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Design Notes

Bondwires and Finite Dielectrics

This example demonstrates Analyst EM extraction and simulation of finite dielectrics and bondwires.


This example shows how to model a bond wire connection from one board into another. The dielectric properties and substrate heights are different on each board. The 50 Ohm microstrip line on each board is connected using a bond wire. The boards share a common ground. We study a situation in which there is a small (air) gap between the boards and a situation when there is no such gap present.

Finite Dielectric Setup

In order to accurately model the finite dielectric and bondwires, the EXTRACT blocks in each schematic will need to be enabled prior to simulation to initiate Analyst simulation.

The finite dielectrics are defined in the STACKUP element in Global Definitions. In the Dielectric tab, Air is defined as an infinite dielectric layer. The finite dielectrics are introduced by appropriate material definition under Material Defs tab. In this example, they are Diel_1 and Diel_2. Then those dielectric materials are assigned to traces in the Materials tab. In this example, the dielectric traces are PCB1 and PCB2. The negative heights of dielectrics are set such that the two PCBs extrude downwards. Then those traces are mapped to Drawing Layers on the EM Layer Mapping tab. With this setup, one PCB occupies EM layer 3 while the other occupies EM layers 2&3. Shapes drawn on PCB1 or PCB2 now represents finite dielectrics.

For extraction, the finite dielectric shapes are drawn in the schematic layout. Then those shapes are enabled for extraction in the Layout tab of the Shape Properties window.

Extraction Setup

For 3D EM Extraction, three additional steps are necessary:

-Synchronize LPF to STACKUP

-Define Z position of Bondwire

-Draw Boundary Shape

In this example, the LPF is already synchronized to the STACKUP, so that the 3D schematic layout view matches 3D EM View. Refer to 3D EM Extraction help for more details on this step.

The Z position for 3D EM elements, such as BWIRES must be defined for proper placement. In this example the element parameters of the BWIRES are set relative to the bottom ground. So it must be placed on the bottom of the enclosure (Z=0). The Z position is set by selecting the element in schematic layout, Right Click > Shape Properties > Layout tab.

The Boundary is added by drawing a shape in schematic layout, and then selecting the shape and choosing Draw > Create Simulation Boundary. Set boundary conditions on the Boundary shape, and then enable it for extraction in the same manner the finite dielectrics were enabled.

Simulation Results

Circuit versus EM results can be compared by toggling ON/OFF Extract blocks. All results agree reasonably well.

Schematic - Bondwire_circuit_model_Gap

Schematic 3D Layout - Bondwire_circuit_model_Gap

Schematic 3D Layout - Bondwire_circuit_model_No_Gap

Graph - Sparameters