What are the important standards that engineers should know to comply with the wiring harness to PCB interface?

When connecting cable components to a PCB, you need more than just physical connections. These interfaces must meet specific industry standards in order to provide the lowest performance across different applications. It is necessary to understand the correct standards for your project when applied to consumer electronics and aerospace systems. This FAQ discusses the most common standards for wiring harness to PCB interface.

What is IPC/WHMA-A-620 standard and how does its category affect connectivity?

The IPC/WHMA-A-620 standard is the main rulebook for manufacturing electronic cable and harness components. It accurately shows manufacturers what is a good component and what is not. These rules can help companies establish functional and long-lasting electrical connections, depending on their intended use.

What is IPC/WHMA-A-620 standard and what requirements does it propose?

The IPC/WHMA-A-620 standard, known as "Requirements and Acceptance of Cable and Harness Components," provides a complete set of rules covering many important steps:

Wire preparation and crimping - specific requirements for stripping wire ends and creating appropriate crimping terminations.

Welding interconnection - acceptance criteria for solder joints within wire harness components.

Connectorization - Requirements for the contacts inside the connector housing and their termination to the wires.

Testing methods - standardized inspection procedures, including visual inspection and electrical testing.

What are the different placement requirements for terminal leads/wires in different product categories?

The placement specifications of terminal leads/wires vary by category, as shown in Figure 1. The following table provides a systematic analysis of the acceptable defect measurement values for different terminal types.

Figure 1. Classification of terminal leads/wires placement based on IPC/WHMA-A-620. (Image: SolderingGeek - YouTube)

For turret and straight pin terminals, Class 1 allows defects smaller than 90 °, while Class 2 distinguishes between defects smaller than 90 ° and defects between 90 ° and 180 ° (requiring process indicators). Class 3 maintains the strictest standards, allowing only defects smaller than 180 degrees.

Forked terminals use a single specification in all categories - defects must be less than 90 °. Hook shaped terminals follow the same pattern as turret and straight pin terminals of the three categories.

For perforated or perforated terminals, Class 1 requires the wire to be in contact with the terminal surface, while Class 2 and Class 3 both require defects to be less than 90 °.

These different levels of rules allow manufacturers to choose the correct quality standards for the use of their products. This helps them strike a balance between manufacturing products at reasonable prices and still being reliable enough to achieve their intended use.

What are the requirements for soldering wire harnesses to PCBs in J-STD-001?

The IPC J-STD-001 standard is another reference for soldering processes in electronic manufacturing. When connecting wiring harnesses to PCB components, this standard becomes particularly relevant as it controls the quality of solder joints. Let's take a look at how this standard applies to your manufacturing process and what specific requirements you need to meet.

J-STD-001 puts forward specific requirements for soldering connections that directly affect the reliability of line to PCB interfaces. For the common through-hole soldering in wire connections, this standard requires electroplated through-hole (PTH) to be filled with solder. It also requires proper wetting of the bucket and leads.

As shown in Figure 2, three types of applications require:

75% PTH minimum filling

Component side 270 ° circumferential wetting

Welding side 330 ° circumferential wetting

Figure 2.3 Cross sectional analysis of solder joint parameters, showing PTH filling requirements (75%) and directional wetting angles on the component side (270 °) and solder side (330 °). (Image: Sierra Circuits)

How does the product category under J-STD-001 affect the welding requirements for wire harness connections?

The J-STD-001 standard defines three product categories corresponding to different reliability requirements:

Category 1- Consumer electronics products that require basic functionality and less stringent requirements.

Category 2- Service electronic products that require extended performance and moderate standard requirements.

Category 3- High performance electronic devices that require sustained performance and the strictest requirements.

For wire to PCB connections in three types of applications, such as military or medical equipment, this standard provides stricter guidelines for solder joint quality. This includes more precise requirements for wire preparation, terminal installation, and solder fillet formation.

The third category requires more thorough inspection procedures. Although visual inspection is effective in many aspects, X-ray inspection may be necessary for partially hidden connections, which is common in compact wire to PCB interfaces.

Determine your product category early in the design process. This selection will guide you in material selection, process control, and quality acceptance standards during the manufacturing process.

When do AS9100 and IATF 16949 standards apply to wire harness connections?

AS9100 and IATF 16949 are professional standards based on basic IPC requirements. AS9100 is suitable for aviation, aerospace, and defense products, while IATF 16949 focuses on automotive manufacturing. Each standard adds industry-specific requirements beyond technical specifications.

AS9100 emphasizes reliability through a controlled manufacturing process for the connection of wire harnesses to PCBs. You must establish written procedures for wire preparation, terminal connections, and PCB soldering. This standard requires appropriate assembly verification procedures, complete part traceability, current assembly instructions, and connection testing protocols.

This standard addresses common failure modes such as insufficient wire length, stress on connection points, and improper force distribution in FFC and FPC connectors. Figure 3 illustrates these failure modes to help you identify and prevent connection issues during the design and assembly process.

Figure 3. Wire to board and FFC/FPC connection standards: correct and incorrect lead length and force distribution configurations. (Image: JST)

IATF 16949 extends the requirements of ISO 9001, particularly for automotive manufacturing. The wiring harness to PCB interface in the vehicle must be able to withstand harsh environmental conditions while maintaining the electrical integrity of power distribution and signal transmission. This standard emphasizes the prevention of failures through early planning of product quality, which helps identify potential connection issues during the design phase.

Automotive applications require environmental resistance testing under temperature, vibration, and humidity conditions. You also need long-term reliability validation, complete component traceability, and process control validation. For electric vehicles and autonomous vehicle, these connections meet both high power and signal transmission requirements, so compliance is critical to vehicle safety and performance.

Conclusion

Choosing the appropriate criteria depends on your application requirements and reliability expectations. Consumer electronics products use IPC/WHMA-A-620 Class 1 for general applications. Industrial equipment benefits from Class 2 standards and has higher performance. Medical and military applications require three categories to achieve high reliability, as connection failures can pose significant security risks.

Aerospace applications require compliance with the AS9100 technical standard. Automotive applications require IATF 16949 to meet environmental and safety requirements. Consider the cost impact when selecting criteria, as higher classification levels require more rigorous testing and documentation. Balance these requirements with your reliability needs to choose the most suitable standards.