PCB Design to Assembly

From the initial design blueprints to the final operational circuit board, the process involves over 20 critical steps, each completed under precise control.

Pre-manufacturing Stage

In the PCB manufacturing process, the pre-manufacturing stage determines the success or failure of the entire project. The core task of this phase is to ensure that design concepts are accurately translated into executable manufacturing instructions.

PCB design begins with engineers using specialized software like Eagle or Altium Designer to create schematic diagrams, defining circuit connections and component layouts.

This step must comprehensively consider critical factors such as signal integrity analysis, thermal analysis, and electrical performance to ensure the final product meets design specifications.

Upon completing the PCB design, standardized manufacturing files must be generated. Among these, Gerber files serve as the internationally recognized format for circuit board graphic data. They precisely document all graphical information—including traces, pads, solder masks, and characters—across every layer of the circuit board.

These files function like construction blueprints for a building, directly determining production feasibility.

Beyond Gerber files, modern manufacturing workflows commonly utilize ODB++ and IPC-2581 formats, with the latter gaining increasing prominence. PCB manufacturers typically offer various standard panel sizes for selection, which must be confirmed with the manufacturer prior to production.

Design for Manufacturability (DFM) analysis serves as a critical safeguard during the pre-production phase.

Responsible PCB manufacturers analyze Gerber files prior to formal production to identify potential manufacturing bottlenecks such as insufficient line width/spacing, inadequate pad spacing, or overly small drill hole diameters.

Traditionally, DFM involved manual file reviews by manufacturers' engineering teams to ensure manufacturability. Today, leading platforms offer free, highly automated online DFM analysis services that generate detailed reports within minutes.

PCB Manufacturing Stage

Cutting is the first step in production, where large sheets of FR-4 copper-clad laminate raw material are cut to the appropriate working board size according to process requirements. For multilayer boards, this process involves both inner and outer layer handling.

In material preparation, laminates and prepreg sheets are key components. Prepreg sheets consist of loosely woven glass cloth “pre-impregnated” with uncured resin, featuring no copper on either side. Laminates comprise resin and glass cloth with copper on both sides, already cured.

Inner Layer Circuit Fabrication

This forms the foundation of PCB manufacturing. After material preparation, the inner core board undergoes acid pickling and cleaning, followed by photoresist coating. Patterns generated by computer output are transferred onto the photoresist, which is then developed to remove unwanted resist.

Post-etching, the resulting inner core board undergoes surface roughening through oxidation to enhance adhesion during lamination.

Laminating Process

Bonding multiple circuit layers into a single unit is a critical PCB manufacturing step. This process involves bonding the inner core board, copper foil, and prepreg under specific temperature and pressure conditions.

Laminating includes systematically stacking layers according to the original design, followed by applying pressure through a press to achieve bonding. These steps follow specific pressure cycles, specifying the pressure and temperature levels applied over a defined time period.

Drilling is a vital process for establishing electrical connections between circuit layers. High-precision CNC drilling machines create thousands of through-holes on the board based on drilling files, enabling component placement and interlayer electrical connections.

For multilayer boards especially, hole positioning accuracy is fundamental to ensuring precise alignment of circuit traces across layers. Drilling causes resin melting, necessitating cleaning of these holes through deburring or etching processes.

Post-drilling, copper plating is essential to create the critical “tunnels” between layers. The drilled hole walls are exposed, non-conductive resin and glass fiber. To establish electrical connectivity between layers, via formation is necessary.

The board is immersed in a specialized solution that activates the hole wall material, making it more receptive to copper ions. This process deposits a thin layer of copper on the hole walls.

In high-density designs, the via-in-pad process is a critical technical choice. It involves completely filling the through-hole with resin or copper paste, followed by grinding and plating, enabling vias to be directly designed over the pads of components like BGAs.

After circuit formation, the board is coated with solder mask ink, forming a protective layer. This shields traces from oxidation and scratches while preventing solder bridging during assembly that could cause short circuits.

Subsequently, component part numbers, logos, and other markings are applied via screen printing or inkjet printing. These provide clear guidance for subsequent soldering and debugging operations.

Exposed copper pads are highly susceptible to oxidation, which compromises soldering quality. Therefore, surface treatment is essential before final delivery. Common processes include hot air leveling (HAL) (cost-effective with good solderability), gold plating (offering excellent surface flatness and corrosion resistance), and OSP (Oxygen-Sulfur-Phosphorus) plating (lower cost and environmentally friendly).

Selecting the most suitable treatment process based on product positioning, application scenarios, and cost budget is crucial.

PCB Assembly Stage

Different types of component assembly require distinct process approaches. Typical electronic assembly methods include full surface mounting, single-sided mixed assembly, and double-sided mixed assembly.

Full surface mounting refers to PCBs where both sides are entirely populated with surface-mount components (SMC/SMD). Single-sided mixed assembly denotes PCBs featuring both SMC/SMD and through-hole components (THC). Double-sided mixed assembly involves both sides having SMC/SMD and potentially THC.

Surface Mount Technology (SMT) has become the mainstream process for modern electronic assembly, offering multiple advantages: reduced thermal shock to components; controlled solder volume leading to fewer soldering defects; suitability for automated production with high efficiency; minimal contamination in solder; and self-calibration effects.

Design for Manufacturability (DFM) remains equally critical during the assembly phase. The electronic assembly process flow is largely defined during printed circuit board design. Each additional process step introduces potential quality defects; the more steps involved, the lower the first-pass yield.

Traditional processes comprise four main steps with a 90% first-pass yield. Replacing wave soldering with through-hole reflow soldering eliminates one step, boosting the first-pass yield to 97%—a significant quality improvement.

Automated assembly equipment is a critical component of modern electronics manufacturing. The automation and mechanization of electronic module assembly and installation yield the greatest efficiency gains in reducing manufacturing complexity.

Key approaches include utilizing automated equipment and batch processing new component libraries, particularly surface-mount components. Preparing electronic components for assembly requires multiple fundamental operations, including de-packaging, incoming inspection, solderability testing, straightening, and lead forming.

Testing and quality control are critical stages for ensuring final product performance. Assembly and soldering of PCBA boards form the core steps of mass production, with quality control integrated throughout.

Prior to mass production, design and process validation must be achieved through functional testing (FCT), in-circuit testing (ICT), and necessary environmental testing. Assessing the stability of the SMT placement process is also vital, requiring assurance of machine placement accuracy and component alignment precision.

Soldering process evaluation is equally vital. Whether using reflow or wave soldering, stability of the soldering temperature profile must be guaranteed. Visual inspection and X-ray examination of solder joints prevent issues like cold solder joints and poor soldering.

Solder quality assessment is also essential, encompassing solder paste composition, flow characteristics, and reflow temperature to ensure robust and reliable solder joints.

High-Density Interconnect (HDI) technology is transforming PCB manufacturing and assembly. With the adoption of BGA and BTC components featuring 0.8mm or smaller lead pitch, traditional manufacturing processes can no longer meet the demands of fine-pitch components. Consequently, HDI PCB manufacturing technology has been developed.

In conventional multilayer board processes, all layers are laminated together in a single step, with interlayer connections achieved through through-holes. In contrast, HDI board processes involve layering conductive layers and insulating layers sequentially, with connections between conductors established via micro-buried/blind vias.

One-Stop HDI PCB Manufacturer and Its PCB Via Filing Capabilities

If you're looking for turnkey HDI electronics manufacturing services (EMS) from hardware development to PCBA fabrication and box-build assembly, you can work with the one-stop HDI PCBA manufacturer PCBONLINE.

Founded in 1999, PCBONLINE has R&D capabilities for HDI projects and EMS manufacturing capabilities, including via filling for stacked vias. It provides 4-to-64-layer HDI PCB fabrication, assembly, and PCBA box-build assembly. You can order various HDI PCBs from PCBONLINE, such as FR4, polyimide (flexible PCB), polyimide + FR4 (rigid-flex PCB), and PTFE/Rogers (high-frequency PCB).

Here'e the PCB via filing capabilities at PCBONLINEL:

• Micriavia filling with copper: laser via size 0.1-0.125mm, priority 0.1mm
• Finished hole size for via-in-pad filling with resin: 0.1-0.9mm (drill size 0.15-1.0mm), 0.3-0.55mm normal (drill size 0.4-0.65mm)
• Max aspect ratio for via-in-pad filling with resin PCB - 12: 1
• Min resin plugged PCB thickness: 0.2mm
• Max via-filling ith resin PCB thickness: 3.2mm
• Making different hole sizes with via filling in one board: Yes
• Via filling with copper/silver: Yes

If you need HDI PCBAs or any other PCBAs requiring via filling, please send your email to PCBONLINE at info@pcbonline.com. We will provide one-on-one engineering support to you.

Conclusion

Via filling is used for creating stacked vias in HDI PCB fabrication, BGA/CSP/QFN IC packaging, and filling PCB via-in-pad with resin during multilayer PCB fabrication. If you need one-stop electronics manufacturing for your HDI PCBA project, contact the one-stop advanced PCB manufacturer PCBONLINE for high-quality PCBA and box-build solutions tailored to your project's needs.