Assignment 05_electronic production
01 characterize the specifications of the PCB production process (group)
To understand what I was going to fabricate, first I investigate a little about PCBs world.
PCB: Printed Circuit Board
For fabricating a basic PCB, you need at least three files:
- Traces (inside cuts)
- Holes (inside deep cuts)
- Outline (exterior cut)
There are other files (like the silkscreen or the solder mask) with information to fabricate the PCBs commercially, but we are not going to used to this assignment.
There are two types of elements in boards:
- Surface-mount technology (SMD): a method for producing electronic circuits in which the components are mounted or placed directly onto the surface of printed circuit boards (PCBs). This is the one we are going to use in this assignment.
- Through Hole Technology (THT): mounting scheme used for electronic components that involve the use of leads on the components that are inserted into holes drilled in printed circuit boards (PCB) and soldered to pads on the opposite side
The most standard end mills are the 1/64-inch and the 1/32-inch, the first one you used for the internal traces and the second one you used to cut through the board.
The machine we have for milling PCBs in Fab Lab Santiago is monoFab SRM-20 , the software to control the machine is only for windows, so I use the PC that is attached to the machine.
I learn about levelling the bed and attach the FR1 with double-sided tape. Then set the screws of the platform and choose the zero of the machine.
You have to be especially careful when you change the end mills because they fall very easily.
Now I'm ready to fabricate.
02 make an in-circuit programmer by milling the PCB
MACHINING
For this assignment, we have to download the files to fabricate a FabISP. For this,I read this web and download the version of files of Bas. Apparently was the more easy one to understand and is a good option for a beginner like me.
In the files I download where:
- fabTinyStar-012_lay.png
- fabTinyStar-012_out.png
- fabTinyStar-012_top.png
- fabTinyStar-012.brd
- fabTinyStar-012.sch
For make the files in mods, I use the “top” that where the traces and the “out”, that in this case contains the outlines and the holes of the PCB. In mods I choose the option for monoFab SRM-20 and upload the “top” file, then chose the specifications for mill traces, calculate and add a module to save the generated file in my computer. I do the same with the outline file but choosing the “mill outlines”.
Once I have generated the files, set the zero in the machine and use the 1/64-inch end mill for traces, I start the fabrication of the PCB. When I finish that file, I change the end mill to the 1/32-inch to cut the outline. It cut well, but the file of outline includes the holes, and the machine cut the outline first and then the holes, the PCB moves so just cut one hole.
To prevent this in mods, I change to reverse the path order and generate the file again. I make a second board, but this time the traces don’t cut well. So I decided to cut the third one and use the other boards to practice the solder.
SOLDER
The basic kit to solder is:
- Tweezers
- Solder Wire
- Fluxx (also there is solder wire that already contains Fluxx, I'm going to use that one).
- Solder Station
- Solder wick
The average temperature to solder with the solder station in 450ºC, but you can adjust it while you are working.
For the final board, I found the Bill of Materiales, which is the list of the specifications of every material and how is packaged. Then I order the elements in my notebook with the name they have in the layout image and avoid confusing the elements.
At first, I practice soldering a few resistors to catch the technique. I have to heat first the square where I want to place the solder and then touch the tip of the solder station with the wire solder. Then grab the elements whit the tweezers (there are tiny elements) the resistor and heat the solder again. After a few test, I get that I have to take out first the solder station, wait until is cold (immediately) and then take out the tweezers.
First I solder the resistors, capacitors and diodes. Then I solder the LEDs (and search how to read the negative pin in the led I have) and the switches. After that, I solder the ATTiny 45 and, finally, the 2x4 jumper. This last choice was not very smart because the ATTiny45 didn’t give too much space to solder the jumper, so that side was tough to solder.
In the end, I use a DMM to analyze if I solder something wrong and I have to clean some traces because I joint it with some solder.
One other thing. When I was soldering the ATTiny, I realize that the board was wrong cut, because where loose two traces that separate the spaces. I check the file, and I was wrong generated, I don’t know how it happened, but I have to search how to correct it in the future. Meanwhile, I do the traces with a cutter for don’t lose all the word I had done.
CONCLUSION
It was a very challenging experience. When I took the Fab Academy, I only had experience in 3D modeling and digital manufacturing, so the weeks that I had to work the most were the first (with git and HTML) and this week. It is very exciting to be able to learn so much from something that I had never ventured before. I know that I am still a beginner, but I am very interested in continuing to deepen my new knowledge and keep learning new tools.
FINAL BOARD
I remake this PCB the week of inputs assignment. I was remaking both of my PCB because neither of PCBs had work, and program them.
Once I have my new FabISP, I test it with the multimeter and something was wrong. I discover that two of the paths of the side switch wasn’t making a connection, so I resold the paths. The resold works.
Then, I burn the fuses and then I program the firmware from vusbtiny_firmware_fabtinystar.tar.bz2
After all, I verify in my system report the device was listed in the USB port.
Finally is working!!
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