IPC-A-600 Acceptability of Printed Boards

Introduction

Printed Circuit Boards (PCBs) are everywhere in every electronic device. But have you ever wondered how companies across the entire electronics supply chain agree on the quality of these boards? Often, one company designs a PCB, another manufactures bare boards, and yet another assembles the components onto them.

How can these companies effectively collaborate, especially in a globalized world? We frequently encounter situations where the PCB supplier is a factory in China, assembly takes place in Europe, and the final client, a company in the USA, integrates the finished subassembly into a larger system. Sounds complicated? Fortunately, there's a solution for this :)

The IPC-A-600 Acceptability of Printed Boards standard helps establish common acceptability requirements between customers and suppliers throughout the supply chain.

In this article, we will explore IPC-A-600, its applications, its scope, and its chapters. Enjoy the read!

History of IPC-A-600

The IPC-A-600 standard is one of the first documents developed by IPC. This organization was founded in 1957, while the IPC-A-600 standard was issued in 1964 and has been continuously updated since then. Currently (2024), the latest version is "K," released in July 2020. Formally, the standard and its version are thus designated as IPC-A-600K.

The history of a given IPC standard and information about the latest version can be easily checked on the IPC website in the "Document Revision Table" section.[1]

Scope of IPC-A-600

IPC-A-600 describes acceptance conditions (target, acceptable, process indicator, nonconforming) on a PCB that can be visually observed. The requirements are divided into two groups:

• Externally observable characteristics. These include characteristics related to PCB edges, solder mask, pad condition, and visible anomalies in the base laminate.
• Internally observable characteristics. These are characteristics visible in a metallographic cross-section, such as cracks in the hole plating, the state of inner layers, inclusions in the plating, and so on.

Relationship with IPC-6010

IPC has developed a IPC-6010 series of standards such as: IPC-6011, IPC-6012, IPC-6013, etc. These standards specify the minimum qualification requirements that manufactured (finished) PCBs shall meet. The IPC-A-600 standard only includes those minimum requirements from IPC-6010 that can be visually assessed on a finished board.

In summary, IPC-A-600 is a set of criteria for visual inspection of PCBs, while the IPC-6010 series (and standard J-STD-003) covers a much broader scope of requirements, many of which are not related to visual inspection.

I recommend purchasing IPC-A-600 and selected standards from the IPC-6010 series (e.g., IPC-6011 and IPC-6012 for rigid boards). This combination provides a complete set of information regarding quality requirements for bare PCBs.

Inspection Rules According to IPC-A-600

IPC-A-600 specifies several rules for inspecting PCBs. Below, I present what I consider the most important aspects. Of course, the full range of requirements can be found in the first chapter of the standard.

• The English version takes precedence. Errors in IPC standard translations sometimes occur. In case of discrepancies between the English and translated versions, the original (English) version always takes precedence.
• The product class is defined by the User. The person conducting the inspection does not determine the IPC product class.
• Apply order of precedence. IPC-A-600 clearly defines how to proceed in the event of discrepancies between the requirements of IPC-A-600 and, for example, the customer's specification. These rules are known as the order of precedence.
• AABUS. An acronym meaning "As Agreed Between User and Supplier." If a particular requirement can be defined per agreement between the customer and the supplier, then this acronym is used.
• Use magnification tools. External feature inspection is performed at a magnification of 3 diopters (about 1.75x). If in doubt, magnification can be increased up to 40x. Metallographic section inspection depends on the feature being analyzed, so the magnification range is between 100x and 500x. More information can be found in IPC-A-600, section 1.5.

Main Chapters of IPC-A-600

The IPC-A-600 standard, version K, includes the following (main) chapters:

1. Introduction

The first chapter introduces the scope and purpose of this standard, IPC product classes, and acceptance conditions. This chapter also includes inspection rules (required magnifications), terms and definitions, and references to other standards.

2. Externally Observable Characteristics

This section discusses aspects related to edges, surface appearance, and hole conditions. Requirements related to pad finish and typical defects, such as nonwetting and dewetting, are also discussed. Below are the main sections of Chapter 2:

• 2.1 Printed Board Edges
• 2.2 Base Material Surface
• 2.3 Base Material Subsurface Layers
• 2.4 Solder Coatings and Fused Tin Lead
• 2.5 Plated-Through Holes - General
• 2.6 Unsupported Holes
• 2.7 Edge Board Contacts
• 2.8 Marking
• 2.9 Solder Mask
• 2.10 Pattern Definition - Dimensional
• 2.11 Flatness

3. Internally Observable Characteristics

This section presents requirements for PCB features that can be evaluated based on a metallographic section. Key aspects include:

• 3.1 Dielectric Materials
• 3.2 Conductive Patterns - General
• 3.3 Plated Through Holes - General
• 3.4 Plated Through Holes - Drilled
• 3.5 Plated Through Holes - Punched

4. Miscellaneous

This chapter covers the requirements for the following aspects:

• 4.1 Flexible and Rigid-Flex Printed Boards
• 4.2 Metal Core Printed Boards
• 4.3 Flush Printed Boards

5. Cleanliness Testing

The final chapter of the standard contains requirements regarding the cleanliness and solderability of PCBs. There is a reference to electrical tests.

• 5.1 Solderability Testing
• 5.2 Electrical Integrity

Note: Certain types of contamination on PCBs can initiate a phenomenon called electrochemical migration.

Summary

The IPC-A-600 standard is a key document defining acceptability requirements for bare PCBs. With this standard, the electronics industry has a common set of requirements useful for customers and suppliers.

I recommend using IPC-A-600 in conjunction with IPC-6011 (general requirements), IPC-6012 (rigid boards), and IPC-6013 (flexible boards).