In this instructable, I am going to show you how to solder electronic components with reflow to build an arduino board.
Most surface mount components can be soldered manually, but if you have several similar boards to build, reflow can be much faster. It is also more or less mandatory when you have components with leads under the package.
In this article, I am showing you how to use a SimplyLeonardo Kit from www.kamijin.com to build an Arduino board using reflow.
Step 1: The Oven
To perform reflow on your component you need a reflow oven.
There are now many options for low-cost reflow ovens. One of the best (that's my opinion) is the Whizoo ControLeo2. It will take you one afternoon to build it, once you have all the components, and making it requires some persistence, but the oven is great and the control flawless. This is what I use for my own reflow experiments and that I show in this article.
Step 2: The Components
Reflow makes sense of course only if you have a majority of surface mount components (SMC or SMD for "device"). If your components are through-hole, then the best it to solder manually or by wave soldering if you produce in volume.
Using surface mount components and reflow used to be complicated and expensive, but it is the norm now for many commercial products, and you too can do it. I am using the DIY kit for our Simply Leonardo board in this example, which include all components to build your own Arduino board.
Step 3: Fastening the Board
Before you do anything with your board, you need to securely fasten your board on the table. One trick of the trade is to position other PCB boards on each side of the board you want to equip. I put four boards, one on each side, and I taped them with masking tape, that is easy to remove and not too sticky.
Step 4: The Silk Screen
Reflow is done in three steps.
1- put soldering paste on your board
2- position components on the board
3- put the board in the oven and heat it
For the first step, the deposit of solder paste, you need a silkscreen. Silk screen are pretty inexpensive these days. A metal one can cost around $10 when you order your PCB, and a milar one is even cheaper. Use metal if you want to solder many boards, they are more durable. Also, unless you produce lots of boards, you don't need the framed one that is much more expensive.
Step 5: Holding the Silk Screen on the Board
You have to position your silkscreen exactly above the pads - this should not be difficult if you have several SMD components. The pads align pretty well. The tricky part is how to make sure that the silkscreen does not move when you apply the paste. I have tested two methods: putting tape on the silkscreen, or holding it with your hand. Both work. Once you have some practice, holding works pretty well and is faster. I am showing here how to put tape on the four angle to hold the silkscreen.
Step 6: Apply the Solder Paste
Applying soldering paste is not very complicated, but requires some skills, and the right tools. Surprisingly, the best tool to apply solder is a simple putty knife that you can buy for few dollars at your local hardware store.
I used some lead free solder and applied the paste in two passes. First pass I push paste on the screen, second pass, I remove the excess paste. I have then to remove the silk screen, and this must be done with great care to avoid moving the paste. What works for me is to use a precision knife and lift one side while holding the other.
Step 7: Position the Components
Now that solder paste is on your board (you can see it if you magnify the picture) you can position the components. Start with the biggest one and the ones with the finer pitch then populate the entire board.
I start with my two Kamijin components, LeonardoInOne and LeonardoPower, then I put all other components. The process of positioning the components is a little tedious but you have to do what you have to do.
I found that using fine tweezers with a magnifying headband works best for me. Note that the positioning does not need to be perfect - during the reflow process, solder will reposition the component by capilarity.
Step 8: Reflow in the Oven
Now all you have to do is very gently remove the masking tape, then put the board in the oven. It is recommended to put the board right in the middle of the oven where temperature is the most uniform.
With ControLeo, provided that you have configured the oven properly, all you have to do is to power the oven and press "start reflow". You can trust ControLeo and let it handle the temperature curve. It works perfectly with lead free solder.
The whole reflow process last around 10mn. I recommend you wait until temperature is back to around ambient to get your board.
Step 9: Though Hole Soldering
It is rare that your board has only SMD devices. There are always some connectors or sensors that are through hole. In the case of SimplyLeonardo, we have the Arduino connectors and the power connector.
A simple way to make sure you connectors are straight is to solder them on top of another arduino board. Then use solder and your soldering iron.
Step 10: Time for Inspection and Test
Your board is now completely assembled.
The reflow soldering gives results that are good looking, much like commercial products.
The last steps I recommend are the visual inspection (some solder bridge may appear, easy to detect) to make sure everything is right, then electrical testing (verify GND and VCC are not shorted and provide the right power) and finally functional testing.
Good luck with your project!