High Aspect Ratio Blind via Reliability Limits under Sequential Thermal Cycling and Z-Axis Stress
High aspect ratio blind vias require low Z-CTE filled laminates and pulse plating to prevent target pad separation during lead-free thermal cycling.
Bare Board Specification
Procurement Standard
Master fabrication documents establish rigid mechanical, electrical, thermal, and dimensional parameters for unpopulated circuit boards prior to component assembly. A bare board specification dictates laminate material selection, copper foil weights, minimum trace widths, hole wall plating thicknesses, and solder mask registration tolerances across the entire panel layout. Procurement contracts reference IPC-6012 or IPC-6013 standards to enforce baseline quality classes for industrial or high-reliability electronic hardware.
The boundary of this document ends at board fabrication and electrical test verification, leaving assembly cleanliness and reflow profile management to downstream assembly standards.
Acceptance Criteria
Quality verification relies on cross-section analysis and automated optical inspection to confirm dimensional compliance. Acceptance criteria mandate microvia fill, barrel copper continuity, dielectric spacing, and solder mask coverage over conductor edges. Microsections prepared from test coupons verify that electrodeposited copper wall thickness meets or exceeds specified class minimums, such as twenty micrometres for IPC Class 2 products.
Ionic cleanliness testing measures surface residues left from chemical etching and plating rinses to prevent electrochemical migration under field voltage.
Material Requirement
Substrate selection establishes the thermal resistance and signal propagation speed of the final assembly. High-frequency applications require specific glass transition temperatures, thermal decomposition limits, relative dielectric constants, and dissipation factors within tight standard deviations. Copper foil specs dictate tooth profile roughness to limit skin effect losses at gigahertz operating frequencies.
Solder mask parameters define dielectric strength, adhesion properties, and chemical resistance against assembly flux solvents. Dimensional stability tolerances bound dynamic warp and twist during wave soldering and reflow processes. Material lot certifications ensure that physical properties remain consistent across successive production runs.
Defect thresholds specified within the document determine panel disposition during final quality audits.