Populating the Board / by Sebastian Morales

Creating the solder stencil

Once the board has been printed, milled or etched. Once the board is ready to be populated, there are a couple of steps that one needs to do first. 

In order to facilitate the process, it is best to apply a uniform layer of solder paste in all the pads where components will be solder. To do this a good practice is to laser etch a sheet of acetate to make the mask.

The settings might vary depending the film used as well as the laser selected. The recommended settings where 10 power 10 speed and seemed to be working fine for my first tests. 

Applying the solder mask

 seconds prior to applying the solder paste

seconds prior to applying the solder paste

Before you even start this make sure all your components are out, once you apply the paste you don't have much time so you don't want to waist it looking for that 1uF capacitor.

It is best if the board is constrained while the solder is applied, that way you don't risk the stencil to move and the solder will be applied on the pads.

After locking the board and positioning the stencil, apply some solder paste at the top or bottom of the stencil. In one uniform (maybe two, max 3) movement apply the paste by gliding a plastic spatula (credit card) over the board.

Carefully remove the stencil, carefully to not smudge the solder paste on the pads.  

 

If everything went according to plan you should have something that looks like this!

Placing components

Perhaps one of my favorite steps in the process. If you followed the instructions you already have everything you need out. Using the manual pick and place make sure to delicately place the components in the right location and orientation. Don't worry if they are slightly crooked, they will magically aligned once the solder flows. 

Melting the solder

Here a picture of the settings used in case they are useful. 

I guess the only other thing to mention is to allow for the machines to heat up before using them.

 

 

I think it is ideal practice to heat all the board a little before focusing on one specific area. Move the heat gun around the entire board, soon you will see the solder change color, transforming from a matte gray to a very shiny silver. You will also see how the solder groups together.

Test before you power

To my naked eye, the board looks great, there seems to be some two resistors bridging (top left). This is not really a problem since they are where already connected in parallel in the schematics. 

Perform some basic continuity tests to make sure only what is supposed to be connected is connected. This can save you some severe damage to your computer (in case you would connect this to your computer).

Programming the board

So you did everything right?

Congratulations, you are almost there. The class website has some great resources, as well as links to more resources. Go there and learn how to properly use the burn the boot loader to later be able to upload arduino sketches.