1	Optimization of MicroSpring^® Contact Design Parameters for Low Pressure Probing
2	Contents Industry Driven Probing Requirements Probing Operating Space Cres Scrub Mark Metrics Case Study Predictive Probing at FormFactor Scrub Mark Cres Customer Validation Conclusion
3	Industry Trends New Bond Pad Stackups Copper metallization Low K dielectric Probing over active area Lower Power Devices, driven by mobile products, reduce test margins
4	Probing Operating Space Cres Vs. Pressure Pressure is an independent variable that modulates both Cres and the scrub mark metric. Must balance two opposing requirements
5	Probing Operating Space Scrub Mark Metrics Length Width Depth Expose lower stack metals Package reliability issues Size/Location Hit passivation # of TD’s Multiple sorts common Double touch recipes common
6	Case Study New Bond Pad Stack-up Metallization Requirements: No exposure of base metal after repeated touchdowns Thin Al over base metal Low, stable Cres Approach: Predictive Probing at FFI Scrub Characterization Cres Customer Site Validation Scrub Characterization Qualification
7	Experimental Setup Predictive Probing at FormFactor
8	Experimental Setup Predictive Probing at FormFactor
9	Predictive Probing Evaluation of Pressure Parameters Pressure is a first order variable for both Scrub mark and Cres. Pressure=Applied Force/Contact Area FFI design parameters and probing recipes can be optimized to control pressure for specific applications. Overtravel K Tip size
10	Predictive Probing Pressure Evaluation Effects of K and Overtravel 15 touchdowns in same spot Standard tip size Blanket wafer with customer metallurgy/stack
11	Predictive Probing Pressure Evaluation Effects of K and Tip Size 15 touchdowns in same spot The low and high g/mil springs were grown from standard to large by repeated touchdowns on a controlled abrasive surface “High” OT for all cases. Tip size is dominant variable.
12	Pressure Surface Relationship For Constant Overtravel
13	Predictive Probing Cres Evaluation Au and Al Coated Substrates
14	Predictive Probing Cres Evaluation Force vs. Resistance – Holm Theory Aluminum Material Properties (from MatWeb): H_al= 15 Kg/mm² r_al= 2.7E-6 W-cm s_f is unknown. Since all other variables are known, the film resistivity for the Aluminum case can be estimated from the experimental data. s_f ~ 2.5E-7 W-cm² Establishing this material parameter allows for more accurate estimates of Cres for future applications.
15	Predictive Probing Summary Customer Site Evaluation Predictive Probing Summary Evaluated significant parameters for scrub mark Design parameters selected for field evaluation Characterized Cres to high resolution Customer evaluation Several cards were evaluated at customer site Varied K, tip size and number of touchdowns Probed test wafers with production metal stack Cres monitored for all tests Objectives: Define design parameters for qualification Define probing recipe for qualification
16	Field Characterization
17	Cres/Scrub Mark Metric Vs. Pressure
18	Product Qualified All Qualification testing passed Lifetime Test ILD damage Scrub Cpk Multiple TD analysis Package reliability
19	Conclusion FormFactor’s MicroSpring Contact probing solution allows for customization for specific applications Overtravel K Tip size Predictive Probing enables FFI to simulate customer environments Validated at multiple customers and applications
20	Acknowledgments Intel Trung Nguyen, Mike Dang, Reuben Gallegos FFI Fred Lane, Eric Watje