PCB testing methods overview

Why PCB testing is so important? What are PCB tests and who should carry them out? Which tests are more suitable for prototypes and which ones for mass production?

There are a lot of questions regarding PCB testing methods. We will answer many of them in this post.

PCB testing as a part of the manufacturing process

Testing is a key element of  PCB design.

PCB designers pay attention to the board’s checks, as they want to be sure that characteristics of PCB functionality are within allowable values.

Some investigations are needed to be conducted with prototypes or limited batches to be confident that the product is ready to be produced at scale; some tests should be done at the end of the production process to be sure that the final product has no flaws. Despite their differences, all these tests check circuit boards for open shorts, defect solder joints, and test their performance.

Circuit board testing methods

Manufacturers use different procedures for  PCB and PCBA checks. The choice of testing approach depends on

• the production size
• PCB characteristics
• product’s uniqueness

Let's take a look at the most used procedures.

Manual Vision Inspection

Manual visual inspection (MVI) is an old and good PCB testing method, which does not require expensive equipment. A specialist can identify such visible defects as:

• bad solder
• lack of details 
• component wrong position
• cracked joints
• interrupted traces

MVI is no longer widely used in mass production because it can’t maintain the high speed and accuracy of testing due to the human factor and the complexity of modern products. Still, it works well in PCB design and small batch production.

Integra Sources engineers do MVI for all PCBs involved in projects. Our suppliers are highly reliable, so the situations when we face the defects are exceptional. For example, working on one of our projects, we have eliminated the incorrect diodes placement. The defect was quickly fixed.

Automated Optical Inspection

Automated Optical Inspection (AOI) is a large-scale production approach. The AOI machine can be placed at the end of the production line for immediate fault detection. It compares the tested PCB photo to the given example.

This method is more accurate than manual visual inspection; yet, AOI equipment requires a lot of time to install and program for every PCB design change. That’s why it is not so good for prototyping.

AOI can be used together with other methods of PCB testing for best results.

Automated X-Ray Inspection

Automated X-ray Inspection (AXI) uses X-rays to generate images of the joints and parts which are out of sight.

AXI is a rather expensive technology, it needs time to install and qualified personnel to operate, so it is generally used in mass PCB production and for complicated board checking.

Our suppliers conduct bounden automated X-ray inspection to examine the soldering and the absence of defects in the circuit boards.

In-Circuit Testing

In-circuit testing (ICT), or “bed of nails”  is highly effective testing. This fully automated and precision equipment is more suitable as a  final testing phase for products with an approved design version.

In-circuit testing powers up each component of the board and automatically checks them open shorts, incorrect orientation, checks resistance and capacitance, giving more than  90% fault coverage.

ICT jigs use fixed probes (“nails”), which are set corresponding with the PCB access points. Nails are able to test the integrity of solder joints and check voltage at test points automatically.

ICT testing fixtures are great for examining

• ball grid array assemblies (BGAs), 
• FPGAs, power up
• LEDs.

Sometimes our clients ask to check components with the help of the PCB test fixture for more confidence.

Flying Probe Testing

Flying probe electronics testing (FPT) inspects a PCB with the assistance of static and movable probes. These “needles” are programmed to test all components of PCB via test points.

Advantages of FCT:

• easier to use and configure
• less pricey than ICT
• needs less area for operation
• less time to install
• provides a high % of defect coverage.

Yet, not everything is so smooth. Disadvantages of  FPT:

• much slower than ICT
• cost per unit is higher than ICT

That is why it is good for small batches or for PCB design.

Stress Tests

Stress Tests are able to find out if the printed circuit board can withstand the maximum possible loads and parameter changes without loss of quality and functionality. The functioning conditions examined can include such parameters as

• temperature
• current
• operating frequency
• other significant parameters

Burn-in testing is one of the stress tests and a way to disclose any problems or defects of the board by using it in extreme or prolonged working conditions. It supplies power to the PCB, usually at its maximum-specified capacity for 2-7 days.
 
Stress tests are in the  HALT/HASS group of methods (Highly Accelerated Life Testing/Highly Accelerated Stress Screening). They are conducted for PCBs that are used in specific areas

• medical equipment
• industrial equipment
• aerospace
• automotive vehicles

PCB designers run stress tests for recently developed items to guarantee that they are safe, reliable, and efficient.

Functional Testing

As the name suggests, Functional Test (FCT) examines the PCB functionality. These tests are typically made at the end of the manufacturing to verify the PCB’s proper work and its compliance with the specifications.

Integra Sources experts make functional testing to be sure of the product safety and performance. Thanks to our suppliers, we rarely face PCB defects. Even if a defect is identified (as was the case with unsoldered contacts on the Bluetooth module in one of our projects), our engineers identify and fix it without problems.

PCB simulations

Sometimes it is not financially efficient to test PCB or certain design components physically. Simulators offer necessary information without additional expenses if testing devices can’t be applied for some reason.

PCB simulation software uses mathematical models to calculate PCB functioning.

Here are the most requested approaches.

SPICE Simulation

Simulation Program with Integrated Circuit Emphasis (SPICE) is a well-known simulator. Various  SPICE software packages have a set of   various functions, but they all execute basic PCB analyses:

DC Operating Point Analysis works with static DC characteristics and estimates all the DC performances in the datasheet.
 
The transient analysis works with the time response and calculates the voltage and current for a certain period.

AC Analysis works with frequency characteristics, computes the small-signal response of a PCB.

IBIS Simulation

Input/Output Buffer Information Specification (IBIS) can be much faster than SPICE with minimal loss of accuracy.

The main component of the IBIS model contains a table with current, voltage, and timing characteristics. IBIS was developed by Intel to provide consumers with precise IO buffer models without endangering their trade secrets because such models contain no transistor-level data about the PCB. Most IBIS models are easy to use and can freely be taken over the Internet.
 
Being a software and hardware development company, Integra Sources gives attention and time to PCB checking. In those rare cases when a defect is discovered, our experts can eliminate it.

More information on this topic: PCB and electronics testing before and during manufacturing - importance, and methods of implementation.