Thermal analysis enables design of new CSP test system

Introduction:

The trend towards increasing miniaturization of consumer electronic goods such as cell phones, notebooks, cameras and computer games has resulted in the emergence of Chip Scale Packaging (CSP) as a method to increase density and reduce cost in the fabrication of semiconductors. To support CSP, alternative approaches to test and verification by OEMs providing wafer prober test equipment are also under development. For CSP, dies must be individually tested. Due to the wide variety of chip styles, the test interface must accommodate many different test item physical configurations.

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Customer Challenge:

A backend wafer prober OEM was in pursuit of a universal CSP test equipment approach that would allow the prober to be reconfigured in the field for new CSP designs. While the OEM was a leader in the areas of wafer handling and probing, they were interviewing consults to provide thermal expertise in the design of complex thermal subsystems. Traditionally, the OEM relied on suppliers for thermo-chucks and refrigeration systems to provide effective solutions for their temperature profile needs. For the new CSP system approach, these traditional suppliers were not able to propose a solution for meeting the higher temperature uniformity and throughput requirements, nor did they know how to handle the many different CSP sizes and shapes. As a result, the OEM turned to Single Iteration for design assistance.

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Single Iteration Solution:

The OEM had established temperature profile requirements for their CSP test system but was unsure of the technical feasibility and cost of fulfilling those requirements. Single Iteration assisted by determining what could feasibly be accomplished and what component and system design requirements had to change in order to meet those requirements. Through the use of our thermal modeling, simulation and analysis tools, an effective method for maintaining temperature uniformity for different package geometries was first developed. The cost breakpoints for meeting various temperature uniformity and ramp rate requirements at specific set points were then derived through solution cost/benefit analysis. The final solution consisted of a multi-stage heating and cooling chuck arrangement to adapt to the different CSP configurations.

In order to assure the customer's development objectives were satisfied, Single Iteration produced a set of control, sensing, heating and cooling system component design specifications that the customer's in-house design team and existing network of suppliers were capable of fulfilling. Single Iteration worked with the OEM's suppliers to assure component interfaces were properly understood and thermal system integration problems were minimized. Single Iteration then provided thermal verification support and post-processing of system test data to authenticate prototype designs against the original specifications.