In PCB design, the same oversight of a PCB's temperature requirements will cost more than balloons and ice cream. You need to know how much heat a PCB is likely to withstand before it starts to suffer structural damage, especially if it is deployed in a high temperature environment.
As you know, FR4 means the rating of the flame retardant F4 properties of the PCB. FR4 PCBs are made of multiple layers of fiberglass epoxy laminates. FR4 PCBs are preferred among manufacturers due to their consistent physical properties.
FR4 PCBs are very strong when exposed to high temperatures, but at certain temperatures, their physical properties change. The heat-resistant properties of FR4 are represented by the Tg, or glass transition temperature, at which it changes from a solid to a soft and rubbery state. Typically, FR4 PCBs are rated for a Tg of 130°C.
In other words, if a PCB rated at 130°C is heated above its glass transition temperature, it will lose its solid state form. Not only will your mechanical structure be unstable, but the electrical performance of the PCB will degrade beyond the rated Tg. This is why the importance of fr4 maximum temperature must be considered when designing PCBs for applications such as oil and gas and automotive where temperatures exceed typical Tg values.
If the application requires a PCB with a higher Tg value, a medium or high Tg PCB needs to be selected. Medium Tg PCBs typically have a maximum temperature of over 150°C, while high Tg PCBs are rated for over 170°C. A PCB with a higher Tg value also has better moisture and chemical resistance, as well as a stronger physical structure under thermal conditions.
Manufacturers will use low Tg PCBs for fabrication unless otherwise stated. PCBs with medium and high Tg are usually more expensive. Materials like S1141 and S1002-M are typically used to produce high Tg PCBs. Lamination of high Tg PCBs involves a lot of heat due to the higher glass transition temperature. From a price point of view, high TG PCBs are more expensive.FR-4 TG150 6-layer blind and buried via medical equipment control board.
Some applications require high Tg PCBs.
A common mistake is to use the tG value to determine the operating temperature of the PCB. When choosing the correct FR4 PCB, a margin of at least 20°C should always be allocated. For example, a lower Tg FR4 of 130°C should have an operating temperature limit of 110°C.
As a PCB designer, you need to understand thermal regulation techniques in your design. The power conditioning module will generate heat and appropriate cooling techniques should be used. Using heat sinks or thermal vias can help prevent hot spots from overheating, pushing the PCB beyond its limits.
The Tg rating and the operating temperature of the PCB are not the only factors that determine its function in high temperature environments. The operating temperature limitations of individual components must also be considered in the design.
Heatsinks help regulate heat dissipation.
For example, military-grade, automotive-grade, and extended temperature components have wider temperature tolerances than commercial or consumer-grade components. Although components with higher temperature tolerance are expensive, they are critical to ensuring the reliability of PCB circuits in the field.
For microcontrollers, it should be noted that lowering their system clock will generally increase their maximum operating temperature limit.
Ideaspcb SMT Fabrication To optimize the design and avoid the FR4 maximum temperature, it facilitates the use of reliable, flexible design and analysis software with thermal analysis capabilities, such as Cadence's. Especially if you are looking for a layout package with any customizable vias, net management and proper analysis, then OrCAD is the way to go.
