High-TG PCB | rating | temperature | FR4 | circuit board | material | 150

High-Tg materials are hardly regarded as a "special technology" today. Especially the automotive industry is requesting such materials for a longer time already but keeps on pushing the boundaries and thus teperature resistance standards. TGs of around 130°C are today's lowest temperature resistance range, while most multilayers are produced with TG150°C. TG stands for „Temepretaur of glass-transition“ meaning the temperature at which the glass fibres inside the FR4 are softening and the material as such is losing stability.

High-TG-Material start at around TG of 170°C. Most high-TG materials up to TG170°C are based on FR4 fibre-glass/epoxy compounds and are produced and processed like standard PCBs. Exceptions are diffefrent drill parameters because these materials contain fillers. Some high-TG materials can therefore be spotted by their appearance: compared to low-TG materials, these materials are opaque and mostly whiter.

What are the advantages of high-TG materials?

The primary advantage of high-TG materials is the higer MOT = „Maximum Operating Temperature“, which also allows higher currents. The MOT is the highest temeprature under which the PCB can permanently operate without being damaged. As a rule of thumb you can deduct around 20°C from the TG as the MOT. This lower temperature is the safety that you should apply as a operating temperature of the TG-value will definitely lead to damaging the PCBs.

How do I classify high-TG materials?

You may apply the follpowng table as classifications:

Why is there sometimes no TG mentioned in material datasheets?

Some common high-frequency materials do not mention TGs in their datasheets. This is due to the original meaning of TG: "temperature of glass transition". Many ceramics- or PTFE-based materials do simply not contain any glass fibres and therefore have no technical TG. Generally, this fact also applies to Polyimides (PI). However, you can usually assume a TG of at least 200°C for Polyimide, ceramics or PTFE-materials. In this case the TG simply stands for temperature resistance. 

You may apply the following values:

Anything special for flexible polyimide boards?

Yes. For flexible printed circuits (FPC) you should always keep on mind that most of them are not pure polyimides but also contain some degrees of exopy. Even if you insist on so-called adhesive-less materials you will have epoxy inside the compound when either coverlay or stiffeners are applied. Therefore, temperature resistance of FPCs are limited through the epoxy, not the polyimide.

What temperature can solder mask resist?

Common solder masks often have temperature resistance below the material-TG. Typical MOTs for solder mask are around 150°C with TWT-cycle-resistance (temperature cycle test) of 65°C to 125°C, sometimes 175°C (100 cycles). For hogh-TG applicatons that will exceed these temperatures we recommend to either buy the PCBs without any solder maks or to apply a special temperature resistant coating after assembly. If you use standard solder masks in high-temperature environments you have to accept that they are turning brownish.

Which high-TG materials can Leiton deliver?

Below high-TG materials are available at Leiton:

When qualifying certain high-TG materials please keep on mind that the materials of prototypes from Berlin differ from mass production materials from China. Please get in contact with us early on, if you need the prototypes from the exact same material like the mass production. We will then deliver prototypes from China.

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High-TG printed circuits in our online calculation!