PCB Testing: Ensuring High Quality Boards

Electronics continue to develop and evolve new, exciting technologies at astonishing paces. While this is exciting for customers, it poses a challenge to manufacturers. Despite shrinking chipsets, more complex, feature-rich designs have a lower overall margin for error. Potentially compounded by the need for a quick turnaround to reach customers or markets within critical windows, the prevalence of defects escaping from manufacturing facilities continues to rise. Thus posing a high financial cost in actual remediation and perceived brand damage.

Simply put, the need for exacting quality control has never been higher. Manufacturers must keep ahead of cutting-edge tools and practices to meet the demands of modern, high-quality PCBs. With modern production’s high stakes and overhead, VSE can assure rigorous and comprehensive testing for any design and every board that passes through the shop.

High-Quality PCBs Use Testing as Production Feedback

The Rule of Ten is a particularly emphatic summation of the escalating cost of defect escape throughout the manufacturing process. It’s more of a rule of thumb than anything hard and fast. It states that defects generally tend to increase in cost by a magnitude with successive steps.

For example, consider a critical routing error like a short between nets or an unconnected pin. If this is discovered before any manufacturing, the cost to fix it is trivial, as a designer needs only to correct files and output new artwork. From then on, however, a defect’s cost will continue to appreciate. This increase is due to the mounting labor and material inputs that will be salvaged or scrapped, depending on the extent of the error. Defects introduced by manufacturing follow a similar pattern. The earlier they are detected and remedied, the more resources are averted from defective boards.

Defect cost is not solely monetary and can have a knock-on effect on clients’ productions. Egregious instances can delay time to market due to low yield or additional time required for rework. Worse yet, defective products in the hands of customers could require expensive recall campaigns and pose a catastrophic liability should these defects pose a safety issue. In other words, quality control is a direct responsibility of the manufacturer, yet failure to heed best practices reflects equally poorly, if not more so, on the contractee.

Testing During Manufacturing Guides and Corrects Defect Analysis

Testing guides manufacturers that the work is being performed as expected, increasing the speed of defect detection and total sensitivity. Although a bulk of testing occurs towards the end of the PCB assembly to ensure that the marriage of SMT and through-hole components are properly bonded to the board mechanically and electrically connected, many intermediate steps throughout fabrication also require validation. A PCB production can be considered as two consecutive, complementary manufacturing jobs:

- Fabrication of the board, where constructing the connective layers, traces, and drilled vias are the primary focus. The mechanical features of the board are also of high interest.

- Assembly, which is concerned with the correct component placement and associated soldering.

Testing, in this sense, can be seen not only as a safeguard but as a constant refinement of the manufacturing process and the design itself. It is ultimately integral to the final operation of the board, seeing as many simulated features need to be evaluated experimentally to confirm proper function and allow for any necessary adjustments. Testing practices are responsible for manufacturing practices, and VSE strives to meet the highest expectations.

Summary of Common PCB Tests and Motivations

Every board is different, and so must be the battery of tests it submits to before receiving the all-clear from manufacturing. Some tests are fundamental to PCB manufacturing and a requirement for any board. Others may be one possible test among an analogous group decided upon certain manufacturing constraints.

Below is a list of some of the most common tests encountered in PCB manufacturing that VSE employs, as well as their particular role in establishing a superior level of quality control:

Reliability testing	Testing, usually visual inspection, that validates the board’s features for a particular IPC Class. Generally, this can be any test to ruggedize a board, improving service life and continuous operation in the field.
Burn-in testing	A stress test of a PCB to weed out infant mortality in the board and components. Testing conditions must be carefully considered to avoid overly aging the device.
In-circuit testing (ICT)	Testing the assembly to ensure basic network properties such as opens, shorts, resistance, capacitance, etc. It can be performed with a bed-of-nails or flying probe. The former requires an upfront cost of designing and fabricating a fixture, while the latter has no such requirement but performs slower on a per-board basis.
Insulation resistance testing	Ensures the safe handling of any members of the cable harness. Tests the insulation material to prevent shocks and burns.
Automated X-ray inspection (AXI) testing	Uses X-rays to peer inside a fabricated board at internal copper layers or underneath components like ball grid arrays (BGAs) to assuage the quality of the solder bond.
Functional testing	Whereas ICT evaluates the correctness of a PCB as compared to its netlist, functional testing aims to dive a bit deeper. Essentially, it gauges whether a device operates as intended concerning circuit outputs, logic blocks, etc.
Visual inspection	Trained inspectors comb over a board and look for defects and manufacturing deviations. There are benefits to using the human eye for testing, such as a greater overall discernment and detection of features that might be borderline cases to an automated system. However, additional support, such as ergonomic lighting, must be considered to avoid strain and fatigue that could undermine the inspection.
Automated optical inspection (AOI)	AOI systems utilize sophisticated tools and algorithms to inspect boards for defects. Coupled with deep neural network (DNN) learning models, they represent the growing field of computer vision, which aims to bolster inspection modes.
Automated testing	Additional general automated testing methods are continuing to evolve with further advancements in technology and applications.

Your Contract Manufacturer Shares Your Quality Concerns

High-quality PCBs are no accident. They are the product of careful design and manufacturing practices combined with the talents of a skilled workforce. Testing forms a crucial feedback loop in the design and manufacturing process and detects defects early to reduce resource investment into defective boards. The importance of test integration into the larger manufacturing structure cannot be overstated. Your customers and clients rely on your products operating optimally over their rated service life with as few hiccups as possible.

Here at VSE, we know our name is as much on the line as your own for your devices, and we embrace our responsibility as a team of engineers committed to building electronics for our customers. Together with our exemplary manufacturing partners, we aim to produce only the finest PCBs that are well-vetted in every conceivable way.

Ready to get started?

If you are looking for a CM that prides itself on its care and attention to detail to ensure that each PCB assembly is built to the highest standards, look no further than VSE. Contact us today to learn more about partnering with us for your next project.