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Quality assurance is the gateway to efficiency.

PCB manufacturers who identify problems early avoid issues that accumulate and become more expensive and difficult to resolve over time. To achieve this, they employ a wide range of tests and procedures that help them diagnose issues on diverse board types.

To help give you an idea of what quality standards you should expect from your PCB manufacturer, we’re sharing 6 of the most common PCB quality assurance tests and their uses.

1. AOI – Automated Optical Inspection

One of the most effective ways to determine if the board has defects is to examine it closely —very closely.

  • AOI uses high-resolution cameras and advanced image processing software to capture images of the PCB. These images are compared against a predefined reference model to identify discrepancies.
  • Optical inspections are used to identify defects such as component misalignment, missing components, incorrect components, soldering defects (e.g., insufficient solder, solder bridges), and other surface anomalies.

Why Do Manufacturers Use AOI Testing for Quality Assurance?

AOI is chosen for its speed and ability to quickly identify and flag visual defects early in the production process.

It is especially useful in high-volume manufacturing, where early defect detection can reduce rework and scrap rates, saving costs.

2. BGA X-Ray Inspection

Optical inspection is quick and easy, but the PCB world is filled with complex designs and multi-layer boards that are often impossible to fully inspect visually. Under these circumstances, manufacturers rely on X-rays.

  • BGA X-ray inspection involves using X-ray technology to penetrate and visualize the internal structures of the PCB.
  • When optical inspection is impossible, x-ray testing is crucial for detecting hidden defects such as solder voids, misaligned balls in BGA packages, internal cracks, and other structural issues that are not visible on the surface.

X-ray inspection is usually performed after soldering and assembly, especially for PCBs with complex components.

How Expensive are X-Ray Inspections for PCB Quality Assurance?

X-ray inspection is relatively expensive due to the cost of X-ray equipment and the need for skilled operators to interpret the images.

However, it’s an invaluable tool for ensuring the quality and reliability of multi-layer boards, which more than makes up for the high cost.

3. Functionality Testing

Just because a board is free of visual defects doesn’t mean it will function like it was designed to.

In order to fully ensure PCB quality assurance, manufacturers also subject PCBs to real-world operational conditions to ensure they perform as intended.

  • Functionality testing includes powering up the board and checking its functionality against design specifications using various testing equipment and fixtures.
  • These tests are necessary to verify electrical performance and that all circuits and components operate correctly under specified conditions.

The cost and complexity of functionality testing depend heavily on the design of the PCB and its intended use.

When is Functionality Testing Performed for Optimal PCB Quality Assurance?

Functional testing is essential when the final operational performance of the PCB must be guaranteed. Therefore, it’s usually performed after the PCB has been fully assembled and soldered. Often, it’s one of the final tests done before the product is shipped.

4. In-Circuit Testing (ICT)

In high-volume production runs where speed and accuracy are at a premium, ICT is a useful procedure for checking a PCB’s electrical properties.

  • ICT involves using a fixture with a bed of nails to contact test points on the PCB. It powers up the board and measures the electrical properties of individual components to verify their correct installation and functionality.
  • ICT can reveal issues such as incorrect component values, shorts, opens, or solder joint defects.

ICT ensures the board is free of basic electrical defects before more comprehensive testing is conducted​. For that reason, it’s done before functional testing ensues.

Why do Manufacturers Choose ICT Over Other Kinds of Electrical Testing?

ICT can be relatively expensive due to the custom fixtures required. These need to be designed and manufactured for each specific PCB layout.

However, the testing itself is very efficient and reliable. For manufacturers producing a high volume of the same PCB, the high speed and accuracy of ICT more than justify the cost.

5. Flying Probe Testing

Flying probe testing is another versatile way to check a board’s electrical properties.

  • Flying probe testing uses movable probes to contact test points on the PCB. Unlike ICT, it does not require custom fixtures, and the probes are guided by software to check for opens, shorts, and component values.
  • The probes help manufacturers evaluate electrical properties such as resistance, capacitance, and inductance, identifying shorts, opens, and incorrect component placements​.

This kind of electrical testing is especially useful for its versatility. It can be performed at multiple stages of a PCB’s development, including after initial assembly and soldering.

How Expensive is Flying Probe Testing for PCB Quality Assurance?

Flying probe testing is a less expensive alternative to ICT because it doesn’t require custom fixtures. This makes it an ideal choice for prototypes and low to medium-volume production runs.

6. Burn-In Testing

A burn-in test involves subjecting a PCB to prolonged periods of operation at elevated temperatures and electrical loads.

  • While similar to functionality testing, it’s performed primarily to identify early-life failures and to ensure the board can withstand its intended operational conditions.
  • Burn-in tests check for potential reliability issues such as component failures, solder joint integrity, and load capacity under stress conditions.

Like functionality tests, burn-in tests are performed after the PCBs are completed but before they’re shipped. This is the optimal time to ensure the long-term reliability of the board.

Why do Manufacturers Use Burn-In Tests for PCB Quality Assurance?

Burn-in testing can be expensive and time-consuming because it requires specialized equipment to maintain elevated stress conditions for extended periods.

However, it’s essential for applications where reliability is critical, such as aerospace, military, and medical devices. It helps ensure that boards that may fail early are identified and discarded before deployment.

How Imagineering Prioritizes Quality Assurance

Every quality assurance test on this list serves a unique purpose. Some are useful for identifying electrical defects early on in production, while others help ensure long-term PCB reliability for customers who can’t afford faulty devices.

However, some of these tests are very expensive and time consuming. It doesn’t always make sense to throw every PCB through the ringer when a particular test isn’t called for or would ultimately waste time compared to a similar test.

The best PCB manufacturers understand how and why to use each of these tests and how they fit into the puzzle of PCB quality assurance.

Imagineering uses our nearly 40 years of experience to build and ensure quality boards for customers in every industry.

If you want to know more about our quality assurance standards or learn more about the equipment we use to ensure high-quality boards every time, contact Imagineering today.