When application-specific thermal test chips are unavailable from IC manufacturers, general-purpose test chips offer an effective alternative. These chips enable engineers to model, measure, and refine thermal designs during the early stages of development, well before production chips are ready. Designed for versatility, they accommodate a wide range of applications while remaining cost-effective. Customization of the thermal profile and package is also possible to meet specific requirements.
Characteristics of Thermal Test Chips
General-purpose thermal test chips should have the following key features:
- Chip Size: Closely approximates the production chip being simulated.
- Maximum Heating Area: JDEC standards specify at least 85% of the chip surface should support heat generation.
- Uniform Temperature Profiles: Includes the ability to simulate localized hotspots.
- Ease of Use: Allows manipulation and measurement of temperature profiles with standard lab equipment.
Design and Implementation
Companies like TEA use innovative designs to create versatile thermal test chips. Their “Unit Cell” approach offers scalability, where small unit cells (1mm² or 2.5mm²) can be combined into larger arrays up to 20×20 unit cells to replicate the size and thermal characteristics of the target chip.
Key features of TEA’s design include:
- 1mm Unit Cells: Includes two resistors for heat generation and one temperature sensor.
- 2.5mm Unit Cells: Features two resistors and four diodes for precise temperature sensing.
- Power Densities: Achieve up to 300 W/cm², making them suitable for high-power applications.
When assembled into arrays, these unit cells enable precise temperature control and simulation, from uniform temperature distributions to specific hotspot scenarios.
Here are some examples of how TEA designs its test chips. It uses a ‘Unit Cell’ approach where each unit cell is small (1mm or 2.54mm squared) yet can be arrayed into larger shapes up to 20 x 20 unit cells in order to mimic the final application-specific chip. Power densities of up to 300 W/cm2 can be achieved.
1mm X 1mm Unit Cell (Courtesy TEA)
2mm x 2mm Unit Cell
Each 2.5mm unit cell has two resistors for heat generation and four diodes for temperature sensing while the 1mm unit cell includes two resistors and one temperature sensor. When configured and tested in an array using a given heat sink, it’s easy to see the precision and versatility of these general-purpose test chips. Below, Unit Cells of different sizes are used to create general purpose test chips of the same size (10x10mm).
(L) 2x4mm Unit Cell in 4×4 Array, (R) 1mm Unit Cell in 10×10 Array
These arrays can be set to mimic the range of temperature gradients from uniform to hot-spot scenarios.
Uniform Temperature Distribution (L) 4×4 Array, (R) 10×10 Array
Two Hot Spots (L) 4×4 Array, (R) 10×10 Array
General-purpose thermal test chips are an invaluable tool for engineers developing early-stage thermal management solutions. Their versatility, scalability, and precision allow for accurate simulations, helping teams optimize designs before production begins. By using these chips, engineers can ensure their thermal designs are robust, cost-effective, and ready to meet application-specific challenges.
