Hey there, Electric Conduction Adhesive
If you’ve spent any time sourcing electronic assembly materials, you’ve probably heard about electric conduction adhesive (ECA) as a game-changer compared to traditional solder. It’s lightweight, flexible, works on sensitive components that can’t stand high solder reflow temperatures, and cuts down on many assembly steps—all things that make it ideal for everything from wearables to automotive sensors. But one question I get asked more than any other when customers first reach out is: “What’s the moisture absorption rate of your ECA?”
At first, I used to think it was a straightforward number. Then I realized how much misinformation is out there. Some suppliers toss around a single percentage like it’s a universal value, while others either avoid the question or give vague answers. Over the past 12 years as an ECA supplier, I’ve tested every batch of our product at least three times, talked to 100+ electronics engineers about their moisture-related failure stories, and learned that moisture absorption isn’t just a “rate”—it’s a critical performance metric that impacts everything from shelf life to long-term reliability. Let me break this down the way I explain it to my team and our clients, no jargon that makes your eyes cross.
First, let’s get one thing straight: ECA isn’t a monolith. There are different types, and their moisture behavior varies wildly. The two main categories are isotropically conductive adhesives (ICAs), which have conductive particles evenly distributed throughout the adhesive matrix, and anisotropically conductive adhesives (ACAs), which only conduct in one direction. Most of the ECAs our customers use day-to-day are ICAs, so that’s what I’ll focus on here, though I’ll note key differences when relevant.
Our ECAs are formulated with a modified epoxy resin matrix—we’ve spent years tweaking that formula to balance conductivity, adhesion, and resistance to environmental factors like moisture. Epoxies are inherently hygroscopic, meaning they absorb moisture over time, but we adjust the resin blend and add surface treatments to our silver (or copper, for low-cost applications) particles to minimize that uptake. That’s why our standard ICA has a moisture absorption rate of 0.8% by weight after 24 hours of immersion in 85°C/85% RH (relative humidity) per IPC-TM-650 2.6.2.1, the industry standard for this testing. Wait, I can already hear some of you—“But I saw another supplier’s product with 0.5%!” Let’s talk about why that number alone is meaningless.
The rate of moisture absorption isn’t a single fixed value. It depends on three things: how the ECA is cured, the environmental conditions it’s exposed to, and the thickness of the adhesive joint. For example, under the same 85°C/85% RH test, a fully cured ECA sample that’s thin (0.1mm, typical for surface mount applications) will only absorb 0.6% after 24 hours, while a thicker sample (1mm, used for power applications) will absorb 0.9%—that’s just the physics of more material to soak in. Curing is even more important: if an ECA isn’t fully cured (say, only 70% cure instead of the recommended 95%), its moisture absorption rate jumps to 1.5% after 24 hours, because uncured epoxy has more voids and polar groups that attract water. I’ve had customers send us parts that failed because they under-cured their ECA, and when we tested the leftover adhesive, its moisture uptake was 2x higher than ours. That’s not our product failing—it’s a processing step that got skipped.
Now, why does moisture absorption matter? Because ECA relies on its conductive network to work. When moisture is absorbed, a few bad things can happen. First, moisture causes the adhesive to swell. If it’s bonded to a rigid component like a PCB or a sensor, that swelling creates stress at the joint. Over time, that stress can crack the conductive network—those tiny silver particles that are touching each other to carry current pull apart, and resistance spikes. We’ve seen this in automotive sensors that sat in a warehouse for 6 months before being installed: the ECA had absorbed 0.7% moisture during storage, and after heating during manufacturing, the joint developed a micro-crack that caused the sensor to fail in the field.
Second, absorbed moisture can lead to electrochemical migration. If you have silver particles in the ECA, moisture provides a medium for silver ions to move. When voltage is applied, those ions can migrate to adjacent traces, creating a short circuit. This is a big problem for high-density PCBs, where traces are only a few millimeters apart. We recently had a client in the consumer wearables space who had a batch of smart watches failing due to random shorts. They thought it was a design flaw, but when we tested the ECA from their supplier, we found its moisture absorption rate was 1.2% after 24 hours—way higher than our product. The combination of high moisture and fine trace pitch was causing silver migration. That’s a failure mode that’s completely preventable if you choose an ECA with properly controlled moisture uptake.
Wait a second—so is lower moisture absorption always better? Not exactly. Let’s talk about storage conditions, because that’s something almost every customer overlooks. ECA is a shelf-stable product, but that only holds if it’s stored correctly. If you leave an ECA cartridge out of the freezer (we recommend storing at -20°C, with a 10:1 dry air purge) for more than 24 hours, it will start to absorb moisture from the air. Once you apply it and cure it, that trapped moisture outgasses during curing, creating voids in the adhesive joint. Those voids don’t just hurt conductivity—they also weaken the bond, making the joint more susceptible to environmental damage later. We always tell customers: the day you take ECA out of frozen storage is the start of your “working time” before it starts absorbing excess moisture. Our ECA has a maximum allowed moisture absorption of 0.5% before curing—so if you let it sit out for 12 hours at 25°C/50% RH, it will hit that threshold, and you shouldn’t use it for high-reliability applications.
I know this sounds like a lot to keep track of, but the good news is that there are ways to mitigate these issues. First, work with an ECA supplier that tests their product the right way, not just the minimum required. We don’t just test 24-hour immersion—we also test 168 hours (7 days) under 85°C/85% RH, which simulates long-term storage or field use. After 168 hours, our standard ICA absorbs 1.8% moisture, and we’ve found that even at that level, it maintains its conductivity for 10+ years under normal operating conditions. That’s the data we give our customers, not just the 24-hour number.
We also tailor our formulations to specific applications. For customers working in high-humidity environments (think marine electronics or outdoor industrial sensors), we have a low-moisture ICA variant that has a 24-hour absorption rate of 0.6% and 168-hour rate of 1.4%—we modified the resin matrix to reduce polar groups that attract water, without sacrificing conductivity or adhesion. For ACAs, which are used for flexible displays and FPC (flexible printed circuit) bonding, moisture absorption is even more critical because the adhesive has to stay flexible. Our ACA has a 24-hour moisture absorption rate of 0.4%, because we use a different resin blend that’s designed to resist moisture while maintaining its elastic properties.
Let’s address a common myth I hear all the time: “Solder doesn’t absorb moisture, so why does ECA need to?” That’s a fair point, but solder is a completely different material. Solder is a metal alloy that melts and forms a metallurgical bond, so it has no polymer matrix to absorb water. ECA is a polymer composite, so its properties are dependent on the polymer’s behavior. The trade-off is that ECA is flexible, lightweight, and compatible with temperature-sensitive components, while solder is rigid and requires high heat. It’s not a matter of which is “better”—it’s a matter of which is right for your application. And for applications where ECA is the right choice, understanding its moisture behavior is non-negotiable for reliability.
Another thing I want to clarify: when we talk about moisture absorption rate, we’re not talking about absolute moisture content. Absolute moisture content is how much water is actually in the adhesive at a given time, while the absorption rate is how fast it takes up that water, and at what point it’s saturated. Our ECAs reach saturation at about 2.1% after 28 days under 85°C/85% RH, which is well above what we see in real-world applications—most electronics won’t be exposed to constant 85% RH for 28 days straight, so our product is more than sufficient for 99% of use cases.
So what should you look for when evaluating an ECA supplier’s moisture absorption data? First, make sure the testing is done to an industry standard, like IPC-TM-650 2.6.2.1. If a supplier gives you a number without mentioning the standard, it’s probably not valid. Second, ask for both short-term (24-hour) and long-term (168-hour or longer) absorption rates. A 24-hour number alone doesn’t tell you how the adhesive will perform over time. Third, ask about how the ECA is stored and handled—does the supplier have protocols to prevent moisture uptake before it reaches you? We ship all our ECA in hermetically sealed aluminum cartridges with desiccants, and we include a COA (Certificate of Analysis) for every batch that lists moisture absorption, cure time, conductivity, and adhesion strength.
If you’re worried about moisture-related issues with your current ECA, here’s a quick checklist to run: Have you been storing the ECA correctly (frozen, in dry conditions)? Are you fully curing it per the supplier’s recommendations? Are you testing the cured adhesive’s moisture absorption as part of your incoming quality control? I can’t tell you how many times I’ve helped a customer troubleshoot a failure, and it turns out they were storing ECA at room temperature for months, then applying it without fully curing it, and wondering why it was failing. The data we provide is only useful if you follow the handling instructions that come with the product.
At the end of the day, electric conduction adhesive is a high-performance material, but it’s not invulnerable to environmental factors. Moisture absorption is one of its most important performance metrics, and it’s something that should be a core part of your ECA selection process, not an afterthought. We’ve spent years refining our ECA formulations to keep moisture uptake as low as possible without sacrificing the other properties our customers need, and we test every single batch to make sure it meets our standards.
If you’re evaluating new ECA suppliers, looking to improve the reliability of your current assemblies, or just have questions about moisture absorption or any other ECA performance metric, we’re here to help. We work with customers across industries—wearables, automotive, industrial, aerospace—and we can tailor a solution to fit your specific application and environmental requirements. Don’t hesitate to reach out to our team to discuss your needs and get more detailed testing data for our products.
Oil Leather Primer References:
- IPC-TM-650 2.6.2.1, Test Method for Moisture Absorption of Non-Metallic Materials
- Liu, J. (2018). Electrically Conductive Adhesives: Fundamentals and Applications. John Wiley & Sons
- Kwon, Y., et al. (2020). “Moisture Effects on the Reliability of Isotropically Conductive Adhesive Joints for Automotive Electronics.” IEEE Transactions on Components, Packaging and Manufacturing Technology
- Sabreen, S., et al. (2019). “Hygroscopic Behavior of Anisotropically Conductive Adhesives for Flexible Display Bonding.” Journal of Adhesion Science and Technology
Guangdong Yrbest High Polymer Technology Co., Ltd.
Guangdong Yrbest High Polymer Technology Co., Ltd. is one of the most professional electric conduction adhesive manufacturers and suppliers in China, featured by quality products and good price. Please rest assured to buy bulk advanced electric conduction adhesive from our factory. Contact us for quotation and free sample.
Address: Room 1701, No. 1, Haitong 4th Street, Nansha Street, Nansha District
E-mail: sal01@ydhightech.com
WebSite: https://www.ydhightech.com/
