When application-specific thermal test chips aren’t available from the IC manufacturer, general-purpose chips provide the next best alternative for allowing engineers to model, measure, and modify thermal design early in the process – before production chips are ready. Available from several manufacturers, these chips have a standardized design to accommodate a wide variety of applications quickly and cost-effectively. Yet, customization of the thermal profile and package is still possible.
Ideal Characteristics
- Chip size that closely approximates the chip being simulated.
- Maximum possible heating area relative to chip size (JDEC standards specify a minimum of 85%)
- Uniform temperature profile across the heating area with the ability to simulate hotspots in specific areas.
- The ability to manipulate and measure different temperature profiles using standard lab equipment.
Design Implementation
Here’s an example of how one company, TEA, designs its test chips. ‘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
