Visual PCBA inspection

PCB Assembly Essentials Part 2: PCB Inspection Methods

Whenever former U.S. President Ronald Reagan spoke publicly, he would typically cite a poignant anecdote, and a memorable sound bite would linger far after the speech. One of the most famous of these thoughtful morsels was “Trust, but verify.” The President was referring to how he would deal with Russia, a traditional political foe. However, this is a wise strategy that can be implemented in the realm of electronics production.

The process of building or constructing circuit boards is fundamentally a two-stage process that consists of fabrication and assembly. During fabrication, the basic bare PCB structure is created; assembly consists of attaching the components, testing and inspecting the overall PCBA. The range of possible circuit board test regimens that validate the quality of the manufacturing process is extensive and may vary depending on the design and intended application of the board. PCB inspection methods, however, are essential board build tasks that are typically performed for all boards.

PCB Testing vs PCB Inspection

What is the difference between testing and inspecting PCBs and PCB assemblies? Although, testing and inspection are done during fabrication and assembly, the following definitions help distinguish between these activities.

Definitions:
PCB testing describes the utilization of equipment to assess a physical or electrical property or characteristic of the circuit board structure. Bend radius, peel pressure and characteristic impedance determinations—measured using a time domain reflectometer (TDR)—are examples of PCB testing.
PCB inspection, which is more accurately termed PCBA inspection, is commonly used to describe the manual and automated inspection techniques and methods where the board’s assembly is evaluated for solder bridging, bad solder joint quality, component placement-footprint layout and/or pad-trace misalignments or other failure modes.

Definitions:
PCB testing describes the utilization of equipment to assess a physical or electrical property or characteristic of the circuit board structure. Bend radius, peel pressure and characteristic impedance determinations—measured using a time domain reflectometer (TDR)—are examples of PCB testing.
PCB inspection, which is more accurately termed PCBA inspection, is commonly used to describe the manual and automated inspection techniques and methods where the board’s assembly is evaluated for solder bridging, bad solder joint quality, component placement-footprint layout and/or pad-trace misalignments or other failure modes.

The specific tests performed may be dictated by the developer or required by standards and regulations. The same is true for some inspections, which fall into one of two general types and have performance criteria defined in IPC standards A-610 and J-STD-001.

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Types of PCB Inspection Methods

As stated above, the purpose of inspecting boards is primarily to identify failure modes. However, there are additional benefits. For example, consistent inspection can be a predictor of potential failures, as well. The degradation of quality over time, even if still within acceptable limits, is a strong indicator that some process adjustment is necessary. Inspections also provide accurate data for PCB yield determinations. This design validation is a critical part of an optimal design development checklist and should make use of both manual and automated PCB inspection methods.

PCB Inspection Method Types

  • Manual

Manual board inspection is the visual evaluation of a PCBA carried out with the naked eye or some other optical equipment. Common tools are cameras and microscopes that provide higher resolutions than can be seen naturally. The advantage of this type of inspection is that it enables technicians or quality control personnel to target specific areas of the board or specific components.

  • Automated

Although manual inspection should be utilized, it is not a substitute for automation. By automating inspection, manufacturing can achieve the fast turnaround times that are required to reach optimal quality during prototype development. The automated process, referred to as automated optical inspection (AOI), employs image processing and software to provide high-level pictures of internal connectivity and vias of the PCBA.

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Inspection is an essential element of the PCB assembly process as it both checks quality and validates the level of quality control of the manufacturing process. At Tempo Automation, the industry leader in high-quality PCBA prototyping and low-volume production, we employ both automated and manual inspection throughout the board-build process to minimize failure mode risks and optimize yield rates.

And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on PCB inspection methods and their importance to the manufacturing process, contact us.

Articles in this PCB Assembly Essentials series:

Part 1:  PCB Yield Calculations

Part 2: PCB Inspection Methods

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