by Robin Bornoff, Mentor Graphics Corp.
This case study, a partner piece to Robin Bornoff/Mentor Graphics’ discussion of fluid dynamics analysis for IC package design, examines how IDT used CFD thermal analysis in a packaging decision for a recent product launch.
February 16, 2010 – Integrated Device Technology Inc. (IDT, San Jose, CA) develops mixed signal semiconductor solutions for digital media and other applications. The company’s power-smart solutions optimize system level performance while maximizing device performance. Controlling semiconductor junction temperature for optimal system performance and lower cost is critical, since IDT products are commonly used in compact platforms such as LCD televisions.
IDT used thermal simulation and analysis in preparation for a recent product launch. This device was a multichip module containing two separate silicon elements — a processor and a clock. The thermal requirements stated that the temperature difference between the two chips was not to exceed 0.1°C. Temperature affects the frequency of both chips, so both must operate at effectively the same temperature.
Two die placement alternatives were in the running: side-by-side on a die paddle, or stacked. Differences in the die-attach material cause the two configurations to differ in thermal resistance. Side-by-side offers lower thermal resistance between the two dice (and lower assembly costs) but requires more board real-estate. Stacked die take up less space but typically have slightly higher thermal resistance and assembly costs. Jitesh Shah, advanced packaging engineer at IDT, created thermal models to compare the two configurations. He looked at a half-dozen design alternatives over ambient conditions ranging from -55°C to 85°C.
Using Mentor Graphics FloTHERM to simulate the alternatives, Shah discovered that the stacked die delivered better performance. "I had assumed that a side-by-side arrangement would provide the best thermal performance since the die-attach materials in that configuration were 3× more conductive than the stacked-die option," Shah said. "But looking more closely at the simulation results, I determined that even with lower conductivity thermal interface material, the stacked-die approach outweighed the expected benefits of the side-by-side approach."
Because the IC is intended for hand-held consumer products with very limited board real-estate, the more space-efficient stacked-die approach provides a significant advantage to end-product manufacturers. In this case, thermal simulation reduced product development expenses by reducing the need for physical testing and late-stage design changes.
Acknowledgment
FloTHERM is a registered trademark of Mentor Graphics Corp.
Biography
Robin Bornoff received a mechanical engineering degree from Brunel U. (UK) in 1992 followed by a PhD in 1995 for CFD research. He is FloTHERM and FloVENT product marketing manager at Mentor Graphics Corp., Mechanical Analysis Division, 81 Bridge Road Hampton Court Surrey KT8 9HH, UK; ph.: +44 (0)20 8487 3084; e-mail [email protected].