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Advertiser-supplied Article By Steve Mansfield-Devine for PCBWay The benefits of quality Inspection Reports for PCBs However much you test your product designs, there will always be factors outside your control that affect your final product. One of the most important of these is the quality of the PCBs you receive from your chosen fabrication house. A ll PCB manufacturers make promises about quality control and standards. It’s crucial for you to know how well they live up to these assurances. That’s where quality inspection reports play a vital role – they are the proof that the PCB manufacturer is meeting its promises. Leading PCB fabs commission periodic, independent laboratory testing of their laminate materials and finished boards. These reports provide you with peace of mind and are also invaluable for ongoing process monitoring, quality assurance, regulatory compliance and certification. PCBWay has published 14 quality inspection reports from tests carried out by Centre Testing International (CTI), an accredited third-party testing laboratory (see the bottom of the page at www.pcbway.com/oem/ quality-control.html). Each examination is carried out with industry-standard methods so that customers can compare the results from fabricators worldwide. This also makes them directly applicable to compliance demonstrations for IPC acceptance standards. As a product designer or electronics engineer, you can use these reports to ensure that the physical hardware of the end product will conform to your 66 stack-up and material set, delivering the necessary reliability, safety and longevity. Thermomechanical tests For example, it’s essential to know how boards will respond to heat, both during assembly and when in use. The glass transition temperature (Tg) is arguably the most important laminate specification for engineers designing boards that will be soldered with lead-free processes or that will operate at elevated temperatures. It’s the temperature at which the resin binder in the laminate stops being rigid, like glass, and changes to a viscoelastic state. This happens over a transition range, but the test results are usually reported as the midpoint. The higher the Tg temperature, the better, because exceeding it can mean the board loses dimensional stability and becomes susceptible to delamination and mechanical damage. The common Tg figure for standard FR4 boards industry-wide is 130140°C. However, PCBWay significantly exceeds this, with a figure of 169.61°C. Similarly, time to delamination (T260, T288 and T300) measures how long a laminate can withstand a specific temperature before the layers separate. It is a better predictor of assembly survival than Tg alone. The most commonly cited specification is T288, which tests the time to delamination at 288°C. The industry standard is typically 5-10 minutes for high-reliability boards, but PCBWay’s tests show times consistently above the top end of the scale. High temperatures also cause decomposition of the resin in the board, resulting in loss of mass and weakness. Most PCB fabricators aim for a decomposition temperature (Td) of 325°C, while PCBWay achieved just over 345°C in its most recent tests. Related to this is the coefficient of linear thermal expansion (CTE) – how much the board will expand or contract for each degree of temperature change, relative to Tg. As the laminate is reinforced with glass cloth, expansion in the in-plane axes (X and Y) are largely constrained. However, expansion in the Z-axis (the thickness of the board) can place significant stress on plated through-holes (PTH), vias and solder joints under reflow and thermal cycling, causing barrel cracking, pad lifting and intermittent open-circuits. For temperatures below Tg, the typical figure for CTE is 50-70ppm/°C. Again, PCBWay significantly improves on this, with a test result of 37.4ppm/°C. These better-than-usual results mean much greater safety margins in both manufacturing and end-use for PCBWay customers. Dimensional and structural integrity Heat is not the only factor. There are also mechanical and structural concerns, such as board flatness (bow and twist), the integrity of inner-layer copper and interconnects, which can be checked by microsection inspection, and solder mask adhesion, which is verified by lattice tests. These are physical aspects of the PCB that are often taken for granted. However, with bow and twist, for example, any board with SMDs that has distortion of more than 0.75% can experience problems such as tombstoning (components that should be flat on the board sticking up, attached only at one end) or the failure of solder joints on ball grid array (BGA) packages. This is something that needs to be kept well under control, and PCBWay’s Practical Electronics | July | 2026 PCB Quality Inspection Reports tests show twist results of only 0.16% and bow of 0.12%; well below the threshold where problems typically start. Dimensional tolerance is another factor that seems simple but can have subtle implications. You might expect that the board will be the exact size, with drill holes in the precise locations, as specified in your Gerber files. However, all manufacturing processes have certain tolerances, and you need to know that these are acceptable for your design. The size report covers finished board dimensions, hole locations, pattern shrinkage or expansion and, in some cases, layer-to-layer registration. This helps confirm that the PCB will fit the mechanical envelope, align with mounting hardware, suit its enclosure and mate correctly with connectors, card edges and components. In addition to reliability and manufacturing problems, poor sizing can also create signal integrity and soldering problems. There can be compliance and certification implications, too. Factors such as safety spacing – for example, between high-voltage and low-voltage sections of the board – need to exceed the minimum allowed values in the final product. Typical industry standards allow a ±0.1mm tolerance for the outline of the board, ±10% for the thickness, and ±50–75µm for drill position, finished hole size tolerances and layer registration tolerances. Electrical and chemical performance One key metric that may be on the minds of many engineers is how well their boards will stand up to high voltages. The voltage resistant test (also known as the dielectric withstanding voltage, or hi-pot test) verifies that the PCB laminate (or solder mask over conductor pairs) can sustain 1000V DC at a controlled ramp rate of 100V/s for one minute without breakdown, flashover, sparkover or excessive leakage current. It is a simple pass/fail test. This is an important test for the certification of mains-connected equipment. With medical devices, it’s essential to ensure compliance with Means of Patient Protection (MOPP) and Means of Operator Protection (MOOP) requirements. Practical Electronics | July | 2026 Related to this is the breakdown voltage. An AC voltage is applied across the test sample, ramped at 500V/s, until there is a catastrophic increase in leakage current or visible arc discharge. It provides an upper limit to the laminate’s dielectric strength under AC excitation. For power electronics designs, such as motors, uninterruptible power supplies, inverters and other cases where high-voltage conductors must be isolated on the PCB surface, solder mask breakdown voltage is a critical parameter. A designer can use these figures to derive the maximum allowable electric field strength under the solder mask and determine the minimum safe conductor spacing. Stable layers A PCB is far from simple. It is a sandwich of laminate substrates, traces and copper layers. How well those layers remain together is obviously crucial. The bond strength is a measure of laminate-to-foil adhesion quality. Low adhesion is a risk that manifests as lifted pads during hand soldering or rework, delamination under thermal shock and trace peeling under mechanical vibration—all of which can result in product failures in the field. The test measures the force required to maintain the peeling of a copper foil from the laminate, the result being the average of multiple tests. For standard FR-4 (fibreglass) boards, the general standard is 100-120N, but PCBWay’s test samples averaged around 220N. The bond strength degrades at high temperatures, which is another reason that having a high Tg value is important. Moisture absorption also creates problems for manufacturing and longterm reliability. For instance, moisture trapped in the laminate can flash to steam during reflow, creating internal vapour pressure that causes popcorning (components flying off), delamination and blistering. In RF and microwave PCBs, moisture absorption can be a primary materialselection criterion because absorbed water changes the laminate’s dielectric properties. This can alter controlled impedances, detune RF structures such as filters and antennas, increase dielectric loss and affect phase stability, particularly in equipment exposed to humidity or temperature cycling in the field. When a PCB absorbs water, its mass increases. The IPC-4101 maximum for standard FR-4 is a 0.32% increase, although PCBWay’s figures are four times better, at 0.08%. Production quality There are also tests that relate directly to the production quality of the PCB. The first of these is porosity, an important factor for any board with a gold surface finish like ENIG (electroless nickel immersion gold), especially those that might be exposed to harsh environments. Microscopic pinholes in the gold surface can expose the underlying nickel or copper, opening up a pathway for corrosion, possibly leading to ‘black pad syndrome’, causing poor solder joints and BGA interconnect failures that may not be detectable until deployment. Sample boards are exposed to nitric acid vapour and then dipped in a An operator applies solder paste to a PCB panel using a stencil in preparation for assembly. 67 Advertiser-supplied Article Above: a multi-head automated PCB drilling machine. Left: AOI (Automatic Optical Inspection) of assembled panelised PCBs. reagent solution. The latter reacts with any exposed copper or nickel to produce visible corrosion spots. These are counted and grouped into three diameter categories: ≤0.05mm, 0.050.51mm and ≥0.51mm. The lower the number, the better. PCBWay’s most recent report shows a perfect result of zero in all categories. Finally, the cleanliness test measures the total quantity of ionisable (ionic) contaminants on the PCB surface. These are the products of flux activators (organic acids, halide activators), electroplating chemicals, etching solutions and handling contamination. They can result in electrochemical migration (ECM), also known as conductive anodic filament (CAF) formation and dendritic growth. In the presence of moisture and a DC field, dissolved ions move under electromotive force and form conductive metallic filaments between adjacent conductors, causing leakage currents, intermittent short circuits and ultimately failure. The board is washed with a solvent mixture, after which its conductivity is measured, the result being normalised to the mass of salt per unit board area. The IPC requirement is a figure of less than 1.0µg/cm2. PCBWay’s report shows a significantly better value of 0.19µg/cm2. This is the result of a wellcontrolled cleaning process and minimal-residue flux due to high process control standards. How to use the reports These reports are not obscure technical documents but tools that exist to provide real-world data to back up assumptions engineers must make during the design process. Engineers can compare Tg, Td, CTE, thickness, dielectric 68 data and weave structure against their simulation and reliability assumptions about power dissipation, impedance and via life, validating their stack-up assumptions. Size, bow/twist and micro cross-­ section dimensions confirm that the fabricator can meet the mechanical tolerances necessary for connectors, enclosures and heavy components. The reports also help engineers select suitable laminates. The size, micro cross-section, CTE/ Tg, bond strength and cleanliness reports provide essential data when seeking to qualify a new PCB or new supplier, especially in the automotive and aerospace sectors. The data can also support reliability assessments by helping engineers justify assumptions about PCB-related failure risks. Signal integrity (SI) engineers frequently make use of the water absorption and micro cross-section reports to be certain that the dielectric thickness doesn’t vary too much from the design specification. If it did, the trace impedance may shift, causing signal reflections and data errors in high-speed buses such as PCIe or DDR4. OEMs can share these reports between design, quality and procurement teams to maintain a documented quality history and to justify changes in materials or suppliers during regulatory audits. Evidence of such tests may be required as part of supplier qualification or periodic audits (for example, for ISO 9001 quality management documentation). Even when the final product is in production, the reports can aid in ongoing process monitoring. Periodic cross-sections, cleanliness and bow/ twist measurements are used as process control metrics and logged in inspec- tion reports to show statistical stability and trigger any necessary corrective actions. Regulation and certification Arguably the most significant benefit of these reports is in regulatory compliance and certification. For example, UL 796 (the Underwriters Laboratories standard for PCBs) requires fabricators to track Tg and bond strength. Automotive and aerospace projects need hard evidence for thermal cycling, vibration, humidity bias and high-temperature storage. PCB-level CTE, Tg, Td, bond strength, bow/twist, voltage and cleanliness measurements are key elements in qualification reports and control plans. Cleanliness reports are mandatory for Class II/III medical devices under ISO 13485. Ionic contamination can lead to leakage currents that interfere with sensitive bio-signals or, in extreme cases, affect patient safety. Similarly, safety standards such as IEC 62368-1 (IT/AV), IEC 60601-1 (medical) and their UL counterparts rely on factors such as voltage resistance/breakdown, dimensional accuracy and more to ensure that the PCB portion of the design is robust. The micro cross-section report is the primary evidence that a board meets Class 3 requirements (such as minimum copper wrap-around at the knee of a hole) for AS9100 certification in the aerospace and defence sectors. Conclusion For engineers, quality inspection reports offer confirmation of technical standards. They also provide confidence that the customer’s design will succeed, which is why PCBWay strives PE to exceed industry standards. Practical Electronics | July | 2026