03
Nov
09

semi stressed PCBs

While working at a now defunct company in 2007, I had a chat with an engineer with regards to PCB design and hobbyist robot construction. Back then , I was rather new to the industry, being a second year undergraduate. At the end of the internship, I took away many experiences and thoughts, but the most interesting lesson learnt was that of semi-stressed PCBs. This may not be new to industry, but I found it to be especially suited to that of the hobbyist industry.

The propective hobbyist can often be characterised by the following requirements – he has little to no access to heavy machinery, fabrication equipment. However, he is willing to outsource certain aspects of his designs, in this case, PCBs. The batchPCB service, or seeed’s propaganda service offer numerous rapid prototyping facilities for printed circuit boards.

The engineer in question was designing a robot for use by secondary school students, and one of the selling points was that all structural parts of the chassis, excluding nuts and bolts, were made from PCBs. His rationale behind it was that he could get the “boards” made with 0.2mm precision, holes predrilled and at a cost comparable to getting a sheet of metal and waterjet cutting the parts out. Fair enough! He used copper fills on both the top and bottom layers for stiffness in the boards. This may not be directly applicable to the traditional hobbyist, but there is potential for the hobbyist in this field. For example, the motherboard for your robot/device may be structural to the robot, being the top subframe. Stiffness and reinforcement in required directions can be achieved by means of copper fills.

However, a risk behind using this method is that solder joints may be susceptible to fatigue cracks due to undue flex in the board, it is essential to consider this in the design process. One solution would be to have some level of damping, on the board, or maybe another subboard as a support. The hobbyist, building a PCB for use in his own home may not have to bother about this though, considering that limited run boards aren’t required to have rock solid reliability with an MTBF of 42582350327503 hours.

I’m sure that this has already been implemented in industry practice, but applications in the hobbyist ecosystem have seen little use of this method (or as much as I’ve seen anyway). The result of using such a method was a professional looking robot that was basically snap together, with near perfect tolerances.

The robot in question looks something like this, but I will continue hunting for better examples.

RoboGP Racer


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