What Causes Insertion Loss in High-Speed PCBA & Cable Assembly?

When This Topic Matters Most

Insertion loss matters most when a high-speed signal path must preserve enough signal strength from transmitter to receiver. It is especially important when the system includes longer routing, multiple interconnect transitions, dense PCB structures or high-speed cable assemblies.

This topic is especially relevant for projects involving:

• AI server hardware
• High-speed IPC systems
• Long PCB trace or cable transmission paths
• Board-to-board or cable-to-board connectors
• HDI or multilayer PCB structures
• Controlled impedance requirements
• Low-Dk / low-Df material requirements
• High-speed cable assemblies
• USB, AOC or active extension cable applications
• Products moving from prototype to mass production

This topic may be less critical for low-speed, short-distance or non-impedance-sensitive circuits. In those cases, standard PCBA assembly and cable assembly controls may be sufficient, depending on product requirements.

What Is Insertion Loss?

Insertion loss describes how much signal energy is lost as a signal travels through an interconnect path. In a high-speed PCBA or cable assembly, this path may include PCB traces, vias, solder joints, connectors, cables and transitions between them.

Ideally, the signal should reach the receiver with enough strength and clarity. In reality, every material and structure in the path introduces some level of attenuation.

Depending on the channel design, connector termination, soldering quality, mechanical assembly variation and cable construction may influence overall channel consistency and contribute to insertion loss.

• Signal frequency
• PCB dielectric material
• Copper roughness
• Trace width and trace length
• Via structure and via stubs
• Connector transitions
• Cable length
• Cable construction
• Shielding and termination quality
• Soldering or press-fit quality
• Manufacturing tolerance
• Assembly workmanship

As operating frequency increases, conductor loss, dielectric loss and discontinuity effects generally become more significant.. In high-speed systems, even small differences in material, routing or assembly quality can reduce signal margin.

Key Insertion Loss Drivers and EMS Manufacturing Control Points

The following table summarizes common insertion loss drivers and how manufacturing control can help reduce production-related risk.

This table does not replace signal integrity simulation or validation. It helps buyers understand how EMS manufacturing execution can support the customer’s high-speed design intent.

PCB Material, Copper Roughness and Stack-Up Factors

PCB material is one of the main factors affecting insertion loss. In high-speed applications, the dielectric properties of the PCB material influence how much signal energy is lost as the signal travels through the board.

Two common material-related considerations are Dk and Df.

Dk, or dielectric constant, affects signal propagation speed and impedance behavior. Df, or dissipation factor, is related to dielectric loss. For high-speed designs, low-Dk and low-Df materials may be considered to reduce loss and improve signal transmission.

Copper roughness is another important factor. At higher frequencies, current tends to flow closer to the conductor surface, often described as skin effect. If the copper surface is rougher, the signal path may experience more loss. For this reason, some high-speed PCB designs may specify low-profile copper options such as HVLP, depending on the application and design requirements.

PCB stack-up also matters. Layer arrangement, reference planes, trace geometry and impedance control all affect high-speed signal behavior. If the stack-up is not clearly defined or not manufactured consistently, the final PCBA may not perform as expected.

From an EMS perspective, the key responsibility is not to redesign the customer’s stack-up. Instead, the EMS partner should review whether material requirements, impedance notes, copper requirements, stack-up documents and assembly requirements are clearly documented before production.

For dense routing, compact component placement or controlled high-speed breakout areas,HDI (High Density Interconnect) PCBs and Multilayer Rigid PCBs may be relevant product categories to review depending on the customer’s design requirements.

Trace Length, Routing and Via Effects

Longer signal paths usually create more loss. As a high-speed signal travels through a longer trace or cable, more energy is absorbed by conductor and dielectric materials.

Routing geometry also matters. Sharp transitions, discontinuities, poor reference plane control or inconsistent trace geometry may contribute to signal degradation. In some high-speed PCB designs, via stubs can also become a concern because they may create unwanted resonance, reflection or additional attenuation.

Back-drilling may be used in certain high-speed PCB designs to reduce via stub effects. However, this is normally defined by the customer’s design and PCB fabrication requirements. The EMS partner can support the project by checking whether back-drilling, impedance control, stack-up notes and assembly requirements are properly documented in the production files.

Insertion loss focuses on forward signal attenuation. If the same channel also has impedance discontinuities that cause reflected energy, buyers should also review the related article: Why Return Loss Matters in AI Server PCBA & Cable Assembly.

Manufacturing Factors That May Affect Channel Loss

Insertion loss is not limited to the PCB. In AI server and high-speed IPC applications, and industrial computing applications, connectors and cable assemblies may also form part of the complete signal channel.

Connector-related factors may include contact geometry, mating stability, alignment, seating, soldering quality and mechanical tolerance. Connector design is normally defined by the customer or component supplier, while assembly should follow the approved component and workmanship requirements.

Cable-related factors may include cable length, construction, shielding, bend radius, termination quality and strain relief. Depending on the interface design, variation in these areas may contribute to insertion loss, impedance discontinuity, skew, return loss or EMI-related issues.

Common Connector-related manufacturing risk include:

• Connector misalignment or damaged contacts
• Inconsistent soldering, crimping or cable preparation
• Poor shield termination
• Uncontrolled cable bending
• Inadequate strain relief
• Rework or handling that changes the signal path

Project-specific cable tolerances, connector requirements and inspection criteria should be defined in the approved drawings or specifications.

DMAX’s current cable product references include a 15-meter USB 3.2 active extension cable with active signal boosting and USB active optical cable solutions supporting transmission distances of up to 30 meters. The applicable USB generation, data rate, connector configuration and validation requirements should be confirmed for each project. 

These manufacturing controls help maintain assembly consistency but do not replace signal integrity simulation or high-speed channel validation.

PCB and PCBA workmanship may be evaluated according to applicable IPC-A-600 and IPC-A-610 requirements. Cable and wire harness workmanship may be evaluated with reference to IPC/WHMA-A-620 when specified. The applicable revision and acceptance class must be agreed before production.

For critical press-fit connector applications, process control may also include insertion force or force-displacement monitoring to confirm insertion quality and reduce the risk of pin deformation, incomplete seating or unstable contact.

Manufacturing Information DMAX May Confirm During NPI

Depending on the project scope and customer-provided documentation, DMAX may confirm whether the information required for quotation, PCB fabrication, assembly planning and applicable inspection is clearly specified. This review does not replace customer design verification or signal integrity validation.

For insertion-loss-sensitive projects, NPI review may include:

• PCB material requirements
• Stack-up documents
• Controlled impedance notes
• Low-Dk / low-Df material requirements
• Low-profile copper or HVLP requirements when specified
• Back-drilling or via control notes when specified
• Connector specifications
• Cable assembly drawings
• Cable length and bend radius requirements
• Shielding and termination requirements
• SMT, press-fit or cable assembly process requirements
• Inspection and testing criteria
• Traceability requirements
• Customer-defined validation responsibilities

DMAX’s confirmed PCBA inspection capabilities include inline SPI, inline AOI and X-ray inspection. These methods help identify solder paste, placement, soldering and hidden-joint defects, but they do not directly measure insertion loss or complete high-speed channel performance.

Additional electrical, functional, cable or customer-specific testing requirements should be reviewed during quotation and NPI to confirm the available method, equipment, acceptance criteria and responsible party.

Testing and Validation Considerations

Insertion loss is usually evaluated during design validation or high-speed channel validation, often by the customer’s engineering team, design partner or qualified laboratory. Advanced methods such as TDR, VNA or S-parameter analysis may be used depending on the application and project requirements.

The EMS partner’s role is to support this process by ensuring that the assembled product is built consistently and according to approved manufacturing requirements.

Depending on the project, inspection and testing may include:

• SPI for solder paste inspection
• AOI for SMT inspection
• X-ray or AXI for BGA, QFN or hidden solder joints
• ICT for electrical connectivity
• FCT for product-level functional testing
• Cable continuity testing
• Hi-pot or insulation testing when required
• Press-fit insertion force or force-displacement monitoring when applicable
• Cable length, bend radius or termination inspection when required
• Traceability records for critical lots or materials

For high-speed cable assembly, quality control may also follow IPC/WHMA-A-620 requirements when specified by the customer. For PCBA assembly, IPC-A-610 criteria may be used depending on product class and application requirements.

Related DMAX Product / Service Pages

For readers evaluating insertion-loss-sensitive PCBA, high-speed interconnects or cable assembly requirements, the following DMAX product categories may be relevant depending on the project scope.

High-Density PCBA Solutions

• Multilayer Rigid PCBs: https://www.dmaxpcba.com/product-detail.aspx?id=13
• HDI (High Density Interconnect) PCBs: https://www.dmaxpcba.com/product-detail.aspx?id=16

High-Speed Cable Assemblies

• USB 3.2 Active Extension Cables: https://www.dmaxpcba.com/product-detail.aspx?id=18
• USB AOC (Active Optical Cables): https://www.dmaxpcba.com/product-detail.aspx?id=19
• USB Type-C Cables: https://www.dmaxpcba.com/product-detail.aspx?id=20
• USB 3.0 Cables: https://www.dmaxpcba.com/product-detail.aspx?id=21

Frequently Asked Questions

Insertion loss is the amount of signal energy lost as a signal travels through PCB traces, vias, connectors, cable assemblies and other interconnect structures. In high-speed applications, excessive insertion loss may reduce signal quality and system stability.

Cable assembly insertion loss may be caused by cable length, cable construction, shielding, connector termination, crimping quality, soldering precision, bend radius and impedance discontinuity. High-speed cable assemblies require consistent workmanship and clear inspection requirements.

PCB material affects insertion loss through its dielectric properties. Low-Dk and low-Df materials are often considered for high-speed applications because they can help reduce signal loss and improve channel performance when used with proper stack-up and impedance control. Copper roughness may also affect high-frequency loss, so some designs may specify low-profile copper such as HVLP.

Yes. While insertion loss is strongly influenced by design and material choices, EMS manufacturing can affect the final signal path through soldering quality, connector placement, press-fit control, cable termination, process consistency, inspection standards and handling control.

Depending on project requirements, DMAX can review PCB material notes, stack-up documents, impedance requirements, connector specifications, cable assembly drawings, cable length requirements, shielding requirements, inspection criteria and traceability needs before production.

Buyers should confirm PCB material, stack-up, impedance requirements, connector specifications, cable assembly requirements, DFM feedback, IPC workmanship requirements, inspection plans and validation responsibilities before production. Early review helps reduce misunderstanding between design intent and manufacturing execution.

DMAX focuses on EMS manufacturing, PCBA assembly, cable assembly and process quality control. Signal integrity simulation, VNA testing and TDR validation are typically conducted by the customer’s engineering team or qualified third-party laboratories. Advanced signal integrity simulation and validation are normally performed by the customer’s engineering team or a qualified laboratory. When such validation is required, the test method, acceptance criteria, sample requirements and responsible party should be agreed before production. DMAX can manufacture samples according to the approved production requirements and provide applicable manufacturing and inspection records.