversed so check before you try connecting anything polarity sensitive to it.

Step 11: Using Your Solder Paste Dispenser...

In order to paste up an SMD PCB you should get the following set up:

  • Clear Clean Work Area - You want a roomy desktop with space for the solder dispenser (mine sits at the rear of the desk), room to lay out all the parts and room to work on the PCB.
  • Lighting - The more the merrier. Decent overhead lighting for the desk and some adjustable task lighting is good. I also have a small bright flashlight for those spots you can't reach with the other lights.
  • Tweezers - You will need these for various tasks. Some straight ones and ones with a bent shape are good to have.
  • Magnifying Lenses - Again the more the merrier. I have a large desktop-mounted one that has lighting. I also have one that you wear as a visor and a couple of normal ones.
  • PCB holder - While you could use the Panavise style the problem is that they can swivel and all the parts can drop off. Best you use one that can stay flat on the desk.
  • Isopropyl Alcohol - You need to keep everything clean so use lots of this. I find it really dries out my hands so make sure you use hand cream. But not while you are working on the project.
  • Clean Rags or Paper Towels - Lots of these are need to not only initially clean the PCB but to clean your hands, syringe tips, etc. I'm sure you will get a PCB 90% pasted up and then smudge it up and have to wipe it clean and start all over. This happens to me often.
  • Small Jars - I find these handy to store syringe tips. I have one partly filled with Alcohol that I use to store syringe tips after use. If you don't do this the residual solder paste will harden and render the tip useless.
  • Small SMD project PCB (and parts) - This is sort of needed.
  • White Paper - I use this to lay out all my parts prior to placement.
  • Pencil - For writing down part information on the paper.
  • Low Height Tupperware Style Container with Lid - If you need to leave the board for a bit (say overnight as your eyes are getting tired) then you can carefully place it in the container and put on the lid. This way nothing can accidentally smudge things. Be careful you don't jiggle it too much when you open it later.
  • Narrow Solder Wick - Used for removing solder bridges.
  • Solder Sucker - Also used for removing solder bridges.
  • Soldering Iron - Surprise! Even though you are using solder paste and a reflow oven you still need a decent soldering iron with a small pointy tip.
  • Multimeter - Best to get one with a diode test mode to look for shorts.
  • Fine Tipped Test Leads - Get some that are really pointy, like "stabby" pointy. Then put something on the tip to protect them (and you) while storing them.

Reflow Oven - Once you have placed the parts on a pasted up PCB, you do have to bake it in a reflow oven. This Instructable details the construction of a pretty decent oven :-). You can find lots of other resources on the web.

Ok, let's start on the project. As an example I am using the SMD Star project a friend of mine has made up. It's a very good beginners kit for getting into SMD. You can even hand solder it if you want. But if that was the case you would not be reading this.

First, carefully open the package and make sure you have all the parts. SMD parts are pretty small and in some cases have no markings. You have to make sure you keep track of them all. The SMD Star comes with a picture showing certain parts as certain colors. The parts themselves are in a paper carrier strip that is colored to match. Make sure you can identify what part goes where and you have no missing bits. As the SMD parts are quite cheap you may find you get extras of some. Do not be tempted to open the clear plastic film covering the part.

Now clean your PCB with a paper towel (or clean rag) soaked in isopropyl alcohol. After this, try to not touch the PCB pads with your fingers as it will get oil on the pads and that is never good. Hold the PCB by the edges. Make sure you put the cap back on the bottle of alcohol every time you are done with it. I have knocked mine over several times and having a flammable liquid splashed around your workbench is not a good idea.

CAUTION: Make sure you work in a well-ventilated area. Probably a good idea to have a fire extinguisher around just in case.

Now put the PCB into a holder. As mentioned, a model that just lays flat on the table is best. The holder has a bit of weight to it and this keeps the PCB from moving around.

At this point I get a piece of white paper (or any lighter color as this makes the parts easier to see) and lay out all the parts. First I draw a line around a section of the paper for each separate value of component. So if there are seven 10K resistors, I create a drawn box large enough for all the parts, write down the part value and I write each one down. So perhaps R1, R3, R4, R6, R11, R78, R80. So now I have a section on the paper with the part value and part numbers. Only now do I remove the plastic covering on the paper parts strip and remove the parts. Then I place one above each part ID. I do this for every part. Make sure that you don't sneeze and you don't have a playful cat. This all takes up a bit of room so make sure you still have a clear area to work on the PCB.

If you have kept the solder paste syringe in a cool place now is the time to get it. Give it some time to come up to room temperature if you have kept it in a fridge. If you do keep it in a fridge keep it in an air tight bag. Do not take it out of the bag till it comes to room temperature. This avoids getting condensation in the solder.

Now remove the end cap you previously placed on the syringe. Place it in the small jar of alcohol. Remove the tip if you had it in the jar and dry it off with a piece of paper towel. It will have a bunch of runny paste and alcohol that you want to remove if possible. Screw this tip onto the syringe and fire off a few test shots into a paper towel. Make sure you clear out the running paste before you start using it on the PCB.

CAUTION: Again have respect for compressed air and wear safety glasses. The air can easily blow something into your face. The syringe holder and connecting air tube should be able to handle the air pressure but one never knows for how long.

Now you can apply the solder paste. Looking at the PCB you can see the pads for the various parts. Judging how much paste to put on a pad is a bit of an art that you will get better at as you get more experience. The pad size is somewhat indicative of the required solder. Another good idea is to dry fit the part ahead of putting on any paste. Look at how the part fits on the pads. This can help you judge not only how much solder may be needed (the part pad size is usually smaller than the PCB pad), it also shows you where on the PCB pad you should put the solder paste. I always try to have the paste located on the PCB pad in the spot where the SMD part solder pads will rest. Solder blob size is a bit of a black art and you will get better as you get more experienced. The great thing is that the solder paste dispenser makes things so easy you'll get many more done. Expect that you need to adjust air pressure and shot duration while you are pasting a board as you need to adjust for pad size or other variables. Don't be afraid to adjust and also a good idea is to make a note of what settings seem to work best.

Put the syringe over a paper towel and fire out a few shots. Wipe off the tip if there are any globs sticking to it. I typically hold the syringe tip at a 70 to 80 degree angle off the board. The idea is that you want the solder to stick to the PCB (kinda like a cow patty for you farming folk) as it gets pumped out of the syringe. Again this is something you will need to practice and will get much better at after a few boards. Make sure the solder blob actually sticks to the PCB and doesn't fall off as you remove the syringe tip.

I try to keep a folded up paper towel that has a little alcohol on it to wipe up anything unwanted and to keep the tip clean.

In general, I have found I typically put on too much solder rather than too little. In most cases it is easier to add solder than to remove it. When it comes to ICs it gets a bit more interesting. If it is a wider pitch size part (like the ICs in the SMD Star kit) you can usually fire a small blob onto each pin pad. For smaller pitched ICs you can lay a bead of solder across all the pins (try to locate where the IC pins will land on the pads). When the board is baked the surface tension of the molten solder pulls it to the separate pins. Either way you'll find you sometimes get solder bridges on parts (most noticeably the ones with fine pitched leads) and you will need to remove these later.

Once you have done all the pasting give the board a once-over to make sure not only have you got solder on all the pads but also that you haven't put solder where it is not needed. If your PCB also has through hole parts these will be added later. You don't want to make it more difficult by accidentally filling up those holes with solder paste.

Now you can start placing the parts. At this time it is really nice if there is a parts list (sometimes referred to as a BOM - bill of materials) so you can track the parts as you place them. If you followed the step above, you will have each part written down on the paper. It is best to start with the smaller parts and work towards the larger ones. Also you should try to work from the inside area of the board to the outside area.

Using tweezers you can gently place each part. Don't push too hard but make sure the part is stuck in the blob of solder. While you can try to keep the parts nicely aligned, don't worry too much as the surface tension of the molten solder will align them as it pleases no matter how you place them. Just make sure they are close to where they should be and all should be good. You may find tweezers that have bent tips make it easier. Or not.

As I place the parts I cross out the part number (like R1) on the paper so show that I have placed it. I like to double check as I go as it is easy to make mistakes. This is not something you want to rush.

While resistors, inductors and ceramic capacitors don't care about polarity, you will have to make sure to pay attention with parts that do care. ICs transistors, LEDs, electrolytic cap, tantalum caps and other parts are polarity sensitive. If you place them incorrectly your circuit will not work (best case) or capacitors may explode and/or burst into flames (worst case). Unfortunately, because the SMD parts are so small finding a marker (like the dot on an IC for pin 1 or a flat spot on a LED or a band on a diode) can be very difficult. Often I have to refer to the parts specification page (search them up on the web) to try to figure out the position. If it is a kit, finding a picture of a completed board can also help confirm your position. Parts like a LED typically have an extremely small dot or other such marker that sometimes you really have to look for.

Once all the parts are placed I give the populated board another once-over. Be careful as an accidental strong bump could shift things and make a mess. Again make sure you are not missing anything and perhaps confirm that each part is correct. At least as much as possible. Some parts do not have any markings so you sort of have to Hail Mary it at some point.

Now if you are not happy with things, you have some options:

You can scrape off all the parts, clean off the solder paste and start all over. If you go this route you have to make sure all the solder paste has been removed. If some is stuck in a hole or elsewhere it will melt when you eventually bake the board and could possibly cause a short or a really hard error to find later. You can try to salvage the parts but again you have to really clean them off and it may not be worth your time.

You could remove some of the parts and just re-work an area of the board. You have to make sure you don't disturb the area you want to save. You also have to make sure the alcohol you use to clean does not dribble into the good area and dissolve the solder paste where you need it. A possibility here is to bake the board after you have done only a certain point. I would expect you could bake a board several times but I have not tried it. YMMV.

However before you proceed with cooking the board:

  • Turn off the power and the air supply to the dispenser.
  • Shut off the compressor (if you are using one) and drain the the air tank.
  • Shut off the air tank valve (if you are using one).
  • Remove the syringe tip and place it in the small jar that is partially filled with alcohol.
  • Remove the end cap from jar of alcohol and place on syringe.
  • Store syringe with solder in cool area (place in air tight bag if placing in fridge).

Step 12: More Using Your Solder Paste Dispenser...

At this point you should have a fully populated PCB with all the parts in the right place and the correct amount of solder paste. It is now time to bake. I use a toaster oven that has been modified to work as a reflow oven. You can find lots of examples on the web. I would recommend investing in such a beast if you expect to do any amount of SMD work. You can possibly use an electric fry pan but I wouldn't. If you don't want to make such an investment then see if you local Maker Space has one. You then have a good reason to join...

But wait! What if you are not ready to cook the board? Or say you have it half pasted up and can't continue till the following day? Good questions. If you need to delay cooking the board, I recommend you at least try to place all the parts. I think the solder paste will start to dry out and you may have issues if you wait too long. I can't say how long this is. A good idea I think is to place a half-finished board into a large flat kind of Tupperware container and seal it with a lid. This may delay the paste drying out as quick and will definitely protect it from inquisitive fingers, errant paper planes and nosey cats... I always make sure I have everything I need for a board (including time) before I start. YMMV How you bake the board really depends on the oven you have. On mine I simply place the PCB (carefully as there is nothing more maddening then getting this far with a PCB and then hitting the oven with it as you place it and mucking it all up. Trust me, I know...) onto the oven shelf, slide the shelf into the oven, close the door and then press start.

CAUTION: In the interest of safety please make sure you use your reflow oven in a well ventilated area.

Make sure the oven is set for the correct temperature for the type of solder you are using. I set mine the 183C for the leaded solder I use. The reflow oven will follow a temperature profile as it bakes the PCB. The reflow action doesn't start till the end when the oven hits the melting temperature of the solder. If you watch the board during the process it seems nothing is happening during the various preheat cycles. Once the reflow temperature is hit you will see the dull grey solder paste turn shiny silver and the parts may shift a little as the solder's surface tension takes effect. Typically the oven will shut off once the reflow cycle is completed. My oven has a servo that cracks open the door to let things cool. Try to let things cool to at least 100C before disturbing the oven. You don't want to jiggle any of the parts while the solder is still molten. Besides you will just burn you fingers if you touch it. Trust me on that one. Once the PCB has cooled you can give it an inspection. I use reading glasses, head mount magnifier, flashlight and a large lighted magnifying glass at various times to get a good view of the PCB. A USB microscope might be a good idea also.

You need to check for a few things:

  • Solder Bridges - This is where a bit too much solder has been used and it has inadvertently joined two or more pins. Basically a short circuit where you do not want one.
  • Dry Solder Joints - This is where there was not enough solder (or it was not placed ideally) and you may need more.
  • Anything Else Of Note - Make sure no part has completely moved out of position or any other strangeness.

Fixing solder bridges is not all that difficult but can be a bit tedious. The first thing to try is solder wick. I use the narrowest one I can find and a small tip on my soldering iron (I tend to use a higher temperature on the iron). Lay the solder wick across the offending area and heat it up. The idea is to heat both the solder wick and the renegade solder, then the melted solder gets absorbed by the wick. If the solder bridge is in an area you can't reach directly, this may still work, as removing the solder from an area you can reach may allow the excess solder you can't reach to flow to the area you just removed. Naturally this assumes these areas are all connected and close to each other You can also use a solder sucker to do the same. You will have to experiment to find the best solution. It is also a bit of an art. You need to become one with the solder. You need to think like solder.

You can also use a multimeter to confirm you have removed any bridges and the details for this are listed below. Dealing with areas that look like they don't have enough solder is easier. First you may want to test continuity with a multimeter. If there is continuity between the pin and the pad it may be fine and not need any fixing. I tend to use too much solder. Spend some time looking at production boards you see elsewhere. Compare these to what your board looks like. Adjust the amount of solder paste you use in future boards accordingly. At this point you have hopefully dealt with any visible defects in the SMD parts.

If your projects has through hole parts you should add them now. These are soldered in place using your normal soldering iron. Again watch for bridges. Now the board should be completely populated with all its parts.

Before you power things up you may want to check for shorts electrically. I tend to do this with ICs and any other part with fine pitched leads. I put the multimeter into Diode test mode. Typically this will give you a beep if the resistance is low. I also use a set of really pointy thin test leads. This will cut through any flux left on the solder and let you get into small spaces. You will also want the schematic diagram for the board you are working on. Starting on pin 1, I place the leads across two adjacent pins. If there is no beep I assume all is well. If there is a beep then I reverse the leased (perhaps an internal part of the IC is passing current). If there is no beep now, I assume all is well. If there is a beep I check the schematic to make sure the pins are not intentionally connected in the circuit or the IC. If so, then I assume all is well. If not, then I look farther into a possible solder bridge. This test doesn't take too long and gives you some additional peace of mind that you haven't got any issues.

After this it is time to power the circuit up and enjoy the results. If you have issues, you have to fall back to your troubleshooting skills. Hopefully you have no issues.

Another important thing to do is make sure you wash your hands. You don't want to get any extra lead into your body. It is probably a good idea to wash you hands anytime you get up and walk away from your soldering station and even more important if you get up to get a snack or drink.

Step 13: Epilogue....

So that pretty much wraps it up.

We have looked at getting a solder paste dispenser, fixing up a few defects your unit may have, connecting it to a compressor or air tank and basic setup. We have also looked at the process of completing a small project, including pasting the PCB, placing the parts, cooking the PCB and basic testing of the completed PCB.

Like many things in life, there are no concrete routes to perfection for all the steps in this process. You will learn as you go and your boards will naturally get better as you get experience...

The CRAMPS CNC controller board is an example of the many SMD style projects you can do much quicker and more reliably now that you have your solder paste dispenser. This is the next project I will be working on.

Thanks for reading this....

And a big thank you to my lovely wife for managing to proof read this document. I am not a writer (I barely passed English) and I'm sure it was quite painful for her to get through it.

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