Massachusetts Institute of Technology
MAS 863 How To Make (Almost) Anything | Fall 2011

Vernelle Noel - vernelle@mit.edu |

WEEK 3 - IN-CIRCUIT PROGRAMMER

Week 3: Make FabISP in-circuit programmer
Monday, October 03, 2011

The assignment for this week was to make an in-circuit programmer. This was another assignment I looked at and thought, "Will I be able to do this...again?”

The day after receiving the assignment I received training by Brian on how to use the Modela Milling machine. From the images that I saw of the board, I thought the programmer was about 2"-3" by 4" or so. In reality it was quite different. The board I had to mill was actually 3/4" x 1.75" in size. We were able to cut 3 boards out of one paper based copper plate.

Milling of board with 1/64" sized bit

I first had to stick a "sacrificial" board onto the Modella with double sided tape, underneath the board that I would be milling. This was because when drilling out the PCB, I may drill deeper than the actual thickness of the board. Be sure that the ends of the double-sided tape goes beyond the limits of the board, so it will be easier to remove. After doing this, I then stuck 3 pieces of double-sided tape onto the back of the PCB I was now going to cut making certain not to let my fingers get on the tape that would be touching the PCB. I placed it EXACTLY over (in the same spot) the sacrifical board and pressed hard on it to ensure it was secure. To mill out the traces of the board I used a 1/64th" endmill, and to cut the board, a 1/32".

After fixing my boards to the Modela, I slid the 1/64" endmill into the Modela and tightened it just so that it was snug. I moved the location of the endmill so that it would go to the "origin" which I would then alter to suit the location of my board and where I wanted to cut. After confirming my origin I carefully released the endmill so that it touched the surface of my board lightly. Dropping it onto the board, can more than likely break the bit.

Cutting of board with 1/32" sized bit

Board after being cut

After I was finished cutting I washed my board. This was advised to aid in preservation of the board. The following day I "stuffed" or soldered my components.

Soldering of components onto PCB.

Soldering is quite a beautiful process where "shiny and smooth" is good! I started from the inside out, lower pieces to higher pieces. Brian gave some pretty good tips for soldering. I employed two methods of soldering my components, it depended on the sizes of the pieces for me. For small components with smaller connections, I would place some flux on the copper trace, then put a little solder on the tip of the iron. Then holding the component down firmly with a tweezer, I would solder the component making sure both the materials were hot enough so that the solder flowed nicely and evenly. For larger components I put a touch of solder on the copper trace on the board, then put the component on it and placed the soldering irion again to melt the solder, component and trace together... so that you felt the component "sit" in the solder. Both methods served me well.

Size of the board compared to a quarter

Above is my board on a photo of the board we were using to guide us in putting everything together.

Completed PCB in-circuit programmer

After my board was programmed I removed the 0 ohm resistor and the solder bridge.

Lessons Learned:

1. When soldering the USB component, be sure to solder the tiny pins onto their copper traces FIRST, then solder the four main points on the outside of the component. I made the mistake of soldering the outside first, then noticed that my tiny pins did not fall exactly on their traces. I tried using the braiding and flux to remove the solder, I even tried a solder vacuum... but none of them worked as well as the hot air gun. I removed the component and started from the smallest to the biggest which I guess is an unbrella rule of thumb to apply when fabricating boards.

2. We all learned from each other... Working with others helps you learn and see a lot. Thanks Brian, Dan, Sarah, Adam, Albert, Eyal, Lining, and Jie.

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