What is High TG Printed Circuit Board?
Well-seasoned PCB manufacturers know that each circuit board type comes with its thermal, chemical, and mechanical properties. High TG PCBs are intended to work in environments with high operating temperatures (equal to or above 170°C).
The ability to work under extreme temperatures requires High TG boards to have good thermal stress resistance. Let’s find out what makes such PCBs usable for certain types of electronic products.
What is FR 4 Material?
The basic laminate material used for producing PCB is FR4. It’s a flame-retardant fiberglass reinforced epoxy material regarded as a standard option for PCB manufacturing. It’s cheap, usable, and can withstand up to 115°C only. High TG modification is what enhances its feasible thermal load to new heights.
You probably have heard about the basic classification of FR4 PCBs, based on the number of copper traces in a board:
- Single-sided PCB. Copper tracing is on the top layer only.
- Double-sided PCB. Copper tracing is on the top and bottom layers.
- Multilayer PCB. Have at least three copper trace layers or more.
Standard FR-4 uses bromine, a halogen elemental that is fire resistant. This laminate material offers a good resistance-weight ratio, adequate moisture resistance, good mechanical strength, and an impressive insulating capacity.
FR-4 succeeds in the matters of compatibility with other components, space-saving, design and flexibility, impedance control, and other parameters. Every its strength, especially temperature requirement, may be emphasized by TG modification.
What is Tg?
The Glass Transition Temperature (TG) is one of the most essential qualities that resin epoxy material may have. It’s a rather mechanical property in opposite to a chemical or electrical one.
TG designates a transition temperature to a polymer or glass, depending on the base material. This is the point at which the material starts changing from a solid to a rubber state. Materials that exceed their TG points do not melt but rather become that rubbery material by undergoing structural changes on the molecular level.
Here are some of the characteristics that High Glass Transition temperature grants you laminate materials with:
- Long delamination durability. TG epoxy fails at much higher temperatures than regular solder paste. It means that TG PCB starts delaminating at a higher operational temperature than regular FR-4 bards. They also have a higher time to delamination.
- Low thermal expansion level. Manufacturing of microelectronics is demanding to the dimensional stability of PCBs. Thermal expansion of TG PCBs starts appearing at extreme temperatures only and often is limited to the smallest values.
- Resistance to high temperatures. Thermal decomposition (Td) is what happens with circuit boards under prolonged exposure to elevated temperatures. Impressive heat resistance is what allows TG boards to withstand high heat loads without losing their functionality.
The mentioned are applicable to TG material overall, while High TG PCBs may have additional properties.
Take a look at what the transfer from solid state to rubber state looks like on the example of TG materials in the image below.
Here is the pool of materials that you may use in the production of high TG PCBs:
- Isola 370HR.
- Ventec VT47.
- IT180.
- Panasonic R1755V/R1650V.
- Kingboard KB6167.
- NP-175TL.
- ITEQ-IT-180A.
- ISOLA 370HR.
- Shengyi S1000-2.
Other types of materials may also be applicable. Their array is being added on and off.
Characteristics of High TG PCB Material
The natural specificities of TG are crucial. But manufacturers are more interested in what characteristics their High TG PCB should have:
- High heat resistance. Temperature durability is one side of the coin, while another one is how a PCB withstands, for one, exposure to direct flame. FR-4 must not ignite after a short exposure of about 10 seconds. High TG boards may even preserve their functionality after a short exposure to a direct flame.
- High Plating Through Hole (PTH) reliability. The continuity of plating material is essential for optimal PCB performance. It especially concerns multi-layer PCBs.
- Low Z-axis Coefficient of Thermal Expansion (CTE). This parameter means the expanding degree of base material along the axis Z. Low values of CTE mean the lower risks of fatal thermal expansion and better PTH reliability as well. It’s often that low CTE is associated with high values of Td.
- High thermal shock resistance. Temperature shocks are rapid, sudden changes in the environment temperature. They may be simulated in a laboratory environment by using air or cold-water exposure of a furnace pre-heated board. TG boards are less prone to such stresses.
- Exceptional thermal fatigue resistance. Thermal fatigue is a permanent change in the structure and functionality of a PCB. They are caused by prolonged exposure to adverse temperature conditions. Such effects do not lead to an immediate failure of a board but may cause cracks and deformations and lead to a shorter PCB lifespan.
Every of the mentioned parameters of TG boards is superior to regular FR-4 PCBs.
You also should pay close attention to several other characteristics of TG materials. It’s important that they have adequate heat dissipation to avoid getting thermal shocks. Here are the three ways in which heat is dissipated in your electronics:
- Conduction. Conductive heat dissipation is the transfer of heat between solid bodies through close contact. For one, the temperature gradient transfers from PCB to a laminate material, then to components placed nearby, and then to surfaces or walls of PCB. External temperature stress shows a reversed dissipation.
- Radiation. Radiative heat dissipation is the effect when the heat generated is absorbed or reflected by a cooler body. For one, having a “cold” component in your device will make heat transfer to it, rather than to your PCB.
- Convection. It’s heat dissipation through moving gas, fluid, or current. The heater air simply moves away from the body.
If you placed your devices with TG PCB in a well-aerated area and took other safety precautions, the lifespan of your device will be prolonged. It’s so because the PCB will be dissipating heat better.
Advantages of High TG PCB
Let’s proceed with reviewing the advantages that High-TG materials and PCBs made of them bring to your manufacture.
- Higher stability
Due to excellent TG PCB’s mechanical resistance and chemical resistance, they can stabilize operating conditions within a device. The lifespan of boards and, consequentially, electronics also increases. TG PCBs reduce the risks of short-circuiting and other common ways in which PCBs may fail.
- Withstand High-Power Dense Design
Another interesting thing about High TG boards is that they suit high-density designs perfectly. Such boards usually have issues with heat dissipation, and TG materials help to cope with this problem to a certain extent. So, they can be used in microelectronics having strict temperature resistance requirements.
- Suitable for Multilayer and HDI PCB
As a rule, multi-layer and HDI PCB boards have dense circuits that minimize the route along which electricity flows. It results in low levels of convective heat dissipation and, therefore, increases the internal temperature. Once again, TG materials are less prone to such adverse effects.
When Do You Need High TG PCB?
When you expect a thermal load of more than 25°C below the TG point of PCB, it’s advisable to replace your FR-4 laminates. The same is for cases when a device may be operating with an internal temperature of more than 130°C. For these occasions, you should consider getting high TG boards that would perform perfectly under such conditions.
Another crucial aspect is the technological migration to RoHS PCB. These are board with lead-free soldering. It requires higher temperature levels to melt and flow. Only High TG material can withstand laminating with RoHS solder paste.
Applications of High TG PCB
Probably you may consider replacing all your FR-4s with high TG boards. But since it’s a costly intervention, here are the industries in which the use of high glass transitions boards is obligatory:
- Industries involved with metal processing. In some niches, such as CNC machining, there are processes involving shaping metal. It includes cutting, grinding, melting, and more. Machines utilized for such purposes are computer-controlled. Their microcontrollers must have High TG boards to withstand temperature fluctuations frequently happening in the operating environment.
- Engine controllers. Electronics involved with the engine’s efficiency also have to withstand high-temperature loads. TG boards help to deal with higher volumes of heat generated with greater RPM during running hours.
- WiFi Boosters. Such communication units may start malfunctioning after hours of working in case of poor heat dissipation. That’s something that TG materials can help with.
- Embedded computer systems. Computer processors, computer memory, peripheral memory, and other components are constantly under high loads. Even if they do not exceed 130°C, prolonged exposure is something that TG material better cope with.
- Low-Cost programmable logic controller (PLC). These are industrial computers adapted for the control of input devices. The use of TG materials is required for extra reliability.
- RFID gateways and portal applications. Such units keep track of goods on the move. Since they are involved with high radio frequency technology, using TG materials for them is advised.
There are additional scopes of application for TG, and you can always find ways to implement them.
Conclusion
High glass transition temperature boards are the modified standard PCBs. They are needed, in the first place, for electronics that operate under high-temperature conditions. The thermal stresses shorten the lifespan of PCBs, while TG materials help to increase board capacity.
There is a vast array of applications in which TG boards are irreplaceable. These include controllers, computer systems, high-frequency electronics, and more. It’s highly advised to get the most out of TG materials in these applications for the best manufacturing outcomes.
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