Saturday, July 5, 2014

Building the FSR Circuit Boards

My friend and I have been busy building the FSR Endstop Controller circuit boards (you can find the entire discussion on the Delta Robot 3D discussion here:!topic/deltabot/2Nvtv4aicKk%5B1-25-false%5D).

Most of the work involved in building these circuit boards is placing the tiny parts onto the circuit board. The smallest parts are 0603 surface mounted devices, which means they’re 0.06” by 0.03” in size. For the first few boards I built, I dumped the parts onto the table, and then used tweezers to put them in place, under a microscope. But it was very time consuming to flip over components if there were upside down or no their side. And I also had to check the polarity of the LEDs carefully.

I did some research into pick and place machines and then ran into a manual pick and place machine: I really like what he’d done, but it was mostly made out of wood, and I don’t have much in the way of word-working skills or tools. I also ran into a nice manual machine that was $199 so I checked out their web site. They were out of stock, so I sent them an email. After about a month I got an email that they were in stock again, but now the price was $399: SteadyHands PnP. By this time I’d already built my own machine for about $50.

I decided to make a machine similar to vpapanik’s machine, but using 3D printed parts. Here are some photos of my finished machine:


You can find information on building this manual pick and place machine here: Building the Manual Pick and Place Machine.



The process of assembling the circuit boards begins with adding solder paste to the circuit board. I created a solder paste stencil and jig, as I described in my post Auto Adjust FSR End Stop Detector. This time I created a stencil that allowed me to add paste to four boards at a time.

Once the solder paste is applied, the next step is to place the components onto the solder paste. This is where my manual pick and place machine enters the picture. This video shows placing a few parts with my manual pick and place machine:

My Manual Pick and Place Machine in operation

After placing all the parts on the circuit board, the board needs to be baked in a reflow oven to melt the solder. This video provides a short introduction to using a reflow oven I purchased off of eBay. I paid $200 for this oven, and it had a flaw—inside they use masking tape in an area that gets rather hot, and causes the masking tape to off gas, producing a terrible smell. I found instruction information and instructions about this here:  T962A SMD Reflow Oven Fix/Hack.

Using a T-962 reflow oven to melt the solder paste and finish the boards

In my previous blog post, I wrote about creating a programmer to upload the firmware to these boards. This video shows using this programmer:

Programming the circuit boards

Finally, here is a longer video showing me placing the other parts on the circuit board:

Longer video of the pick and place machine

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