Prototype Number 1

For our first work in the shop, we decided to start very simple and designed a fixture that was just used to align the processor when placed in the socket. This fixture just references off the sides of the processor socket and uses those to guide the processor into the proper alignment so that the screws and bracket can be easily inserted and tightened. The problem with this design is that it became very obvious that getting the fixture to slide on and off with the processor in the socket was going to be tough to deal with. After evaluating this design we decided to use a different approach in the next step of the design.

Prototype Number 2

The second design iteration was a milled pocket that held the heat sink, processor and bracket and was aligned with the PCB by locator pins. The screws could be dropped in through holes milled in the pocket and then tightened down with the fixture still in place. The basic idea behind this prototype was to see if the pocket milling process was possible on the CNC mill and to see if the holes above the pocket could align the screws with the holes in the socket. This prototype was largely a success as it showed that our design idea worked but still let us see what needed improvement on the next iteration.

Prototype Number 3

The next step in our prototype was to have some way of aligning the pocket with the processor on the board consistently. In order to accomplish this, we took the same pocket milling idea and applied it to a hinged fixture that used a pocked milled in the base to hold the PCB and a pocket in the lid to hold the heat sink and bracket in place. Once the heat sink and fan had been lowered down onto the board you could tighten the screws down and lift the lid. The processor and board would then be mounted and ready to go. Figure 5 and 5a show pictures of this prototype.

Prototype Number 4
The next step in our design was to figure out a way of holding the heat sink and bracket in the fixture while it was being lowered into place via the hinged lid. We needed a method that didn't require extremely tight machining tolerances and would be simple to install and use. After consideration of frictional methods and mechanical claps we opted to use vacuum suction to hold the heat sink in place. Vacuum was a simple method and with the low weight of the heat sink it was an ideal solution. We had several options for generating the needed vacuum, the first idea was a simple plunger/collar that we built in the shop and we attached to one of our earlier prototypes for testing
Fan Tester
One of the next areas we decided to tackle was designing a fan tester that could tell the user whether a fan was bad without requiring a visual inspection. The current tesing method for fans at Jabil was to plug it in and see if the fan ran or not. Jabil was unhappy with this method as it didn't account for cases where the fan was not running at a high enough speed to keep the processor cool. A new method to reliably and quickly testing fans was needed but how this was accomplished was left up to us. After doing some research, what we came up with was a method that would test the fan's speed and return a green light if the fan was good, or a red light if the fan was bad. We accomplished this by designing a circuit that measures the current ripple given off by the brushless fan. By measuring the current ripple we can figure out how fast the fan is going and use the remaining portion of the circuit to display a red light for speeds below a given RPM value and a green light for speeds above a given RPM value.
Final Prototype
After choosing a dispenser, we started work on the final prototype which included a lot of the suggestions passed on to us by our contacts at Jabil circuit. The final prototype included all the ergonomic improvements, including a constant torque hinge for use convenience, relocated rails for easier placement of the PCB and hand hold slots so that users could pick up the board easier. Other things we included were locator pins for easier PCB placement, LED's for the fan tester were integrated into the fixture, and a pressure plate to account for the stack up tolerances that can occur on the circuit board. The final prototype was also much more modular than previous designs, meaning that if repairs or modifications are needed they will be much more simple to make. The fan testing unit and vacuum were attached via connectors which are housed in a NEMA enclosure that sits behind the fixture. The Reason for the NEMA enclosure is to organize the workspace effectively while preventing users from modifying settings on the equipment once it has been calibrated.