Metallization Method
Micro-fabrication techniques build high-density interconnect patterns through a combination of subtractive and additive electroless copper deposition. The modified semi-additive process starts with a thin layer of metallic seed deposited over a dielectric base, followed by photolithographic patterning to define the circuit geometry. Electroplating then thickens the copper traces within the photoresist openings, after which the resist removal and flash etching strip away the original seed layer to isolate final conductors.
This sequence allows for tighter feature definition than traditional panel plating because the metal growth remains restricted by the resist wall during the build phase.
Fabrication Tolerance
Fine pitch requirements drive the adoption of this approach in advanced substrate production. Narrower trace widths and tighter spaces emerge from the controlled growth of metal columns within photoresist channels, which eliminates the undercut side-etching common in fully subtractive etching of thick copper foils. Small variations in plating current density affect trace sidewall angles, requiring consistent bath chemistry to ensure predictable impedance across large panels.
High density interconnect structures depend on this precision to minimize signal crosstalk and maintain structural integrity during the lamination of subsequent insulation layers.
Inspection Protocol
Automated optical systems detect irregularities in width or spacing by comparing manufactured features against design data files. Surface defects such as copper nodules or resist residues interfere with electrical performance and appear as discrepancies during high magnification scanning. Measurement of the conductor profile reveals the effectiveness of the seed layer removal, confirming the absence of electrical shorts between parallel lines.
Finished circuits require verification of these physical dimensions to confirm adherence to the electrical load capacity specified for the board.
