With the popularization of free prototyping services for high-layer-count PCBs (6 layers and above), the corresponding process specifications are also being continuously improved. High-layer-count boards have complex structures and high process difficulty. Their free fabrication specifications not only uphold basic process requirements but also establish specialized standards for critical challenges such as interlayer alignment and impedance control. This article focuses on the process specifications for free fabrication of high-layer-count PCBs, analyzes technical key points and application boundaries, and provides reference for high-end R&D projects.

**Specialized Specification Requirements for High-Layer-Count Boards**

The free fabrication specifications for high-layer-count PCBs raise the technical threshold beyond foundational standards. Regarding layer count, current specifications support free prototyping for 1-6 layers, with some manufacturers extending this to 8 layers, though typically requiring enterprise-verified customers for application. The stack-up structure must be clearly labeled, with symmetrical lamination design as the default to prevent warping due to uneven stress. Requirements for trace width/spacing precision are higher, with outer layers supporting down to 3/3 mil and inner layers not less than 4/4 mil, necessitating LDI (Laser Direct Imaging) technology to ensure routing accuracy. Impedance control becomes a core specification metric; high-frequency signal layers must specify impedance values, with tolerances controlled within ±7% to meet the needs of communication products. Blind/buried via processes are typically not included in the free offering; through-hole designs or paid upgrades are required.

**Enhanced Specifications for Materials and Processes**

High-layer-count boards impose more stringent requirements on materials and processes, with specifications clearly defining enhanced standards. The laminate must use brand-name, Grade A base materials with a Tg≥150℃ (such as Shengyi, Rogers), rejecting low-quality materials to ensure interlayer stability. Copper weight configuration needs optimization: typically 1oz for outer layers, 0.7oz for inner layers, with critical signal layers optionally using 2oz copper thickness to improve current-carrying capacity and signal integrity. The lamination process should adopt a multi-stage pressing method, controlling the heating rate to ensure interlayer adhesion strength ≥1.8N/mm and avoid delamination risks. The etching process must utilize high-precision etching lines to minimize trace width deviation, ensuring alignment accuracy between circuits on different layers, with alignment errors controlled within ±25μm.

**Application Boundaries and Specification Limitations**

The free fabrication specifications for high-layer-count PCBs clearly define applicable scenarios and limiting conditions to prevent project delays from over-reliance on free resources. Applicable scenarios mainly include R&D verification for consumer electronics, industrial control, and communication equipment; they do not support fields with high-precision requirements like aerospace and medical devices. Specification limitations typically include a maximum board size not exceeding 20×20cm, with charges applied for larger areas; special base materials (e.g., high-frequency boards, aluminum substrates) are excluded from the free scope and require paid customization. Process limitations also include no support for special requirements like laser drilling or halogen-free materials. Projects needing such processes must opt for paid prototyping or negotiate upgrades with the manufacturer.

**Measures to Ensure Specification Implementation**

The successful implementation of free fabrication specifications for high-layer-count PCBs requires manufacturers to possess corresponding technical capabilities and management systems. Manufacturers need to be equipped with intelligent panelization systems, increasing panel utilization to over 92% to dilute costs through economies of scale. Specialized inspection workflows must be established, adding items like interlayer alignment checks and impedance testing, supported by professional inspection equipment. Simultaneously, manufacturers should provide technical consultation services to help engineers interpret specifications and optimize design schemes, preventing designs from exceeding the free scope due to improper planning. For enterprise-verified customers, some restrictions may be appropriately relaxed, offering customized specification adaptation services to meet mid-to-high-end R&D needs.

The refinement of process specifications for free fabrication of high-layer-count PCBs promotes the democratization of high-end PCB technology. R&D teams must rationally assess the boundaries of these specifications and choose appropriate fabrication solutions based on project requirements. Manufacturers, meanwhile, need to continuously improve the adaptability and implementation strength of these specifications through technological upgrades and management optimization, achieving a win-win situation for technological innovation and cost control.