Manufacturing and testing electronic products is like dealing with squabbling siblings. PCB testing is a necessary expense that, if done correctly, can prevent larger, more embarrassing losses when the product is launched.

　　Functional PCB (Printed Circuit Board) testing is performed at the end of the manufacturing process to ensure that the manufactured components will not immediately fail or have a shortened lifespan.

　　Let's differentiate PCB functional testing services from other PCB tests, and then understand the specifics and advantages of each test.

　 　PCB Functional Testing Services

　　The functional types of PCB testing include:

　　X-ray Inspection

　　Micro-Sectioning Analysis

　　PCB Contamination Testing

　　PCB Solderability Testing

　　Time Domain Reflectometry Testing (TDR)

　　Peel Test

　　Float Test

　　Why Functional Testing over Other Types of PCB Testing? Functional PCB testing has some clear advantages, such as:

　　Saving money by not having to provide testing equipment to the Electronic Contract Manufacturer (ECM) Works effectively in conjunction with in-circuit testing and flying probe testing (see below). It's possible to test nearly every PCB being shipped (rather than a small sample) so that debugging can be done before the product reaches the customer.

　 　How PCB Functional Testing Works

　　A PCB functional testing system checks the entire assembly, not just its components. This type of board testing simulates the environment the assembly will need to perform in. With functional testing, up to 100% of the product can be tested before the ECM ships the product to the Original Equipment Manufacturer (OEM, that's you).

　　 Here are some popular PCB functional tests and how they work:

　　PCB X-Ray Inspection Services

　　Automated PCB X-ray inspection, also known as AXI, involves displaying 2D or 3D digital images of each layer of the board. Therefore, inspection is done in a single step. The procedure allows for a view of how the entire board works. Schematics provide a reference for comparison.

　 　Advantages of AXI include:

　　Internal view. Hidden elements are no longer hidden, and their functionality can be checked.

　　Complex PCBs, even those with RF shielding, can be inspected.

　　AXI does require trained and experienced operators, but this is not a problem if you work with a contract electronics manufacturer you trust. Despite the extra personnel expense, the testing can save significant time and cost.

　　PCB micro-sectioning, sometimes called cross-section analysis or metallographic preparation, uses a 2D sample to reveal internal workings. This test helps identify:

　　Opens

　　Shorts

　　Solder reflow

　　Component defects

　　Thermomechanical issues

　　Micro-sectioning is destructive to the Device Under Test (DUT), but through micro-sectioning, poorly performing components can be removed. The component is then placed in cured epoxy resin, exposed through abrasion, and compared to a functioning component.

　　Upon close examination, technicians can see:

　　Board thickness

　　Solder joint failures

　　Metal layer discontinuities thickness

　　 PCB Contamination Testing

　　PCBs are contaminated in far more ways than we'd like to admit, including:

　　Flux residues

　　Reaction products

　　Human byproducts

　　Handling

　　Consequences of contamination can include:

　　Corrosion

　　Degradation

　　Metallization

　　PCB contamination happens frequently. Therefore, testing for it is crucial to ensure the component functions properly.

　　Contamination testing, also known as the Resin-Solvent Extraction Resistivity (ROSE) test, aims to discover high amounts of ions and contaminants on a board. The process involves a zero-ion or other ion testing unit drawing ions from the board into a solvent. The ionic contamination is then measured and plotted on a curve to compare it to industry standards.

　 　PCB Solderability Testing

　　Testing the solderability of components and PCB pads helps to:

　　Reduce assembly problems, such as improper solder mask usage

　　Ensure surface robustness

　　Increase the probability of reliable solder joints

　　Confirm that storage does not adversely affect solderability

　　This test is applicable to multiple production factors:

　　Solder assessment

　　PCB coating assessment

　　Flux assessment

　　Quality control

　　Benchmarking

　　Time Domain Reflectometry Testing (TDR)

　　While it's designed to identify faults and discontinuities in metal cable connectors and other circuits, it's also applicable to PCB testing.

　　Specialized TDRs can be used to locate faults in high-frequency boards, especially those that act as transmission lines. The instrument can detect reflections, revealing un-soldered pins in ball grid arrays, shorted pins, etc.

　 　PCB Functional Testing Services - Peel Test

　　Generally speaking, peel tests for flexible adhesives measure resistance to highly localized stress. Specific to PCBs, this test measures the force required to peel a laminate from the board.

　　PCB Float Soldering Test

　　Float testing, also known as thermal stress testing, is used to determine the amount of thermal stress a circuit board's holes can withstand. This includes the temperature range and the number of heating-cooling cycles the circuit board can withstand.

　　This test can reveal potential delamination and poor solder joint connections.

　　There are many other PCB assembly testing methods that may be more suitable than those listed above. These include:

　　In-circuit testing (ICT): Also known as bed-of-nails testing, this inspection uses needles and access points designed into the PCB to connect the circuit and determine values. In-circuit PCB testing helps your contractor determine if any electronic components are defective. Using ICT, the procedure can be performed without powering on. This protects the components from damage.

　　Flying probe testing: This can check various factors such as resistance, inductance, and short circuits without power.

　　Automated optical inspection: Uses photographs of the circuit board to compare it to the schematic.

　　Burn-in test: This provides information about the PCB's ability to work under high temperatures. The cost is reduced output and potentially shorter product lifespan. However, the data collected can help engineers understand the causes of defects and modify the design to improve reliability before entering the burn-in phase.