IPC 6013 for Flexible PCBs: What you need to know?

Introduce

The IPC 6013 is a key specification standard developed by the Institute for Printed Circuits (IPC) that provides comprehensive guidelines for the design, fabrication, testing, and end-use requirements of flexible printed circuit boards (PCBs). This specification is part of the larger IPC 6000 series of documents, which set the standard for excellence in PCB manufacturing and quality assurance. Key Aspects of IPC 6013 for Flexible PCBs are including classification of flexible PCBs, design guidelines, material specifications, fabrication, assembly and so on.

Importance of IPC 6013 for the Industry

Adherence to IPC 6013 standards is crucial for manufacturers, designers, and end-users of flexible PCBs. It ensures that flexible PCBs are produced to the highest quality standards, offering reliability and performance consistency across various applications. For industries relying on the unique capabilities of flexible PCBs, such as wearable technology, medical devices, and aerospace, compliance with IPC 6013 is essential for ensuring product safety, durability, and effectiveness.

By following IPC 6013 specifications, companies can also facilitate better communication and understanding between designers and manufacturers, streamline the production process, reduce costs through improved efficiency and yield, and ultimately deliver superior products to the market.

Classification of Flexible PCBs

IPC 6013 defines several types of flexible PCBs based on their construction and intended use:

• Type 1: Single-sided flexible PCBs with or without stiffeners. These consist of a single conductor layer on a flexible dielectric film.
• Type 2: Double-sided flexible PCBs with plated-through holes, with or without stiffeners. These have two conductor layers with an insulating layer in-between and are accessible from both sides.
• Type 3: Multilayer flexible PCBs with three or more flexible conductive layers with plated-through holes, with or without stiffeners. These PCBs have multiple layers of conductor and insulating material, offering more complex circuitry and higher density interconnections.
• Type 4: Rigid-flex PCBs, which are multilayer circuits comprising rigid and flexible PCB layers that are laminated together into a single structure. This type combines the mechanical stability of rigid PCBs with the flexibility of flexible circuits.

IPC 6013 also categorizes flexible PCBs into three classes based on the level of product quality and reliability required, which directly correlates to the complexity of the application and the environment in which the PCB will operate:

• Class 1: General Electronic Products, intended for products where the primary requirement is the function of the completed assembly. These are typically consumer-grade products that do not require extended life or extreme reliability.
• Class 2: Dedicated Service Electronic Products, designed for products that require higher reliability and extended life, but not to the level of Class 3. These are typically used in industrial or commercial products where higher performance and reliability are needed but are not critical.
• Class 3: High Reliability/Military-Grade Products, intended for products that demand continued performance or performance-on-demand. These are often used in military, aerospace, and medical devices where failure is not an option, and the PCB must function under extreme conditions.

Plating Requirements

In flexible circuits, plating typically uses “button plating” or “pad plating,” a method focusing on plating just the surface pad and hole rather than the entire board surface. This approach means that the plating requirements for flexible or rigid-flex circuits are generally less extensive compared to rigid circuit boards, reflecting the unique manufacturing and performance needs of flexible PCBs.

The IPC 6013 specification includes detailed tables for plating requirements across various types of flexible and rigid-flex PCB designs, including through holes, blind and buried vias, micro-vias, and buried via cores. Each table provides specific plating requirements tailored to the unique characteristics and performance needs of these different PCB configurations.

Quality Requirements

The quality requirements for flex and rigid-flex PCBs do indeed share many similarities with those of rigid PCBs, particularly concerning plated-through holes (PTH), microvias, and internal plated holes, as they have analogous breakout requirements across both types of specifications. Conductor quality, copper weight tolerances, and several other specifications are largely consistent between the standards for flex, rigid-flex, and rigid PCBs to ensure reliability and functionality.

Nevertheless, due to the distinctive properties of flexible materials, there are several differences in the quality requirements:

Bow and Twist: For rigid PCBs, bow and twist are critical measurements reflecting the board’s flatness. However, for flex and rigid-flex circuit boards, these measures are not as relevant because the materials are inherently designed to be flexible. Thus, bow and twist specifications typically apply only to the rigid areas of rigid-flex boards.

Material-Specific Considerations: Flex circuits utilize unique materials like coverlays, stiffeners, and adhesives, which do not have equivalents in rigid PCBs. Therefore, the IPC standards for flex and rigid-flex PCBs address specific issues related to these materials, such as:

Soda Strawing: This occurs when the coverlay lifts around a trace. While not ideal, it can be an acceptable condition provided it does not impede the functionality of the board.
Coverlay Creases: Creases in coverlay films can be acceptable as long as they do not lead to delamination, which would compromise the circuit’s integrity.
Foreign Materials Under Stiffeners: The presence of foreign materials under stiffeners is permissible within certain limits, generally not exceeding 5% of the stiffener area, to avoid any detrimental impact on board performance.
Quality assurance for flex and rigid-flex PCBs involves a careful balance of applying relevant standards from rigid PCBs while accommodating the unique aspects of flexible circuitry. It requires specialized knowledge to interpret these standards correctly and ensure that the flex and rigid-flex PCBs manufactured will perform reliably in their intended applications.