What is ASTM D1894?
ASTM D1894 is a standard test method for determining the static and kinetic coefficients of friction (COF) of plastic films and sheeting when sliding against a specified surface. The test measures the frictional resistance between two surfaces and helps evaluate their sliding behavior under controlled conditions.
In this case, we customized the ASTM D1894 method to simulate the client’s specific application and evaluate the frictional behavior of polymer pads against a silicon (Si) wafer under different temperature conditions.
What Was the Client Looking to Evaluate?
The client requested an ASTM D1894 coefficient of friction test between polymer pads installed on a mechanical arm and a silicon (Si) wafer. The client required testing at ambient, sub-zero, and elevated temperature points to simulate real-world operating conditions. The objective was to evaluate the friction behavior of the polymer pads against the silicon wafer and generate relevant data to support the client’s research work.
What Were the Testing Challenges?
Challenge 1: Testing at Extreme Temperatures
ASTM D1894 testing is typically performed at room temperature. The primary challenge was therefore to develop a reliable test approach that could accommodate both low and high temperatures while maintaining the required test configuration.
The testing needed to replicate the client’s operating conditions without compromising the stability of the friction test or damaging the silicon wafer.
Challenge 2: Maintaining a Stable Test Setup
The mechanical arm assembly that the client provided was too heavy to place directly on the silicon wafer. Using the complete assembly could have introduced excessive stress and potentially damaged the wafer.
A stable configuration was therefore required to hold the polymer pads against the wafer while maintaining the required test load.
The Customized Testing Approach by Matestlab
The team developed a customized testing approach to address the temperature and setup requirements while maintaining the intended test configuration.
1. Solution for Elevated-Temperature Testing
For the elevated-temperature testing, the testing facility utilized a heating chamber. The team developed a plan to position the oven at the edge of the friction tester, allowing them to perform the high-temperature test while maintaining the required test configuration.
2. Solution for Sub-Zero Testing
For the sub-zero-temperature testing, technicians used liquid nitrogen to control the temperature inside a large insulated cooler positioned in front of the friction tester.
To protect the silicon wafer from potential damage, the team inverted the test setup. This configuration allowed the silicon wafer to remain stationary while the polymer pads moved against its surface, enabling technicians to perform the friction test under the required conditions.
3. Solution for Maintaining the Test Load
To overcome the weight limitation of the mechanical arm assembly, a custom fixture was designed and fabricated. The fixture held only the polymer pads against the silicon wafer while maintaining the required test load.
This provided a stable test configuration and helped prevent unnecessary stress or damage to the silicon wafer during testing.
A Balanced Testing Plan
After confirming the customized test setup, the project was divided into two testing phases. Phase I
A total of six tests were planned across:
● Ambient temperature
● Sub-zero temperature
● Elevated temperature
Phase II
A total of eight tests were planned across:
● Ambient temperature
● Sub-zero temperature
This phased approach allowed the client to evaluate the coefficient of friction under different temperature conditions while also validating the customized test method.
What Were the Analysis Results and Interpretation?
After completing the testing and reviewing the results, we confirmed that the coefficient of friction decreased as the temperature was reduced. The customized testing approach allowed the team to adapt the ASTM D1894 method to the client’s specific application and temperature requirements.
Discussion and Conclusions
The customized ASTM D1894 coefficient of friction test successfully simulated the client’s real-world application by evaluating the interaction between the polymer pads and silicon wafer under ambient, sub-zero, and elevated temperature conditions. Through a customized test configuration, temperature-control approach, and specially designed fixture, the team addressed the testing challenges while maintaining a stable test setup. The resulting friction data provided the client with the information needed to support their research.
FAQs
- Can ASTM D1894 be performed on materials other than plastic films and sheeting?
Ans: Yes, the ASTM D1894 test method can commonly be adapted and used for various sheet-like or flexible packaging materials beyond basic plastic films
- What are static and kinetic coefficients of friction?
Ans: The static coefficient of friction represents the resistance to initiating movement between two surfaces, while the kinetic coefficient of friction represents the frictional resistance while the surfaces are already sliding.
- Why is coefficient of friction important for polymer and silicon interfaces?
Ans: COF data can help evaluate sliding behavior, surface interaction, movement resistance, and performance under different operating conditions, supporting material selection and product development.
