A Complete Guide to PCB Through Hole Design: Core Techniques Explained

Temperature changes pose a more severe challenge to through-holes than we imagine. Especially in multilayer boards, the difference in the coefficients of thermal expansion of different materials during reflow soldering causes the via walls to experience enormous stress. If the copper thickness is insufficient or there are weak points, cracks are almost inevitable.

I believe that it’s better to focus on process control rather than trying to fix things afterward. Establishing process files for each batch to track the lifespan of the chemicals is more effective than simply relying on final testing. After all, the reliability of vias cannot be solved by a single step; it is the result of the coordinated efforts of the entire manufacturing chain.

Recently, we adjusted the angle of the oscillating device during electroplating, improving the chemical exchange efficiency within deep holes. Although it was a small change, the uniformity of copper thickness at the center of the hole was significantly improved. Sometimes, solving problems doesn’t require high-end equipment; addressing the details of existing processes is often more effective.

I’ve seen too many projects fail due to PCB via issues. Sometimes, a seemingly insignificant defect in the hole wall can render the entire board unusable. I remember once encountering a strange phenomenon while debugging an industrial control board: after running for a period of time, the signal became unstable. Initially, I thought it was a chip overheating or a software problem. After several days of troubleshooting, I discovered it was a poor contact in a via for a critical signal.

That experience made me realize that the quality of vias often determines the lifespan of the entire board. Especially when working in environments with large temperature differences, the differences in the thermal expansion coefficients of materials can pose significant challenges. When temperatures fluctuate repeatedly, the different expansion and contraction rates of various materials can easily lead to stress concentration at the hole walls.

Many people think drilling is simply a matter of making a hole, but there’s much more to it than that. If drilling parameters aren’t adjusted correctly, such as too high a spindle speed or improper feed rate, micro-cracks invisible to the naked eye can easily remain on the hole walls. These cracks may not initially affect functionality, but over time, coupled with environmental factors, they will gradually expand, eventually leading to connection failure.

The process of removing adhesive residue is also frequently overlooked. If residue isn’t thoroughly cleaned, the electroplated copper layer may not adhere properly. I’ve seen boards that performed perfectly during testing, but after a few months of operation under vibration, through-holes began to intermittently disconnect.

When selecting materials, it’s crucial to be mindful that not all boards are suitable for high-frequency or high-temperature applications. Some manufacturers use cheap substrates to reduce costs, resulting in boards that malfunction shortly after being used in automotive electronics.

The most frustrating thing is that these problems often don’t manifest immediately; they’re like time bombs hidden inside the board, and by the time they’re discovered, actual damage has usually already occurred.

Therefore, when I design PCBs now, I pay special attention to vias, especially those carrying high currents or critical signals. I’m willing to spend more to ensure reliability, since the cost of later repairs is often much higher than the cost of prevention.

Many people easily overlook a detail when designing PCBs—those seemingly insignificant through-holes. I spent a considerable amount of time researching this issue and discovered it’s far more complex than imagined. The design quality of PCB through-holes directly affects the stability of the entire board, especially under high temperature and humidity conditions.

I remember once testing a multilayer board where all parameters initially appeared normal, but after several hours of continuous operation, the signal began to malfunction. Upon disassembly and inspection, it was discovered that the plating in several critical locations was faulty, causing unstable connections between layers. This experience made me realize that I couldn’t just look at surface parameters; I had to consider the various variations in actual applications.

Now, I pay particular attention to the processing quality of vias, especially those that need to carry large currents. Different substrate materials have different requirements for plating thickness; sometimes, increasing it by a few micrometers can significantly improve reliability. This requires adjustments based on the specific usage environment; simply applying standards won’t solve the problem.

Another easily overlooked factor is the effect of the coefficient of thermal expansion. When the temperature changes, the different degrees of expansion of the materials in each layer can create stress on the via structure. I’m used to simulating extreme conditions during the design phase and preparing contingency plans in advance, because modifying them after mass production is too costly.

In fact, there are no universal solutions for these kinds of problems; it’s more about accumulating experience. Every time I encounter a new case, I record the handling process and gradually develop my own judgment criteria. This kind of learning through practice is much more useful than simply reading theoretical materials. I’ve seen many people focus excessively on surface issues when dealing with PCB through holes, neglecting the most fundamental aspects. Sometimes you spend a lot of time adjusting plating parameters, only to find that the root cause of the problem was actually planted much earlier.

Take drilling, for example. Many people think that as long as the hole diameter is correct, it’s fine, but it’s not that simple. Once, our factory received a rush order, and to meet the deadline, we increased the drilling speed by 20%. As a result, the through-hole yield of this batch of boards dropped by half. Upon cutting them open, we found that the hole walls were like they’d been chewed by a dog; those uneven areas became potential hazards in later processes.

The most troublesome issue is drill residue. Do you think soaking it in chemicals will solve the problem? Once, we performed a standard desmear procedure, but a cross-section inspection still revealed tiny specks of residue on the hole walls. These things aren’t visible normally, but once the board undergoes high-temperature reflow soldering, the thermal expansion and contraction will cause cracks in those weak points.

I now pay particular attention to the desmear process. It’s not simply a matter of following the standard procedure once and being done with it. You have to adjust the processing time according to the board thickness and hole size. Too short a time won’t clean thoroughly, and too long might damage the substrate. Once, we were making a batch of thick boards, and the regular processing time wasn’t enough. We had to switch to segmented processing to solve the problem.

Actually, there’s a simple way to judge the effectiveness of adhesive removal—use a magnifying glass to look at the reflection on the hole walls. If you see an uneven matte surface, there’s probably still residue. This is much faster than waiting for the slab report; you can immediately adjust the production line if you find a problem.

Ultimately, PCB manufacturing is a constant process of striving and overcoming challenges. Today you might solve the hole wall roughness issue, and tomorrow you might stumble on drilling contaminants. But each time you discover and resolve a problem, the next batch of boards will be more reliable.

I’ve seen too many people take the vias on PCBs for granted. Those small metal holes may seem insignificant, but they bear the important responsibility of connecting different circuit layers. The problem is that many people think that as long as they pass inspection during production, these vias will continue to function stably.

In reality, the true test of a via’s reliability often comes after it’s installed in equipment. I’ve encountered many such cases: everything works perfectly when it leaves the factory, and no problems are found after components are installed, but after the equipment runs for a while, inexplicable malfunctions begin to occur. Sometimes the signal is intermittent, sometimes there’s no power at all.

The most frustrating thing is the insidious nature of these problems. You might spend several days troubleshooting, only to find the problem lies in a seemingly intact via. This kind of failure often doesn’t happen suddenly, but rather develops slowly over time. Temperature changes, equipment vibrations, and even the minor pressures of daily use constantly test the durability of these connections.

I remember a particularly typical case: a batch of circuit boards all passed factory testing and ran well for the first few months after customer installation. Until one day, they started malfunctioning one after another, and upon disassembly and inspection, it was discovered that several critical vias had developed micro-cracks. These cracks were very hidden and difficult to detect without specialized equipment.

This situation made me realize that evaluating the quality of a PCB cannot rely solely on the factory test results. It’s more important to consider its performance in real-world usage environments. Especially for equipment requiring long-term stable operation, the requirements for every detail should be even more stringent.

Now, whenever I design a new circuit board, I pay special attention to the treatment of through-holes. It’s not just about whether their dimensions meet standards, but also about whether their coefficient of thermal expansion at different temperatures matches the surrounding materials, and whether they can withstand the expected mechanical stress.

Sometimes I think we should re-examine the definition of PCB quality. True quality shouldn’t just be perfect performance at the factory, but stable performance that withstands the test of time. After all, for users, a device that can work reliably for a long time is far more valuable than a product that merely passes factory testing.

This makes me more focused on thinking from the user’s perspective. As designers, we need to anticipate all the situations the product might encounter in actual use, rather than simply being satisfied with meeting the minimum requirements of industry standards. After all, truly good products are those that allow users to forget about the technical details.

Every time I see those densely packed PCB through-hole designs, I think about one question—have we complicated something simple? I remember last year when I was debugging a six-layer board, I found a signal that kept intermittently working and failing. It took me two whole days to discover that a micro-crack had appeared in a 0.4mm through-hole during the third reflow soldering.

Many people immediately bring out all sorts of high-precision testing equipment, but what’s most easily overlooked are the most basic physical laws, such as the matching of thermal expansion coefficients. When you drill a 0.2mm through-hole in a 1mm thick board, the hole diameter to board thickness ratio reaches 5:1. This value becomes a potential source of problems during repeated thermal cycles.

I’ve seen too many engineers focus on the copper plating thickness, but few pay attention to the adhesion between the hole wall and the substrate. Sometimes, even if the copper layer thickness meets the standard, if there are slight imperfections in the substrate surface treatment, the hole wall can easily separate without the naked eye under conditions of large temperature variations. This is especially noticeable in low-temperature environments.

A curious phenomenon exists: everyone is pursuing small hole diameters, but few consider the lifespan of the drill bit itself, especially micro-drills smaller than 0.3mm. These bits begin to wear after about 200 holes, at which point the hole wall quality deteriorates sharply. This is often obscured in the process parameters provided by manufacturers.

Regarding pad design, I’ve noticed many blindly pursue the minimum ring width. However, for high-frequency signals, sometimes appropriately increasing the pad size can improve reliability, especially for test points requiring multiple rework. Insufficient pad space can easily lead to pad detachment during secondary soldering.

Recently, while working on an automotive electronics project, I encountered a new problem: when the board thickness exceeds 2mm, the depth of plating for through-holes becomes a bottleneck. We processed a 1.6mm board without issues using standard parameters, but when switching to a 2.4mm thick board, a noticeable thinning of the plating layer was observed in the middle of the hole wall. Adjusting the plating parameters resolved the issue.

What strikes me most is how much young engineers rely on simulation software. Once, during a review meeting, a colleague confidently stated that the simulation showed the via impedance was perfectly within specifications. However, actual testing revealed a deviation exceeding 15%. Later, cross-sectioning revealed that drilling slag from the drilling process hadn’t been thoroughly removed, leading to poor plating adhesion.