--- title: How to Select Proper PCB Copper Thickness description: Effective utilization of PCB copper thickness will reduce failures in thermal cycle testing, improving overall reliability of your circuit board. image: https://www.epectec.com/images/5oz-copper-through-holes.jpg --- [![Epec Engineered Technologies](https://www.epectec.com/images/logo.png "Epec Engineered Technologies")](https://www.epectec.com/) [![Epec Engineered Technologies](https://www.epectec.com/images/logo.png "Epec Engineered Technologies")](https://www.epectec.com/) - [Articles](https://www.epectec.com/articles/) - [Blog](https://blog.epectec.com/) - [Webinars](https://www.epectec.com/webinar/) - [Videos](https://www.epectec.com/videos/) - [Case Studies](https://www.epectec.com/case-studies/) - [News & Events](https://www.epectec.com/news/) - [Customer Portal](https://system.netsuite.com/c.406760/site/NSlogin.html) - [About](https://www.epectec.com/about/overview/) - Back - [Company Overview](https://www.epectec.com/about/overview/) - 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[Register](https://secure.epecpcb.com/epec/index2.jsp) - [Home](https://www.epectec.com/) - [Blog](https://blog.epectec.com/) - How to Select Proper PCB Copper Thickness Share This Page: [LinkedIn](https://blog.epectec.com/#linkedin) [X](https://blog.epectec.com/#x) [Facebook](https://blog.epectec.com/#facebook) [Email](https://blog.epectec.com/#email) # How to Select Proper PCB Copper Thickness [![Al Wright](https://blog.epectec.com/hubfs/Blog-Authors/al-wright.jpg "Al Wright")](https://blog.epectec.com/author/al-wright) Written by [Al Wright](https://blog.epectec.com/author/al-wright) Posted on December 31, 2013 at 1:40 PM ![Al Wright](https://blog.epectec.com/hubfs/Blog-Authors/al-wright.jpg "Al Wright") - [Tweet](https://twitter.com/share) Selecting the optimal [heavy copper](https://www.epectec.com/pcb/heavy-copper.html) thickness to apply to the plated through hole (PTH) plays a critical factor towards the overall reliability of the printed circuit board. There are two key elements to consider when determining optimal PCB copper thickness. The first is the current capacity of the barrel for acceptable heat rise. The second is the mechanical strength determined by the copper thickness, hole-size and whether or not there are any support vias. ## Choosing Your PCB Materials There are a variety of dielectric materials that [circuit board manufacturers](https://www.epectec.com/pcb/) and designers can choose from such as the standard FR4 (operating temp. 130°C) to high-temperature polyimide (operating temp. 250°C). If your application will be prone to extreme environments or high-temperature situations, consider using a more exotic material, but if the circuit traces and plated vias are standard 1 oz/ft2; will they survive the extreme conditions? A test method has been designed specifically for the printed circuit board industry to determine the thermal integrity of a finished circuit product. Thermal strains come from various board fabrications, assembly and repair processes, where the differences between the coefficient of thermal expansion (CTE) of Cu and the PWB laminate provide the driving force for crack nucleation and growth to failure of the circuit. Thermal cycle testing (TCT) checks for an increase in resistance of a circuit as it undergoes air-to-air thermal cycling from 25°C to 260°C. [![Check Out Our Heavy Copper PCB Design Ebook!](https://no-cache.hubspot.com/cta/default/707152/172df46e-6c02-4f35-83e5-a35e41862e20.png)](https://cta-redirect.hubspot.com/cta/redirect/707152/172df46e-6c02-4f35-83e5-a35e41862e20) Any increase in resistance is an indication of a breakdown in electrical integrity via cracks in the copper circuit. A standard coupon design for this test utilizes a chain of 32 plated through holes, which is considered to be the weakest point in a circuit when subjected to thermal stress. ![PCB with Heavy Copper Plated Through Holes](https://www.epectec.com/images/5oz-copper-through-holes.jpg "PCB with Heavy Copper Plated Through Holes") *Printed Circuit Board with Heavy Copper Plated Through Holes* The TCT results clearly show that the failure rate, no matter what the board material, can become unacceptable. Thermal cycle studies done on standard FR4 boards with 0.8-mil to 1.2-mil copper plating have shown that 32% of circuits fail after eight cycles (a 20% increase in resistance is considered a failure). Boards with exotic materials show significant improvements to this failure rate (3% after eight cycles for Cyanate Ester), but are prohibitively expensive (five to 10 times material cost) and difficult to process. An average surface-mount technology assembly sees a minimum of four thermal cycles before shipment, and could see an additional two thermal cycles for each component repair. Regardless of what material is being used the TCT results will clearly distinguish failure rate resulting in an unacceptable board. Thermal cycle studies done on standard FR4 boards with 0.8-mil to 1.2-mil copper plating have shown that 32% of circuits fail after eight cycles (a 20% increase in resistance is considered a failure). Boards with exotic materials show significant improvements to this failure rate (3% after eight cycles for Cyanate Ester), but are prohibitively expensive (five to 10 times material cost) and difficult to process. An average surface-mount technology assembly sees a minimum of four thermal cycles before shipment, and could see an additional two thermal cycles for each component repair. ## Summary Effectively and efficiently [utilizing heavy copper circuit boards](https://www.epectec.com/pcb/heavy-copper.html) would reduce or eliminate most failures altogether. Plating of 2 oz/ft2 of copper to a hole wall reduces the failure rate to almost zero (TCT results show a 0.57% failure rate after eight cycles for standard FR4 with a minimum of 2.5-mil copper plating). In effect, the copper circuit becomes impervious to the mechanical stresses placed on it by the thermal cycling. --- ## Key Takeaways - **Copper thickness drive’s reliability:** The durability of plated through holes depends on both electrical performance (current capacity and acceptable heat rise) and mechanical strength (copper thickness, hole size, and via support). - **Material selection impacts performance:** Standard FR4 can be sufficient for many designs, but high-temperature materials like polyimide or Cyanate Ester provide better reliability in extreme environments, though at a much higher cost. - **Thermal cycling exposes weaknesses:** Air-to-air thermal cycle testing (25°C to 260°C) is the industry benchmark for identifying failures caused by copper cracks and laminate stress, with PTHs being the weakest point under stress. - **Standard plating shows high failure rates:** FR4 boards with 0.8–1.2 mil copper plating exhibit up to a 32% failure rate after just eight cycles, highlighting the limits of thin copper layers in demanding applications. - **Heavy copper plating reduces failures dramatically:** Increasing plating to 2 oz/ft² (about 2.5 mil copper thickness) cuts the failure rate to less than 1%, making the board nearly impervious to thermal and mechanical stresses. - [Tweet](https://twitter.com/share) Topics: [Printed Circuit Boards](https://blog.epectec.com/topic/printed-circuit-boards) --- [Next](https://blog.epectec.com/what-is-the-smallest-bend-radius-of-a-membrane-switch-tail) | [All posts](https://blog.epectec.com/all) | [Previous](https://blog.epectec.com/what-is-an-overmolded-cable) [![New Call-to-action](https://no-cache.hubspot.com/cta/default/707152/0b7422c3-0d03-445a-b85c-8059dd50bba6.png)](https://cta-redirect.hubspot.com/cta/redirect/707152/0b7422c3-0d03-445a-b85c-8059dd50bba6) ## Leave a Comment --- ## Related Posts --- ### Recent Posts --- ### Posts by Topic - [Printed Circuit Boards (157)](https://blog.epectec.com/topic/printed-circuit-boards) - [Product Design (132)](https://blog.epectec.com/topic/product-design) - [Battery Packs (118)](https://blog.epectec.com/topic/battery-packs) - [Cable Assemblies (99)](https://blog.epectec.com/topic/cable-assemblies) - [Flex & Rigid-Flex PCB's (92)](https://blog.epectec.com/topic/flex-rigid-flex-pcbs) - [Electronics Industry (61)](https://blog.epectec.com/topic/electronics-industry) - [User Interfaces (54)](https://blog.epectec.com/topic/user-interfaces) - [Quality Solutions (32)](https://blog.epectec.com/topic/quality-solutions) - [Flexible Heaters (30)](https://blog.epectec.com/topic/flexible-heaters) - [Events, Training, and Support (9)](https://blog.epectec.com/topic/events-training-and-support) - [RF Products (7)](https://blog.epectec.com/topic/rf-products) - [CNC Machining (3)](https://blog.epectec.com/topic/cnc-machining) - [Fans & Motors (1)](https://blog.epectec.com/topic/fans-motors) See All --- --- ### Need Help with A Project? 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