Test PCB Board : Complete Testing Methods and Best Practices

As a PCB manufacturer, we always conduct testing with a number of stages, because if you’ve ever designed a PCB and sent a beautifully routed board to JLC, waiting eagerly for delivery, unboxing it like a new iPhone, only to find out later that a single microscopic solder bridge is enough to turn your masterpiece into a glorified coaster. This is exactly why PCB testing exists, and we are focused more extensively on it.

PCB testing is like a basic “health checkup” of your electronic product before it is allowed to live a productive life. However, in the world of electronics, we utilise various types of machines and test methods, which will be discussed further in this blog. PCBs undergo multiple levels of testing, each designed to catch a different kind of defect. In this detailed guide, we will examine every PCB testing method and outline the testing order. We will see why each stage is absolutely essential. It is always a good idea to verify whether a PCB manufacturer consistently applies these techniques in practice.

Why Thorough PCB Testing Matters

PCB testing is a structured process that verifies the electrical and functional correctness of a PCB. This is all done after the board has been manufactured and assembled. Here the goal is pretty simple:

The manufacturer must ensure that the PCB works exactly as designed for every unit. After the PCB fabrication and component placement, checks are run on soldering quality, and functional behaviour. For all these tests, PCB manufacturers have a well-designed testing pipeline to reduce circuit failures and production delays.

Cost of Failure vs. Costly Field Returns

As we already know from the introduction, cost and time are the two significant factors in testing. A failure caught early in manufacturing typically costs pennies to fix, and the same failure discovered in the field can cost hundreds or even thousands. Here is the basic 10x rule with breakdown:

Failure During PCB Fabrication (Bare Board Stage): This can cost between low and moderate because the defect is detected at the bare board end itself, so we can scrap or remake the board before components are added.

Failure During Factory Testing: It can cost moderately to high because of assembly time, soldering cost, and a few components, including labour and rework time. However, it is still cheaper than dealing with customers.

Failure at Customer Site: It costs too much because of:

• Return logistics
• Replacement units
• Damaged customer trust
• After-sales service labour

Due to warranty claims and negative reviews, damage to future sales is inevitable.

Key Industry Standards in PCB Testing (IPC-6012 & IPC-A-600)

To ensure every PCB meets global quality expectations, the electronics industry majorly follows IPC standards. Two of the most important ones related to PCB testing are:

IPC-6012: Performance Requirements for Rigid PCBs

This standard defines the minimum manufacturing quality a bare PCB must meet before assembly. It also defines three quality classes, from consumer-grade (Class 1) to high-reliability military/medical (Class 3). It sets rules for:

• Conductor width/spacing tolerances
• Copper plating thickness
• Via quality and barrel integrity
• Solder mask accuracy
• Surface finish requirements

IPC-A-600: Acceptability of Printed Boards:

IPC-A-600 is the visual inspection bible for PCB quality. While IPC-6012 defines how a PCB must be built, IPC-A-600 defines how it should look when properly built. It provides:

• Acceptable vs defective examples
• Cross-section images of vias and pads
• Criteria for holes, pads and solder mask
• Defect limits for different classes of boards

Together, these two standards form the foundation of modern PCB testing practices.

Why So Many Different PCB Tests?

Because no single test can detect all defects. Each method specialises in detecting specific types of issues; the flow chart below shows the exact flow of testing.

• Bare Board test for broken tracks, shorts, bad vias
• SPI for solder paste quality
• AOI for visible placement & solder defects
• X-Ray to see hidden joint issues (BGA/QFN)
• ICT for electrical connectivity & component values
• Power-Up test to see safe power behaviour
• Functional test for product functionality

This multi-layered testing strategy builds confidence in the final product.

Must-Know Testing Methods:

1) Bare Board Electrical Testing:

This type of test is run before any component is soldered, just because we want to test the traces and copper fills. In this type of test, a general electric continuity probe is used to search for open and short circuits, as well as to identify any unplated via failures and incorrect net routing. This prevents expensive components from being placed on a defective board.

2) Solder Paste Inspection (SPI):

SPI uses 3D measurement to check the solder paste volume on a circuit board as it matters a lot: too much paste can cause bridging on small components. And if the paste volume is less, there will be a missed connection, and it will be seen as an open joint. If the paste does not reflow as expected, issues such as poor adhesion and tombstoning may arise due to that.

3) Pre-Reflow AOI:

Automated Optical Inspection tests are run after the solder inspection to verify that all components are correctly placed. An AOI machine, as its name suggests, automatically identifies the orientation and polarity marking on the components. If any ambiguity is found, the area will be highlighted. Fixing errors is now extremely easy; simply lift and replace the respective components.

4) Post-Reflow AOI:

This is the primary check after the reflow soldering is done and components are attached to the PCB. There may be several issues due to the reflow, all of which are discussed in a separate blog post, along with the reflow soldering guide, here. The Post reflow AOI searches for solder bridges, open joints, and lifted leads. In the same step, it identifies misaligned packages and cold solder joints. AOI ensures 80–90% of surface-level issues are caught.

5) X-Ray Inspection (AXI/MXI):

These tests are used explicitly for BGA, QFN, LGA and Micro-BGA. X-ray provides internal solder ball inspection and void percentage detection under BGAs. These techniques are mainly used where the AOI cannot reach because these joints are invisible to the AOI. It is used to detect issues such as head-in-pillow and shortened internal pads.

6) In-Circuit Testing (ICT) or Flying Probe Testing

After the visual inspection, tests for network connectivity and analogue parameters are complete. In these checks like power rail measurements and component values are confirmed once again. A flying probe is used for lower volumes, and ICT fixtures are used for mass production.

7) Functional Test (FCT)

When designing something, the most important question is:

“Does the product actually work?”. To ensure it does, the industry must follows the exact guidelines provided at the time of ordering, including data for:

• Sensor calibration
• Wireless communication
• Protocol testing
• Motor control
• Display output
• Firmware execution

Functional testing validates real-world performance.

Common PCB Defects and How to Catch Them Early

Even the best-designed PCB can fail due to tiny manufacturing imperfections. Every PCB manufacturer uses identifying tricks to detect issues in the early stages. But the good news is that nearly all of them can be caught early using AOI, X-ray, ICT, and functional tests that we have discussed in detail. But here is a top 8 failure checklist to perform during fabrication:

Top 8 Failures:

Here are the most common defects you must watch for:

1. Short Circuits: These are often caused by excess solder, which forms bridges between fine-pitch pads.
2. Open Circuits: These errors occur when solder is missing or when tracks are broken during the reflow process.
3. Cold Solder Joints: This error is encountered when the mechanically weak solder breaks under vibration.
4. Tombstoning: These are small SMD resistors/capacitors that lift on one side due to uneven reflow tension.
5. Void Formation: These are the air pockets in solder joints formed especially under BGAs.
6. Skewed Components: When the solder is uneven, it can cause intermittent or open connections.
7. Component Value Errors: Wrong resistor or capacitor value placed.
8. Delamination or Layer Separation: Due to poor lamination pressure or excessive heat in the bare board.

Quick Environmental & Reliability Tests

Boards must withstand long-term use, vibration and extreme temperatures. Although the product is produced in a lab hence environmental testing guarantees that your design also works in actual conditions.

Thermal Cycling and Burn-In Basics:

1. Thermal Cycling: The PCB is subjected to a range of temperatures, such as –40°C to +85°C. It checks for stress failures, material expansion mismatches, and solder joint fatigue. Repeated heating and cooling reveals weak joints and cracks before customers do, which is why it matters.

2. Burn-In Test: For eight to seventy-two hours, the PCB operates continuously at a high temperature (such as 55 to 70°C). Under load, every component is under stress. Infant mortality failures, or early-life failures, are captured by burn-in. When combined, these tests greatly lower warranty problems in the field.

In-House vs Outsourced Testing

Not every business needs a full testing lab. There are also some small businesses that have trouble affording space, machines, and skilled labor. It depends on how complicated and how many products you have to test whether you do it in-house or hire someone else to do it.

When to Do It Yourself and When to Outsource

Do It In-House When:

• You’re in the prototyping or early development stage.
• You need rapid iteration and debugging.
• You have low to mid-volume production.
• You require custom functional testing or firmware-based tests.
• The cost of fixtures is not justified for outsourcing.

Outsource Testing When:

• You’re in mass production.
• You need ICT jigs, AOI, SPI, and X-ray, which are too costly to own.
• Certification testing is required (EMI/EMC, UL, CE, automotive).
• You want statistical process control and yield optimization.

2025 Trends You Should Know

PCB testing is evolving at a faster pace than ever, thanks to advancements in automation and AI. As boards become smaller and more powerful, traditional inspection tools are being upgraded with more intelligent algorithms.

AI Inspection and High-Speed Board Testing

1. AI-Based AOI Systems:

Modern AOI machines use machine learning to:

• Reduce false positives
• Identify patterns of recurring defects
• Automatically adjust inspection thresholds
• Detect solder issues even on shiny or uneven surfaces

AI-based AOI is becoming standard in mid- to high-volume SMT lines.

2. High-Speed Electrical Testing:

High-speed digital boards (PCIe, DDR5, MIPI, SerDes) demand:

• TDR-based impedance checks
• Eye diagram analysis
• Automated SI/PI verification
• Faster flying probe systems capable of GHz-level measurement

By 2025, automated SI/PI testing during production will no longer be a luxury; it will become essential as boards move towards GHz frequencies.

Best Practices and Conclusion:

We have covered almost everything and answered most of the queries. PCB testing is not a choice, but a necessity for every manufacturing house. With this knowledge, you can also see the process of your board in a fab house and monitor if the tests perform as expected.

Some best practices that can be followed during a design are to add test points to:

• Ground
• All power rails
• Key signals (RESET, SWD, UART, clock pins)
• Add Clear Orientation Markings for AOI
• Use Fiducials for the AOI machine

We should have proper documentation with a test procedure, which is given as remarks to manufacturers. In this way, if the design under test causes any problem and does not perform as specified, it is easy to identify at an early stage. The tests mentioned above are mandatory for every design and must be completed in sequence. To get more knowledge about any test, you can ask JLCPCB for help.