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PCB Coating Selection Guide: Mastering Mechanical Stress for Durability

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Is mechanical stress silently damaging performance and lifespan of your PCBs? From assembly soldering heat to operational vibrations, stress continuously attacks circuit boards, threatening solder joints, traces, and ultimately, reliability. Your PCB’s crucial defense against these forces is the appropriate conformal coating.
 
This guide delves into the topic of mechanical stress in PCBs, exploring what it is, why it matters for coatings, how to select the optimal coating to withstand it, and why conformal coatings like epoxy and Parylene are the industry’s frontline defense. ELE PCB ensures your boards survive and thrive under pressure!

What is Mechanical Stress in PCB?

Understanding Definition & Formula

Mechanical stress is the internal force that generates interaction between parts within an object when the object is deformed due to external causes (force, humidity, temperature field changes, etc.) to resist such external causes and to try to restore the object from its post-deformation position to its pre-deformation position.
 
In the context of PCBs, mechanical stresses are mainly generated due to external forces, temperature changes and other factors during the manufacturing, assembly and use of the board. 
For example, when soldering electronic components to a circuit board during the assembly of a PCB, mechanical stresses are generated inside the PCB due to thermal expansion and contraction during the soldering process; during use, the board may be subjected to external forces such as vibration, bending, and so on, which will also generate mechanical stresses.
 
Mechanical stress can be expressed simply by the formula σ = F/A.
(where σ denotes stress, F denotes external force, and A denotes area under stress)

Why PCBs are Prone: Material Mismatch(CTE Differences)

structure of multillayer
In the PCB structure, different material layers (e.g., copper foil layer, insulation layer, etc.) have different physical properties, such as the coefficient of thermal expansion. When the temperature changes, these material layers expand or contract to different degrees, resulting in mechanical stresses.
 
For example, the coefficient of thermal expansion of copper is larger than that of some insulating materials, and when the temperature rises, the copper foil layer expands more than the insulating layer, which generates stresses between the layers.

Why Conformal Coating is Critical for Mechanical Stress Protection?

Protecting the Integrity of the PCB

An important role of PCB coating is to protect the PCB from the external environment. The coating improves the board’s resistance to abrasion and corrosion, and prevents stress caused by corrosive substances.
 
If an inappropriate PCB coating is chosen, mechanical stress may cause cracks, delamination and other damage to the PCB, while a suitable coating can absorb or disperse mechanical stress and prevent these damages from occurring. In a vibrating environment, this coating can serve as an intermediary layer that dampens the stresses imposed on the internal structure of the PCB.

Ensuring Stable Electrical Performance

  • Keep the proper layout
Mechanical stress can alter the layout of the lines inside the PCB, which means changing their spacing and further affecting electrical performance, capacitance, inductance, and other parameters. Coatings can reduce or disperse localised stress concentrations caused by mechanical loads, while also reducing friction between materials and improving lubrication, thereby reducing mechanical stress.
 
  • Reduce pulling effect on solder joints
When the PCB undergoes some mechanical stress, this may cause the internal solder joints to be pulled. The coating can reduce the pulling effect on the solder joints to some extent and avoid problems such as cracking of the solder joints. This ensures the connectivity of the circuit, which is also very important for maintaining electrical performance.
Preventing Solder Ball Defects on PCB 1
Preventing Solder Ball Defects on PCB

Maximizing PCB Lifespan & Reliability

Among the long-term use of PCB, mechanical stress is the most essential factor in the aging and damage of PCB.
 
An appropriate PCB coating can enhance the oxidation resistance of materials by influencing their electrochemical properties, effectively resisting the long-term effects of mechanical stress, slowing down the aging of PCB and prolonging its service life.
the surface coating of a PCB board
Parylene Conformal Coating
Parylene Conformal Coatings

Key Coating Properties for Stress Resistance

Chemical Stability

The coating material applied to the PCB should be highly chemically stable and not easily react with other material on the board. It should also have strong corrosion resistance to ensure good performance even after long-term exposure to harsh environments.
 
Take epoxy resin coating as an example, its structure produces a large resistance to external chemicals such as acids, alkalis, solvents, among others, which have difficulty passing through and diffusing into the interior of the coating, thereby avoiding chemical attack.

Mechanical Strength

To avoid wear and tear caused by friction or impact during long-term use, the protection coating should be hard and durable.
 
For example, the high strength of epoxy resin coatings is mainly due to their highly cross-linked molecular structure, making the epoxy resin extremely hard and impact resistant after curing.

Chemical or Physical Adsorption

The coating and the PCB’s substance should stick together properly. If the coating’s adhesion to the PCB is poor, it can flake off under mechanical stress and thus lose its protective effects towards the PCB. In such a situation, it becomes imperative that the coating be able to develop a good chemical bond or physical adsorption on the surface of a PCB, resilient enough to withstand mechanical stress.

Case Study: Strength of Epoxy Resin Under Pressure

The capability of epoxy resin to retain structural integrity under mechanical stress depends on the following mechanisms:

  • Highly Crosslinked Network Structure

Epoxy resin, due to its curing, acquires a highly crosslinked structure that provides extremely high mechanical strength and rigidity. Thus, when such structures are put under an externally applied stress, the possibility of deformation or rupture of the structure becomes less likely.

  • Reinforcement of Nanoscale Fillers

Mixtures of graphene oxide and cerium oxide (GO-CeO₂); good dispersion of these kinds of nanomaterials in epoxy resins may notably increase their hardness, modulus of elasticity, and wear resistance. GO-CeO₂ addition increased the adhesion strength of the epoxy coatings from 7.3 MPa to 12.2 MPa in comparison with the original epoxy resin, which remarkably improved their wear resistance.
At the same time, epoxy resin can further optimize its mechanical properties by adding different fillers (e.g., silica, graphene, etc.) as required. For example, the addition of silica can significantly improve the wear resistance and hardness of epoxy resins.

  • Appropriate Toughness Improvement

The addition of flexible chain segments (e.g., polyether amines) allows epoxy resins to form internally dispersed microphase structures. These microphases can absorb and disperse the stress by their own deformation when subjected to stress, thus protecting the integrity of the entire coating.

The toughness of the epoxy resins may be improved by the addition of thermoplastic resins, such as polyethersulfone PES, which enables them to absorb energy rather than immediately fracture under mechanical stress. For instance, PES-toughened epoxy resins exhibited a 14% and 106% increase in tensile and impact strengths, respectively, which was a great merit in terms of retaining structural integrity.

As can be seen from the above case study, the performance of protective coatings can be further enhanced by strengthening the material, filling it with nanoscale materials and improving flexibility. Through these methods, the impact of PCB mechanical stress can be minimized.

Selecting the Right PCB Coating to Combat Mechanical Stress

Except for epoxy resin mentioned above, there are many other types of PCB conformal coatings. A good selection of PCB protection coating can improve PCB durability.
Selecting PCB coatings for vibration resistance requires comparing critical properties:
Coating Type Hardness Flexibility CTE Compatibility Stress-Resistance Properties
Acrylic (AR) Medium-High Low-Med Moderate → Prone to micro-cracking Cost-effective but brittle under thermal cycling
Silicone (SR) Low Extreme Excellent → Elastic buffering Best flexibility, absorbs vibration/bending
Urethane (UR) Medium-High Medium-High Good → Fatigue-resistant Balanced abrasion resistance + flexibility
Epoxy Very High Very Low Poor → Delamination risk High compressive strength, CTE mismatch issues
Parylene Medium Excellent Exceptional → Conforms molecularly Ultra-thin, CTE adapts to substrate
Thin Film/Nano Tunable Tunable Engineered Nanofillers optimize CTE/toughness

If you want to get more informations about confomal coatings of PCB board, please read this blog:

The Ultimate Guide to Conformal Coating for Circuit Boards

Click Here

Conclusion

It is important to mitigate the effects of mechanical stress when designing and manufacturing PCBs. One simple and effective way to protect PCBs from stress is to apply protective coatings. Enhancing the durability and stability of these coatings ensures the performance of the PCBs and extends their service life.
 
ELEPCB is a PCB manufacturer with over 10 years of experience, equipped with very advanced production lines that guarantee the quality of our products and decades of experience in the field of senior engineers for your customized PCB products. With lots of certificates and strict quality control, our conformal coat stands out for excellent performance and long-term durability.
 
Ready to Protect Your PCBs from Mechanical Stress?Request a Free Coating Consultationwith ELEPCB’s Experts!

References

Zhang Y, Lin H, Dong K, Tang S, Zhao C. Comparison of the Properties of Epoxy Resins Containing Various Trifluoromethyl Groups with Low Dielectric Constant. Polymers (Basel). 2023 Jun 28;15(13):2853. doi: 10.3390/polym15132853. PMID: 37447498; PMCID: PMC10346801.

Zhu Li, Lu Huang, Fei Han, et al. “Preparation and Comprehensive Protective Performance Study of Thickened Magnolol Epoxy Resin Coatings”. Materials Protection, 2024, 57(3): 70 – 79, 97. DOI: 10.16577/j.issn.1001 – 1560.2024.0057.

Ma, Lingwei; Wang, Xuanbo; Wang, Jinke; Zhang, Juantao; Yin, Chengxian; Fan, Lei; Zhang, Dawei. Journal of Materials Science (IF = 3.5). Pub Date: 2021 – 02 – 25. DOI: 10.1007/s10853 – 021 – 05932 – z.

R. Jayasinghe, M. Ramos, A. Nand, and M. Ramezani, “Enhancing Mechanical and Tribological Properties of Epoxy Composites with Ultrasonication Exfoliated MoS2: Impact of Low Filler Loading on Wear Performance and Tribofilm Formation,” Department of Mechanical Engineering, Auckland University of Technology, Auckland 1010, New Zealand; Faculty of Engineering, University of Auckland, Auckland 1010, New Zealand, 20XX. [Correspondence: maziar.ramezani@aut.ac.nz]

Luo, Lida; Wang, Qihui; Ma, Qian; Wang, Qingwei; Liu, Jin; Ding, Linfeng; Jiang, Weizhong. “A Novel Basalt Flake Epoxy Resin Coating Modified by Carbon Nanotubes”. Received: 19 Sep. 2019; Accepted: 26 Oct. 2019; Published: 31 Oct. 2019. State Key Lab. for Modification of Chemical Fibers and Polymer Materials, Donghua Univ., Shanghai 201620, China; Eng. Res. Ctr. of Advanced Glass Mfg. Tech., Ministry of Educ., Donghua Univ., Shanghai 201620, China; Shanghai Chengjian NichiReki Special Asphalt Co., Ltd., Shanghai 200436, China. Correspondence: wqwq888@dhu.edu.cn (Q.W.); linfeng.ding@dhu.edu.cn (L.D.); jwzh@dhu.edu.cn (W.J.).

A. Rudawska, M. Frigione, A. Sarcinella, V. Brunella, L. Di Lorenzo, E. Olewnik – Kruszkowska, “Properties and Performance of Epoxy Resin/Boron Acid Composites”, Faculty of Mechanical Engineering, Lublin University of Technology, Nadbystrzycka 36, 20 – 618 Lublin, Poland; Department of Innovation Engineering, University of Salento, Via Arnesano, 73100 Lecce, Italy; Department of Chemistry, University of Torino, Via P. Giuria 7, 10125 Torino, Italy; Faculty of Chemistry, Nicolaus Copernicus University in Toru´n, Gagarin 7 Street, 87 – 100 Toru´n, Poland, 20XX. [Correspondence: mariaenrica.frigione@unisalento.it]

R. Kumar, P. Bhagoria, M. R. Bharadwaj, V. Tiwari, “From quasi – static to dynamic: Experimental study of mechanical and fracture behaviour of epoxy resin”, International Journal of Impact Engineering, Vol. 195, 2025, pp. 105101. ISSN 0734 – 743X. [Online]. Available: https://doi.org/10.1016/j.ijimpeng.2024.105101. (https://www.sciencedirect.com/science/article/pii/S0734743X24002264)

H. – S. Jung, Y. Park, C. – W. Nah, J. – C. Lee, K. – Y. Kim, C. S. Lee, “Evaluation of the Mechanical Properties of Polyether Sulfone – Toughened Epoxy Resin for Carbon Fiber Composites”, Fibers and Polymers (IF 2.2), Pub Date: 2021 – 01 – 19, DOI: 10.1007/s12221 – 021 – 9261 – 4.

樊玮洁,徐听,徐夫轩,等. 环氧涂层钢筋混凝土梁的涂层破损检测及疲劳寿命研究[J]. 中国港湾建设,2024,44(5):9-15. DOI:10.7640/zggwjs202405002.

H. Liang, W. Tian, H. Xu, Y. Ge, Y. Yang, E. He, Z. Yang, Y. Wang, S. Zhang, G. Wang, Q. Chen, Y. Wei, Y. Ji, “Reprocessable Epoxy–Anhydride Resin Enabled by a Thermally Stable Liquid Transesterification Catalyst”, Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Department of Chemistry, Tsinghua University, Beijing 100084, China; School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China; Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China; Electric Power Research Institute, China Southern Power Grid Co., Ltd., Guangzhou 510623, China, 20XX. [Correspondence: weiyen@tsinghua.edu.cn (Y. Wei); jiyan@mail.tsinghua.edu.cn (Y. Ji)]

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I am an experienced engineer specialized in the electronics field with valuable sales expertise and a determined mindset. If we can be of use to one another rest assured that there is no other more professional option on the market than myself.
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Benjamin is the general manager of ELE PCB, a leading PCB design and manufacturing company based in China. He has over 10 years of experience in the PCB industry, and has been involved in various projects.

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