PCB Assembly Design Guidelines

Input Data Requirements

Bill of Materials (BOM)

A complete and accurate BOM is required for all PCB assembly projects, including flexible PCBs. The BOM must include:

• Manufacturer Part Numbers (MPN) for accurate component identification
• Supplier Part Numbers (SPN) if specific distributors are designated
• Reference designators (e.g., R1, C2, IC3) for clear identification and tracking
• Quantities per PCB or assembly
• Detailed descriptions including package types and tolerances
• Vendor information where applicable, particularly for critical components

For flexible PCBs: Include the material type of the flexible PCB in the BOM.

Component Placement List (CPL)

Also referred to as Pick and Place, Centroid, or XY files. The CPL defines the precise location, orientation, and board side for each component and is required for automated assembly.

The CPL must include:

• X and Y coordinates for each component
• Component orientation/rotation
• Board side (top or bottom)

For flexible PCBs: The CPL must also include information on the board's flexed state during assembly.

Component Types

The following component types apply to both rigid and flexible PCBs. For flexible PCB assembly, stress considerations during flexure must be taken into account for all component types.

Through-Hole Technology (THT)

A mounting method where component leads are inserted through drilled holes and soldered. Suitable for robust connections and larger components in industrial and high-durability applications.

For flexible PCBs: THT should be avoided in areas of high flexure.

Plated Through-Hole (PTH)

An enhanced THT method where holes are plated with solder, providing superior mechanical strength and electrical conductivity. Used in high-reliability applications including aerospace and defense.

For flexible PCBs: PTH should be avoided in areas of high flexure.

Surface Mount Technology (SMT)

Components are soldered directly onto the board surface. SMT supports high-density placement and is the standard for modern electronics assembly across commercial, industrial, and advanced technology applications.

For flexible PCBs: Select SMT components that can withstand flexure stresses.

Mixed Technology

Combines THT and SMT on the same board where robust connections and high-density placement are both required. Used when design requirements cannot be met by a single assembly method.

Package Types

The following package types are supported for both rigid and flexible PCB assembly. Stress considerations are required for flexible PCB designs.

Footprint Review

Accurate footprints are essential for reliable assembly and to prevent rework across all PCB types.

• Ensure precise alignment between the manufacturer's recommended land pattern and PCB pads across all layers
• Use datasheets for correct component dimensions and markings
• For THT: drill sizes should be slightly larger than lead sizes in accordance with IPC standards
• For fine-pitch SMT: minimize solder mask webbing (e.g., 0.08 mm for green mask) to avoid solder bridging
• Use correct pad shapes and sizes to prevent tombstoning and other assembly defects

For flexible PCBs: Footprint design must account for dimensional changes that occur when the flexible PCB is bent.

Paste Layer Review

Solder paste layers define where solder paste is applied during assembly. Accurate paste layer data is required for consistent solder joint quality.

• Paste layer apertures should match pad dimensions 1:1
• Include fiducial markers to ensure accurate alignment during automated placement
• Stencil design should be based on board specifications and component requirements

For flexible PCBs: Stencil design must account for dimensional stability during printing. Ensure the PCB remains flat and adequately supported during paste application, as flexible materials may deform under stress.

Bill of Materials Review

In addition to the initial BOM submission, the following guidelines apply during BOM review:

• Include MPN and quantity per PCB for all components
• Use consistent reference designators and descriptions in accordance with industry standards
• Maintain up-to-date part numbers reflecting any design revisions
• Prioritize components with reliable availability to minimize lead times and supply chain delays

For flexible PCBs: Confirm that the flexible PCB material type is included in the BOM.

Component Placement Review

Correct component placement is critical for assembly quality, thermal performance, and long-term reliability.

• Avoid placing components too close to board edges — maintain adequate clearance for handling and processing
• Single-sided SMT placement is preferred for cost-effectiveness in standard production
• Maintain adequate spacing between components to prevent shorts and facilitate rework
• Ensure simultaneous pin entry during reflow for discrete components to improve solder joint reliability
• Place larger components before smaller ones to optimize the assembly sequence
• Optimize component placement for thermal management and airflow, particularly for high-power devices
• Consider connector accessibility in the context of the final product design

For flexible PCBs: Avoid component placement in flex zones to minimize stress on components during bending.

PCB Layout and Design Review

PCB layout and design directly affect manufacturability, assembly quality, and overall performance.

• Recommended board size: minimum 50 mm x 50 mm, maximum 420 mm x 420 mm
• Consider panelization for smaller boards to optimize production efficiency
• Adhere to industry-standard clearance and spacing rules in accordance with IPC requirements
• Design for testability to support quality control and troubleshooting
• Ensure proper grounding and power distribution to minimize noise and support reliable performance

For flexible PCBs: Bend radius, material selection, and layer stack-up are critical design considerations and must be specified clearly in the design data.

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