Moebius Cylon Raider 003

[04032012 0435]

Third Design

There is no noticeable changes to the third design of the PCB except that it is now ready to accept the SOIC version of the chip. I have made this decision (And I hope I am right) because there is no way I can do wave soldering at home. OK, I can buy an oven but now is not the time since I am running out of time. Moreover, solder paste for SMDs are so rare here. You can see the size comparison of each of the microcontroller packages. On the left is the DIL version, which you will normally buy from shops. In the middle is the SOIC version, which I have ordered and on the right is the SOPP version which I have decided not to go ahead (and now I am stuck with the little buggers. But fear not, when I experiment with wave soldering and ICSP, I think I will use them). I ordered the SOIC in the 'LF' version instead of the normal 'F' prefix because this version allows me to work with voltages as low as 2.0 volts. This effectively means that the circuit's operating voltage range is now 2.0volts to 5.5volts.

 

These two PCBs are actually the same size. The one on the left is for the SOPP chip while the one on the right is for the SOIC chip. When I got the board, I was puzzled why the tracks are so narrow compared to the first effort weeks earlier.

 

It was not until I got the SOIC chip to the board did I realised what had happened.The software design was correct but when it was printed out with a laser printed, the image shrunk. Here, on this photo, you can see the pads for the 'legs' of the SOIC chip which was barely wide enough. So, it was another call to the vendor...

 

Here is the comparison again. This time, the PCB was badly etched and so, after sometime removing the tracks it was still unusable. But it really did make the vendor aware of the problem with their printer.

 

Finally, the PCB came back and this is the final revision and is correct size. Phew.

 

Now I have three versions of the board. The top one was the SOPP version, which I rejected. You can see how fine the 'legs' are, which normal soldering with a solder wick method will not help much and might even heat the chip too much. The bottom is the final design but at the wrong size. The correct size is the one in the middle. Do not worry if the image looks a bit weird as my Nokia n8 could only take limited macro shots. I had to use a magnifying glass to achieve this shot but at the cost of image quality.

 

 

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