Evaluating Semi Additive Process Yield Factors for High Density Substrates
Semi-additive yield depends on seed layer adhesion, lithographic trench verticality, and differential etch undercut control across sequential build-up layers.
Trace Height Uniformity
Physical Consistency
Geometric measurements describe the variation in the thickness of copper conductors across the entire surface of a printed circuit board. Maintaining trace height uniformity is essential for controlled impedance designs where a change in copper thickness alters the electrical characteristics of high-speed signals. It is a direct result of the plating and etching processes.
Copper height matters.
Plating Control
Variations often occur because the current density in an electrolytic plating bath is higher at the edges of a panel than in the center. Shields balance this. If the thickness varies by more than a few microns, the resulting signal distortion can lead to timing errors in digital circuits or power loss in RF applications.
Inspection Method
Quality control teams verify this property using non-destructive eddy current sensors or by taking cross-sections of coupons located at the panel periphery. Poor trace height uniformity can lead to issues during the subsequent assembly steps, such as uneven solder paste application or difficulty in achieving a reliable bond with fine-pitch components. A consistent copper height across the board ensures that the electrical performance matches the simulations created by the designer.
This dimensional stability is a primary requirement for advanced multi-layer boards.