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Welcome to the history of our project's design!

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The Final Force Measurement Tool and the Mock DUT Assembly

The final designs of the Force Measurement Tool (left) and the Mock DUT Assembly for the X16 SLK.

Final Design of the Mock DUT

The Mock DUT has assumed a similar adapter to that of the Force Measurement Tool, however has received some major changes. The Mock DUT itself is made out of Copper, and is completely modular so it can be easily transferred from one adapter to the next. There is a thermostatic switch located on the bottom of the Mock DUT for safety reasons, and to prevent an unwanted overheat of materials. Captive screws are once again utilized for ease of access, and the heater is a 250W swaged cartridge heater, capable of reaching our desired temperature of 155°C in 10 seconds. The Mock DUT screws in to the adapter, once again utilizing captive screws from the bottom of the adapter. This prevents the Mock DUT from moving around during testing.

How about the Mock DUT?

Above shows two early iterations of the Mock DUT Design. We wanted to utilize a similar approach to the Force Test Fixture, including an adapter to attach onto the SLK heads individually. This time, the adapter would be made out of an insulating material, such as Ultem®, instead of Aluminum, to prevent any thermal damage from reaching the SLK.

Final Assembly including Force Receiving Plate

The final assembly, with X16 adapter attached to the SLK, pushing against the force receiving plate.

Final Design of the Force Measurement Tool

The final design of the SLK Force Measurement Tool is shown above for the X16 SLK Head. Captive screws are implemented for ease of use, and dowel pin alignment holes are seen at the top surface as well. The factor of safety (FOS) was increased by adding a secondary wall thickness, filling in the large void inside the adapter.

Iterating on that Design Choice

Above shows the several preliminary design iterations that were made to the Force Measurement Tool. Iteration 1 began with one adapter for all SLK Head sizes, however that proved to be unreasonable. Iteration 2 accounted for on-board dowel pin son the SLK Heads used for alignment, however further iteration 3 cleaned up and created a solid force measurement tool.

Finalizing a Design Choice

We decided to go with creating an adapter that could fit each SLK head (X16, X2, and X1) individually, with an S-Beam load cell reading the load applied. Shown above are two iterations of our preliminary designs.

The main problem here, again, was that the plate was rather large, and interfered with the space of nearby X16's. Also, this design would be extremely clunky for customers who purchase this force diagnostic tool, especially because they would be trying to attach it upside down, and screws could be falling out, etc.

Brainstorming Early Design Ideas

Spring and Rail Concept: Use ultrasonic sensors to measure deflection of springs, calculating force applied through displacement of the spring

Problems: This was essentially what Cohu currently does. They calculate the force applied by knowing how much pressure they input through a piston, which controls how much the SLK pushes down. Another major design flaw was that it needed an extremely accurate ultrasonic sensor. See spreadsheet below for simple cost analysis.

Simple cost analysis of an ultrasonic sensor capable of meeting the required resolution needed

Mounting onto the SLK Head Itself Concept: Create an adapter capable of mounting onto each individual SLK head itself, rather than having one force receiving plate.

Advantages: Removes moment arm created at sensor mounting location. All forces are directly axial.

Disadvantages: The X16 and X1 SLK heads are drastically differently sized. To make one adapter fit all three head sizes, the adapter would interfere with other X16 heads during testing.

Flat Plate Concept: Have one single load receiving plate, that SLK heads push down against. To measure one SLK head individually, the operator would insert a puck in between that head and the plate, and subsequently lower the plate by a fixed amount.

Problems: A moment arm is created at the sensor mounting location. This would adversely affect sensor readings, and readings needed to be accurate to ±0.1%. Also, it is undesirable to move the z-location of the force receiving plate, as it would be quite heavy and in an awkward position (under the Eclipse XT). Furthermore, to remove that undesirable moment arm, linear rails were considered. However, excessive friction is then introduced into the system as ball bearings rub against each other in a attempt to keep the loading completely axial.

Exploring Different Types of Sensors

From left to right: S-Beam Load Cell, Button Load Cell, FlexiForce® Sensor, Spring Fixture, and Ultrasonic Sensor

All these different sensors were considered early on in the design process to find which sensor best fit our application.

The Socket Layout Kit (SLK)

From left to right: The X16 SLK, X2 SLK, X1 SLK

Individual X16 SLK Head

These are currently all existing SLK head sizes existing. Due to the parallelism of the SLK's, individual heads can be added or removed at any time.