G'day! Welcome back to the factory. Today, we're going to be applying solder paste to a PCB panel using a solder paste stencil and stenciling machine. If none of that means anything to you, we have a video that introduces the PCB manufacturing process. Let's get started!

Solder paste is applied to a PCB panel through a stencil. The stencil is cut just so the solder paste only goes exactly where it's needed - that's on the component pads on the panel. As you can probably imagine, with small electronics, correct alignment of the stencil with the panel is critical.

Enter the stencil machine. This is a manual stencil machine. The machine allows repeatable alignment of the stencil with the panel so that you can paste panel after panel quickly. I'll set up this machine for this design so you can see the workflow. Let's get started!

I'm going to secure the panel to the fixture plate on the stencil machine using these supports. There's a three millimeter hole machined in every panel. There's a pattern of three millimeter holes and there's a matching three millimeter pin in the support, so when we come over to the fixture plate, I can roughly center the panel with the supports. The remaining two supports don't have those alignment pins in them, but for ease of setup, I found that two pins seems to be enough.

With the panel placed generally, I can now loosely fasten the supports in place. Now that we have a generally centered panel with the stencil loosely centered on the fixture plate, I can now see where I want to provide additional supports. This is just four points of contact, so there's a lot of bowing that the panel can do at the moment. So now that I now have a general location, I know that I want to support each one of these PCBs and for that, we use these machined brass pins. This pin is machined to go into the fixture plate into any of the holes.

I usually start by scattering the pins out to provide support. I have seen online that some people use a machine's piece of aluminium billet as a large block to sit in the space of the panel. To make sure each individual PCB has adequate support, I like to perform a little tap test.

Next up, fit the stencil to the hinge. This just gets held in place by two clamps. Make sure it's the same orientation as the design in your panel. To adjust the height, we have four screws that are the same on each side. Unlock the locking screws and then adjust the height adjustment screws. Perform a little tap test and listen for any drumming. If there's a gap between the stencil and the panel, the sound will change. Once that's all good, lock the screws.

Remember the panel is only loosely positioned on the fixture plate. I leave it like this so that I can manually get the alignment pretty good before bothering with the fine adjustments. I found this to be a really fast way to get started. If I can manually bring those pads into the apertures and once that's close enough to get started, carefully open the machine and carefully remove.

The panel is fixed in place and roughly aligned. For the fine alignment, I like to do the coarse alignment first because the fine adjustments on this machine only have about 25 millimetres of travel. I can see that the bottom pads are basically filling the stencil in one corner, but in the opposite corner they're shifted to the side, so there's a little bit of rotation. I'll use the angle adjustment screw to bring those in. There's this kind of round robin adjusting process that I go through where you get things just a little bit better each time.

For the stenciling, I'll need a spatula for depositing solder paste onto the stencil and a squeegee for actually performing the stenciling. Today I'm using a lead-free Chip Quick brand solder that is a T3. It's really important to make sure the solder paste is at room temperature before starting. I tried a couple of times before I got impatient with solder paste that hadn't been out of the fridge too long and it was just a mess. Gloves on, it's time to apply the paste. the pads and then just slowly peel it off

Solder paste needs to be applied to the stencil with a spatula. It always seems like you need more than you think, so I'm going to be quite generous because you can always reclaim the paste from the stencil afterwards. This next part feels very much like a craft. I freely admit that I don't have this down perfect yet. There seems to be a perfect angle, pressure, and speed to get the stenciling process just right. This seems to be the most risky part of the whole process, so if you're new to this (I still am), then have a play.

I'm going to set my angle at the top of the stencil and just do a firm wipe down. I'm looking for streaking left behind in the stenciling. Some areas of the stencil are completely clean and others leave behind a residue of solder paste. I've done a pass in one direction, I'd like to do a pass in at least two, so this time I'll go 90-degrees. All the pads look like they've been filled, so I'll recover the paste.

Back at the start, I mentioned the three millimeter alignment pins that hold the panel in place. The height of those pins is quite important. I like to set the height so that they stick out of the panel just enough to engage with the stencil, but not enough to stick proud of the stenciling surface. If you're dragging a stainless steel squeegee across your stencil, you don't want to be dragging it over some hard alignment pins that are sticking up through it.

Now that we've pasted our panel, we have to recover it from the stencil machine. I don't really know if there's a best way to do this, but my method that seems to work for me is to just very slowly crack open the panel until you see all the solder paste and all the pads, and then just slowly peel it off.

The holes have disappeared, which means the panel is sticking to the stencil. That looks pretty good, so let's jump on the microscope and have a closer look. Maybe our viewers can provide some feedback on how this looks. In general, I'm pretty happy with how this turned out. I think I could definitely work on my technique; there are a few pads that are looking a little lopsided, which may have been from a final pass I did with the squeegee. I might have pulled the solder to the side a bit. You can see a bit of underspray or something, but I don't think that's a problem for this board.

This is a great board for learning how to stencil because these are very forgiving components. This workflow evolved around this particular machine, but I'm sure it's transferable to other manual machines as well. If you're a solder stenciling aficionado, I'd love to hear your thoughts or any comments about squeegee angle pressure. What do you think of these results? Do you have a favourite solder paste? The best place for that is in our forums. Thanks for watching!