Virtually every electronic product manufactured today is powered by one or more printed circuit boards (PCBs). In the past few years, designers have pushed the limits of these thin sheets of conducting material, engineering them to fit a series of integrated circuits and critical connections with smaller sizing requirements. To keep up with these rapid advancements, PCB assembly (PCBA) providers must conduct quality assurance testing capable of thoroughly examining assemblies and detecting defects in nearly microscopic packages. Flaws in defining characteristics such as size and power consumption not only directly impact the individual boards on which they are found, but they also jeopardize the entire manufacturing process and supply chain. In high volume production runs, even an occasional deformity will undermine manufacturers’ fundamental goal of achieving higher yields with lower defect rates and reduced costs.
PCBA providers can not simply trust that suppliers– even reputable ones– are performing quality assurance checks automatically. They must also validate each assembly with their own inspections in order to provide original equipment manufacturers (OEMs) with the highest quality part for their end user product.The most commonly utilized PCB quality inspection methods and tools of today are:
- Visual – For low volume production runs, one effective form of inspection is for someone (often the person who performed the assembly) to simply look at it with their own eyes. This doesn’t just mean a quick glance; they must meticulously check each connection in a well-lit environment.
- Microscope – To put less of a strain on their eyes, inspectors can use handheld optical tools such as magnifying glasses or jeweler’s loupes to achieve enlarged views of the board’s components. For an even closer look, they can use USB microscopes that project PCB connections onto a large screen for detailed inspection.
- In Circuit Tests – This capacitance test encompasses two different methods of electronic inspection: bed of nails and fixtureless. Bed of nails testing contains a series of small spring-loaded pogo pins that press into various test points to measure resistance. Fixtureless or flying-probe testing sends machine-operated probes across the PCB to check test points at breakneck speeds.
- X-Rays – X-rays offer a non-invasive, though expensive, way to visually inspect for proper PCB assembly – the same way that one would compare to a photograph or microscopic image.
- Saws – Slicing through a PCB with a saw is destructive to the individual board, but can provide valuable insight into the bigger picture of the overall assembly process.
- Automated Optical Inspection (AOI) – AOI systems are available in cheap and commercial grades. Cheap AOI systems utilize inexpensive webcams in conjunction with Open Source Computer Vision (OpenCV) to compare webcam PCB images with those of a “perfect” board and identify incongruences or defects. Commercial AOI uses higher quality cameras and RBG LEDs to reflect light and check for connection faults and solder quality.
- Functional Testing – This testing method is essentially a full trial run of the PCB once it has been manufactured. Operators power on the PCB and program it to perform a series of self-tests.
- Inspection cameras – A preferred tool for PCB quality assurance, inspection cameras allow operators ergonomic viewings with the naked eye. These high-resolution camera images are projected onto computer screens and manipulated such that microscopic details can be inspected and easily shared with different departments for further review.
Floor staff conducting final PCB assembly inspections must be trained on a few key quality control metrics to achieve the ultimate goal of enhanced reliability with reduced board complexity and component count. Two effective quality standards are defects per unit (DPU), which measures the number of defects on each board, and defects per million opportunities (DPMO), a normalizing factor that measures the total number of defects on a million boards of different complexities. With these two metrics, manufacturers can track both product and process quality. Lead engineers can also review boards’ layouts and routing paths to determine if any layers need to be added for optimized circuitry. Stack-up layers can be added as needed to balance the board relative to the center of its Z-axis. Final touch checks include confirming that nodes and circuits are protected from unwanted noise, verifying the existence of solder masks between pins and vias, and ensuring the board’s silk-screening is evident to the user.
With so many devices depending on PCBs as a power source, it’s imperative that quality assurance is prioritized from the board manufacturing to the assembly process. Not only do thorough inspections produce better quality products for OEMs, but they also identify process improvements that boost efficiency, lower production time, and reduce costs for contract manufacturers. Syscom Tech takes pride in training our staff in quality assurance and providing specialized equipment and tooling to inspect every board we create. In addition to partnering with high caliber suppliers, we perform in-house inspections on every assembly that comes through our doors to ensure we meet our customer’s exact specifications and quality requirements, every time.
