Surface quality becomes part of the circuit
Film continuity and pattern resolution depend on substrate roughness, defects and cleaning. State local surface criteria in functional areas instead of specifying only average roughness. A polished substrate does not remove the need to qualify adhesion and the deposition stack.
Define functional layers and pads
Adhesion, resistor, conductor and barrier layers may have distinct roles. Specify resistor parameters, conductor loss and bond-pad metallurgy according to the application. A common final color or nominal gold finish does not establish equivalent wire-bond performance.
Validate over temperature and frequency
For precision resistors, review temperature coefficient and drift after assembly exposure. For RF, include conductor thickness, roughness, transitions and package parasitics. A nominal 50-ohm line calculation is only an initial geometry estimate.
Engineering example
A fine-film RF circuit may meet its bare-substrate simulation but fail after a lid and bond wires are added. Include those structures in the model and measure the completed package.
Before you release the design
- Specify functional-area surface quality.
- Define the metal/resistor stack and attachment method.
- Use electrical and adhesion witness structures.
Sources and further technical reading
Manufacturer references support the material and process context. Worked examples and checklists are engineering guidance; they are not test results or supplier guarantees.